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Since I plan to add a few more cells to my LiFePO4 pack, I am making some changes to my box and this provides a perfect opportunity to verify my cells individually.

I'd like to test my TS LFP160 cells after having done 7000 miles and thought I'd try find a way to discharge some or all of the cells to see how long it takes to get down to 2.5V or close to it. I basically want to determine if I have any bad cells or cells with drastically reduced capacity. I don't have any speciaized equipment and would be trying this in a more or less household environment. I'm thinking of doing a slow discharge of 0.3C or 50 amps to dissipate approx. 153 watts of energy. Based on my calculation, I would need a 0.06 ohm resistor and appropriate contactor. This is where I get stuck a bit.

Which resistor would I be best advised to use?

I realize that there are many options like graphite resistors, sliding contact resistors, golf cart starting resistors, older forklift resistor based motor controllers, old electric furnace elements....

Can anyone offer any good advice or point me to a source for a good resistor/contactor to use for this type o battery test?
 

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Harbor Freight has a battery load tester, with voltmeter and ammeter, for about $50. It's good up to about 500 Amps. I aim a fan at the base of mine if I'm doing high current or extended testing. I've had the carbon pile inside literally glowing red for minutes at a time, with a fan blowing at the base of it. Note this will work for a cell or small number of cells, do not hook your whole pack up to it!
Since I plan to add a few more cells to my LiFePO4 pack, I am making some changes to my box and this provides a perfect opportunity to verify my cells individually.

I'd like to test my TS LFP160 cells after having done 7000 miles and thought I'd try find a way to discharge some or all of the cells to see how long it takes to get down to 2.5V or close to it. I basically want to determine if I have any bad cells or cells with drastically reduced capacity. I don't have any speciaized equipment and would be trying this in a more or less household environment. I'm thinking of doing a slow discharge of 0.3C or 50 amps to dissipate approx. 153 watts of energy. Based on my calculation, I would need a 0.06 ohm resistor and appropriate contactor. This is where I get stuck a bit.

Which resistor would I be best advised to use?

I realize that there are many options like graphite resistors, sliding contact resistors, golf cart starting resistors, older forklift resistor based motor controllers, old electric furnace elements....

Can anyone offer any good advice or point me to a source for a good resistor/contactor to use for this type o battery test?
 

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Since I plan to add a few more cells to my LiFePO4 pack, I am making some changes to my box and this provides a perfect opportunity to verify my cells individually.

I'd like to test my TS LFP160 cells after having done 7000 miles and thought I'd try find a way to discharge some or all of the cells to see how long it takes to get down to 2.5V or close to it.
Is the vehicle operational? If so, drive it. Go until you reach what you think is 90% of your range. Measure and then drive a 1Ahr loop until the first battery reaches 2 V resting. Then you get range information too.
You can top off the low battery and continue driving, testing and charging until all the batteries are balanced.
Gerhard
 

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Yep, that's the unit. Yes, the knob is spring loaded. Mine is a bit touchy for low currents (< 50 Amps), but pretty steady above that. LiFeP batteries have stable voltage for most of a discharge, so you don't have to twiddle the knob too much to do a test, but you do need to be there and watch things.

Something fun I do with mine is also use it as a quick charge unit. If I put a 12V battery right on 1 to 3 cells it would horribly overcurrent them. With the HF tester spliced into the circuit, I can control the charging current and do a far faster charge than the RC charger will support.

Safety: I trust everyone is wearing safety goggles. I have been wearing safety goggles, ear plugs, and full clothing. I put a folded moving blanket over the batteries (propped up so air can cool them). I also do the testing on a welding table. So far I've just had one notable venting event, but I plan ahead as if a cell might blow up under the high current testing.
David,

Thanks for the fast reply. Is this the unit?



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

Just want to be sure.

Is the load knob spring loaded on this unit?

If it is and I want to keep a constant load for a sustained period of time, I guess something has to be rigged up or reworked to keep the load knob from dropping back down.
 

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Francis,

Thanks. This looks very interesting. I read the product description and specs. There is a mention that constant power testing is supported with the pro software upgrade.

Do you have the plain CBAIII or the CBAIII Pro with Software upgrade?
I have the plain one. I do not understand what more the pro gives, both are the same 40amp input limit.
Francis
 

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Discussion Starter #10
Is the vehicle operational? If so, drive it. Go until you reach what you think is 90% of your range. Measure and then drive a 1Ahr loop until the first battery reaches 2 V resting. Then you get range information too.
You can top off the low battery and continue driving, testing and charging until all the batteries are balanced.
Gerhard
Gerhard,

All my cells and battery box were removed from the car so taking a drive at this point is not possible. Thanks for the input just the same.
 

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Discussion Starter #11
Francis,

When using the CBAIII, do you select the <auto-check> profile or create your own profile?

If you use the <auto-check>, my guess is that you probably also select "Li-ion" as battery type since I don't think the LiFePO4 selection is available in the CBA software?

I would also be interested to know what you use for the rest of the Test settings if it's not much trouble. For example, the CBA user manual recommends or uses 2.8 volts as the test cutoff voltage which sounds alright to me.
 

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Safety: I trust everyone is wearing safety goggles. I have been wearing safety goggles, ear plugs, and full clothing. I put a folded moving blanket over the batteries (propped up so air can cool them). I also do the testing on a welding table. So far I've just had one notable venting event, but I plan ahead as if a cell might blow up under the high current testing.
What were the conditions of venting? At 500 amps discharge? Size of cell? Were you running it up and fully down in a short period? Was the battery extremely hot right before venting?

I figure you are using small cells than something in the 160-200Ah range since that would be a little more than 3C for a 160Ah cell. It took Rickard about 3/4 discharged at 4C almost constant to overheat and vent CALB cells.
 

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The cells being tested were 10 Ahr China HiPower batteries (similar to a Headway 10 Ahr in specs). Spec is 10 C discharge and 5 C charging. I was over 4 minutes into an 11 C (over spec) discharge when 3 of 4 cells vented. The case temperature was 93 Celsius on the hottest cell, the one that did the most spectacular vent. It had a little steam cloud around it for a few seconds. It smelled like hot antifreeze to me (not much of a sniff, I quickly cut the power and ran outside). There was a couple of teaspoons of electrolyte on the table. 2 of the vented cells then self discharged at 0.1 V per day after that -- clearly ruined. A 3rd cell that had wept a little electrolyte has continued to work great.

I now monitor all my cells for temperature, and for testing I'm keeping it < 70 Celsius. For my road going use I plan to run < 60 Celsius. I found some MSDS sheets that said Thundersky batteries (different manufacturer, but I presume similar chemistry) has EA that will vent at 77 Celsius and is easily ignited.

For the data hounds, here are results from testing I did:
http://explodingdinosaurs.com/9electric/celltest

What were the conditions of venting? At 500 amps discharge? Size of cell? Were you running it up and fully down in a short period? Was the battery extremely hot right before venting?

I figure you are using small cells than something in the 160-200Ah range since that would be a little more than 3C for a 160Ah cell. It took Rickard about 3/4 discharged at 4C almost constant to overheat and vent CALB cells.
 

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DavidDymaxion, Right, I get usernames mixed up sometimes and was thinking in context to the Thundersky capacity range. Makes sense with 10Ah the cells for sure. I was thinking if someone tried to drain a 160Ah cell from full that the load tester would go turn into molten metallic goo long before the cell was empty. My misinterpretation.
 
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