Power Supply Running to hot

[Jbliss]

Hi Guys

I have a power supply and it running 10v to high its at 60v and i need 50v to power an amp how can i solve this is there a 50v reg i can use or is there a simpler way.
at the moment the amp gets way to hot and i don't want to damage it!!!
please help 

[Jbliss]

pls help

[SuzyC]

You are not offering enough info or specifications or schematic or ratings of the pieces involved for anyone to be able give you any real help.

Ask the goceries man.

[rolycat]

Is this amp the Silicon Chip Classic-D design you were building from a kit a month or so ago? It is specified to run from 40-60 V, so it shouldn't be overheating.

Have you tested the amplifier successfully with a lower voltage supply, or are you just assuming that the 60V is the problem?

[ElektroQuark]

I can't even understand clearly your question.

[Jbliss]

Hey rolycat
Are you sure on the PCB it is marked 50v on the input, I was assuming this was the problem. could you recommend a way me a way to work out what the problem is?? and trouble shoot..

and yes this is the same amp transformer arrived today

thanks so much

[rolycat]

Hey rolycat
Are you sure on the PCB it is marked 50v on the input, I was assuming this was the problem. could you recommend a way me a way to work out what the problem is?? and trouble shoot..

and yes this is the same amp transformer arrived today

thanks so much

Yes, that amplifier is specified to work at up to 60V. The online constructional article in EPE suggests a maximum of 57V, so as to keep well within the 63V rating of some of the capacitors. This is the no-load DC voltage you will get after rectification of a 40V transformer.

The article also has a comprehensive test procedure for the amplifier. Is there not a similar procedure in the assembly instructions for your kit?

[Jbliss]

yeah i have completed the test procedure and all the voltages were there, however many of the components get way to hot

[sean0118]

What are you connecting to the amplifier?

[Jbliss]

just running it in test mode

[Jbliss]

There a 4 1 watt restores that get really hot

[w2aew]

There a 4 1 watt restores that get really hot

Did I miss a schematic somewhere?

[Jbliss]

Ok to clear things up I'm feeding the amp 62.4v and it is rated for 40 to 60 could those extra 2 volts be causing heat problems
it the 4 1watt resistors sorry forgot to link in diagrams. if it no the 2v can any one suggest whats gone wrong.

[w2aew]

It's doubtful that the extra 2V is causing excessive power dissipation in those components.

Which resistors are getting hot?  There are more than 4 1W resistors in that schematic.  If you're talking about the 4.7k resistors in series with the Zener diodes, then they will run pretty warm normally, since they're dissipating more than 1/2W.

[Jbliss]

well there getting really hot most likely 150 degrees. and another question is the amplifier expecting a signal that has already been pre amplified
Thanks a lot just getting into electronics

[w2aew]

well there getting really hot most likely 150 degrees. and another question is the amplifier expecting a signal that has already been pre amplified
Thanks a lot just getting into electronics

Are you talking about R2A, R2B, R3A and R3B?
Have you verified that they are indeed 1W (or higher) sized components?
Have you measured their value to ensure they're 4700 ohms each?
Have you measured the voltage across the zener diodes that they're connected to?

Excessive heat means that they're dissipating a lot of power.  Measure the voltage across them and the value of the resistors, and calculate the power dissipated.  (you'll have to lift one leg of the resistor to measure it, don't measure it's value "in circuit").

[mikerj]

Ok to clear things up I'm feeding the amp 62.4v and it is rated for 40 to 60 could those extra 2 volts be causing heat problems
it the 4 1watt resistors sorry forgot to link in diagrams. if it no the 2v can any one suggest whats gone wrong.

Those resistors will be running very hot: ((62.4-5.6)^2)/4700 ~0.7 watts each.  That's probably too much for a 1 watt resistor unless you have some air movement.

At 50v the power dissipation drops to 0.42 watts, it will still be running pretty warm but should be fine. 

62.4 volts is also way too close to the 63v rating of the decoupling caps, you either need to reduce the voltage or increase the voltage rating of the caps.

[Jbliss]

if i were to replace those resistors with 5watt ones would this help

[Jbliss]

and is it possible to use a zener diode to limit the voltage coming out of the power supply.

[rs20]

if i were to replace those resistors with 5watt ones would this help

They'd still dissipate the same amount of heat (in terms of watts), but because they'd be larger, they'd be better at dissipating that heat, and so would run cooler. So in short, yes.

and is it possible to use a zener diode to limit the voltage coming out of the power supply.

As expressed by others, reducing the voltage coming from the power supply will not fix your problem. To answer your question, you can soooort of use Zener diodes like this, but there are better ways to do it. A diode drops about 0.7V, so if you want to reduce the power supply voltage by 7V, you can use a string of ten diodes in a row. Each one will dissipate 0.7V * (supply current)A; make sure they can take the heat.

[mikerj]

As expressed by others, reducing the voltage coming from the power supply will not fix your problem.

On the contrary, reducing it to the 50v design voltage would reduce the power dissipation in those resistors by around 40%.  Reducing the supply by a couple of volts won't make any significant difference though.

[Tac Eht Xilef]

Yes, that amplifier is specified to work at up to 60V. The online constructional article in EPE suggests a maximum of 57V, so as to keep well within the 63V rating of some of the capacitors. This is the no-load DC voltage you will get after rectification of a 40V transformer.

Those resistors will be running very hot: ((62.4-5.6)^2)/4700 ~0.7 watts each.  That's probably too much for a 1 watt resistor unless you have some air movement.

At 50v the power dissipation drops to 0.42 watts, it will still be running pretty warm but should be fine.

62.4 volts is also way too close to the 63v rating of the decoupling caps, you either need to reduce the voltage or increase the voltage rating of the caps.

Good ol' Silicon Chip and their "f'k'it, sensible operating margins are for other people" attitude. They've got a long history of trusting that transformers put out their rated voltage at all times, and I've lost count of the number of circuits they've published where they sail too close to the wind - or just flat-out ignore - voltage &/or power ratings of components. Same goes for anything auto-related they publish.

Hell - just assume that, if it's not battery powered & has components rated more than 1/4W, then they've got it wrong. It's probably easiest to treat any SC project that doesn't blow up within a few months as the exception that proves the rule...

[Jbliss]

Ok so my plan at the moment is to get some bigger 5watt resistors and possibly get some big didoes and try and drop the voltage going into the thing . maybe a fan because at the moment it works but running at that temp.....  not for long. any one got any ideas on how I can drop the voltage coming out of the transformer.
thanks guys

[rolycat]

Ok so my plan at the moment is to get some bigger 5watt resistors and possibly get some big didoes and try and drop the voltage going into the thing . maybe a fan because at the moment it works but running at that temp.....  not for long. any one got any ideas on how I can drop the voltage coming out of the transformer.
thanks guys

If you are using a toroidal transformer, you might be able to carefully remove the outer insulation and unwind a few turns at a time of the secondaries until you achieve the required voltage. You can then cut the excess wire to size, strip it and replace the insulation. This would avoid the wasted power of most alternatives. Obviously care is required since the voltages are high enough to be potentially dangerous.

Edit: This will proportionally reduce the VA rating of the transformer.

[Jbliss]

if i were to replace those resistors with 5watt ones would this help

They'd still dissipate the same amount of heat (in terms of watts), but because they'd be larger, they'd be better at dissipating that heat, and so would run cooler. So in short, yes.

and is it possible to use a zener diode to limit the voltage coming out of the power supply.

Hey if i was to try this would I use standard rectification diodes or zener or would both work because they both give a voltage drop. Of course properly rated
 

As expressed by others, reducing the voltage coming from the power supply will not fix your problem. To answer your question, you can soooort of use Zener diodes like this, but there are better ways to do it. A diode drops about 0.7V, so if you want to reduce the power supply voltage by 7V, you can use a string of ten diodes in a row. Each one will dissipate 0.7V * (supply current)A; make sure they can take the heat.