Thank Goodness For Two Batteries

[GaryMayo]

Long work week. Sunday afternoon at 5pm locked up shop and headed to the lake. As my wife was removing sail covers, I tried lighting up the diesel engine on our 32 ketch. DEAD! Nothing, not a click. Sitting at the dock was not what I had in mind, watching the battery charger warm things back up.

Then I remembered we have two batteries. With an easy switch of a couple wires, she fired up and off we went onto the lake from our slip at the marina.

Several hours later we returned, and I unhooked the battery. No use having two dead batteries.

This winter I will do a bit of electrical work on the boat and look for the gremlin that tried to spoil my evening at the lake.

Someone with a cellphone camera was kind enough to swap images this evening.

[osirissail]

It is quite common in boats that have two or more independent battery banks to install a battery switch with the "common" connected to the engine starter and the #1 position connected to the dedicated engine starting battery. Then the house bank or another battery bank is connected to the #2 position on the battery switch.

That way you can leave the "engine starter" battery switch in the "Off" position to protect the battery from any discharge related to the engine starter system.

Likewise, it can be also left in the #1 position for normal operation of the engine starting system.

Or in case of an old or deceased engine starting battery the switch can be moved to the #2 position and allow engine starting without any risk of connecting the dead battery to the good battery.

Just be sure to block off or buy a battery switch that does not have a "Both" position. Also some battery switches have the "Both" position such that the switch can be moved from "Off" to "1" or "2" without having to transit "Both." These are the preferable style battery switches to use for this purpose as a screw or bolt can be attached to the switch to physically prevent the selection of "Both."

[GaryMayo]

I have that switch. New one, along with a new circuit breaker box. The problem with being new, the seller had them installed and no one ever hooked them up. Or at least they were all unwired when I purchased the boat.

My diesel mechanic looked it over when he did some repairs to the engine, but I sensed a little head scratching while he was looking it over, so I told him to just hook up one battery to the starter switch. Worked all season till today. We had let the boat sit about a month.

I will hook a charger to the discharged battery tomorrow to bring that back up and I guess I should look for a marine electrician.

The batteries were purchased new this spring. One deep cycle battery and one engine starting battery.

I have seen boats totaled in electrical fires. One a couple slips from mine. Not a pretty sight. Do not want to live that first hand.

[robinco]

My boat has three battery banks (only one battery in each bank though for space reasons) with each one switched independently. One house bat, one starter bat and one dedicated fridge bat.

I can parallel either of the other two to the starting battery, or both of them at once if need be. They all charge together using 2 voltage sensitive relays which disconnect when the engine is stopped.

Double (triple?) insurance I suppose. I did my own wiring because the boat's wiring was a real mess when i bought it. I've never had problems with the system, which works really well for me.

[Azul]

Install the 1/2/ALL switch (Guest makes the one most people use) and get a small inexpensive solar panel to keep your batteries up while you are away (you can buy a package with an inexpensive panel and charge controller together on Amazon.) The whole job will only take several hours. It isn't good for the batteries to not stay at full charge, and if you have both hooked up and the switch in the ALL position your alternator will charge both while you are running. It takes a long time to charge a weak battery and this system will keep you from going onto the lake with one dead battery and another one with only a partial charge, which will sometimes lead you to being stranded. Until you do this, I wouldn't shut off your engine while you are away from the dock.

This one is under $100, but keep in mind that if you run your batteries down it may take several days to bring them back up to full charge:
Sunforce 50033 15-Watt Solar Charging Kit

[osirissail]

Having several batteries "in parallel" might not be the best way to accomplish the objective of being able to start the engine when the dedicated engine start battery has failed.

Basically, it is recommended that you have a means of disconnecting to failed engine start battery and then connecting an alternative battery to the engine starter. Normally, the failed engine start battery has either been discharged due to a "leak" or a load that was not "switched off" - or - the battery has internally failed.

Connecting a good alternative battery in parallel to the failed battery will rapidly, if not instantly, drain all the energy in the good battery into the failed battery. If the failed battery has a internal dead short it is quite possible that you will melt or catch the battery connecting cables on fire due to the extremely large amperage "dump."

The OP's method of physically disconnecting the start battery cable from the starter and then physically connecting a cable from the alternative battery to the starter is one way to safely accomplish the goal.

Another is to have a separate battery switch installed and wired as I described in my post #2 that accomplishes the same thing.

Currently it is recommended that all battery positive terminal cables have a "bus fuse" of sufficient amperage size that is mounted close to the physical battery. This fuse is solely a "safety" device that will open the battery cable circuit if excessive amperage flows down the cable in order to prevent the cable from catching on fire. Below is an example of such a bus fuse.

[Azul]

Osirissail I understand the point that you are trying to make. OTOH, the advice you gave does nothing to keep his batteries from being discharged slowly while he is away from the boat and failing prematurely from disuse. Sure, the deep cycle one will probably fail after the starter battery using it this way. He is on a lake, not cruising bluewater or dealing with strong currents/lee shores. The worst thing that can happen to him is that he drives to his boat on a pretty day and can't get it started, which is costly indeed when you are using a boat on a limited basis and paying for depreciation/insurance/dock fees/maintenance etc all year. I have fished offshore since 3rd grade in the sixties and 99% of people's boats used for this purpose rely on the battery setup I described only without a solar charger to insure they are able to restart their engine. Yes, without solar you should turn the switch to off when away to keep from draining the batteries with a light turned on or something similar but not having a both setting means that your alternator cannot charge both batteries during the already limited time you are motoring. No need to have the batteries in parallel with a two bank switch, unless you want them to be by placing the switch to ALL. Physically disconnecting your extra battery and avoiding a switch with an ALL setting seems extreme to me. The setup I described is pretty foolproof and will keep his batteries in good condition for a long time. $100 well spent, and you don't even need to remember to turn your switch off.

[osirissail]

Not sure about your terminology. In boat electrical charging systems from either a shore power charger or the engine alternator, it is common to use either a "battery charging isolator" or a "battery Combiner" to charge multiple independent battery banks.

The battery isolator is merely a diode system that delivers alternator/battery charger current to each battery bank but does not allow current to flow in the opposite direction so as to keep the batteries isolated from each other.

The battery combiner is a voltage sensing relay attached to the battery that the alternator/or shore power charger is connected to and then closes when it senses a full battery to allow charging of the "other" battery bank.

What I was describing was systems to protect your good battery from being damaged by a "dead" battery along with protecting against electrical fires started by excessive current flows in battery cables.

Self-discharge of any battery in good condition can be compensated for by installing a solar panel system like your link shows. But such systems will not recharge a dead or excessively drained battery. For that you need a shore power charger or an engine alternator.

Typically folks purchase "cheap" auto batteries for "starting batteries" as they generally work just fine. However, the lifespan of such batteries can be rather short. And occasionally you will get such a battery that fails prematurely. In those cases having an alternative way to get a good battery connected to your engine starter without having to manually disconnect cables and reconnect them can save a lot of grief. Whatever works for you . . .

BEP MARINE Relay at West Marine

CHARLES MARINE Marine Multi-Battery Isolators at West Marine

[Ex-Calif]

Originally Posted by GaryMayo

I have that switch. New one, along with a new circuit breaker box. The problem with being new, the seller had them installed and no one ever hooked them up. Or at least they were all unwired when I purchased the boat.

My diesel mechanic looked it over when he did some repairs to the engine, but I sensed a little head scratching while he was looking it over, so I told him to just hook up one battery to the starter switch. Worked all season till today. We had let the boat sit about a month.

I will hook a charger to the discharged battery tomorrow to bring that back up and I guess I should look for a marine electrician.

The batteries were purchased new this spring. One deep cycle battery and one engine starting battery.

I have seen boats totaled in electrical fires. One a couple slips from mine. Not a pretty sight. Do not want to live that first hand.

So currently there is no way to turn off the battery supply to the starter?

That's not so good. If it is wired this way I suspect the boat may have some small drains on the battery continuously. This means the battery may stay charged a week but probably not a month.

Get the batteries wired properly as soon as possible. Here is a pretty common wiring diagram with a 1-2 switch.

I am not opposed to the both switch in a simple electrical system. This allows you to parallel the batteries with the engine on and charge both banks. An alternative is to have a small solar panel to charge the start battery or a combiner and use the alternator to charge the house/second battery.

[alar]

Hi I have two batteries on my sailboat. Also the off, 1,2, & both switch. My question is how much does the engine need to run to keep them up good. I use the lights very little. I also use the the engine very little. I motor away from my mooring for about ten minutes and return after sailing running my engine for about ten minutes. I sail once or twice a week. Will this keep my batteries up, should I let the engine run longer, should I consider a solar charger?

[Azul]

Originally Posted by alar

Hi I have two batteries on my sailboat. Also the off, 1,2, & both switch. My question is how much does the engine need to run to keep them up good. I use the lights very little. I also use the the engine very little. I motor away from my mooring for about ten minutes and return after sailing running my engine for about ten minutes. I sail once or twice a week. Will this keep my batteries up, should I let the engine run longer, should I consider a solar charger?

This is a good question and you will get lots of different opinions which can sometimes get extremely technical. You are probably not motoring long enough to completely charge your batteries, more on this later. In general, the cheapest and least fussy solution is to get a solar panel and charge controller that will charge your batteries to 14.4 V and tell you with an idiot light that the batteries are fully charged. End of worries. Or you could buy a $20 digital multimeter and learn how to use it to check your batteries every time you are on the boat and get a feel for what is going on, you probably will find your batteries are never fully charged. Batteries that are not kept fully charged will sulfate more quickly (degradation of the plates occurs) and thus not last as long. Your alternator may be only charging your batteries to 12.8 or 13.0 V, even if you have a fancy Balmar with a SmartReady internal regulator (Voltage is what pushes charge into the batteries like an air pump pushing air into a tire) which means they are never fully charged giving you less backup power to use and less longevity. If you want to get fancy you can worry about how long a small panel will take (maybe days instead of hours) to recharge your batteries, whether to install a remote temperature sensor, how much distance and what size wire between the panels, controller and batteries etc etc etc etc.

[Bay Man]

The issue of a dead battery at dock got me thinking of another issue. What about all batteries dead at sea? Rather than sail it into the slip, is there something shy of another stand by battery ( that may also be dead) that can be used to start the engine? Isn't there some type of auto emergency jumper thingy that could be charged up and brought along?

[Azul]

Originally Posted by Bay Man

The issue of a dead battery at dock got me thinking of another issue. What about all batteries dead at sea? Rather than sail it into the slip, is there something shy of another stand by battery ( that may also be dead) that can be used to start the engine? Isn't there some type of auto emergency jumper thingy that could be charged up and brought along?

Yes, they do make those things. Car dealers use them to jump start cars on the lot with dead batteries. They are expensive for a good one and still need to be kept charged. Great for the trunk of a car but probably not the best or most cost effective solution for a boat. Bad to have around children that like to experiment. The point is, if you have two healthy, well charged batteries and isolate one of them with a switch you should be ok. IMO for the amount of money we spend on boats in a year, any boat kept in the water not on shore power that leaves the dock and that has sufficient room ought to have a 50 W solar panel and a cheap HQRP type charge controller (mine was $47) to keep their batteries up or recharge them if they do something stupid like running both batteries too low to start the engine, at least by the next afternoon on a sunny day ha. I also don't see the point of spending money on a "starting" battery when you can have two deep cycle batteries for the same money. Very few sailboats with auxiliary engines require more cranking amps than even a small deep cycle battery will deliver (my 27 HP Yanmar requires only a 70AH rated battery) and they offer greater redundancy. Before studying about batteries to buy a solar system, for decades I had no idea that my batteries were constantly undercharged and just prayed that only one would fail at the same time or if far offshore fishing I just wouldn't cut the engine off.

[Ex-Calif]

Originally Posted by alar

Hi I have two batteries on my sailboat. Also the off, 1,2, & both switch. My question is how much does the engine need to run to keep them up good. I use the lights very little. I also use the the engine very little. I motor away from my mooring for about ten minutes and return after sailing running my engine for about ten minutes. I sail once or twice a week. Will this keep my batteries up, should I let the engine run longer, should I consider a solar charger?

On a simple boat you can consider a simple solution. I have an older version of the attached that only has 3 leds (Green, Yellow, Red) - It gives a general idea of charge state and has been fine for my needs for about 5 years.

[Bash]

I solve a lot of these problems by carrying a set of jumper cables. Interesting thing is that I've had several occasions to loan them to friends in an anchorage, but I've never had to use them myself.