Looking at fitting the Cyrix-ct 12/24V-120A Battery Combiner to charge the trolling motor battery on my boat. The starting battery is a sealed expanded calcium, the trolling motor battery is a 120ah AGM and the engine's alternator puts out 16 amps.
Will this combination work to keep my batteries charged?
I'm currently using a basic VSR which continually switches while running the engine. Will the Cyrix-ct 12/24V-120A Battery Combiner solve this problem?
Thanks
Cyrix is a VSR so what do you expect to be different?
As per the Cyrix-ct manual, there is no voltage loss as the Cyrix-ct battery combiner automatically connects batteries in parallel when the battery reaches a preset voltage and also disconnects when the voltage is below float level. It also has intelligent battery monitoring to prevent repeated switching.
Hence my question...
Hi @Leezor, welcome to the Community!
Unfortunately that's not quite so simple to answer.
The Cyrix-ct is a VSR, albeit smarter than your average VSR, but if your start battery isn't reaching and staying above the Cyrix's connect voltage threshold (~13.3v), then the Cyrix likely won't behave much differently than your existing VSR.
Most likely what you see currently happening is your start battery reaching the "connect" voltage of your existing VSR, so it closes and joins the two banks together, then the load presented by the depleted trolling battery drags down your start battery voltage to below your VSR's "disconnect" voltage, so it opens, the start battery voltage rises without the trolling battery load on it, the VSR connects again, and so on.
While the Cyrix is microprocessor-controlled and has several intelligent features to prevent "fluttering", and while these features may be enough to prevent this same scenario from occurring when using it, the reality is that how precisely it will behave depends on a number of circumstances which are not really possible to quantify beforehand.
Long story short, you would be better advised to look into upgrading the alternator, if possible... or you could look into a splitter/isolator like the ArgoFET. There, however, you run the risk of burning up your alternator by putting too high of a load on it, asking it to charge both batteries at once, so yes, ultimately the best solution here is to upgrade the alternator or add an alternative charging source to the trolling battery, such as a solar panel and controller, that would keep it mostly charged so that when your VSR combines your two batteries while underway the trolling battery doesn't present such a significant load to the start battery and they can both receive their top-off charge from the alternator.
Thanks Justin, appreciate your detailed response. Unfortunately upgrading the alternator is not an option on small outboard engines.
Will keep an eye on it, have the same set-up on 3 different boats and it seems to operate ok if I give the 120ah AGM a good charge with my 240v charger every few weeks.
Thanks again
