Avoiding spark

Quick question, i have a 72v battery nominal and the bac8000 controller, when i go to connect the terminal from the battery to the controller theres a spark which is expected. However it causes a bit of a burn on the connector as seen in the image and would like to avoid that. Now its only going to be connected and disconnected a few times because it should stay on there permanently, but for the very few times i do connect and disconnect is there a solution for this? Was thinking maybe a resistor that i could put in between the terminal and controller connection temporarily but not sure exactly which one?




https://ibb.co/NZP0RKs

Run the current through a mechanical contacter with a resistance across the terminal?

Or manually use a short piece of wire connect a piggy back precharge resister into the circuit... before connecting the main leads.. Or buy an antispark connector... or a ssr, maybe would do it. The inrush of current whne completing circuits is a thing electricians have been fighting for eons... lol... There are ways...

Search " precharge resister'...

https://en.wikipedia.org/wiki/Pre-charge

The main concern with a resistor is to avoid blowing it when you use a tiny low wattage one. So you need to use Ohm's law to select a resistance value high enough for your voltage that not too much current can flow. You could try a resistor with as many ohms as your battery has volts. I made a precharge jumper like this and it works but not needed on 72v with Andersons just clean the terminals periodically.

flat tire said:

The main concern with a resistor is to avoid blowing it when you use a tiny low wattage one. So you need to use Ohm's law to select a resistance value high enough for your voltage that not too much current can flow. You could try a resistor with as many ohms as your battery has volts. I made a precharge jumper like this and it works but not needed on 72v with Andersons just clean the terminals periodically.

Click to expand...

yea as i thought i needed a resistor, looking at the ones available, i wasnt sure exactly which one i would need as they are measured by ohms. For my battery 72v nominal 84v hoc how many ohms would the resistor need? As you mentioned i might be able clean the terminals as im only going to be connecting and disconnecting it to and from the controller a few times, but i think i tried and had a bit of trouble removing the burnt mark. Im wondering how much damage the spark does as you can see from my picture. When calculating Ohms dont you have to take into consideration the amps coming from the battery as well? in my case 17 cells in parallel capable of pushing 20 amps cont, so 400amps ish?

I just told you how many ohms. Looks up ohm's law and calculate yourself for a reasonable value of current flow. The resistance causes a big voltage drop which restricts the amount of current flow. Your battery can only put out its 400 amps without a big resistance in the way.

In short: YOU NEED TO UNDERSTAND OHM'S LAW before you post a reply or do anything else for that matter.

Just switch your connectors for ones that have the resistor built in.
https://www.amazon.com/XT90-S-Femal...t=&hvlocphy=9033288&hvtargid=pla-493178443843

You plug the connector in part way, the capacitors (the cause of the spark) in the controller charge through the resistor spark free, then a second or two later, you push the connector the rest of the way in. No fuss, no mess, no sparks.

Drunkskunk said:

Just switch your connectors for ones that have the resistor built in.
https://www.amazon.com/XT90-S-Femal...t=&hvlocphy=9033288&hvtargid=pla-493178443843

You plug the connector in part way, the capacitors (the cause of the spark) in the controller charge through the resistor spark free, then a second or two later, you push the connector the rest of the way in. No fuss, no mess, no sparks.

Click to expand...

I'm aware of the xt90 connectors but I have 1/0 cable running from my 18650 pack with bus bars. So that wouldn't be a option unfortunately.

maarkmohamed said:

Drunkskunk said:

Just switch your connectors for ones that have the resistor built in.
https://www.amazon.com/XT90-S-Femal...t=&hvlocphy=9033288&hvtargid=pla-493178443843

You plug the connector in part way, the capacitors (the cause of the spark) in the controller charge through the resistor spark free, then a second or two later, you push the connector the rest of the way in. No fuss, no mess, no sparks.

Click to expand...

I'm aware of the xt90 connectors but I have 1/0 cable running from my 18650 pack with bus bars. So that wouldn't be a option unfortunately.

Click to expand...

Here, simple diagram... http://www.avdweb.nl/Article_files/Solarbike/Motor-controller/Input-capacitor-pre-charge-cable.jpg

1. Plug in auxiliary
2. Plug in power connector
3. Unplug auxiliary

brumbrum said:

maarkmohamed said:

Drunkskunk said:

Just switch your connectors for ones that have the resistor built in.
https://www.amazon.com/XT90-S-Femal...t=&hvlocphy=9033288&hvtargid=pla-493178443843

You plug the connector in part way, the capacitors (the cause of the spark) in the controller charge through the resistor spark free, then a second or two later, you push the connector the rest of the way in. No fuss, no mess, no sparks.

Click to expand...

I'm aware of the xt90 connectors but I have 1/0 cable running from my 18650 pack with bus bars. So that wouldn't be a option unfortunately.

Click to expand...

Here, simple diagram... http://www.avdweb.nl/Article_files/Solarbike/Motor-controller/Input-capacitor-pre-charge-cable.jpg

1. Plug in auxiliary
2. Plug in power connector
3. Unplug auxiliary

Click to expand...

Very simple, thank you

Even a small wattage resistor will work as the precharge only takes about a second. If your controller is shorted or you have another load like a dc-dc, the resistor will burn and act like a fuse.