blew out a battery capacity tester. where to start?

[brandnewb]

I am very new to electronics so please forgive me if I use incorrect terminology. I really want to learn though.

I accidentally dialed one of the knobs too far and drew too much current while running a capacity test on a Lifepo4 prismatic 48V nominal battery bank that was fully charged at 58V.

A spark came out of under the heat sink/fan and the fan stopped spinning.

I have removed the heat sink now to investigate if I can repair but I am not seeing any damage/burnt element(s) on the front and back side.

Does anyone have a suggestion on how to start to determine what blew?

 

[Harald Kapp]

Most likely one or more of the transistors are defect.
De-solder them one by one and test them. Or replace them all if you have no way to test them.

Going to be difficult with the two smaller ones as these are SMD soldered with the back of the tabs and will require some thermal energy to pry them loose.

 

[brandnewb]

Most likely one or more of the transistors are defect.
De-solder them one by one and test them. Or replace them all if you have no way to test them.
View attachment 53840
Going to be difficult with the two smaller ones as these are SMD soldered with the back of the tabs and will require some thermal energy to pry them loose.

thank you. ok so I realize now then that components can be blown without a visual indication like burn marks. good to know.

I will try getting them loose with my soldering station.

Let's assume I am able to. How do I test them?

 

[Harald Kapp]

How do I test them?

That will depend on what these are. Let's identify the components first. In the ideal case you'd have a component tester - I suppose you don't .
A few simple tests can be done with a multimeter, a power source (battery) and a possibly resistor.

 

[Alec_t]

Unless it's a camera artifact there seem to be soot deposits on two of the fan blades, close to the fan centre, suggesting at least one of the transistors in that area emitted the magic smoke.

 

[brandnewb]

Unless it's a camera artifact there seem to be soot deposits on two of the fan blades, close to the fan centre, suggesting at least one of the transistors in that area emitted the magic smoke.

than you Alec for pitching in. in this case though it is just the way light is refracted which creates dark areas. when I hold the blades towards a light source I see nothing of note.

 

[Alec_t]

Ok.

 

[H2814D]

Looking at the photograph, the largest component circled (squared) in red appears to have a hole near the top leg in the black plastic part of the component. That may be where the "spark" emitted from the device.

 

[brandnewb]

could be indeed.
Anyway the day has arrived that I will setup my soldering station and give removing those components the old college try. I'll keep everyone updated of my progress.

Perhaps the back side of those components, that is now hidden from view by the board, show some burnt spots

 

[brandnewb]

ugg sorry guys, it turns out that only having a soldering station that I've never used before (never soldered before actually) without any de-soldering tools is not a great start

Please bear with me as I wait for some additional tools to arrive.

 

[Harald Kapp]

without any de-soldering tools is not a great start

Good to have de-soldering tools, but not a necessity:
Cut the leads of the components that are most probably defect anyway near the pcb, then you can withdraw pin by pin by heating each solder joint one after another. To clean the holes, a little solder wick goes a long way, or use a piece of uninsulated stranded wire if you don't have solder wick. Even a thin lead from a pen may be used to poke into the liquid solder and free the hole from solder.
Counterintuitively as it sounds: often it helps to first add fresh solder as this also adds flux and helps to liquify the old solder. Or add pure flux, if you have, but you may have to clean the pcb afterwards to remove flux residue.
To remove the two smaller components you will require a lot of energy as these are soldered with their metal tabs to the pcb. A soldering iron with a big tip that stores lots of energy and can transfer that energy quickly to the component is helpful. It may also help to heat the component with a heat gun in addition to the soldering iron. Be careful not to scorch the pcb, though. Can be a bit tricky.
Remember: The components are most probably defect anyway, so any further damage from removing them is not an issue.

Start with the big component, it is the one most likely to be defect.

 

[brandnewb]

hooray... sort of.
I am happy that I managed to get the IRFP260 (power mosfet) removed.
Worried that I am only making things worse ;(



Did I wreck the board or is there still hope?

Anyway the other 2 components (STPS41H100CG) are low drop power skotkky rectifiers

The mosfet is what the heat sink and fan was placed on.

I'll read some about how to test the mosfet and come back if I get stuck or have results.

 

[brandnewb]

If I come across as if I know any of those components then please allow me to confess that I just searched online and copy paste what I found

 

[brandnewb]

sweet, found a video on how to test a mosfet using a multimeter. thing is there is apparently a distinction between p and n channel. Does anyone know how to determine what channel type this one is? I did not see it in the manufacturer's datasheet for this component

 

[brandnewb]

never mind, it's an N channel. I recognized an image in the datasheet that I also saw in the video I mentioned

 

[Harald Kapp]

Did I wreck the board or is there still hope?

The pcb doesn't look too bad. Clean up the pads a bit and you should be good to go.

Tip: To test the diodes you don't have to remove them completely. Simply lift the pins with the tab still soldered to the pcb (much easier than lifting the tab).
Measure from the floating pins to the tab. You should "see"two diodes:

A1-K and A2-K both should read as normal diodes and no conductivity between A1-A2. If you confirm this by measuring, you can re-attach the pins to the pcb.
My guess is that the MOSFET is the most likely defect here.

 

[brandnewb]

thank you

I am not sure I follow though. What is a tab? Is that K in your image? If so then the mosfet to be tested does not seem to have a tab ;(

Also I did not find a way yet to determine which side of a component is up so that I can use the schematics from the data sheet to determine what the gate, drain and source pins are. Is there a technique to do so?

 

[brandnewb]

ahh I understand now, you were referring to the 2 other components and not the mosfet that I already removed.

 

[brandnewb]

that will save a tremendous amount of time and mutilation of the board

 

[Harald Kapp]

What is a tab? Is that K in your image?

Yes.

the mosfet to be tested does not seem to have a tab

It has, but it is covered by plastic. The tab is where the mounting hole is. You see parts of the tab where there is no plastic:

You also see this metal tab when looking at the back of the mosfet where there is no plastic.

The tab is not relevant to testing the mosfet as you have access to S, D and G through the pins.
It is different with the diodes. Here the tab is an integral part of the connections (cathode).

which side of a component is up

Up (better: front) is where the label is printed. The diodes are mounted with their back to the pcb. The mosfet was mounted with the front to the pcb, back to you.