Where i need some advice is on the ignition live … I could easily connect up to IGN.. but the pump would immediately start drawing 50amps.. where can I find a 12v supply that is only live once the engine has been started ?
No really easy answer I can think of - maybe others can?
So, oil pressure, alternator voltage and engine revs are the obvious indicators that the engine is running and could be used as "sensors". Of these, the easiest solution I can think of would be to have a voltage detector on any available +ve battery circuit to trigger a circuit to operate a relay when the voltage is greater than ~13 volts, i.e. when the alternator is running. That's exactly what you want anyway, the 50A draw to occur only when the alternator is charging. You'd have to ensure the suddent 50A draw doesn't drop the voltage too much, else the trigger would oscillate on/off - maybe a Schmitt Trigger in the circuit would assist in preventing this. A bit of experimentation with the best trigger circuit and voltage setting might be needed.
Having done a bit of research, these "off the shelf" solutions would seem to have the functionality required:
A "Battery Protector" should do the job, (~£20), but is only rated at 10A, so an additional relay would be needed:
Link
Alternatively, this device, (~£30) would appear to do the job very neatly:
Other options:
This module, with the addition of a higher Amperage relay (or changout of the on-board relay);
Ebay link
Also, there are VSR's (Voltage Senstive Relays) that might do the job very simply. I've never used one but, technically, it looks as though it should do the job:
Link
There are programmable VSR's (PVSR's) too, with some built-in voltage trigger points:
Link
Plenty of cheaper PVSR variants on Amazon too:
Link
WARNING: All the (P)VSR's are designed to operate by connecting to a secondary battery and a load (such as your pump), but I can see no reason (from the published data) why these devices shouldn't work with just a load and no battery, but "AI" says a secondary battery is essential for VSR's to work.....
Some ideas to mull over
KIMI 1 : 1st Gen, "hybrid" 1983 silver S2 running gear in a 1985 S3 shell, SORN'd, long term resto project
KIMI 2 : 1st Gen, 1983 silver S2 - now sold to Ian Mothersole on here.
KIMI 3 : 1st Gen, 1983 red S3
Plus a 2004 Full Bridgeported RX-8
