SWX02 48 to 36v

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Oldie   100 µW

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SWX02 48 to 36v

Post by Oldie » Jul 26 2021 5:31pm

Hey guys

I need some advice.

I currently have a 700c 48v SWX02 Bafang 17amp controller and a 48v 12ah battery. Top speed is 19mph and climbs 10% hills at 8-10mph. I weigh around 105kgs.

I want to get a spare hub motor. I can get the SWX02 in a 48v or 36v.

Would I see any improvements in speed or torque if I got a 36v SWX02 and replaced my current wheel?

Would it still be reliable?

Your thoughts please.

Thanks

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motomech   1.21 GW

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Re: SWX02 48 to 36v

Post by motomech » Jul 26 2021 8:19pm

I currently have a 700c 48v SWX02 Bafang 17amp controller and a 48v 12ah battery. Top speed is 19mph......
That's really slow for those components and I wonder what the motor speed-range is. What is the motor code stamped on it's housing? Is it a frt. or rear mounted install?
'11 Motobecane Fathom team, Bafang SWX02-13T, 14S (54V) LiPoly, 9-FET 17A controller. Schwalbe Marathon's, 24 to 25 MPH.
Hobie Passport Kayak w/ Watersnake 18# motor, 12S LiPoly (46V) to golf cart 12V converter, 4 mph

Oldie   100 µW

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Re: SWX02 48 to 36v

Post by Oldie » Jul 27 2021 2:53am

Hi

It’s a rear mounted hub.

The controller is integrated into the battery case.

These are the numbers stamped on the motor

RM G020.250.D 16
1904110009

The company that sells these kits states the following.

the Bafang SWX02 48V code 16 is a 5:1 geared hub motor optimised to climb hills for heavy people. It has a huge torque at low speed.

Thanks

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motomech   1.21 GW

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Re: SWX02 48 to 36v

Post by motomech » Jul 27 2021 8:54am

Ok, you have answered your own questions.
The only replacement controller will be the same thing, nothing more powerful is available. The only way of getting a 20 plus Amp controller in the system is to by-pass the internal unit and wire-in an external one.
The very slow speed-rating of the motor limits the top speed.
The fact that you are climbing very steep hills and your climbing speed is falling to dangerous levels indicates you dare not try a higher speed-rated motor. (The first rule of hub motors is to never allow the climbing speed to fall below 1/2 the top speed. At that point, the motor starts to make more heat than motive force) Try and keep the climbing speed 9 mph and above.
The only way you can have more speed and maintain/improve climbing ability is to replace the entire system with a larger one, ie; larger battery, controller and motor. Larger hub motors take you into the 5 Kg. range, like the Bafang BPM.
If hills are part of the route, hub motors require a compromise and you hard up against one.
The hub motor, in general, is the most reliable component in the system and I don't think keeping a spare is a necessary hedge.
Better to just ride your bike and save for a mid-drive or a system w/ a larger motor.
Note; If the gearing on the bicycle allows it, you can gain 1 to 2 mph by pedaling "on top" of your max speed and strong legs can raise the climbing speeds a bit too. This usually requires an 11T small sprocket and chain rings of 44T and up.
'11 Motobecane Fathom team, Bafang SWX02-13T, 14S (54V) LiPoly, 9-FET 17A controller. Schwalbe Marathon's, 24 to 25 MPH.
Hobie Passport Kayak w/ Watersnake 18# motor, 12S LiPoly (46V) to golf cart 12V converter, 4 mph

Oldie   100 µW

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Re: SWX02 48 to 36v

Post by Oldie » Jul 27 2021 11:41am

Hi

I appreciate everything you have said and yes you are correct.

I have only one hill on my way home. It normally takes 2 minutes tops to get up the hill. I always pedal at the same time.

What I wanted to do was buy a 2nd kit minus the battery for my other bike.

I only wanted to know if the 36v hub would give any improvements at all rather than a 48v hub using the same controller and battery.

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E-HP   100 MW

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Re: SWX02 48 to 36v

Post by E-HP » Jul 27 2021 1:49pm

Oldie wrote:
Jul 27 2021 11:41am
Hi

I appreciate everything you have said and yes you are correct.

I have only one hill on my way home. It normally takes 2 minutes tops to get up the hill. I always pedal at the same time.

What I wanted to do was buy a 2nd kit minus the battery for my other bike.

I only wanted to know if the 36v hub would give any improvements at all rather than a 48v hub using the same controller and battery.
If you're running 48V already, then intentionally moving to a 36V of the same type doesn't make much sense. Just get a 48V version with the winding your prefer. You may have additional torque initially with a slower wind, or a faster top speed with a faster wind. You should decide what's important to you and choose what works for you.

There are more options than just choosing 36V vs 48V, as seen here. You can get either voltages with different speed (windings) options, higher speed = lower winding count, lower speed = higher winding count:
https://www.aliexpress.com/item/1005002 ... ffbfa7ee-1

Similarly here, where they provide different winding options (that equate to different top speeds):
https://hilleater.ca/bafang-swx02-rear- ... n-winding/

If you do go with 36V, then the the speed with be proportionally faster at 48V (48/36 x RPM).

Oldie   100 µW

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Re: SWX02 48 to 36v

Post by Oldie » Jul 27 2021 5:16pm

Many thanks for the informative reply.

The reason I considered the 36v was after lots of reading many people overvolt motors hence I thought it was a good idea.

So if I want a higher top speed I should just stick to 48v and get a low winding count motor.

If all being equal. Both motors same winding for example 11t. One was 36v and the other 48v which would be better?

Would the 36v not be 33% faster in speed and torque?

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E-HP   100 MW

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Re: SWX02 48 to 36v

Post by E-HP » Jul 27 2021 6:57pm

Oldie wrote:
Jul 27 2021 5:16pm
If all being equal. Both motors same winding for example 11t. One was 36v and the other 48v which would be better?

Would the 36v not be 33% faster in speed and torque?
No difference.

The motor "voltage" isn't really a rating. In a lot of cases, a motor described at 36V 350W and one described at 48V 350W, are the same motor. Voltage can be used to impute the current a motor could handle continuously if you know the motor's rating (watts). So if you have a 350W motor, and you run it at 36V, then the motor can handle 350/36 = 9.72A continuously. If you run the same motor at 48V, then it can handle 350/48 = 7.29A continuously.

Since they are basically the same motor, then the one running at 48V will have a speed 48/36 = 1.333 times faster than at 36V (although wind resistance won't make it perfectly proportional, since the resistance increases with speed).

The higher voltage will extend the torque curve out, which will provide more acceleration at higher speeds than the lower voltage. As they approach their respective top speeds, the torque drops. In the following example, you can see that the 36V system's torque starts to drop at 8mph, reducing acceleration as it approaches it's top speed. The 48V system doesn't start dropping until 11mph, and at 21mph, when the 36V system maxes out, the 48V system still has double the torque available (28NM vs 15NM), so it can continue accelerating to 26.4mph.
https://ebikes.ca/tools/simulator.html? ... bopen=true

Oldie   100 µW

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Re: SWX02 48 to 36v

Post by Oldie » Jul 28 2021 1:50am

Thank you. This make sense.

I will stick to a 48v hub.

Now to decide on the winding and motor.

The SWXO2 has served me well. Should I stick to the same or is there a better motor to go for? It needs to be plug and play as my current hub has a 9 pin connector that plugs straight in.

Cheers

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