Build your own loadbank.

Hi,

You're right in your assumptions.

I work with units that require large load banks. They are made of shelves of resistors, inserted in a cabinet with forced air cooling through a fan below it. It's about 1 square meter area, 2 meters high, and requires that inlet and upper air exit is opened to ambient due to the high air flow and temperature. There's no magic. You'll need cooling to dissipate the energy.

I cannot think in anything more simple and cheap that incandescent bulbs, it was a good idea. Add a cooling fan, and some contactors, and a good step load system could be done.

If you cannot install the equipment in some area that allows you to admit and exhaust air from and to ambient, there's also the solution of putting in water heaters in a closed circuit with a cooling tower, or, if your tests are not taken in too much time, even in an opened circuit. But, if the service factor is not too high, you could run it for a short time and let it cool, I don't think this is the case by what you've written.

We've bought one from www.simplexdirect.com . Take a look for some ideas.

Thank you for the reply. I did not find the Simplex line when I was conducting ny research. My lab is equipped with a large volume exhaust fan if I need it for dissipated heat. I have also bounced around the idea of using HVAC sheet metal (the kind used in duct work). Enclose the ducting over the exhaust fan, and install the load inside the duct work w/ conduit run to a switch panel controlling each step of the load.

Perfect.

But pay attention to your spec, that gets up to 26 KW...

If it's needed, you'd better install it outside.

Regards.

I'll point out that 130V @ 200 A is 26KW, which is a huge amount of power to dissipate in a cabinet, cooled or otherwise. If you are able to build such a thing, I'd suggest pulsing your current through the load at a very low duty cycle to keep the heat down.

The 130VDC load would consist of 4 rectifiers rated @ 15A each for a combined output of 7.8KW. The 24VDC model is the only one that carries a 200A total output. Thanks for the idea though.

Interesting problem, I would go with a group of fan forced electric heater(s) located outside the lab. Light bulbs are a good idea but again put them outside with a rain cover and a fan.

Big non inductive resistive loads can be had at a price. I have built loads using carbon resistors but not quite this large. You can get non inductive resistors up to 5kw but they are expensive Farnell part number WDBR2 2kw and WDBR5 5kw. These are thick film on steel plate.

2006 CATALOGUE page 1051 this is for pulse rating not continuous use max voltage up to 2500v dc. see www.Farnellinone.co.uk if UK based phone 08701-200-200.

Surely light bulbs (Tungsten filiment) are partly inductive?

All the best.

a few years back, some of my uni mates built a rig for testing and analysing PC power supply units. the load in that was only rated for about 500W (way overkill then). the heat that even that generated was impressive. if your thinking of dissipating 7.8kW, DON'T do it inside your lab unless you want to turn it into a giant oven. spray booth ovens for auto body shops use similar power.

In the old days we used brine tanks. I have seen brine tanks utilised up to 10 MW (yes . . . mega watts). I myself have used a 55 gallon drum, two electrodes suspended on an insulated mechanism to raise / lower them in the water in the drum, then put one tablespoon of salt in the 55 gallons of water and could get about 350 kW at 480 volt. This sounds dangerous for all the obvious reasons, but large generator set manufacturers had automated versions of this on their roofs in the 50-70's and some still in use today. Cheap, and it works just fine. Very adjustable also since immersion level and salt content can tune this down to fine levels. Careful not to lean on the drum during the test or you may get the electromechanical version of Viagra.

Would this chemical load solution work on DC?

Not sure. Never tried DC. Probably it would work. Easy and safe to just try dropping two wires in glass of salt water with a AA 1.5 VDC battery and see if it is dead in a few hours.

We have 35 generators ranging from 25kw to 400kw, i would like to build a salt water load bank. Could you advise me on how to build one of these load banks, for 3 phase and 1 phase purposes. Should i use tap or distilled water, length of electrodes, distance electrodes must be apart, amount of water, amount of salt.

An assembly of fan-cooled bare-wire resistive elements (built in a tunnel like arrangement) with a fan works well. Metel-sheathed heating elements also work (power is limited however). All these will work on AC and DC and are easily configurable for various wattages. A water bath with a resistive element also works, and can be made fairly simply. The resistance can be varied like a variable resistor by having the removable wire clipped to the bare element (dont try this with high power DC as the load will chemically disentegrate).

The test lab I worked at previously had some fairly bodged equipment like the above (but it all worked). All were simple and cheap to manufacture (in fact all were built out of spare parts for free).

You still have to get rid of the heat (venting it out a door or window using a large flexible air conditioning stule conduit or hose perhaps).

My reply to:
1. RidgeRunner--------------If you run a professional Lab the consider for Inductive [Lagging PF] loads also. And Modular- Not in a sense of Rack_mounting but by cnnecting in parallel or series to increase the power ratings and side by side to achieve multiple-Test setups.Forced-cooled.But aviod Incandescent-Bulbs. Ther will be lot of Light & Uncontrolled-Heat in Lab.
2. PetroPower in #9-------------------I had been in a setup where we used it for AC & DC Power supply testing upto 100KW/KVA,
For AC Non-Inductive & Inductive. Hi-Power Inductors added to Dip-Plate for Indu8ctive load testing.
In DC Testing Polarity to plates were altered regularly in some setups & DC Power Supplies were loaded by an inverter & AC Test Loads were used.
a. Electric-Water-Valves to control Water & Salt were used.b. To Regulate load Dip-Plates were raised or lowered by motor-poerated mechanism.

Regards