Smoked Capacity Tester

[Zwy]

For the most recent 280ah 12v battery I hooked it up to an inverter with a know efficiency rating ...

Not needed as the inverter efficiency will not have any effect on the reading thru the shunt. It just takes more or less Wh thru the shunt which is in between the battery and the inverter.

then hooked up a 1500w ceramic heater through a Victron shunt... It was so much faster to do the test even if the results are a few Whr one way or the other, it doesn't really matter to me.

I will only be using this small capacity tester to run the individual 314ah cells at 3.2v

 

[Mattb4]

A bit more money for this battery load tester than the open circuit board style that I happened to see over at Ebay today. It does look a bit more heavy duty and being able to work with 1-150vDC up to 400W, 40A. I wonder if anyone has one of these units? I might splurge for one when my next SS check arrives. It does not mention having any software for graphing the test results on a computer which would be nice.

 

[BarracudaBob]

This has motivated me to use the Florida Man's Dummy Load and a Victron Smart Shunt for my Capacity Testing. No watts were waisted all were put to good use.

Post in thread 'Battery Capacity Tester'

Feb 21, 2025

Found some 1500 Watt ones. Ordered.
View attachment 279311

Update: They came in today and I measured their resistance. 7.9, 7.7, 8.3, 8.2 Ohms so combined it is 2.006 Ohms. This would put a 100ah 51.2V battery at around 0.25C (22A - 28A) discharge. Perfect for a test. Most of my batteries are at that or below in production.

Let the fun begin.

• BarracudaBob

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[angelosw9]

I've ordered the FET to replace the smoked one, but also saw this in another thread, and it looks a lot more robust than mine that failed, & not that much more expensive - ordered the 450w.

https://www.aliexpress.us/item/3256803271477363.html?gatewayAdapt=glo2usa

It's a power Mosfet and you should really look at hte datasheet for it... power by itself means little with mosfets, it's highly dependant on their operation mode, to get 450w it has to be working in switching mode within parameters like lenght of pulse, gate voltage drive etc... if the circuit drives the Mosfet in DC mode ( not switching / pulsed ) there're limits on the voltage and current it can withstand, the datasheets have graphs with voltage / current / power for different switching pulses and in the bottom left corner there's a square for DC safe operation with voltage & current, you will e surprised how a 450w mosfet behaves looking at those graphs, the problem being that unlike a transistor which regulates how much current flows it works better as a switch which lets current flow or not flow. The ideal circuit would have power resistors as load ( or even car headlight bulbs ) and use the Mosfet in switch mode to regulate the current.

 

[Wolfpack7483]

It's a power Mosfet and you should really look at hte datasheet for it... power by itself means little with mosfets, it's highly dependant on their operation mode, to get 450w it has to be working in switching mode within parameters like lenght of pulse, gate voltage drive etc... if the circuit drives the Mosfet in DC mode ( not switching / pulsed ) there're limits on the voltage and current it can withstand, the datasheets have graphs with voltage / current / power for different switching pulses and in the bottom left corner there's a square for DC safe operation with voltage & current, you will e surprised how a 450w mosfet behaves looking at those graphs, the problem being that unlike a transistor which regulates how much current flows it works better as a switch which lets current flow or not flow. The ideal circuit would have power resistors as load ( or even car headlight bulbs ) and use the Mosfet in switch mode to regulate the current.

Realize this isn't ideal, and don't plan on it getting heavy use, or pushing the 450w limit when I do use it. It's not 450w through a single Mosfet. It's 150w through 3 modules in parallel.

 

[wpns]

It's 150w through 3 modules in parallel.

And if there’s any current imbalance between them, you might be overloading one while the two others are loafing.

 

[Wolfpack7483]

And if there’s any current imbalance between them, you might be overloading one while the two others are loafing.

Hopefully, I'll be able to measure the power split between the 3. If not, I should be able to detect temperature differences between the 3 with my thermal camera.

 

[WattSecond]

A bit more money for this battery load tester than the open circuit board style that I happened to see over at Ebay today. It does look a bit more heavy duty and being able to work with 1-150vDC up to 400W, 40A. I wonder if anyone has one of these units? I might splurge for one when my next SS check arrives. It does not mention having any software for graphing the test results on a computer which would be nice.


View attachment 278117

I bought this tester from Aliexpress and it works great. Never loose the instruction sheet, it's not an intuitive interface.

 

[Wolfpack7483]

My 3 module (150w each) unit arrived yesterday. It makes the "smoked unit" look like a toy in comparison. 4 Mosfets with 4 power resistors/ module. The heat sink is about 10x that in the smoked unit. The add on modules are actually TX-910 CPU coolers.

 

[Wolfpack7483]

After top balancing my Vatrer server rack battery, I used the new capacity tester on it. I set it on 400w constant power. It seemed to be rock solid. I took thermal readings multiple times during the test. It was pretty constant 160 - 165 deg "hot spot" readings on all 3 modules. After 13 hrs 4 min 25 seconds, single cell low voltage took it out after 101.158 Ah. I may end up building a case for it, but works fine without.