Brushed vs brushless

[drsolly]

I have two 250 watt motors, on two different bikes.

One is a brushless, sensored, one is brushed. Both have 20 inch wheels. Both came from a bike branded as "Synergie", that brand no longer exists, I think. One of the bikes frames (aluminium) broke, so I built the brushed motor into a different 20 inch wheel frame (a downtube viii H, front wheel drive). The brushless is rear wheel drive. I'm running them both from 8S Lipo. Each bike is about 20kg (exceluding battery), I'm about 200 kg.

Riding the bikes, I can't really feel any difference, either in acceleration, in speed, or in how well they start up from rest. They pull around 30-35 amps max, and get up to about 20mph on the flat.

So what is the difference in performance between brushed and brushless? I had thought that brushless would be somewhat better, because so many well-regarded motors are brushless. But I can't feel a difference.

 

[Ykick]

There's tons of variations at work/play here but all things being similar, as in your description, motor power performance is not gonna be a huge difference.

Basically, 250W is 250W. Sure, some "losses" can add up and speed ratios become an influence for purposes of comparison but the rotational "work output" is gonna be around 250W.

Having ran both (still have brushed on an old beach cruiser) the major improvement of BLDC is practically no maintenance. And if BLDC Phase wire, Hall sensor repair/maintenance is ever required it's certainly not the MESS of cleaning away brush dust.

BLDC also offers a much wider range of rotational control. That may not be important for many eBike designs but the more advanced you want to take speed, torque and regen performance BLDC quickly jumps ahead of the pack.

 

[friendly1uk]

Brushes are a service item. Brushless motors are maintenance free.

 

[gogo]

Brushes typically add a wee bit of heat compared to brushless, and the dust may need to be blown out periodically according to service duty. Hub motors make access to the brushes more difficult, but not any worse than opening a brushless to get at the hall sensors. Seems like hall sensors cause people on this forum more grief than brush issues cause. Brush replacement is not a frequent task and not something even worth mentioning in the vs. tally.

Brushed can behave better coming off zero rotation. You might get slightly better efficiency with a brushless.

Brushed doesn't tolerate increased voltages and amperages as well because the brush material and commutator aren't designed for it. If you could change those out easily brushed could be hot-rodded, too. Brushless hubmotors are better candidates for hot-rodding.

 

[drsolly]

OK, then to summarise:

Given that I already had a brushed motor, and a bike that needed to be motorised, there's no reason to avoid using it. Eventually, it will need new brushes.

Thanks to everyone for the information.

To which I would add, at which time I'll probably find that I have no idea where to get replacement brushes because I don't know who made the motor. There's a chance that when it reaches that point, it'll be cheaper/easier to replace the motor! I'm running it slightly overvolted; 8s instead of the 7s battery it came with. My guess is that that won't make much difference to service life, and only a little difference to speed, but it makes an immense difference to the cost of batteries (I'm using Hobbyking 4S 20C hardcase, and paying $25 for 5ah).

 

[gogo]

I'd guess that small of voltage increase shouldn't be a problem for the brush material, but during peak loads you can be adding up to 14%, or maybe slightly more, extra heat to them and the rest of the motor.

 

[friendly1uk]

Brush replacement is not a frequent task and not something even worth mentioning in the vs. tally.

They last about a 5th as long. In all cases where brushless can replace brushed, brushed is no longer used.

I spent about 2 years reconditioning motors. I have seen one or two in that time. Some twice.

Getting new brushes is often a case of filing some down that are too big. Because it's all ancient.

The only reason a bike would use brushes is to cut controller costs.


Anyone that had train sets or scalextrix knows brushes are problematic.




Perhaps you don't mind the bother, but I certainly wouldn't want it. It is a guarantee you will break down. A part that is wearing away constantly. Mostly at start up. So not for throttle driven bikes as you describe.

Why don't you agree? I can't see how you could be more in touch with this than I am. Yet you try and undo my post. I don't get it.

 

[gogo]

… I don't get it.

You are correct, sir.

 

[Skalabala]

I would also like to see some in-detail comparison.
Best will be to monitor the Wh/km or mile of both?

 

[Matt Gruber]

in 30+ years i've NEVER had to replace brushes. maybe it is just me! Got my 61 vette in 1975, replaced the starter drive in 1983, but Never the brushes. Drove it saturday and it started right up.
None of my power tools ever needed brushes, not even my skil driver from 1985.
So, if you are wearing out brushes, go brushless. otherwise, don't worry about it. my brush scooters 12 yrs old work fine.
For safety, use as low amp a fuse as possible, so, if the controller shorts, it will pop the fuse, and not throw you off. That is the main problem with brush motors, they can break your neck!

 

[drsolly]

I use a 40 amp fuse on all my bikes; when I look at the amps-peak reading on my wattmeter, it's in the region 30-36 amps.

If I were buying a motor now, I think I'd get brushless, I can certainly see the maintenance advantage. But since I had a brushed motor just sitting there, and a beautiful bike that needed a motor ...