Precharge timer

j bjork

100 kW
Joined
Aug 31, 2018
Messages
1,967
Location
Linköping, Sweden
Has anyone done anything like that? A timer, so when you turn on "ignition" first a relay to the precharge resistor turns on. Then after 2 seconds or something, the contactors turn on.

Or better, some kind of a differential voltage sensor. So when the voltage before and after the contactors are close to equal, the contactors turn on.
Is there circuits like that to buy, or how could one be built?
 
I bought this timer:

7lgD2VB.jpg


It probably is more advanced and bigger than it needs to be for my use, and I think it would be possible to build something more suitable with a 555 timer or something. But I will do some tests with this and see how it goes.
It doesn't seem like it is possible to set 1second for the precharge like it says, more like 3 seconds or something like that. I will do some tests with an oscilloscope to see for sure later.
 
This is sometimes a requirement in EV racing I have read. Chris Jones on here did a write up years ago cause he needed to fully cut all power on the contactor and needed a timed precharge to do it.

I'll try to find the thread and link it. he used a transitorized circuit. Yeah seartch through "Chris Jones " old posts.
 
Thanks, is that jonescg?
I will be looking in to his build and see if I find something interesting. It would also be interesting with a isolation protection circuit, that cuts the high voltage if there is any contact with either hv + or - and the chassis. I don't understand in the rules if it is necessary, but it is a good safety feature to have anyway.
 
j bjork said:
I bought this timer:

7lgD2VB.jpg


It probably is more advanced and bigger than it needs to be for my use, and I think it would be possible to build something more suitable with a 555 timer or something. But I will do some tests with this and see how it goes.
It doesn't seem like it is possible to set 1second for the precharge like it says, more like 3 seconds or something like that. I will do some tests with an oscilloscope to see for sure later.

Did this work for you?
 
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