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Smoked Capacity Tester

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Wolfpack7483

Solar Enthusiast
Joined
Dec 21, 2023
Messages
218
Location
Charlotte, NC
I posted in the Vatrer thread my cell voltages, showing the runner cell almost 200mv ahead, just prior to single cell overvoltage. Will asked if I had tested the capacity of the Vatrer & I haven't. Got to thinking about that & looked at the specs on my 150w tester that I've used on 12v batteries. I didn't realize it was rated for up to 200v. Figured I could run a test in about a day & 1/2. I "re-familiarized" myself with the tester on a 12v battery &set things up for the test.

I used ring connectors for the battery terminals & xt60 connectors between the battery and the tester. I made sure both knobs on the tester were fully counterclockwise so they would be zeroed. Plugged the xt60s together to start the test. The fan immediately "took off" overspeed for a couple seconds, then sparks flew and everything died. Any idea what I did wrong? I'm attaching a picture of the tester after I removed the fan. Those are not the leads I used for the test. 20250211_091253.jpg
 
Were you testing a 12vDC battery? I do not understand your reference to 200v rating on the load tester.
 
Most of these have an upper limit of 10amps ....


Is it possible you still had it set for the voltage of 12.8 and when you connected it you sent 4 x the current through the FET?

Other question - did you have it connected to an external power supply for the device itself verse using the battery under test as the power supply? If it was using the battery under test I would expect the symptoms you describe.
 
What setting were you running the load tester on? Constant Current/constant power/constant resistive load/constant voltage?

Constant current with a 48v battery any higher than about 3-4A will blow the device if the device does not take any action to reduce the current.

I don't know how big your battery is but at 3A a fully charged 100ah battery is going to take at 33 hours or more.
 
robbob2112 said:
Most of these have an upper limit of 10amps ....


Is it possible you still had it set for the voltage of 12.8 and when you connected it you sent 4 x the current through the FET?

Other question - did you have it connected to an external power supply for the device itself verse using the battery under test as the power supply? If it was using the battery under test I would expect the symptoms you describe.
Click to expand...
I had set the minimum voltage alarm @ 40v. I was under the assumption it sensed voltage input, as there wasn't an adjustment in the set up parameters for voltage. In the specs it says : Voltage measuring range 0.00V - 200V.
 
rogerheflin said:
What setting were you running the load tester on? Constant Current/constant power/constant resistive load/constant voltage?

Constant current with a 48v battery any higher than about 3-4A will blow the device if the device does not take any action to reduce the current.

I don't know how big your battery is but at 3A a fully charged 100ah battery is going to take at 33 hours or more.
Click to expand...
The only adjustments are for current - Coarse & fine. As you adjust, it indicates the power in the readout. Instructions say to rotate both knobs fully counterclockwise (to zero) before test, which I did. I'd planned on about a day & a half for the test.
 
Wolfpack7483 said:
I had set the minimum voltage alarm @ 40v. I was under the assumption it sensed voltage input, as there wasn't an adjustment in the set up parameters for voltage. In the specs it says : Voltage measuring range 0.00V - 200V.
Click to expand...

My tester looks just like yours except purple board - it allows for more setting like they describe and has 4 x 2w resistors in the corners

Were you powering the unit from either a buck converter or a 12v wall wart? If it got 48v in on the units power connector that does the fan and electronics it would just fry after a second or less.
 
robbob2112 said:
Most of these have an upper limit of 10amps ....


Is it possible you still had it set for the voltage of 12.8 and when you connected it you sent 4 x the current through the FET?

Other question - did you have it connected to an external power supply for the device itself verse using the battery under test as the power supply? If it was using the battery under test I would expect the symptoms you describe.
Click to expand...
The external power is from 120v, fed from my inverter. This battery was removed from service (obviously).
 
robbob2112 said:
My tester looks just like yours except purple board - it allows for more setting like they describe and has 4 x 2w resistors in the corners

Were you powering the unit from either a buck converter or a 12v wall wart? If it got 48v in on the units power connector that does the fan and electronics it would just fry after a second or less.
Click to expand...
The electronics were unaffected, they still work.
 
The other thought is the MOSFET didn't have any thermal paste between it and the heat sink ? or if it did it was the old water/ceramic type that dries up and acts as an insulator verse a good paste.
 
sunshine_eggo said:
IMHO, the accounts of these types of units failing seems all too common even when operated in accordance with their limits and well under the maximum specifications.

IMHO, they're shit and should be avoided.
Click to expand...
Based on what part burned, I would suspect that the 180w limit is overly optimistic. Maybe they got 180w of sustained heat by running it in an ambient temp of < 0C/32F... The reviews of similar looking devices have photos of failures that look exactly like your failure.

Any idea what the current was when it blew up?
 
sunshine_eggo said:
IMHO, the accounts of these types of units failing seems all too common even when operated in accordance with their limits and well under the maximum specifications.

IMHO, they're shit and should be avoided.
Click to expand...
I had one that failed after running several tests (24vDC battery). The fan stopped operating and it overheated. I have looked about for a decent quality load tester and finding ones that handle 48vDC LiFePO4 batteries is not common or inexpensive. You do have to pay special attention to the testers specifications since items like saying it can measure voltage is not the same thing as being able to test a battery of that voltage.

These open board type testers seem to be most suited to individual cell testing.
 
rogerheflin said:
Based on what part burned, I would suspect that the 180w limit is overly optimistic. Maybe they got 180w of sustained heat by running it in an ambient temp of < 0C/32F... The reviews of similar looking devices have photos of failures that look exactly like your failure.

Any idea what the current was when it blew up?
Click to expand...
It should have been zero. I'd rotated both adjustment knobs fully counterclockwise per the instructions.
 
rogerheflin said:
It should not have blown at 0 unless that device really cannot run at 50v. The similar devices I see claim 200V but that seems pretty unlikely to me.
Click to expand...
I was surprised, to say the least. Glad I had on safety glasses and gloves. A lot of times I think that's overkill, but you never know....
 
I am running a capacity test right now - using a 1500w heater - through the inverter and it is drawing 110amps off the battery -- it should be finished in about 30 hours... 12.8v300ah (well 280ah in reality because that is what the cells are)

With larger batteries it can be better to run a capacity test with a shunt that does history *victron* ... then you can put a MUCH higher wattage item on it to run the battery down..
 
Apparently I never learned to do math, but

300 * 12.8 = 3842 / 1500 = 2.56hrs... so it should have finished in 2.56hrs

Whoops I did math, darn, I shall have to lay down until the feeling returns to my body
 
I use the same load tester, and have blown up two of the semiconductors under the heat sink. It’s pretty startling after the first.

Despite the, in my case, the 150 watt rating, it turns out that at higher voltages like 24 and 48 the combined dissipation and switching voltage derate the max load spec significantly.

At 48 volts I keep the power below 50 watts.

The transistor is replaceable and I have two more spares for that purpose.
 
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