What would be the maximum current I can feed my 36v 250w Bafang BPM motor running at 48v?

[John_S]

Hi guys.

I've not posted on here in years. Hope you're all doing well.

I'm building an e-bike with a 36v 250w BPM code 16 motor running at 48v in a 26" wheel . The battery is 48v 20ah with a 30a BMS, and I'm using a 48v 35a controller with adjustable current.

Is anyone able to let me know what the maximum current is that I can supply to this motor at 48v without causing damage to the motor? My last setup had a 48v 500w BPM that I ran at 30 amps. However, I now want to switch to a road-legal motor. Am I right in saying that the 250w BPM should be run at a lower current than the 500w version? If so, what current would you suggest?

Many thanks.

 

[Nealh]

The rating doesn't really mean anything except it is legal, afaics a hub whether marked 250,350 or 500w are all the same. So one can apply whatever current it will take, 20a should be fine which is 960w max.
A guy on the german forum put 35/40a thru a 250w swxk without it breaking though did use some ferro fluid inside.

 

[John_S]

The rating doesn't really mean anything except it is legal, afaics a hub whether marked 250,350 or 500w are all the same. So one can apply whatever current it will take, 20a should be fine which is 960w max.
A guy on the german forum put 35/40a thru a 250w swxk without it breaking though did use some ferro fluid inside.

From what I've heard, the 500w version of the BPM is more powerful than the 250w/350w version, as it has thicker wire in the windings. The old forum member D8veh, who'd had experience with both versions, would mention this in some of his posts. I'd like to supply around 26a of current to my 250w BPM. Would you say it could handle that when running at 48v? Thanks

 

[Nealh]

If d8veh aka vfr reckoned they were thicker then I would go against his say so. 26a is poss one may need some inner cooling.

 

[WheezyRider]

May find some useful info on the BPM here on this old post on ES:

Bafang/BPM geared-hub specs, teardown, and pics

Page 2, Bafang web-catalog http://szbaf.com/product.asp?page=2&pid=1&cid=0&keywords= Green Bike Kit http://www.greenbikekit.com/index.php/electric-motor/bldc-bpm-500w-36v.html E Life Bike http://www.elifebike.com/peng/pic.asp?ModID=PicS224&TypID=S220062 BMS-Battery...

endless-sphere.com

Did you just buy this BPM "new"?

 

[John_S]

May find some useful info on the BPM here on this old post on ES:

Bafang/BPM geared-hub specs, teardown, and pics

Page 2, Bafang web-catalog http://szbaf.com/product.asp?page=2&pid=1&cid=0&keywords= Green Bike Kit http://www.greenbikekit.com/index.php/electric-motor/bldc-bpm-500w-36v.html E Life Bike http://www.elifebike.com/peng/pic.asp?ModID=PicS224&TypID=S220062 BMS-Battery...

endless-sphere.com

Did you just buy this BPM "new"?

Thanks for the link. I'll take a look at that thread. I bought the motor from a German retailer on Ebay, described as "new other": https://www.ebay.co.uk/itm/184322065430

 

[WheezyRider]

Interesting, says "37V 250W" - seems an unusual voltage. Also, code 16 is a very slow wind for that voltage. 192 rpm unloaded - will struggle to get to 15 mph at 37V. However, should have loads of torque. Also, overvolting to 48V should mean you can get to reasonable speeds. BPM motors are quite scarce these days.

It also looks sensorless, will this cause you issues with your controller?

 

[Nealh]

37v typical china spelling error, they can be lazy and non fussy with QC.

 

[WheezyRider]

37v typical china spelling error, they can be lazy and non fussy with QC.

I'm not so sure. I wouldn't expect a big company like Bafang to make such a mistake. One possibility is that someone has made a copy and got that detail wrong, or perhaps Bafang made a 37V version for a battery pack with a slightly different chemistry, giving 3.7V per cell.

 

[John_S]

Interesting, says "37V 250W" - seems an unusual voltage. Also, code 16 is a very slow wind for that voltage. 192 rpm unloaded - will struggle to get to 15 mph at 37V. However, should have loads of torque. Also, overvolting to 48V should mean you can get to reasonable speeds. BPM motors are quite scarce these days.

It also looks sensorless, will this cause you issues with your controller?

Yes code 16 is a very slow wind. That's why I'm running it at 48V, and the wheel has a 2.4" thick tyre to make its diameter larger (larger wheel = faster motor). I've calculated that it should do around 19mph on a full battery.

The controller I'm using is a 35a one from PSWPower, which I believe is compatible with this sensorless BPM motor.

37v typical china spelling error, they can be lazy and non fussy with QC.

Yes that would be my guess too.

I'm not so sure. I wouldn't expect a big company like Bafang to make such a mistake. One possibility is that someone has made a copy and got that detail wrong, or perhaps Bafang made a 37V version for a battery pack with a slightly different chemistry, giving 3.7V per cell.

Its hard to say for sure, but my guess would be its just a spelling error.

I would hope that my motor is an original Bafang one rather than a copy. Do you know if there's a way I can check this?

 

[WheezyRider]

I would hope that my motor is an original Bafang one rather than a copy. Do you know if there's a way I can check this?

Difficult to know for sure. One thing to check is that the BPM motor is meant to be around 4.5 kg, whereas in the add on eBay it says 3kg. So check the weight of it. You could open it up and look at the internals to see if anything looks amiss. Then there is the serial code, does it look right? Do the numbers make sense?

I did find this for the model number (JS-033), although it wants you to register to be able to download it:

BPM 型电机技术说明书BPM motor technical ... - Bike-emotion.org

BPM 型电机技术说明书BPM motor technical ... - Read more about motor, suzhou, technical, rated, manual and bafang.

www.yumpu.com

One bit on the last page may be of interest:




If you do open it up, it should look like this:

 

[Nealh]

BPM should be approx.4.4- 4.5kg.

 

[John_S]

Difficult to know for sure. One thing to check is that the BPM motor is meant to be around 4.5 kg, whereas in the add on eBay it says 3kg. So check the weight of it. You could open it up and look at the internals to see if anything looks amiss. Then there is the serial code, does it look right? Do the numbers make sense?

I did find this for the model number (JS-033), although it wants you to register to be able to download it:

One bit on the last page may be of interest:

If you do open it up, it should look like this:

Thank you for your detailed reply, and the effort you went to to find out this information for me.

As far as I can tell, my motor is genuine. The model number JS-033 is clearly one that comes from Bafang themselves.

I looked at some photos of a couple of other BPM motors. The motor I have looks the same, other than the fact that 37V is written on it instead of 36V, and it also has different connectors at the end of the three motor wires. Its serial number is 1603027264, which as far as I know looks normal. I don't have a weighing scale, but the motor does feel more like 4.5kg than 3kg. I'll buy a scale tomorrow to weigh it.

As mentioned, my guess is that the 37V stamping is just a spelling error.

I'll limit the controller current to under 25a, as instructed by the user manual.

I assume that the motor I have is several years old. As long as its unused (as advertised) and has been stored okay, its lifespan from when I begin using it will not be shortened due to its age, right?

 

[WheezyRider]

Thank you for your detailed reply, and the effort you went to to find out this information for me.

As far as I can tell, my motor is genuine. The model number JS-033 is clearly one that comes from Bafang themselves.

I looked at some photos of a couple of other BPM motors. The motor I have looks the same, other than the fact that 37V is written on it instead of 36V, and it also has different connectors at the end of the three motor wires. Its serial number is 1603027264, which as far as I know looks normal. I don't have a weighing scale, but the motor does feel more like 4.5kg than 3kg. I'll buy a scale tomorrow to weigh it.

As mentioned, my guess is that the 37V stamping is just a spelling error.

I'll limit the controller current to under 25a, as instructed by the user manual.

I assume that the motor I have is several years old. As long as its unused (as advertised) and has been stored okay, its lifespan from when I begin using it will not be shortened due to its age, right?

Glad to be of help. I am also interesting in getting hold of a BPM or CST, so I am watching with interest how you get on with it. I am tempted to get one, but I am worried about the sensorless configuration.

37V might not be a spelling error. Some Li-ion batteries are quoted as having a 3.7V nominal voltage, so a 10 cell pack would be 37V. However, these days most focus is on battery chemistry giving 3.6V nominal voltage. It could have been a batch of motors that were destined for bikes with 37V packs, but they didn't take off, so the motors were left in storage somewhere. I wonder if they were designed for heavy cargo bikes due to the slow wind code.

The datasheet link should explain the serial number and give you an indication of the date of manufacture. I imagine these motors are probably 10 years old and were superseded by the BPM II. However, if not used, it's unlikely they would have deteriorated in storage and let's face it, it's going to be significantly better than a lot of the 250W motors available on the market in the UK at the moment.

 

[Nealh]

Sensorless jsut means the controller/motor combo will be a little noisier then normal but one isn't talking loud loud. They also reduce the chance of Hall failure an inopertion as there is nothing to fail. A Kt controller should work sensor less but if not one can but unsensored specific controllers.
Whether the hub is 36 or 37v matters not is for 36v battery chemistry, year ago pouch cell chemistry was mor widley used so the nom voltage was 3.7v where as cylindrical cells are 3.6v nom.
I have a front BPM at 20a it is a beast of a motor and once even melted the fuse holder with too much power/heat applied to the 6 mosfet controller.

 

[WheezyRider]

Sensorless jsut means the controller/motor combo will be a little noisier then normal but one isn't talking loud loud. They also reduce the chance of Hall failure an inopertion as there is nothing to fail. A Kt controller should work sensor less but if not one can but unsensored specific controllers.
Whether the hub is 36 or 37v matters not is for 36v battery chemistry, year ago pouch cell chemistry was mor widley used so the nom voltage was 3.7v where as cylindrical cells are 3.6v nom.
I have a front BPM at 20a it is a beast of a motor and once even melted the fuse holder with too much power/heat applied to the 6 mosfet controller.

I think you're right Nealh, Lipo packs were popular some years back and they are 3.7V nominal per cell. So the motor could have been designed for use with Lipo batteries. Not that the motor itself cares

Looking at the serial number 1603027264 - according to that datasheet, if that is right, it looks as if the date of manufacture was 2nd March 2016 and the motor sequence number was 7264.

 

[John_S]

Well, a small update. I've been using this motor now for around three weeks, and it has been very impressive. I've not noticed it to be in any way different from my old 500w version. It runs just as well and with as much torque. The only difference is that this motor is legal, which to me matters a lot. I've also bought another of this motor which I can use after my first one gives way. As its a slow wind (code 16), I've been running it at 48V (in a 26" wheel with a normal sized tyre), and it has decent speed, doing 16-18mph on the flat when unrestricted. However, I've set the cutout at 27kph (17mph), in line with the 10% of leeway allowed above the 25kph limit.

One of you mentioned that you're also interested in getting hold of a BPM motor. BPMs seem to be extremely rare now, even moreso road-legal ones. This seller only has a few left in stock, and I don't know if they're available anywhere else, so this would be your chance to get hold of one.

 

[StuartsProjects]

Did you check that the speed reported by the controller is accurate ?

 

[WheezyRider]

Well, a small update. I've been using this motor now for around three weeks, and it has been very impressive. I've not noticed it to be in any way different from my old 500w version. It runs just as well and with as much torque. The only difference is that this motor is legal, which to me matters a lot. I've also bought another of this motor which I can use after my first one gives way. As its a slow wind (code 16), I've been running it at 48V (in a 26" wheel with a normal sized tyre), and it has decent speed, doing 16-18mph on the flat when unrestricted. However, I've set the cutout at 27kph (17mph), in line with the 10% of leeway allowed above the 25kph limit.

One of you mentioned that you're also interested in getting hold of a BPM motor. BPMs seem to be extremely rare now, even moreso road-legal ones. This seller only has a few left in stock, and I don't know if they're available anywhere else, so this would be your chance to get hold of one.

When you say "48 V" what is the real nominal voltage of your battery? Is it a 14s config pack (50.4V)?

 

[John_S]

Did you check that the speed reported by the controller is accurate ?

Yeah I've checked that the speed reported is correct. I've compared the speed with a GPS speedometer on my phone, and it is accurate.

When you say "48 V" what is the real nominal voltage of your battery? Is it a 14s config pack (50.4V)?

I'm not sure of those details unfortunately. All I know is that it is listed as 48V. This is the battery: https://www.dhgate.com/product/ebike-lithium-battery-48v-20ah-lithium-ion/384948639.html
I bought it four years ago, and its still running fine and doesn't seem to have lost any range yet (at least, not that I've noticed).