Confused about battery sparking

[ArtieKendall]

This is about as "Beginner's" as you can get, but I am totally confused.

In a four-year-old video, Will says that when you first connect the battery, there is always a spark, and he proves it by getting a pretty big spark when the touches the cable to the positive terminal.

at 7:02.

In a newer video, he says that if you get a spark when you connect the battery, you are doing something wrong.

at 6:37.

Is this because newer batteries have a BMS that has a built-in resistor or something?

I also notice that in the older video, Will has a fuse attached to the lug of the cable connected to the positive terminal, but not in the newer one. But I've also seen recent videos where there is a fuse on the cable.

And for a final bit of confusion, I've seen videos where people just hold a big resistor in their hand and put it between the cable and the positive terminal when first touching it, "to allow the capacitors to charge."

So can someone explain when you should expect a spark, when you should have an inline fuse, when you should use a resistor to pre-charge, etc.?

Thank you.

 

[sunshine_eggo]

 

[rodrick]

connection can create a spark that can trip the protection features on the bms so a pre charge resistor is required. on a 12 volt standard battery with a small inverter you will get a spark but won’t hurt anything but on higher voltage and large inverters especially with Lifepo batteries you need to pre charge

 

[ArtieKendall]

I guess I'm no good at Google. This answered a lot of my questions, thank you!

Still wondering about the fuse on the cable, though.

 

[pablo131]

nice video. Do you have to do this on hybrid MPP inverter too?

 

[Lt.Dan]

I guess I'm no good at Google. This answered a lot of my questions, thank you!

Still wondering about the fuse on the cable, though.

A lot of new batteries are coming with DC Circuit breakers on them. It technically is safe(ish) without a fuse, but still recommended. It all depends on the setup.

 

[rodrick]

Fuse to protect the wiring if you have a cable capable of 100 amps fuse with a 100 amp fuse

 

[Lt.Dan]

Fuse to protect the wiring if you have a cable capable of 100 amps fuse with a 100 amp fuse

Not entirely true. You should definitely fuse to the wire size, but the fuse size should not be the exact size the wire is rated for. The fuse should be sized for 80% of what the wire is capable of. You want to protect the wire, not run it on the edge of melting.

 

[PreppenWolf]

Some inverters and/or batteries have built in precharge resistors. And its becoming more common now for inverters to have them. That said I personally always use a resistor because it requires minimal extra time.

 

[rhino]

If you want to make it more foolproof for other people besides you who may be having to do that there is this document that shows you how to integrate the pre-charge resistor directly into the switch: https://diysolarforum.com/resources/inverter-disconnect-switch-with-precharge.60/

 

[JWLV]

In regards to the resistor, how big do you need? Any particular ohm rating?

 

[sunshine_eggo]

In regards to the resistor, how big do you need? Any particular ohm rating?

#2 pencil exposed at both ends.

 

[Lt.Dan]

#2 pencil exposed at both ends.

I can't tell if a joke or not? Does that work?

 

[sunshine_eggo]

I can't tell if a joke or not? Does that work?

No joke. About 6Ω and can more than handle the Watts.

 

[hwy17]

60w or 40w incandescent light bulb works good too, hold the socket metal of the light bulb to the battery while you touch the inverter lead to the center contact of the light bulb.

 

[JWLV]

I can't tell if a joke or not? Does that work?

The graphite in #2 pencils are somewhat conductive. I've used pencils to draw a line to create a small resistive connection on PC boards for testing purposes.

 

[pablo131]

nice video. Do you have to do this on hybrid MPP inverter too?

anyone?

 

[curiouscarbon]

 

[JoeHam]

In regards to the resistor, how big do you need? Any particular ohm rating?

I use these :

Amazon.com: YiePhiot 2PCS 50W 25 Ohm Resistor Aluminum Case Wirewound Chassis Mounted Compatible with Ring Doorbell, Nest Hello Doorbell, SkyBell Doorbell Etc : Industrial & Scientific

Amazon.com: YiePhiot 2PCS 50W 25 Ohm Resistor Aluminum Case Wirewound Chassis Mounted Compatible with Ring Doorbell, Nest Hello Doorbell, SkyBell Doorbell Etc : Industrial & Scientific

www.amazon.com

Cheap enough to keep a few lying around for when I can’t find my pencil ?.