Starter battery VS. Reserve Battery

[Medic 4 U]

Although I have a stink boat (power boat) (I'm sure my sailing father is rolling over in his grave...), but I do have a wife that needs to be able to be cooled down for medical reasons quickly, so I think he would understand. Why I have a power boat, and the need to have the need for AC...

Here is what I have done. It is a little more than what you have, since I have two engines, but if you look at only half of what I have done you would be good. I think you might want to buy something called a battery separator. It does exactly what it says, it separates the batteries. Mine sits between by stater battery, (I think that is what you are calling your reserve battery), and my house battery bank. It allows the battery banks to stay connected to the other battery down to 12.8 volts, at which time it 'separates' them, electrically, thus allowing my engines to always have at least 12.8 volts to start. Then, when the engine's alternators hit 13.2 volts, after I start it, the separators close, and it allow the alternators to charge their respective batteries of the house battery bank. You see, my engines each have 55 amp alternators, but I have 4 1000 amp Odyssey brand AGM batteries. So, I have a special heavy duty solenoid between battery 2 & 3, that when either engine's ignition key (they're gas engines) is switched to 'on' position, the solenoid opens, which cuts the 4-battery house bank in half. That way when either engine starts, AFTER the starter battery reaches 13.2 volts, the battery separator for that starter battery will only connect that battery to 2 more batteries, so my 55 amp alternator will not get over worked. In your case though, I think a battery separator would be a wise investment to make sure you will always have a battery that will allow you a battery to start your engine. It'seither that, or buy yourself on of those little jump packs. Happy Sailing...

[Islander2]

I have house and start banks of batteries and they are joined and draw both banks down until the start battery gets to 12.7 and then switches it off. This gives you more AH in the initial phase and also has the benefit of drawing and recharging your start bank sensibly without it going too low. Sounds to me like you don't have enough house AH given the need to switch to a start bank.

[SuW]

Originally Posted by Islander2

I have house and start banks of batteries and they are joined and draw both banks down until the start battery gets to 12.7 and then switches it off. This gives you more AH in the initial phase and also has the benefit of drawing and recharging your start bank sensibly without it going too low. Sounds to me like you don't have enough house AH given the need to switch to a start bank.

Yep, we recently added a starting bank to the house batteries connected by a combiner switch. (Old install was two house banks that had been moved to accommodate a hot water tank. Long cables as a result.)

We had difficulty starting the Yanmar 3GM in cold weather. It was a little reluctant even in warm weather. When we added the starting battery we relocated the house bank and shortened and replaced all the wiring. We found some ugly stuff - lots of corrosion, dubious crimps and the main negative lead from the batteries just pulled out from the lug!

Now the engine starts very smartly. On this experience I'd say one reason for bad starting is bad wiring. It's always worth checking.

[nilespf]

Originally Posted by ontherocks83

I am sure I am splitting hairs, but I am curious as to the benefits of one set up over the other. My boat and engine are relatively small so I don't draw a lot of power on the house side or starting side. (Catalina 30 with a 21 hp Universal)

On my last boat and on the way I'm planning to set it up on my current boat is, I have a House bank and a Reserve bank. I run everything off of the house bank including starting the engine. There is an echo charger connecting the two so when the house bank is charging so is the reserve bank. My thinking is that in normal conditions I don't have to worry about switching batteries and everything is done off the House bank. If something goes wrong with the house i.e. I draw it too low or there is an internal short, I can switch to my reserve bank (1 12v battery) and start and run everything off that to hobble home. Ideally the reserve battery should always be in good shape since it will have a very easy life of only being charged and occasionally test starting the engine.

The other set up that I've had some advise to do is to use a dedicated start battery and only have the house wired to aid starting in an emergency. My concern with this (which is unlikely) is that if my House bank were low and when I go to start and my well used starter battery is bad for what ever reason, then there is no reserve to start.

Again I am sure I'm splitting hairs, but I am curious if there is a reason/benefit/whatever, to do it one way over the other that I am not aware of or am missing. Thanks

I suspect someone has already stated this but on my boat I use a dedicated start battery bank. The start batteries are direct connected to the engine and from the engine to a start disconnect switch feeding the battery buss. The house batteries are direct connected to a house disconnect switch feeding the battery buss. If necessary I can isolate the start battery from the house load using the start disconnect switch. If the house battery is dead I can use it's disconnect switch to take it off the buss.The draw back to this scheme is I have to choose to take the start battery bank off the house buss via the disconnect switch.



Comparing a single bank with switched in reserve or dual bank configuration (separate start), the dual bank always is using the start battery(s) and if they have begun to misbehave you may get some heads up. If using a dual bank configuration, I suggest wiring so as to be able to use either bank to start the engine.



There was a good thread on alternator load dumps that addresses pitfalls in abbynormal wiring of disconnect switches.


Good luck

Phil

[guyrj33]

There are a lot of good reasons to choose an asymmetric two bank setup, consisting of a starting battery and a house bank of appropriate size.
you'll need appropriate switching to be able to use either bank independently for starting and for house loads, you'll also need the ability to combine both banks for charging and starting if both banks are low.
Lot's of people have provided opinions and diagrams on how to accomplish the above. I still use the original (1973) 1-2-both-off switch to accomplish the setup described above.
I have a sailboat with 80AH start battery, 2x6V 225AH house bank, 70amp Balmar alternator, 3 stage voltage regulator. My batteries last 7-10 years.

[parkstone bay]

Let's look at the OPs first question/premise, which is - in essence - "What happens if/when both my 'main' and my 'reserve' battery system, (leaving aside the configuration for a moment) are unable, either individually or grouped together in some way, to start my engine?". The short answer is "you're in deep doo-doo". Thus the question should really be: "How do I minimise the risks of this happening?" . On a lot of small boats, you use just one battery to start the engine, and to power the house/domestics; after all it's good enough for pretty well every road car that's ever been built. Most boaters, though, feel the consequences of not being able to start your engine are high enough to warrant a different system. The best, and it really cannot be argued, is to have separate starter and house batteries, and also - and I suggest this is critical - to arrange your charging system such that the start battery is always charged. This can be done cheaply by using a Voltage Sensitive Relay, or more expensively, though probably electrically preferable, by using a diode splitter. Either way, the start battery is always charged preferentially to the house battery. It is (almost) impossible to have any unintended load on the starter battery: the only thing that takes current is the starter motor itself (unless you've a real problem with the wiring). It is, however, extremely easy to leave the boat with load draining the house battery - a VHF radio, a hi-fi, lights, bilge pump on "auto", etc. My boat is a 21ft MB, with a 24 hp inboard. The main house load is the coolbox; it uses about 4.5 amps. If we stop for a 6 hour picnic it gives the battery quite a drain. So, the OP should very seriously consider separating his starter and house battery

[john61ct]

That was never in question, taken as given that whether dedicated-Starter or Reserve design, either is separated from the main House while there are loads greater than the energy inputs.

And any significant ongoing loads in a boat where ICE is rarely run, will require a proper deep cycling bank, that is also universally known, not up for debate except among the ignorant, or Wally-warrantee scammers.

Stinkpots of course have a completely different situation with high amps available on demand, often more than would ever be required, so in that context this discussion is essentially moot anyway.

As the Cruisers Sailing Forum, the sailing part needs to be assumed by default.

[ontherocks83]

Originally Posted by parkstone bay

Let's look at the OPs first question/premise, which is - in essence - "What happens if/when both my 'main' and my 'reserve' battery system, (leaving aside the configuration for a moment) are unable, either individually or grouped together in some way, to start my engine?". The short answer is "you're in deep doo-doo"...…………….


So, the OP should very seriously consider separating his starter and house battery

I appreciate the input, but that was not my question at all.

I stated that I had / have 2 separate banks and wanted to know what people's thoughts were on bank 2 being either a start bank, or a reserve bank.

[ontherocks83]

Originally Posted by Maine Sail

About the only time a "house + reserve" system would be used is on a boat that already has an existing 1/2/B switch. If that is the case, and it's not worthwhile to do a switch re-configuration, then it can work. Just be sure you check/test the reserve bank occasionally to ensure it is operational when or if you need it.

1/2/B Switch Thoughts & Musings (LINK)










.

By the way this is what I have decided will work best for me, with weekly testing of the reserve bank i.e. every Friday night after work I start with the reserve bank and then switch to and only use the house.

[john61ct]

Make sure that both banks' wire gauge & fuses will handle whatever the biggest possible loads are (+20%)

https://forums.sailboatowners.com/th...0#post-1324216

Note that thread's point is really on getting the switches wired to redirect loads not sources. Maine Sail response to my "Reserve as opposed to dedicated Starter" concept was here

https://forums.sailboatowners.com/th...0#post-1346551

After which I started new threads.

I have not reviewed all this from 2 years ago to see how much I-now still agrees with I-then. 8-)

[Cutterman]

[QUOTE=Tillsbury;2982814]Definitely house and start. House is as big as you can make it, managed for best ability to provide continuous current while maintaining best state of health. Start battery is a high CCA sealed unit. Completely different type of battery with completely different requirements. Both used every day and both under battery monitor at all times.


I'm with Tillsbury and Moderator on this although their boats are larger than mine and boat size affects opinions. My boat is 33'3" OA with moderate overhangs so it is more sensitive to its payload than larger boats. My solution is to keep the 450Ah deep cycle house bank and 70CCA sealed aircraft engine starter batteries completely separate for the reasons Tillsbury states.

Other than solar and wind, the only generator on board is the main engine so there is a reserve start battery which I alternate about once a month with the active one to keep them both in good condition. Both start batteries also provide an emergency source of power to the HF radio because they are located higher up in the boat than the house bank.

There is a dual alternator system on the engine that also trickle charges the active start battery when the engine is running. A Projector DC/Solar charger automatically charges the start battery from the solar panels or directly from the trickle charger, whichever source is producing the most power at the time.

For a boat the size of mine, this seems to be the most secure solution when weight is really important.