Ideas for a power supply 3kW testing load??

[Chris Wilson]

I think I would find a "dummy load" for testing power supplies useful. I don't want to spend big on a programmable load, something basic would be adequate, but I would like to dissipate 60V at 50 Amps for say an hour, so water cooling looks promising. I could stick it in the loft space alongside my upstairs shack and feed mains water in and let it drain into the guttering, with a permanent mains water flow. Ideas for dissipating 3kW?? Thanks

[Seekonk]

2,000W 120V heating are cheap and about 7.5 ohms (higher than calculated value).  I recently bought a couple on Amazon for a dump load and they were less than $7 each shipped. Not sure of the thread, but likely common. It would take some welding.  Eight of those would get you there and could be series/paralleled to an assortment of values.

[Chris Wilson]

That's a good idea, thanks, but I am in the UK where nearly everything is 240V so I would have to do some maths. What about kettle elements....? Hmm.

[JFJ]

What about kettle elements....? Hmm.

Five 12V 600W immersion heaters, connected in series, would provide the load that you require. If mounted in a 50 litre tank/cylinder, the water temperature would be raised by about 50°C after one hour of use (enough to run a nice relaxing bath after completing your power supply test).

[Nusa]

Any kind of dumb resistance that can handle the current without failing will work.

Here's an extremely simple DIY approach that may give you ideas:

[SeanB]

Remember the heater elements do have a rather large positive temperature coefficient, so the cold resistance might be a little lower than hot resistance.  A few water heater elements will do as a load, and if the needs are for only rough and ready then they do fine. If it was Ac I would recommend a largish plastic bucket with salt water in it and some stainless steel plate electrodes on a holder so you can control lift and the amount of plate immersed. rough, but will safely disconnect itself on water getting too low.

Otherwise for a non water cooled thing some steel roof strapping, suitably long and coiled up so it does not short out, will provide a substitute.

[ddelectrical]

Maybe just some oil filled radiators would work. Seen these used on a wind turbine as an over-run dump.

[mmagin]

Here in the US at least, certain wattages of electric water heater replacement elements are quite common and cheap.  They screw into a certain thread size.

[Armadillo]

Any kind of dumb resistance that can handle the current without failing will work.

Here's an extremely simple DIY approach that may give you ideas:

I think it should be named the "Lipo early death approach"

[Armadillo]

I would hack up another 3kW PSU to dump output back to input.
For instance, if your DUT is a 3kW buck converter, then I will build a 3kW boost converter. Run the DUT in CV output mode, and run the recirculation converter in CC input mode. The CC and CV product is actual testing power.

So expensive but an interesting subject. Can you elaborate it. So where is the load aside from inefficiencies losses?

[daqq]

Use simple big ass resistors from ebay?

Buy a spool of resistive wire, make a few coils from it, put them in front of a fan? I did that, it works.

12V or 24V car lightbulbs?

[Chris Wilson]

Some good lateral thinking here chaps, excellent ideas abound, thanks for all the input. I think I'll look at heating elements first, at least I can heat water for "something" whilst fiddling! Cheers.

[Bendba]

Hi,

Just making a little note about the number of elements you would need. If you were to buy elements designed for 240v, you would need a rated 3,000W x (240V / 60V) ^ 2 = 48,000W and on top of that, you might have to account for the relatively high positive temperature coefficient.
And it would get worse if you try to dissipate the same power at lower voltage.

Note that if you can buy overseas and find elements designed for 120V, you'd only need 3,000W x (120V  / 60V) ^ 2 = 12,000W

Edit:

I got a couple more ideas, some might be too expensive or too much out of the box.

- use a dc to dc converter to step up to the elements rated voltage. Or down to a more standard voltage.

- charge a battery bank with the 3000W and reuse the power later for something useful/fun.

- use a mechanical load. For example, a restricted pump. If you use a variable reduction, you end up with a very flexible load.

- a big electrolysis tank if good ventilation is available. You can easily vary the load by varying the immersion of the electrodes.

[Kjelt]

Have you found a workable solution that you can share?

I need to test a 3kW powersupply with 40V and 60A would be enough.
I used 1000W 230V bulbs and even bathroom ceramic heaterunits of 2kW but they only consume a few amps at 40V.

So now I am thinking of two options:
1) buy 40 car lamps of 60W/12V and put them in a S4/P10 configuration resulting in 48V/50A load cost would be around €60.-
or
2)take 58 meters of 1,5mm² copper install wire (aprox. 0,65 ohms), put it in a bucket of water resulting in a load of 45V/70A cost around €15.-

What did you come up with in the end?

[Nusa]

48V water heater elements are available (used for solar/wind-power based water heaters) at a reasonable price. 600, 1000, 1500, 2000 watts seem to be the common sizes. Even at 40V, those should be in the ballpark. Plus some kind of water tank to heat, of course.

[amyk]

One of the advantages of having a swimming pool.

As a rough estimate, 3kW will raise the temperature of 1L of water by ~0.72 degrees C per second, or 43 deg/min.

[Kjelt]

So I did a short test and this works very well (for a short period ofcourse unless you have a swimming pool as amyk pointed out  )
The short pieces of the wire that is not submerged gets pretty hot as expected.

Finally I could see if the supply was working correctly and fixed, it still makes a bit of a complaining noise now and then but this puppy is old and does not need to do his work all day long, now and then an hour or so with short burst intervals.

[doktor pyta]

@Kjelt
By the way: do You have some more photos of this power supply?
I haven't seen any Delta Elektronika internals. Seems to be well built.

[Kjelt]

If you only asked this morning because i closed her up this afternoon 
It took me a half hour and a plastick hammer so I am reluctant to open her up again
In short it is old school 90s design, everything is analog electronics, no cpu nothing in there and that is why they are easily fixable. If you like i can sent you the schematics i got from Delta, since they introduced a newer generation with digital display this one is no longer secret.

[Zucca]

beefffy old lady!

[djacobow]

Mike of Mike's Electric Stuff (active on this board) did a video on cheap and cheerful dummy loads a couple of years ago:

[Bendba]

If you only asked this morning because i closed her up this afternoon 
It took me a half hour and a plastick hammer so I am reluctant to open her up again
In short it is old school 90s design, everything is analog electronics, no cpu nothing in there and that is why they are easily fixable. If you like i can sent you the schematics i got from Delta, since they introduced a newer generation with digital display this one is no longer secret.

Hi,

Any chance you could share the schematics? I'd be interested.
Thanks

[stj]

a kettle is 2-3Kw,
and it has free liquid cooling. 

[Kjelt]

If you only asked this morning because i closed her up this afternoon 
It took me a half hour and a plastick hammer so I am reluctant to open her up again
In short it is old school 90s design, everything is analog electronics, no cpu nothing in there and that is why they are easily fixable. If you like i can sent you the schematics i got from Delta, since they introduced a newer generation with digital display this one is no longer secret.

Hi,

Any chance you could share the schematics? I'd be interested.
Thanks

Sure check your pm