# Contactor specification



## major (Apr 4, 2008)

Ravishankar said:


> Hi,
> 
> I want to know how a Contactor is specified. The motor controller I have needs 144V dc. So I am using 48 cells of LiFePO4. But how do I chose the contactor: by the volatge or the current handling capacity (max current drawn by the controller), or both ? Also do I need two contactors ? One with an emergency kill switch..?


Hi Ravi,

A contactor is just a relay. It has a coil which will pull in the main contacts. The coil is isolated from the main contacts. The coil typically uses a low voltage low current as a control signal to turn on (pull in or make) the main contacts. Example of a coil would be 12 volts at less than an ampere. The main contacts are the switch in the high power circuit. The contacts need to be rated for the maximum voltage of the system to which they must break (switch open or turn off), which in your case is the fully charged open circuit voltage for the 144V battery plus maybe a safety factor, so I'd say like 200 VDC. Make sure the contacts are rated for DC as AC (only) rated contacts may not handle DC. Also the contacts must be rated for the current, so use the average battery current in your system to match the continuous rated current for the contactor. And because the contactor needs to interrupt fault current, it needs to have an appropriate interrupt rating. This should be in the neighborhood of the short circuit battery current. 

I like to use 2 contactors in the battery circuit, one each in the negative and positive leg. The negative one acts as the initial system turn on and emergency disconnect. The positive contactor handles the motor controller turn on and pre-charge.

There is actually a lot more involved but that should be the basics. I really like the Kilovac EV200 which is suitable for almost all conversions, quality and small.

Regards,

major


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## swoozle (Nov 13, 2011)

I see that the EV200 is rated at 500A carry. For folks that are running systems (like the Soliton) that will do more than 500A peak, is this adequate? In other words, is the EV200 rated capability a constant current spec or is it a true peak limit?

Thanks!


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## major (Apr 4, 2008)

swoozle said:


> I see that the EV200 is rated at 500A carry. For folks that are running systems (like the Soliton) that will do more than 500A peak, is this adequate? In other words, is the EV200 rated capability a constant current spec or is it a true peak limit?
> 
> Thanks!


I believe 500A is the continuous current rating for the EV200. Check the specification from the manufacturer to be sure. Those specifications will also include charts from which you can determine the overload capabilities. You do not have to match the continuous contactor rating to the peak controller rating.

And another thing to consider now that we have monster controllers available, are the other components in your system like the motor and the battery. Is it really necessary to have a contactor with a continuous rating of 2 or 3 times that of the motor? The motor would turn to ash long before the contactor.

And I think the Soliton has the EV200 contactor(s) inside. You may want to use another outside for emergency or otherwise disconnect.

http://relays.te.com/datasheets/ev200.pdf

major


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## Ravishankar (Jan 26, 2009)

major said:


> Hi Ravi,
> 
> A contactor is just a relay. It has a coil which will pull in the main contacts. The coil is isolated from the main contacts. The coil typically uses a low voltage low current as a control signal to turn on (pull in or make) the main contacts. Example of a coil would be 12 volts at less than an ampere. The main contacts are the switch in the high power circuit. The contacts need to rated for the maximum voltage of the system to which they must break (switch open or turn off), which in your case is the fully charged open circuit voltage for the 144V battery plus maybe a safety factor, so I'd say like 200 VDC. Make sure the contacts are rated for DC as AC (only) rated contacts may not handle DC. Also the contacts must be rated for the current, so use the average battery current in your system to match the continuous rated current for the contactor. And because the contactor needs to interrupt fault current, it needs to have an appropriate interrupt rating. This should be in the neighborhood of the short circuit battery current.
> 
> ...


Thanks major. I will check out for a local Tyco dealer. Is there any Albright or other make you know of that can meet the specs. The controllers maximum current draw is 250A. Continous is 80A. Motor power is 10KW rated and 20KW peak ?


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## major (Apr 4, 2008)

Ravishankar said:


> Thanks major. I will check out for a local Tyco dealer. Is there any Albright or other make you know of that can meet the specs. The controllers maximum current draw is 250A. Continous is 80A. Motor power is 10KW rated and 20KW peak ?


Albright makes a good robust DC contactor. It is only rated to 96V IIRC. I think some guys run it at high voltage. Fairly new to the market is Gigavac. There are no doubt others. Just have to search


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## frodus (Apr 12, 2008)

check ebay for EV200, it's one of the cheapest places to find them, brand new. 

What controller are you using with it?


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