# Contactor Help! Sevcon Controller



## ysrman (Oct 6, 2015)

I am almost done with my EV Model T with leaf lithium packs. The last step is to figure out my contactor issue. The Sevcon controller is supposed to Chop the 84V to 24v on the contactor control wires. This feature is turned on but when i put a volt meter across the control wires i am getting 84V. the contactor is a 24v coil so gets hot and stops working which the speed controller does not like so the car will not go. I am not sure if it is a problem with the controller or what but either way i need to find a solution. I have been unable to find a 72v range contactor. Do these exist? or would i be better off just putting a voltage reducer (84vdc to 24v) in the control wire line. or would this freak out the sevcon controller? Thank you in advance. I look forward to posting the build as soon as it is done.


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## Hollie Maea (Dec 9, 2009)

ysrman said:


> I am almost done with my EV Model T with leaf lithium packs. The last step is to figure out my contactor issue. The Sevcon controller is supposed to Chop the 84V to 24v on the contactor control wires. This feature is turned on but when i put a volt meter across the control wires i am getting 84V. the contactor is a 24v coil so gets hot and stops working which the speed controller does not like so the car will not go. I am not sure if it is a problem with the controller or what but either way i need to find a solution. I have been unable to find a 72v range contactor. Do these exist? or would i be better off just putting a voltage reducer (84vdc to 24v) in the control wire line. or would this freak out the sevcon controller? Thank you in advance. I look forward to posting the build as soon as it is done.


What contactor do you have? If you have a built in economizer, it will fight with the Sevcon PWM and get hot and fry it.

Also, make sure your contactor voltage on the controller matches the coil voltage rating. If, say, it's outputting 24V but you have a 12V coil, it's going to get very hot and probably fail.

If you have a contactor without an economizer circuit, and you are matched in the controller software, it should work properly.


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## ysrman (Oct 6, 2015)

Hollie, Thank you for the reply. I have a Tyco 500A 24v coil contactor. I dont believe it has an economizer. I finally found the reason for the 80v across the coil and have remedied it. now i get a chopped 24v properly. i think i have found the real issue with the contactor. Every time the contactor closes the sevcon controller draws a lot of current momentarily. this has been welding the contactor closed. the controller then has no way to open it and will not load up the next time. this must be a common problem that people have experienced. What is the best solution to soften that first load?


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## frodus (Apr 12, 2008)

Whats the part number of your Contactor?

What did you set the pull in voltage of the contactor via the Sevcon DVT software?

What else do you have powered from the Contactor?


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## pm_dawn (Sep 14, 2009)

ysrman said:


> Hollie, Thank you for the reply. I have a Tyco 500A 24v coil contactor. I dont believe it has an economizer. I finally found the reason for the 80v across the coil and have remedied it. now i get a chopped 24v properly. i think i have found the real issue with the contactor. Every time the contactor closes the sevcon controller draws a lot of current momentarily. this has been welding the contactor closed. the controller then has no way to open it and will not load up the next time. this must be a common problem that people have experienced. What is the best solution to soften that first load?


The controller should precharge to a user set voltage before closing the contactor. That precharge should be handled over the key-switch circuit.

There might be something else that is also switched on with the contactor (DC/DC, Heater etc) that gives the high inrush current when the contactor closes.

Or you might have set the voltages in the DVT at to low values to engage the contactor.

for example if you set the engage voltage of the contactor to 30v you will have some 55v of voltage difference over the contactor when it closes.

if you raise the engage voltage to 70v you will have less voltage over the contactor when it closes.

Please check your settings and also make sure that other equipment that might be feed by the contactor (DC/DC etc) also has some kind of precharge that is fast enough for the controller.


Regards
/Per


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