Bafang Rear Hub Motor Questions

[robintb]

I have a 2014 Batribike granite pro with a 250w rear hub motor (see photo)- can anybody tell me is this likely to be a geared motor or gearless? Can't see a model number....

I'm also wondering if the motor is up to full strength - it struggles on steep hills on maximum assist - is this normal? I'm not that heavy but am I expecting too much?

The battery has just been re-celled by Jimmy at Insat, so no problems there....

The other thing I'm wondering about is regen braking - I live in a super hilly area, so I've read you can retrofit regen braking if the controller and motor are suitable....The controller is made by DMHC and has a couple of extra wires (black/purple) which I wondered whether they were for hooking up regen.... Be useful to reduce brake pad wearing, if not for actually charging the battery!

Any advice greatly appreciated!

 

[Nealh]

Bafang geared hub and likely not a very powerful one, one from the small swx range of hubs.
The gutlessness could be due to the winding speed of the hub/motor rpm, if the winding speed is too high then it will be crappy for hill climbing.
The controller looks like it is a speed controller that gives max current in each pas level and a differing max speed in each level, is this so or can you tell us different ?

From reading the controller label it is a speed controller then you will be better using PAS1 or 2 on hills then PAS 5.
My guess is you will be better to replace the controller and display with a KT17/20a & LCD3 combo for current control and more power.

Forget about regen braking it us too inefficient for bike use as bike speeds are too low.

 

[vfr400]

It's a geared motor and probably quite powerful. The problem is that the power is regulated by the controller at 14 amps. You can take it up to around 17 or 18 amps, which will be quite an improvement.

There's a shunt in the controller which tells the CPU how much current is flowing. By changing it's resistance, the controller gets a false reading for the current because it doesn't know the resistance has changed, so it allows more current.

You change its resistance by adding solder to it. A blob of solder has virtually no resistance, so if you solder a quarter of the length of the shunt, you get about 25% more current.

That's the rough way of doing it, which is sufficient for most.

The main thing to be aware of is that if you have a weak battery, it can trip-out if you overload it. Most reasonable batteries can deliver 20 amps. Don't do that mod if your battery is old and saggy. Maybe try 10%.

If you want to do it more precisely, you can buy a cheap wattmeter and measure the current before and after. To get Mac current, spin up the motor with max throttle or max PAS in first gear and slow the motor right down with the brake.

 

[robintb]

Thanks NealH.... I have no idea about how the controller achieves this, but will try your suggestion of PAS1 or 2 on hills, not sure I quite understand why this might be (!) but happy to give it a go!

 

[robintb]

You change its resistance by adding solder to it. A blob of solder has virtually no resistance, so if you solder a quarter of the length of the shunt, you get about 25% more current.

ok! just watched a video on someone doing this.....looks doable....any other side effects of doing this?

 

[robintb]

Hi Vfr, Will I lose top speed with this mod or just gain grunt at low speeds?
Capped at 15mph here so don't want to lose any of that......

You can take it up to around 17 or 18 amps, which will be quite an improvement.

 

[wheeliepete]

I've been running one of these Bafang motors with a 20 amp KT controller/LCD3 for a couple of years with no problems. I don't use full power that often, but it's nice to have it there if/when needed. BTW, no loss of top speed with shunt mod/soldering, just a bit of extra grunt for hills.

 

[robintb]

I've been running one of these Bafang motors with a 20 amp KT controller/LCD3 for a couple of years with no problems. I don't use full power that often, but it's nice to have it there if/when needed. BTW, no loss of top speed with shunt mod/soldering, just a bit of extra grunt for hills.

Thats great, thanks! I think I'll try the shunt mod first and if I kill it, I'll go for the KT controller. Where's the best place to get it/is KT the brand or just the protocol? ebay seems a bit random....

 

[vfr400]

Hi Vfr, Will I lose top speed with this mod or just gain grunt at low speeds?
Capped at 15mph here so don't want to lose any of that......

It gives more grunt. It'll change the speed on the road in the low to mid range, but won't make much difference once you go over somewhere around 15 mph. The only real downside is it reduces your range because you're using up the battery faster.

There are loads of threads on this subject because we've been doing it on similar controllers and motors for more than 10 years. Do a google search for "shunt mod" on this forum to See them all. there are various pictures that explain it better. Look for my posts and any by Deleted Member 4366, who's the guy that taught me everything I know.

 

[robintb]

It gives more grunt. It'll change the speed on the road in the low to mid range, but won't make much difference once you go over somewhere around 15 mph. The only real downside is it reduces your range because you're using up the battery faster.

There are loads of threads on this subject because we've been doing it on similar controllers and motors for more than 10 years. Do a google search for "shunt mod" on this forum to See them all. there are various pictures that explain it better. Look for my posts and any by Deleted Member 4366, who's the guy that taught me everything I know.

Righto, thanks for that. have been slowly trawling through it now....presumably it only reduces range when its being worked 'hard' i.e. PAS5 when I try to push it trying to get up hills. Otherwise, on the flat, I'll be able to lower the PAS level for the same drive as before the mod and therefore retain similar current draw in these moments?

 

[vfr400]

I think you have a speed control PAS function, so you get the same power on all levels at low speed. These type of controllers have the fierce startup characterise, compared with other types. Increasing the current will make the startup a bit fiercer.

 

[robintb]

I think you have a speed control PAS function, so you get the same power on all levels at low speed. These type of controllers have the fierce startup characterise, compared with other types. Increasing the current will make the startup a bit fiercer.

It doesn't feel like the same power on all levels at low speeds - if I bump up through the PAS, it pulls harder from take off, rather than it being just as powerful in PAS1 as PAS5 at low speeds....

Maybe I'm just being a newbie on this though....

 

[wheeliepete]

Where's the best place to get it/is KT the brand or just the protocol? ebay seems a bit random....

KT is the brand Kunteng. Ebay can be very confusing if your not sure what you are buying, your best to buy from a trusted seller like PSWPower direct. It's worth getting a speed sensor, pas sensor and throttle with your order to avoid poss. compatability issues. LCD3 is a popular choice of display.

36V/48V 500W 6Mosfets 20A Brushless DC Sine Wave Controller - PSWPOWER.com

www.pswpower.com

 

[robintb]

Thanks Wheelie Pete.

So have just done the shunt mod! I went about 2/3 up one of the legs of the shunt (only 1). So about 20-25% of total length I reckon...immediate improvement noticeable on hills, and pick up is much better. Thanks for all the help here - lets hope I haven't overcooked it

 

[wheeliepete]

It doesn't feel like the same power on all levels at low speeds - if I bump up through the PAS, it pulls harder from take off, rather than it being just as powerful in PAS1 as PAS5 at low speeds....

Sounds like you may have current control then. Speed control usually makes it hard to ride in low assist at low speed from my experience.
Glad to hear shunt mod has improved performance.

 

[robintb]

Last one on this, so how much does it matter with the shunt mod if I'm a bit messy with the soldering... Basically I didn't go more than 2/3 up the leg, but it was thicker then just a bit of tinning.... Definitely blobby

 

[vfr400]

Quality doesn't really matter. You're only making it easier for the current to get from one pad to the other. The size of blobs doesn't make a massive difference. Blobs are better than a thin coating..

 

[robintb]

Quality doesn't really matter. You're only making it easier for the current to get from one pad to the other. The size of blobs doesn't make a massive difference. Blobs are better than a thin coating..

That's good, cos I made a mess! Thanks for all the collective help

 

[mike killay]

One question I have is, do you have to solder up the shunt leg from the pad of solder at its foot, or can you just solder along the top of the shunt?

 

[vfr400]

One question I have is, do you have to solder up the shunt leg from the pad of solder at its foot, or can you just solder along the top of the shunt?

Anywhere you like. It makes no difference. The only important thing is how much of the length has been soldered.