Wiring up 2 batteries...what will this do?

[betadog808]

Hey guys,
   I was thinking of wiring up a second battery for my boat where I could have one for starting and one for accessories...At the moment I only have a Blue Sea System 1, 2, 1/2, and off switch. I believe this wiring scheme will work, but I think in the config, my accessory battery will also pull from the starter battery, correct?

Is there a way to have it so I can charge both batteries from the engine but be able to use the acc battery without drawing from the starter battery?  Otherwise, maybe I'll just have the acc battery totally separate and charge before each outing. 

Forgive my drawing...and yah, that is a AM/FM radio on the bottom left... :biggrin:

Thanks!


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[Threeweight]

Use a Blue Sea Add-A-Battery kit, with their automatic charging relay (ACR).  It will isolate the Starting and House batteries when the engine(s) are off (or starting), but connect them to share the charging output of the motor when the engine is running.

If that is a Blue Sea switch in your diagram, you would have an unswitched (no way to shut-off) connection to Battery #1, while the engine only charges one battery at a time.  You want a switch of some kind as close the battery as possible on almost all of your loads, so that in case of a short of catastrophic wiring failure you can shut off power to as much of the wiring as possible and reduce the risk of a fire.  Exceptions are a single VHF radio and a single bilge pump.

Here's the wiring diagram for the Add-A-Battery kit:

[Holoholo808]

Not a huge issue but the Blue Sea ACR will not provide start isolation unless you have a signal (12 VDC usually from your starting/ignition circuit) going to it. The issue there (probably more prevalent with higher HP engines with high starting current) is that, if the batteries are combined, you can have a system voltage drop that could  damage electronics.

This is mostly academic but definitely a possibility. I'm sure a couple of the resident electrical gurus can chime in regarding the risks of not hooking up the wire to start isolation.

I checked with the good Honda mechanic here (I doubt WB would know) regarding where to tap off of the starting circuit for the isolation signal and he of course recommended not to tap into the harness on the controls side.

I've been bad and didn't hook up the start isolation and haven't had any issues yet...

I went the Blue Sea ACR route so let me know if you want to check it out in person.

[Diablo]

Not a huge issue but the Blue Sea ACR will not provide start isolation unless you have a signal (12 VDC usually from your starting/ignition circuit) going to it. The issue there (probably more prevalent with higher HP engines with high starting current) is that, if the batteries are combined, you can have a system voltage drop that could  damage electronics.

This is mostly academic but definitely a possibility. I'm sure a couple of the resident electrical gurus can chime in regarding the risks of not hooking up the wire to start isolation.

I checked with the good Honda mechanic here (I doubt WB would know) regarding where to tap off of the starting circuit for the isolation signal and he of course recommended not to tap into the harness on the controls side.

I've been bad and didn't hook up the start isolation and haven't had any issues yet...

I went the Blue Sea ACR route so let me know if you want to check it out in person.

The ARC is only closed combining the batteries when a charging source is available. So when you are on the water when you start you will only draw from the start battery. The exception to that is if your trolling motor was running and charging the bats.
Most dual battery switches allow you to combine the batteries if you need to. Now if that was because your start battery was dead the start battery should be isolated with another switch for the just the start battery or pulling the start battery fuse. That would keep the start battery from drawing down the house battery (acc).

[Holoholo808]

The ARC is only closed combining the batteries when a charging source is available. So when you are on the water when you start you will only draw from the start battery. The exception to that is if your trolling motor was running and charging the bats.
Most dual battery switches allow you to combine the batteries if you need to. Now if that was because your start battery was dead the start battery should be isolated with another switch for the just the start battery or pulling the start battery fuse. That would keep the start battery from drawing down the house battery (acc).

Thanks for clearing that up. I got confused with another old thread about house voltage problems and electronics failures.

Looked up the techs specs on the Blue Sea site and the ACR won't combine until it sees above 13 (or 13.6 depending on what page you look at) volts for 30 seconds. Its basically taking the human out of the equation as far as combining or isolating the batteries and in a lot of cases that's a good thing.

[betadog808]

Thanks guys...Can someone with electrical knowledge explain why in my diagram both batteries don't drain together(unless I'm in 1+2) as the negatives are always connected regardless of which battery positive I connect to?

[DevMah]

Both batteries drain but one is recharged by the motor.

[DevMah]

 The start battery drains when the motor is cranked over... but once running is topped up by the motor charging system.

The ACC battery will only drain unless you switch it to the main engine to charge.

This is why three weight is advising you to use a ACR is that both batteries are recharged while having the protection to keep you start battery isolated.


Dev

[GregE]

When 3 Wt speaks........  listen   :biggrin:

[betadog808]

Weird...from what research I've been able to find, if you have the switch in the correct position, you can charge either or both.  And depending on the switch position, you can have the accessory stuff drain from just the accessory battery and spare the starter battery.  I just wanted to understand why as the negatives are always connected...

[Threeweight]

http://www.boats.com/resources/12-volt-basics-for-boaters/

[DevMah]

Weird...from what research I've been able to find, if you have the switch in the correct position, you can charge either or both.  And depending on the switch position, you can have the accessory stuff drain from just the accessory battery and spare the starter battery.  I just wanted to understand why as the negatives are always connected...

The negative (B-) are common between both batteries, charging system (B-) and the block of your motor.

The positive side is where the switching is done.

I strongly do not recommend combining batteries this is only a "Hail Mary" option to get you started....if one of your batteries is shorted it can damage the other by combining (putting them in parallel).
This is why the ACR is recommend as it will only combine when safe conditions in both batteries are present (safety combine both your batteries with one charge source).

Yes you can charge either battery one at a time with the switch but I do not recommend combining...unless you have voltmeters on both batteries and know what you are doing.



Dev

[Packman]

I would eliminate the switch in the Blue Seas diagram. That is what I have, the batteries are connected by the isolator, when the engine is on both batteries get charged, when the engine is off the batteries are separated (when the voltage between them drops below 13 volts or so).  I do have a switch that will combine both batteries in the case of the starter battery not having enough juice to start the engine.  Simple and automatic, I have never had a problem with this setup.  I renew my Optima batteries every 5 years or so.

[DevMah]

I would eliminate the switch in the Blue Seas diagram. That is what I have, the batteries are connected by the isolator, when the engine is on both batteries get charged, when the engine is off the batteries are separated (when the voltage between them drops below 13 volts or so).  I do have a switch that will combine both batteries in the case of the starter battery not having enough juice to start the engine.  Simple and automatic, I have never had a problem with this setup.  I renew my Optima batteries every 5 years or so.

This can be done with ACR also, please note that a isolator will have 0.6 to 0.7 volts dropped each Diode junction.
They both work well but the ACR is more common on outboard installs.


http://info.waytekwire.com/blog/battery-isolators-vs.-automatic-charging-relays-acrs-thursday-throwdown

https://www.bluesea.com/resources/58/Battery_Isolators_and_Automatic_Charging_Relays

https://www.bluesea.com/resources/1366

Dev

[DevMah]

I would eliminate the switch in the Blue Seas diagram. That is what I have, the batteries are connected by the isolator, when the engine is on both batteries get charged, when the engine is off the batteries are separated (when the voltage between them drops below 13 volts or so).  I do have a switch that will combine both batteries in the case of the starter battery not having enough juice to start the engine.  Simple and automatic, I have never had a problem with this setup.  I renew my Optima batteries every 5 years or so.

FYI
Isolators operate like one way check valves, they have no voltage sensing between batteries.
A isolator is just two diodes back to back, to forward biased a PN junction it takes approximately 0.7 v (open the check valve).
So for a alternator to charge a battey with a isolater the charge voltage has to be 0.7 v higher than the battery voltage.
On outboard engines at low RPMs most times the voltage dose not exceed this threshold... so no charging could occur... VS a ACR has no voltage drop so it is able to charge at lower voltages.

A 12v battery has a open circuit voltage of approximately 12.6 to 12.7 v so for a isolater to charge you will need to exceed 13.4v ( 12.7 v+ 0.7 v)
Dev

[SB Steve]

Forgive my questions, as they have been likely answered in this thread, but I still a little confused as to how the ACR works and which battery/switch combo I should use.  I have been going over the blue seas diagrams as I diagram my re-wiring project.

I presently have a start battery and house battery hooked up to a 4-way switch (1/2/both/off) with no ACR.  I assume that with this set-up only the battery that is switched on is being utilized and charged.  (with the exception of bilge pump which is straight wired to one of the batteries for example)

Most of the blue seas diagrams I have seen using an ACR use the 3-way battery switch (1/combine/off) with 4 terminals compared to the 4-way switch with 3.  If I am not mistaken, this system charges both batteries as needed.  I assume when it is switched to 1, the start battery allows draw to the motor and also activates the house battery for all other functions.  The combine feature is only used in emergencies. 

I guess my question is how will an ACR work with the 4-way switch, or should I consider getting a 3-way instead?  Does the ACR have to be also be connected to the ignition wire to work properly?

On side note, what else should be straight wired to the house battery other than the bilge...VHF?

Hope my questions make sense, it is probably something simple that I am just not getting.

[DevMah]

Hope this sheds some light
I am going to answer this as I go through your post

Forgive my questions, as they have been likely answered in this thread, but I still a little confused as to how the ACR works and which battery/switch combo I should use.  I have been going over the blue seas diagrams as I diagram my re-wiring project.

I presently have a start battery and house battery hooked up to a 4-way switch (1/2/both/off) with no ACR.  I assume that with this set-up only the battery that is switched on is being utilized and charged.  (with the exception of bilge pump which is straight wired to one of the batteries for example)

correct only the battery selected to the engine is being charged.



Most of the blue seas diagrams I have seen using an ACR use the 3-way battery switch (1/combine/off) with 4 terminals compared to the 4-way switch with 3.  If I am not mistaken, this system charges both batteries as needed.  I assume when it is switched to 1, the start battery allows draw to the motor and also activates the house battery for all other functions.  The combine feature is only used in emergencies. 

correct

I guess my question is how will an ACR work with the 4-way switch, or should I consider getting a 3-way instead?  Does the ACR have to be also be connected to the ignition wire to work properly?
The 4way has four positions off, battery 1, battery 2, and combine. You can use the 4 position but your are limited to having your house and start on the common pole, or you can add a second switch off the ACC battery.

The ACR is wired across both batteries, it dose not care if you are on battery 1 or 2, it will combine when it sees a charge voltage at either battery.



On side note, what else should be straight wired to the house battery other than the bilge...VHF?
any device that requires memory


Dev

[SB Steve]

Hope this sheds some light
I am going to answer this as I go through your post

Forgive my questions, as they have been likely answered in this thread, but I still a little confused as to how the ACR works and which battery/switch combo I should use.  I have been going over the blue seas diagrams as I diagram my re-wiring project.

I presently have a start battery and house battery hooked up to a 4-way switch (1/2/both/off) with no ACR.  I assume that with this set-up only the battery that is switched on is being utilized and charged.  (with the exception of bilge pump which is straight wired to one of the batteries for example)

correct only the battery selected to the engine is being charged.



Most of the blue seas diagrams I have seen using an ACR use the 3-way battery switch (1/combine/off) with 4 terminals compared to the 4-way switch with 3.  If I am not mistaken, this system charges both batteries as needed.  I assume when it is switched to 1, the start battery allows draw to the motor and also activates the house battery for all other functions.  The combine feature is only used in emergencies. 

correct

I guess my question is how will an ACR work with the 4-way switch, or should I consider getting a 3-way instead?  Does the ACR have to be also be connected to the ignition wire to work properly?
The 4way has four positions off, battery 1, battery 2, and combine. You can use the 4 position but your are limited to having your house and start on the common pole, or you can add a second switch off the ACC battery.

The ACR is wired across both batteries, it dose not care if you are on battery 1 or 2, it will combine when it sees a charge voltage at either battery.



On side note, what else should be straight wired to the house battery other than the bilge...VHF?
any device that requires memory


Dev

Cheers Dev!   

Glad I was not totally barking up the wrong tree.  It seems that when I do my re-wiring, I should go with the 3-way battery switch in order to utilize the ACR and Start battery as intended.

[diodon]

 :applause:

[Threeweight]

On the switch in the diagram I posted, there is no "1" setting... it is "on, off, combined".  On works as you described... starting battery connected to motor, house battery connected to accessory loads, but both circuits isolated from each other.  The ACR functions as the "bridge" between the two circuits to share charging current  from the motor(s), but only connects them when it detects the proper conditions, then cuts out when conditions are not met.

On a smaller Arima, I think the Blue Sea Add-A-Battery "mini" is all you need (for motors putting out 65 amps or less from their alternator).  Bigger applications, or if you want overkill, the full size Add-A-Battery is rated for up to 120 amps.  I used the full size on my old Arima 17 with my 90 Suzi, and now on my tin can with the big Honda 225.  If the mini had been available, I'd have used it on the Arima as it is a little more space efficient. 

[Fisherdv]

 I'm glad you mentioned that 3WT. I was trying to decide if the mini was ok for my application. My motor has 27 amps alternater, and 22 amp battery charging power. So the mini should be the correct size for my application correct? I currently have only one battery with no switches at all. So if I add a second battery is that all I need is that Blue Sea add a battery mini kit with ACR? Thx

[Threeweight]

The kit + cables + the battery.

[Fisherdv]

Would both batteries have to be of the same type and CCA rating? Can I add one "new" battery and still use my current battery with that mini blue sea ACR kit? I was was under the assumption that it's not a good idea to mix new and used Or does it not matter with that ACR mini kit?

[SB Steve]

On the switch in the diagram I posted, there is no "1" setting... it is "on, off, combined".  On works as you described... starting battery connected to motor, house battery connected to accessory loads, but both circuits isolated from each other.  The ACR functions as the "bridge" between the two circuits to share charging current  from the motor(s), but only connects them when it detects the proper conditions, then cuts out when conditions are not met.

On a smaller Arima, I think the Blue Sea Add-A-Battery "mini" is all you need (for motors putting out 65 amps or less from their alternator).  Bigger applications, or if you want overkill, the full size Add-A-Battery is rated for up to 120 amps.  I used the full size on my old Arima 17 with my 90 Suzi, and now on my tin can with the big Honda 225.  If the mini had been available, I'd have used it on the Arima as it is a little more space efficient.

Good call 3WT.  I will only need the mini.  My motor puts out less than 40 amps.  It will save me $ and space!

[DevMah]

Would both batteries have to be of the same type and CCA rating? Can I add one "new" battery and still use my current battery with that mini blue sea ACR kit? I was was under the assumption that it's not a good idea to mix new and used Or does it not matter with that ACR mini kit?

I recommend that they should be... but I have seen many installs with non matching batteries.

https://www.optimabatteries.com/en-us/experience/2014/04/can-i-connect-dissimilar-batteries-parallel


Dev