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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
hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks,
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#2
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isolation transformer
On 22/11/2017 18:50, Stu jaxon wrote:
hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Does your ohmeter say there is a connection across both sides? ie an autotransformer. |
#3
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isolation transformer
On Wednesday, November 22, 2017 at 1:50:46 PM UTC-5, Stu jaxon wrote:
hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Most voltage-converter transformers are auto-transformers and do not provide isolation. As Mr. Cook suggests, see if you get continuity from the primary to the secondary. http://www.electronics-tutorials.ws/...er/trans28.gif This is an auto-transformer. Peter Wieck Melrose Park, PA |
#4
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isolation transformer
On 11/22/2017 01:50 PM, Stu jaxon wrote:
hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: |
#5
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isolation transformer
On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote:
On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? |
#6
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isolation transformer
On 23/11/2017 7:16 AM, Stu jaxon wrote:
On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? -- Trevor Wilson www.rageaudio.com.au |
#7
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isolation transformer
On Wednesday, November 22, 2017 at 3:41:45 PM UTC-5, Trevor Wilson wrote:
On 23/11/2017 7:16 AM, Stu jaxon wrote: On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? -- Trevor Wilson www.rageaudio.com.au to protect my equipment, i picked up a new hobby. |
#8
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isolation transformer
On 23/11/2017 7:46 AM, Stu jaxon wrote:
On Wednesday, November 22, 2017 at 3:41:45 PM UTC-5, Trevor Wilson wrote: On 23/11/2017 7:16 AM, Stu jaxon wrote: On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? -- Trevor Wilson www.rageaudio.com.au to protect my equipment, i picked up a new hobby. **An isolation transformer won't protect your equipment. An isolation transformer is used to assist in protecting the operator (though that is far from guaranteed). Why do you imagine that an isolation transformer will protect your equipment? What sort of equipment? What do you imagine the transformer will protect your equipment from? -- Trevor Wilson www.rageaudio.com.au |
#9
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isolation transformer
On November 23, 2017 7:46 AM, Stu jaxon wrote:
On Wednesday, November 22, 2017 at 3:41:45 PM UTC-5, Trevor Wilson wrote: On 23/11/2017 7:16 AM, Stu jaxon wrote: On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? to protect my equipment, i picked up a new hobby. From what? And when you say 'surge protector', could you also have 'surge arrestor' (for much un-predictably higher un-controlled voltage input) in mind, as well? To start with, your hobby device power processing should connect to an un-insulated copper or aluminum wire that should be in properly grounded and secured contact with your facility's (cold) water main. Additionally, use specifically GFCI-advertized outlets when you think there is danger to people or property. It says that in the recent NEC- book rules, doesn't it? |
#10
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isolation transformer
On Wednesday, 22 November 2017 20:46:18 UTC, Stu jaxon wrote:
On Wednesday, November 22, 2017 at 3:41:45 PM UTC-5, Trevor Wilson wrote: On 23/11/2017 7:16 AM, Stu jaxon wrote: On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? to protect my equipment, i picked up a new hobby. Your comments indicate that you most likely have several misunderstandings. It's your choice but would probably help you to say a lot more about what you're doing. NT |
#11
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isolation transformer
On 11/22/2017 03:16 PM, Stu jaxon wrote:
here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? That unit appears to be intended for those situations where, say a 120 VAC appliance sold in the U.S. is to be used in another country like the UK on 240 VAC (also assuming the U.S. appliance can cope with 50 Hz vs 60 Hz). Vice-versa for using a UK-marketed appliance in the U.S. Most likely it's a single winding transformer with a tap(s), which makes it an autotransformer (no input-to-output isolation). But it could also have separate primary and secondary coils. No way to tell from a picture or not having a schematic. Sincerely, -- J. B. Wood e-mail: |
#12
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isolation transformer
Some basics:
a) Isolation transformers are designed to protect users under some conditions, and *certain* types of equipment under *VERY* limited conditions. Those latter applications are primarily under hospital and research conditions where an isolated ground is not enough. Generally, RF-shielded rooms use isolation transformers in their power-supplies, for example. But, no equipment protects against deliberate stupidity or carelessness. If one inserts oneself into the circuit, one will be stung. b) Voltage adjustment transformers tend to be as inexpensive as possible per-watt. A true isolation transformer would have very nearly twice as much conductor in it as a simple auto-transformer. Not t mention more core material as well - I am careful not to use 'copper' or 'iron', as very cheap devices will use neither. c) Any unnecessary equipment adds a degree of unnecessary complexity - and with it an opportunity for error. I have a 110/220 step-up/down transformer purchased in Saudi Arabia with no markings at all. It came with a Euro/US adaptor that could plug into either side. So, I engraved "High Side" and "Low Side" on. Imagine me going the 'wrong way' in actual use. Not so bad going from 110 to 55 volts. But 220 - 440 V, not so good either. If you need to step up/down, check the equipment. A surprising amount of vintage audio equipment has multi-tap primary transformers that might require only a simple change in wiring, and a surprising amount of modern consumer electronics have smart supplies that do it all automatically. Otherwise, a brand-name surge protector (with a downline equipment warranty) will be your best option to protect your equipment. Peter Wieck Melrose Park, PA |
#13
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isolation transformer
Stu jaxon wrote:
On Wednesday, November 22, 2017 at 3:41:45 PM UTC-5, Trevor Wilson wrote: On 23/11/2017 7:16 AM, Stu jaxon wrote: On Wednesday, November 22, 2017 at 2:39:09 PM UTC-5, J.B. Wood wrote: On 11/22/2017 01:50 PM, Stu jaxon wrote: hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks, Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, -- J. B. Wood e-mail: here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.? **No. It's a step-down transformer, or autoformer. No way of knowing, unless you can contact the manufacturer, or measure it yourself. I doubt that it is an isolation transformer. Which begs the question: Why do you need an isolation transformer? -- Trevor Wilson www.rageaudio.com.au to protect my equipment, i picked up a new hobby. Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. This prevents noise differentials between ground and output. There is always voltage sag, so a120 vol output is at full load. More perhaps too much with small load. Could be 10- 15% over 120 volts. This is not a test transformer with isolated output from ground referenced mains. Some have voltage regulation too. Greg |
#14
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isolation transformer
On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote:
Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. That's only true of SOME isolation transformers; the ones used for bench safety when working on live equipment do NOT make the neutral-ground connection. |
#15
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isolation transformer
On Tuesday, 28 November 2017 23:08:59 UTC, whit3rd wrote:
On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote: Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. That's only true of SOME isolation transformers; the ones used for bench safety when working on live equipment do NOT make the neutral-ground connection. quite. And building site transformers earth the centre tap. Re noise, there's the capacitance... NT |
#16
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isolation transformer
whit3rd wrote:
On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote: Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. That's only true of SOME isolation transformers; the ones used for bench safety when working on live equipment do NOT make the neutral-ground connection. All commercial isolation transformers must inform to code. All Tripplite isolators are grounded. It worries me some think it's all the same. Easy enough to examine or measure. Still can be a problem on equipment needing a ground configuration for the circuitry. Greg |
#17
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isolation transformer
On Wednesday, November 29, 2017 at 12:22:46 AM UTC-8, GS wrote:
whit3rd wrote: On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote: Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. That's only true of SOME isolation transformers; the ones used for bench safety when working on live equipment do NOT make the neutral-ground connection. All commercial isolation transformers must inform to code. All Tripplite isolators are grounded. Commercial isolation transformers are leakage-tested, but the ground-neutral connection is not always present. Tripplite also makes smart power strips that won't work if plugged into an isolation transformer that doesn't strap ground-to-neutral. So, they work with isolated (hospitals, sometimes) power only if you add a Tripplite isolator. details are here, in the reviews section: https://www.tripplite.com/for-patient-care-vicinity-ul-60601-1-medical-grade-ps-4-15a-hospital-grade-outlets-safety-covers-15-ft-cord~PS415HGULTRA/ |
#18
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isolation transformer
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#19
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isolation transformer
On Wed, 22 Nov 2017 14:39:04 -0500, "J.B. Wood"
wrote: Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. |
#21
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isolation transformer
On Thursday, 7 December 2017 21:17:18 UTC, Michael Terrell wrote:
tabbypurr wrote: On Tuesday, 28 November 2017 23:08:59 UTC, whit3rd wrote: On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote: Commercial isolation transformers get rid of common mode noise, and since one leg of output is tied to ground, forms a new local neutral. That's only true of SOME isolation transformers; the ones used for bench safety when working on live equipment do NOT make the neutral-ground connection. Quite. And building site transformers earth the centre tap. IOW, they convert the European 240volt system to the American 120V/240V system. They output 110v centre earthed, so nothing is over 55v ac from ground. It was the building site standard until RCDs made 110v not really needed. NT |
#22
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isolation transformer
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#23
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isolation transformer
On Fri, 8 Dec 2017 01:14:00 -0500, Michael A Terrell
wrote: Unless they didn't want to replace all their existing power tools? The wiring is US, even if the transformer is only 50%. Not all of our power tools are 120 VAC. Some are 240, and others are 480 VAC, three phase. I've always wondered why so many foreign countries have 240volts as their standard voltage. We in the U.S. do just fine with 120v, except for heating devices and some very large motors. So why do they continue to use 240volts in these foreign countries? If for no other reason, it's considerably more dangerous..... I know all too well how getting shocked from 120v feels, and although I have never gotten shocked by 240v, I know it's a lot worse. Both voltages can kill a person, but I'd think that 240 kills faster... |
#24
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isolation transformer
Very simplistic:
240 VAC Hot/Neutral is much more efficient than 120 VAC Hot/Neutral. Euro (residential) distribution is primarily three-wire ungrounded three-phase with varying phase-to-phase voltage. Grounding is done at the distribution transformer. Whereas North American distribution is 4-wire three-phase with single-phase 120/240 secondary distribution. Grounding in NA is done at multiple points. Bottom line, Euro distribution allows either much more power on the same distance/size conductor, or the same amount of power to be transmitted twenty (20) times further for the same size conductor. Again, a benefit of learning from others. Post War Europe - when power-to-the-people became the norm rather than the exception was not rich in resources. So, a system that permitted more efficient distribution became a significant advantage. Very simplistically. Peter Wieck Melrose Park, PA |
#26
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isolation transformer
On 12/8/2017 2:25 PM, wrote:
I know all too well how getting shocked from 120v feels, and although I have never gotten shocked by 240v, I know it's a lot worse. Working at Northrop Aircraft, I had to deal with 120, 240 and 480 volt systems. To put it simply, 120 will get your attention and you let go of it. 480 will knock you on your ass. 240 however with grab hold of you and hang on. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
#27
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isolation transformer
On Friday, 8 December 2017 20:28:25 UTC, wrote:
On Fri, 8 Dec 2017 01:14:00 -0500, Michael A Terrell wrote: Unless they didn't want to replace all their existing power tools? The wiring is US, even if the transformer is only 50%. Not all of our power tools are 120 VAC. Some are 240, and others are 480 VAC, three phase. I've always wondered why so many foreign countries have 240volts as their standard voltage. We in the U.S. do just fine with 120v, except for heating devices and some very large motors. So why do they continue to use 240volts in these foreign countries? If for no other reason, it's considerably more dangerous..... it's safer and cheaper It's also barely practical to run a 3kW heating device on 110v. Our 240v 13A delivers 3.1kW per socket no problem. I know all too well how getting shocked from 120v feels, and although I have never gotten shocked by 240v, I know it's a lot worse. Both voltages can kill a person, but I'd think that 240 kills faster... it sure does. Deaths from electrical fires greatly outnumber electrocutions, and less current reduces the risk of those. NT |
#28
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isolation transformer
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#29
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isolation transformer
wrote:
On Wed, 22 Nov 2017 14:39:04 -0500, "J.B. Wood" wrote: Hello, and do you have a particular make and model number of device in mind? An marketed as an AC isolation transformers usually doesn't provide voltage conversion with input (primary) to output (secondary) energy transfer solely via magnetic coupling. There are also adjustable autotransformers (e.g. the venerable Variac brand) that, for example, takes 120 VAC at input and can provides 0-130 VAC output. The primary and secondaries of these devices aren't conductively isolated (as an ohmmeter test will confirm). There are also devices which combine both isolation and adjustable autotransformer function in one enclosure. Or you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and follow it with an adjustable autotransformer, keeping in mind the maximum AC current/power ratings of the devices. Sincerely, I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. Greg |
#30
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isolation transformer
On Sunday, December 10, 2017 at 3:48:23 AM UTC-5, GS wrote:
make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. Properly designed Isos are vastly over-sized for the rated load. Which is why a good isolation transformer is not cheap, and a cheap isolation transformer is not good. Can't have both - new, anyway. The Iso in my Heath is rated at 4A, fused at 3A, weighs around 10 pounds and does not sag. Some of the hospital-grades units I have worked with in the past were heavy enough to be a major PITA to lift or move, and rated in the 8 - 10 A region. Peter Wieck Melrose Park, PA |
#31
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isolation transformer
On Sunday, 10 December 2017 08:48:23 UTC, GS wrote:
wrote: I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. I can't imagine how that could be worth patenting. Many patents have no value. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. It would take an unusually tiny transformer to be that badly regulated. NT |
#33
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isolation transformer
On connecting transformers back to back to make an isolation
transformer. A pair of 6.3 filament transformers, back to back, was a popular kluge back in the '60s, but NOT for use as an isolation transformer for testing radios. Yes it was an isolation transformer, but it was to provide an isolated 120 VAC for a B+ supply on small projects. That 5 amp secondary at 6.3 volts translates to only 270 mA on the primary side. Two transformers back to back is only going to be good for about 200 mA load on the "isolated" side. AA5 "hot chassis radios from "back then" were typically 30 to 40 watts. That's 250-349 mA. This would be marginal at best. It never fails to amaze me the number or ways people can come up with to do things the wrong way. Then the amount of time they waste trying to justify it. -- Jeff-1.0 wa6fwi http://www.foxsmercantile.com |
#34
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isolation transformer
On Sunday, 10 December 2017 18:31:33 UTC, Foxs Mercantile wrote:
On 12/10/2017 8:14 AM, tabbypurr wrote: On Sunday, 10 December 2017 08:48:23 UTC, GS wrote: There was an old patent using two neon sign type transformers back to back. I can't imagine how that could be worth patenting. Many patents have no value. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. It would take an unusually tiny transformer to be that badly regulated. "Neon sign transformer" They are DESIGNED to be baldy regulated. High voltage to strike the initial arc, then sag down to a sustaining voltage. Same design with fluorescent ballast transformers. Both are designed for a specific purpose, not to be used in some *******ized lash up. which is one reason why no sensible person would use such a lash up NT |
#35
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isolation transformer
wrote:
On Sunday, 10 December 2017 08:48:23 UTC, GS wrote: wrote: I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. I can't imagine how that could be worth patenting. Many patents have no value. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. It would take an unusually tiny transformer to be that badly regulated. NT In my experience 10% droop is pretty good. 15% more common. I'm just talking transformers in general. A Feroresonant one will do good. Greg |
#36
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isolation transformer
wrote:
On Sunday, 10 December 2017 08:48:23 UTC, GS wrote: wrote: I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. I can't imagine how that could be worth patenting. Many patents have no value. I think I missed something in middle, like carbon trace resistors. Greg The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. It would take an unusually tiny transformer to be that badly regulated. NT |
#37
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isolation transformer
On Tuesday, 12 December 2017 08:38:21 UTC, GS wrote:
tabbypurr wrote: On Sunday, 10 December 2017 08:48:23 UTC, GS wrote: wrote: I reaad on some website where someone took two 120 to 240 volt transformers, connected both 240 windings together and ended up with 120 on the secondary, completely isolated from the AC line. This makes sense, for someone who has two such transformers on hand. But would not make sense to buy two transformers. There was an old patent using two neon sign type transformers back to back. I can't imagine how that could be worth patenting. Many patents have no value. The problem with isos, you get higher voltage with no load than normal, and droop 10-20% with load.. It would take an unusually tiny transformer to be that badly regulated. NT In my experience 10% droop is pretty good. 15% more common. I'm just talking transformers in general. A Feroresonant one will do good. Greg Isolating transformers are not eh same animal as small appliance transformers. For the latter, you only need to get up to 12VA to get 15% regulation and 50VA to get 10%. Isos are more typically 500VA or more. NT |
#38
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isolation transformer
On Tuesday, December 12, 2017 at 3:38:21 AM UTC-5, GS wrote:
In my experience 10% droop is pretty good. 15% more common. I'm just talking transformers in general. A Feroresonant one will do good. Sola-type CV transformers put out a wretched wave-form. If your connected device is sensitive to mains noise, they will not work out so well. They will also back-feed noise in some cases. It is important to understand that a purpose-made isolation transformer is designed not to sag, and is not-ever-never-ever operated at the margins of its theoretical design. They are operated at a limit well below their theoretical capacity for just this reason. Back-to-back kluges are the product of desperation or a McGyver type with a small brain, emphatically not any sort of long-term or permanent application. Peter Wieck Melrose Park, PA |
#39
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