Looking for a way to Bulk discharge 4S Lipo

[teslanv]

I want to test some 5000mAh 4S LiPo cells (14.4V Nominal) at a high C-rate - Like 20C (100A), which would be around 1500 Watts continuous.

I am looking for some kind of load like a big light bulb or ???, and preferable CHEAP.

Thought about an inverter, but a 1500W inverter is around $100, and don't want to spend THAT much for this project.

Any thoughts?

 

[Hillhater]

Have a look at this...
It may give you a few ideas.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=47207&p=692097&hilit=2000+amp

 

[major]

I have some extra locomotive braking resistors which I use. They are 1 to 1.5 kW and 0.12Ω. About 10 pounds edge wound. Gives a constant resistance as it heats and repeatable tests. The exact resistance is stamped on it so you can use a voltmeter across it to monitor the current. Of course it won't be a constant current discharge because the current will decrease as the battery voltage drops. Being edge wound it is easy to clamp on the element midway to get less resistance. They'll handle 100A easy. $20 and you pay shipping. PM me if interested. Isn't messy like the wrench in the bucket of oil and doesn't wreck your tools :wink:

 

[Matt Gruber]

are you trying to see how fast you can ruin them?
would be lots more fun to go up a steep hill at high speed.
it seems the max c rating is for one or maybe a few times. i think it is there to warn the user how many amps might be available to start a fire if there is a short.
for instance my 18650 konion cells are rated 10c, 15 amps, but anything over 5 amps is impractical due to sag, heating, and shorter cycle life.

 

[Ykick]

Some of us parallel surplus household heater elements, irons, ovens, space heaters, etc., in order to achieve significant static testing loads.

1500W@120VAC reated heater element draws about 12.5A. Apply 60VDC, Amps drop to about 6A with a resulting 360W or roughly 1/4 the Watts at full VAC rating.

 

[teslanv]

Some of us parallel surplus household heater elements, irons, ovens, space heaters, etc., in order to achieve significant static testing loads.

1500W@120VAC reated heater element draws about 12.5A. Apply 60VDC, Amps drop to about 6A with a resulting 360W or roughly 1/4 the Watts at full VAC rating.

Kinda what I Had in mind. How about a 4500w 240v water heater element in a bucket of water?

 

[Ykick]

How about a 4500w 240v water heater element in a bucket of water?

If you're only applying 4S RC Lipo (about 16V) that's maybe 1.2A or a little under 20W. Doubt it needs to be in a bucket of water to disipate that? Even at 60VDC (16S) that 4500W is maybe only about 280W?

Lowest voltage and highest wattage is what you're looking for. For my previous example - 1500W@120VAC toaster oven element delivers about 360W on 60V (16S RC Lipo).

Of course, you can parallel more elements together but if you also series more cells and bump voltages up you'll get significantly more heat/Watts.

Otherwise, if sticking with 4S voltage range you might wanna look into Carbon pile automotive battery load tester? Fairly inexpensive and should allow for a significant low voltage load.

http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html

Here's a guy doing an RC Lipo test with one of these Carbon Pile load testers:
[youtube]faKSSRuZUQs[/youtube]

 

[teslanv]

I think that's what I am looking for. $55 at Harbor Freight.

Thanks Ykick.

 

[Ykick]

You're welcome. And for 4S voltages that's probably a very good choice.

Surplus AC heater element stuff is really only practical when testing full pack voltages north of 50V IMO.

 

[Punx0r]

Wow. I had no idea such a neat piece of kit existed for such a reasonable price Good to see the 130A turnigy wattmeter also seemingly fairly accurate on its readings.

 

[Hillhater]

I notice there are 100a max load testers on HF for $20 !
.. Not sure i would want 100A running through those 10g leads and 4mm bullet connectors for very long !