How to prevent Sparking when connecting batteries with an MGM controllers

[bdebde]

Plug in the deans (-neg and resistor) then the 5.5mm (+pos)

And I can still charge with the deans (no adapters) as all my chargers have deans.

bdebde, that looks nice and neat. Time to take out the soldering iron again once the controller comes back from MGM.

Originally Posted by joeling

Hi,

This is a very useful thread. I nominate this to be a sticky.

Regards,
Joe Ling

I second the sticky status. I had found this info on the MGM site, but I would have know it a lot sooner if it were a sticky. Good info for everyone running high powered brushless.

Originally Posted by bdebde

Plug in the deans (-neg and resistor) then the 5.5mm (+pos)

And I can still charge with the deans (no adapters) as all my chargers have deans.

Cool. I'm going to have to stop by ratshack soon and figure out which resistor I need for my 4s and 5s (5000mah, roughly) packs. The theory end of it I'm not real clear on.

[BrianG]

The resistor value is not dependant on pack capacity, but pack voltage and capacitance of your particular ESC.

The ESC capacitance will determine the resistor value. The battery voltage will determine the resistor power rating.

If you don't mind waiting between 8 and 10 seconds for the caps to charge, use a 2200 ohm 1w resistor. That will be fine for anything up to 40v battery and an ESC capacitance of 1000uF (which is pretty typical). If your battery voltage is lower, that's fine.

If there is enough interest, I can add a page to my "R/C calculations" site to assist in choosing the proper resistor and provide drawings on how to do the necessary wiring.

If you're up for it, that'd be great. I really like the deans layout, that is very simple and intuitive and then you plug the main power in with the bullet connectors. I think that's the method I'm going for.

I assume there's no detriment to having that resistor plugged in all the time with the deans connector?

As much as I generally understand electric theory, sometimes sitting down and calculating it goes over my head. I just don't sit and pay enough attention, really. :)

[BrianG]

Done!

Look for the "No Spark" Calculator

Thanks for that. A little extra wiring for some peace of mind. I've always hated that big spark, it just seems wrong and dangerous to the lipo pack.

[Patrick]

So can you leave the resistor plugged in while driving or will the resistor get burnt out? It would look neater than having it unplugged.

I have ran mine with the "no spark" lead still connected. I can't see any reason why you would need to disconnect it when running. All the currant will flow though the path of least resistance eg. deans plug, bullet connect etc.
Cue BrianG or one of the other guru's to chime in here with more technical reasons why.

[BrianG]

Technically, whether you leave the small connector plugged in or not depends on your choice of connector type. If there are any exposed terminals where they have a chance to touch against anything, I'd just leave them connected. Other than that, it makes no difference.

[Finnster]

I prefer to disconnect mine as I'm drawing a bit over 600mW on a 1/2W resistor. I left it in once for a while and it got a bit warm. Its easier/safer for me than trying to find a 1W resistor and redoing it. If you've got headroom in the resistor I don't see a big need to unplug it as long as it stays cool.

[BrianG]

Once you connect the main connectors, there should be NO heat on the resistor AT ALL. However, if you leave the main connector apart, that will heat up the resistor and slowly drain the battery.

[Finnster]

Hmm that's not what seemed to happen to mine... It's still a live circuit, you should get some current flow over the resistor, yes? Could have been from motor/wire heat from the run.... but I didn't really investigate it much. I am talking about leaving it plugged in while driving the car.

Maybe mike can offer this in a kit for the MGM's with wires, resistor, and connectors to make it easier for everyone to set this up