Bafang CST or BPM

Alan Quay

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Dec 4, 2012
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My next two builds will both be offroaders, with pretty much identical spec. I just can't decide between the CST or BPM motors.

Both mech disc brakes, hardtail MTB, front sus, alloy frames. both 24 speed. Both will be rear wheel drive on knobbly tyres, and both will have 20ah li-ion batteries.

The saving is a couple of hundred dollars between the two.

Your expert opinions would be very much appreciated.
 
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With the BPM, you have to include the cost of an 8 speed DNP free-wheel if you can find one, otherwise you won't be able to pedal fast enough. The CST allows you to have whatever gearing you want. Try Cyclezee for the free-wheel. The CST is 270 rpm, so 22mph in a 26" wheel, or 24 mph with a KU123 controller and over-drive wired up on a switch. The problem with the BPM is that it's a bit of a lottery which one you get. The 201 rpm is usually code 13 for about 18 mph and the 328 rpm is usually code 10 for about 25 mph. You can get the 10% overdrive on the BPM too to adjust the max speed a bit. You need to make it clear to the supplier that you want a particular speed. Both 500w motors have the same power and feel. The CST is marginally quieter.

There's two versions of the BPM. The BPM 2 has a screw-in side-plate, which is very difficult to remove for servicing. The CST and BPM1 have bolt-on side-plates, which are easy to remove.
 

103Alex1

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Sep 29, 2012
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I think the other difference is that the BPM motors (unless they have recently been changed) have the grey nylon planetary gears whereas the CST uses the blue composite gears like on the American BMC V4 hub motors on its clutch plate. Well, the ones from BMS Battery do at least. The material is meant to be harder / more robust or something. Or so I understand !

Riding the bike unpowered is supposedly better with the cassette mounted with no freewheel as on the CST versus the BPM freewheel arrangement. But if that's the case the difference is likely not as significant as having a geared hub motor as compared to a direct drive one.
 
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Alan Quay

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Ok, I'm sold on the CST, thanks for your opinions.

I guess the next question is KU or S series controllers?
 
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The S series allow you to use the pedal sensor, which is quite convenient and you can switch the power on and off from the display. The PAS on the KU series is a complete waste of time; however, you can make a cruise control easily enough, which is nearly as good. The KU series have the over-drive on the the three-speed switch, which gives a 10% speed boost. You can still switch the power off using the ignition wire on the KU, but I'm not sure of the residual current drain. It's certainly low enough to leave it for a couple of days. If you go for the KU123, it's worth opening it up to check the main tracks from the battery to the FETs. On some, they're reinforced with wire, but not on others. I've seen three, where the solder on the tracks got so hot that it melted, so, if not already reinforced, I'd drizzle a thicker layer of solder on there.
 

103Alex1

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Sep 29, 2012
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Also ... the S12S is for running sensored, S12P for running sensorless. However the KU123 can run either sensored or sensorless so if you have any issues with Hall Sensors you can still run CST on it fine in either mode. I run mine sensorless .. doesn't seem to make much if any difference.

Does anyone know what amps the S12S runs at as compared to the S12P ? Same ?

EDIT :- apparently the S12S runs @ 23A whereas S12P runs at 29A and KU123 runs at 29-30A max. So if you want to run 30A sensored it looks like KU is the only way from these three.
 
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Alan Quay

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I'm not all that bothered about the how good the pedal assist is, but I do want to be able to run up to 29 amps. So I guess it's just about sensors and displays.

I've only ever used sensored motors. What difference does it make?
 
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It depends on the motor and controller, some work sensorless OK, but others run rough. Some motors don't start so well, especially big direct drives, and lastly, there's supposed to be an efficiency advantage when running sensored because of the more accurate timing.
 

103Alex1

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Sep 29, 2012
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^^ for throttle only I still think it's the best option and didn't change my controller when the new ones came out. Subject to upgrading the relevant connectors like phase wire bullets etc. But then I run a Cycle Analyst and Dave made me a FET switch to isolate the controller so the LCD thing isn't an issue.

My CST doesn't run rough sensorless and any efficiency gains are probably minor with a 20Ah battery so if you want the display then the S12P is probably a VFM compromise that's a doddle to install if you aren't going to put a Cycle Analyst shunt & display in.

The KU123 gives you most options on how to run the motor but a bit more faffing about and I think a Cycle Analyst adds a great deal both in-ride (monitoring power input) and after. But it's b****y expensive.
 

Alan Quay

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OK, that's two complete CST rear kits ordered, with 20ah batteries, S12P controllers, displays, and a pile of bits n bobs. With luck it'll be here before Xmas.
 
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Deleted member 4366

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It might be worth adding a KU123 controller to your order to keep as a spare, or to try sensored. The extra cost is minimal. You can email them if you want one added. Hopefully you already added some torque arms to your order.

Did they say anything about an extra $60 for each battery? Ask them now to clarify the situation.
 

Alan Quay

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....
Did they say anything about an extra $60 for each battery? Ask them now to clarify the situation.
Yes, no, well sort of. They now have an extra item that you can order, which is called 'Extra Shipping Cost Or Other Cost'. I ordered one. It was 1 USD. I assumed that it added a specific dellivery ammount. Apparently it ensures that it's sent by TNT.

Total shipping cost was over 400 USD.

I will email and clarify.
 
D

Deleted member 4366

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That's not how it works. When they tell you that the extra shipping costs $60, you use that system to order 60 of them, so that the money is tracked against an order through your account. Before, you had to send it direct to their Paypal account, but the records wouldn't show what it was for. I guess it caused a lot of problems when doing their accounts.

I guess that means you only have to pay $119 extra now!
 

Alan Quay

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I asked them to confirm the postage situation, and got the following reply:

" Hi, send your order by TNT ? Is ok ?".
 
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I guess that f you answer "yes", you'll be accepting the additional charge whatever it is. It woul be nice if they told you how much it would cost.
 

Alan Quay

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I guess that f you answer "yes", you'll be accepting the additional charge whatever it is. It woul be nice if they told you how much it would cost.
So far, so good. I haven't been asked to pay any more, and the package is listed as 'in transit' with TNT, expected tomorrow.
 
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Alan Quay

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Dec 4, 2012
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The goods have turned up, and I have so far not been asked to pay any extra postage, or any import duty. May get a letter at some point I guess.

All present, correct and well packaged. Good job BMS Battery!

Interestingly, it looks like batteries under 100 wh are allowed, and mine are both 3.2v, 10ah ones according to the paperwork. I suspect those are nominal values, and that fully charged each one is closer to 41v and 20ah :)
 

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