Ebmx melting throttle button

[skuzzlebut]

Just made a sick electric bmx. 12v 250w gear reduction chain drive motor, running on 20v drill batterys. More than enough for some added fun at the skatepark at gets me about 20-30kmph on flat ground. Throttle applied while pedaling makes short work of hills. I'm trying to run it without a controller to save on space and cost. I keep melting the intermittent buttons I'm using as throttle, they are all I need but need something more hd for when i run the motor for long periods uphill. Variable speed would be nice if possible on a intermitent button. I'm using a 12/24v 20amp heavy duty button from Amazon. I saw they do make a 50 amp but the issue with the last 20amp one was the plastic housing around the contacts melted to the point they separated internally and I doubt a 50 amp button would fix that issue. Any advice?

 

[amberwolf]

I had 2 pwm controllers and they melted even though they were rated 72v or so, however they were cheap. they just have a knob to adjust the power and a button to controll so hard to work both at once. I am liking the turbo button as well lol only problem is the wheel shifting (chain loosens) at stop or low speed and a lot of strain on the system.

Without details on the ones that failed I couldn't say for sure why, but:

Generally it sounds like they weren't meant to operate motors (inductive loads can be different from resistive ones, and require different designs; also brushed motors make craploads of RF at the brushes that can blow up FETs), and/or were not meant for the amount of current you are drawing (which as previously noted could be as high as a hundred amps or more at startup and under higher loads).

I've seen numerous ones on ebay, amazon, etc with an on/off switch and a separate pot to control speed that are not meant for use on ebikes, etc., most with open-cage covers, that would require active fan cooling to do anything close to their claimed ratings for more than a few seconds, if even that. Most are rated for low current, 5-10A, sometiems claiming a "max" of two or three times that, but that's a few seconds burst at most.

Most of these things are really cheaply designed and built, and don't really have much heat dissipation or a good current-limiiting design, so when excessive loads occur and they should be rolling back PWM duty cycle, they don't, or don't do so fast enough, and the FETs heat up so fast they just pop. If they had better heatsinking and active cooling, they might survive long enough to get past that anyway, but even that won't save one that cant' actually do proper current limiting. There's even plenty of really cheap brushed scooter / ebike motor controllers that have this problem, including some of the YKK brand ones discussed here and there on ES.

But it's all just speculation without specifics on what the failed units were, and exactly how they were used.

 

[E-HP]

Well, a relay is just a remote controlled switch, so it is just on and off. If you are using a resistive (potentiometer) throttle, it could be wired to activate the relay when it is rotated far enough, essentially all the way on, but it wouldn't give you any variable control.

The coils on a mechanical relay can draw 100mA or more. I don't think a hall based throttle can provide that, since it's really only designed to provide a voltage signal to the controller.

 

[amberwolf]

The coils on a mechanical relay can draw 100mA or more. I don't think a hall based throttle can provide that, since it's really only designed to provide a voltage signal to the controller.

That's why I stated "If you are using a resistive (potentiometer) throttle".

The typical hall based throttle (ss49e or clone thereof) coudln't operate at the votlages needed for the typical relay as discussed in this thread; usually theyre around 6v, maybe 8v absolute max supply voltage. There are 5v-coil relays, and there are hall sensor that could be used that can handle those voltages.

But as you note, it's unlikely any of them are able to source or sink as much current as the average relay coil for the size relays needed here would use. Some tiny relays use very tiny coil currents, and could possibly be used this way if a diode was also used across the coil to prevent damage to the hall from flyback current as the coil turns off...but it would still only be a switch, not a variable control.

 

[E-HP]

That's why I stated "If you are using a resistive (potentiometer) throttle".

The typical hall based throttle (ss49e or clone thereof) coudln't operate at the votlages needed for the typical relay as discussed in this thread; usually theyre around 6v, maybe 8v absolute max supply voltage. There are 5v-coil relays, and there are hall sensor that could be used that can handle those voltages.

But as you note, it's unlikely any of them are able to source or sink as much current as the average relay coil for the size relays needed here would use. Some tiny relays use very tiny coil currents, and could possibly be used this way if a diode was also used across the coil to prevent damage to the hall from flyback current as the coil turns off...but it would still only be a switch, not a variable control.

It's probably better to fry a throttle than it is to burn out the 5V regulator in the controller. Just a bad idea no matter how you look at it.

 

[amberwolf]

It's probably better to fry a throttle than it is to burn out the 5V regulator in the controller. Just a bad idea no matter how you look at it.

I don't really understand what you mean, since we were talking about using a throttle to switch a relay coil on/off, not even using a controller?

 

[E-HP]

I don't really understand what you mean, since we were talking about using a throttle to switch a relay coil on/off, not even using a controller?

doh! misread it.

 

[glennb]

Could use a limit switch. Micro one would fit in a throttle housing,

That's if you really have a thing for vroom vroom style throttles. Otherwise, there's neater options.

Still good to use a limit switch in some way though I reckon, because to my ear they're the best sounding of all switch types, very satisfying click they make, similar to relays.

Momentary push buttons with coil springs are awful, make no sound at all.