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Old 08-18-2014, 08:50 AM   #1 (permalink)
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Installing main contactor in battery pack?

Hi again,

Just wanted to get some opinions on locating the cars main contactor at the battery pack.

I am hoping to be able to locate my battery pack at the rear of the vehicle in a removable single unit. The idea being that undoing a few bolts would allow the entire battery pack to be removed as a single unit.

So i was thinking, why not put the main contactor in this removable unit?

I see in many builds the main contactor is located in the engine bay. This seems like the most convenient location but when the contactor opens it still leaves the cables from the battery pack to the contactor live with high voltage.
If the contactor was co-located with the battery pack then when the contactor was open the high voltage would be contained to just the battery pack area.

Because i am trying to make the battery pack easily removed for maintenance. Having the contactor inside the removable unit means no hazardous voltages would exist outside the pack, making its removal much easier and safer. (provided the controllers capacitors had been discharged and the pre-charge resistor was switched not permanently connected)

I would also locate the pre-charge contactor and resistor in this removable unit.

So the removable unit would have positive and negative high voltage connections as well as low voltage main contactor and pre-charge contactor coil connections. The low voltage connector would also have the BMS communications circuit in it.

Bad idea?

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Old 08-19-2014, 03:18 AM   #2 (permalink)
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Bad Idea? I hope not! LOL!

That's exactly what I plan to do, for the reasons you stated. Seems like a pretty good idea to me.

I've already got the batteries ( 48 Nissan Leaf modules ) and the GigaVac contactors for that part of the job.

I especially like the aspect of NOT having over 400VDC live going from the back to the front with no control.

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Old 08-19-2014, 04:55 AM   #3 (permalink)
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FWIW, Honda Insight packs have a contactor (well, at least some kind of battery/ignition operated switch) halfway down the pack so it bears no charge when the contact is off.
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Old 08-19-2014, 06:39 AM   #4 (permalink)
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I think it's a good idea. The contactor & precharge relay control on your AC controller just requires a single wire running and returning to the contactor. Either the positive or negative line of the coil. It would maybe add another ohm to the coil, but that wouldn't hurt anything. And I think the coil wires are usually rated for 600v (at least on the tyco ev200), so you wouldn't need to worry about that. I just thought about how an EV200 uses an economizer... That means a high frequency signal on a long wire. I suppose you should twist the wire together as it runs to the controller & back to the contactor if you want the controller to turn it on. Or you could just flip a switch in the car to close the contactor.
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Old 08-19-2014, 10:07 AM   #5 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
I think it's a good idea. The contactor & precharge relay control on your AC controller just requires a single wire running and returning to the contactor. Either the positive or negative line of the coil. It would maybe add another ohm to the coil, but that wouldn't hurt anything. And I think the coil wires are usually rated for 600v (at least on the tyco ev200), so you wouldn't need to worry about that. I just thought about how an EV200 uses an economizer... That means a high frequency signal on a long wire. I suppose you should twist the wire together as it runs to the controller & back to the contactor if you want the controller to turn it on. Or you could just flip a switch in the car to close the contactor.
Just want to check my understanding of the economizer and how it works.
The economizer is a simple circuit that after the contact closes it basically switches the coil current on and off rapidly. So rapid that the coil doesn't have time to release between cycles and because the current is only on part of the time you get an overall reduction in power usage to maintain the closed contact. yes?

So this on and off cycling means that the wires feeding the current to the economizer is essentially an high frequency signal even though it is connected to a DC source.

If so then couldn't we just put a capacitor across the coil connection to charge when the coil current is off and supply the coil with current when the economizer turns the coil current on? So then the run of wire from the controller at the front of the vehicle is just a DC current. No high frequency signals.
It would mean a slight delay in the economiser opening the contactor when the DC supply is removed, but i wouldn't imagine it to be a lot. Probably only the time it takes for one economizer cycle at whatever frequency it is chopping the DC coil current.

Last edited by Astro; 08-19-2014 at 10:08 AM.. Reason: Spelling, doh.
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Old 08-19-2014, 10:40 AM   #6 (permalink)
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That's a good question. I don't know if a cap would work. That's my thinking of how the economizer works too. It would be PWM'ing into a capacitor, which might be hard on the transistor, but I'm not sure. Maybe you could add an R and then a C, so it wouldn't be as hard on whatever is switching?
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Old 08-19-2014, 11:01 AM   #7 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
That's a good question. I don't know if a cap would work. That's my thinking of how the economizer works too. It would be PWM'ing into a capacitor, which might be hard on the transistor, but I'm not sure. Maybe you could add an R and then a C, so it wouldn't be as hard on whatever is switching?
Sorry Paul i described that badly. What i meant was a capacitor on the DC supply to the economizer close to the economizer, not on its PWM output side. So that as the economizer alternated between drawing current and not the capacitor would be supplying current whilst the controller would be supplying a much more constant current to keep the capacitor charged. So the current from the controller would have only a small amount of ripple in it rather than an on off square wave.
That way there wouldn't be a high frequency signal on the long wire from the controller at the front of the vehicle to the contactor at the back of the vehicle.
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Old 08-19-2014, 11:08 AM   #8 (permalink)
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Oh, yes! I think that would be helpful. Wow, with all that stuff on the left, my really short responses take up a lot of space. haha
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Old 08-19-2014, 11:53 AM   #9 (permalink)
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Sounds good to me. I say locate the contactor as close as possible to the main power source.
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Old 08-23-2014, 09:06 AM   #10 (permalink)
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Thank you all for the input.

I will be locating the contactor in the battery area at the rear of the car.

I am glad nobody came up with a significant reason not to do this.

My batteries will be mounted under the vehicle where the petrol tank used to be so an easy and safe way to remove the entire battery pack is a must and mounting the contactors in the pack will make this possible.

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