Second house battery

Trophy21

Trophy21

Crew Member
I want to wire in a second house battery to run a 2000w inverter and 12v fridge in my cuddy. I thought I would run the second battery in parallel through a battery switch to my house battery, so I could isolate the second house battery when on the hook. I would then run the fridge through a switch so I could turn it on or off the 12v system. The inverter would run a one cup coffee maker. The idea would be I could isolate the second house battery as well as have the charging system charge it while running or hooked to shore power. The question is would this be a good way to do this or is there a better way? Any conserns with running the batteries in parallel?
Thanks in advance for any advise.
 
You pretty much have to run the batteries in parallel if you want to have the second house battery included in your existing charging system. Not sure why you need to isolate the house battery when on the hook. Could you not just turn the inverter off when you don't want the draw of the fridge/coffee maker?
 
If two batteries are in parallel, the weakest battery will be the one charging, the other won't charge!
So you have to at least use a battery isolator between the alternator and the two batteries. The isolator will then charge them as they need it, but...
Lots of guys are recommending the Blue Seas system from previous questions that I have read.
 
First, deep cycle & starting battery's need to be charged differently. If not, the deep cycle will fail prematurely. On my boat I have a voltage regulator (for when running)/battery charger (for at the dock) that charge the house battery bank (two 8-D's in parallel) using a deep cycle charging profile. The house battery then charges the start battery via a dc-to-dc charger using a starting battery profile. All the components except the battery charger are made by Balmar (www.balmar.net).

The above statement by Goathorns is true; to work in parallel, the batteries need to be identical in both make/model and battery age.

Sailboaters have a problem similar to your's; the house battery is not big enough to provide their power needs in between charges, so they often run the engine while not moving just to charge their battery's. They install high capacity aftermarket alternators that charge extra-fast.

Battery switches are known to break your alternator if switched while the engine is running.

I would start by calculating what your house battery needs to provide in "amp hours" and the a possible solution would be to maintain your current set-up & install enough new house battery's to satisfy the "amp hours" needed. I wouldn't doubt a single 8D deep cycle would meet your needs.
 
This diagram is from Blue Seas' website; link to that page below. It also contains a clear description of the Blue Seas switches over conventional battery selectors.
https://www.bluesea.com/resources/681

3_battery_bank_small.jpg


You can - and should - install their ACR to isolate the starting battery from the house battery bank. Then you just chain off your second house battery and a switch from the house battery in the diagram shown below. I'd suggest you contact them directly for wiring schematic to suit your exact application.

7650_diagram1.png
 
Sounds complicated the way you have described. I have 2 group 29 house batteries ( purchased new at the same time) hooked in parallel. No switches. I use the Blue Sea ACR and it works great. Leave it and forget it. I also have a 12volt fridge but no inverter. Never had a low battery issue. For coffee I use a single butane burner which works fantastic.
 

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[QUOTE="ericl, post: 810907, member: 8891"
Battery switches are known to break your alternator if switched while the engine is running.
[/QUOTE]

Sorry if this is a little off the main topic but it is still related to boat battery wirng/charging.

I've never heard that switching the batteries while the motor was running could fry your alternator. If that were the case I'd think you'd hear that complaint quite regularly. The only thing I've ever read was you could fry your alternator by switching to off while the motor is running.

If Eric's statement is true then I'm kind of surprised that I'm just hearing about this now. Perhaps that may have been true with ancient battery switches, but I think any modern ones aren't prone to that problem (other than switching to off).

Anyone else experience an alternator failure in a properly wired system simply by switching batteries.
 
I think most marine battery switches are "make before break" if I'm not mistaken. if you switch to off when running, then switch to battery 2 or all then you would have broken the continuity and could suffer consequences. arcing in the switch or alternator, etc. just my understanding anyways but might not be right.
 
Trophy21 said:
I want to wire in a second house battery to run a 2000w inverter and 12v fridge in my cuddy. I thought I would run the second battery in parallel through a battery switch to my house battery, so I could isolate the second house battery when on the hook. I would then run the fridge through a switch so I could turn it on or off the 12v system. The inverter would run a one cup coffee maker. The idea would be I could isolate the second house battery as well as have the charging system charge it while running or hooked to shore power. The question is would this be a good way to do this or is there a better way? Any conserns with running the batteries in parallel?
Thanks in advance for any advise.
Click to expand...

Why would you isolate your house batteries from each other? You can run a load and charge at the same time.
 
bigdogeh said:
I think most marine battery switches are "make before break" if I'm not mistaken. if you switch to off when running, then switch to battery 2 or all then you would have broken the continuity and could suffer consequences. arcing in the switch or alternator, etc. just my understanding anyways but might not be right.
Click to expand...

That is exactly what I was referring to. All modern switches should be of the "make before break" type of switch. Simply switching between batteries or banks should not be risking damage to your alternator with those type switches as far as I know. Switching to "OFF" while the motor is running is a completely different thing. That will cause your voltage to spike and fry your charging diodes. I believe a warning is included on every instruction pamphlet on marine battery switches not to switch to off with the motor running.

Simply switching batteries or banks should not cause damage while running as far as I know. Can switching batteries while running cause damage as long as you don't disregard the warning not to switch to "off". If it can cause damage simply by switching batteries while running I'd certainly like to know.
 
The switch is setup so off on bottom so you can switch while running ie the switching from 1 both 2 is always in contact not breaking any continuity
 
Thanks for jogging my memory about the switch. The problem is if anyone should make a mistake while switching.
Back to the OP; most sailboaters report using around 50 Amp hours per day for the fridge. Given an 8D battery has over 200 Amp hours of charge, at a safe 50% discharge would give 2 days operation w/o running the motor.
Coffeemakers seem to run around 800 watts. To convert to Amp hours: 800 watts/12 volts = 66 Amps. One hour of coffee pot operation = 66 Amp hours. Now you are down to one day between battery charges.
 
Sir Reel said:
I have 2 group 29 house batteries ( purchased new at the same time) hooked in parallel. No switches. I use the Blue Sea ACR and it works great. Leave it and forget it. I also have a 12volt fridge but no inverter. Never had a low battery issue. For coffee I use a single butane burner which works fantastic.
Click to expand...


+1 for this setup.

the BlueSeas add a battery kit has the ACR (auto charge connect/discharge disconnect) and a Battery switch (OFF/ON/emerg combine). While ON the house and start battery are isolated (and combined automatically by the acr)
***truly a set and forget setup!!!!

id rather have two house batterys in parallel and discharge 25%, then have two seperate house batterys and dischage one 50% and the other none. They will last longer in parallel


Lightyears ahead of what i used to do with the start on battery 1, troll/play music while anchored on battery 2, switch back to 1 to start, then combine on way home to charge both.... (never mind the times i forgot to switch)
 
Trophy21; a word of caution:

Be sure to use a proper method when connecting the inverter i.e. proper gauge wire & fuse. 2000 Watts @ 12 volts is 166 Amps needs gauge 00 wire.
 
Thanks for all the input guys! Work has been getting in the way of this project. I have decided to run 2 house batteries in parallel with an acr and switch for both and not switching the house batteries from each other.
 
image.jpeg image.jpeg image.jpeg Got my inverter in and working. Fresh coffee while fishing, can't wait to try it out!
 
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