Firstly, I want to say I know exactly how a brushed motor works, what I don't understand is how it can possibly work which such high amperage. I've had an endless amount of heavy duty switches that can probably handle switching a kitchen stove on/off solder themselves into the "on" position simply from the arcing due to the very high amps these ebikes pull.
This got me thinking, the brushes in the motor itself ARE switches, so how can they survive that amperage and arcing without soldering itself? Is it the motion that prevents any soldering from taking place? How do they survive the stress of switching high amp currents so often?? My switches fried on the first attempt.
It was funny when it happened once, firstly my bike doesn't have a motor controller now, I wired a relay to replace it, so I was riding once and was just pedaling without giving any throttle for a while and thought "wow this bike is really easy to ride without the motor today, it's usually harder". At one point I decide to press the throttle button and feel no noticeable difference, I thought "Geeze, the battery must be completely dead!". After a while it was getting really suspicious, I was barely pedaling yet maintaining 25-35km/h, so I decided to stop pedaling to slow down... I barely slow down at all... so I put the brakes and slow down, but as soon as I let go my speed picks up and I'm still not pedaling, it was more than obvious as this point that the relay had soldered itself in the "on" position and the motor was on full power all along (my battery is severely damaged, making it hard to tell the difference between off and on, literally)!
You can see a photo of the melted relay here, note that this was NOT caused by a short but simply by the motor pulling more amps than the relay could handle (rated for 13A at 120 VAC, and 10A for either 277 VAC or 30 VDC). The damaged relay is on the left, the new one is on the right (obviously). You can see the "common", "normally open" and "normally closed" contacts have all molten into a blob of metal! What I now do to not pass the limit is I pedal manually up to 15kph, at which point it takes less than 10A to make the motor work, I need to accelerate myself but hey, it's better than no ebike at all! I'm getting a new controller in the mail soon, but without the pedal assist feature I loved so much, but it's better than my current setup still!
This got me thinking, the brushes in the motor itself ARE switches, so how can they survive that amperage and arcing without soldering itself? Is it the motion that prevents any soldering from taking place? How do they survive the stress of switching high amp currents so often?? My switches fried on the first attempt.
It was funny when it happened once, firstly my bike doesn't have a motor controller now, I wired a relay to replace it, so I was riding once and was just pedaling without giving any throttle for a while and thought "wow this bike is really easy to ride without the motor today, it's usually harder". At one point I decide to press the throttle button and feel no noticeable difference, I thought "Geeze, the battery must be completely dead!". After a while it was getting really suspicious, I was barely pedaling yet maintaining 25-35km/h, so I decided to stop pedaling to slow down... I barely slow down at all... so I put the brakes and slow down, but as soon as I let go my speed picks up and I'm still not pedaling, it was more than obvious as this point that the relay had soldered itself in the "on" position and the motor was on full power all along (my battery is severely damaged, making it hard to tell the difference between off and on, literally)!
You can see a photo of the melted relay here, note that this was NOT caused by a short but simply by the motor pulling more amps than the relay could handle (rated for 13A at 120 VAC, and 10A for either 277 VAC or 30 VDC). The damaged relay is on the left, the new one is on the right (obviously). You can see the "common", "normally open" and "normally closed" contacts have all molten into a blob of metal! What I now do to not pass the limit is I pedal manually up to 15kph, at which point it takes less than 10A to make the motor work, I need to accelerate myself but hey, it's better than no ebike at all! I'm getting a new controller in the mail soon, but without the pedal assist feature I loved so much, but it's better than my current setup still!
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