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technomadia avatar image
technomadia asked

Cyrix-ct with two engines & starting batteries?

Our boat has two engines - and thus two 8D starting batteries and two 12V alternators for charing them.

There is a battery bridge relay that can combine the two starting batteries to help start the engines - but it is non-functional.

Rather than replace the old relay - would a Cyrix-ct or Cyrix-i do the job?

Is there any downside of using it in this configuration? All the documentation I have found is focused on combining a starting and a house battery - but is there a reason not to use it for two starting batteries?

I like that if one alternator fails - the other engine's alternator will still be able to charge both starting batteries this way.

And at some point soon I plan to replace one of the 12V alternators with a 24V alternator for charging the house battery bank. Once I do this, the single remaining 12V alternator should be able to charge both starting batteries easily through the Cyrix.

Is there any downside to doing this?

Thoughts?

- Chris

Cyrix Battery Combiner
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boekel avatar image boekel ♦ commented ·

I don't see any reason to do this as that, just use a manual combine switch, it will only have to be used when something is wrong, and if that's the case you have to 'dive into it' anyway.

When charging both batteries from one alternator than it can make sense, but if you have a voltage compensating option I'd just use a diode bridge (less things to go wrong)

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technomadia avatar image technomadia boekel ♦ commented ·

What do you mean by having a voltage compensating option?

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boekel avatar image boekel ♦ technomadia commented ·

sorry that is basic electrical knowledge..
your chargers (alternator in this case) should measure at the battery terminals what voltage is at the battery, so it can compensate for voltage drop in cables and diode bridges.

there are also low voltage drop devices but a little more expensive. (or indeed use a relay)

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technomadia avatar image technomadia boekel ♦ commented ·

I thought that was what you meant - but with two alternators and two start batteries I'm not really sure how that could be set up now in a way that would continue to work well with only one alternator.

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2 Answers
Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·

Having the Cyrix between two starter batteries makes sense!, the advantage over a diode slitter is that the Cyrix relay works in both directions and is practically free of losses. Beside this there is even a start assist function which would help start on " both" batteries.

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agocorona avatar image
agocorona answered · 
Hi Jo, how do i check the start assist? do you have a different scheme from that of the Victron manual?
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