# Electric Motorcycle Wiring Design



## ga2500ev (Apr 20, 2008)

jegues said:


> Even gents,
> 
> We're working on designing the wiring diagram for our low and high power circuitry for an electric motorcycle.
> 
> We're contemplating a configuration like the one attached in the figure below,


You image didn't show because you need an account to access. I made a copy and attached it below for everyone to see.


> I have a couple questions regarding the best way in which to power our electric motorcycles circuitry.
> 
> *1) First question, is it problematic to place the ignition switch on the bike directly between the high voltage 48V bus and the 48V:12V isolated DC-DC converter?*


Yes.


> (I've been told we should not be doing this, and I'm not sure why)


Because the ignition switch is rated for 12V.


> If so, how can we safely power our circuitry whenever the ignition is turned on?


By using a contactor to switch the 48V power to the DC-DC that is controlled by the ignition switch.




> We do have access to a *switched* isolated 48:12V DC-DC converter meaning that it can be turned on and off via electrical signal applied to a control pin on the device, but without the 12V supply from the output of the same DC-DC converter we have no means to generate the control signal to the DC-DC converter to turn it on. For example, if the control signal is to be sent from the microcontroller, the microcontroller would need to be powered on, and this wouldn't be the case if the 48:12V DC-DC converter was switched off.


This connundrum is usually resolved by adding a small 12V battery on the 12V side of the system. That way you can have 12V power even when the ignition switch is off and can use that battery to power up the DC-DC. Then the output of the DC-DC can be used to recharge the battery.

Typical cycle and car batteries are large so that they can have sufficient power to crank the starter. Obviously with an E-bike, that function is no longer necessary. So even a small SLA gel-cell will be sufficient to provide battery power for the functions you require.




> *2) Second question, how do I know whether or not a pre-charge circuit is necessary for our DC link capacitor connected across the terminals of our battery bank?*


Always. It needs to be little more than a reed relay and a series resistor that charges the caps before you close the main contactor.



> *
> 3) Third question, is there any advantage to using a contactor over a solid state relay?*


Contactors usually handle more power, are more reliable, and are cheaper.


> *
> 4) Finally, can anyone spot any obvious flaws in the schematic above that we may have missed or not yet have noticed?*
> 
> Thanks again!


I'll leave that for someone else to tackle.

ga2500ev


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