Electric Motorcycle Wiring Design

[jegues]

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,



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? (I've been told we should not be doing this, and I'm not sure why) If so, how can we safely power our circuitry whenever the ignition is turned on?

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.

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?

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

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

Thanks again!

 

[chuckey]

It is not an ignition switch, unless you have hidden an IC engine somewhere, its a 48V isolator. There seem to be a shortage of fuses in your block diagram. Contactors have a low contact volt drop, but a finite life and significant driving power, auxillary contacts can be fitted too provide further functions easily. Power semiconductors need to be heatsinked and are prone to over voltage spikes, low driving power do not wear out.
I would have fed the 48V batteries to the isolator via a 100A fuse then straight into the converter/motor driver. From the isolator feed via a 5 A fuse to the control gear via an " ignition switch". Control the inverter via the micro.

Frank

 

[jegues]

It is not an ignition switch, unless you have hidden an IC engine somewhere, its a 48V isolator.

We have no hidden IC engine, so it must be an isolator.

There seem to be a shortage of fuses in your block diagram.

Agreed. From what you've said below you've recommended a,

i) 100A fuse between the batteries and the isolator
ii) 5A fuse from the isolator to the control gear via an "ignition switch"

In ii), what is the control gear, and what are you referring to as an "ignition switch"? This is not the isolator(What I originally referred to as the ignition switch), correct?

Contactors have a low contact volt drop, but a finite life and significant driving power, auxillary contacts can be fitted too provide further functions easily.

This should work well for our application.

Power semiconductors need to be heatsinked and are prone to over voltage spikes, low driving power do not wear out.

We are currently testing our module at half our full battery voltage (~24V) and have the module itself bolted to a thick block of aluminum as a heatsink. Eventually we will apply thermal paste to further heat sink the module.

I would have fed the 48V batteries to the isolator via a 100A fuse then straight into the converter/motor driver. From the isolator feed via a 5 A fuse to the control gear via an " ignition switch". Control the inverter via the micro.

I'm sorry but I'm having a hard time understanding the schematic you are describing. Could you possibly sketch me a quick diagram (microsoft paint is fine) of how you would connect things?

Thanks again!

 

[chuckey]

" you referring to as an "ignition switch"? ", I was being silly, its not an ignition switch, its a "on" switch?
Frank

- - - Updated - - -


Got left of last posting!

 

[jegues]

" you referring to as an "ignition switch"? ", I was being silly, its not an ignition switch, its a "on" switch?
Frank

- - - Updated - - -

View attachment 101390
Got left of last posting!

This is much more clear now.

Is there an issue if the rider tries to turn off the ignition key while current is being drawn from the batteries? Isolators aren't meant to interrupt current flow, right?

 

[chuckey]

The isolator is for making the battery/motor circuits safe so should not be used for intermittently stopping the bike. The fuse is also not designed to be pulled in and out to stop the bike, its the "on" switch that does that. If the electronic motor control electronics fail THEN the isolator can be used . Its like stalling a car if the ignition switch jams on.
Frank