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I would like to use a Cyrix-ct 12/24V 120A with a second battery that's also charged by a solar panel. The Cyrix is bidirectional, so a fully charged battery on a sunny day will also charge the first (starting) battery. Will both batteries be used if I start the engine in that situation? Will this effectively be a start assist? Obviously, I would want to do that with my AGM battery.
Hi Tom. In theory it might, but in practice likely wouldn't under heavy start load. But you can add an external 'start button' which will connect the two batts for 30 seconds, then open. See here..
https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-ct-120A-230A-EN.pdf
It's actually called "Start Assist".
Hi John, thanks for your reply. I allready installed a button that way but only intend to use it in an extreme situations as it will kill the AGM if you use it frequently. That’s why I’m asking about the scenario with a charging solar panel on the second battery. Would the car start on both batteries without me intitiating a “start assist”?
Yeh, all you can do is try it. A lot will depend on the size of your batts and the size of your start load. Pb's aren't noted for holding a strong V under serious load, and a start load will likely overwhelm any contribution from small pv anyway. How far the V sags will determine your success. I'm sure you've seen the literature, but I'll post it anyway for other peeps..
https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-ct-120A-230A-EN.pdf
A start button is a good idea, rather than a switch, which can be forgotten or bumped inadvertently. A 30 sec connection shouldn't cause much grief between standing batts, as the delta V should be minimal, and unlikely to transfer much Ah in that short time.
In practice, you may never be aware if both your batts are being used to start your engine, but if it won't wind over a quick push on that emergency button should fix it. Don't overlook cloudy days either, when the pv boost may be close to non-existent.
And oh, I may actually grab one of those gizmos for my own setup..
