12/24V Switchover Relay - How does it work? (2 Viewers)

[96TrailSurfer]

Hi Everyone,

Could someone explain to me how exactly the 12/24V relay works based on the FSM wiring diagram.

As far as I can tell from the diagram:
1. + from the LH battery connects to the first (left hand) terminal on the 12/24 switchover relay and directly to terminal C on the starter
2. - from the LH battery connects to chassis and to the second terminal on the relay
3. + from the RH battery connects to the third terminal on the relay
4. the fourth terminal on the relay connects directly to ground chassis

So if the +12V from the LH battery is always connected to the starter, and the starter grounds to the chassis, what does the relay do to give 24V to the starter?

UPDATE: Looks like there is a major error in the FSM diagram I posted - the starter battery (LH) does NOT connect directly to chassis ground, it only connects to ground via the 12/24 relay.

- When the relay is off, LH- is grounded to chassis.
- When the relay is on, LH- is connected to RH+, thus putting them in series and creating 24V on the lead from the LH battery to the starter relative to chassis ground from the RH battery.

 

[AirheadNut]

It is a little hard to tell from that diagram, here is a post I made a few years ago that has diagrams from another manual that are a little easier to follow:
Post in thread 'HDJ81 24v Starting System Issues'
HDJ81 24v Starting System Issues - https://forum.ih8mud.com/threads/hdj81-24v-starting-system-issues.975039/post-12033740

 

[96TrailSurfer]

It is a little hard to tell from that diagram, here is a post I made a few years ago that has diagrams from another manual that are a little easier to follow:
Post in thread 'HDJ81 24v Starting System Issues'
HDJ81 24v Starting System Issues - https://forum.ih8mud.com/threads/hdj81-24v-starting-system-issues.975039/post-12033740

Looks like there is a major error in the FSM diagram I posted - the starter battery does NOT connect to chassis ground, it only connects to ground via the 12/24 relay.

When the relay is off, LH- is connected to chassis.
When the relay is on, LH- is connected to RH+, thus putting them in series and creating 24V on the lead from the LH battery to the starter relative to chassis ground from the RH battery.

 

[AirheadNut]

Yeah, that was confusing me too. The relay essentially switches the ground side of one battery from chassis ground to the positive side of the other.