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Author Topic:   Dual Battery Installation
irishcreamer posted 12-01-2009 10:21 PM ET (US)   Profile for irishcreamer   Send Email to irishcreamer  
Hello Everyone. I am moving forward with my rewiring project and seek your collective wisdom. Below I will lay out some project goals, parameters, and a link to my proposed wiring diagram. Rewiring of the boat is a daunting task but I think I am on the right track. I very much appreciate any insights and suggestions you might share.

A 1989 Outrage 18 outfitted with a 2004 Mercury OptiMax 150-HP outboard. Currently there is a single group-24 starting battery in the starboard splash well and stock wiring under the dash.

I would like to install a dual battery system in the console complete with load isolator, automatic charging relay (ACR), and on-board AC charger.

Main Engine - 2004 Mercury Optimax 150 HP
Fish Finder
Chart Plotter
Bilge Pump
Nav Lights
12 Volt Outlet
On-board AC Battery Charger
Gauges on Dash

I would like to set up the system so that I can easily add the following: Live-Well Pump, Kicker, Stereo, 12 Volt Outlet

After some research and advise from a local marine electronics shop, I created an initial wiring diagram: SMWireDiagramv10.jpg

Battery Isolator Switch - Blue Sea PN5511e
ACR - Blue Sea PN7610
DC Subpanel - Blue Sea PN5026
Onboard Charger - Guest 2620A
Switch Panel - ?
Positive / Negative Buses - Blue Sea PN?
Wires - Ancor?
Battery 1 (Engine Load) - ?
Battery 2 (House Load) - ?
Circuit Breakers - ?

Some questions that immediately come to mind:
1) Batteries. I am leaning towards Group 27 batteries for extra capacity but what kind to get? Lead Acid vs. AGM? Also, I hear conflicting advise on the importance of using a starting battery for the Optimax. Can I run two deep-cycle batteries? Or would two starting batteries make more sense?
2) Wire Gauge. I am concerned about the voltage drop from the console to the engine. What gauge wire should I use? Initially I am thinking 2AWG for all the engine, acr, switch wiring and 10AWG for the switch panel to sub-panel wiring. Your thoughts?
3) Circuit Breakers. Do I need some circuit breakers in the main circuit? The marine electronics installer I met with today said I do not as long as the house loads have fuses (which they do in the subpanel) but I have a sneaky suspicion I should have a breaker somewhere in the main circuit.
4) On-board AC Charger. Where to wire this into the circuit?

Thank you,

jimh posted 12-01-2009 11:26 PM ET (US)     Profile for jimh  Send Email to jimh     
The wire gauge size will be based on the length of the run and the maximum current. Since the system voltage is below 50-volts, the wire size will be determined by the voltage drop that can be tolerated. ANCOR's website has a wire size calculator. It is in their technical data section. Here is a good discussion from the archives:

Battery Cable

The battery charger is not a load on the battery. Most battery chargers include wiring harnesses to connect to the battery terminals.

A primer on small boat power distribution is given in . This will show you where to put circuit breakers for secondary power distribution and for individual loads.

Battery choices have been discussed in many prior discussions, probably dozens of them, so including a discussion of battery choices here, among all the other topics, may best be held in abeyance. I recommend you follow the advice of the engine manufacturer. Generally in the installation manual for an engine there is quite specific instruction regarding what sort of battery is recommended for a particular engine. I would be bound by those recommendations.

newt posted 12-02-2009 11:01 AM ET (US)     Profile for newt  Send Email to newt     
Regarding your question [on circuit breakers in the main power circuit]: My Revenge is wired so that the primary house feed from the batteries to the panels behind the dash does not go through either of the main battery switches. In other words, if the battery selector switch is off, I still have house power. The primary feed runs through its own 50-ampere switchable breaker located close to battery #2.

The 50-ampere breaker has been a source of trouble. In the two seasons of ownership, I have replaced it once, and now need to replace it again. The only time I need house power without power to the engines is in the driveway if I put the radio on or play with the electronics, so I may opt to wire the primary house feed to one of my battery switches with an inline fuse for circuit protection. The advantage to this is that I could then select which of the two batteries will power the house circuit.

jimh posted 12-03-2009 08:51 AM ET (US)     Profile for jimh  Send Email to jimh     
Regarding circuit breakers which are also used as ON-OFF control switches for the branch circuit they are feeding: some circuit breakers are designed to be routinely operated and can be used for ON-OFF control or as switches, but others are not. Circuit breakers designed for routine use as ON-OFF switches usually are noted as having a rating for switch duty, and their actuator will generally be a handle or toggle to permit easier operation. Circuit breakers not intended for use as ON-OFF switches will generally have a control actuator that is a pop-out button, and such controls are somewhat awkward to operate as ON-OFF switches.

The manufacturer BLUE SEAS has a good website with technical information. I recommend you read their information under the topic heading

DC Main Overcurrent Protection Requirements

and to facilitate this for you, I provide this hyperlink:

Feejer posted 12-03-2009 03:51 PM ET (US)     Profile for Feejer  Send Email to Feejer     
Check out the BEP products

number9 posted 12-03-2009 06:44 PM ET (US)     Profile for number9  Send Email to number9     
For our information what type and brand of switchable breaker are you referring to?
"The 50-ampere breaker has been a source of trouble."
jimh posted 12-03-2009 10:40 PM ET (US)     Profile for jimh  Send Email to jimh     
I do not understand the question. I am not referring to any particular 50-ampere breaker as being troublesome for me. Perhaps you are asking Newt.
irishcreamer posted 12-04-2009 12:26 AM ET (US)     Profile for irishcreamer  Send Email to irishcreamer     
I think number9 means to ask the question of newt.

Updating the diagram and components and will add more in the next few days.

In other news, prop testing on Sunday!

number9 posted 12-04-2009 08:52 AM ET (US)     Profile for number9  Send Email to number9     
For our information what type and brand of switchable breaker are you referring to?
"The 50-ampere breaker has been a source of trouble."

Originally addressed to wrong member. Do not want to recommend problematic electrical parts.

andygere posted 12-04-2009 11:14 AM ET (US)     Profile for andygere  Send Email to andygere     
I used a BEP marine switch cluster with integral VSR, and details of my install are here in the archives. The only thing running off the start battery is the main engine. Everything else, including the kicker and the kicker charging system, are wired to the house battery. No hiccups in the 3 years or so I've used the system. Also, while I considered adding an on-board AC charging system, I never bothered. The Optima AGM batteries hold their charge really well and I've never really needed to add charge to them from a source other than the outboard. This includes long periods of non-operation. Food for thought, you may want to hold off on that addition and see if it's really necessary.
andygere posted 12-04-2009 11:31 AM ET (US)     Profile for andygere  Send Email to andygere     
One more thought: Why go through the trouble and expense of putting the batteries in the console? The Outrage 18 can certainly handle the weight in the stern without a problem, and if you go with AGMs, the required amperage can be supplied from a unit with a group 24 footprint, so they don't take up much room. Avoiding the cost of the longer lengths of heavy battery cable will go a long way towards offsetting the more expensive batteries. Also, dry storage space is at a huge premium in these classic Whalers, and you may regret giving much of it away to your batteries, which are perfectly happy sitting in the splashwell as Bob intended.

As far as a circuit breaker goes, install one on the positive cable going from the house system to the fuse panel as close to the battery switch as possible. I purchased a standard panel mount marine circuit breaker, and made a small teak panel for it that hangs from the starboard gunwale board such that the switch is inverted under the gunwale where it can be easily reached, but is protected from knocks, bumps and spray. BEPwiring.jpg IMG_0697.jpg

irishcreamer posted 12-05-2009 01:33 AM ET (US)     Profile for irishcreamer  Send Email to irishcreamer     
Thanks for the input and links. I will continue to update this post as I proceed with this project. Feedback welcome particularly if you can stop me from doing something colossally stupid.

I understand that BEP clusters will perform the same function as the Blue Sea Systems ACR and Isolator switch. I am using Blue Sea components because my local marine electronics installer uses them exclusively and will likely assist in the final installation.

Hi Andy. I am sure the transom can take the extra weight but I would feel better with a more balanced boat. The Opti (433 lb), oil reservoir (20 lb), two batteries (100 lb), and eventual kicker (100lb) will around 650 lb on the back and that seem excessive to me. Interesting that you opted out of the On-board charger. I figure if I am going through all this trouble to update the electrical system I should just include it now rather than trying to add later. Also, if the on-board charger can also function as a battery maintainer that would pretty cool.

Moving forward, please follow link for updated diagram: SMWireDiagramv12.jpg

1) Batteries
After much reading, CW searching, and speaking to both Mercury and Blue Sea Systems I am leaning towards a Starting battery for the engine and a Deep Cycle for the house load. The Mercury Optimax is very sensitive to cranking amps and I believe it is important to honor the Mercury recommendation for a cranking battery contrary to many recommendations to just use dual Deep Cycle batteries. A Deep Cycle is naturally suited for the house load of electronics and water pumps. The two main concerns I have relate to the use of two non-identical batteries:
1A) Potential for ACR chatter or otherwise poor performance. Blue Sea confirms that the ACR will function just fine with my proposed configuration of a Starter and Deep Cycle.
1B) Charging of two non-identical batteries in parallel by the engine’s alternator when ACR is closed. Interstate recommends using identical batteries as an ideal scenario. Unclear to me how harmful this would be to the batteries but they are both 12V so should be “okay?”
1C) Ability for House battery to start the engine if Engine battery fails. The Interstate Group 27 Deep Cycle SRM-27B has 845 MCA and the Optimax requires 1000MCA. If the Engine battery runs low, with the batteries combined won’t they put out the 1000MCA together? Rare I think that batteries fail so abruptly that they are completely dead so the engine battery would likely contribute something.

Reading my A,B,C concerns it is apparent to me that the ideal solution is to have two identical batteries that magically act as Deep Cycle and Starting batteries. As it turns out AGM batteries will alleviate the concerns but they are pricey and a likely future upgrade.

2) Wire Gauge
Spoke with Mercury and for installations where the Optimax is greater than 20 feet from the batteries (one-way) they recommend 1/0 AWG wire so that is what I will go with. As for the other wires, I denoted the gauges in the legend of the wiring diagram. Feedback welcome.

3) Circuit Breakers
Further research needed. For main house circuit protection, possibly a 187 Series Thermal Circuit Breaker Surface Mount(BS PN 7139 50 AMP)between Battery Switch and Positive Bus bar. For engine circuit (any possibly battery 1 or battery 2 path to engine) no breaker per the advice of many. An in-line fuse on ACR grounding wire. Some form of fuse/breaker protection for AC Relay.

4) On-Board Charger
I am looking at the Guest 2620A and Guest 16202 on-board chargers ( ). Both are three stage chargers but the 16202 is an intelligent charging system that allows user specification of battery type. I would like for my charger to safely and efficiently charge the batteries and be flexible on battery type.
4A) Would also like the charger to function as a battery maintainer at times in place of a trickle charge system. Unclear to me if either charger can do the latter. Thoughts??
4B) If my understanding is correct, when the AC On-Board charger is charging the ACR will be closed and the batteries will essentially be charged while connected in parallel. Seems to me it would be better to have the ACR forced open or otherwise disabled while the AC On-Board charger is charging, especially if Battery 1 and Battery 2 are not of the same specifications. My logic seems to agree with Blue Sea ( ) and I should be able to include an AC Relay which will disable the ACR while AC On-Board is charging. Not sure quite how to do this yet so will investigate further. sitotis, if you are reading this, how did your installation ( ) turn out? Any advice on the AC Relay?

number9 posted 12-05-2009 07:01 AM ET (US)     Profile for number9  Send Email to number9     

I didn't realize the newer 185 series CBs were available and was going to recommend the older, similar 185. Switchable CB is definitely a good choice.
Probably doesn't make much difference to you, but I looked at some info on the Bussmann site and the older 185 has a higher IP rating of 67 versus the 187/66.
IP, second #:
6 - Protected against temporary flooding of water, e.g. for use on ship decks - limited ingress permitted.
7 - Protected against the effect of immersion between 15 cm and 1 m.

jimh posted 12-05-2009 05:02 PM ET (US)     Profile for jimh  Send Email to jimh     
The interconnection of two batteries, an ACR switch, and dual battery chargers makes for a complicated problem. I don't have a good answer for you.

If we ignore the ACR for a moment, the situation is very simple. There are two batteries, they're isolated electrically, and they each are connected to an isolated charger output. The problem starts when the ACR is added.

The ACR will tend to close when it senses the voltage on the primary battery is above threshold, indicating excess charging current is available. This could lead to problems. What comes to mind:

--when the ACR closes, the charger outputs are connected in parallel. This means the charger MUST be able to tolerate this configuration. Check carefully that the charger permits this. Otherwise the charger might be damaged by connecting its two outputs in parallel.

--if one battery is in a much lower state of charge than the other, the charger may not be able to maintain the terminal voltage of the paralleled batteries above the threshold of the combiner. This could lead to the ACR chattering on and off.

A better arrangement might be to configure the ACR in some way that it was disabled when the battery charger was operating. One way to do this might be to use a 120-VAC relay wired in parallel with the charger power. If the charger is powered ON, the relay closes. The relay contacts signal the ACR to not combine. (This assumes that option is available on the ACR. Some models have that feature.)

newt posted 12-07-2009 07:42 AM ET (US)     Profile for newt  Send Email to newt     
Number 9 - The switchable breaker I refer to is an Ancor 551650 that looks like this one. circuit-breakers-switches-and-accessories

In fairness to Ancor, I am using the breaker in a somewhat wet location and they do not claim the breaker is waterproof, although they claim weather resistant. I simply replaced in kind what was there previously.

Neither Bluesea or Ancor have a fully waterproof circuit breaker with the same form factor that I need.

number9 posted 12-07-2009 01:32 PM ET (US)     Profile for number9  Send Email to number9     

Appreciate the info on the CBs, those are good breakers, just not in a wet environment.

andygere posted 12-07-2009 03:17 PM ET (US)     Profile for andygere  Send Email to andygere     
Sounds like a well thought out plan, lots of ways to skin this cat.

The only time I've experienced chatter of the VSR is when the house battery is really drawn down. The one load I have that does this is a halogen spreader light that I sometimes use when cleaning the boat up after dark. Once I start the motor, advancing it to fast idle for a minute or two brings the charging current up enough to stop the chatter, and when the house battery voltage recovers the chattering ends and I go back to 600 rpm. In sum, it's no big deal. I am using identical Optima Blue Top AGM batteries, but it was the same story when I had combination type lead-acid units. Since the relay operates on voltage, as long as the house battery voltage is maintained, I don't think it matters what type of battery you use, so long as it is similarly sized. BEP provided a chart that states the required size of the second battery relative to alternator output. I like the idea of a deep cycle for house loads and a start battery for starting, but in reality, the house loads on these small boats are so light I think the combo batteries are fine, be they AGM or lead-acid. The key thing is to meet the motor spec for MCA, and you've got that covered. An alternative may be to use one pure start battery and a combo for the house loads. If you add a kicker later on, it may give more longevity than a deep cycle will for the relatively high current loads of the kicker starter motor.

Contrary to what Jimh says (and I consider him an expert on marine electrical topics) I think the VSR systems are pretty simple, particularly the pre-engineered units now available. In my mind, they take the guess work out of operating the battery system, and ensure both batteries are always charged, the start battery always isolated, and the two can be paralleled in an emergency. Adding a battery charger does not really change things in my opinion. As long as the on-board charger is wired directly to each battery, and the batteries are switched off, the VSR should not activate. It's a normally open relay, and it closes when it sees 12.6 volts on the start battery, which requires the start battery switch to be in the on position. Here's a link to the BEP diagram that shows how it works (page 2). Battery%20Management/Battery%20Charging/Clusters/714-100A/710-100A_Inst. pdf I suspect the Blue Seas system works the same way, check it out.

I was at the boat this weekend, and snapped a few pictures of the circuit breaker installation. Since you are going with batteries in the console, you have a lot of options on where to mount it, but I'll include the photos here for others that may be interested. breaker1.jpg Breaker2.jpg

Good luck with the project, and keep us posted with photos and details. You'll be glad to have spent the time on it now, because having a reliable electrical system really eliminates a lot of frustration later on.

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