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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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Safely discharging a capacitor
Going to attempt to change the capacitor on my tumble dryer... Its a 8
micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? |
#2
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Safely discharging a capacitor
paulfoel wrote:
Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Does your meter support capacitance? if not you're wasting you're time, these are only a few pence anyway in a maplins outlet. -- Sir Benjamin Middlethwaite |
#3
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Safely discharging a capacitor
In article .com,
"paulfoel" writes: Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Most likely it is discharged through the motor windings unless the switching is such that it gets disconnected, although relying on the motor windings being intact is not smart when the thing is known not to be working properly. Secondly, it probably has a bleed resistor built in, although those can fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel |
#4
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Safely discharging a capacitor
fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 David |
#5
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Safely discharging a capacitor
"paulfoel" wrote in message oups.com... Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Does the motor have brushes and a commutator? If so, change the brushes before you start looking elsewhere, they're seldom expensive and are a consumable item. Capacitors may or may not last the life of an appliance but brushes are certain to wear from day one and are usually the first suspect in a misfiring/intermittant motor. With brush type motors, the brushes wear down and consequently less pressure is applied by the spring, causing a higher resistance/poorer connection between brush and commutator. An arc is caused, which heats the brush and can deform the casing causing the brush to stick, making the problem increase exponentially. It also causes the commutator to become blackened which makes matters even worse. I'd take out the brush carriers and check the brushes move freely and that there's plenty of length left on them. Also check the commutator is clean. If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave |
#6
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Safely discharging a capacitor
"vortex2" wrote in message .. . Must be interesting when you accidently short one of these! Nah - that's nancy stuff for kids ..... real man stuff here! http://www.amasci.com/amateur/capexpt.html |
#7
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Safely discharging a capacitor
On 21 Dec 2005 04:23:18 -0800, "paulfoel"
wrote: Assuming it is still ' live' how do I discharge it to make it safe? Stick a big screwdriver across it. This is bad advice for capacitors in general, but for these motor capacitors used on 240V AC only it's OK. There is minimal likelihood of there being any charge left in there, you're only shorting it to make _sure_ before you touch it by hand. If it _had_ been charged up by the Workshop Pixies beforehand, then it just costs you a screwdriver and a pair of trousers. If you're fooling with HT DC on capacitors, then fit proper bleed resistors before you start and make yourself a discharging stick with a resistor in it. |
#8
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Safely discharging a capacitor
"Dave D" wrote in message ... "paulfoel" wrote in message oups.com... Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Does the motor have brushes and a commutator? If so, change the brushes before you start looking elsewhere, they're seldom expensive and are a consumable item. Capacitors may or may not last the life of an appliance but brushes are certain to wear from day one and are usually the first suspect in a misfiring/intermittant motor. With brush type motors, the brushes wear down and consequently less pressure is applied by the spring, causing a higher resistance/poorer connection between brush and commutator. An arc is caused, which heats the brush and can deform the casing causing the brush to stick, making the problem increase exponentially. It also causes the commutator to become blackened which makes matters even worse. I'd take out the brush carriers and check the brushes move freely and that there's plenty of length left on them. Also check the commutator is clean. If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave nonsense it is clearly an induction motor. |
#9
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Safely discharging a capacitor
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#10
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Safely discharging a capacitor
"powerstation" wrote in message ... Dave nonsense it is clearly an induction motor. Probably, but I'm not at the OP's house to take a look and be certain this is the case, and as the symptoms are classic signs of worn brushes, I thought I'd mention it in case. The rest of my advice about looking for bad connections before replacing components is perfectly valid as well. Dave |
#11
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Safely discharging a capacitor
"vortex2" writes:
fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 A capacitor with a digital readout? Now they've gone over the top! --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#12
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Safely discharging a capacitor
powerstation wrote: "Dave D" wrote in message ... "paulfoel" wrote in message oups.com... Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Does the motor have brushes and a commutator? If so, change the brushes before you start looking elsewhere, they're seldom expensive and are a consumable item. Capacitors may or may not last the life of an appliance but brushes are certain to wear from day one and are usually the first suspect in a misfiring/intermittant motor. With brush type motors, the brushes wear down and consequently less pressure is applied by the spring, causing a higher resistance/poorer connection between brush and commutator. An arc is caused, which heats the brush and can deform the casing causing the brush to stick, making the problem increase exponentially. It also causes the commutator to become blackened which makes matters even worse. I'd take out the brush carriers and check the brushes move freely and that there's plenty of length left on them. Also check the commutator is clean. If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave nonsense it is clearly an induction motor. Yep. It is. |
#13
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Safely discharging a capacitor
I worked for many years in the domestic appliance repair trade. To
discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good In the absense of a neon device you could use a light bulb or a resistor of a suitable value. btw, I`ve never seen a tumble dryer in the UK with a brush type motor, always induction motors with either capacitor or relay start. Ron(UK) -- Lune Valley Audio Public address system Hire, Sales, Repairs www.lunevalleyaudio.com |
#14
Posted to sci.electronics.repair,free.uk.diy.home,uk.d-i-y
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Safely discharging a capacitor
Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? Does the motor have brushes and a commutator? If so, change the brushes before you start looking elsewhere, they're seldom expensive and are a consumable item. Capacitors may or may not last the life of an appliance but brushes are certain to wear from day one and are usually the first suspect in a misfiring/intermittant motor. With brush type motors, the brushes wear down and consequently less pressure is applied by the spring, causing a higher resistance/poorer connection between brush and commutator. An arc is caused, which heats the brush and can deform the casing causing the brush to stick, making the problem increase exponentially. It also causes the commutator to become blackened which makes matters even worse. I'd take out the brush carriers and check the brushes move freely and that there's plenty of length left on them. Also check the commutator is clean. If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave nonsense it is clearly an induction motor. Yep. It is. There is a TB regarding capacitors on White Knight TD's, the fault is caused by the capacitor being affixed too close to the motor, the spare part now includes a bracket to move it further away. Sometimes even when the part is replaced the motor subsequently burns out if the windings have been damaged by a stalled motor. |
#15
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Safely discharging a capacitor
On Wed, 21 Dec 2005 15:09:16 -0000, "Dave D" wrote:
Probably, but I'm not at the OP's house to take a look and be certain this is the case, and as the symptoms are classic signs of worn brushes, I thought I'd mention it in case. How many tumble driers use brushed motors? How many brushed motors also have a capacitor? Now this assumes that it _is_ a capacitor of course. If it does have a brushed motor, I wouldn't be surprised if it had a line filter instead and these can look very similar to capacitors. |
#16
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Safely discharging a capacitor
"Ron(UK)" wrote in message ... I worked for many years in the domestic appliance repair trade. To discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good In the absense of a neon device you could use a light bulb or a resistor of a suitable value. The neon tester will only get you to around the 70 volt level. Still not a bad idea. That way you can see if it is charged to the full voltage. If you are going to use a light bulb, you may as well use the screwdriver as when the bulb is cold the resisitance is very low. |
#17
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Safely discharging a capacitor
Ralph Mowery wrote:
"Ron(UK)" wrote in message ... I worked for many years in the domestic appliance repair trade. To discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good In the absense of a neon device you could use a light bulb or a resistor of a suitable value. The neon tester will only get you to around the 70 volt level. Still not a bad idea. That way you can see if it is charged to the full voltage. If you are going to use a light bulb, you may as well use the screwdriver as when the bulb is cold the resisitance is very low. In theory, but a neon strikes around 70/90 volts, it maintains down to a much lower voltage and will drain much of the charge. try it. Using a bulb, you get a flash of light, using a screwdrive you get a big bang and a flash of hot metal - better watch your eyes. Ron -- www.lunevalleyaudio.com |
#18
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Safely discharging a capacitor
"Ron(UK)" writes:
I worked for many years in the domestic appliance repair trade. To discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good In the absense of a neon device you could use a light bulb or a resistor of a suitable value. btw, I`ve never seen a tumble dryer in the UK with a brush type motor, always induction motors with either capacitor or relay start. Not sure how you'd get down to a few V if going through a neon tester. They typically drop out at around 50-60 V. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#19
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Safely discharging a capacitor
vortex2 wrote:
fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 David Does anybody worry about the inrush current to these, and what that does to one's alternator? -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#20
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Safely discharging a capacitor
Sam Goldwasser wrote:
"Ron(UK)" writes: I worked for many years in the domestic appliance repair trade. To discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good In the absense of a neon device you could use a light bulb or a resistor of a suitable value. btw, I`ve never seen a tumble dryer in the UK with a brush type motor, always induction motors with either capacitor or relay start. Not sure how you'd get down to a few V if going through a neon tester. They typically drop out at around 50-60 V. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. Indeed. And they draw so little current that it'll take forever to discharge a big capacitor using one. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
#21
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Safely discharging a capacitor
CJT wrote:
vortex2 wrote: fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 David Does anybody worry about the inrush current to these, and what that does to one's alternator? No. Car wiring is radial from the battery to alternator and from the battery to load. The impedance of the battery is much lower than that of the alternator radial circuit - thus transient currents will be met almost entirely by the battery. You may like to think what effect the starter motor has on the alternator. Also, the energy stored in a capacitor depends on the capacitance and on the square of the voltage. Rather than have a 1F capacitor on the 12v line, it would be much better to go to the higher voltage power rails of the amplifier and stick beefy capacitors there. -- Sue |
#22
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Safely discharging a capacitor
nonsense it is clearly an induction motor. Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. I've got a Creda washer sitting in my basement right now awaiting arrival of a set of brushes amoung other things, no idea how it ended up on this side of the pond but it's a cool little machine. |
#23
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Safely discharging a capacitor
http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 A capacitor with a digital readout? Now they've gone over the top! They went over the top years ago, those capacitors have been available for a while. Just try to find a car CD player anymore that looks at home in anything but a gaudy racer boy Japenese compact. Seems like they're all fugly and bubbly, loaded with useless distracting blinky lights and buttons so small and jumbled it's impossible to operate them safely while driving. |
#24
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Safely discharging a capacitor
Palindr˜»me wrote:
CJT wrote: vortex2 wrote: fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 David Does anybody worry about the inrush current to these, and what that does to one's alternator? No. Car wiring is radial from the battery to alternator and from the battery to load. The impedance of the battery is much lower than that of the alternator radial circuit - thus transient currents will be met almost entirely by the battery. You may like to think what effect the starter motor has on the alternator. While this is true, don't forget that the starter motor will never be operating under load while the alternator is producing any current unless you're jump starting another car. |
#25
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Safely discharging a capacitor
On Wed, 21 Dec 2005 19:56:57 UTC, James Sweet
wrote: nonsense it is clearly an induction motor. Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. But we were talking about a dryer. They seem to use induction motors (well, mine does). -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by Avenue Supplies, http://avenuesupplies.co.uk |
#26
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Safely discharging a capacitor
"James Sweet" wrote in message news:dsiqf.694$2B5.463@trnddc01... nonsense it is clearly an induction motor. Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. I've got a Creda washer sitting in my basement right now awaiting arrival of a set of brushes amoung other things, no idea how it ended up on this side of the pond but it's a cool little machine. But its NOT a washing machine he's fixing ! its a tumble drier |
#27
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Safely discharging a capacitor
nonsense it is clearly an induction motor. Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. But we were talking about a dryer. They seem to use induction motors (well, mine does). All the ones I have ever seen are, because they revolve the drum slowly, a washing machine needs to spin at high speed |
#28
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Safely discharging a capacitor
On Wed, 21 Dec 2005 19:59:50 GMT, James Sweet wrote:
http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 A capacitor with a digital readout? Now they've gone over the top! They went over the top years ago, those capacitors have been available for a while. Just try to find a car CD player anymore that looks at home in anything but a gaudy racer boy Japenese compact. Seems like they're all fugly and bubbly, loaded with useless distracting blinky lights and buttons so small and jumbled it's impossible to operate them safely while driving. Thats because youy get a really good one bult nto any car that chavs don't buy. |
#29
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Safely discharging a capacitor
In article dsiqf.694$2B5.463@trnddc01,
James Sweet writes: Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. I've got a Creda washer sitting in my basement right now awaiting arrival of a set of brushes amoung other things, no idea how it ended up on this side of the pond but it's a cool little machine. A European washing machine operates its motor at a large number of different speeds (and even gradually vary the speed in some cases) throughout various stages of the wash cycle, and depending on the wash program selected. This is most easily done with a universal motor combined with an electronic speed control board and servo feedback. (It used to be done with an induction motor and solenoid operated gearbox 40 years ago, but that's more expensive and a lot less flexible.) Tumble driers only have to be able to reverse the drum, but don't need to change the speed. For this simpler requirement, an induction motor tends to win. -- Andrew Gabriel |
#30
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Safely discharging a capacitor
On Wed, 21 Dec 2005 18:37:10 GMT, CJT wrote:
vortex2 wrote: fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it. -- Andrew Gabriel I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems. Must be interesting when you accidently short one of these! http://search.ebay.co.uk/search/1-fa...QQfclZ4QQfnuZ1 David Does anybody worry about the inrush current to these, and what that does to one's alternator? its nowhere as bad as what a statrter motor does...alternators are limited anyway. |
#31
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Safely discharging a capacitor
Bob Eager wrote:
On Wed, 21 Dec 2005 19:56:57 UTC, James Sweet wrote: nonsense it is clearly an induction motor. Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. But we were talking about a dryer. They seem to use induction motors (well, mine does). Yeah somehow I missed that we were discussing a dryer. The matching Creda dryer does in fact have an induction motor in it, weird to see a clothes dryer that will plug into a 15A 240v receptacle, US dryers are almost universally 4KW. |
#32
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Safely discharging a capacitor
Tumble driers only have to be able to reverse the drum, but don't need to change the speed. For this simpler requirement, an induction motor tends to win. Why do they have to be able to reverse the drum? I've never seen a dryer that did that, obviously they must exist but I'm not sure of the benefits. |
#33
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Safely discharging a capacitor
Thats because youy get a really good one bult nto any car that chavs don't buy. Would be nice, but I'm afraid back in '84, '87 and '88 respectively, cars didn't come with CD players of any sort, hence my need to install aftermarket units in mine. Not to mention I'm still not aware of any OEM units that will play MP3 discs, an essential feature to me that made all earlier CD players virtually obsolete. 10 hours of music on one disc, no more fumbling with CD's in traffic. |
#34
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Safely discharging a capacitor
On Wed, 21 Dec 2005 20:34:49 UTC, James Sweet
wrote: Why do they have to be able to reverse the drum? I've never seen a dryer that did that, obviously they must exist but I'm not sure of the benefits. Loads of them do it[1]...helps to untangle the clothes. [1] except in the backwards USA? -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by Avenue Supplies, http://avenuesupplies.co.uk |
#35
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Safely discharging a capacitor
In message .com,
paulfoel writes Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one. I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have? Assuming it is still ' live' how do I discharge it to make it safe? It depends what's across it, stick a screwdriver across it - that'll discharge it -- geoff |
#36
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Safely discharging a capacitor
In message , Slurp
writes Nah - that's nancy stuff for kids .... real man stuff here! http://www.amasci.com/amateur/capexpt.html Where does one start, any site that had the following in the disclaimer 'DISCLAIMER: the experiments described below are fantastically dangerous, and they are described without reference to the many precautions needed to guarantee the experimenter's safety. Accidentally discharging these capacitor banks through your body can not only kill, but can explode flesh and bone.' Followed by 'PARENTS: I supply no detailed plans for reproducing these experiments. Also, these experiments require large and expensive lab equipment which is not obtainable by children. (And the plans for an atomic bomb are safe for children too, because kids can't afford to buy kilograms of Plutonium!) If your kids have access to 5,000 volt high-current power supplies, then they are already in great danger, whether or not they read about my capacitor discharge experiments below.' Has my respect! -- Andrew Sinclair http://www.smellycat.org |
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Safely discharging a capacitor
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#38
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Safely discharging a capacitor
In uk.d-i-y powerstation wrote:
If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave nonsense it is clearly an induction motor. According to my Electrical Engineering professor at university *all* electrical machines (including transoformers) are really induction motors. -- Chris Green |
#39
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Safely discharging a capacitor
wrote in message ... In uk.d-i-y powerstation wrote: If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure. Dave nonsense it is clearly an induction motor. According to my Electrical Engineering professor at university *all* electrical machines (including transoformers) are really induction motors. -- Chris Green Motors with squirrel-cage rotors can be used on single-phase alternating current by means of various arrangements of inductance and capacitance that alter the characteristics of the single-phase voltage and make it resemble a two-phase voltage. Such motors are called split-phase motors or condenser motors (or capacitor motors), depending on the arrangement used. Single-phase squirrel-cage motors do not have a large starting torque, and for applications where such torque is required, repulsion-induction motors are used. A repulsion-induction motor may be of the split-phase or condenser type, but has a manual or automatic switch that allows current to flow between brushes on the commutator when the motor is starting, and short-circuits all commutator segments after the motor reaches a critical speed. Repulsion-induction motors are so named because their starting torque depends on the repulsion between the rotor and the stator, and their torque while running depends on induction. Series-wound motors with commutators, which will operate on direct or alternating current, are called universal motors. They are usually made only in small sizes and are commonly used in household appliances. |
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Safely discharging a capacitor
"Andy Dingley" bravely wrote to "All" (21 Dec 05 14:16:40)
--- on the heady topic of " Safely discharging a capacitor" AD From: Andy Dingley AD Xref: core-easynews sci.electronics.repair:352066 AD free.uk.diy.home:47734 uk.d-i-y:545608 AD On 21 Dec 2005 04:23:18 -0800, "paulfoel" AD wrote: Assuming it is still ' live' how do I discharge it to make it safe? AD Stick a big screwdriver across it. Now why ruin a perfectly good screwdriver?! You should see mine, it's full of big burned out pits from starting up cars at the solenoid. Mind that disharging those 50 volt 100,000uF audio amp supply caps is a little more hazardous than say a 6.8uF AC motor start cap. (grains of salt -...) A*s*i*m*o*v .... You may be a tech if you're entertained by a 6-pack and sparking HV. |
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