Testing a 25 amp PSU at full load

[Phil G4SPZ]

Thanks to everyone for their helpful suggestions and for the very useful links, especially to the Manton schematic which I have printed out for future reference In the end, I opted for the water-cooled option which has been running nicely for 20 minutes now at 20 amps and the power supply is comfortably warm.

Thanks again,

Phil

[ronbryan]

Phil

I suggest you keep an eye on your Avo Model D for overheating. I have been told that Avo 8 meters are not continuously rated at their full load of 10A, so a similar intermittent rating restriction may apply to the Model D as well.

Ron

[Phil G4SPZ]

Good advice, Ron, but I did think about that, having worked on plenty of Avos and seen the shunts! You're probably right that they aren't continuously rated, the high current ones anyway. Once I was satisfied about the value of the current, I bridged out the Avometer, as it's voltage stability I'm most interested in. The test leads are still in circuit but they are pretty robust.

The water is tepid now, about 30 degrees C.

Bulbs do have a low on resistance OK as long as the PSU can cope.

[Station X]

Five off topic posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=104276

[threeseven]

Earlier today I remembered another option I could have offered for you to use, one of my selection of heavy Avo shunts! Shunt takes the grunt and saves the dissipation in the meter. Ah well.

[7severn7]

Be aware, although pretty good, these PSUs are not entirely without their problems.
Check out the various web links including http://www.qsl.net/pa3fqh/ep920/ep920.html and http://www.stonefisk.com/index.php/2...tion-to-the-ma

[vu2nan-nandu]

Originally Posted by Phil G4SPZ

Can anyone suggest a cheap but rugged DC dummy load that will take 300 watts (12 volts at 25 amps) continuously? Half a dozen car headlamp bulbs would work, but I would have to buy them! Maybe a projector lamp, or a swimming pool lamp? As this is only for a one-off test, I don't want to spend too much money.

Hi OM Phil,

Using car headlamp bulbs to test a PSU with protection has its problems!

http://nandustips.blogspot.in/2013/0...-quickfix.html

73,

Nandu.

[KeithsTV]

I used one of those large rheostats, the sort we used to use at school and university, to test a 10A PSU I built about 30 years ago. Due to a fault in the current limit circuit it started oscillating and I had a 10A square wave running through the resistor making it "sing" at a few hundred Hz.

Keith

[dave cox]

As merlinmaxwell pointed out the initial low resistance of bulbs can be problematic. My cheap skytronics 30/10 PSU has (strangely) a fold-back current limiter that seems to prevent start-up at less than ~ 0.6 ohm - even though the PSU can happily (happy being a relative thing) deliver 10A at 6V. Ceramic glow plugs, from a diesel engine, cause a similar problem due to their wide variation in resistance with temperature.
dc

[petertheorgan]

just keep it simple -
stick the resistors in a bucket of water

[mole42uk]

i remember some guys testing a large-ish 3-ph generator by connecting the three phase outputs onto plates in a tank of water. Once the generator was running, they poured salt into the water to load it up.
Quite spectacular!

[paulsherwin]

For anyone considering the car headlight route, Poundland sell 'bulb kits' containing a selection including a 60/55 headlight bulb. Three of these with both filaments connected should do nicely and you'll have a few spare bulbs for the car, though I don't imagine the quality is up to much.

[G3PIJpeter]

If you pass DC through a solution of salt (sodium chloride) in water, the result will be chlorine gas (choke), hydrogen gas (bang) and caustic soda solution (drain cleaner). AC reverses every cycle (Herz) and so the solution gets too confused to decompose - at least, that's what my A-level chem told me.
- Peter

[Nicklyons2]

I have a 12V 250W N.O.S. projector lamp; if anyone wants it PM me.

[G6Tanuki]

Originally Posted by G3PIJpeter

If you pass DC through a solution of salt (sodium chloride) in water, the result will be chlorine gas (choke), hydrogen gas (bang) and caustic soda solution (drain cleaner). AC reverses every cycle (Herz) and so the solution gets too confused to decompose

Indeed. I've seen a big multi-Megawatt military-marine power system tested by connecting a set of large metal plates to the thing and then craning them progressively lower into the dock to increase the load.

It's amusing to see the Tyne boiling!

[Phil G4SPZ]

It's nice to see the recent spate of interest in this thread. As the OP, I ought to report back on the successful outcome of my chosen method of "lots of enamelled copper wire in a bucket of water" depicted in post #21.

After two hours at 20 amps, things had stabilised and the water was comfortably warm, whilst the power supply was very hot indeed. However the output voltage hadn't changed at all. So I concluded that the supply was probably safe to be used with my intermittent 15 amp load provided by my FT857.

Thanks for everyone's contributions!

Phil

[Herald1360]

Originally Posted by G6Tanuki

It's amusing to see the Tyne boiling!

Presumably resulting in "Fog on the Tyne"