Electric Bikes - Is my fuse too small ??

Hi. I bought a master ebike at an auction. It has 3 brand new 12amp 12volt batteries in it. They are 3 batteries in a series = 36v. When i try to accelerate anything over 1 mph, the fuse blows. It is a 1 amp, 250volt buss fuse. Is this fuse too small in amperage? Maybe someone put the wrong fuse in the fuse holder by mistake. 1 amp seems pretty small to me for a 36volt ebike. It also has a generator of some sort which is powered when pedaling. Should I try a bigger fuse? If so....what size amperage? The fuse holder can only hold a 3/4" inch long fuse. I am including pix of the bike , the battery box , the powered hub on the rear tire and the fuse. If anyone can help on this it would be greatly appreciated.

Ohm's law - volts x amps = watts or 36V x 1A = 36W yes, that fuse is way too small IMO. Try something between 10-20A or even a 30A shouldn't hurt anything if the controller is decent. A fuse for an eBike is more for short circuit or peak protection anyway.

Ohm's law - volts x amps = watts or 36V x 1A = 36W yes, that fuse is way too small IMO. Try something between 10-20A or even a 30A shouldn't hurt anything if the controller is decent. A fuse for an eBike is more for short circuit or peak protection anyway.

Thank you Broadway for your help. Two questions: 1. What does "IMO" mean? 2. Also, how did you know the fuse was too small from an electrical point of view? I mean, I do not know a darn thing about ohms, amps or volts or any combination thereof. I see you came up with 36 watts. How did you know 36 watts is too much power for the 1amp fuse? I would appreicate any help you can give as I want to build my own ebike someday and would need to have a better understanding of electric. ANY help you or anyone could give would be more than appreciated.

IMO = in my opinion.

You should do some searches about "ohms law" since it's a major thing to understand for all things electric. By the formula VxA=W, I calculated your 1A fuse would only pass/deliver/carry 36 Watts at your 36V operating voltage before it blows. Most eBike motors draw at least 200W and judging from your photos I would guess yours being closer to 400W capability. Therefore, divide 400W by 36V and you get = 11.11A would be the minimum fuse amp rating to pass that much power to the controller/motor.

Just to be extra safe, you could start with a 10A fuse but if that blows - 20-30A will probably be just fine as long as the controller is of decent quality. If you read specs about controllers, most will say they demand between 20-35A. 20A is most common and you probably won't hurt anything if you start with that rating fuse.

As I said - fuses in these eBike circuits are often more for short-circuit protection. Just in case a wire get's chaffed or rubbed by something on the bike frame - a short like that will blow even a 30A fuse before you do much further damage from a short circuit.

Good luck - cool looking eBike! I like rear drum brakes (Very Japanese) and remember if you learn enough about Ohm's law you'll eventually be able to make all kinda battery chemistries work just fine for many years down the road.

Your 3 12 AH SLA (sealed lead acid) batteries probably total a combined weight of roughly 30-35lbs. Someday, when those are worn out, if you have the knowledge to implement lithium chemistry the same AH capacity would only weight about 10lbs. 20lbs is a pretty good weight savings for any bike.

The good thing about your ride is that battery weight is spread-out along the middle of the frame offering much better weight distribution than hanging batteries, motor, controller and your butt over a rear wheel.

I melted the plastic of a 20 amp automotive blade-type fuse. It didn't blow, but after a year of use the plastic was so melted that it wouldn't come out of the fuse holder. My controller draws 700+ watts at 36v when I'm starting up (and it's a pedal-first controller).

Yes, a 1 amp fuse is too small. Do what Broadwayjoe says: start with 10A but be prepared to move to something larger if you're blowing fuses.

i have a 36v 12ah setup also running a 500w wheel and blew fuses until i reached 25a. i don't know if that is good or bad but i have been riding almost daily for 6 weeks and no harm has been done yet.....

i have a 36v 12ah setup also running a 500w wheel and blew fuses until i reached 25a. i don't know if that is good or bad but i have been riding almost daily for 6 weeks and no harm has been done yet.....

Here again Ohm's law formula VxA=W - 36V x 25A = 900w, tells us that your system might be pulling a few more watts than it's nominal 500w rating. I suggest you carefully check all wiring and connectors - after a good hard ride, run your hand along all wires/connectors - looking for some heat. If you have some wire/connector loses, that might explain why you need nearly 900W fuse capacity for a 500w rated motor.

Might not be anything wrong except maybe you got a motor/controller capable of slightly more than spec output? Electronics is not a very exact science when it comes to tolerances, components, etc.

Hi. I bought a master ebike at an auction. It has 3 brand new 12amp 12volt batteries in it. They are 3 batteries in a series = 36v. When i try to accelerate anything over 1 mph, the fuse blows. It is a 1 amp, 250volt buss fuse. Is this fuse too small in amperage? Maybe someone put the wrong fuse in the fuse holder by mistake. 1 amp seems pretty small to me for a 36volt ebike. It also has a generator of some sort which is powered when pedaling. Should I try a bigger fuse? If so....what size amperage? The fuse holder can only hold a 3/4" inch long fuse. I am including pix of the bike , the battery box , the powered hub on the rear tire and the fuse. If anyone can help on this it would be greatly appreciated.

Boy, is it ever too small! Normally a fuse on a vehicle is sized to prevent the wiring from overheating and catching fire in the event of a serious overload. The size fuse depends on how thick the wire is. A 10 gauge wire can be fused at 30 amps, 12 gauge at 20 amps and so on.

I would look hard for a sticker that indicates the correct fuse size. Lacking this, measure the wire diameter (the copper conductor, not the insulation). 10 gauge = 0.1019" 12 gauge = 0.0808". Sometimes the wire gauge is stamped on the insulation also.

Note also that the fuse voltage rating should equal or exceed the battery voltage. There are a lot of 32 volt fuses out there which should NOT be used in your case.