Need help identifying SMD fuse

[unimatrix93]

Hey everyone, I could use some help identifying these two SMD fuses:

I'm not sure if they are 2A or 20A. Are they slow or fast acting?
They are coming from a e-scooter BMS panel:


They are located on the output circuit and the battery is a 21.6V 10.2Ah Li-ion battery.
The fuses are blown, OL even on MOhm territory.

The size parameters are 6.7mm x 2.4mm.

Thank you!

[sam_sam_sam]

I can be about 75% sure that they are 20 amp fuses what I can not tell for sure is if they are slow blow type but my guess is that are probably slow blow type but what I can not tell you what type of slow blow type they are because in some series slow blowing fuses there different types but in any case you need to find out what what cause them to blow which is going to be more important information to know

I would use and incandescent light bulb instead of the fuses that is rated for the voltage of this battery pack and see if it glows if so how bright is the light bulb with no load on the output it should not glow at all if it does then you might have an issue with the output mosfets for the BMS protection board circuit and will need to be repaired before you can use it again

You can use automotive type lights for this purpose let say that it is a 36 volt battery pack you could use three of them in series and then you would have a 36 volt test light bulb testing fixture to do the test that I was explaining earlier just above this paragraph but be extremely careful with what you are doing and please take your time when working on these BMS protection board because if create a short circuit it will cause a fire and will be extremely hard to put out

If you find that there is an issue with mosfets the next step would be to remove the BMS protection board from the battery pack and then you can safely work on the BMS protection board when you think that you have repair it run the same test again with the light bulbs and see if you still have an issue with the light bulbs glowing or not if not put the charger to the BMS protection board and activate it again and remove the charger and see if the light bulbs are glowing again or not if does the light bulbs glowing when the charger is hooked up they should be but how much they are glowing will depend on the state of charge the battery pack is then I would test the motor on the scooter and see if it runs and how bright is the light bulbs glowing

[unimatrix93]

I can be about 75% sure that they are 20 amp fuses what I can not tell for sure is if they are slow blow type but my guess is that are probably slow blow type but what I can not tell you what type of slow blow type they are because in some series slow blowing fuses there different types but in any case you need to find out what what cause them to blow which is going to be more important information to know

I would use and incandescent light bulb instead of the fuses that is rated for the voltage of this battery pack and see if it glows if so how bright is the light bulb with no load on the output it should not glow at all if it does then you might have an issue with the output mosfets for the BMS protection board circuit and will need to be repaired before you can use it again

You can use automotive type lights for this purpose let say that it is a 36 volt battery pack you could use three of them in series and then you would have a 36 volt test light bulb testing fixture to do the test that I was explaining earlier just above this paragraph but be extremely careful with what you are doing and please take your time when working on these BMS protection board because if create a short circuit it will cause a fire and will be extremely hard to put out

If you find that there is an issue with mosfets the next step would be to remove the BMS protection board from the battery pack and then you can safely work on the BMS protection board when you think that you have repair it run the same test again with the light bulbs and see if you still have an issue with the light bulbs glowing or not if not put the charger to the BMS protection board and activate it again and remove the charger and see if the light bulbs are glowing again or not if does the light bulbs glowing when the charger is hooked up they should be but how much they are glowing will depend on the state of charge the battery pack is then I would test the motor on the scooter and see if it runs and how bright is the light bulbs glowing

Thank you for your detailed answer.

So what you mean that I should check the output with a lightbulb before I install the new fuses in.
I have a 24V incandescent truck light bulb.
How should I check it? Can I connect the lightbulb directly the positive and negative of the output plug and see if it glows or not? Can I do it with the fuses desoldered from the board? I desoldered them so I could measure them out of the circuit and also measure their size.

[sam_sam_sam]

To do the testing that I was talking about you put the light bulbs where the fuse were

[unimatrix93]

To do the testing that I was talking about you put the light bulbs where the fuse were

I tested it with the lightbulb and it glows.
I soldered the one wire to the fuse's top pad and I touched the other wire to the B-.
I't wouldnt glow on the lower pad.

Where should I look for the problem? MOSFEts maybe?
Should I disconnect the B+ terminal from the BMS board before I start measuring right?

[sam_sam_sam]

You did not follow my instructions I said you put the incandescent light bulb instead of the fuses and see if the light bulbs are glowing if not then try changing the battery pack first then try running the motor of scooter in both case you should see the light bulbs glowing to certain extent but not at full brightness if you have full brightness and you are not charging or the motor is not running you need to investigate what is causing the issue

What you did dose not tell me anything except that the battery pack has voltage and light the bulb but it does not tell me if something is wrong with the BMS protection board or with the charging circuit or is there something wrong with electric motor or the controller

Depending what your results are will depend on how to proceed with the next steps to try to determine what caused the fuses to blow