Computer Power Supply Converted to 13.8V for Radio

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Re: Computer Power Supply Converted to 13.8V for Radio

Post by sureshot »

Excellent that's a really stable tolerance, good luck with what ever the intended final load will be. :D

Oh if a radio is part of the load put 1 meter between the psu and radio, no extra electrical filtering should be needed, but if there is noise and i doubt there will be, get a ferrite ring and make about half a dozen turns of the power cable around the ring, but i doubt your need it, dont forget in line fuse and rated cables for high current. ;)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by Clint »

I have a lot of 24A server psu's all superb quality, but the fan is extremely noisy would need to make up a way of fitting a much bigger fan in size to quieten it down.
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by sureshot »

Clint wrote:I have a lot of 24A server psu's all superb quality, but the fan is extremely noisy would need to make up a way of fitting a much bigger fan in size to quieten it down.
Clint wrote:I have a lot of 24A server psu's all superb quality, but the fan is extremely noisy would need to make up a way of fitting a much bigger fan in size to quieten it down.
You could always re case the unit in a new enclosure add 120mm axial fan etc add some panel meters variable voltage, current limit, do all sorts with the unit, test it first be a shame to get all the gear and it failed or proved inefficient. :)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by sureshot »

Quote came out twice oop's :D
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by hdjmings1 »

right im going to try this one again, this time i have a different psu, got it from someone for a tenna, here is some pics
IMG_2026.JPG
IMG_2027.JPG
i no im a beginner but i can find where the 5v line goes to the voltage reg if anyone could help it would be nice

in the psu board there are 2 ic chips the bigger one says CP4940603 and the other 1 says TPS3150P
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by sureshot »

Not sure what you meant, think your trying to find the +5 volts source, is this for the idea of using it as the main secondary output at 13.80 volts if modded ? if different why are you trying to trace the +5 volts rail source, i don't claim to be an expert, and circuits will vary from different units and manufacturers. :)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by hdjmings1 »

going to "attempt" lol to do what he has done in this topic, make the 12v 13.8v , he used 5v to turn the 12v into 13.8v because the volt regulation was controlled by the 5v
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by sureshot »

Ok i thought you might want to try that, ive never done one from the +5 volts rail as the less than 1.8 volts is no bother really to me, but i can see wanting to give it a go, as in most but not all, max current can be had from this output, the only issue is slight variations from one unit to another.

Have you had a look back at the OP's build see if you can get any info there ? i would look on line for a couple of schematics for comparison of the secondary outputs from those drawings and see if any ICs match what you have and if the circuit components tally up with any schematic in searches. :)

PS. Also have a look in a search for others that have done this using the +5 volt rail, i know in some units its quit easy, its if your ATX is a good Donner.
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by NITRO »

well done on a great post ;) have to admit tho, i wouldent have the first clue where to start and would probably blow the psu , or the rig ( quite likely both ) to bits if i attempted anything like that :oops: .... good job bud 8)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by hdjmings1 »

Hi can anyone help, in the pic you will see a pc psu thats been modded, you will also see a 2k variable resistor when i turn this it alters The voltage, but the voltage max out at something like 12.6v, can this 2k resistor be changed to get more output say to 13.8v?
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by Woodyardboy »

hdjmings1 wrote:
13 Jul 2012, 21:19
well pulling 14.7 amps the voltage at the terminals stay at 12.08v, when no load is on the supply the standered volts are 12.09/12.1v

but the real test will be tomorrow :lol:
that seemed to work out fine for you, I'm going to have a go at this myself in the coming weeks, I'll let you know how I get on. 8)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by alphard »

What would happen if used a 220 ohm power resistors instead of 10 ohm one for the load?

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Re: Computer Power Supply Converted to 13.8V for Radio

Post by scan125 »

I used to design, safety analyse and test SMPS (Switched Mode Power Supplies) for a living. For those new/novice at SMPS then the following may be of information/education for you.

When designing an SMPS with multi voltage outputs (like a PC supply) then the crucial part of the design is the transformer. Basically you have a single primary winding and multiple secondary windings. To take full advantage of switched mode technology then ideally you *only* modulate the primary winding and *rely* on the secondary windings to be well coupled and accurate turns ratios to give you your secondary voltages. So for a 12V secondary with 50 turns then the 5V secondary would need to be 21 (20.833333). So turns ratios are one factor. Another factor is which output is likely to suffer the largest tolerable voltage variation with anticipated load variation. Say this was the 5V heavy current output. This would be the output that you take the control loop feedback from. We are not done yet. The windings have to be made with adequate gauge wire to minimise voltage drop. If the current variation in say the 5V winding varies from 5A to 25A then the voltage drop variation will be 5:1. e.g. from 0.1V to 0.5V. Now the feedback loop will take care of this by raising the drive to add 0.5V to the 5V output so we still have 5V. However the constantly loaded 12V output (ignore it's IR losses) will now be increased by 12/5 * 0.5 = 1.2V. So now the 12V output is 13.2V.

So getting the SMPS design right and cost effective is a delicate balancing act. In the above 12V to 13.2V example we could add a series regulator to regulate this 1.2V variation. But series regulators need an operational overhead voltage, say 1.5V so are 12V winding now has to be 13.5V. An of course we now have an undesirable power loss and cooling problem to cater for. Or instead of a series regulator we could use a DC-DC converter (read another SMPS within an SMPS) so now even more complexity and cost.

In this example we have only consider a two voltage output PSU. A PC PSU has far more outputs to cater for.

And just when you think your design is done and bench tested you then have all the safety and EMC (electromagnetic testing compatibility) tests to pass. Almost certainly when you get you PSU (or any other product into the EMC test chamber) it will fail to pass one or more of the test criteria and you have to go and sort those items out.

All fun and games :)
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Re: Computer Power Supply Converted to 13.8V for Radio

Post by lsrlut »

Thanks for your sharing, really helpful to us.

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Re: Computer Power Supply Converted to 13.8V for Radio

Post by scan125 »

lsrlut wrote:
07 Feb 2020, 01:07
Thanks for your sharing, really helpful to us.
Well you are welcome. It is a long time ago since I designed SMPS (Switched Mode Power Supplies) or indeed all sorts of electronic/semiconductor power supplies ranging from the small to the large 10kW (lower voltage) and 300kV (higher voltage) units.

My personal preference is analogue linear PSUs simply because they are easier to design, have far less issues (switching currents, RFI and more importantly operating range) but can/do waste power and thus require improved cooling.

One thing that people do not possibly know is that SMPS control loop requires an operating window. e.g. 12V @ 500mA to 10A. Below e.g. 500mA then the control circuits will try to contain the desired voltage of 12V but will actually go into an unstable mode of operation. You may get a 12V supply but the electrical noise, RFI and ability to accommodate load changes will be severely limited. In worse case scenarios then over voltage conditions can occur. Quality supplies will have protection (added design and production cost) for these exceptions. Cheaper unit may not have.

To be honest I quite happy to be out of the switched mode power design arena and happily retired.

My advice for punters looking at power supplies is:

1) Go for globally recognised names and then check out end user reports
2) End user reports. e.g. My "x" supply performs well, produces minimum electrical noise affecting my RF reception, and is of robust design
3) Weed out poorer reports even if the price point is very tempting.

As not only a past PSU designer I've tested to death, fire, explosion, fumigation, ....... the power supplies for companies I've worked for. Thankfully industry wide and units shipped the amount of dangerous and even lethal PSUs is very very low.

To put things into perspective even a simple non switching power supply that produces no switching noise or other RFI side effects is and has been a safety liability. Enter the Lithium self destructing batteries where fire is an optional ingredient. Or batteries that leak acid, or fumes, or .......
Nick - Author Of: Scan125 - Scan75 - DriveR8 - http://www.nick-bailey.co.uk

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