Battery box over-current protection bypass

[finhudson]

Performing this modification will allow you to draw more current from your battery box. I tested the maximum current before the modification at 0.3A and the maximum current after at 6A.

I have often found the over current protection built into the power functions battery boxes to be set a bit too low, for example, it is very limiting when using RC buggy motors. I opened up a battery box to see how easy the over-current protection would be to bypass, and it turned out to be very easy. My method is shown below:

(Warning: performing the following modification will void the warranty of your battery box. Do not draw high currents for long periods of time because it may lead to overheating.)

(I will not be responsible if you try it and break something)

1) Open up the battery box to gain access to the circuit board

Remove the screws, then use a screwdriver to begin to pry out the battery holder, once it is about 5mm out, push in the plug on the top, and then fully remove the battery holder.

2) Prepare the electronics tools for bypassing the over current protection

You will need: A soldering iron, solder, wire cutters, wire strippers and tweezers.

A helping hands tool is optional but it helps.

3)Bypass the over-current protection

This step is much simpler than it sounds, all you need to do is solder a wire over the polyfuse on the circuit board.

First you need to locate the polyfuse, as shown in the image below

The polyfuse rapidly increases in resistance when a high current passes through it. This is how the over-current protection works: when a high current passes through the polyfuse, the increase in resistance causes the current to drop back down again.

To bypass the polyfuse, all you need to do is solder a wire across it. First you need to tin the wire so it can be soldered more easily.

With some solder on the tip of your iron, heat up the wire from the back. Apply solder to the wire from the front and you will see the stands of wire absorb some of the solder. Now tin the other end of the wire and move onto the next step.

Now all you need to do is solder the wire over the polyfuse. Use tweezers to hold the tinned end of the wire on one side of the polyfuse, then heat it up with the soldering iron to reflow the solder joint. Repeat this with the other end of the wire to achieve a result like in the picture below:

4) Reassemble the battery box and you are done!

Notes:

Do not embark on this project if you do not trust your soldering skills, soldering irons get very hot and could easily burn you.

If the switch does not move after the battery box is reassembled, open it up again, remove the piece of wire, and replace it with a thinner one so that is does not jam against the switch.

Edited July 21, 2015 by finhudson

[BusterHaus]

Have you done any testing on how long you can draw 6 amps before something starts smoking?

Also, here's a tip to those who are new to soldering: use a flux core solder or just get a little jar of flux. It makes a huge difference in the work.

[dr_spock]

For electronics soldering rosin-flux cored solder should be used. Do not use acid flux cored solder or acid flux. Those are meant for plumping work like soldering copper water pipes.

Would it be better to desolder the polyfuse from the board and solder in a small piece of wire or flat metal in its place? It looks like it is just surface mounted.

[finhudson]

Have you done any testing on how long you can draw 6 amps before something starts smoking?

Also, here's a tip to those who are new to soldering: use a flux core solder or just get a little jar of flux. It makes a huge difference in the work.

I haven't tested 6A continuous, but I have tested 4A with a prototype for an inline voltage booster I'm working on. It all worked fine, the batteries just warmed up a little bit.

I agree with you about the rosin core solder, it make the whole process much easier

Would it be better to desolder the polyfuse from the board and solder in a small piece of wire or flat metal in its place? It looks like it is just surface mounted.

Electrically, this would make no difference, but if you needed a polyfuse for another project I guess it could be worth doing

Edited July 22, 2015 by finhudson

[Odinkuijpers]

I just bypassed my the current limiter on my spare battery box, and I'm wondering, has anyone ever had any burning/melting afterwards?