ACR + battery tender = bad idea?
 

I've got a two battery setup including a Blue Sea ACR. Small stereo + little sitting around = no need for shore power through the summer.

Is it a bad idea to hook up a battery tender in the winter without disconnecting the ACR? It seems that one battery would hit 13V, then the ACR would close... of course a tender can not keep up with the current needs, and voltage would drop and maybe open the ACR. Seems like a lot of cycling and stress on the battery that was charged first.

thoughts?

If you pull the ground wire off the ground terminal of the acr it's an easy way to bypass it.

What type of battery switch do you have? If you have the Blue Sea Dual-Circuit Plus switch, the ACR will be isolated from the batteries with the switch off. Charger should be connected directly to the batteries.

TigeMike, I've got the one below.
http://www.bluesea.com/products/5511e/featured

The switch is wired in parallel to the ACR. While the switch is off, the ACR still has access to both batteries.

flapjack,
Since you do have an ACR, this can increase your dependence on shore charging. Just check your voltage on both batteries independently after a day out on the water. If the voltage measures in the mid 12 volt range then you may be okay from week to week. If lower, then this is an indication that you need to supplement the boat's charging system with shore power charging through every week.
A tender/maintenance/minder/trickle charger is adequate in an application where you normally place the boat into storage with a full charge which might also be a boat with a system containing a very modest stereo or one that is used at rest for short cycles only. If the boat comes home with deep battery depletion after long play times at rest and/or a large stereo, then you should have a more powerful dual bank smart charger.
While a tender/etc. is not ideal for all systems, it is still better than no charger at all and should extend your battery life.

Then all you need to do is relocate the 2 cables going to the A and B posts of the ACR, from the switch posts shared by the battery cable to the other 2 posts on the switch. These would be the same 2 posts that all the boat electronics should be connected to.

good idea. This is what you are recommending, correct?
http://i.imgur.com/Hie7v59.jpg

David, Rob, and Mike,
Thanks for your ideas and insights.

Thats it! You are welcome, glad to help.

Since I have a dual battery on-board charger, I simply pull the ground wire off the ACR before I plug in the charger.

I sometimes forget to plug it back in, but since my setup defaults to charging the house battery, I just run the stereo battery down faster - not a big deal since both are deep cycle AGM's and gets plugged in after each use.

^^^^ Then trigger the ACR with an AC driven relay. Automatically separates when the charger is plugged into AC and automatically defaults to normal when the charger is unplugged. Nothing left to remember.

I should probably get off my ass and do that. Would take one less step in my boating process, though I'll have to come up with how to grab the AC off the charger to trigger the relay (I don't want to cut/splice the AC plug to do that). Could also trigger a DC relay via the ignition switch, as I would never have an instance where it would be running and plugged in at the same time.

^^^^ Easy enough to sacrifice a short extension cord and do the connections plus protect the relay inside a common PVC junction box.

David,
Why are you recommending a relay over the TigeMike set-up? Is it so you can leave the switch at "on" while shorepower is connected (and listen to the stereo and stuff)?

Thanks again.

IIRC, nitrousbird has a traditional dual bank switch. If so, then his switch cannot isolate the batteries from the ACR like your switch can. SO in that case, the relay will open the ground circuit to the ACR automatically, when the shore charger is in use.

Mike and I normally agree. And we do in this case also. If you have an ACR with a dual circuit switch it's just way to easy to throw the manual switch whenever you trailer the boat or splash the boat. To me that should be pretty automatic. But some people are using the ACR without a manual switch and there are those who want the operation to be totally automatic in every sense. In the case of the AC relay, it is automatic everytime you plug in or unplug the AC charger cord. Just options.

In my case I have the switch, but my stereo memory is on that switch (though obviously easy to change that). I also run the stereo, lights, etc. when the boat is on the trailer and plugged in (why have a radio in the garage when I can fire up the system on the boat that is parked in there?).

I do like the extension cord + PVC box idea.

I have a new 14 tige z3 with the eibd system. I'm about to put a dual bank charger on my 2 batteries. Will have have to rewire any thing, or can I go directly to the batteries? I am not familiar with the factory eidb set up from tige.