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Fuse melting...but not blowing on Power Wheels

Posted: Jan 14 2022 6:23pm
by unclejemima
I've got a old Gaucho Power Wheels from the early 90's ish.

Originally it was powered by a 12v battery with a on/off switch pedal and high range, low range and reverse.

I've kept the gear selector with high/low/reverse...and added a 1000watt 48/60v ebike controller and a 0-5v 'gas pedal'.
It's now being powered by either one or two 18v Ridid power tool batteries (depending on how fast I'm letting the kids go).

I replaced all the wiring to 14Ga wire, added cooling for the motors.

I have a 30amp mini fuse it the middle (it would generally blow a 20 amp)
The 30 amp fuse does not blow...but even just running one of the 18v batties things get hot. Wires get hot to touch and I noticed the FUSE has started to melt!
melted 30a mini fuse.jpg
melted 30a mini fuse.jpg (94.09 KiB) Viewed 143 times
So...what do I do? Would going to 12Ga wire help cool things down? Should I limit the accelerator pedal travel to limit power output? Is the OEM high/low switch an issue (I have no clue how it does high low as its somehow cutting voltage in half, even if running on only one battery)

Looking for options as I don't want to have any issues. I'm thinking the high/low switching is an issue with some sort of extra heat being generated from that complex switching setup.


Re: Fuse melting...but not blowing on Power Wheels

Posted: Jan 14 2022 11:18pm
by amberwolf
The root problem is likely to be a crappy fuseholder that simply doesn't hold onto the blades correctly, so resistance at the connection itslef is too high. Common with inline (and een panel mount) blade fuseholders like this.

You can see pitting (typically caused by arcing from very poor connections) on the blade on the left, is probalby on the right too. Arcing means the connection is so bad that there isnt' actually a connection anymore, and electricity has to jump the gap and make it's own. While doing it, it's plasma, and is very very very hot, and tends to melt things and set them on fire. (that's what welding metals uses).

Additionally, if the original system was sized for a smaller fuse, then it means some component(s) in it weren't intended to be used at the higher current. If the fuse was blowing before, it means it was doing it's job and protecting that stuff. If it's not blowing now, then that stuff isn't being protected as designed.

If wires get hot, they are too small for the current flowing thru them, and need to be replaced before insulation fails, a short occurs, and a fire starts.

Same for all the switches in there--if they are not rated for the *DC* current you are using them for (which you would need to use a meter at the battery output to check under load), they can overheat and distort their casings, allowing the same kind of poor connection, arcing, and fire potential that the fuseholder now has.

If they aren't rated for the *DC* voltage being used, they can weld shut from arcing during connect or disconnect. (usually disconnect). Then they don't break their connection...if they have two connections to make, one in each rocker direction like the ones I've worked with, then if you push hard enough on them (like with the gear lever's added leverage on the rocker) it can actually make the second connection while the first is still welded "on", and short directly across whatever it is supposed to switch. For certain wiring setups, that can mean a direct short across a system, and a fire or destruction of parts.

As an example, if that is like the ones I've taken apart, it has a tiny 2" wide 3-4" long can style brushed motor in it driving a plastic gearbox.... Not designed to take much of a load, nor for very long at a time. Cooling them may help...but they're still not intended for what they're being put thru now. Brushes wear out a lot faster at higher voltage; if you're using the 18v batteries in parallel it's not as bad, but if in series for 36v that's three times the design intent. (the motor might be rated for higher, but none of the ones I've handled were marked with useful numbers, just Johnson Controls and a long custom-motor-model-number).

The ones I've had apart have a little flat square mustard colored thermistor in there too, inside a ventilated plastic shell. That was used to create the high/low gear by switching it in and out of circuit--in circuit it's low gear as it drops voltage across the thermistor's resistance, reducing voltage and current to the motor and slowing it down. The reverse just swapped the motor wires to run it backwards.

The higher current plus the higher voltage means even more watts dissipated in any resistance between the positive battery terminal and the negative (wires, switches, connectors, fuses, fuseholders, motors, etc. all have resistance.

There have been some threads in the last few months about better inline fuses and fuse holders. This is one I remembered:

Re: Fuse melting...but not blowing on Power Wheels

Posted: Jan 18 2022 3:36am
by thepronghorn
30A mini fuses are going to run pretty hot. I would increase the fuse to a larger package such as ATO if you can. If you want to stick with the mini, you should be running at least 12AWG to try to move the heat away from the fuse.

Re: Fuse melting...but not blowing on Power Wheels

Posted: Jan 18 2022 1:16pm
by unclejemima
Thanks guys!

Switched to 12ga wiring and to a standard size blade fuse (not mini)

Will post results after my swap.