Battery Position with rear hub motor

[MikeSSS]

The bike is a 1997 Mongoose full suspension, the rear hub motor is a MAC. There is no usable front triangle on this bike, and thus no good place to mount a battery in the front triangle. The new battery is too big to mount under the down tube.

The new battery is a 14s, 8p, 52v, 20ah, it weighs 12.2 lb. To put this in perspective, the gel cell 36v battery I started with 6 years ago weighed 25 lb, the 13s, 4p, 13.5ah lithium battery that followed the gel cells weighed about 6.8 pounds.

Three mountings were tried: top of a rear rack, on top of the "top tube", and along the side of the top and down tubes.

Little difference was noticed when riding. This is probably because the weight of the battery is a small fraction of the combined weight of the bike and rider. All three mountings rode well. Mounting in a bag on top of the rear rack was the most convenient.

A significant difference occurred when stopped, especially when stopped on a steep climb or when stopped awkwardly and trying not to fall. The weight of the battery on top of the rear rack could cause the bike to pivot upward and backward about the rear axle, as if in a slight wheelie. The front end of the bike could come up off the ground and scoot to the side causing balance to be lost.

The best battery location when stopped was battery mounted on the left side of the frame tubes, about where it would be mounted if the bike had a front triangle, except battery is offset to the left of bikes center plane. Yes, the left side battery location does interfere with pedaling, but I sit facing slightly leftward because my right foot is on a bit sideways. A pedal extension on the left side helps prevent pedaling interference. Installing and removing the battery is easy. The slight off center weight is not noticeable. I don't pedal hard, preferring to spin, so the pedal extension probably won't be a problem.

Battery on top of the top tube looked wrong and quickly got the stopped bike out of control when trying not to fall. Riding was not a problem though.

Well that's it, side mounting a relatively thin battery actually works pretty well. Better still, it makes a wider range of full suspension bikes suitable for ebike conversion, while using a large capacity battery.

Hope this helps somebody.

 

[dogman dan]

I'm kind of in the same boat, with a 2005 giant Y frame bike, and rear geared hub. At one point I put 48v 10 ah of lipo on a rack, 8 pounds, and another 8 pounds on a handlebar mount that was sturdy, not just a hanging bag. That worked real good.

But then I got the waterproofed luna battery, and pretty much had no choice but to put it on the rear rack. about 12 pounds, making 2 pounds over my usual comfortable limit of 10 pounds on rear racks for dirt riding.

It would be a big problem if I rode real technical trails a lot, but after a year or so, you do just learn to adjust. you just lean on the bars a bit more on the uphills, especially if giving it the gas. One reason I got the honda 100, was to ride stuff the e bike balks on, too steep, too rocky, too sandy. So I ride the tougher trails and roads on that. Same area as the bike trails has even more riding for gas.

It still causes excess tail wag in a fast slalom type trail with quick tight turns, so I just ride it slower. But not that slow! Still fun as hell. Airborne balance no problem, I just don't do flying at my age. Still works ok enough for the bike trails in my area that I like the best.

 

[John in CR]

Time for a different full suspension frame...one that has proper space for batteries. I tend to start thinking about my next build while my current build is still in progress.

 

[999zip999]

Some older Kona and Trek full suspension bikes have large triangle frames.

 

[goatman]

ive been hanging mine under the triangle

https://endless-sphere.com/forums/viewtopic.php?f=6&t=104027

 

[dogman dan]

Yeah, better bike would be real good. Trouble is,, I've been trying hard to wear out that giant for 10 years. Can't seem to be done. Its is on its 3rd or 4th fork but the frame is still rock solid. The thing is a tank. But you can't get a good fork for that frame anymore, just so so forks. I do need to get a new bike with tapered headset, and when I do it will be one able to take a mid battery of some kind, even if it won't fit the wolf battery.

 

[MadRhino]

Big hubs need a good suspension, high pivot and long shock. The kind of bike that never have any room for a battery in the triangle. So, either you forget about a triangle battery, or forget about having a proper suspension with a hub that is more than 20 lbs.

A custom frame could solve this, but the development of a good suspension frame for a fast bike is a long and expansive process. So far all box frames that I have tried were bucking horses, with a tail impossible to tune when built with a big hub.

My solution is modular battery, split in 2 or 3 battery modules that can be fitted on a bike that has a long shock in the triangle, little or no triangle space at all. Then the good, robust and well designed suspension frames are possible to build well balanced with a 30 lbs hub motor, most needing only minor mods.

You can compromise speed and terrain of course, but that is not a solution for me. A big mid drive would, but then again, long and expansive to build reliable. I would build one if I was still young enough to enjoy jumping. Now, a sub 100 lbs fast bike that can drop from 3 ft high is good enough.