# Wiring theory for Contactors, DC-DC Conv., Charger



## hallkbrdz (Jan 2, 2018)

Here are my thoughts....



> The first one shows a contactor on each of the HV cables while the other uses it only on the positive cable. Why? It would seem that having dual contactors would create a backup cutoff in case one contactor fails. Yes?


If the contactors are sized appropriately using only one should not be a problem. Yes, a second one does provide redundancy, but so does a manual shut-off switch or battery disconnect.



> Why does one diagram use sequential contactors? It seems the second contactor only serves to enable HV to the DC-DC converter. Why wouldn’t you just connect the converter’s HV lead to the switched side of the contactor (same as controller lead)?


The BMS should drive the contactors, but for some reason neither of these diagrams include a BMS. In the case of an Orion2, you supply system voltage (~12v) and then it looks to make sure the battery is in a good condition. If so, and the system is set to "on", then the contactor will be shut and will apply voltage for the motor controller and/or DC/DC converter.[/QUOTE]



> Connections; one diagram uses the contactor’s studs to connect multiple wires while the other uses the shunt. Does it make any difference If I connect two or three wires to a stud, whether that stud is on a contactor, shunt, or stand-alone?
> And, shouldn’t all positive legs be fused?


I would personally not connect more than one thing to the studs and would use a connector bus. However it probably just shows it in a notional way. You can fuse either the negative or possitive legs, it makes no difference for HV since the frame is not used as ground.

Bryan


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## Jb24601 (Aug 29, 2019)

If I may continue this discussion about wiring theory;
Is there a best practices for connecting the pieces in this discussion; the DCDC converter, the HV pack, the Charger, contactors, shunts, fuses, etc?
Are there Do's and Don'ts?
For the sake of discussion, I submit the following pictures of three schematics I found for DC motor systems. (I think this will apply to AC systems also, but I'm not an AC guy). Please allow that cutoffs, fuses, etc. have been omitted for this discussion.
They are similar, but different. Is one better than the other? Why?
Let's assume that in all examples the contactor on the positive leg is closed on the start input. In example A, start closes the only contact. In example B, start only closes the positive leg, the other contactor is separately switched. In example C the start input closes both contactors.
Thank you for your comments.


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## hallkbrdz (Jan 2, 2018)

Maybe this will give you some ideas. This is how the various systems are being installed for my racing kart using an Orion2 BMS and Kelly controller. I only use one contactor. The charger is off board.


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## Tremelune (Dec 8, 2009)

The short and long answer is that it depends.

The purpose of the contactors is to prevent fires and electrocution. You want the long leg of the wiring to be "off" unless you're driving (and maybe charging). It will depend on the location of your batteries and motors; how and where you wire it.

I don't believe there's a great need to switch both positive and negative, but I did on my build because I used Leaf contactors and they were already there...The important bit is breaking the circuit.

I have my charger connected directly to the batteries because they're both in the same location. This means I can charge without having to juice up the big wires to the engine bay. I don't think it matters all that much, and probably depends on your component locations more than anything. If your batteries are liquid-cooled, you'll probably want the contactors on and DC/DC running.

With regard to where to connect the DC/DC converter...I have mine wired to only be on if the car is driving, because there's no real benefit to having the car "off" if you're using the DC/DC...In other words, if I'm just sitting in the car listening to music or enjoying heated seats, why not have the water pump running, too?

Here's what my setup looks like...I have the batteries and charger in the back with the inverter, motor, 12v battery, and DC/DC in the front engine bay:


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