# Contactor for my e-Motorcycle



## BenNelson (Jul 27, 2007)

Hello!

Could somebody please give me some advice on using a contactor on my electric motorcycle?

That cycle is the first real electric project I have ever done. It is a motorcycle with an Etek motor and an Alltrax 24-48V AXE controller.

Right now, there are 3 Optima Yellow Top batteries to run it.

I have just been using a battery cut off switch as sort of a master power key for the cycle. I figured that would be OK, because there shouldn't be any power running through everything as long as the throttle isn't turned.

I have a bunch of parts off a 36V electric forklift.
I pulled off a contactor and tested it by running 36 volts to the small power connectors on it. The contactor snapped shut, and then sprung back open when I broke the circuit. That's exactly how a contactor is supposed to work, as far as I know.

I set the multi-meter to measure amps. The contactor pulls almost axactly an amp. Since this is a 36V battery pack, that means 1 amp x 36V system voltage = 36 Watts. Does this sound right? Is that typical power usage for a contactor?

Do I really need a contactor? What advantage do I gain for my 36 watts used?

I also wanted to see about using the key switch from the forklift as an ignition key for the motorcycle. ( The cycle frame did not originally include the ignition unit). Is one amp at 36 volts too much to be running through a little key switch? I would imagine that everything in the forklift ran on the full pack voltage. I didn't see any sort of DC/DC converter on it. I noticed that the strobe light on it was rated to run on 12 to 80 volts. I think that was so it could run straight off the main battery pack voltage.

Do I have all this right? Is there anything else I should be thinking about?

The contactor I am using here is a Prestolite JCA-4002E. There are a couple other contactors that I have that are also off that same forklift, which are a different brand, and it looks like 2 of them are also reversing contactors.

I have also heard that you need to have a resistor for the PWM controller when using a contactor, but have never been able to nail down the exact how or why.

Thanks in advance,

-Ben
Cycle Link


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## sharp21 (Mar 11, 2008)

I was looking at your bike thinking "ive seen that somewhere..."
Turns out I just replied to your post on ecomodder!
Your bike is a real inspiration
S>


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## Damon Henry (Jul 26, 2007)

Putting that contactor in is a great idea. It is possible that your controller will fail full on, and your battery cut off switch is likely to weld shut rather than break the circuit for you which means you have no way to stop until the batteries run down. Having said that, I have been running my motorcycle for several years with the exact same switch and no contactor  I've had one sitting on my shelf for a couple of years that I have been meaning to install.

One amp is not unusual for that size of contactor. Running it at a lower voltage will make it use less current, but a lower voltage will also make it activate slower. There is a thing you can build called an econimizer circuit that will make it use a lot less current, but you will have to google it to find out more.

If there are no ratings on your key switch there is no way to know if it will work with this contactor but to try it. I think since it came off the forklift it is likely to work just fine.

One thing you need to understand about a contactor is that it creates a huge voltage spike when you turn it off and the coil deenrgizes. This spike is across the switch and any electronics hooked to that circuit. The simplest way to defeat this spike is to add a diode across the contactor coil. By this I mean the positive and negative leads that turn the contactor on and off. If you are playing with the contactor and you turn it on and off by touching a wire to one of the leads instead of wiring in a switch, you will see a large spark when you disconnect the wire. That large spark is caused by the voltage spike. When you add the diode the spark will be greatly reduced or disappear all together.

If you look at the schematics for your Alltrax you will see that they include the diode across the contactor. This is to protect their controller from that large spike.

damon


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## BenNelson (Jul 27, 2007)

I looked through the Alltrax diagrams and used a diode and resistor as per their information.

Radio Shack had the right diode, but the closest resistor was for only half the resistance - forunately it was in a two-pack, so I just wired both in series!!!

I did not get a good closeup of the resistor and diode when I put this together this morning, but I did make a video!!!

The contactor is under the seat, next to the controller, behind the top two batteries.

http://www.youtube.com/watch?v=G0sUrXSU9Ok#GU5U2spHI_4


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## Damon Henry (Jul 26, 2007)

Very nice  That is exactly how it is supposed to work. Realize that the resistor they include in the diagram is a precharge resistor. It means that now your controller always has voltage to it even if you have the key off. The resistors limit the current, plus you should have the key switch signal hooked up, so the motorcycle can't actually move with the key off, but your controller leads are now live. 

They include this resistor to save the capacitors that sit at the front of the controller. When you just turn on a switch the controller momentarily sees a huge inrush of current as the capacitors fill up. This eventually wears the capacitors out and causes the controller to fail, so having this resistor is another good thing.

damon


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## Dennis (Feb 25, 2008)

> They include this resistor to save the capacitors that sit at the front of the controller. When you just turn on a switch the controller momentarily sees a huge inrush of current as the capacitors fill up. This eventually wears the capacitors out and causes the controller to fail, so having this resistor is another good thing.
> 
> damon



The resistor is not for protecting the capacitors, but instead is for preventing the contactor silver tips from pitting when they close shut from the sudden inrush of current from no charge on the capacitors. Pitting is very bad for the silver tips as they will start to lose contact surface area and get black as well. The end result is the contact tips will have an increase in resistance resulting in high heating and eventual complete failure. The repair kits for contactors are not cheap!!! So the resistor is money well spent versus the other option!


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## BenNelson (Jul 27, 2007)

I already had a seperate thumb switch for turning the controller on and off. This is on the right handlebar, in place of an original start/run/kill switch.

Because I have that resistor crossing the contactor, does that mean the cycle could be moved with the contactor open by just turning on the thumb switch and twisting the throttle?

If so, I will have to change some wiring a bit for safety and anti-theft.


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## Damon Henry (Jul 26, 2007)

Actually the resistor is there to save the capacitors. I'm not saying that is does not also help the arcing problem.

Electricity is often compared to waterflow and the inrush current slamming the capacitors is the equivilant of water hammer on the plumbing.

I guarantee you that if you blow up your controller and call Alltrax for a warranty replacement the first two things they will ask is if you had a diode or some other voltage spike supression across your coil and a precharge resistor. Of course Ben has both now, so the point is moot.

damon


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## Damon Henry (Jul 26, 2007)

No, the bike will not move because the resistor limits the current to just a few hundred millamps which is not nearly enough to make the motor spin. 

damon


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## Dennis (Feb 25, 2008)

In all my years of working with capacitors I have never blown one up as you say will happen when no current limit is used. Now I have seen contactors fail from arcing caused by capacitor current inrush...


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## Damon Henry (Jul 26, 2007)

Ahhh, there is the disconnect. I didn't mean to infer that the capacitors will be destroyed rather it shortens their life and the controller will fail prematurely. It's funny because in all the years I have been working with EVs I have never heard of the precharge circuit being for the benefit of the contactor, but I can certainly see your point 

damon


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