Common ground

warezaholic said:
Can two different voltage systems (48 volt and 12 volt) share a common ground? If not why?

Sure. Inside your motor controller is one example with the logic section being at a fixed voltage lower than pack voltage. Another is a DC/DC converter where you step the pack voltage down to 12V for lights, horn, etc.
 
Thanks! I ask because I am thinking to use the bike's power switch ground to activate the separate 12 volt light switch system (with separate battery).
 
Just a thought, but it's sometimes good to have your lights on a completely different system, so if you have to shut down the drive system you can still have lights running to pedal home... And I like to have a demountable light or just a regular flashlight for trying to find out why the drive just stopped in the dark... :|
 
warezaholic said:
Thanks! I ask because I am thinking to use the bike's power switch ground to activate the separate 12 volt light switch system (with separate battery).
Ummm - that's a bit of a leap from the question you asked....

It's unclear exactly what you have in mind, but with the more obvious circuit choice of common battery Vbatt(-)s switched to common controller/light Gnds:
parking the bike with Bike battery switched OFF and the lights switched ON will leave the two batteries in series with the 12V battery having reverse polarity. Depending on the lighting system (incandescent, LED with blocking diode, etc), current will likely flow through the bike battery/controller in the forward direction and the 12V battery/lights in the reverse direction.

An ungood situation from more than one perspective....
 
Just to throw more confusion on this. You could also have a common positive, too. Your 12 volt and 48 volt systems could share the same positive side, if the grounds were separate. You could also have the ground side of the 12 volt tied to the positive side of the 48 volt with no problem. Or you could do it the other way around.

I'm assuming you're trying to control both the bike and the lights off one switch? It should work fine as long as only 1 side of each system is common
 
Thanks everyone, very informative answers!

Drunkskunk, You're correct, thanks for a little more confusion (lol), but I think that the suggestion that I keep the two systems separate is best to my needs because if I need/want to use the antiquated pedal system my lights will still help keep me safe from the fast moving world of pedestrians!

I replaced the thumb with a twist throttle on my Asian import, 1000 watt wheel and my grandkids were having fun on the bike and the motor got hot and blew a fuse and I wonder if it's caused by the new throttle or because of the weight of using the wheel on a 26" tricycle, with a 70 pound battery plus the weight of the pilots? The kids were giving it full throttle and maybe that was a contributing factor?

I think it requires a 20@ fuse and if this continues, is there a chance that the throttle is too extreme for the system? And if so, is there a way to affix a governor rig to it?
 
Thanks everyone, very informative answers!

You're correct, thanks for a little more confusion (lol), but I think that the suggestion that I keep the two systems separate is best to my needs because if I need/want to use the antiquated pedal system my lights will still help keep me safe from the fast moving world of pedestrians!

I replaced the thumb with a twist throttle on my import, 1000 watt wheel and my grandkids were having fun on the bike and the motor got hot and blew a fuse and I wonder if it's caused by the new throttle or because of the weight of using the wheel on a 26" tricycle, with a 70 pound battery plus the weight of the pilots? The kids were giving it full throttle and maybe that was a contributing factor?

I think it requires a 20@ fuse and if this continues, is there a chance that the throttle is too extreme for the system? And if so, is there a way to affix a governor rig to it?
 
Pretty much all throttles send the same signal voltage to the controller.. I would chalk that one up to operator excitement...lol
 
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