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View Full Version : Sevcon Gen4, CANBus, and Isolation



__Tango
09 November 2012, 0125
hey folks, so i'm working on the wiring for the Gen4 for my bike. However, one thing i'm a little confused about is: do i need to keep the traction pack and Sevcon Gen4 isolated from the 12V circuitry.

From this thread: http://www.elmoto.net/showthread.php?243-Isolated-vs-non-isolated-DC-DC-converter i think that i should keep the 12VDC circuit and the 120VDC traction circuit isolated from each other. There seem to be only two places where they would be connected:


The key switch: however i can use an isolated solid state relay (like a crydom d0207) to handle this so that it stays isolated.
The CANBus: The CANBus needs to have all of the nodes having a common ground. I'm using an arduino board with a "can shield", which is normally run off of the 12V circuit. The CAN shield isn't isolated, so in order for it to work i need to move the arduino on the traction pack circuit.


Does this sound right? In order for me to move the arduino to the traction circuit, i have to be able to convert ~120VDC down to around 5-8VDC. I can do this since i have a second (Vicor, isolated, 120V->8V) DC-DC converter that I can use. However, if i do this, my next quesion is: The Vicor is an isolated DC-DC. Can i have the two sides of the DC-DC converter share a common ground? In this case, the common ground isn't going to be grounded to the frame (the isolated 12V system is). Will the Vicor be able to deal with this scenario? Am I "just doing it wrong"?

I can post a wiring diagram if needed...

Thanks.

__Tango
09 November 2012, 1658
Here are some pictures of what i'm talking about

This first one shows that there are two separate/isolated circuits (well there are supposed to be isolated). The Red/Maroon circuit is the 12V circuit (lights, horn, ignition). The Orange circuit is the high voltage, traction circuit.

Where the CANBus connects from the controller to the Arduino (Shown by bright red dashed lines), the high voltage traction circuit is connected to the 12V circuit (thus destroying the isolation).

http://electriceptor.files.wordpress.com/2012/11/sevconquestion-12.png?w=500 (http://electriceptor.files.wordpress.com/2012/11/sevconquestion-12.png)

One way to do this would be to make an isolated CAN adapter. But that would take a fair bit of effort (designing a new arduino shield).

I'm trying to figure out how i can do this more easily given the parts i have or can create quickly.

Here's one solution i can think of: Use my other existing 24V DC-DC to create a second circuit, and then tie the grounds together (traction/second 24V circuit). Then run the arduino off of this circuit. However i'm not sure if this is possible or advisable (having the ground from the traction and second 24V circuit tied together).

http://electriceptor.files.wordpress.com/2012/11/sevconquestion-2.png?w=500 (http://electriceptor.files.wordpress.com/2012/11/sevconquestion-2.png)


Whaddya think?

SplinterOz
09 November 2012, 1711
-- delete -- asked for diagram after you had already posted. Me slow.

frodus
09 November 2012, 2115
Why not use the power supply from the Sevcon? Then no extra power supplies. It ought to supply the Arduino at least.

Looks like there's 12V and 5V on the pinout on the controller. I think it's NOT isolated from Battery, but it also depends on what you're doing with the Arduino.

Call me and we can go over it tomorrow.

Skahle
12 November 2012, 1633
I would add the isolation on the CAN bus side of the Arduino so it can connect to the vehicle ground and +12V. That way if you connect a laptop to the Arduino for programming, logging...etc. you won't be connecting the laptop to your traction battery.

Steve

frodus
12 November 2012, 1649
To isolate you need to either build an isolated repeater or use a single chip solution... emailed ya.

I'm digging into whether you news it though. The sevcon Gen 4 size 8 CAN is isolated.