Additional security device

Right, this was suggested in a fred a bit back and i wanted to confirm your thoughts on the idea...

I bought a really cheap 40A resettable 12v trip (£2) off fleabay. I have an isolator switch in the battery box. If i fit the trip in parallel to the isolator, am i right in thinking that with the isolator switch "on", the trip will be OK but if the isolater is "off" the power required for the starter will trip the resettable trip to the Off position if someone tries to hot wire it?

The reason is purely so the stereo doesn't forget all the chanels and settings i've put in when i take off the isolator switch!

Will this work - does the starter take enough power to trip it when the isolator is "off" and will the trip be completely bypassed when the isolator is "on"?

yes, it will be fine.
you don't need a 40A one though - 2A will be enough.

yu really wanta double pole switch, so that it isolates the trip when "on"

Treworgey 90 said:

yes, it will be fine.

you don't need a 40A one though - 2A will be enough.

Click to expand...

I figured, only the 40A one was incredibly cheap (£2 delivered to me door!) and was all there happened to be on fleabay when i looked so i bought it! Any idea how many watts the average starter motor uses on a cold startup?

150-200a

you always like to comdooleekate fings dunt yer Daft?

The Mad Hat Man said:

yu really wanta double pole switch, so that it isolates the trip when "on"

Click to expand...

and if i don't have one is there a danger that the resistance of the isolator might cause the trip to trip anyway?

odenne said:

and if i don't have one is there a danger that the resistance of the isolator might cause the trip to trip anyway?

Click to expand...

I don't think so!

Why not try it? - easy enough.

it is possible that current will be drawn through both the switch and the trip - and will trip the trip . the ideal way to do it is to switch between the trip and the devices, with the common to the battery, but if you cant - try it and see. if the trip keeps popping, you know why - if it dont, yu is OK.

odenne said:

Any idea how many watts the average starter motor uses on a cold startup?

Click to expand...

Mr Ohm says that P = V x I so assume 200A x 12v = 2.4Kw

but you'll find that the transient power requirement during startup will often be many times that hence the need for batteries with CCA ratings in excess of 500-600A

i concur entirely with Mr shawn