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Author Topic: How to "test" a power supply?  (Read 3496 times)
W7EJT
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Posts: 132




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« on: December 06, 2012, 06:28:57 PM »

I have a Astron RM-35a power supply that I would like to verify performance.

Anyone have an easy way to test performance under a 20 amp (or so) load? (not using the transceiver as the load) thx
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W0BTU
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« Reply #1 on: December 06, 2012, 06:47:40 PM »

How about a hunk of #14 or #12 AWG CU, long enough to be 0.69 ohms? That would draw 20 amps @ 13.8 volts.

I wouldn't connect it for more than a couple of seconds or so. The wire will be dissipating 276 watts.
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W8JX
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« Reply #2 on: December 06, 2012, 06:53:35 PM »

A .75 ohm  200 watt  or 4ea 3 ohm 50 watt resistors in parallel would work for this test and be close enough
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--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
N4CR
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Posts: 1650




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« Reply #3 on: December 06, 2012, 07:04:39 PM »

Car headlamps. Used from a junkyard. Stack as many as it takes to make you happy.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K5LXP
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« Reply #4 on: December 06, 2012, 08:04:10 PM »

http://www.eham.net/ehamforum/smf/index.php/topic,78213.0.html

Mark K5LXP
Albuquerque, NM
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WB6BYU
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« Reply #5 on: December 06, 2012, 08:20:08 PM »

Quote from: N4CR

Car headlamps...



On the sealed dual-beam headlamps usually the low beam goes out first, and you
have to replace the whole thing.  I keep a couple around for testing power
supplies and batteries.
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KA4POL
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Posts: 1864




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« Reply #6 on: December 06, 2012, 09:45:53 PM »

Good quote. As I mentioned there, it is easy to build your own variable dummy load for a power supply.
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WX7G
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Posts: 5908




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« Reply #7 on: December 07, 2012, 12:15:08 AM »

How about a hunk of #14 or #12 AWG CU, long enough to be 0.69 ohms? That would draw 20 amps @ 13.8 volts.

I wouldn't connect it for more than a couple of seconds or so. The wire will be dissipating 276 watts.

Good idea. 100' of #18 wire is 0.65 ohms and it will handle 20 amps all day unless it's tightly coiled.
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G3RZP
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« Reply #8 on: December 07, 2012, 02:21:43 AM »

Or 16 or 18 gauge iron fence wire  - you won't need so much
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W7EJT
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Posts: 132




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« Reply #9 on: December 07, 2012, 05:15:30 AM »

OK, thanks for all the great suggestions! Will try them in the coming days!

Thanks, again and 73

Alan
Myrtle Beach, SC
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AD4U
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Posts: 2150




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« Reply #10 on: December 07, 2012, 05:33:44 AM »

Car headlights are great and cheap, but they take up a bit of space to store.

Keep your eyes open.  At a hamfest several years ago a guy was selling 1 ohm 250 watt resistors for a buck each.  I bought 10.  By seriesing or paralleling them, I can test most any 13.8V PS to its rated capacity.

Dick  AD4U
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K5LXP
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« Reply #11 on: December 07, 2012, 06:11:20 AM »

Or 16 or 18 gauge iron fence wire  - you won't need so much

Right.  My "heavy duty" 6V/75A load uses a small coil of steel fence wire submerged in a bucket of water.  My "light duty" one uses steel picture hanging wire.  I guess the "advantage" of using a long length of copper wire would be to have a greater area to dissipate the heat.


Mark K5LXP
Albuquerque, NM
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W0BTU
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« Reply #12 on: December 07, 2012, 07:53:06 AM »

100' of #18 wire is 0.65 ohms

I didn't realize it would take so much copper wire. Steel fence wire seems like a better idea.
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KE3WD
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Posts: 5694




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« Reply #13 on: December 07, 2012, 09:32:50 AM »

Years ago, we built loads to test power supplies using steel electric fence wire, and in a few cases, we used constantin wire taken from copper/constantin thermocouple wire.

After ascertaining the length of wire needed for the desired load, the wire was threaded through some rather simple forms made from that now-unavailable/likely illegal asbestos board, but I should think that one could find good substitutes for that today.  Phenolic or Fiberglass circuit board material (G4 or he likes) comes readily to mind.  Drill holes in strips made from the board such that wire can be threaded through like the desired coil form. 

Then, these assemblies were lowered inside plastic 5 gal buckets and in one instance, a large plastic trash can (because that load wouldn't fit into the 5 gal buckets) -- and readimix standard portland cement was mixed and poured overtop to the brim.  Vibrate out the air pockets. 

When set, this made what we used to call the world's largest ceramic resistor <g>. 

Those loads turned in yeomen's service for years, were used on everything from the Telco supplies mentioned here through industrial strength UPS systems designed for hospitals and airports in the design, development and testing. 

Takes quite some time to heat up that much cement to the point where you have to stop and let it cool back down.  Some of those UPS systems were left driving those cement "resistive loads" -- which is what they were in actuality -- for long periods of time, overnight even. 

Cost was minimal when compared to what's available off the shelf for $$ as laboratory resistive loads, and these were pretty much the exact same thing. 

For AC 120V testing, I purchased several of those Delonghi brand oil filled radiators designed to be used for heating small apartments or rooms and just plugged them in as loads.  The things have two power levels that simply switch the two resistors in and out of parallel operation, they are already overheat protected, the 1500W models proved to be quite up to the task of proofing AC UPS units, generating systems, etc. and it was easy to use more than one if the load needed was higher. 

73
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K4JJL
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Posts: 476




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« Reply #14 on: December 07, 2012, 11:39:10 AM »


For AC 120V testing, I purchased several of those Delonghi brand oil filled radiators designed to be used for heating small apartments or rooms and just plugged them in as loads.  The things have two power levels that simply switch the two resistors in and out of parallel operation, they are already overheat protected, the 1500W models proved to be quite up to the task of proofing AC UPS units, generating systems, etc. and it was easy to use more than one if the load needed was higher. 

73

I've done that before, too, when adjusting the carburetor on my generator.  I've also used strip heaters out of a furnace with the centrifugal fan.
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