Zilla FAQ23 Dec 2007 12:14 pm

Some people choose to use one contactor to break the B+ lead to the controller in the usual way plus a additional contactor to break the B- lead of the battery pack for extra redundancy or safety. By the way, this is one way to turn off your DC-DC if you choose to wire it to turn off with the key. A few things are important in this case:

1) The B+ contactor must be wired as shown in the Zilla diagram and must use a snubber diode. Preferably it would use the snubber diode that came with the Hairball.
2) The B- contactor must be on before you try to “start” the Zilla using the start input on the Hairball. I suggest doing this by having the B- contactor turn on with the “ignition on” power that also drives the Key input on the Hairball. Be sure that you do not use the Accessory lead on your ignition switch as that will not work correctly since it drops out when your ignition key is turned to the start position.
3) In this case you must wire the Hairball Start signal separately to your start wire. You must not use the option of wiring the Start in parallel with the Key input or it will keep the Hairball from performing the start sequence correctly.
4) You should have some form of snubber diode on all contactor coils to avoid damaging other parts of your electrical system. In this case the one on the B- contactor could be any type. Albright contactors often come with a diode and that one would be fine for this use.


2 Responses to “How do I wire a second contactor into the negative lead of a Zilla system?”

  1. on 25 Apr 2008 at 10:03 pm Doug Weathers

    Hi Otmar,

    Could you elaborate on using the B- contactor to turn off the DC-DC converter? This sounds like a good idea.



  2. on 29 Apr 2008 at 1:01 pm Otmar

    Hi Doug,
    The way to control the input power to your DC-DC converter using the negative contactor is to connect the DC-DC input on the B- connection of the Zilla, and the positive DC-DC input to the positive connection of your battery pack. It is important that the positive connection is not on the Zilla as that would overload the precharge circuit of the Zilla.

    One more thing to watch out for is that many DC-DC converts will put a small load on the 12V side of the system even when they are off. This load can drain your 12V battery faster than the Hairball by itself would and therefore may require yet another relay to turn it off. I myself leave my DC-DC on 24/7 and have it set for 13.8V float charge on the SLI battery.
    I hope this helps,