Power Supply Running to hot  - Page 1
Forum section: electronics / beginners

author: Jbliss
author_rank: Regular Contributor
timestamp: July 07, 2015, 12:57:13 pm
content: Hi GuysI 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

author: Jbliss
author_rank: Regular Contributor
timestamp: July 07, 2015, 01:21:50 pm
content: pls help

author: SuzyC
author_rank: Frequent Contributor
timestamp: July 07, 2015, 01:35:33 pm
content: 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.

author: rolycat
author_rank: Super Contributor
timestamp: July 07, 2015, 01:44:44 pm
content: 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?

author: ElektroQuark
author_rank: Unknown
timestamp: July 07, 2015, 01:45:33 pm
content: I can't even understand clearly your question.

author: Jbliss
author_rank: Regular Contributor
timestamp: July 07, 2015, 03:11:30 pm
content: Hey rolycatAre 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 todaythanks so much

author: rolycat
author_rank: Super Contributor
timestamp: July 07, 2015, 03:42:23 pm
content: Quote from: Jbliss on July 07, 2015, 03:11:30 pmYes, 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?

author: Jbliss
author_rank: Regular Contributor
timestamp: July 08, 2015, 02:25:59 am
content: yeah i have completed the test procedure and all the voltages were there, however many of the components get way to hot

author: sean0118
author_rank: Frequent Contributor
timestamp: July 08, 2015, 03:27:54 am
content: What are you connecting to the amplifier?

author: Jbliss
author_rank: Regular Contributor
timestamp: July 08, 2015, 04:10:20 am
content: just running it in test mode

author: Jbliss
author_rank: Regular Contributor
timestamp: July 08, 2015, 05:11:44 am
content: There a 4 1 watt restores that get really hot

author: w2aew
author_rank: Super Contributor
timestamp: July 08, 2015, 01:44:42 pm
content: Quote from: Jbliss on July 08, 2015, 05:11:44 amDid I miss a schematic somewhere?

author: Jbliss
author_rank: Regular Contributor
timestamp: July 08, 2015, 02:15:34 pm
content: 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 problemsit the 4 1watt resistors sorry forgot to link in diagrams. if it no the 2v can any one suggest whats gone wrong.

author: w2aew
author_rank: Super Contributor
timestamp: July 08, 2015, 02:24:46 pm
content: 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.

author: Jbliss
author_rank: Regular Contributor
timestamp: July 08, 2015, 02:42:24 pm
content: well there getting really hot most likely 150 degrees. and another question is the amplifier expecting a signal that has already been pre amplifiedThanks a lot just getting into electronics

author: w2aew
author_rank: Super Contributor
timestamp: July 08, 2015, 02:57:36 pm
content: Quote from: Jbliss on July 08, 2015, 02:42:24 pmAre 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").

author: mikerj
author_rank: Super Contributor
timestamp: July 08, 2015, 09:16:06 pm
content: Quote from: Jbliss on July 08, 2015, 02:15:34 pmThose 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.

author: Jbliss
author_rank: Regular Contributor
timestamp: July 09, 2015, 03:59:01 am
content: if i were to replace those resistors with 5watt ones would this help

author: Jbliss
author_rank: Regular Contributor
timestamp: July 09, 2015, 08:17:38 am
content: and is it possible to use a zener diode to limit the voltage coming out of the power supply.

author: rs20
author_rank: Super Contributor
timestamp: July 09, 2015, 08:30:11 am
content: Quote from: Jbliss on July 09, 2015, 03:59:01 amThey'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.Quote from: Jbliss on July 09, 2015, 08:17:38 amAs 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.

author: mikerj
author_rank: Super Contributor
timestamp: July 09, 2015, 09:22:57 am
content: Quote from: rs20 on July 09, 2015, 08:30:11 amOn 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.

author: Unknown
author_rank: Unknown
timestamp: July 09, 2015, 09:25:02 am
content: Quote from: rolycat on July 07, 2015, 03:42:23 pmQuote from: mikerj on July 08, 2015, 09:16:06 pmGood 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 thatdoesn'tblow up within a few months as the exception that proves the rule...

author: Jbliss
author_rank: Regular Contributor
timestamp: July 09, 2015, 02:12:21 pm
content: 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

author: rolycat
author_rank: Super Contributor
timestamp: July 09, 2015, 09:34:12 pm
content: Quote from: Jbliss on July 09, 2015, 02:12:21 pmIf 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.

author: Jbliss
author_rank: Regular Contributor
timestamp: July 13, 2015, 04:23:49 am
content: Quote from: rs20 on July 09, 2015, 08:30:11 am

author: Jbliss
author_rank: Regular Contributor
timestamp: July 13, 2015, 04:32:05 am
content: 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

author: rs20
author_rank: Super Contributor
timestamp: July 13, 2015, 04:56:20 am
content: Quote from: Jbliss on July 13, 2015, 04:32:05 amAll of the above will work, even Schottky diodes will beOK. Of course you have to calculate based on the forward drops of your chosen diodes; a 0.7V silicon diode will dissipate 0.7W at 1A (nice and warm but fine), but a 5V zener will dissipate 5W at 1A (smoke).

author: Jbliss
author_rank: Regular Contributor
timestamp: July 13, 2015, 05:02:53 am
content: could i use some 1n4004

author: rs20
author_rank: Super Contributor
timestamp: July 13, 2015, 06:00:44 am
content: What's the supply current? Try doing the calculation yourself, and we'll check for you.