Water Pump

[Olazz]

Guys, I have a 12v water pump that draws a Max of 3.5 amps.
It has no switch and I want to wire it to an auxiliary battery.

The question is, do I need to run it via a relay and switch or can I run it straight off a switched ciggy lighter plug?
If I do run it off a switch and a relay(direct to battery) any idea of the fuse rating I need?

Help greatly appreciated.

 

[Jon Wildsmith]

most ciggy lighter sockets should handle 3.5 amps ok. For a fuse then 5 amp gives a little head room and if that keeps blowing you know the 3.5 amp figure was wrong and the ciggy socket may not be so happy with the real figure in that case. If you hard wire it with a switch you could use a switch that can handle 3.5 amps (e.g. the popular Carling ones are rated 20 amps) and avoid the extra complication of a relay.

 

[Nuclear Chicken]

Most ciggy lighters are fused at 15 or 20A so should handle the 3.5A with ease. As Jon says a decent rated switch avoids the needs for a relay for that tiny load.