Hi,
I have been running my power amp from an auto transformer for a few hours using the 220v tap from mains voltage of 240v.
It is a kilowatt transformer and i estimate i have pulled no more than 2 amps from it during the listening session.
I put my hand on it after the session to check the temperature and it was very hot.
Even after leaving the amp off with the autotransformer still plugged in and on, it remained very hot.
Is this normal, my lower current variac ran the amp at the same levels without heating up?
Regards
Craig
I have been running my power amp from an auto transformer for a few hours using the 220v tap from mains voltage of 240v.
It is a kilowatt transformer and i estimate i have pulled no more than 2 amps from it during the listening session.
I put my hand on it after the session to check the temperature and it was very hot.
Even after leaving the amp off with the autotransformer still plugged in and on, it remained very hot.
Is this normal, my lower current variac ran the amp at the same levels without heating up?
Regards
Craig
anatech, i purchased it from a local radio shop secondhand with no markings on it although i suspect it may be this model as it looks exactly the same.. and the guy in the shop mentioned somthing about Farnell.
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=1166382&N=401
It says between 50 and 60hz so i guess its ok with either.
Can i connect the earth wire from the amp and the earthwire from the wall socket togeather through the autotransformers casing (screwed onder the bolts each side) ?
Or am i causing problems with this arrangement.
Thanks
Craig
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=1166382&N=401
It says between 50 and 60hz so i guess its ok with either.
Can i connect the earth wire from the amp and the earthwire from the wall socket togeather through the autotransformers casing (screwed onder the bolts each side) ?
Or am i causing problems with this arrangement.
Thanks
Craig
Hi Craig,
If that is the one, you should be fine.
Connecting the earth grounds though the case should be okay. I would generally have used a common connection point for the transformer case and equipment ground from your wall outlet. They both work, make sure there is no paint to insulate the connection in either location.
Can you measure the current draw of the autoformer on it's own? It's possible there is a shorted turn. That will heat it up pretty good.
-Chris
If that is the one, you should be fine.
Connecting the earth grounds though the case should be okay. I would generally have used a common connection point for the transformer case and equipment ground from your wall outlet. They both work, make sure there is no paint to insulate the connection in either location.
Can you measure the current draw of the autoformer on it's own? It's possible there is a shorted turn. That will heat it up pretty good.
-Chris
Hmm,
no load connected it measured spot on the 220v mark and consumed 130mA, this seems too low to indicate a shorted winding.
Its looking like it may not have a high enough current rating for the amp which is depressing because it is one big hunk of iron.
Even with the amp at idle the current draw from the mains through the autotransformer is 200mA, and with the music pumping at past what i was listening to before it only hits 0.35A average?
I have no idea why it was so hot?
Regards
Craig
no load connected it measured spot on the 220v mark and consumed 130mA, this seems too low to indicate a shorted winding.
Its looking like it may not have a high enough current rating for the amp which is depressing because it is one big hunk of iron.
Even with the amp at idle the current draw from the mains through the autotransformer is 200mA, and with the music pumping at past what i was listening to before it only hits 0.35A average?
I have no idea why it was so hot?
Regards
Craig
or,
it just gets hot. did you measure it? rule of thumb: if you can keep your hand on it for a minute or so, it's 45C or less. at around 55C you will pull your hand off right away.
leave it for a few hours and feel it again. Large bits of metal can retain heat for a good long time.
anecdotal evidence: I used to work with a particular type of heated valve that had a 5 to 7 pound chunk of stainless steel for the body of the valve, and under normal operating conditions it was heated to 150 deg. C.
It had to sit for MANY hours before cooling enough to handle after the heaters were switched off... I usually left it overnight or at least until the end of a shift.
it just gets hot. did you measure it? rule of thumb: if you can keep your hand on it for a minute or so, it's 45C or less. at around 55C you will pull your hand off right away.
leave it for a few hours and feel it again. Large bits of metal can retain heat for a good long time.
anecdotal evidence: I used to work with a particular type of heated valve that had a 5 to 7 pound chunk of stainless steel for the body of the valve, and under normal operating conditions it was heated to 150 deg. C.
It had to sit for MANY hours before cooling enough to handle after the heaters were switched off... I usually left it overnight or at least until the end of a shift.
Hi,
Ok, i just listened to half an albums worth at uncomfortable listening levels.
The current into the auto transformer hit no more than 0.4 amps.
the amplifiers bias does creep up but seemed to reach a stable level at 0.3 amps. By this point the autotransformer was getting hot, not as hot as before but that was after 2 hours, but it was definatly getting hotter as time went by.
With the amp off and the autotraffo hot it still measured 130mA.
Stocker, when the transformer was hot going by your scale i would say it was approaching 55 degrees. I could hold my hand on it for about 5 seconds before getting a strong urge to pull away
.
Regards
Craig
Ok, i just listened to half an albums worth at uncomfortable listening levels.
The current into the auto transformer hit no more than 0.4 amps.
the amplifiers bias does creep up but seemed to reach a stable level at 0.3 amps. By this point the autotransformer was getting hot, not as hot as before but that was after 2 hours, but it was definatly getting hotter as time went by.
With the amp off and the autotraffo hot it still measured 130mA.
Stocker, when the transformer was hot going by your scale i would say it was approaching 55 degrees. I could hold my hand on it for about 5 seconds before getting a strong urge to pull away
.Regards
Craig
Hi Craig,
I have to agree with jaycee here. My mains measure around 120 VAC here at 60 Hz. My autotransformers and variacs only get a little warm after running for hours. I have a strong suspicion that there is something wrong there.
There has to be something wrong to draw 130 mA and dissipate 30W with no load connected. I'm thinking shorted turn or a defect in the laminations. My money is on a shorted turn.
-Chris
I have to agree with jaycee here. My mains measure around 120 VAC here at 60 Hz. My autotransformers and variacs only get a little warm after running for hours. I have a strong suspicion that there is something wrong there.
There has to be something wrong to draw 130 mA and dissipate 30W with no load connected. I'm thinking shorted turn or a defect in the laminations. My money is on a shorted turn.
-Chris
Thanks for replies guys.
Jaycee, the rails are only 10v higher but that puts them at +/- 85V whereas the schematic shows 75V (above 75V and some of the transistor ratings are exceeded).
I replaced the autotraffo with a huge Drake power transformer of which i am using the primary winding as an autotransformer.
This transformer is about 2x the size or more of my autotransformer and this one only gets warm after an hour or so plugged in and connected with my power amplifier (power amp is off).
Although... i have had it on for about 3 hours solid now and it's gradually getting hotter!
Basically it is behaving just as my autotraffo did, but taking longer because its bigger.
This can only mean 2 things in my mind, my ammeter is not making accurate measurements and my amplifier draws current when off.
Im getting my more accurate multimeters out of the loft and making some more current meaurements ASAP.
Regards
Craig
Jaycee, the rails are only 10v higher but that puts them at +/- 85V whereas the schematic shows 75V (above 75V and some of the transistor ratings are exceeded).
I replaced the autotraffo with a huge Drake power transformer of which i am using the primary winding as an autotransformer.
This transformer is about 2x the size or more of my autotransformer and this one only gets warm after an hour or so plugged in and connected with my power amplifier (power amp is off).
Although... i have had it on for about 3 hours solid now and it's gradually getting hotter!
Basically it is behaving just as my autotraffo did, but taking longer because its bigger.
This can only mean 2 things in my mind, my ammeter is not making accurate measurements and my amplifier draws current when off.
Im getting my more accurate multimeters out of the loft and making some more current meaurements ASAP.
Regards
Craig
Hi Craig,
Have you considered using an 18 ~ 24V transformer in a buck configuration? Get one with 1.5 to 2X the max current draw of your amp. The secondary is in series with your wall supply. One way it will increase the voltage to your amp, the other it will reduce (or buck) the voltage.
This transformer will be much smaller and less expensive.
-Chris
Have you considered using an 18 ~ 24V transformer in a buck configuration? Get one with 1.5 to 2X the max current draw of your amp. The secondary is in series with your wall supply. One way it will increase the voltage to your amp, the other it will reduce (or buck) the voltage.
This transformer will be much smaller and less expensive.
-Chris
Thats interesting i wasnt aware you could do that.
When you say one way it will increase voltage and the other it will decrease voltage do you mean flip the connections on the series transformer?
I may resort to this if my heating issues are too serious with this new traffo im using.
Regards
Craig
When you say one way it will increase voltage and the other it will decrease voltage do you mean flip the connections on the series transformer?
I may resort to this if my heating issues are too serious with this new traffo im using.
Regards
Craig
I want to lose about 20v, maybe 25 because the mains here seems to be closer to 247V.
So all i'd need is a transformer with a secondary current of say 15 amps (the amps primary fuse is 6.3A) and a voltage of 12.5-0-12.5
then just wire the whole secondary in series with my live connection?
I guess i'd have to measure the output voltage before connecting it up incase it was increasing it by 25v, and if so reverse the connections accross the secondary.
Do i also need to connect the primary to the mains? you mentioned i could also reverse this.
Stocker, i dont understand how my transformer could be oscillating? could you expand a little?
PS.
i checked with a solartron multimeter and it measure 130mA with or without load for the new transformer too.
Regards
Craig
So all i'd need is a transformer with a secondary current of say 15 amps (the amps primary fuse is 6.3A) and a voltage of 12.5-0-12.5
then just wire the whole secondary in series with my live connection?
I guess i'd have to measure the output voltage before connecting it up incase it was increasing it by 25v, and if so reverse the connections accross the secondary.
Do i also need to connect the primary to the mains? you mentioned i could also reverse this.
Stocker, i dont understand how my transformer could be oscillating? could you expand a little?
PS.
i checked with a solartron multimeter and it measure 130mA with or without load for the new transformer too.
Regards
Craig
no, the circuit! if the power supply or whatever it's powering is oscillating, it will draw current possibly at frequencies higher than your equipment is designed to measure current. Then the autotransformer retains the heat for a while when the load is removed due to high thermal mass...
I have been inside a few autotransformers myself. If you open them, usually there is a bare metal surface on each coil for a bushing to contact all round the circumfirence... is this surface in good condition? If you have a good low-ohms measuring range, maybe you could measure directly on the bare windings at this point to check for shorted coils...
I have been inside a few autotransformers myself. If you open them, usually there is a bare metal surface on each coil for a bushing to contact all round the circumfirence... is this surface in good condition? If you have a good low-ohms measuring range, maybe you could measure directly on the bare windings at this point to check for shorted coils...
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