750w hub motor 48v and 12amp, any potential problems?

[Bike7777]

Can I use a 750w rear hub motor with a 48v battery and 12amp controller or would this cause a motor problem or cause some other problem?

 

[Bike7777]

No because that's only 576W, if your motor is rated at 750W, you won't get the best performance out of it.

The only potential problem that I could think about is that, 750W motor has bigger stator, so lack of power "might" cause the motor to work less smoothly.
You know when you're about to go out of battery power, the motor makes this pulsation (on/off) feeling?
I doubt it will happen because 500+W is still plenty of power, it will probably be like riding on Level 1 assist, but if I were to guess, that "could" only be the problem.

Thanks for replying. I asked the question because I am thinking about buying my first ebike or building one.

 

[AHicks]

My thought is you're going to smoke that 12a controller pretty easily. The controller should be sized for AT LEAST the motor's capacity. Better yet, it should have excess capacity (known as overhead). Excess controller capacity is cheap insurance, assuring you long contoller lifetime and also to minimize any chance the controller will act as a power bottleneck between your battery and the motor. Absolute minimum capacity for a 750w motor and 48v battery would be something in the 20-25a range.

 

[Dewey]

I think @AHicks might be referring to the power rating of the mosfets in the controller. 5 years ago I burned out a first gen 36v bbs01 controller by setting it to 20a, they replaced the mosfets for better ones after April 2016 and my replacement controller runs happily at 18a

 

[AHicks]

Is this how it works?

Here's my understanding (I could be wrong):
The controller is there to regulate the electricity that's been sent to the motor.
If you have a weak controller, that just means less electricity sent to the motor.
The way you could smoke the controller is if you have, say 72V battery on a 48V controller.

So the controller is there to regulate the speed, electricity, etc.. that's sent to the motor.
But if you're using 48V battery on a 48V controller, I don't think you could do the damage to the controller?

You have the right idea, but you need to factor in the capacity of the components used in the controller, as well as the ability to handle amperage.

 

[AHicks]

If you have a programmable controller, yeah I guess you could burn it like that.

But my point is, even in your case, was the motor (BBS01) the main cause of burnt controller?
Even if you're running BBSHD, TSDZ2 and what have you, it sounds like the fact that you set your controller to 20A was the problem, not the motor.

Um, nope. That 20a setting in the Bafang setup SHOULD be acting as a safety valve. Others (Thomas!) can tell you with a bit more certainty what the max safe setting should be to prevent burn downs on the BBS02, but I'm thinking it's 17a? . I know we can run up to 30a settings safely on the BBSHD and Ultra motors.

 

[AHicks]

Hmm, as long as it's set to 12A, which is what the controller is meant for, it likely won't go over the capacity. (?)

That said, I agree with getting a better controller.

People with 750W motor are using 35A controller (like Bolton RadRover), so 12A is a bit too weak.

So back up for a second and ponder the question why would the Bolton kit use a 35a controller when they could get away with a smaller one?

Bottom line, controllers are something like motors in that you cannot run 100% capacity full time, especially if operating in less than perfect conditions. Sticking a controller in a bag or confined space where it's not able to shed heat properly is a good example of less than perfect conditions.

 

[AHicks]

Thinking about it for a minute, I suppose if the performance loss were not a factor, you could use a 12a controller in that setup. The question being whether or not the components in that controller would hold up when passing 12a. How long would it take to to overheat them to the point of failure. If they could hold, there a good chance it would be rated for a higher capacity. That's why we see the Bolton (KT) controllers rated at 35a max with slightly less capacity shown for a better idea of what it can really handle without overheating

 

[Dewey]

If you have a programmable controller, yeah I guess you could burn it like that.

But my point is, even in your case, was the motor (BBS01) the main cause of burnt controller?
Even if you're running BBSHD, TSDZ2 and what have you, it sounds like the fact that you set your controller to 20A was the problem, not the motor.

Bafang seemed to increase the width of the stator by 20% from my bbs01 to the bbs02, then changed the design again for the bbshd to absorb heat over a longer time before overheating. I burnt out my controller experimenting with the settings and without a thermometer inside the controller, the motor casing felt warm to the touch after a hill climb but the smell of burning plastic right before the controller failed meant I knew I’d gone too high.

Re: the Bolton 35a controller, I thought I read on other threads it can trip the BMS on the battery of some Rad bikes, the 25a electrobikeworld controller seems to offer a decent 50% power increase over stock but without risk of this problem.

 

[Bike7777]

My thought is you're going to smoke that 12a controller pretty easily. The controller should be sized for AT LEAST the motor's capacity. Better yet, it should have excess capacity (known as overhead). Excess controller capacity is cheap insurance, assuring you long contoller lifetime and also to minimize any chance the controller will act as a power bottleneck between your battery and the motor. Absolute minimum capacity for a 750w motor and 48v battery would be something in the 20-25a range.

Thanks for replying. I am new to all this ebike stuff so I will continue to learn more before I buy my first ebike or build my first ebike.

 

[harryS]

For example, if you have 48V battery and 12A controller, even if you put GMAC there, I think the controller will still provide 576W and that's it, it won't go 2000W or whatever motor may be capable of.

I don't think motor is what's determining the current that's going to the motor, the controller is.

Exactly. Some controllers are programmable, but what we can program is less current. For example. my wife mentioned yesterday that after I put a 48V pack on her bike, she felt the pedal effort was too low.

It's a KT controller, and the display allowed me to cut the current by up to 50%. Since 48V is 33% more than 36V, I dropped her current by 30% by changing a setting.

See the "soccer goal" on this controller. It's a metal shunt resistor. The controller uses it to tell when it hits the maxiumum current designed into the controller. Speed hackers often add solder to fatten up the metal so they can get more current, and blkow up their MOSFETs.

 

[AHicks]

Okay but is that how it works though?
If you use 12A controller, it won't go above 12A (at least that's what I thought? )
I don't think it will go pass 12A (?)

For example, if you have 48V battery and 12A controller, even if you put GMAC there, I think the controller will still provide 576W and that's it, it won't go 2000W or whatever motor may be capable of.

I don't think motor is what's determining the current that's going to the motor, the controller is.

You are assuming the controller is capable of passing 12a reliably for a 100% duty cycle. I say that's not very likely. IF you knew for sure what that controller would pass safely, and that load was never exceeded for any length of time, THEN maybe your argument would hold water. In any case, I'm not going to find out the hard way. I have no intention of purposely placing a bottle neck (time bomb) between any battery and motor combo I own - for any reason. You do as you like. Telling folks a 12a controller is a viable solution (under any conditions) for feeding a 750w motor is on you. I say it's a terrible idea....

As far as the RAD BMS (2017 model), I have my 35a KT controller set for 20a max out of concern for the size of the wire used internally within the battery. I don't remember for certain the ga. used, but it was either 14 or 16ga. In any case, asking that wire to pass everything available from the batteries I thought a bad plan if long term durability was a concern. 4 years later that plan has proven itself as a good one. I have an easy 1200w on tap any time I ask for it, and I can count on using that much power without issue. Call it a conservative setup if you'd like....

 

[Dewey]

As far as the RAD BMS (2017 model), I have my 35a KT controller set for 20a

I watched one of Bolton's videos last night where Kyle mentioned you can reprogram the 35a controller amperage, it sounds like a real benefit particularly for Rad single speed owners who may climb the occasional hill to be able to gain more torque with a plug and play 3rd party controller.

 

[Gionnirocket]

Okay but is that how it works though?
If you use 12A controller, it won't go above 12A (at least that's what I thought? )
I don't think it will go pass 12A (?)

For example, if you have 48V battery and 12A controller, even if you put GMAC there, I think the controller will still provide 576W and that's it, it won't go 2000W or whatever motor may be capable of.

I don't think motor is what's determining the current that's going to the motor, the controller is.

A controllers rating is its ability to pass current reliably... You can easily exceed its rating with a motor that is too large as the controller hardware doesn't limit.
A basic rule gleened from the electrical code is that a motor should be no more than 80% of a controllers rating for reliability.

 

[AHicks]

I watched one of Bolton's videos last night where Kyle mentioned you can reprogram the 35a controller amperage, it sounds like a real benefit particularly for Rad single speed owners who may climb the occasional hill to be able to gain more torque with a plug and play 3rd party controller.

As long as they realize they're playing with fire. With something like a big KT controller (like the 35a model for instance), they could easily overheat that motor playing in the hills I would think. Short hills, that are topped in just a few seconds, no big deal. It would be the longer or more difficult hills that might do you in, where full power has been in use for several minutes.

I've done 3 KT conversions recently (in the last year), each costing less than 100. but they were not plug and play, leaving the installer to figure out a few connections - and with basically no directions to do that. They have several "waterproof" versions now, using the Bafang and Julet connectors. I used a 17a for the first, and a newer 22a w/light wire (controlled by the PAS switch/display) for the second 2. All 3 are working really well on 500w motors. They have all of the same settings (parameters) as the Bolton kits. Noteworthy maybe, is that the 22a is able to supply nearly 1000w to the 500w motors. They REALLY scoot with 1000w on them, but you would need to be careful for sure. Great for crossing busy roads or climbing that short easy hill. Just don't get carried away using full power for more than a few seconds and you'll be fine. KT recommends the waterproof 22a for both 500w and 750w motors. KT 17a and 22a are both very compact for installation in cramped areas.

 

[Dewey]

they could easily overheat that motor playing in the hills I would think. Short hills, that are topped in just a few seconds, no big deal. It would be the longer or more difficult hills that might do you in, where full power has been in use for several minutes.

For sure, I was thinking about this video review of the stock RadMission and the guy doing the review who is a former Ironman athelete was really struggling up short steep hills with the single speed gearing.

 

[Gionnirocket]

No I didn't assume that, because I know that controller (almost) always gives continuous and max power ratings.
I thought the controller had this computer chip or something to restrict the power after 10 seconds (for example) if current gets to the max.

a programmable controller may. . . but it's rating is all about what the hardware is capable of handling. The hardware rating does not restrict current.

 

[AHicks]

Ohh okay I see.

So if it wasn't programmer right, the it can burn out the controller.

More like if it wasn't built using components capable of handling the power you're asking it to handle. Like the Rocket says, it's about the hardware (electronic components).