Charger Bike

Hello,

There's this bicycle in my garage... It's a "Charger". It belonged to my late son. After his second DUI, he needed something with no license requirements to make it up the hill to our house.
The bike dates from the mid 90's. It was pretty hot stuff for the time, with a 24V motor mounted in the frame driving the rear wheel via a chain. Said rear wheel has a 7-speed Shimano hub. The front forks have shock absorbers. The two 12V SLA ( lead acid ) batteries are in a plastic box, along with the control and charging electronics. The bike had no throttle - it would help you when you pedaled.

Said electronics are long dead. I thought to resurrect it - bought & installed a pair of brand new SLA batteries. Left them to charge overnight. Came out the next morning, and the whole garage smelled like battery crap. The batteries had swollen up like little balloons( sigh ).

So now I am embarked on a new project - to bring this bike up to date with a lithium ion battery pack. I got a boatload of 18650 cells from batteryhookup, and a fancy charger/tester that tells their capacity in milliamp-hours. A package of nickel strips. A "k-weld" spot welder. An old aircraft battery to power the k-weld. Need a box for the battery ( on order from Amazon ), because although it does deliver the current, it's not as liquid-tight as it once was, and when you pull great gobs of current out of it, it *spits*.

I had gotten a cheap Chinese welder board - IIRC $25 including probes - but it didn't work reliably. Basically, I would put approximately one zillion spots on each battery, and hope that enough of them "took" to have the strap stick on. Reading about the kweld, I just had to have it. Would have been cheaper to just buy a premade battery pack .
But now I'll be all set up for any battery projects that come around.

The original electronics package is large and heavy - with 2 SLA batteries, the charging circuitry ( you open a little door and pull out the line cord ). I think a pack of 18650's will be much lighter.

I don't know how much power the motor takes under load. Am hoping a 7S5P pack will be adequate. Or is it 5P7S? I bought a 20A BMS on Amazon. We'll see how it does.

7s5p might not be enough do you know how many watts the bike motor was rated at?
Later floyd

Don't know the watts of the bike motor. Very little documentation on the Web. You search for "charger bicycle" and you get lots of hits for chargers for ebikes. I plan to put together a pack and see how it does. I can run the bike up the hill and measure the amps draw. If it doesn't make sense, I'll tear the pack apart and change it.

Besides just a raw pack, I also need some sort of controller. The bike has some sort of sensor to know how hard you're pedaling. Not sure I can figure that one out. I see there are controllers on amazon,ebay etc. But those use a twist grip.

What's the model number of the eBike? That might help narrow down the search results

The motor may have a hp rating or watt rating printed on the motor or maybe a part no.with the manufacturer could really help. Might not even say hp or watts.

Later floyd

Here's a web page about the bike: http://abc.eznettools.net/D300013/X300109/eBike1.html.

The motor is hidden in a plastic shroud.
Here's another web page:
https://abc.eznettools.net/D300013/X300109/ChrgrFAQS.html
Which has some info about the motor! They quote 375W of "shaft horsepower" and "up to 36 Amps" of peak power.
...Which means I need a bigger BMS.

It seems that Electroportal still has a functional website - maybe they can sell me a new electronics box? But what's the fun in that? Honestly, I need
an electric bike like I need a hole in the head . But it's a fun project.

yeah, I'd say go with an ESC that can do 40A. That way you aren't taxing it when you need full power. Besides, going with their electronics, you're limited to 20mph and "assist only" when going up hills. What fun is that?

OK, I slapped it together. Made a 29V 10 amp-hour pack from Pegatron modem batteries from batteryhookup. Balanced them with the tool on this website. Welded the tabs with the Kweld. A 24V brushed controller from Amazon. Also a twist grip throttle - one of those with the little voltage display. Chopped the connectors, soldered and shrink wrapped everything together, and hung it all on the bike with cable ties. This is all just to see if it works - I planned to mount everything properly once I proved the concept.

It successfully carried me up the hill. HOWEVER, I don't think it's going to work. Not really. Why?

.... The pedals are in lock step with the hub. When the motor moves the bike, it moves the pedals also - which is very disconcerting. I don't think it's going to be usable. Very disappointing.

You need to have a bike overrunning clutch. This is what allows the wheel to turn w/o turning the pedals.

If you don't use the electric motor, does the pedals freespin? If so, I wonder if there's something that needs to be modified to make the motor allow the freespin

The motor has its own separate chain and sprocket. But I think the two sprockets - one for the motor, the other for the pedals - are essentially bolted together. I think there is an overrunning clutch ( built into the nexus7 hub ) between the sprockets and the wheel.

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Something like this?

https://www.amazon.com/STARTER-CLUTCH-CARTER-FLANGE-OVERRUNNING/dp/B01MRB4LHN

If the dimensions were right, I could replace the sprocket at the pedals.

Are you using the same chain driven by the pedals as the one driven by the motor? ie, 1 chain and not 2.

Maybe some pictures could help see your setup.

Here are a few pix. The motor is in a plastic fairing above the pedals. On the rear wheel, there are two sprockets, one for the pedals, one for the motor, both on the
R/H side of the nexus7 hub.









Please excuse the messy install - I was just in a hurry to see it work .

I think the most practical fix would be to put a freewheel on the pedal sprocket. And I'm sure I can't buy such off the shelf. I'll have to remove the plastic fairing and see what's inside, and how much space there is. Hopefully enough so I can shoehorn something in. I do have metal cutting and welding capabilities. And a pedal
crank turns pretty slowly, so it doesn't have to be exquisitely balanced.

Am thinking to get the go-kart freewheel that I saw on Amazon, get a new pedal sprocket, cut out the inside and MIG weld it to the outside of the freewheel. Or something like that.

... and a quick google shows that it *might* be possible to *buy* an actual pedal sprocket with a freewheel in the middle!

I popped off the R/H chain fairing. It makes it much clearer how the thing works...







I also removed the R/H crank arm.

Web searching shows that it's not totally unknown to see a freewheel on the crank. Shimano used to do them ( the FFS - Front Freewheel System ). Also,
they seem to be used on mountain bikes. AND on center-drive ebikes.

There is a little plastic sprocket contacting the pedal chain. It's attached to a little electrical thing with some wires going out. I imagine it's a strain gauge, and
that's how the auto pedal assist system worked.

I ordered a front freewheel, pedal arms and chainwheel from sickbikeparts.com. So with any luck, I'll be riding in style by the weekend. Front freewheels are apparently not uncommon on mountain bikes.

OK, the front freewheel is installed. One complication was that sickbikeparts offers 30-tooth sprockets and 36 tooth sprockets...and the existing sprocket is 33 teeth. I chose 30 teeth because I'm old and weak, and need all the help I can get to make it up the hill . Of course, the chain got all loose and I had to remove a few links. Then the chain for the motor got loose. I was starting to research parts for the (tiny, nonstandard ) chain when I realized that the whole motor assembly was on a pivot with an adjustment screw. A couple of turns on that adjuster got the motor chain tight again.

The bike rides MUCH better with that front freewheel. I can actually get on it, hit the throttle, and go. Almost like a motorcycle.

HOWEVER:

It's not very strong. Not strong enough to get me up the hill without pedaling. And the bottom gear is VERY low with that 30T front sprocket. To comfortably pedal, I need at least second gear, which puts the motor at even more of a disadvantage. So I have some troubleshooting to do.

First thing is better battery connectors. I used the cheap connectors that came with the controller, and they're quite warm after a short ride. I obtained a baggie of AMASS
XT60's, which should be better.

Then - what about the controller? I used a "Wingsmoto 24v 500w Motor Speed Controller Electrical Scooter E Bike Bicycle Tricycle Brush Motor Control Box " from Amazon.

Lastly, the battery itself. It's a 7s5p that I made of Pegatron modem cells from batteryhookup. Just a hair over 10 amp-hour capacity per the repackr tool. I put it together with substantial nickel straps spot-welded with the kweld. HOWEVER - the individual cells are rated only 2A per cell. So that's 10A total. 10A at 28V is 280W maximum. I have a 20A BMS on it.

I think I need to instrument it. Strap a meter to the handlebar, ride up the hill and see what voltage and current is produced. I have a no-contact DC current probe rated 0-60A. Not super accurate, because readings will change when the bike turns in the earth's magnetic field - but close enough for govt work. Or, if I want to get real answers, instead of a meter, I should strap up a battery powered digital oscilloscope ( yes, I have one ). Hook one input to the motor voltage, another one to the current probe. Then I'll be able to see the PWM pulses driving the motor, both as voltage and current.

Another thing to try would be to just hook the battery directly to the motor - with a switch - and see if it makes more power. If so, the controller is a weak spot.

If it turns out that the battery is not adequate, I might bite the bullet and buy a set of brand new high-current cells - Samsung or LG - 3600mA-h, and put together a pack with the 40A BMS I've got sitting on the desk here.

OK - I upgraded the battery connectors to the Amass XT60. I think it made a difference. Still not too strong though. I strapped a multimeter to the handlebar with masking tape, connected a current probe to one of the motor leads. Rode up a slight incline, I was seeing currents between 28A and 50A.

On this very short test ride, the battery got seriously warm.

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Just ordered 36 new LG MJ1 18650 cells from batteryjunction. These are rated 3500mA-h and 10A continuous output. I shall make them into a 7s5p pack ( got one extra cell just in case ) and package it with a 40A BMS. I suspect that the internal resistance of the existing pack is choking down the motor.

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...and going back to the basics, I cleaned and lubed the chains; checked the tires, they were way low. Performance is a bit better, but still no cigar. I want it to carry
me up the hill at 10-15 mph without pedaling. Is that unreasonable?

It seems that the question was not written by a person.

Built the new battery pack - 7S5P LG MJ1 cells, a 40A BMS. Bike got a little faster. But not much. I guess it is what it is. It does carry me up the hill at about 5 mph.

Maybe try connecting another battery in parallel and see if it makes a difference. Or, just add another 1s5p in series to get 8s5p total and see if it's like more voltage.

Higher voltage should give you faster top speed, more parallel should give more torq. Altho, there is a limit to torq (at voltage to be fair). But, you could make sure to give it all the power the motor wants.