LadyInBed
Well-Known Member
So do I, fit and forget.
Solar Power to charge two batteries
- Thread starter dolabriform
- Start date
lampshuk
Well-Known Member
Hi, Paul.
Sorry: took my eye off the ball on this one.
My setup is 2x "hybrid" 110Ah lead-acid household batteries (cheapos from Battery Megastore or some such, with 80A claimed CCA).
I use them on "Both" for starting and charging (engine or mains so far) and "1" or "2" depending on the date. The idea being to age them somewhat symmetrically.
If I designate one permanently as "engine" (as the smarter gadgets like the Cyrix assume) I am effectively halving the household battery capacity.
Long term I need to re-arrange. Right now the batteries are within 3 feet of the engine start motor, but for some reason that must have seemed good to the designers, the battery switch is under the chart table on the opposite side of the boat, so there's about 12 feet of unnecessary cable run to the switch and back to the starter. Instead of doing that I may try to figure out where to put a dedicated start battery, but that is a much more difficult undertaking.
Drifter's battery use is quite low (eg no fridge or radar), but with more extensive use of the autopilot I think I will soon be down to 2 or 3 days capacity at most, hence the need to get more serious about solar.
Sorry: took my eye off the ball on this one.
My setup is 2x "hybrid" 110Ah lead-acid household batteries (cheapos from Battery Megastore or some such, with 80A claimed CCA).
I use them on "Both" for starting and charging (engine or mains so far) and "1" or "2" depending on the date. The idea being to age them somewhat symmetrically.
If I designate one permanently as "engine" (as the smarter gadgets like the Cyrix assume) I am effectively halving the household battery capacity.
Long term I need to re-arrange. Right now the batteries are within 3 feet of the engine start motor, but for some reason that must have seemed good to the designers, the battery switch is under the chart table on the opposite side of the boat, so there's about 12 feet of unnecessary cable run to the switch and back to the starter. Instead of doing that I may try to figure out where to put a dedicated start battery, but that is a much more difficult undertaking.
Drifter's battery use is quite low (eg no fridge or radar), but with more extensive use of the autopilot I think I will soon be down to 2 or 3 days capacity at most, hence the need to get more serious about solar.
PaulRainbow
Well-Known Member
That's bad practice, all of the time the switch is on both your batteries are in parallel and susceptible to be discharged, leaving you with no way to start the engine.
The Cyrix will not know, or care, what label or designation you have given a battery, it will just ensure that both batteries get charged from whatever charging source you use. The solar controller, connected to one battery will charge both, the alternator connected to the other battery will also charge both. Even leaving the 1-2-B switch in place, this is still an upgrade, as both batteries get charged without any user intervention, removing the risks associated with leaving the switch on "both".
If you are alternating batteries in normal use, i don't see how keeping one just for the engine halves the domestic capacity, unless you are currently using both batteries, which is really a bad idea.
You do need a re-think, but i wouldn't necessarily get hung up on the battery switches being where they are. If the cables are suitably rated it won't matter. Having a small, dedicated, starter batter, on its own switch, with the two current batteries, also on their own switch, would make a vastly better system. You then have two batteries that you can use together without fear of being unable to start the engine.
If you fit the solar now, using a suitable Victron controller (allowing for you future plans), along with the VSR, you will instantly have a much better system. No more leaving the switch on "both". You can then add additional panels or make the other upgrades at later dates.
lpdsn
Well-Known Member
You really don't need even one 110Ah battery to start the engine (assuming it's not some 800bhp jobbie). I'd suggest you could get a small dedicated starter battery optimised for the purpose and parallel the two 110Ah batteries as a domestic bank. (I wonder how I could automate this post and get it included in all similar threads
)lampshuk
Well-Known Member
Thanks, Paul. Just a couple of points:
I think I wasn't quite clear in my meaning about the 1/2/B regime. The batteries are only on "Both" when charging, either by engine or mains, so that reduces (but does not eliminate) the risk of one battery discharging the other. When draining, the batteries are on either 1 or 2 depending on whether the day's date is odd or even.
Looking at the wiring diagram of the Cyrix it's pretty clear that it is designed for separately wired starter and household batteries, only being able to combine the 2 for start purposes. That put me off, but you're saying it would be OK to retain the 1/2/B switch to allow switching of the load, but allow the Cyrix to just manage the charging sources. It seems a pretty good device, and not too expensive. I need to check the starter current for a Volvo Penta 2003 to see which Cyrix model will do the job.
Adding a starter battery is clearly the best way to go, but far from straightforward given the space I have available. I think I will make incremental progress in that direction.
Thanks for the advice,
Martin.
I think I wasn't quite clear in my meaning about the 1/2/B regime. The batteries are only on "Both" when charging, either by engine or mains, so that reduces (but does not eliminate) the risk of one battery discharging the other. When draining, the batteries are on either 1 or 2 depending on whether the day's date is odd or even.
Looking at the wiring diagram of the Cyrix it's pretty clear that it is designed for separately wired starter and household batteries, only being able to combine the 2 for start purposes. That put me off, but you're saying it would be OK to retain the 1/2/B switch to allow switching of the load, but allow the Cyrix to just manage the charging sources. It seems a pretty good device, and not too expensive. I need to check the starter current for a Volvo Penta 2003 to see which Cyrix model will do the job.
Adding a starter battery is clearly the best way to go, but far from straightforward given the space I have available. I think I will make incremental progress in that direction.
Thanks for the advice,
Martin.
PaulRainbow
Well-Known Member
You are still at risk when set to both, albeit only if a battery fails in a particular way, if you only use "both" while charging. But, the solar panel will always be charging (during daylight) whilst away from the boat, so you would need to leave the switch to "both" all of the time you are away.