got sparked when connect mppt to battery, bad??

[kaizday]

Hi,
so i just assembled my lifepo4 back, double check everything w bms and all. but when i connected the pos wire (neg has already connected to the bms neg) to the pos battery, i got sparked.

nothing else was connected to either battery nor the mppt at the time, and i was 99% sure i didnt short anything.

so question is, is that an abnormal thing? i thought spark only happens when either short or connect battery to an inverter. maybe because i connect the wire in the wrong order, as in, i should have connect the wire from the battery to the mppt instead?

after that, my overkill solar BMS didnt report anything out of ordinary. is there anything i should be worried about?

thanks much

 

[shadowsteve]

There must have been something connected to the DC wires when you attached the battery. Anything with reasonable size capacitors in it will have a sudden connection draw (spark). A large inverter will be a nice fat spark unless you pre-power it through a resistor

 

[Mcgivor]

Did you by any chance have an inverter connected? Even turned off the capacitors will cause a spark on initial connection.

 

[kaizday]

nope. i have nothing else connected, especially the inverter. the SCC wasnt connected to my panels either. just the battery and the bms.

is a 40a SCC considered a 'reasonable size capacitor'? it turns on instantly the moment i connect the wire.

 

[Mcgivor]

The SCC takes it power from the battery, personally I use a disconnect to isolate so a spark, if any, would not be seen. What are you referring to, a small spark or large, a SCC is considered an extremely light load but a load none the less, so a small spark may be possible.

 

[Bubba1]

I would not worry about it. You are supposed to plug the balance wires in last. Whenever you mess with the positive or negative unplug balance wires.

 

[kaizday]

I would not worry about it. You are supposed to plug the balance wires in last. Whenever you mess with the positive or negative unplug balance wires.

this i didn't know. thanks.

 

[shadowsteve]

My one style of BMS has a connection for a positive feed (for battery heaters) so it's already alive when I plug in the balance wires. The other ones don't have that so connecting the balance wires powers it up. Either way they are first thing removed and last thing connected.

The SCC will draw power when first connected so a spark of some size is to be expected. I also have mine connected thru a breaker so I can power it off without disconnecting wires

 

[Zil]

The CC needs a bit of power to come on. A small, quick spark is expected. If a large long duration spark, a bright arc, you have a short or some high load connected.