use a relay to switch power source

A

adambryan

Member
Im working on electrics in the van.

i want to use a relay that will flip between the engine when its on and then a portable power supply when its off.

I've got these relays and gave it a try but it didnt work :( has anyone done anything similar and if so how?
 
What do you want to switch?

12v from engine and 12v from power pack?
 
1658218068780.png


So you'd need to run an ign. feed wire as well..

So the leisure and starter batteries are (With suitable fuses, each end!) connected to one of the 30A - The top (07a) would be Leisure and the bottom (07) would be Starter.
When +12v is detected on 08 (Engine running) the relay switches the 30A to run off the Starter (07).
The downside is you'll need to charge the Leisure up as it won't charge from the system.

*Top tips*
Adequately fuse the cable! each end - no-one likes a van fire
If the Leisure battery gets too 'low' you'll start blowing fuses from the inrush current when it switches.
 
Last edited:
G00seman said:
View attachment 165714


So you'd need to run an ign. feed wire as well..

So the leisure and starter batteries are (With suitable fuses, each end!) connected to one of the 30A - The top (07a) would be Leisure and the bottom (07) would be Starter.
When +12v is detected on 08 (Engine running) the relay switches the 30A to run off the Starter (07).
The downside is you'll need to charge the Leisure up as it won't charge from the system.

*Top tips*
Adequately fuse the cable! each end - no-one likes a van fire
If the Leisure battery gets too 'low' you'll start blowing fuses from the inrush current when it switches.
Click to expand...
Hi, thank you this is really clear.

I've presently got one wire from the fuse box running on the acc 12v.
As I only want it to take power from the front when the engine is on, could I run that feed to both the lives you've drawn as 07 and 08.
The 7a as the jackery type pack?

What fuse value do you suggest too
 
@G00seman has you covered.

Remember to use cable big enough for your loads. Ie 2.5mm/4mm (account for length)

Fuse all battery conections with suitable size fuse to protect the cable. Ie 10-30A


Use a suitable rated relay for the purpose.... Ie if your loads are 15A then use a 30A relay.
 
If you used the portable power pack & just left it plugged in to the van, when the van was running it would charge, & and when it wasn’t it wouldn’t. Sort of does what you want it to do automatically, unless I’m missing summat.
 
Salty Spuds said:
If you used the portable power pack & just left it plugged in to the van, when the van was running it would charge, & and when it wasn’t it wouldn’t. Sort of does what you want it to do automatically, unless I’m missing summat.
Click to expand...
This relies on you remembering to unplug it every time you turn the engine off, otherwise it'll drain the Starter (including during Start/Stop)

With the split system it uses the alternator (to indirectly provide power) through the Starter battery whilst engine is running and then clicks back over to Leisure when it's off with no danger of draining the Starter (as OP asked).

As you say, you could use the Alt. through a DC/DC to charge the leisure, but that's a different (and more costly/complicated) scenario. (I went from the relay to/split to a DC/DC - needed to run a bigger cable to handle current etc. ) I reused the relay as a remote power switch for the inverter, so I could tuck it under the seat (it has a fan and I didn't need it running continuously)
 
Last edited:
@Dellmassive @G00seman
thanks guys could just do with knowing if i can run the 12v accessory circuit feed from the front on the one cable currently installed to both the ignition and 12v supply lugs, and the leisure to the other.

I only want it to be on when the engine is on to at least acc or alternatively taking feed from the pack, dont need to charge it there as will plug it in somewhere else as needed.

Thanks again
 
G00seman said:
This relies on you remembering to unplug it every time you turn the engine off, otherwise it'll drain the Starter (including during Start/Stop)

With the split system it uses the alternator (to indirectly provide power) through the Starter battery whilst engine is running and then clicks back over to Leisure when it's off with no danger of draining the Starter (as OP asked).

As you say, you could use the Alt. through a DC/DC to charge the leisure, but that's a different (and more costly/complicated) scenario. (I went from the relay to/split to a DC/DC - needed to run a bigger cable to handle current etc. ) I reused the relay as a remote power switch for the inverter, so I could tuck it under the seat (it has a fan and I didn't need it running continuously)
Click to expand...
If you used an ignition fed feed e.g. dash cig socket, it would only charge when the van was running. You already have the capability to do what you need to do, built into the van.
 
adambryan said:
sorry to pester you, but can you confirm the answer to my question about using one 12v feed from the acc fuse row to power both the lugs you identified needing a 12v supply from the front. Thank you
Click to expand...
Yes that would be fine, provided the cable is correctly fused.
 
Hi again, so for some reason, this is causing various fault codes when the piggy back fuse is plugged in to all the spares on the ACC rail.
Its been in there for about 14 days already but started this caper today. Not sure why at all.

Im thinking about getting a split charge instead.

Whats 'best' for the 6.1?
 
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