Load testing batteries?

AlexLTDLX

AlexLTDLX

Administrator
Staff member
Hi All,

I'm looking for ideas on how to load test my two packs before I install them in the car. Today I picked up 3 500 amp carbon pile load testers from Harbor Freight. Two of them were faulty out of the box - 1 had the ammeter lead disconnected (which I fixed); and 1 has a broken disc limiting the load to about 100 amps. I've also learned that trying to run 3 in series is almost impossible - you're constantly trying to turn knobs to balance the load between them, and it's impossible to do it with any precision in the short time you've got before things overheat.

I have two 35 volt packs to test; I'd like to test each pack up to about 400 amps. Individually testing the packs is fine; in fact that's probably preferred.

Here are the ideas I've thought of and rejected:

1. Cheap toasters. I'd need at least 70 of them at 35 volts. That's too many toasters.

2. Nicrome wire. It would work, but I'd need a lot of relatively heavy gauge wire, and it would be a grid about 4' high and probably about 4' wide, and if it fell over while testing... well, let's just say anything it landed on would instantly toast...

3. Cheap hot plates. Same problem as the toasters.

4. Carbon discs. I found some guy selling fairly heavy-duty ones on ebay; not chineseum garbage. No real issues with this, but I'd have to make it. I have the machine tools and welder to do it, but time? Not so much.

5. Just test it in the car. Problems: what if a pack melts? It'll be in the trunk where I can't see it. And blasting around at over 130mph with half my car engulfed in flames (the half that has the gas tank in it) isn't my idea of a good time.

6. Salt water load tester. This idea literally just popped into my head while typing this, and believe it or not, it's an actual thing: https://waterstorage.tpub.com/TM-55-1930-209-14P-9-4/css/TM-55-1930-209-14P-9-4_166.htm Not really seeing a huge issue with this, except I might not be able to get the resistance low enough. Don't know, I really haven't looked into it yet.

Anyone got any great ideas?
 
I would look into off grid / solar / back up inverters which have the right DC input range ... and power my house with it, LOL
 
Do you still have a friend with a dyno? You're looking to dump something less than 23 horsepower. I'm imagining a rig with 4 or 6 starters, wired in series-parallel turning a dyno as hard as they can for a couple of seconds. How you rig them to connect to the dyno exactly is where the fun is. Probably not the least expensive, nor the easiest, but I think it would make for the coolest youtube video of the list so far and does anything else matter really? A hub dyno would be much easier. Or, because we're only talking about 23 hrsprr; a little bit of math, a heavy-ass concrete cylinder (55 gallon barrel filled with concrete?), and an RPM counter you could BYO "lawnmower" dyno.

What's that? You don't have a bunch of time? Pffff.
 
Some very interesting ideas. BTW, I did think of the lightbulbs; even using 1kW bulbs (studio lights), you'd need at least 60 of them. I did not think of putting the power back into my house or the starter idea. But I did stumble across something on ebay...

I ended up buying 30 carbon pile discs last night from a vendor on ebay and I'll "roll my own" carbon pile. The discs I bought are for a 1000 amp high-quality tester:

I sent a message to the seller and (suprisingly), I got a very thorough answer. Straight from the seller:
www.ebay.com

Mersen Carbon Pile Discs Set of 10; NEW and UNUSED; 4" OD x 1" ID x 0.25" | eBay

These discs are in mint condition! They serve as pieces in carbon pile resistors and are ready for use! Material - 2020 (Carbon). I will do my best to respond as quickly as possible.
www.ebay.com

"
It depends on how long your tester will be pulling 500 amps and for what duty cycle. For a particular 12V tester it required about 20 discs and it would do1000A tests for 30 seconds and it would handle a 25% duty cycle. So an estimate would be 12V X 1000A X 30sec = 360000Wsec: 360000 / 20 = 18000Wsec/disc: 36V X 500A = 18000W. So maybe 1 disc per second. You will probably want 20-30 discs. Thank for looking. I hope to do business with you. I adjusted the shipping to give a discount if you buy more than one set."

I ordered 30 discs. And returned the three Harbor Freight testers. I guess I'll be shooting a video or two on that project...

Now I need to shoot a video about the first finished pack. It weighs A LOT more than I expected... haven't weighed it yet, but it's probably over 30 lbs, maybe 40. And there will be a second. At least they'll help with traction (and wheel stands)!
 
You must log in or register to reply here.
Top