Dual Hub Ebike Batteries

[cwilli63]

I have a 36v 500w front wheel ebike now and want add another rear wheel 36v 500w kit and run
both kits to one throttle powering both motors to one battery, but I'm confused about the battery.
What size battery should I purchase for this type project that will not damage the motors, controllers or
batteries?......

 

[6zfshdb]

Any 36v battery should work. The largest capacity available would be preferable. Since you're using a common throttle, the best efficiency would be achieved if the same motor / controller kits are used on the front & rear. That way, the motors will have the same torque characteristics and won't fight each other.

 

[harryS]

THe one pack will work for testing, but ideally, I believe you should have a battery that can deliver the peak current for both controllers. Two 20A controllers needs a pack that can deliver 40A. If it was only a 25A pack, you'll limit the acceleration, which is why you went with two motors. Not so bad, but if it's only half charged or if the cells aren't high power cells, there may be enough voltage sag to drop the voltage below the minimum voltage of either controller, and it will shut off.

I've seen it happen on my bike with one 25A controller and experimenting with some of my smaller capacity batteries. Shuts off as soon as I blip the throttle.

 

[cwilli63]

THe one pack will work for testing, but ideally, I believe you should have a battery that can deliver the peak current for both controllers. Two 20A controllers needs a pack that can deliver 40A. If it was only a 25A pack, you'll limit the acceleration, which is why you went with two motors. Not so bad, but if it's only half charged or if the cells aren't high power cells, there may be enough voltage sag to drop the voltage below the minimum voltage of either controller, and it will shut off.
I haven't add the rear wheel yet I'm just doing the research, but both controllers are carrying 22amps each, I know how to install everything but the confusion are the batteries, it's almost like running one 48v 1000w ebike conversion kit with a 48v battery.
I've seen it happen on my bike with one 25A controller and experimenting with some of my smaller capacity batteries. Shuts off as soon as I blip the throttle.

Any 36v battery should work. The largest capacity available would be preferable. Since you're using a common throttle, the best efficiency would be achieved if the same motor / controller kits are used on the front & rear. That way, the motors will have the same torque characteristics and won't fight each other.

 

[cwilli63]

I'm already getting 30-35mph with the front wheel only will adding another rear wheel double the speed, if not I'll forget this project.....

 

[MarkF]

Speed will be the same technically. You will be adding torque so better hill climber. One motor can't spin faster than the other .

 

[tomjasz]

I'm already getting 30-35mph with the front wheel only will adding another rear wheel double the speed, if not I'll forget this project.....

40mph is a wall. You won’t get much of an increase in speed but you’ll have one helluva climber. Expecting 60mph is just plain, well, dumb... Who the F#$& expects to safely ride a bicycle at 60-70mph?

 

[6zfshdb]

I seriously doubt adding a second motor will double your speed. You might see a modest increase of say 10 mph, but the bike will accelerate to that speed much faster. Keep in mind, most bicycles, ebike or conventional, aren't designed for the speeds you are hoping to achieve. Components like tires, tubes and brakes to name a few, may not handle that kind of abuse.

 

[cwilli63]

I seriously doubt adding a second motor will double your speed. You might see a modest increase of say 10 mph, but the bike will accelerate to that speed much faster. Keep in mind, most bicycles, ebike or conventional, aren't designed for the speeds you are hoping to achieve. Components like tires, tubes and brakes to name a few, may not handle that kind of abuse.

Should I purchase 36v or 48v battery that was my first question?....

 

[6zfshdb]

The controller you show is rated at 36V. Using a 48v battery could cause damage.

 

[Dylon Desbiens]

I just did this exact set up. two 18v drill batteries for 36V two 36v hub motors, and two controllers. Its just a torque increase but with that being said it will technically give you more average speed while riding because it will handle incline and regular riding conditions that much better. Here is my build if you want to check it out. Filmed the whole thing Building The Worlds Smallest Electric Bike

 

[tomjasz]

A better scheme with some details you might think about incorporating.

 

[cwilli63]

I just did this exact set up. two 18v drill batteries for 36V two 36v hub motors, and two controllers. Its just a torque increase but with that being said it will technically give you more average speed while riding because it will handle incline and regular riding conditions that much better. Here is my build if you want to check it out. Filmed the whole thing Building The Worlds Smallest Electric Bike

IF I purchase a 36v 12AH lithium battery for the setup I'm trying to accomplish will the system shut down when the battery is half full, I've had a lot of comments but not one
person has answered the initial question, what size battery I should purchase at least give me some options....

 

[Dylon Desbiens]

IF I purchase a 36v 12AH lithium battery for the setup I'm trying to accomplish will the system shut down when the battery is half full, I've had a lot of comments but not one
person has answered the initial question, what size battery I should purchase at least give me some options....

No it shouldn't shut down until its dead as long as its 36v... I did the two drill batteries 18V 6AH because they're tiny. You have to make little custom set up to do it but worth it in my case because I was going for small.

 

[cwilli63]

No it shouldn't shut down until its dead as long as its 36v... I did the two drill batteries 18V 6AH because they're tiny. You have to make little custom set up to do it but worth it in my case because I was going for small.

Then I can use the batteries I have now (36v 12AH sla) to power two front an rear 500w hub motors, two controllers connected to one throttle. I just want everything to run and operate
smoothly.......

 

[Dylon Desbiens]

I posted my own thread on it but I am having a problem after getting this set up. My front wheel spins full throttle but after half throttle my back wheel stops spinning while the front still spins full. More details on wiring on the thread but I am hoping someone has ideas. I also just want my bike to work smoothly.

 

[cwilli63]

Don't expect a straight up answer on this website, that's why I'm doing all my research now before I purchase my rear wheel kit. I'm curious though did you wire your throttle
to your two controllers like in my diagram I have at the top of my post. I think I understand how to wire my battery, but it's the throttle that gives me pause......

 

[batmick1]

I seriously doubt adding a second motor will double your speed. You might see a modest increase of say 10 mph, but the bike will accelerate to that speed much faster. Keep in mind, most bicycles, ebike or conventional, aren't designed for the speeds you are hoping to achieve. Components like tires, tubes and brakes to name a few, may not handle that kind of abuse.

I saw the picture of this department store bike with low-end rim brakes etc. and immediately had the same thought. Even at the current speed indicated, I personally would not ride this bike.

 

[Dylon Desbiens]

Don't expect a straight up answer on this website, that's why I'm doing all my research now before I purchase my rear wheel kit. I'm curious though did you wire your throttle
to your two controllers like in my diagram I have at the top of my post. I think I understand how to wire my battery, but it's the throttle that gives me pause......

Yea my thumb throttle wiring is the same but I also have the yellow wire + that goes to the battery plus and blue wire (Power lock wire output) that Is wired to the thinner red Ignition + wire on each controller.

 

[cwilli63]

Do you have a throttle like this? If you do try connecting all the colors to both controllers and see what happens, if you have not already tried that.......