+500 watt loads for battery testing

Batteries, Chargers, and Battery Management Systems.
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kfong   1 MW

1 MW
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Joined: Sep 02 2008 11:34am
Location: SE Michigan, USA
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+500 watt loads for battery testing

Post by kfong » Oct 27 2011 11:04pm

When I needed a higher load to test my battery and the fets on the Smart Switch, I had a tough time coming up with anything that was practical and effective. I thought of using lights, but that seemed bulky and inefficient. I wanted something that was as compact as possible. I thought of trying to use a nichrome wire under water, but that just vaporized. I know some have tried hot plates and oil heaters but the resistance on those devices usually are 10 ohms or higher, same with irons, ect. Some have mentioned regenerative loads but unless I can convert 50 volt down to 12, or in my case 27volt for the Hyperion, that wasn’t going to get me anywhere. A transistor load bank would be nice, but I would have to design one and make a circuit board, using standard high wattage ceramic resistors didn't appeal to me either since they tend to be big and pricey as well.

It occurred to me a heat gun might be workable but I didn’t like all the heat focused. Then I remembered I had an old electric portable heater that worked in a similar fashion. I took it apart and hit paydirt. This was perfect for what I wanted to do. The wire elements were thick and durable. I then came up with an easy way to adjust the resistance by shorting out the outer wires with a thin copper sheet. I’m able to soak up 560 watts at 45 volts drawing about 12.6amps. I’m tempted to shorten the wires more but not sure how heat resistant the plastic housing is and I didn’t want to push my luck with the shortened elements even though it's only a slight glow. The unit says 1500 watts but I didn’t get a chance to see how hot it functioned before I modified it. For now I’m quite happy with the results since it close to cruising speed on a bike.

I’m interested in what other have come up with that can push over 500 watts since I would like to build something in the 1000-1500 watt range. A thought that occurred to me is to center tap my current setup and have 4 parallel resistor banks to spread out the current load, since my main concern is hot spots. hmmm? I might just have to do that.

Here are pictures of the resistive load.
Front cover.jpg
Front cover.jpg (82.98 KiB) Viewed 473 times
Internals.jpg
Internals.jpg (74.39 KiB) Viewed 473 times
sideview.jpg
sideview.jpg (82.4 KiB) Viewed 473 times
There are two heating elements, I ended up paralleling them together.
heating element.jpg
heating element.jpg (70 KiB) Viewed 473 times
You can see the thin copper sheets I inserted at the bottom of the elements. I had to short out the outer portion to bring my resistance to 4 ohms.
Modification.jpg
Modification.jpg (54.9 KiB) Viewed 473 times
I kept the fan on 110AC since it was not easily replaced with a DC version. Too bad though, It would of made a nice portable DC heater.
in use.jpg
in use.jpg (70.64 KiB) Viewed 473 times
in use2.jpg
in use2.jpg (65.53 KiB) Viewed 473 times
Here are the results of my Konion pack, I had suspected I was loosing capacity. Last year I was getting a little over 9 amp hrs. I'll have to chart this again next year to see how much more it has decreased. You can see after the smart switch shuts off at 33volts, the voltage recovers to 35v. I then turned on the smart switch to see it repeat and settle at 34.8v.
Results.jpg
Results.jpg (70.91 KiB) Viewed 473 times

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