Fra avatar image
Fra asked

Fuse for Start assist on cyrix relais...

Good morning, I would like to know which fuses and cables dimensions I need for THE START ASSIST function on cyrix relais 12v 120 amper. If I got a exhausted start engine battery, a lot of current will pass through it.

Now I got four 50 amper fuses on the positives of the three batteries (1 engine and 2 services) and on cyrix..... I'm worried thei will broke, if I start engine with Start assist function.

Thank you for your answer.

Cyrix Battery Combinerstarter battery
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1 Answer
Paul B avatar image
Paul B answered ·

As long as the total load does not exceed the stated capacity of the relay you are ok, if it does then a bigger relay would be needed

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hejira avatar image hejira commented ·

I have similar concern to Francesco. My yacht service bank has 315 Amp capacity (3x105 A batteries) and my Cyrix-ct 120 is protected by a 120A fuse. I don't know how many Amps the starter motor draws when firing up the engine. Starter motor is rated at 1.4 Kw, which equates to 116 Amps. But I believe that electric motors draw many times their running amps when they first start. My service batteries are each rated at 800A for instantaneous power during engine cranking (My starter battery is similar). So, if the starter takes more than 120A, the Cyrix fuse will blow. Is this correct?

Would top of the range 400A Cyrix model even be OK, with the instantaneous load it may see during starting? The 400A model is 5 times the price of the 120A (which I already have), So I would need some hard evidence to consider using start assist.

What would I need for my system?

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