My Unusual (Alternate) Dual Battery Setup

[Bruce]

I added a second battery last year. My primary reasoning was to provide additional power for the refrigerator which is a 1 amp hour 24/7 load. I used DieHard Platinum Group 31 AGM batteries which have worked very well so far. Both batteries are connected to a battery disconnect switch where I can choose which battery is powering the boat or use both batteries at the same time. The factory engine cables are connected directly to the battery disconnect switch. The house load is connected through a low voltage disconnect (LVD) preventing the house load from running the batteries so low that they would be damaged or could not start the engines. Both batteries are charged via an on board charger when shore power is available.




I considered using a typical starter and house battery setup. With two batteries of equal size the capacity of the starter battery would be wasted. If I wanted to have a true starter battery it would be a small one. Our engines are small and a jet ski sized battery or small motorcycle battery would be sufficient to start them. I decided that I wanted to make both batteries available to the house loads.

When I started using this setup I would turn one battery on at a time leaving the other as a backup. I did not want to risk needing a jump if both batteries ran down. Now that I have become comfortable that the low voltage disconnect will prevent battery discharge and with the electrical load of my boat I leave both batteries on.

One interesting discovery is that that key switches are powered through the house load wiring. So you must have power to the house circuit to start the boat.

The low voltage disconnect has an override switch that reconnects the house loads when pressed. The override switch needs to be connected to a power source that is not switched by the LVD.

Using this setup I am able to run the refrigerator for approximately 100 hours before the LVD disconnects the house load which is very convenient for multiple day outings. At that point the batteries are at a 50% charge leaving plenty to start the engines. Using a traditional setup would halve that run time. This would also benefit members who want to power a large stereo setup.

 

[OperationROL]

Nice! I can see you put some thought into it.

 

[kthrash]

What LVD Switch did you use?

 

[Bruce]

What LVD Switch did you use?

The Blue Sea LVD was the only one that I could find https://www.bluesea.com/products/7635/m-LVD_Low_Voltage_Disconnect

 

[kthrash]

Thats actually not a bad idea..

 

[2nazt]

With this setup @Bruce I guess there isn't a need for an ACR? As you have a large enough reserve off batteries I would assume. I am trying to get an idea as a dual battery set up is next on my list. I just plan on a normal radio and hanging out nothing major. I like the built in safety to the batteries and always being able to startup with the LVD.

 

[Wayloncle]

Mine are wired like this as well, without the LVD, when I bought the boat it was already set up and I just assumed it was wired for one battery for starting and the other for everything else because that's what I've read the most about how people have theirs done.

After messing with it I realized it isn't separated, I also just go from off to both batteries. I just have stock stereo and a few times while listening for an extended anchoring, I switched it to one battery, just in case.

 

[2nazt]

@Wayloncle so the system will get some charge from stator, the ACR just cycles between batteries correct?

 

[Bruce]

@Wayloncle so the system will get some charge from stator, the ACR just cycles between batteries correct?

The ACR charges the starting battery first then charges the house battery once the starting battery is fully charged.

 

[Wayloncle]

@Wayloncle so the system will get some charge from stator, the ACR just cycles between batteries correct?

I don't have an ACR, I don't think, I've never hooked a charger to them and have never had them be low on charge. I always turn them off as soon as I was out of the water and flushed, I use to check them with a multimeter often because I was worried about them draining and not charging enough for the shorter rides I'd go on and they have never been low. But I did use the boat at a minimum once a month while in FL, I didn't start it for about 4 months until about a month ago and it fired right up. I have a solar charger that I was going to hook to it while in storage, I just haven't done it yet.

 

[2nazt]

So in this non conventenial set up the ACR is not used or needed @Bruce

Thanks @Wayloncle just getting a gauge on what I need to order for this upcoming project.

 

[subysti]

I don't under stand why you wouldn't use an acr? The ACR completely isolates the house battery from the starting battery so you never risk losing your starting battery. I know the LVD protects you but with 1 good deep cycle battery I think you will get much longer run time than with 2 starting batteries, thats what they're designed for. Also starting batteries don't like to be drained down and recharged too many times or they quit on you. Just like in you car, once that battery goes dead on you its never the same again. Starting batteries are goods for short bursts of high amps not long slow draw down. As far as the ACR goes they depend on the brand you use. The Blue Seas ACR will charge both batteries together after a short delay, a few seconds, the BEP DVSR that comes with the Yamaha's charges the starting battery completely first then charges the 2nd battery bank. One reason I want to swap out the stock ACR for a Blue Seas. But this is all just my .02

 

[Bruce]

I don't under stand why you wouldn't use an acr?

An ACR could be added to the system but I do not feel the need. I primarily rely on shore power to recharge the batteries and the battery switch acts as a manual ACR as whichever battery(s) is selected is charged.

I have two group 31 100 Ah deep cycle AGM batteries. If they were configured in a traditional starter and house setup I would be able to draw 50 Ah before reaching the safe disscharge point on my house battery. As is I can draw 100 Ah before the LVD kicks in and still have plenty of power to start the engines.

 

[swatski]

SO glad you guys revived this thread, I have been looking for something like that for a while now. Missed it completely, very happy to have found it here, now.

I am having such a hard time deciding on the battery setup, currently running on a single monstrous group 31 AGM deep cycle. Love it, and with a Lithium jump pack that I carry, I just can not decide if I need a second battery or not. I actually have hard time wrapping my head around the problem of all the bad compromises and waste intrinsic to essentially any multiple battery setup, versus the simplicity of what I have now...

I did not think of the LVD idea - that is brilliant. I think that is exactly what I need and what I am going to do. I am upgrading my stereo in a very substantial fashion, and this has been on my mind a lot. Now - with the single big deep cycle, shore power at the dock for my Pro300 onboard charger, the jumper pack, and now the added LVD - I will be good to go.

Thank you, @Bruce . I feel much better now that I finally came across a plan that I like. Love this forum.

 

[2nazt]

@Bruce do you recall what fuse holders you used during install. For the small 10amp ground. Also size you ran for override switch and also from switch? They are the last pieces I need for this install. I don't see a size listed in instructions to the remote switch. I was thinking running a 100 amp from switch to LVD

 

[Bruce]

@Bruce do you recall what fuse holders you used during install. For the small 10amp ground. Also size you ran for override switch and also from switch? They are the last pieces I need for this install. I don't see a size listed in instructions to the remote switch. I was thinking running a 100 amp from switch to LVD

The only fuse I added was for my second house circuit that goes to a switch panel for accessories that I added. There are two 15 or 20 amp fuses on the load side of the LVD. I used one of these fuse holders https://www.amazon.com/gp/product/B008CVPE8C/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I ran 18 guage speaker wire for the override switch. It is likely oversized but was handy. One thing I need to correct is that the power source for the override switch needs to come from the supply side of the LVD.

I ran a short off the shelf battery cable from the switch to the LVD.

 

[2nazt]

Okay thank you I saw in the installation diagram to run a fuse from switch to LVD one to ground bus and inline fuse for override. So just trying to confirm. Is there a need for a fuse between switch and LVD if everything else is fused after to each component?

I planned on running cables with no fuses to switch and on common run engine cables and cable to to LVD. Then run accessory cable from factory and one to a bus bar for other future items. Then fuse each new system I add after buss bar.

 

[Bruce]

My diagram may be confusing. My starter and stators are on the supply side of the LVD (before the LVD). Only the house (accessory) loads are on the load side of the LVD. This way my engines start normally regardless of the LVD's state.

From my perspective the two 20 amp fuses on the load side of the LVD limit the current through the LVD to 40 amps. The only reason to add a fuse between the switch and LVD would be if you were concerned about the LVD itself shorting and drawing more current than the switch could handle. I believe that scenario would be best handled by large fuses between the batteries and switch.

 

[2nazt]

@Bruce as always thank you sir for your time and knowledge.

 

[Bruce]

@Bruce as always thank you sir for your time and knowledge.

You are very welcome. We had our lake fun on Saturday. Today we are having dinner with my parents then waiting for dark to blow some stuff up!