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Power to switch controller on

Posted: Wed Mar 18, 2020 5:41 pm
by Santacruz
I am just finalizing my build.
I am wiring in the 18F 8kw controller I bought a while back.
I have a pre charge system set up. It checks the circuit then charges the capacitors and then switches the relay for main power.
This is controlled from a 12v key switch.
My question is, can I use the relay power (when it switches on) to power the ignition switch of the controller or does this have to be powered first?

Re: Power to switch controller on

Posted: Wed Mar 18, 2020 11:58 pm
by PVadmin
Here is the recommended sequence:
1. Connect pre-charge circuit to charge the capacitors (have to be all the way up to the battery voltage, not just 12v or so)
2. Connect the main power (normally that would be the battery positive to the controller batt+ via a circuit breaker, relay, or such)
3. Connect the ignition to the battery positive to turn the controller on (ready to drive)

If the question is specifically whether you can connect the Ignition wire to 12v, instead of the battery voltage, the answer is No.
The battery voltage goes to via the ignition to the controller step down converter where it's reduced to 15v or so. This voltage is used to drive the mosfets and is further stepped down to 5v to power the low voltage electronics. Battery state of charge is also measured via the ignition wire so that the MCU knows when to shut off the mosfets on over or under voltage events. You want to power the ignition from the battery positive.
Santacruz wrote:
Wed Mar 18, 2020 5:41 pm
I am just finalizing my build.
I am wiring in the 18F 8kw controller I bought a while back.
I have a pre charge system set up. It checks the circuit then charges the capacitors and then switches the relay for main power.
This is controlled from a 12v key switch.
My question is, can I use the relay power (when it switches on) to power the ignition switch of the controller or does this have to be powered first?

Re: Power to switch controller on

Posted: Thu Mar 19, 2020 2:39 am
by Santacruz
Okay, thank you.
Sorry my post was not clear.
My set up is, 12v key switch to precharger. This uses a resistor to charge up capacitors. When charged, the precharger sends 12v to the relay, that then connects the battery to the controller.
My question is whether I could connect the ignition power to the main battery power that is switched by the relay.
So when the caps are charged up, the relay would supply full battery voltage to the controller and ignition wire.
I was just trying to avoid have 2 key switches.

Re: Power to switch controller on

Posted: Thu Mar 19, 2020 5:17 pm
by PVadmin
Yes, you can turn on the ignition together with the main battery. The voltage supplied to the ignition is the same as in the battery positive terminal. You may want to add a 1A fuse in line if the wire going to the ignition.

Re: Power to switch controller on

Posted: Fri Mar 20, 2020 3:57 am
by Santacruz
Okay.
Thank you very much for the advice.

Re: Power to switch controller on

Posted: Sat Mar 21, 2020 3:11 pm
by Santacruz
Sorry for all the questions, but one last one.

From the controller I have a yellow and red wire in a plug labelled ignition.
If I understand the wiring diagram, then the red is battery voltage from the battery supply to the controller and the yellow is battery voltage when connected to the red wire.
As the main supply on my build will switch the power on to the controller, can I, then just use a 1amp fuse to bridge the red and yellow ign. wire (Plug)

Re: Power to switch controller on

Posted: Wed Mar 25, 2020 2:34 pm
by PVadmin
Yes, you can do that.
Santacruz wrote:
Sat Mar 21, 2020 3:11 pm
Sorry for all the questions, but one last one.

From the controller I have a yellow and red wire in a plug labelled ignition.
If I understand the wiring diagram, then the red is battery voltage from the battery supply to the controller and the yellow is battery voltage when connected to the red wire.
As the main supply on my build will switch the power on to the controller, can I, then just use a 1amp fuse to bridge the red and yellow ign. wire (Plug)

Re: Power to switch controller on

Posted: Wed Mar 25, 2020 3:15 pm
by Santacruz
Thank you very much for the advise.