$40 electric bike

I picked up this bike for forty bucks.
It has a nimh pack and charger that works well.
It has a li (?) pack that does not charge.
The bike is a beach cruiser ( read: corroded ) that works well.
It is 100% operational, almost no miles and the bearings are ALL smooth and
quiet! The motor functions normally and is quiet. It operates on the
twist grip normally.

Pros: Cheap, fully functional, light weight.

Cons: 250 watts @ 24 v. corroded ( some call that "patina" , yeah, right)

Options: I have a maximum of 14S 10 P of 1835 2.5ahr Sanyo cells just sitting around
ready to be made up into a pack.

Question: Does anyone have any experience with this bike/motor and how much I can over-volt

the motor and controller without buying or blowing anything up? I have only short , moderate hills

and cooling time in between those short moderate hills.

Goal: I do not want to fry anything on this light weight ( cough, cough, cheap) bike.
but, for forty bucks, I am willing to get it "toasty" just for fun. Anyone?

Pictures?

one more time

$40 the right price, bike worth at most $20, the motor worth about $20.

Perfect for fun experimentation, slap a new 48v controller on it and let er rip till she melts.

Correct me if i am wrong but does your dropouts have a space of 150mm? From the picture it looked that way. If it is true you might have lucked out and can replace that geared motor with a powerful 3000w motor.

You can run it at 48v and a cheap generic Chinese 9FET controller, if possible trim it down to 18 amps. Instead of the default 25amps.

I did that with a 24v geared hub motor and it screams up to 40+km/h lots of fun since they are built to be optimized to 24v. So double the volts will increase the speed dramatically.

EDIT* The stock controller may not handle 48v. May handle 36v, best way to know for sure is open it up.

Smaller motors are the most sensitive to amps, due to the added heat and the smaller copper mass. However, they are also sensitive to volts in the sense that they will try to reach the (higher) top speed when given a full throttle signal, but the low amps will only provide weak acceleration...meaning the controller will feed it the max amps for a longer amount of time as the bike slowly crawls to top speed.

I'd get a sensorless 6-FET controller that can use both 36V or 48V. Perhaps start with 36V and see how many amps you can feed it until heat begins to be an issue. If the top speed is adequate at 36V, there would be no need to go to the higher voltage/higher top speed. If you simply wanted to try out 48V, it should be easy to do. If you go "a bridge too far" and melt the motor, they are cheap to replace...or upgrade to a bigger one. The BPM is an affordable upgrade from this size.

If you open it up the motor...clean and re-grease the gears with synthetic high-temp front disc brake grease for automobiles. It is cheap and quite good. Also, perhaps cut the hall wires is such a way that they can be easily re-soldered should you desire to use them in the future. After cutting the wires inside the hub, solder them to a cheap temp sensor. An LM-35 has three leads and a 10K thermistor has two, but one each of the leads is a 5V supply (positive) that can be tapped from the hall sensor board, to feed both sensors. That leaves 5 hall wires already threaded through the axle, and three leads from the two sensors (or simply solder the 5 leads to the 5 wires). Both of these temp sensors are less than $2 each, and once the motor is back together you can hook them up in the future in a variety of ways...

I have a similar motor and prefer its roller brake above disc or rim brakes. Disc is subject to vandalism and rim is dependent on trueness.

Mine is rated for 36V and I've put 56V into it. It ran fine, but I never heat stressed it and haven't operated it much. The heat path goes most quickly through the axle, so if you can't do the internal temperature sensor modification suggested by spinningmagnets, the same sensor placed on the axle will also yield useful information. I'm not sure which side the motor heats up quicker, but the brake might distort the readings on that side.

Wow! What a lot of great suggestions!
When all this work lets up I'll take a look at the caps in the speed controller.
Then I can make a decision on how hard or whether to abuse it.


Bob K

Brush or brushless? How many conductors going into the motor? If only 2 it's brushed motor. There was a time 24V brushed motors were fairly common.

I've got an orginal 24v brushed motor running great on 36V battery with stock controller for several years now. Majority of 24V controllers can handle 36–40V.

I have been really busy with work and holidays.

The right thing to do with this $40 e-bike was to spend $7 on a new
shifter cable, cycle the battery a few times to bring it up to capacity,
and sell it for $147 . I had 6 people lining up for it
on Craig's List so it was a fast sale.
Next project

Bob K said:

I have been really busy with work and holidays.

The right thing to do with this $40 e-bike was to spend $7 on a new
shifter cable, cycle the battery a few times to bring it up to capacity,
and sell it for $147 . I had 6 people lining up for it
on Craig's List so it was a fast sale.
Next project

Click to expand...

Nice ROI. good for you. I probably would have been one of those 6 people lined up for it. A jar of Mothers, a scotch bright pad and a few hours of elbow grease and that bike would be gleaming.