Hi, I'm new, looking to get a bit more out my eBike.

[Pedcheese]

Hi all, I'm new here.

About 6 months ago I built myself a cheap ebike commuter.
I bought one of these. http://www.ebay.co.uk/itm/Electric-Bicycle-E-Bike-Motor-Conversion-Kit-26-Rear-Wheel-48V-1000W-Hub-Cycle-/172348979639?hash=item2820ccb9b7:g:ve0AAOSww5hZGQ5u

A cheap MTB and a 15Ah battery.


I've put 800 Miles on it now (cycle paths) and am very very happy with it. I really don't have any complaints, It's plenty fast on the straights and I only use about 60% of my battery on my trip. The speed sensor and "limiter" are not fitted/in use.

I get a solid 25-30mph on the straights with her (depending on the length). I've had a max 35mph out of her going downhill, but I backed off as it really doesnt feel very safe above 30mph (for me). The only thing, I wish it had a bit more grunt going uphill. Is there anything simple (and safe) that I can do to get a bit more power out of it. I believe I read that the motor itself will be perfectly safe operating slightly above 1000w.

The battery I have is from China, It's claimed 15Ah. I cant remember the exact specifications for it and I can't find the order again but it looks something like this.

I have no reason to suspect it is anything other than as was listed and is serving me well so far. Still holding the same charge it always did. Speed and range I'm getting is in keeping with what others report for 48v 15Ah.

Basically can I easily get the wattage up? Safely? I understand I will use more battery juice doing this, but I have a good 40% buffer to play with anyway. so not fussed about that. What would you recommend?

Thanks.

 

[Fordulike]

See what the rated amperage is on the controller and replace it with a higher amperage one. For example, if the one you have is rated at 20A, then replace with a 25A or even a 30A controller.

I personally wouldn't go above 30A with that battery.

You could also do a shunt mod on existing controller, but this may affect the controller reliability. Better to just buy a suitable controller.

 

[Pedcheese]

Thanks, Simple as that?
I'll check the controller that came with the bike but I "assume" it's 20Amp (as 20A @ 48V = 960W).
I seem to remember the battery saying max output 25Amps. but might have been 30. I deliberatley picked the highest I could find. (But being Chinese it could just be waffle).
Would you think it's safe to pull 30A out that battery? Do you think I would notice a big difference going from 20 to 25A? I'm guessing
@48V: 20A = 1000w, 25A = 1200w, 30A = 1400w

Is it possible to just mod the controller I have?

Thanks.

 

[Pedcheese]

OK the controller says on it 48V, 26A, 1000W
Which is odd... Because I make that 1248W ?

I keep my battery sitting on a cool pack and it never gets more than every so slightly warm. If that determines how many amps are safe to pull?

What about giving it more volts? instead of Amps?
Lets say I had another battery, 12V or so. And wired it to a switch that I could use as a "boost" for going up hills?

 

[Fordulike]

Voltage will increase speed, but won't give you any advantage on hills, due to the fact that the motor will be vastly inefficient when climbing. Most of the extra power will be wasted in heat. The controller you have now is probably at the limit for your current battery. The motor is the direct drive type and renowned for being weak on torque, unless you feed them monster amps.

Solutions are plentiful, although not cheap!

You could change the motor for a geared hub type. Change over to a crank drive. Or you could use a higher amperage controller with that motor, but would most likely need a higher capacity/better celled battery, or run the risk of killing the existing battery pretty quickly.

What kind of budget have you got for improvements?

 

[Pedcheese]

Budget is really about £0 just now lol. Was just checking if there was something "safe, easy and cheap" to do. In the future, I would consider going 2WD (as below).

Thanks. Makes sense. I guess you can have cheap or great but you can't have both!
To be honest, as I said I am very happy with it and would much rather have longevity out of it than push it to gain a slight improvement. And I guess pedalling up the hills will make me fitter. Also, if I carry a lot of speed into the hills it's not too bad at all.

What I might do in the future is just get another 1000w motor and battery for the front wheel. Wire it to the existing throttle. 2WD. That should see me with plenty power and nothing's getting stressed out. For the moment I'll leave her as is. She's doing well.

 

[Fordulike]

What I might do in the future is just get another 1000w motor and battery for the front wheel. Wire it to the existing throttle. 2WD. That should see me with plenty power and nothing's getting stressed out. For the moment I'll leave her as is. She's doing well.

Woah, that'll be one heavy muther mofo, and expensive

If you want to keep your existing battery, then look at the likes of the Bafang BPM hub motors, or Bafang BBS02/HD. Then you'll have the best of both worlds, speed plus fantastic climbing ability.

 

[Pedcheese]

Sure it would add some weight. But if I went 500W it would only cost me about £250 (£150 for the wheel and £100 for a 36v 7.5Ah battery). With the help from the existing 1000w motor 7.5Ah should have plenty range.

 

[Woosh]

what surprises me is the number of people who are not informed about the disadvantage of gearless motors, that they are low torque high speed motors. High speed needs high torque unless you can feed a gearless motor with 30A-50A to have a decent hill climbing performance.
A gearbox essentially multiplies the torque by its reduction ratio, in the Bafang BPM (or similar motors from other brands), it's 1 in 5. A gearbox in a hub motor adds about $25 to the buying price but multiplies the torque by a factor of 5. Really not much in the amount you guys spend on the whole kit for the work that it does.

 

[Pedcheese]

I totally understand that, but my reason was cost and incognito. It isnt $25 more. The motors you suggested to me (although no doubt very good) are coming in at about £600!) compare that the to £150 I paid for mine is a huge increase.

To be honest I'll just leave her as is for now anyway. The big thing for me was to make it cheap and discrete. I passed my rail ticket savings at 500 Miles. So every ride now is money in my pocket over getting the train. If I had gone for a £600 motor then the battery would probably die before I made a saving, and I would be into 2019/2020 before I made a saving. Also there are very few hills on my commute. So again, I am happy with what I have, was just checking in to see if there was anything obvious I was missing.

 

[Woosh]

The motors you suggested to me (although no doubt very good) are coming in at about £600!)

no, it does not.
bmsbattery charge $135 for a BPM with rim and spokes.
https://bmsbattery.com/ebike-kit/585-bafang-bpm2-36v500w-rear-driving-e-bike-motor-wheel-ebike-kit.html
similar models from different brands cost about $80-$100 without rim and spokes.
A gearless 1500W motor costs about $80 without rim and spokes.
I sell the BPM kit without battery and charger - everything except the battery and charger for £225.

 

[Pedcheese]

Ah fair enough. I didn't see any of this when I bought mine. But now I have it I'm as well sticking with it. Now I know for next time.

 

[Deleted member 4366]

There's a very simple £0 mod you can do to solve your problem. All you have to do is add a bit of solder to the shunt or one of the shunts if it has more than one. In most controllers, the shunt sits behind the end plate, so all you have to do is remove a few screws to access it, otherwise, you have to remove all the screws and slide the contents out to get at the shunt. Each 10% of the shunt you solder increases torque by 10%. You should aim for about 20% first. Don't go higher than 30% or you might find the battery over-current control tripping. Give the shunt and solder plenty of time to heat up. Try and get some thickness/blobs to the solder, but be careful that it doesn't drip on other components or run through the pcb onto the other side. If you do it, let us know how you get on. I've done about 30 controllers without any problems. Some of those controllers went to forum members, who did many thousands of miles with them.

Here's an example:

before


after

 

[Pedcheese]

How bizarre. How does that work. I assume decreasing resistance?

 

[Deleted member 4366]

The controller is programmed with a current limit. It knows how much current is flowing by measuring the voltage drop across the shunt, which is of known resistance, typically 0.005 Ohms. If you add solder, it reduces the shunt's resistance, which throws off the controller's calculation and makes it measure less current than is actually flowing, so it allows more.

 

[Pedcheese]

Clever.

I have a multimeter. What should I aim for for 30amps?

 

[Deleted member 4366]

That's about right. Multimeters normally can't measure high currents or low resistances like that without a shunt. I use a cheap wattmeter if I want to be precise, but after doing many, I figured out that it correlates closely to the length you solder, i.e 10% length = 10% more current.

 

[Pedcheese]

oops I meant what resistance across the shunt should I aim for for 30Amps end result

 

[Deleted member 4366]

It depends on what it is now. 20% more current means 20% less resistance.