Controller and throttle advice please

npdp72

Finding my (electric) wheels
Aug 9, 2014
9
0
52
Hi,
I'm building a small electric trike for my 7 year old.
I plan to use a Bafang 250W hub motor in a 20" wheel for drive, I have this already and its the un-sensored version.
The trike will not have pedals (and will only be used off the public highway).

Can anyone advise on a good controller and throttle to buy?

With the motor being un-sensored and having no pedals I need the controller to be good enough to start up properly from a standing start.
I would also like to rig up reverse if at all possible, although I recognise this might not be very easy, since bikes don't tend to often have reverse!
Any good ideas on this would be welcomed!

As this is really just a bit of fun I don't want to spend too much, so a cost effective solution would be great.
I will probably use two 12V sealed lead acid batteries for power, LiPo would be nice but probably cant justify the expense.

Thanks in advance for any advice offered!
:)
 
D

Deleted member 4366

Guest
You can get controllers which can reverse the motor direction. I had a load, but they're all gone now. They had a pair of jumper wires that reversed the direction each time you touched them together. You'd have to study all the wiring diagrams on the ebay and Aliexpress listings to find one.

If you don't want reversing, the KU63 from BMSBattery used to be very good, but they've changed it to a new version now, which I haven't tried yet.
 

npdp72

Finding my (electric) wheels
Aug 9, 2014
9
0
52
Thanks for the reply d8veh.
I will try and find a controller on ebay with the reverse function.

Is there any problem with overspeccing the controller, for example going for a 36V 500W controller even though the motor is rated 24V 250W?

One more question, might be a silly one, the hub motor has the following marked on it:
BFSWXB24V250W255R
20 - 1109223443

Am I right in thinking that this is a brushless motor?

It looks very much like this one and has a similar number:
http://www.e-bikeconversionkit.com/e-bike-motor-SWXB.htm
But there is nothing here that actually states these are brushless.
 

Alan Quay

Esteemed Pedelecer
Dec 4, 2012
2,351
1,076
Devon
If it has three wires, then it's a brushless.

Running at 500w, up from 24v to 36v will add half as much again top speed - are you sure that what you want that on a trike for a 7yo?
 

npdp72

Finding my (electric) wheels
Aug 9, 2014
9
0
52
If it has three wires, then it's a brushless.

Running at 500w, up from 24v to 36v will add half as much again top speed - are you sure that what you want that on a trike for a 7yo?
I wasn't thinking of upping the battery voltage, I just wondered if the spec of the controller has to exactly match that of the motor, or whether there's any possible disadvantage to using a higher voltage / wattage controller?
 

Alan Quay

Esteemed Pedelecer
Dec 4, 2012
2,351
1,076
Devon
Oh, I see.

It won't work I'm afraid. The controller has a low voltage cutout (LVC) . A 36v controller will stop at 32v (ish).

Power is governed by the controller, which will restrict the current. On a 500w controller this will be around 22amps.
 
D

Deleted member 4366

Guest
Our Chinese friends often get mixed up with what things mean and do. Self-study means that the controller can figure out the correct phase and hall sequence to make the motor work. Normally, it doesn't give reverse, but the controller has no way of knowing which way the motor is turning, so it can get it wrong. It's possible that each time it self-studies, it reverses the direction so that you can always get it right, eventually. Therefore, it's possible that it can work as a reverse switch.

Having said all that, it doesn't look like it can run sensorless, so no good for you.

Your motor is a 24v 255rpm Bafang SWXB, which means 20 mph at 24v in a 26" wheel or 15 mph in a 20" one. At 36v, it will therefore do about 22 mph, which is about right for its power, but is that too fast for a 7 yr old?

That Ebay controller looks promising, but it doesn't mention the current. It'll probably be between 12A and 15A, which will be more than enough for a 7 yr old.
 

npdp72

Finding my (electric) wheels
Aug 9, 2014
9
0
52
It's possible that each time it self-studies, it reverses the direction so that you can always get it right, eventually. Therefore, it's possible that it can work as a reverse switch.
That was my thinking, it might be worth giving this controller a go on the basis that worst case I have to settle for no reverse.

Unless anyone can recommend a different controller that is known to have a proper reverse function?

Having said all that, it doesn't look like it can run sensorless, so no good for you.
It does say on the ebay listing:
Can work "with hall" and "without hall" brushless motor.

I assume this is referring to the Hall Sensor, or lack of one.
Or, should I have reason to doubt this do you think?

Thanks for the help so far!
 

jhruk

Esteemed Pedelecer
May 13, 2009
318
68
Unless anyone can recommend a different controller that is known to have a proper reverse function?
I don't think you're going to get reverse drive with that motor whichever controller you use. I believe the SWXB is like most geared hub motors in that it has a one way clutch, which disconnects the motor core when free wheeling. The motor will run backwards but the clutch will prevent any drive to the wheel.

I suppose you could weld up the clutch, but fitting a direct drive or rarer clutch less geared motor would probably be easier.
 
D

Deleted member 4366

Guest
Of course! What was I thinking about? I better go and stick my head in an ice bucket for a bit.
 
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OldBob1

Esteemed Pedelecer
Oct 11, 2012
355
117
Staffordshire
How about a brushed motor and put a change over switch in the motor wires.
Must be loads of second hand 20 " brushed motor wheels out there?
 
D

Deleted member 4366

Guest
Yes and yes. Get the type 2 (3 in the pull-down I guess), which is the old KU65. You can't use the three speed switch in the type 1 without hall sensors.
 

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