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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Isolation transformer draws excessive current under no load condition
Hi all,
Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference: http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet: http://attachments.temcoindustrialpo...120x240Pri.pdf I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. |
#2
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Isolation transformer draws excessive current under no load condition
On Feb 10, 8:17*am, JW wrote:
Hi all, Is there any reason that a 120VAC to 120VAC *isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. |
#3
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Isolation transformer draws excessive current under no load condition
JW wrote in message ... Hi all, Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference: http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet: http://attachments.temcoindustrialpo...al_FB_1Ph_120x 240Pri.pdf I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. If there are shorted turns then there would be a difference in DC ohms of each coil, assuming they should be the same for 120/120 |
#4
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Isolation transformer draws excessive current under no load condition
On 2/10/2012 8:17 AM, JW wrote:
Hi all, Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference: http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet: http://attachments.temcoindustrialpo...120x240Pri.pdf I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. If it's actually dissipating 300W, it will get very warm. |
#5
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Isolation transformer draws excessive current under no load condition
2.5 amps seems like an awful lot of current, in-phase or not.
It sounds as if the unit is "defective" in some undefined. Or it might be that the transformer's inductance is too low. |
#6
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Isolation transformer draws excessive current under no load condition
It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Gareth. |
#7
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Isolation transformer draws excessive current under no load condition
On 2/10/2012 11:22 AM, Gareth Magennis wrote:
It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. As a go/no-go test, you can put an incandescent light bulb in series with the transformer and see how bright it gets. But at 300W, you shouldn't have any trouble sensing transformer temperature rise with your hand. OR Wrap the transformer in insulation and plot the temperature vs time...weigh the transformer to guess at heat capacity and calculate the power from that. So, several ways to "do that". Gareth. |
#8
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Isolation transformer draws excessive current under no load condition
On 2/10/2012 10:38 AM, William Sommerwerck wrote:
2.5 amps seems like an awful lot of current, in-phase or not. First guess, I'd have to agree. My Old Stancor 250W transformer draws 9W 18VA .15A RMS unloaded. It sounds as if the unit is "defective" in some undefined. Or it might be that the transformer's inductance is too low. One more thing to try. Make sure you're not paralleling a primary and secondary winding. Hook up one winding to the AC. Measure all 4 voltages very accurately. How you connect the windings can make a difference. Small changes in coupling due to the arrangement of the windings can produce small differences in the output. When you start paralleling them, you can get one winding fighting another. If that's the case, energizing only one of the 4 windings with the others disconnected should make the problem go away. It's not impossible that a manufacturing defect screwed up the turns count on one of the windings. In a transformer this big, if you have a shorted turn, you should be able to smell the result. Depending on how close the transformer is to the box, the metal box represents a shorted turn. All the flux is SUPPOSED to be inside the core....supposed to be. I don't expect taking it out of the box would make any significant difference, but I'd try it before scrapping the device. But the real diagnostic is to measure the real power consumed. You can chase your tail trying to solve a problem that doesn't exist. Try the series light bulb. |
#9
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Isolation transformer draws excessive current under no load condition
On Feb 10, 9:40*am, nesesu wrote:
On Feb 10, 8:17*am, JW wrote: Hi all, Is there any reason that a 120VAC to 120VAC *isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. Sounds VERY reasonable for a 15kVA transformer. 2.5 A suggests coupling ratio on the order of 0.982, not bad for an AC mains transformer that weighs that much. If it bothers you, you can add a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. Or, ignore it and let your house wiring dissipate a bit of power less than 1W ? |
#10
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Isolation transformer draws excessive current under no load condition
On Feb 10, 1:36*pm, Robert Macy wrote:
On Feb 10, 9:40*am, nesesu wrote: On Feb 10, 8:17*am, JW wrote: Hi all, Is there any reason that a 120VAC to 120VAC *isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet.. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. Sounds VERY reasonable for a 15kVA transformer. 2.5 A suggests coupling ratio on the order of 0.982, not bad for an AC mains transformer that weighs that much. If it bothers you, you can add *a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. Or, ignore it and let your house wiring dissipate a bit of power less than 1W ? ARRRGGG! That'll teach me NOT to do my own research. Now, I have to reply to my OWN posting! ok your transformer is the 1kVA version of that series, the smallest transformer. current of max load is 1kVA/120 or 8.3A. reactive current is 2.5 A that implies the core reactive impedance from its inductance is around 3.3 to 1 Seems a little low, but in range for a super cheap transformer that will get hot while running. I would have expected more like around 1A, or less. Here are some 'good' rules of thumb: The core inductance reactance is probably 5 to 10 times the load impedance, I've seen as low as 3 times. The winding resistance is usually split half in pri and half in sec. actually more like 45% in primary and 55% in sec.and the total is less than 1/10 of load impedance. So the transformer is in 'range' but that current does seem pretty high for what should be a high quality transfomer. Could be a short somewhere. Depending on how the transformer is wound, you may or may not learn much from measuring the DC resistance of each winding. You could power each winding with 120Vac and measure the current of each winding, but then again. If you don't need much power through this thing, like less than 500W, wire it for 240/240 and that'll lower the core current for you. |
#11
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Isolation transformer draws excessive current under no load condition
On 2/10/2012 12:36 PM, Robert Macy wrote:
On Feb 10, 9:40 am, wrote: On Feb 10, 8:17 am, wrote: Hi all, Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. Sounds VERY reasonable for a 15kVA transformer. Huh??? Federal Pacific SE120N1F FT2036 - Isolation Transformer 120 x 240 Primary 120/240V Secondary - 1 kVA 60Hz 2.5 A suggests coupling ratio on the order of 0.982, not bad for an AC mains transformer that weighs that much. If it bothers you, you can add a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. Or, ignore it and let your house wiring dissipate a bit of power less than 1W ? |
#12
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Isolation transformer draws excessive current under no load condition
"mike" wrote in message ... On 2/10/2012 11:22 AM, Gareth Magennis wrote: It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. As a go/no-go test, you can put an incandescent light bulb in series with the transformer and see how bright it gets. But at 300W, you shouldn't have any trouble sensing transformer temperature rise with your hand. OR Wrap the transformer in insulation and plot the temperature vs time...weigh the transformer to guess at heat capacity and calculate the power from that. So, several ways to "do that". Gareth. |
#13
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Isolation transformer draws excessive current under no load condition
"mike" wrote in message ... On 2/10/2012 11:22 AM, Gareth Magennis wrote: It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. Er, not everyone lives in North America. I happen to live in the UK. Tell me again how you might measure the power consumption of a transformer. Gareth. |
#14
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Isolation transformer draws excessive current under no load condition
"Gareth Magennis" writes:
What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Buy a Kill-o-watt; a useful tool to have around. -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#15
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Isolation transformer draws excessive current under no load condition
In message
, Robert Macy writes On Feb 10, 1:36*pm, Robert Macy wrote: On Feb 10, 9:40*am, nesesu wrote: On Feb 10, 8:17*am, JW wrote: Hi all, Is there any reason that a 120VAC to 120VAC *isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? Part reference:http://www.temcoindustrialpower.com/...rs/FT2036.html datasheet:http://attachments.temcoindustrialpo...o/Federal_FB_1... I finally got around to wiring this transformer, and I noticed something that doesn't seem quite right to me. I have it wired for 120VAC (H1 connected to H3 and H2 connected to H4) and it seems to be working as I get about 120VAC on the secondary, ( wired X1 to X3 and X2 to X4) but with no load on the secondary, the transformer is drawing 2.54 Amps. Looking for a sanity check I guess. I'm beginning to think the thing may be defective... Email to the Temco has produced no response as of yet. As a quick test, disconnect all the windings from each other and then power up any ONE winding and see what the current draw is. I see that it is a 15kVA rated, so it is not unreasonable that the magnetizing curent is that high, but the actual power dissipation would be much less than that current suggests. It is probably working correctly, but a bit of an overkill for the average workbench. Neil S. Sounds VERY reasonable for a 15kVA transformer. 2.5 A suggests coupling ratio on the order of 0.982, not bad for an AC mains transformer that weighs that much. If it bothers you, you can add *a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. Or, ignore it and let your house wiring dissipate a bit of power less than 1W ? ARRRGGG! That'll teach me NOT to do my own research. Now, I have to reply to my OWN posting! ok your transformer is the 1kVA version of that series, the smallest transformer. current of max load is 1kVA/120 or 8.3A. reactive current is 2.5 A that implies the core reactive impedance from its inductance is around 3.3 to 1 Seems a little low, but in range for a super cheap transformer that will get hot while running. I would have expected more like around 1A, or less. Here are some 'good' rules of thumb: The core inductance reactance is probably 5 to 10 times the load impedance, I've seen as low as 3 times. The winding resistance is usually split half in pri and half in sec. actually more like 45% in primary and 55% in sec.and the total is less than 1/10 of load impedance. So the transformer is in 'range' but that current does seem pretty high for what should be a high quality transfomer. Could be a short somewhere. Depending on how the transformer is wound, you may or may not learn much from measuring the DC resistance of each winding. You could power each winding with 120Vac and measure the current of each winding, but then again. If you don't need much power through this thing, like less than 500W, wire it for 240/240 and that'll lower the core current for you. The symptoms described sound very similar to using a 60Hz transformer on a 50Hz supply (as might happen if you are using American equipment in Europe), and the transformer hasn't got enough iron in it - so it's saturating. However, that's not what you are doing. If saturation IS the problem, you can usually confirm it (under no-load conditions) by winding the supply voltage up on a variac, and measuring the current the transformer draws. It will rise suddenly when the core starts to saturate. Although the problem is much more likely to be shorted turns, a quick test for saturation might be interesting. -- Ian |
#16
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Isolation transformer draws excessive current under no load condition
On 2/10/2012 1:57 PM, Gareth Magennis wrote:
"mike" wrote in message ... On 2/10/2012 11:22 AM, Gareth Magennis wrote: It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. Er, not everyone lives in North America. I happen to live in the UK. Sorry for your loss. Tell me again how you might measure the power consumption of a transformer. Not sure how repeating myself helps, but here goes. I'd plug it into a Kill A Watt meter. That's how I got the other experimental results I mentioned in this thread. I also disclosed several other techniques. If you would read the parts you snipped, I also gave you several other ways to estimate the power consumption of a transformer. If you don't have a readable utility meter or a stopwatch or a light bulb or a voltmeter or a scale or a thermometer or a hand, you probably should look elsewhere for advice. I'm all out. Wait..... I think I figured out how to do it with a used tea bag, the chime from Big Ben and a plate of fish and chips. Nope, you're still gonna need the hand. Gareth. |
#17
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Isolation transformer draws excessive current under no load condition
On Feb 10, 1:57*pm, "Gareth Magennis"
wrote: "mike" wrote in message ... On 2/10/2012 11:22 AM, Gareth Magennis wrote: It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. *It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. Er, not everyone lives in North America. * *I happen to live in the UK. Tell me again how you might measure the power consumption of a transformer. |
#18
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Isolation transformer draws excessive current under no load condition
On Feb 10, 4:00*pm, mike wrote:
On 2/10/2012 1:57 PM, Gareth Magennis wrote: "mike" wrote in message ... On 2/10/2012 11:22 AM, Gareth Magennis wrote: It's not unusual for a transformer to draw some amps when unloaded. That's what inductors do. The current should be out of phase with the voltage. What you care about is POWER. Measure the RMS power consumed by the transformer. That's what counts. How might you do that? (I don't have a power meter kicking around) Sure you do. It's on the outside of your house and goes round and round...They send you a bill every month. My base load is 200W, so an additional 300W would be easy to see. The newer ones simulate round and round with an lcd display and have a flashing IR led that can be used to measure actual power quite accurately. If you have an old Palm III vintage PDA, I can send you a program that lets you point the IR window at your power meter and graph consumption...but a stopwatch counting the display works as well. It's best to turn off everything you can to reduce the base load and improve the precision of your measurement with and without the transformer connected. If you wanna spend a few bucks, the P3 Kill A Watt meters are very handy in this application. Er, not everyone lives in North America. I happen to live in the UK. Sorry for your loss. Tell me again how you might measure the power consumption of a transformer. Not sure how repeating myself helps, but here goes. I'd plug it into a Kill A Watt meter. *That's how I got the other experimental results I mentioned in this thread. I also disclosed several other techniques. If you would read the parts you snipped, I also gave you several other ways to estimate the power consumption of a transformer. If you don't have a readable utility meter or a stopwatch or a light bulb or a voltmeter or a scale or a thermometer or a hand, you probably should look elsewhere for advice. *I'm all out. Wait..... I think I figured out how to do it with a used tea bag, the chime from Big Ben and a plate of fish and chips. Nope, you're still gonna need the hand. Gareth. Thanks! I needed that after the sleep-induced blather I posted |
#19
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Isolation transformer draws excessive current under no load condition
"Robert Macy" If it bothers you, you can add a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. ** You are a total ignoramus about transformers. FYI: Magnetising current is not inductive - it is highly non linear with peaks at each zero crossing. ..... Phil |
#20
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Isolation transformer draws excessive current under no load condition
"JW" Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? ** Is that 2.54 amps RMS or not ? In any case, is it getting rather hot and making a humming noise ? If not, then all is OK. The magnetising current will drop significantly when a full load is applied. BTW: Adding capacitance in parallel has no effect on the tranny whatsoever - and it will make the PF worse. ..... Phil |
#21
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Isolation transformer draws excessive current under no load condition
On Feb 11, 6:55*am, "Phil Allison" wrote:
"Robert Macy" If it bothers you, you can add *a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. ** You are a total ignoramus about transformers. *FYI: *Magnetising current is not inductive - *it is highly non linear with peaks at each zero crossing. .... *Phil Phil makes a good point about the terms being thrown around here. Magnetizing current is NOT core inductance current. It is magnetizing current. The better the core material the less this current will be. Back to the core' inductance...The core's inductance is usually 5 to 10 times the impedance of full load. You use a pair of windings to get to 1kVA, therefore per winding is 500VA, so at full load each winding is capable of 120Vac at 4.17A into a RESISTIVE load of 28.8 ohms. Now, the core winding's inductive reactance is at least 3 times that usually more than 5 times that or, 144j ohms [the j signifies reactive impedance of the core and that the current through the inductor will be out of phase with any load by 90 degrees.] At 60Hz that core's inductance will be about 382 mH. When wired in parallel to achieve the full 1kVA capability and NO LOAD each winding will have approx 0.834A for a total of 1.67A current. Of course this is reactive current and does not consume significant power. To get rid of such inductive reactive currents, which cause a 'lagging' power factor, it is possible to add a parallel capacitor essentially in resonance taking it to near zero, thus 'correcting' the power factor. Industrial consumers with lots of motors often have a rack [building] full of such capacitors that are switched in and out depending on the correction they need. It is of note that the current is ALWAYS there, even at full load, in parallel with your load. If the transformer is made properly, the waveform will be fairly linear, if the core is starting to saturate, the current at the peaks will increase due to that saturation A reasonable model predicts lower current than you saw, but 2.5A is still possible, just seems high. Further the winding resistance is often less than 1/10 of load, which implies less than 3 ohms, probably more like 1.5 ohms per winding. since they're in series to the load. The magnetizing current is not really the same as the core inductance current with the core inductance current in parallel with the load, albeit 90 degrees shifted. Magnetizing current is actually what it takes to 'turn on' the magnetic material. Really shows up if you try to measure the core's inductance with a little meter and only put 0.1Vac across a winding, you'll find the inductance you measure is almost nil. All caused because you haven't supplied the required 'magnetizing current' to overcome the material's coercivity. Hope this is more clear. |
#22
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Isolation transformer draws excessive current under no load condition
"Robert Macy" If it bothers you, you can add a high quality AC cap in parallel around 55 uF. That should 'resonate' out the reactive current assuming 120Vac, 60Hz yields around 127 mH. ** You are a total ignoramus about transformers. FYI: Magnetising current is not inductive - it is highly non linear with peaks at each zero crossing. Phil makes a good point about the terms being thrown around here. ** The one doing the chucking about is YOU - pal. Magnetizing current is NOT core inductance current. ** But includes it. Back to the core' inductance...The core's inductance is usually 5 to 10 times the impedance of full load. ** Wrong - it is way more than that. The NON LINEAR magnetising current increases with applied voltage and rise sharply as the max rating is approached. Now, the core winding's inductive reactance ..... ** Is so high the resulting current flow barely matters. At 60Hz that core's inductance will be about 382 mH. ** It is far more likely to be many Henries. To get rid of such inductive reactive currents, which cause a 'lagging' power factor, it is possible to add a parallel capacitor essentially in resonance taking it to near zero, thus 'correcting' the power factor. ** FFS - give up on this crap. You cannot correct the PF of an unloaded AC supply tranny with a parallel cap !!! It is of note that the current is ALWAYS there, even at full load, in parallel with your load. If the transformer is made properly, the waveform will be fairly linear, if the core is starting to saturate, the current at the peaks will increase due to that saturation ** In reality, the ONLY significant current flow occurs around each voltage zero crossing. BTW: Toroidal AC supply transformers are different. Inductance is way high and I mag is almost non existent up to the rated input voltage at the rated frequency. ..... Phil |
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Isolation transformer draws excessive current under no load condition
Wait.....
I think I figured out how to do it with a used tea bag, the chime from Big Ben and a plate of fish and chips. Nope, you're still gonna need the hand. Gareth. I'll bet you don't have a Passport. |
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Isolation transformer draws excessive current under no load condition
On 2/11/2012 3:49 PM, Gareth Magennis wrote:
Wait..... I think I figured out how to do it with a used tea bag, the chime from Big Ben and a plate of fish and chips. Nope, you're still gonna need the hand. Gareth. I'll bet you don't have a Passport. I'm intrigued. How do you use a Passport to measure transformer losses? If you don't have a hand, you can't even pick it up. |
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Isolation transformer draws excessive current under no load condition
On Feb 11, 5:13*pm, mike wrote:
On 2/11/2012 3:49 PM, Gareth Magennis wrote: Wait..... I think I figured out how to do it with a used tea bag, the chime from Big Ben and a plate of fish and chips. Nope, you're still gonna need the hand. Gareth. I'll bet you don't have a Passport. I'm intrigued. *How do you use a Passport to measure transformer losses? *If you don't have a hand, you can't even pick it up. I don't see how a radar detector is going to help him. http://www.ukspeedtraps.co.uk/passport8500.htm |
#26
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Isolation transformer draws excessive current under no load condition
On Fri, 10 Feb 2012 19:22:33 -0000, "Gareth Magennis"
put finger to keyboard and composed: Measure the RMS power consumed by the transformer. How might you do that? (I don't have a power meter kicking around) My local Aldi has these for AU$13: http://aldi.com.au/au/html/offers/28...12-01-30-08-10 The meter also reports the power factor. Same model number (GT-PM-04), probably made by Globaltronics: http://www.teknihall.nl/index.php?id=1129&L=nl - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
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Isolation transformer draws excessive current under no load condition
On Sun, 12 Feb 2012 01:05:04 +1100 "Phil Allison"
wrote in Message id: : "JW" Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? ** Is that 2.54 amps RMS or not ? Yes. I've measured it with the same result using both a Watts Up meter and a Fluke 87. In any case, is it getting rather hot and making a humming noise ? Making a humming noise, yes. It's not getting hot, the external temperature rise of the case is only about 10c. If not, then all is OK. The magnetising current will drop significantly when a full load is applied. Nail. Head. My test setup and how this all started: 120V in is being fed to a variac, then to the isolation transformer, then the load. On the secondary of the transformer I added a toggle switch that would connect the secondary in series or parallel depending whether I wanted 120V or 240V out. When I first wired up everything as I stated in my OP, being on the cautious side I placed a 1.5A fuse into the variac so if I mis-wired something there'd be no damage. Well, on first power up I slowly raised the voltage on the primary and at a little over 110V the fuse blew. The actual wattage when the primary is at 120V is only 42W as measured by the Watt meter. Here's why - the power factor is really crappy at just about .15. This would explain everything. I wonder if this is typical of a 1KVA transformer? I never thought to check the wattage being drawn... BTW: Adding capacitance in parallel has no effect on the tranny whatsoever - and it will make the PF worse. Noted, and thanks. Also, thanks to everyone else for their input - some very good thoughts. It would appear that there's no problem after-all. |
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Isolation transformer draws excessive current under no load condition
On Fri, 10 Feb 2012 12:34:41 -0800 mike wrote in
Message id: : Depending on how close the transformer is to the box, the metal box represents a shorted turn. All the flux is SUPPOSED to be inside the core....supposed to be. I don't expect taking it out of the box would make any significant difference, but I'd try it before scrapping the device. It's potted inside the box, so that's not possible. In any case it would seem that there's no problem (see my other post), thanks. |
#29
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Isolation transformer draws excessive current under no load condition
Out of curiosity, I took out my Tenma 72-545 1.5A isolation transformer.
On my Kill A Watt, it draws 60 mA unloaded, 3W / 7VA, with a power factor of 0.48. I assume the current without a load varies with the primary inductance, not the rated capacity. So the 2.45A drawn by the OP's transformer seems to be unnaturally high. |
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Isolation transformer draws excessive current under no load condition
On Feb 13, 5:45*am, JW wrote:
...snip... Adding capacitance in parallel has no effect on the tranny whatsoever *- and it will make the PF worse. Noted, and thanks. ...snip... Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, which means the amount of power you drop in your wiring [and pay for] will be less. Adding caps is a STANDARD way to adjust power factor to 1. Used by the industrial power consumers that are heavily penalized for lagging power factor. It is cheaper for them to add a building full of caps, just to shift their PF and pay less for power. If you do the analysis of power consumption throughout a standard AC mains power distribution, you will find that a lagging power factor [caused by motors, etc] INCREASES the power required to simply get billable wattage to you. And, it's surprisingly large. |
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Isolation transformer draws excessive current under no load condition
"Robert Macy" ** Is there any way to shut fools like you up ?? Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - because that idea is 100% STUPID. YOU are an obsessed IDIOT with a one track mind. **** off. .... Phil |
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Isolation transformer draws excessive current under no load condition
"JW" "Phil Allison" Is there any reason that a 120VAC to 120VAC isolation transformer would draw 2.54A on its primary when there is no load present on it's secondary? ** Is that 2.54 amps RMS or not ? Yes. I've measured it with the same result using both a Watts Up meter and a Fluke 87. ** Good. In any case, is it getting rather hot and making a humming noise ? Making a humming noise, yes. It's not getting hot, the external temperature rise of the case is only about 10c. ** Sounds about normal for a large e-core tranny The actual wattage when the primary is at 120V is only 42W as measured by the Watt meter. ** That is pretty high actually - a typical 1KVA tranny has about 6 to 8 % power loss at full load. Here's why - the power factor is really crappy at just about .15. This would explain everything. ** Not everything. You have to know that the current waveform is distorted - THIS fact is causing the poor PF when unloaded. .... Phil |
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Isolation transformer draws excessive current under no load condition
On Feb 13, 4:37*pm, "Phil Allison" wrote:
"Robert Macy" ** Is there any way to shut fools like you up ?? Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute *IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - *because that idea is 100% STUPID. * *YOU are an obsessed IDIOT with a one track mind. * ***** *off. ... *Phil I stand by what I said as technically correct. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. Quit spewing vitriole, making erroneous statements, *and* misleading. CONTRIBUTE, EDUCATE, and LEARN! |
#34
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Isolation transformer draws excessive current under no load condition
"Robert Macy" ** Is there any way to shut fools like you up ?? ---------------------------------------------------- Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - because that idea is 100% STUPID. YOU are an obsessed IDIOT with a one track mind. **** off. I stand by what I said as technically correct. ** LOL - that only makes you a BIGGER ****ing idiot. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. ** Shame you cannot supply one that backs up your idiotic comments about unloaded transformers. Listen PAL !!!!!!!! YOU are nothing but a lying, bull****ting NUT CASE !! Clueless to the core. FOAD. .... Phil |
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Isolation transformer draws excessive current under no load condition
On Feb 13, 8:04*pm, Robert Macy wrote:
On Feb 13, 4:37*pm, "Phil Allison" wrote: "Robert Macy" ** Is there any way to shut fools like you up ?? Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute *IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - *because that idea is 100% STUPID. * *YOU are an obsessed IDIOT with a one track mind. * ***** *off. ... *Phil I stand by what I said as technically correct. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. Quit spewing vitriole, making erroneous statements, *and* misleading. CONTRIBUTE, EDUCATE, and LEARN! What are your PFC capacitors doing when the transformer supplies a load? And if you were to switch them out when there was a load on the secondary, wouldn't it make more sense just to open the primary when there was no load? Then you wouldn't get any idle current draw at all. |
#36
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Isolation transformer draws excessive current under no load condition
On Feb 13, 9:15*pm, "Phil Allison" wrote:
"Robert Macy" ** Is there any way to shut fools like you up ?? * *---------------------------------------------------- Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - because that idea is 100% STUPID. YOU are an obsessed IDIOT with a one track mind. **** off. I stand by what I said as technically correct. ** LOL - *that only makes you a BIGGER ****ing idiot. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. ** Shame you cannot supply one that backs up your idiotic comments about unloaded transformers. Listen PAL *!!!!!!!! YOU *are nothing but a lying, bull****ting *NUT CASE !! Clueless to the core. FOAD. ... *Phil There is a difference between CANNOT supply reference material, DID NOT supply reference material, and WILL NOT supply reference material. I simply DID NOT for several reasons. Takes a lot of time. Your attitude appears closed, thus, I did not expect you to take the time to read what I took the time to research for you; and not sure anyone else is interested. However, I AM INTERESTED, and upon searching, found over 15,000 related articles. The artricles either dismiss the small effects/ distortions and then describe linear transformer models, or support the models I use/modified/developed. However, after one of the most promising articles also misused the term 'magnetizing current' as I had; I decided to rederive my transformer model from basics. I already have distrust for information in printed sources. I'm going to specifically look into whether the nonlinearity of the magnetizing current does lessen with load. I suspect that in an isolation transformer it does NOT, because the full voltage pretty much remains constant across the core. However, in an audio matching transformer, going from no load to full load drops the voltage across the core approx. in half and indeed the magnetizing current would then change, with less voltage across the core, the magnetizing current would also lessen. If the core material of an isolation transformer is extremely high quality with low coercivity, whether the transformer is loaded, or unloaded, will make small difference to the inductive current flowing through the core, BECAUSE the voltage the core must sustain stays pretty constant, whether unloaded or fully loaded. The inductive current through the core appears in parralell to the load and is pretty much constant. Being summed in quadrature just makes it appear that it is getting smaller. For example consider an isolation transformer that has 1A core current (assume linear) with NO LOAD, one would measure 1A of current flowing. Now load the transformer with a relatively small 5A load, now one would measure only 5.1A, which makes the core current APPEAR to be less as load increases, when in actuality, the core current has stayed the same 1A inductive current. = sqrt( 5*5 + 1*1 ) = 5.1 Is your comment that the core's current decreases with load based upon such observation? Your personal attack is unwarranted. I'm not a "...lying, bull****ting NUT CASE !!" But this discussion is not about how you perceive my character, rather this discussion is about explaining whether the OP's transformer is broken or not, based upon his observation that the transformer's leakage current is 2.5A. From that question the discussion has become a positive LEARNING experience! so, STICK to the SUBJECT. However, thanks for the pricelss comment: "Clueless to the core." LOL! What did I do to deserve such PUNishment? |
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Isolation transformer draws excessive current under no load condition
On Feb 14, 9:35*am, spamtrap1888 wrote:
On Feb 13, 8:04*pm, Robert Macy wrote: On Feb 13, 4:37*pm, "Phil Allison" wrote: "Robert Macy" ** Is there any way to shut fools like you up ?? Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, ** Absolute BULL**** !!!!!!!!! which means the amount of power you drop in your wiring [and pay for] will be less. ** Absolute *IDIOCY !!!!!!! Adding caps is a STANDARD way to adjust power factor to 1. ** But never used with an off load transformer - *because that idea is 100% STUPID. * *YOU are an obsessed IDIOT with a one track mind. * ***** *off. ... *Phil I stand by what I said as technically correct. Many, many technical journals, text books, and supporting calculations based upon terms of definition confirm what I said. Quit spewing vitriole, making erroneous statements, *and* misleading. CONTRIBUTE, EDUCATE, and LEARN! What are your PFC capacitors doing when the transformer supplies a load? And if you were to switch them out when there was a load on the secondary, wouldn't it make more sense just to open the primary when there was no load? Then you wouldn't get any idle current draw at all. The cap in parallel will continue to 'remove' the inductive current - as far as the AC mains sees it. The inductive current remains whether the transformer is loaded or not. Completely disconnecting everything from the AC mains will always save power. As far as I know, no industrial power consumer adds caps just for transformer core currents, only for large motors that are extremely inductive loads. |
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Is there any way to this MORON up ?
"Robert Macy = Troll " ** Is there any way to this MORON up ?? ( Load of totally absurd crap deleted ) .... Phil |
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Isolation transformer draws excessive current under no load condition
"Robert Macy" ** Is there any way to shut fools like you up ?? ---------------------------------------------------- Shame you cannot supply one that backs up your idiotic comments about unloaded transformers. Listen PAL !!!!!!!! YOU are nothing but a lying, bull****ting NUT CASE !! Clueless to the core - pun intended. FOAD. .... Phil |
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Isolation transformer draws excessive current under no load condition
On 14/02/2012 12:52 AM, Robert Macy wrote:
On Feb 13, 5:45 am, wrote: ...snip... Adding capacitance in parallel has no effect on the tranny whatsoever - and it will make the PF worse. Noted, and thanks. ...snip... Adding caps will indeed have NO effect on the tranny, but WILL improve the PF as seen by your AC mains, which means the amount of power you drop in your wiring [and pay for] will be less. Adding caps is a STANDARD way to adjust power factor to 1. Used by the industrial power consumers that are heavily penalized for lagging power factor. It is cheaper for them to add a building full of caps, just to shift their PF and pay less for power. If you do the analysis of power consumption throughout a standard AC mains power distribution, you will find that a lagging power factor [caused by motors, etc] INCREASES the power required to simply get billable wattage to you. And, it's surprisingly large. But, except for the extra power dissipated in the household wiring, is not measured by the meter, and not included in the billed energy units. Sylvia. |
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