one relay per coil?? or run em both off one??

[jhicok]

i'm gonna use some 30-40 amp bosch style relays to hook up my new dyna green 3ohm coils when they get here... should i relay them individually or together??? i was thinkin together to make sure they always have the same voltage no matter what.. but i was wondering what others thought. i'm also going to put in an inline fuse to this relay. should i use the same amperage fuse as is in the stock box for the ignition circuit or go a bit bigger?

[tkent02]

One relay is plenty, two would give you a spare should one fail. No likely with the Bosch relays, I have been using them on things like this for decades and none have ever failed. Of course an extra relay tucked under the seat someplace gives a spare too.
The original fuse size is fine, isn't it ten amps?

[Steve]

With a three-ohm coil in a 14-volt circuit, each coil will be handling 4.67 amps.
Running both coils off the same relay will draw 9.3 amps through the relay contacts.
WELL within the 30-40 amp rating.

Yeah, one relay is plenty.

By the way, five-ohm coils will draw 2.8 amps each, for a total of 5.6 amps.

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