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Wiring a second battery -- Suzuki 9.9 elec start

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AlMo
1st Mate

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USA
55 Posts

Initially Posted - 09/15/2018 : 10:45:59

Hey all,
I inherited this boat with two separate 12v Deep Cycle Lead/Acid marine batteries: one for starting the 9.9 Suzuki (has alternator to keep the start battery topped up) and a 100w solar panel for the "running" battery).

Maybe I have read too much on this subject, but I bought a Blue Sea "add a battery" A/B/both switch with a separate isolator to replace the original 5" diameter Master Switch. The installation manual comes with several "possible" configuration diagrams, but I have seen warnings about burning out the diodes in the alternator if there is no battery load in the circuit.

Anybody done this upgrade? Current (ha!) plan is to leave red and black leads full-time connected to the starting battery, run a pair of 10 AWG wires back to the isolator, then connect each battery's "hot" to the A/B switch.

What I am trying to accomplish:

Outboard charges both batteries when switch is in "both"
Solar panel charges at least cabin battery with switch off, bonus if I can charge both with solar (A/B switch off) without needing a second isolator
Both batteries stay topped up without draining each other
No fires onboard

Any advice / thoughts are appreciated!

Thanks,
Al

1978 C25 "X Lives" #1035
SR/SK

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 09/15/2018 : 14:20:46

With all due respect, my recommendation (to take or leave) is a marine electrician. I'm nervous about amateur designs for systems with things like isolators and multiple charging sources. I also suggest making sure appropriate fuses are involved between the batteries and the circuits--there are fuses made specifically for that purpose. (I think ABYC standards require them now, so an electrician would include it by default.) If you "know what you're doing," then have at it. Just be aware that a marine surveyor will recognize your work...

My boat has two batteries, and the 1-Both-2-Off switch controls both where the charge goes from the motor and which battery(ies) are connected to everything else. So if I want to use one battery for the "house" (saving the other for starting), I just select it. (My motor takes a little more to start than yours!) When the motor is running, I set it to Both for charging, and in most cases just use Both all the time. (The switch is designed so you can switch from 1 through Both to 2 without breaking the circuit with the alternator. Only Off does that.)

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

islander
Master Marine Consultant

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3992 Posts

Response Posted - 09/15/2018 : 15:45:34

Curious about your 100w solar panel. Should be about 5.5 amps output and should easily keep your batteries topped up but my real question is that it is physically large and I am wondering where you keep it or have it mounted.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

sethp001
Mainsheet C-25 Tech Editor

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Response Posted - 09/15/2018 : 16:03:31

Advising to hire a professional is sound and safe advice. Many of us don't hire professionals because we want to learn to do ourselves, or don't want or can't afford to hire a professional. Some of us think that by hiring professionals, we're simply paying someone to screw something up when we can screw it up ourselves for free. Or maybe many professionals don't do as good a job as we would because they don't care about the project like we would. Personally, I don't trust professionals and so I do everything myself. It takes me longer, and might be more expensive considering the time involved, but I'm satisfied knowing I can rely on what I've done. (I'll be rebuilding the transmission on my Suburban over the next two weeks...) Philosophy aside...

I suggest not bothering with the battery isolator and not relying on your outboard to charge your batteries. Your outboard's relatively low-output alternator will do little to charge one, let alone both, of your deep cycle batteries, unless you motor for extended hours on end. Small outboard alternators are generally designed to top up a small starting battery. Instead of a small starting battery, you have a nice deep cycle battery that you've been using for a starting battery. Traditional automatic battery isolators cause a voltage drop to the second battery as well, which would make this even less efficient for the house ("running") battery.

Instead, I suggest installing only the manual battery isolator (the A/B/Both) switch, and using it like Stinkpotter describes using his, above. I also suggest letting your solar panel charge both batteries, which will do much more for you than your outboard's alternator can. You would leave your manual switch set to both to keep both batteries charging from the panel.

For wiring, connect the positive lead from your motor to the common post on the manual switch, and negative to your negative bus bar. Make sure to install a fuse on the positive wire; an inline fuse is easiest; try a 30A fuse. (A 30A fuse might be undersized for the wires from your motor, but if it's undersized and works, that's okay!) Connect the positive lead from your solar panel to the common post on the switch, and negative to your negative bus bar. Make sure to install an a fuse on the solar panel's positive wire. Also install a fuse on each positive wire from each battery to the battery switch.

A note about fuse size selection: select a fuse that has an amperage rating that is the same or is lower than the max amperage for the size of the wire. Here's a handy wire size chart from Sail Magazine: https://www.sailmagazine.com/cruising/handy-wire-selection-chart

Lastly, with a 100W panel, I suggest looking into a solar charge controller. (I presume you don't have one since you did not mention it.) A solar charge controller will cut charging current to your batteries when they reach max charge at 14.1V, which prevents overcharging. Here is a high-quality, low-demand unit on eBay at a significant discount (I have no connection to the seller.) I deleted the link because it was screwing up the formatting on this thread. Search for "Mastervolt Solar Chargemaster Battery Charger/Regulator 131802000 SCM-N20 New!" on eBay and you'll find it. The seller is asking $138.75.

Another nice thing about the solar charge controller, is that you can connect it directly to the positive terminals on your batteries, instead of going through the manual switch (as I described above for a panel only installation). So you can leave the battery switch off and still keep your batteries charged.

(Sort of a separate conversation, but why not?) That controller is a pulse-width-modulation (PWM) model. When your solar panel is at peak operating voltage, it will step your panel voltage from 17V (or whatever your panel's max rating is) down to no more than 14.4V to prevent your batteries from being overcharged, and your electronics from getting fried when the batteries are fully charged and can no longer serve as a voltage sink.

PWM works by pulsing (rapidly and intermittently cutting off) the 17V from your panel so that it averages to no more than 14.4V to your batteries. If you want to spend more, you could get a more efficient multi-point-power-tracker (MPPT) charge controller. The MPPT will convert more solar power to usable power for your batteries by converting high voltage (at peak times during the day) to more current (voltage drops to below 14.4V, current increases), and stepping up low voltage (at off times during the day, or cloudy conditions) so that some current still goes to your batteries (voltage increases to 14.4V, current drops). This works by the equation power=voltage*current. In unit form, that's W=V*A. For more info about this power conversion concept, Google buck converter.

Last note, the solar charge controller at the link above is a multi-stage, so it will also charge at lower voltages depending on the voltage (state of charge) it senses from your batteries, like 13.3V, etc.

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

Edited by - sethp001 on 09/15/2018 16:28:40

AlMo
1st Mate

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USA
55 Posts

Response Posted - 09/15/2018 : 23:04:24

Wow, that is a buncha useful feedback, THANKS all!!! Yes the solar still is a big unit with a solid frame that basically charges when I am docked, have rigged it up with a connector and stow it in the aft bunk when underway. I'd agree it is probably too bulky for full-time use, but I am working on getting all incandescent bulbs replaced with LEDs, and plan to replace the 650w depth sounder transducer with a Hawkeye that is rated at 250w.

As a Radio Amateur (Ham) I feel I have enough background in Physics and electronics to take care of wiring the boat; also, have a brother that has spent a life servicing industrial generators and is no amateur with batteries and wiring. Fusing correctly is of course a priority, as is also the concern about arcing/sparking given the nearness of an alcohol stove, kerosene lantern and white gas cabin heater. Not sure which of those I'll keep anyway.

The isolator is a relay, not diode type, so doesn't show the typical .62 v drop Seth mentions. And it is rated for Marine use, so sparking isn't a big concern. (Another reason to contract a pro, though!)

Interesting about PWM, I plan to look into it, although first need to decide on a semi-permanent solar installation, Perhaps two smaller panels would fit better and be able to charge both batteries simultaneously without one draining the other due to internal resistance my brother tells me is common any time you hook two batteries in parallel without an isolator. The regulator that came with this panel is certainly nothing special; I think it is made by Coleman, produced in PRC no doubt. Boat is currently docked in solar region 2 (Western OR) where solar is a "summer-only" event. So is my sailing so far, luckily.

Thanks everyone again for the input and thoughts!

1978 C25 "X Lives" #1035
SR/SK

Davy J
Master Marine Consultant

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1511 Posts

Response Posted - 09/16/2018 : 05:31:13

I'll just inject this, if I were rigging a new to me C25 again, I would employ two AGM batteries connected in parallel and have the solar panel charge both. The AGM's are dual purpose and will start a small outboard without problem. They will give double the amp hours of a single battery. And in the case of running them down too low, you could pull start the outboard to get going again.

This is how I rigged up my solar panel on my C25:

http://www.catalina-capri-25s.org/forum/topic.asp?ARCHIVE=true&TOPIC_ID=22843

Davy J

2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay

AlMo
1st Mate

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Response Posted - 09/16/2018 : 07:06:26

Davy,
Looks like a good way to mount it, wouldn't interfere with mainsheet/traveler, and that appears to be about the same monster as I have, do you know what type of regulator you are using? And you are saying it is OK to wire two GlasMat batteries in parallel? I am guessing you aren't employing a battery isolator also?

1978 C25 "X Lives" #1035
SR/SK

Edited by - AlMo on 09/16/2018 07:08:03

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 09/16/2018 : 07:44:48

I would probably wire it like Dave did. Just keep things simple. Having a separate battery for starting works for big engines that can't be pull started. The solar panel can be directly wired to the 2 batteries in parallel ( one big battery) Pos. To the pos. Post on one battery and neg. To negative post on the other battery. This will charge both battery's as they are essentially one battery. Use a charge controller.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 09/16/2018 07:46:18

Davy J
Master Marine Consultant

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1511 Posts

Response Posted - 09/16/2018 : 07:44:58

I used this simple 8 amp charge controller:

About $20.00 at HD or WM

AGM's wired in parallel with output of controller wire to positive of one battery and the negative of the other battery. Be sure to use proper fuses. Basically the two batteries become one large battery.

You could, of course, use a more high tech controller. But I never had a problem here in the Florida sun.

Davy J

2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay

Voyager
Master Marine Consultant

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5231 Posts

Response Posted - 09/16/2018 : 19:44:18

We�ve been talking here all about the supply side of the equation with very little regard for the demand side. It�s great to have two group 27 batteries in parallel delivering up to 180 AH (really only want to discharge to 50% at 90AH) and 100W solar plus 6-12A from the engine alternator.

But a power budget also has a demand side:
How many AH will you use starting your engine? 40A for 10 seconds?
Do you have power hungry radar and refrigeration on board?
Do you have an inverter to produce 120VAC for a notebook computer (~90W)?
Does your music system or TV take 2-3 Amps for several hours listening or watching?
Are your incandescent navigation lights or cabin lights taking ~25W apiece (2A)?

You should develop your boat�s power budget, which is relatively simple. In an average week, how many hours of each power consuming device do you use?
Think about anything you�re running whenever the boat is running daytime or nighttime. VHF, music, depth & speed, chartplotter, running lights, steaming light, anchor light. When you�re in the slip or hanging out on a mooring or the hook, how many Amp Hours do you use?
It�s a spreadsheet of amps times time all week.
Then think of your charging resources:
You might motor for 2-3 hours a week. With my Honda that�s 12A x 3 hours or 36 AH.
If the boat sits for 5 days all day in the sun with a 5.5A solar supply, figure 10 hours at 5.5 daily or 5 x 10 x 5.5 or 275 AH per week
Of course these are maxima as it requires that the batteries can accept the full current at all times.

Using a power budget approach you can determine whether your power sources match your power requirements. And how much power budget margin you might have.

In my case I have a single group 27 conventional battery with a 25W solar panel and 12A engine alternator. I have never needed a supplemental mains-powered battery charger. I use LED lighting, a handheld GPS, 2A music system, 1A depth and speed and a 2A VHF radio. At anchor I have a 1A 12VDC electric fan and 2A music system. I only occasionally sail at night with my navigation lights and if I�m motoring at night I use the bow light plus navigation lights. But then I�m running the engine alternator.

My power budget is net positive.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 09/16/2018 19:48:51

AlMo
1st Mate

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Response Posted - 09/16/2018 : 21:52:42

Great stuff, Bruce! Yes the power budget is fine until my wife needs to plug in her CPAP LOL. I am working on LED-ify all cabin and running/mast lights this off-season, and as I may have mentioned above, am going with a much lower wattage depth sounder transducer, a piece of equipment I consider necessary when underway or about to drop anchor. GPS/Chartplotter is used intermittently while underway, so far the sound system is a bluetooth speaker and tablet, neither weigh too heavily on the consumption side. I don't know if this boat was built with a kerosene lamp and white gas heater, but there they are when the batteries near the end of their Amp-Hour run. And there's always Marinas and good old 110v drops in a pinch. I guess I didn't buy this particular boat to be a "sea gypsy," although just finished a very interesting read entitled "Get Real, Get Gone" which was chock full of tips on how to stretch your retirement or other $$$s with a sailboat as primary residence, gotta say, at 66 years old I don't see that in my *near* future (see the remark about the CPAP machine :).

Davy, my regulator looks pretty similar to that one, still not sure about the "one big battery" statement, even with AGM; I am pretty sure that two batteries, even if bought at the same time, one will end up discharging the other, causing replacement of both rather than one (prematurely). At least that is the whole argument for using a battery isolator between the two, as I understand it. Lots of people want the second battery for a party van or the like, pull off to the side of the road and crank tunes; you really want the van to start after a couple hours or overnight of thumping bass etc. Once it starts it is a trivial exercise to charge the "party battery" but the van's alternator probably puts out 200 A.

1978 C25 "X Lives" #1035
SR/SK

Voyager
Master Marine Consultant

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5231 Posts

Response Posted - 09/16/2018 : 22:59:41

AlMo
I too have a CPAP that I use on Passage while overnighting. It goes back a few years and had a built-in 120 AC plug plus a 12 VDC input at 2-3 A. Runs all night and takes 18-24 AH. It provides an unheated passive humidifier. My newer CPAP, unfortunately, has a standard computer-type wall-wart power supply, and it requires a lot more power than my older one. I leave that one home. A long few-day trip can tax your power budget but motor sailing and shore power will keep you good. If all else fails, you can always pull the pull starter on the engine.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Davy J
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1511 Posts

Response Posted - 09/17/2018 : 03:34:03

quote:
still not sure about the "one big battery" statement, even with AGM; I am pretty sure that two batteries, even if bought at the same time, one will end up discharging the other, causing replacement of both rather than one (prematurely).

This has not been my experience. My current boat carries four Group 31 AGM batteries and three solar panels. Two of the batteries, in parallel, are the "house batteries". They power everything on the boat except the freezer. They are connected to one large 200w solar panel and are also connected to the alternator. They are also the batteries that start the 27 hp Westerbeke diesel.

The other set of batteries, connected in parallel, are completely seperate from everything else. The are powered by two 50w solar panels. Their only function is to power the freezer.

This set-up has been running the boat for almost five years. The longest time away from the dock has been 27 days at anchor.

Don't know how long they will last, but so far so good.

Davy J

2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 09/17/2018 : 07:55:53

If you have a selector switch and charge both batteries together, whether by the alternator or a solar panel, you are connecting them in parallel via the switch. If one "goes bad" before the other (probably due to being repeatedly discharged separately), it will affect the charging of the other. I believe that's true even with an isolator, but I could be wrong...

I always replace both of my batteries at the same time, theoretically to reduce the odds of one reducing the effectiveness of charging both, or discharging the good one when used together. And to the extent that I use them separately (for "house" and "starting"), I rotate those responsibilities so over time they're getting about the same usage. But I mostly use them together, and switch to Off to disconnect them when not in use. My first pair of ordinary "dual purpose" batteries went seven years before they showed they were weakening--then I put in two new ones. But everyone has different usage and charging--especially my $+!nkp*+.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 09/17/2018 07:58:44

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