Cyrix-ct - which model for lead/acid starter and gel leisure combo?

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eat asked Jan 4, '19

Cyrix-ct - which model for lead/acid starter and gel leisure combo?

Hi, I have an almost all Victron system in a large truck:

- 1 kw 6 panel solar array (2 parallel banks of 3 panels each)

- Victron MPPT 150/35

- Victron C24/1200/25 Inverter/Charger

- Leisure Batteries: 2 x Victron Gel 220AH / 12v in series (24v)

- Chassis/Starter Batteries: 2 x 130AH lead acid 12v in series (24v)

- Alternator is rated 90A

- Complete system is 24v

- Remote interfaces and Victron battery monitor

I now wish to add a Cyrix-ct to interconnect the leisure and starter/chassis battery banks, primarily so that solar/shore power will top up the starter/chasis battery when parked up for a while.

Questions:

1) Is the Cyrix-ct OK for use with this combination of lead/acid starter/chassis and gel leisure batteries?

2) Which rating of the Cyrix-ct should be used?

3) Are there any issues (e.g. sensing voltage drop) if the Cyrix-ct is mounted within 0.5m of starter/chassis battery but the lead to leisure battery bank is aprox. 2.5m?

Cheers:)

AGM Battery Cyrix Battery Combiner

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Answer 1 · 2019-01-04T22:04:51Z

wkirby answered · Jan 04, 2019 at 10:04 PM

Your MultiPlus Compact has the ability to support a starter battery. Inside is a terminal for connecting a second battery (Max 4A). This is specifically designed for keeping a starter battery topped up whilst on shore power, it will not use the starter battery for powering loads.

You could forget the Cyrix and use this functionality instead.

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eat commented · Jan 05, 2019 at 07:42 PM

Thanks, I had forgotten about that and it would certainly be an option for when I have shore supply. However, the reality is that I am often without a shore shore supply but in locations where I have plenty of solar energy and want to use the energy from that to top up the starter battery when I am not moving very much.

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wkirby ♦♦ eat commented · Jan 05, 2019 at 08:32 PM

The Cyrix-ct is bidirectional, so the truck's alternator could end up charging the leisure battery.
If you only want energy to go in one direction, from Leisure to Starter then perhaps the ArgoFET 100-2 is for you.

1) I don't think it's a problem to go from Leisure -> Starter batteries because you only want to top the starter batteries up.

2) I can't see you needing more than the 120A version in day-to-day use as long as the starter battery is not dead.

3) The cable lengths won't be a problem, just as long as the cable is sized correctly.

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Answer 2 · 2019-01-07T22:18:51Z

eat answered · Jan 07, 2019 at 10:18 PM

Thanks for the additional suggestion of the ArgoFET - all of the literature looks like it is really intended for Starter battery > Leisure battery setups and not the other way around. Do you know if it limits current flow leisure > starter (if connected in that arrangement) to ensure that when engine starting I am not drawing current from the leisure batteries? I know I could add an isolating switch between the starter battery and the Argo but then I would have to remember to operate that manually when parking/starting.

In principle, I like the idea of a battery combiner but what always concerns me is that the alternator (I have an old large truck with brute force alternator) may well run up to 14.8v whereas the maximum for the very expensive gell batteries is 14.2v; and in float just 13.8v . It's a pity that there is not a battery combiner with settings for different battery types on each connection.

BTW, I used 12v examples above even though my system is 24v so double all of those numbers.

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