eHam

eHam Forums => Misc => Topic started by: AK4YA on September 12, 2012, 07:33:30 PM



Title: power supply testing
Post by: AK4YA on September 12, 2012, 07:33:30 PM
I have 2 weeks to test this acopian 50v/8amp/400watt linear regulated power supply.

Two 24v 250w projector bulbs in series caused it to drop down to 7volts.  I used 18ga wires crimped.  Was this an accurate test?  I know the load was probably a bit too stout for this PS but was thinking it shouldn't have dropped that low.

Any thoughts?


Title: RE: power supply testing
Post by: W8JX on September 12, 2012, 08:05:05 PM
Not really a good test because the bulbs will have a much higher resistance when cold and only draw lower wattage when fully heated. You overloaded supply. You need a power resistor (over combo of several in parallel equal to) 6.25 ohms to create a 8 amp load.


Title: RE: power supply testing
Post by: AK4YA on September 12, 2012, 09:18:20 PM
Yup. The series DC resistance was 1 ohm.  Definitely overloaded PS at first for sure.  Where can I find some high wattage resistors like I need

Thanks


Title: RE: power supply testing
Post by: KH6AQ on September 12, 2012, 11:58:24 PM
Digikey stocks 225 watt resistors for $11.90 each. The part number for the 10 ohm is FVT200-10-ND.



Title: RE: power supply testing
Post by: AK4YA on September 15, 2012, 04:02:18 PM
Well thanks a ton for the tip. Got a 12 and 16 ohm 300 watt each 10% tolerance resistors and in parallel they are 7.2 and the power supply didnt blink.  How can i measure ripple?  Just find someone with an oscope?  Any other tests i can run?


Title: RE: power supply testing
Post by: WB2WIK on September 15, 2012, 04:57:04 PM
Ripple (which should always be tested under full load) is easily measured with an oscilloscope, but can also be measured with an AC VTVM or other accurate AC voltmeter.  I usually use an old Ballantine 300 AC VTVM for this stuff, or a scope.


Title: RE: power supply testing
Post by: AK4YA on September 15, 2012, 05:50:02 PM
Ripple (which should always be tested under full load) is easily measured with an oscilloscope, but can also be measured with an AC VTVM or other accurate AC voltmeter.  I usually use an old Ballantine 300 AC VTVM for this stuff, or a scope.

Is it safe or even useful to even try my fluke dvm set to AC to try to do this?  For a solid state hf fet based 300watt amp, what tolerances should i be looking for?


Title: RE: power supply testing
Post by: KD0REQ on September 16, 2012, 05:36:40 PM
you should be able at those voltages to just grab a $3 Harbor Freight cheapo for "geez, is this dangerous or not?" testing.  start clicking the AC voltage scale down from 200 volts to whatever until you can read the ripple.

I've done it with my good toys, the Beckman and the Fluke, and no harm, no foul.  but if you're worried, heck, get a chinese hockey-puck meter and consider it disposeable if you learn a hard lesson.

I am not a professional engineer, nor do I know any any more, but if I want -40 or better output ripple, I would like to see at least that on my power supply, and preferably 70 or 80 down.  sorta depends on the amplifier's sensitivity to common-mode noise, and that depends on the worst stage of the amp.  that's not my strong suit, figuring that, so I go for basically nothing, and see how it sounds.


Title: RE: power supply testing
Post by: AK4YA on September 16, 2012, 06:26:21 PM
thanks for the help everyone.  Well I put it on my fluke DVM set to mV AC and it settled down to 1mV under load while output VDC was 48.1.  would that be sufficient for solid state amplifier operation?


Title: RE: power supply testing
Post by: W8JX on September 16, 2012, 07:26:00 PM
thanks for the help everyone.  Well I put it on my fluke DVM set to mV AC and it settled down to 1mV under load while output VDC was 48.1.  would that be sufficient for solid state amplifier operation?

Yes it will do fine


Title: RE: power supply testing
Post by: MDNITERDER on October 08, 2012, 05:25:29 PM
 Here is something that maybe an interest to you.

Building an Adjustable Constant Current Load
http://paulorenato.com/joomla/index.php?option=com_content&view=article&id=91:constant-current-load&catid=4:projects&Itemid=4 (http://paulorenato.com/joomla/index.php?option=com_content&view=article&id=91:constant-current-load&catid=4:projects&Itemid=4)