Two-battery/Two-engine Operation

[santiago]

It occurs to me, after owning my [2001 Boston Whaler OUTRAGE 26] boat [with twin Mercury OptiMax 225-HP engines] for five years, that I don’t understand the battery system operation at all (I guess I just had my head in the sand since nothing had gone wrong so far). After we had a dead battery, I looked at the warning on the battery switch door; it says never operate in parallel--which I’ve done maybe 100 times since we’ve owned the boat.

I’ve always just set both [battery switches] to “All” [and this] has never caused a [problem]. This advice came from a guy we hired to go out with us when we first got the boat, so the warning is bad or we’ve been super lucky. I always assumed--I know--that the Port [battery] powered the Port [engine] and the Starboard [battery powered] the Starboard [engine], and the alternator would charge both [batteries] when the engines were running.

We ran the batteries to the point to where they were dead by listening to music and accidentally leaving a water pump on the other day. We needed a jump which made me think about how the system should work. We’ve never had a [problem]--despite the bilge pump being run all winter in this El-Niño year--with just adding a solar panel hooked to each [battery].

I will now set the switches to the correct position going forward but I still don’t understand it:

--accessories seem to work only off of the starboard battery

--should I always set to "ALL" when starting? And then [change the battery switches to] the 1 and 2 positions when running?

--should I then turn off the port battery to make sure I can start if anchored for a while?

--charging just the first battery will allow [engine starting], and I assume that’s because they are hooked up in-line?

I guess I’m lucky not to have gotten into more trouble so far. In any case I think I need two new batteries, but that will be a good starting point to do this better.

Thanks

[Editor's note: I deleted a sideways picture of the text of the battery switch warning label. Here is the text of the label:

PORT BATTERY NORMAL OPERATING POSITION = 1
STBD BATTERY NORMAL OPERATING POSITION = 2

TO PARALLEL BATTERIES, SET BOTH SWITCHES TO THE ALL POSITION.
RETURN TO NORMAL OPERATING POSITION AFTER STARTING.
DO NOT OPERATE BOAT WITH THE BATTERIES IN PARALLEL.
SERIOUS ENGINE ELECTRICAL DAMAGE MAY RESULT.

--jimh]

[jimh]

If your boat conforms to the wiring that I show in my REFERENCE article on two-battery/two-engine wiring typical for a Boston Whaler boat, you can see the connections and read the operating instructions there. Here is the assumed wiring arrangement:



The image comes from my article at

Dual Battery Wiring
http://continuouswave.com/whaler/reference/dualBattery.html

I believe that Boston Whaler is consistent in their boat wiring, and there is a strong probability your boat was originally wired as shown in my article. Exactly how it is wired now is difficult to determine from one picture of the switches, but it appears to still be wired as the factory intended.

The battery shown in your image looks like the connections are in sad condition.

It is hard to read the warning because the text is sideways, so I transcribed it and deleted the sideways picture.

I’ve always just set both [battery switches] to “All” [and this] has never caused a [problem]. This advice came from a guy we hired to go out with us when we first got the boat, so the warning is bad or we’ve been super lucky.

It is not reasonable for me to accept your proposal, which I would restate as follows:

PROPOSED: that some random guy anyone hires to demonstrate how to run a Boston Whaler boat knows more about how the boat's primary power distribution should be configured than the Boston Whaler company, who designed the power distribution system and provided explicit instructions on how to operate the system.

I cannot find any basis to affirm your proposal. I would take the opposite position: The boat primary power distribution system should be operated in the manner described by its designer, the boat builder, and random advice from some fellow hired to demonstrate how to run the boat that contradicts the builder's instructions should be ignored.

It is ABNORMAL to continually set both battery switches to ALL in order to start one of the engines. Each engine should be easily started from its own dedicated battery. The use of the ALL position is probably never needed except in emergencies, for example, if neither battery alone could provide enough power to crank the engine and start it. Only then would it be appropriate to use the ALL position.

It is ABNORMAL to continually set both battery switches to the ALL position when the engines are running. This ties together two batteries and two charging systems, and by connecting everything together in one common circuit there can be unanticipated results, even damage.

Each battery should receive charging current from its associated engine. However, since you have been running the battery switch incorrectly in the ALL position for a long time, there is a chance you have damaged the alternator, rectifier, or regulator circuits of one of the engines. You should perform a test of the charging system on each engine to establish that each engine is providing battery charging current.

...charging just the first battery will allow [engine staring], and I assume that’s because they are hooked up in-line?

I do not understand your terminology "hooked up in-line." I don't know what sort of electrical connection you are trying to describe. I would interpret "in-line" as a series connection. That makes no sense electrically. Also, I am not sure if "hooked up in-line" refers to the batteries or the engines. Please clarify what you are asking about.

Generally in any electrical circuit there is no need to make any assumptions. Electrical current follows predictable paths, and the paths are shown in the wiring diagram. One discovers where the electrical current WILL flow based on the wiring diagram. Sometimes external circuit paths enter, such as a circuit path created by corrosion or unintended contact with another conductor. But one never needs to operate on assumptions about a circuit--just get the wiring diagram of the circuit and see what electrical behavior will occur.

[jimh]

--accessories seem to work only off of the starboard battery

Based on the assumed wiring (see my REFERENCE article) the source of power for the rest of the boat appears to follow the setting of one of the two switches. Whether it is the Port battery switch or the Starboard battery switch might vary. It seems clear only one battery can be drained by the house loads--unless you have placed the battery switch associated with that circuit in the ALL position. In that case you will drain both batteries, just as happened in your case. That situation is precisely why you should follow the boat builder's instructions and NOT operate with the batteries tied together.

Note that in the wiring we presume to be used, if either the Port or Starboard battery switch is in the ALL position, then both batteries are in parallel for all loads. If the other switch is set to OFF, it will only disconnect its engine or loads from the paralleled batteries.

[jimh]

Re the wiring shown around the two battery switches in your image (above):

My inference is that someone has been fiddling around with the wiring. Boston Whaler would NEVER have left all those nylon wire wraps with cut-offs that make little knife-edges waiting to rip off your skin. Boston Whaler would NOT have have wire with BLACK insulation connected to the POSITIVE circuitry of those switches.

This is somewhat typical for boats. Once they leave the factory the electrical wiring becomes a mess of haywire and owner-added or dealer-added circuits.

[santiago]

Jim, thanks very much. That helps. Here is the other battery if that helps any. Yes the connections have a lot of grease around them. I've not had any electrical work done to it since we bought it and have only replaced a couple of water pumps and the VHF but hooked that up to the wiring that was already there. The batteries were replaced while back by the local merc dealer but we've kept it on the water in SF Bay so kind of a nasty environment...

[santiago]

Well in any case I'll agree that I stupidly listened to someone who I thought knew more than I did (which was nothing) but was clearly not knowledgeable about this system. I'll set the switches correctly going forward and see if they are charging OK/ follow the recommendations going forward. Thanks.

[jimh]

If the pictures show grease on the terminals, then that's good. To me it looked like corrosion. But grease is better than corrosion. In a saltwater environment it will be hard to keep corrosion at bay. Check with a local boat yard to see what they recommend--maybe grease is the best method.

I recommend checking each engine separately to see if the engine is properly charging the battery. When you run them all connected in common, one of the charging circuits can be damaged by the other. A quick check:

--measure the battery terminal voltage when the engine is not running; it should be around 12.7-Volts if the battery is in a full charge state or close to it;

--start the engine associated with that battery; run the engine at a fast idle speed;

--measure the battery terminal voltage with the engine running at fast idle; it should be above 13.0-Volts, perhaps as much as 14.0-Volts; this indicates the engine is delivering charging current to the battery.

As long as you see the battery terminal voltage rise when the engine is running from the non-running voltage, you can assume there is charging taking place. If the voltages are not exactly what I mentioned, don't worry, unless they are very much higher or lower.

[jimh]

I notice that the two batteries are both labeled "DEEP CYCLE." A battery of that type is not really designed for engine cranking. To use a deep cycle battery for engine cranking one usually has to get a larger battery--both larger physically and one with more capacity--than would be needed if you used a engine-starting battery.

Check the Mercury owner's manual for the OptiMax engines to see what size battery is recommended; look for the specification of Marine Cranking Amperes or MCA. Usually a big V6 outboard will specify a battery with an MCA rating of over 800-Amperes, and as high as 1,000-Amperes.

To get an MCA rating of 1,000-Amperes in a deep-cycle battery usually requires a really large battery.

Also, OptiMax engines are fussy about their battery power. They do not like to run on a weak battery.

When a battery is discharged completely, particularly an older battery, there is always a loss of capacity that will never be restored completely by recharging. Avoid running down the batteries to low state of charge. It is better to only discharge the batteries to, say, 80-percent charge, then re-charge them.