LocostUSA.com

Reposting a question that "Disappeared" last night.

For a non-Locost repair I need to be able to drop 24v to 12v to power an MSD-6 box or even conventional ignition.
So I've bought a unit to do that.
In order to be able to turn the engine off I need to be able to also switch another lead from the same 24v/12v source for the coil to distributor.
I will have 24v coming from the ignition switch.
I must feed 12v to the coil, and be able to disconnect that to shut off the engine.
It seems a relay should be able to do this, or will the mixed voltage be an issue?

I've never been able to locate my reference book for this sort of question since I moved house about a year ago.
Web search did not help, but I'm certain the experts here laugh at my trivial ignorance and will take pity on me to provide an answer.

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If I must be a one-man PC free zone, so be it!

All you need to do is make sure you have a relay rated for 24V on the coil.

The contacts will be able to interrupt the 12V just fine.

A quick look on Amazon has this pop up, but I know you can get 24V "heavy truck" relays pretty cheap elsewhere.

https://www.amazon.com/dp/B07QPF86XG
https://www.amazon.com/dp/B073TY88MN

As far as pins, 24V switched to the coil on 85 and 86, then 12V to 30 and your load to 87.

I had an answer all written out before today's reboot.

Coils and contacts in a relay are generally isolated from each other. Mixing the 12V and the 24V circuits are acceptable. Assuming you are interrupting the 12V output of the converter, You could add a series resistor to the 12V coil in the relay and feed it the 24V. Size it the same ohms as the coil. That will drop the voltage seen across the coil to 12V. Make sure the wattage of the resistor can easily handle the E^2/R or ~169/resistance.

But I like 300D50's answer better. It will be controlled by 24V and easily handle either the input to the 24-12V converter or it's output. Just don't confuse it with a 12V relay if it ever fails.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Bosch, #0332019203

$7.00 at summit racing.
I will buy a spare too!

Now if the voltage drop device would just show up I might have my Rover running again.

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If I must be a one-man PC free zone, so be it!

I like. Ten times better, and priced well within range.

If you are running two 12v batts, why do you need a drop?

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Because just tapping one battery is bad form, it WILL damage the battery over time.

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If I must be a one-man PC free zone, so be it!

Who said anything about using one battery? It can be done by isolating the 12 and 24 grounds but it is simpler and easier to go with a drop. You connect the 24v and 12v positives together but ground the 12v bits between the batts.

Bad form or not, you could use one batt if you switched the battery leads regularly to balance but that would be a hassle/extra mx.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12