Combining battery banks with a solenoid

[mitiempo]

I am currently working on a boat with a solenoid for combining battery banks. When the ignition is on the normally open solenoid closes combining the banks for alternator charging. When the ignition is turned off the solenoid opens isolating the banks. At first I thought it wasn't a great idea but the more I think about it the more sense it makes. I am not recommending it to anyone but it does seem like a poor man's ACR in a way.
The shorepower charger goes to each bank for AC charging.

Can anyone see anything wrong with this arrangement? I searched the net and all I could find referred to vehicles, both off-road and RV's. No mention of marine use but I can't see any real difference.

[Maine Sail]

Brian you lose a LOT of good protective features doing it that way. ACR's like the Blue Sea or Yandina make and break only when charging voltage is present or not present hence the generic term "voltage sensitive relays" pr VSR's. Key on relays can be combined without the alternator charging which can lead to depletion of a good bank into a drained bank or different sized banks being combined under other than charging circumstances..

With an ACR it would break on a voltage drop if the good battery had the voltage sucked below 13v and with a simple key on relay the good battery could have the CA sucked out of it as the relay would not open in low voltage only when the key is turned..

[mitiempo]

Thanks Maine

I thought of that - it's combined whenever the ignition is on regardless of battery condition or if charging voltage is present or not. Also means both batteries are really used for starting whether you want them to be or not.

I still lean to the Echo for most situations. I like the simplicity and reliability I have seen so far.

[btrayfors]

Brian,

Aside from the problems Maine mentioned -- which I agree with -- another problem I see is you'd be combining different types and sizes of batteries. Presumably, the start battery is much smaller than the combined house batteries, and it's near full charge always. Also, you could be combining different battery chemistries is you had, e.g., flooded house batteries and an AGM or gelled starting battery.

I agree with you re: the EchoCharge. It's a dandy device and is appropriate for most situations...much better IMHO than battery combiners, ACRs, and the like.

Let's pray that Xantrex doesn't fool with it's design or manufacture :-)

Bill

[Stu Jackson]

Bill,

I, too, agree.

As far as the echo charge is concerned, buy a few now, you'll be good until you sell the boat!

As we've been saying for quite some time now, though, if your ec or combiner craps out, there's always the B switch position! (when your engine is on). Isn't so automatic, but works!

[mitiempo]

Bill

I agree with Maine as well.

Different chemistry issues exist with an ACR as well. The problem with the solenoid is the banks are in parallel as soon as the ignition switch is on, with the ACR only when the voltage rises from alternator output. If the start is charged and the house is at 50% the start will try to charge the house bank. Bad with AGM's certainly. It is hardly something I would recommend. But in a down and dirty way it does work, in this case with a flooded start battery and a small house bank.

I also hope Xantrex leaves the Echo Charge as is and keeps producing it.

[Maine Sail]

Originally Posted by mitiempo

I also hope Xantrex leaves the Echo Charge as is and keeps producing it.

I have been bugging Blue Seas to build one for a while with no luck. Perhaps you guys could start requesting one too and they might listen. I am so fed up with Xantrex it is not even funny. Installed an inverter today and it was missing pieces. Took an hour on the phone for them to find how to send me four screws. When that stuff happens with Blue Sea it is a 30 second phone call and the part is in the mail.