# Choosing a contactor



## flashedarling (Jun 30, 2008)

I'm building a 72v motorcycle which I'm trying to get a max continuous current of 200A (more than I'll need but I'm engineering plenty of room into it). I'm planning on using a 12v aux pack to run my headlights and trip the contactor. This one looks like it would serve my needs but it lists a Contact voltage of 36V when I intend to use twice that. I'm not sure I understand why contact voltage matters as the contactor has no voltage drop across it. Is this a fine contactor to use though or is there another I should try.

As a side note I'm going to use a Kelly 72v controller, will I still want the precharge circuit to protect it? Also where can I find high amp switches I can use in my system?


----------



## frodus (Apr 12, 2008)

get one of these:
http://www.wesgarde.com/newproduct_Kilivac.shtml

and be done with it. Uses 0.15A @ 9-36V coil input, 500A continuous, 2000A break capability, don't need a diode (built in), 12V up to 900V rated contacts.

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

for $99 its a deal, and its sealed. Its a hell of a deal. If you can find it cheaper ANYWHERE ELSE in quantity of 1, I'd be VERY surprised.



As for the kelly, YES, you NEED precharge... assume its always needed... period. It has more to do with saving the contacts on the contactor so they don't switch under load.

As far as the high voltage switch, why would you need a high voltage switch?


----------



## madderscience (Jun 28, 2008)

As for the question about why the contacts themselves (not the coil) have a voltage rating, it has to do with interrupting the current. Too high of voltage over too small of an opening with cause an arc to be sustained, which would be bad. Also take note that there is a big difference between an AC rated contactor or switch and a DC rated one. We should all be using DC rated contactors and switches in our EVs.


----------



## PatricioIN (Jun 13, 2008)

frodus said:


> get one of these:
> http://www.wesgarde.com/newproduct_Kilivac.shtml
> 
> and be done with it. Uses 0.15A @ 9-36V coil input, 500A continuous, 2000A break capability, don't need a diode (built in), 12V up to 900V rated contacts.
> ...


Not trying to steal the thread.. but.. I've seen these in other conversions. Are these really able to handle up to 900v.. like, if I wanted to use one in a future EV car at with say a Curtis 1231C and 144V... this contactor would be acceptable? I ask because it's much cheaper than the Albright I bought for my current EV.


----------



## flashedarling (Jun 30, 2008)

frodus said:


> As far as the high voltage switch, why would you need a high voltage switch?


I was planning on doing this layout from the stickied thread on EV High Voltage. I was thinking about having a master switch for the emergency disconnect rather than just a connector.








Now I realize that I won't have very much current running through the precharge switch, which is the point isn't it? How many Amps does the controller need for precharge though?


----------



## piotrsko (Dec 9, 2007)

electronic theory says that the initial current will be infinite with a 2*PI/1 [might be e square root function here, my theory is old like me] reduction as the internal reactance of the caps increase due to charge over time. In practice, the current will get limited to a value slightly below the maximum of the controller. NTW it is a short term current value, time wise and the controller should be able to deal with it.


----------



## frodus (Apr 12, 2008)

PatricioIN said:


> Not trying to steal the thread.. but.. I've seen these in other conversions. Are these really able to handle up to 900v.. like, if I wanted to use one in a future EV car at with say a Curtis 1231C and 144V... this contactor would be acceptable? I ask because it's much cheaper than the Albright I bought for my current EV.


The 156V corbin sparrow (myers nmg) uses them in their vehicle. Lots of other conversions use them. They're a GREAT contactor. We've used them in a couple of conversions (my motorcycle at 120V/200A peak and a truck with floodies).

They really are rated to 900V, 500A continuous... they're not cheap contactors.... I just happen to have FOUND them for cheap


----------



## dimitri (May 16, 2008)

Just got one of these on Ebay for $63 , what a great deal!

Thanks for the tip Frodus


----------



## frodus (Apr 12, 2008)

No problem....

I'm one of the cheapest guys on here  
My bike hasn't broken $1000 yet.... with batteries.

$63 is a steal! great job.


----------



## BHall (Aug 1, 2007)

Heck yea! Smokin Deal! Just picked one up from eBay too! Thanks for the lead!

Brian


----------



## flashedarling (Jun 30, 2008)

dimitri said:


> Just got one of these on Ebay for $63 , what a great deal!
> 
> Thanks for the tip Frodus


You just made that eBay store another sale. They ought to give you yours on the house! 

I'm still curious about how much current I should give the controller during precharge. I also know that in the "High voltagen-off" thread that he uses a start-step device to automatically flip one and then the other. Is there a simpler way to do this than the device he is showing off. I'm not electronics fiend but it seems like there must be some way to either have a timed delay or detect when the current through the precharger drops enough to switch it.


----------

