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problem with capacity tester?

I’m limiting my capacity testing to 10A (on a 150W model) precisely because I’m worried higher currents will damage the flimsy design over a >24h test.

Draining a full cell takes twice as long, but 10A also makes the math exceedingly easy...
So far I've had no problem running at 20 amps or above, just waste heat. But my sample size is 3, so still a long way to go.
 
So far I've had no problem running at 20 amps or above, just waste heat. But my sample size is 3, so still a long way to go.
There are some pics in the early part of that video I posted showing discoloration of the PCB under the MOSFETs. These cheapo testers will run at 20A but clearly not with the same longevity.

As far as an actual capacity test,10A or 20A is not that different as far as a ‘light load’ theoretical capacity.

To test capacity at more typical load levels of 60A (in my case), I’m going to connect my 3kW inverter and run an 1800W space heater full-bore...
 
There are some pics in the early part of that video I posted showing discoloration of the PCB under the MOSFETs. These cheapo testers will run at 20A but clearly not with the same longevity.

As far as an actual capacity test,10A or 20A is not that different as far as a ‘light load’ theoretical capacity.

To test capacity at more typical load levels of 60A (in my case), I’m going to connect my 3kW inverter and run an 1800W space heater full-bore...
I'm just looking at the heatsink/fan combo they put on these, and compare them to ones rated to cool a 125 watt CPU. They will indeed run much hotter, there just isn't enough heatsink/fan to avoid it. I did get one of the 180 watt rated testers, it has dual fans and heatpipes, it is much more likely to actually last (especially if restricted to 150 watts). I might try replacing the heatsink thermal compound since I have some good stuff, but I just haven't done it yet.

Once it gets to March/April here, I'm not running a heater as a load, an air conditioner, maybe, but certainly not a heater. :)
 
I'm just looking at the heatsink/fan combo they put on these, and compare them to ones rated to cool a 125 watt CPU. They will indeed run much hotter, there just isn't enough heatsink/fan to avoid it. I did get one of the 180 watt rated testers, it has dual fans and heatpipes, it is much more likely to actually last (especially if restricted to 150 watts). I might try replacing the heatsink thermal compound since I have some good stuff, but I just haven't done it yet.

Once it gets to March/April here, I'm not running a heater as a load, an air conditioner, maybe, but certainly not a heater. :)
Improved thermal paste and/or a better fan might position you to do more through one of these cheapo capacity testers, I’m just not convinced it’s worth it.

A real high-current (realistic-current) test goes well beyond what one of these cheapo units can ever achieve and 10A can characterize the theoretical low-current capacity of a cell as effectively as 20A (just 2X more slowly).

I’d prefer to not stress my unit so it will last longer and be less likely to give my flakey readings/behavior.
 
I have one of those Chinese capacity testers with the fan. I have used it in the past to test 60 AH and 100 AH batteries without problems. Now that I am testing 280 AH cells at 18 amps (max I can get it to go) I noticed that the voltage displayed on tester is 0.3 volts less than that measured at the input of the tester. So my test stops when the cell is at 2.8 volts because the tester thinks it is at 2.5 volts.

Is this typical?
I am testing my second set of 8 x 280Ah LiFePO4s, and noticed contrasting voltages similar to your "voltage displayed on tester is 0.3 volts less". ... I may order a 2nd of those fan heater Ah tester to be able to Ah test two cells at a time (on next LiFePO4 build), plus to compare the contrast of 2 Ah testor results; ...as I wonder about the accuracy (I am getting 270Ah on 280 Ah rated LiFePO4 at 20A draws, and a little more if I run the Ah testor a 2nd time at 10A or 5A) ... I wonder about their accuracy when I see the contrast of voltages I can measure at the battery being tested, the termials on the Ah tester, and then the volts shown on Ah Testors' LCD. They are cheap enough to order two (if you have time for an order from AlibabaExpress/ just saw $37 each to USA) ... Please to see my mine cut off at set voltage, and not fail at that function. When ordering 8 + bigger Ah batteries; I think getting two of those on way is an idea worth considering ... I am wondering if those more experience than I accept the first Ah reading at the 20 amp draw, vs measuring a few more Ah by dialing the amp draw down to 10 amps, or 5 amps, and running Ah meter again for a few more Ahs (I get up to 8 more Ahs on a second measure) ???
 
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The heatsink is directly connected to the Drain of the power MOSFET! so be real careful.
 
I am testing my second set of 8 x 280Ah LiFePO4s, and noticed contrasting voltages similar to your "voltage displayed on tester is 0.3 volts less". ... I may order a 2nd of those fan heater Ah tester to be able to Ah test two cells at a time (on next LiFePO4 build), plus to compare the contrast of 2 Ah testor results; ...as I wonder about the accuracy (I am getting 270Ah on 280 Ah rated LiFePO4 at 20A draws, and a little more if I run the Ah testor a 2nd time at 10A or 5A) ... I wonder about their accuracy when I see the contrast of voltages I can measure at the battery being tested, the termials on the Ah tester, and then the volts shown on Ah Testors' LCD. They are cheap enough to order two (if you have time for an order from AlibabaExpress/ just saw $37 each to USA) ... Please to see my mine cut off at set voltage, and not fail at that function. When ordering 8 + bigger Ah batteries; I think getting two of those on way is an idea worth considering ... I am wondering if those more experience than I accept the first Ah reading at the 20 amp draw, vs measuring a few more Ah by dialing the amp draw down to 10 amps, or 5 amps, and running Ah meter again for a few more Ahs (I get up to 8 more Ahs on a second measure) ???
LiFePO4 cells will always deliver more Ah at lower C-rated current discharge, so it really depends on why you are performing capacity testing:

1/ to check whether cells meet specifications (which requires 0.5C discharge @ 25C +/-2C).

2/ to determine what capacity you can count on in your use-case (which means discharging close to whatever will be your most common discharge rate).

3/ to determine how well-matched your cells are (which means whatever discharge rate is most convenient, as long as it is the same for all cells being tested.
 
I have already burnt through a 180W one, using 5A at 28V. Strangely enough, it worked fine for 8 hours constant the night before....didnt even feel as though it was getting warm. Got the spark, right under the fan base. RIP wee tester.?
 
I have already burnt through a 180W one, using 5A at 28V. Strangely enough, it worked fine for 8 hours constant the night before....didnt even feel as though it was getting warm. Got the spark, right under the fan base. RIP wee tester.?
I burned one up too. I saw the flame from under the fan. Poof ?
 
I burned one up too. I saw the flame from under the fan. Poof ?
You guys are making me happy I decided to limit discharge currents to 10A, even at 3.2V.

Any idea whether the failure to experienced was caused by power (W) or current (A)?

I’m only running 10A @ 32W not but need to decide whether I want to test my 24V battery at 6A / 150W or should also back that off to a lower total wattage (I have the 150W model)...
 
I burned one up too. I saw the flame from under the fan. Poof ?
Yes same here...although i had pushed it right to its limit the previous night (179W all night)
Guess they simply aren't robust enough....had it not been bought from china, i might have tried returning it....in reality, it wasn't ran outside spec...but we all know by now, take the spec and half it...lol
 
You guys are making me happy I decided to limit discharge currents to 10A, even at 3.2V.

Any idea whether the failure to experienced was caused by power (W) or current (A)?

I’m only running 10A @ 32W not but need to decide whether I want to test my 24V battery at 6A / 150W or should also back that off to a lower total wattage (I have the 150W model)...
definately need to back it off...180w tester toasted at 5A on 24v nominal pack

edit...i'll just add, it was one of the push button set ones, not the dial ones, which i've had no issues with.
 
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I did at least 40 tests at 15 amps (single cell). The only problem I had is the power supply died after the first couple of tests. I bought a new one and no problems since.
I set the cutoff to 2.2 volts so that it actually ends closer to 2.5. I replaced the wires with larger gauge and I use ring terminals everywhere.
Worked great. Accurate (as compared with Victron BMV-712)
 
definately need to back it off...180w tester toasted at 5A on 24v nominal pack
Wow, so 125W killed your 180W tester!

Did you get a temperature reading before it fried? One of the weaknesses pointed out in that video I linked is that there is no High Temperature Disconnect or even High Temperature Alarm.

can you post a picture of your PCB under the heatsink?

Also, did you remove the fan and check out the thermal grease - many of us found next to none and added more...
 
Wow, so 125W killed your 180W tester!

Did you get a temperature reading before it fried? One of the weaknesses pointed out in that video I linked is that there is no High Temperature Disconnect or even High Temperature Alarm.

can you post a picture of your PCB under the heatsink?

Also, did you remove the fan and check out the thermal grease - many of us found next to none and added more...
yes, thermal grease was ok ....will post a pic shortly
 
Wow, so 125W killed your 180W tester!

Did you get a temperature reading before it fried? One of the weaknesses pointed out in that video I linked is that there is no High Temperature Disconnect or even High Temperature Alarm.

can you post a picture of your PCB under the heatsink?

Also, did you remove the fan and check out the thermal grease - many of us found next to none and added more...
Think it was sitting at 28v , so 5A = 140W to toast.
 
I had been discharging 3.5V and I switched to 48V but forgot I couldn't crank the amps all the way up.
The same spot is burned on mine.
I had a spare and it still works.
Both of mine discharged single cells full blast many times.
They don't like rapidly cranking past 185W
When I slowly went past 185W it just turned off.
 
Transistor mounted dead-bug so a heatsink could be added.
Is it the only power dissipating element? You could mount a suitable resistor externally to dissipate about half to 3/4 the power, for certain battery voltage range and current.

Is that MOSFET or bipolar?
MOSFETs need considerable derating below their datasheet specs when used for DC/linear operation. They're optimized for switchers.
 
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