Wiring a relay

[Phil_D]

Hi guys, im adding a water pump into my van and have already run a two core cable from the battery to where the switch will be and from the switch to the pump.

Just realised the little 12v switches you get have pretty pants amp ratings so i will probably need to use a relay so the switch doesnt burn out. The max draw of the pump is 4.5a.

I've not messed about with relays before but it seems you need power from the battery to the relay, and also a power supply to the switch... as a lot of my units are now installed in the van running an additional cable will be a pain. Thinking about just splitting the power cable thats already there with a 3 way wago with one leg going to the switch and the other to the relay - Is anyone here all over this stuff and know if this is an acceptable way to do it?

 

[Anguz]

perfectly acceptable just put a suitable fuse at the battery end

 

[Beanwood]

How far is the switch from the pump, and is it easy to run a single wire between the two?

 

[Morrisman]

If you’ve already run the wire, heavy enough to power the pump, the relay can go anywhere really. It can be powered from the heavy wire to the relay, with just a light wire from the switch to activate it.

 

[Phil_D]

If you’ve already run the wire, heavy enough to power the pump, the relay can go anywhere really. It can be powered from the heavy wire to the relay, with just a light wire from the switch to activate it.

Nice, yeah it’s a 4mm2 cable so I’ll just run a small cable off that to the switch with a 3a inline fuse. The cable will be fused at the batter end but it’ll be too big to protect the small cable to the switch

 

[Phil_D]

How far is the switch from the pump, and is it easy to run a single wire between the two?

Not easy now the wall panels are on and units are in!

 

[Phil_D]

perfectly acceptable just put a suitable fuse at the battery end

Smaller online fuse needed just before the switch too though right? The fuse at the battery end will be rated too high to stop the smaller cable to the switch getting fried

 

[Anguz]

You could but if its only 4.5amp pump, wont be a big fuse feeding it all? depends how long and how small your switch wiring is

 

[Phil_D]

You could but if its only 4.5amp pump, wont be a big fuse feeding it all? depends how long and how small your switch wiring is

Maybe, fuse board isn’t sorted yet but whatever size goes in there isn’t going to protect the cheap switch I’ve got that’s probably only rated to 3a.

Switch wiring may only be 30cm or so, I’ll have to see what size wire I’ve got left but probably either 1 or 2.5mm (pump wiring is 4mm)

 

[gaz1]

Hi guys, im adding a water pump into my van and have already run a two core cable from the battery to where the switch will be and from the switch to the pump.

Just realised the little 12v switches you get have pretty pants amp ratings so i will probably need to use a relay so the switch doesnt burn out. The max draw of the pump is 4.5a.

I've not messed about with relays before but it seems you need power from the battery to the relay, and also a power supply to the switch... as a lot of my units are now installed in the van running an additional cable will be a pain. Thinking about just splitting the power cable thats already there with a 3 way wago with one leg going to the switch and the other to the relay - Is anyone here all over this stuff and know if this is an acceptable way to do it?

i really dont see the need for you to use a relay from the switch to the pump

a switch would be just fine for what you want when is needed even with the caravans or homemade camper vans that switch to pump the water from the tank to your sink is ample enough and no relay is used inbetween

with like the caravans side of it an isolater switch is better to be considered when in transit to shut off all apliances when in transport

 

[Phil_D]

i really dont see the need for you to use a relay from the switch to the pump

a switch would be just fine for what you want when is needed even with the caravans or homemade camper vans that switch to pump the water from the tank to your sink is ample enough and no relay is used inbetween

with like the caravans side of it an isolater switch is better to be considered when in transit to shut off all apliances when in transport

Not quite, the pump can draw 4.5a and the amp rating of the switch I have is unknown but likely 3a which means it would burn out quickly.

I could go out and get a different switch but Halfords sell a relay for £5 that will do the job by the looks of it

 

[gaz1]

ok then then this should help you out this is the caravan wiring way for you with relay

https://www.eribaforum.co.uk/mwf/attach/42/1242/Pumptaprelayfittinginstructions.pdf

 

[Beanwood]

If you want to excuse the drawing then this should work.
You can run contact 30 from the cable already running to the live (unswitched) side of the switch

 

[Phil_D]

If you want to excuse the drawing then this should work.
You can run contact 30 from the cable already running to the live (unswitched) side of the switch
View attachment 449837

Thanks mate! I’ve actually gone for option B, all bench top tested and working fine