Power pick-up: Best options?

Humpty · Post by **Humpty** » Mon Dec 07, 2009 9:16 am

As the title suggests....

What's the best source for powering the EDIS/MJLJ set-up?

My recently started set-up (air cooled VW) is getting it's power from the ignition wire that went to the positive side of the OEM coil...

Is this a suitable source or should I be looking to hook into a stronger, more direct source of power?

Cheers in advance...

spitfire50 · Post by **spitfire50** » Mon Dec 07, 2009 12:15 pm

Humpty,
On my installation I used the old ignition switched wire to operate a relay, and supplied the contacts from a separate source that is more directly fed by the alternator and battery.
Cheers, and hope this helps,
Paul

Humpty · Post by **Humpty** » Mon Dec 07, 2009 12:54 pm

Yeah it sure does Paul.... I think that's a really good idea.... I was thinking about fitting a fuel cut-off in there also... So the relay idea is working for me.... Now to remember how to wire in a relay!!!!

NITROPIXIE · Post by **NITROPIXIE** » Mon Dec 07, 2009 7:43 pm

There is no need to add a relay to power the EDIS, coil pack or mjlj. The amount of current which the mjlj, edis and coil pack draws will be approx the same as what the original coil did. Its probably better not to power the ignition from a relay as there will be less chance of a break and/or interference.

I would suggest using a relay to switch a fuel pump as they can sink quite a bit of current.

To contradict what i have just said in the top paragraph, if you supply power to the fuel pump and ignition at the same point ie a relay, then if the circuit should fail then you wont get a dangeously lean event as you would in the top circuit if you still had ignition and no fuel. However this crcuit could cause interference from the fuel pump to the ignition system.

Just some points to consider.

DannyP · Post by **DannyP** » Tue Dec 08, 2009 2:43 am

Nitro, you could use two separate relays triggered from the same source, no? All the power comes from the same place anyway, I don't think it matters too much.

I used the old coil power for two relays, one for EDIS/Megajolt and another for the coil. The whole shebang is powered by a 10 gauge wire fused at the battery. Overkill I know, but my ignition works GREAT. My fuel pump is up front on a separate circuit (rear mid-engine, tank in front).

alexander · Post by **alexander** » Tue Dec 08, 2009 12:30 pm

on the subject of fuel cut off relays.. i realise there are several ways of achieving that, but the one i chose is to buy a safety relay intended for lpg installations. they are on while there is a regular pulse from the LT coil trigger wire, but shut off if that stops for more than about 2 seconds.

NITROPIXIE · Post by **NITROPIXIE** » Tue Dec 08, 2009 7:44 pm

Alexander yes the tachyometric relays are very good for this and is a very good idea for safety's sake. You also get a fuel pump prime when the ignition is turned on with some of them.

A fuel pump output on the megajolt would be a really good idea and would replace the need of a tachyometric relay. I bet with a bit of reprogramming one of the current outputs could do this.

Dannyp, yep no problem having 2 relays, but like you said just a little overkill.