# Controller isolation



## veperformance (Aug 17, 2007)

you dont need to isolate your power transistors from the drivers but you need to drive you transistors very precisely or they will die very fast.
If you can drive the low side of your supply it is much easier to design.


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## Greenflight (Sep 13, 2007)

Yeah, I know I don't need too, but it's a basic safety feature I try to follow: Traction pack must be isolated from the vehicle frame. That way, if you're holding the hood up with one hand, and you happen to graze a connection with the other, you don't get zapped.  

Since the 12v is grounded to the frame, if the transistor shares a common ground, you end up grounding the traction pack to the frame.

What do you mean by driving the low side of the supply?


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## veperformance (Aug 17, 2007)

in that case you can use opto coupler so both circuit stays insulated from each other , as for driving low i mean driving your - is low side and the + is the high side


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## Greenflight (Sep 13, 2007)

Yeah, I thought about that, but what do I use to drive the IGBT on the other side of the opto coupler? A voltage regulator off the high voltage? Seems like that would waste a lot of power.  

How do those isolated dc/dc converters work? Something like that would be ideal. I just can't imagine how they work.  

I get that about the low and high- I was just wondering how driving the low side makes it easier.


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## Greenflight (Sep 13, 2007)

I knew there had to be a simple solution!  

http://cgi.ebay.com/DC-DC-Converter...yZ117000QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


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## veperformance (Aug 17, 2007)

that converter wont help since you need about 14v to drive most mosfet on the low side witch is simpler to drive ,are you building the controller to feed dc directly to a dc motor from your battery pack ?
I admit that i burned quite a few parts in the process of designing such a unit.I must now decide if i will parallel 4 mosfet with 1 drive or use independent drives.


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## Greenflight (Sep 13, 2007)

ve, do you have schematic for your project? I'd like to get an idea of what you're working on.

Yep, just a basic DC motor controller. All it's got to do is output a pwm based on the position of a throttle sensor... Seems easy, right?  

There's other converters out there... I think there's a couple 12/12 models, maybe higher. Anyway, I'm looking at using a single high performance IGBT, which shouldn't need that much voltage for switching. Seems to me most of the datasheets I've looked at specify like 7v max- not sure though.


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## veperformance (Aug 17, 2007)

I'm working on a complete ev conversion kit , motor-controller-power control.since it's a prototype i'm not allowed to share the details for now.when i'm done i may be able to help.


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