Do I have a dedicated start battery?

[DoubleD]

Please check my logic.



I have a new to me 1991 Caliber 33 that has two Dyno M27m/100Ah batteries and a standard battery selector on the breaker panel (Off/1/All/2). I was trying to determine which was the dedicated starter battery, but I don't think either are. I haven't traced all the wiring, but the engine will start when selecting battery 1 or 2 and the various 12v items on breakers will also work on 1 or 2. Based on this I'm assuming I don't have a dedicated start or house battery and everything can run off of both. Am I missing anything?

[Jammer]

Does the engine crank when the battery selector is set to "off?" It may be wired to one or the other bank. Or it may be wired to the selector switch, as you describe.

[Tetepare]

The engine will start on whichever battery you select. With two equal batteries it doesn’t matter which you call start and which you call house.

[DoubleD]

Jammer, I'm not sure if I tried to start the engine with switch off. I'll try that later today when at the boat.



Tetepare, Maybe my question should be, do I have a dedicated house battery? My concern is accidentally drawing down both batteries, such that I cannot start the engine.


thank you

[Be Free]

Originally Posted by DoubleD

Jammer, I'm not sure if I tried to start the engine with switch off. I'll try that later today when at the boat.



Tetepare, Maybe my question should be, do I have a dedicated house battery? My concern is accidentally drawing down both batteries, such that I cannot start the engine.


thank you

While you are testing to see if the engine will start with the battery switch in the "OFF" position you will also need to see if any of the house loads work with it off.


Anything, house or engine, that works in the "OFF" position is wired directly to at least one of the batteries.

[wingssail]

Assuming that your engine won't start in "Off" position (I assume it won't), then you can designate either battery as your "Start" battery.

You just have to remember not to switch to "Both" to avoid running down both batteries.

This is a much maligned approach but we've quite happily and successfully using it for 35+ years. We keep Battery 1 as the house battery and Battery 2 as the start battery, (although we usually start on the house battery rather than bother switching it). If Battery 1 is low and won't crank the engine we switch to "2" or "Both" and start the engine.

We've gone one big step further: The charging sources (Charger, Alternator/Solar) all feed directly to the house side of the battery switch, so we can charge either battery separately (they can all be turned off individually as well).

Downsides?

• You have to remember to switch to Battery 2 once in a while to keep it charged up.
• You must not switch to "Off" when the alternator is charging which can blow the alternator diodes
• Nothing is automatic, you have to manage the whole system yourself, no black boxes to do it for you
• You need some good monitoring displays (LCD or Analog) to see what is going on. (we have: Battery Voltages, House Usage amps, Alternator Output Amps, and Solar Output amps)

We really do prefer a simple solution in which we ourselves are in charge instead of a fully automatic system which is a black box in which you cannot see what it is doing.

That's not a common approach or a recommended approach. It's just our approach.

[cal40john]

If it is wired as most people do that don't have other things such as an electronic battery connector, battery switch position 1 is connected to one battery, and battery switch position 2 is connected to the other battery.

You put the switch to both when the engine is running to charge both batteries. When you stop the engine you select 1 or 2 depending on which is your house battery. Now you are only discharging the selected battery. The other is not connected to anything.

If you have significantly run down your house battery, switch to the start battery before starting your engine.

Since your two batteries are the same in your case pick one to be the house battery.

[smac999]

Originally Posted by DoubleD

Please check my logic.



I have a new to me 1991 Caliber 33 that has two Dyno M27m/100Ah batteries and a standard battery selector on the breaker panel (Off/1/All/2). I was trying to determine which was the dedicated starter battery, but I don't think either are. I haven't traced all the wiring, but the engine will start when selecting battery 1 or 2 and the various 12v items on breakers will also work on 1 or 2. Based on this I'm assuming I don't have a dedicated start or house battery and everything can run off of both. Am I missing anything?

this is how most older smaller boats are wired. if both batteries are the same you need to dedicate them yourself. IE just call 1 start and 2 house or vice versa. while running you need to put to all so both charge. at anchor you would move to 2. and drain 2. and then the next day, if 2 is low, 1 is full to start. once started, back to all to charge.

the hicup is if there are devices direct from a battery. then that one should be the house, and it's already decided for you. so you need to look at all the wires.

[Pete7]

That's a fairly standard fit for older yachts. The good news for a smallish out lay it can easily be improved. Remove the 1/2/off switch. Parallel the existing batteries into one house bank and add a smaller engine start battery. Use separate battery switches and a VSR to provide power from the alternator to the engine start battery and from there to the house bank. BEP make a good switch and VSR set up with emergency cross connect if the engine start battery fails.

The main advantage is it doubles your house bank.

Pete

[S/V Illusion]

You have good info to figure out half the puzzle.
Once you figure out the answer others have suggested, don’t forget to consider how charging occurs both from the engine alternator and whatever charger you have to ensure both batteries are charged properly regardless of the switch position.

[wingssail]

Originally Posted by S/V Illusion

...you have to ensure both batteries are charged properly regardless of the switch position.

S/V Illusion, this advice implies some sort of battery combiner, VSR, or other automatic device. While this is recommended by most electricians and preferred by many boaters, it is not a "must have" unless the OP wants it.

He, (and you) presumably still has a eyes, a brain and fingers to turn switches, so that level of automation is still optional.

[sailingharry]

Wings' solution is super easy and super effective. The one improvement that I would make when the opportunity presents itself is to make the house (or primary) bank as large as you can fit and the other (or what I called my "get out of jail free card" ) as small as can reliably start your engine. This allows your limited battery space to give you the largest house bank while still giving you a reserve to start the engine if you screw up. On my little Sabre 34, my primary bank was 2 Trojan golf cart batteries, and my other bank was a Group 24.

[DoubleD]

Thank you everyone for your replies. I was down at the boat today and nothing runs when the switch is Off, other than the automatic bilge pump. I finally picked up some distilled water to top off the batteries and they shockingly needed 2/3 of a gallon between the two. At some point I'd like to add a larger house bank, but the overall load is fairly small, so not urgent. To many other more critical projects, such as cooling system inspect and clean



thanks again

[Jammer]

Originally Posted by wingssail

S/V Illusion, this advice implies some sort of battery combiner, VSR, or other automatic device. While this is recommended by most electricians and preferred by many boaters, it is not a "must have" unless the OP wants it.

It is my experience that VSRs are flakey, and difficult to troubleshoot when they fail. YMMV.

While mine is a minority view, I believe that on a sailboat with a reasonable amount of solar, there is no reason to have a separate start battery. In that circumstance the only adverse consequence of a dead battery bank is that you might be late for work.


The concept of a separate "start battery" is a holdover from an era when electrical systems were less reliable and charging sources less diverse.

[smac999]

Originally Posted by Jammer

While mine is a minority view, I believe that on a sailboat with a reasonable amount of solar, there is no reason to have a separate start battery. In that circumstance the only adverse consequence of a dead battery bank is that you might be late for work.

or waking up at 4am to a draging anchor after 4 days of no sun. and the engine doesn't start. and you smash into the rocks.