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Old 04-07-2020, 12:06   #1
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Keeping a start battery charged

I have never used a start battery as I don’t see the logic in one, but have now gotten a new Odyssey battery I need to find a use for and was thinking maybe use it as a generator start battery, generator doesn’t have its own alternator, I have a Blue Seas ACR in spares and it would be simple to just use it.
But here is the problem as I see it, with the ACR you would be subjecting the little Odyssey to a full absorption charge every day, with it already at 100% SOC and over time, surely that will kill it.
So how do people keep their start batteries charged, if by using an ACR, it’s going to kill it by overcharging it every day, day in and day out?

Along the same lines, I will soon have a new bank, but will keep most of the old bank for redundancy, but don’t plan on using it. I am going to isolate it with the battery switch and just use my little shorepower charger that can charge two independent banks once a month or so to keep it fully charged.
All my charging is done usually by my inverter / charger and Solar, and I wasn’t going to connect them to the back up bank.

But the ACR seems to be a flawed concept, does it not?
If at the beginning of the day, my big bank is at 12.5 V as it’s discharged, but the starter bank is at 13V cause it’s fully charged,won’t you first discharge it when the two banks combine, then overcharge it when the voltage gets back to absorption?
It would seem that a trickle charger would be better and not the ACR?
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Old 04-07-2020, 12:39   #2
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Re: Keepinmightg a start battery charged

Might look at battery isolators. Made from diodes which prevent current back flow and provides about .5 -volt drop plus to minus so might ease up on charging the start battery every day.


Victron MPPT solar controllers ease up on the absorption voltage because of the cycle you describe. If you are in the absorption mode level charging most every afternoon, then the voltage is reduced slightly to keep from cooking LA batteries.


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Old 04-07-2020, 13:01   #3
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Re: Keeping a start battery charged

if the ACR is doing it's job, It will only connect the batteries when the voltage on the primary (charger-attached, house) bank is higher than the secondary (starter) bank. So no worries about drawing down the starter battery. An ACR is only an issue if the charge profiles of the 2 banks are very different (like GEL vs FLA).
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Old 04-07-2020, 13:02   #4
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Re: Keeping a start battery charged

There's a little device that is called a combiner, like $60+ that automatically directs charge your start battery but doesn't overcharge it ....and doesn't interfere with the charging of your bank. Made by several companies for decades. Forget the name, I'll see if I can find it.
Basically it ties the banks together until charge is reached. Combined batteries will equalize their charge by nature, so one can't really be over charged. (ie: if you put a low 10 volt battery and a 13 volt batter together, they will equalize in voltage.)
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Old 04-07-2020, 13:13   #5
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Re: Keeping a start battery charged

My start batteries (2 banks) are only charged by the engine alternators and shore charger. So they get charged on shore power / generator or while running. When I add solar, it'll charge the house bank only.



I do have ACRs, but they're interlocked to the engine ignitions. Alternators charge the start batteries, then ACRs allow charging of the house bank, but only with the engines running. With the engines off, the ACRs are disabled and the 3 banks are charged independently.
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Old 04-07-2020, 13:36   #6
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Re: Keeping a start battery charged

I have a simple solution to your dilemma, but most of CF readers won't approve of it. Sorry, this is just the way I am.

Go simple, go manual, know that less is more.
  1. Connect the house bank to a Off-1-2-Both switch, position 1
  2. Connect the start battery to position 2.
  3. Connect the output of all charging devices to the house side of that switch.
  4. Connect the battery sense wire of the regulator to the house side of that switch.
  5. Connect the engine start power cable to the house side of that switch
  6. Install a meter which can measure either bank.
Normally your battery switch will be in position 1, running off of the house batteries, (also charging the house system, also starting from the house system).

You can charge the starting battery by changing the switch to position 2.

Once it is charged switch back to position 1 and leave the start bank alone, not connected to any devices, none.

Check Battery 2 from time to time to see it's state of charge.

Charge it when it needs it (rarely).

Even switch to battery 2 from time to time and start the engine with it (a better check).

At any time you can even combine both batteries to "both" for starting, if everything is low.(it won't be).

If you leave the switch on "Both" and let it all run down, it's on you.

You need no ACR, no isolators, no combiners, or any extra stuff, just your own brain.
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Old 04-07-2020, 13:51   #7
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Re: Keeping a start battery charged

Quote:
Originally Posted by wingssail View Post
I have a simple solution to your dilemma, but most of CF readers won't approve of it. Sorry, this is just the way I am.

Go simple, go manual, know that less is more.
  1. Connect the house bank to a Off-1-2-Both switch, position 1
  2. Connect the start battery to position 2.
  3. Connect the output of all charging devices to the house side of that switch.
  4. Connect the battery sense wire of the regulator to the house side of that switch.
  5. Connect the engine start power cable to the house side of that switch
  6. Install a meter which can measure either bank.
Normally your battery switch will be in position 1, running off of the house batteries, (also charging the house system, also starting from the house system).

You can charge the starting battery by changing the switch to position 2.

Once it is charged switch back to position 1 and leave the start bank alone, not connected to any devices, none.

Check Battery 2 from time to time to see it's state of charge.

Charge it when it needs it (rarely).

Even switch to battery 2 from time to time and start the engine with it (a better check).

At any time you can even combine both batteries to "both" for starting, if everything is low.(it won't be).

If you leave the switch on "Both" and let it all run down, it's on you.

You need no ACR, no isolators, no combiners, or any extra stuff, just your own brain.
This is great solution for those that are perfect and never, never forget. I used that system for years and forgot just once which left me with no way to crank the engine anchored in an isolated harbor in the south Bahamas.
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Old 04-07-2020, 14:04   #8
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Re: Keeping a start battery charged

Xantrax echo charger.
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Old 04-07-2020, 14:07   #9
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Re: Keeping a start battery charged

Quote:
Originally Posted by skipmac View Post
This is great solution for those that are perfect and never, never forget. I used that system for years and forgot just once which left me with no way to crank the engine anchored in an isolated harbor in the south Bahamas.
Well, that is BS now days when everyone has multiple ways of charging batteries. But OK, first you have to ask yourself why your system was on "Both" at that time anyhow?

I am not perfect, I forget stuff all the time, but if I were to put my system on "Both", (or switch to batt 2 when batt 1 is already discharged) then I know I am playing with fire, and I would take special precautions. For example I hang a yellow sticky somewhere where I cannot miss it, reminding me.

But in 34 years I rarely RARELY, put that switch on to "Both" and walk away, or switch to "2" when batt 1 is down, and walk away. Just NEVER, ever, do it.
That is not forgetfulness, it is a rule you just don't break. No one is going to forget that they are not supposed to touch that switch casually. Doing that is not forgetfulness, it is stupidity.

Finally, if you screw yourself, let the solar put a charge on the starting battery and at some point you'll have enough to crank the engine.

PS, the OP has a hand cranked genset. He won't ever be in that position.
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Old 04-07-2020, 14:09   #10
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Re: Keeping a start battery charged

Quote:
Originally Posted by a64pilot View Post

But the ACR seems to be a flawed concept, does it not?
If at the beginning of the day, my big bank is at 12.5 V as it’s discharged, but the starter bank is at 13V cause it’s fully charged,won’t you first discharge it when the two banks combine, then overcharge it when the voltage gets back to absorption?
It would seem that a trickle charger would be better and not the ACR?
It combines when one bank is over 13.3v. A small solar array may takes hours to bring a big 12.5v house bank to 13.3v. At which point the acr would come on and both would be at say 13.2 or 13.3.

A battery over 13v is not draining.
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Old 04-07-2020, 14:36   #11
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Re: Keeping a start battery charged

I went with Balmar Duo Charge for the start battery. Seems to be idiot proof so far. Not sure it would do a whole second bank though.
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Old 04-07-2020, 14:46   #12
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Re: Keeping a start battery charged

Echo charger, trickles it off the main bank when main bank is charged adequately , Has worked perfect for last 7 years.
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Old 04-07-2020, 14:55   #13
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Re: Keeping a start battery charged

We use a plain car relay bridge active when the engine is ON.


But I think this is only done when the house and start batts are very much alike in capacity and type.


b.
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Old 04-07-2020, 14:56   #14
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Re: Keeping a start battery charged

Quote:
Originally Posted by wingssail View Post
I have a simple solution to your dilemma, but most of CF readers won't approve of it. Sorry, this is just the way I am.

Go simple, go manual, know that less is more.
  1. Connect the house bank to a Off-1-2-Both switch, position 1
  2. Connect the start battery to position 2.
  3. Connect the output of all charging devices to the house side of that switch.
  4. Connect the battery sense wire of the regulator to the house side of that switch.
  5. Connect the engine start power cable to the house side of that switch
  6. Install a meter which can measure either bank.
Normally your battery switch will be in position 1, running off of the house batteries, (also charging the house system, also starting from the house system).

You can charge the starting battery by changing the switch to position 2.

Once it is charged switch back to position 1 and leave the start bank alone, not connected to any devices, none.

Check Battery 2 from time to time to see it's state of charge.

Charge it when it needs it (rarely).

Even switch to battery 2 from time to time and start the engine with it (a better check).

At any time you can even combine both batteries to "both" for starting, if everything is low.(it won't be).

If you leave the switch on "Both" and let it all run down, it's on you.

You need no ACR, no isolators, no combiners, or any extra stuff, just your own brain.
I’m pretty much going to do that with the two banks, except connect everything to bank #1 which will be the one in use, leaving one usually unused charger to bank #2 to keep it topped off every once in a while.

But that leaves the start battery, it will undergo absorption voltage every day until the bank is at 2.2 amps acceptance, which of course includes it as the ACR will have combined the two, that’s unacceptable, that will eventually surely dry out the electrolyte.

I’ve just about decided that from a financial perspective and ease of use etc that an inexpensive battery minder connected to it is the best way, then when the generator is running, the battery minder is powered, and they go to float or turn off when the battery is fully charged, just they are tiny little chargers, but that’s all a small Odyssey battery would need that is only used to start a one cylinder Kubota anyway. Generator run time is never over a coupe of hours anyway.

But yes if I ever do kill both banks, I have a Honda that can power a 100 amp charger, and with a start battery my generator can power both chargers for a 185 amp total, that would start the engine and add theoretically another 165 amps.

Without a battery failure I don’t understand how you could kill a bank on a boat thats being used. As a matter of course I check the bank in the morning and in the afternoon.
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Old 04-07-2020, 15:02   #15
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Re: Keeping a start battery charged

Our setup is similar to wingssail's. Two banks, #1 is house, #2 is starter. Run through the standard 3-way switch.
  • Passive charging (solar/wind) runs directly to house bank (#1).
  • Shore power charger is a dual charger, so can charge both banks at the same time.
  • Engine alternator charges the bank selected at the switch.
Our routine is to switch to #2 bank to start the engine. We leave the switch on the starter bank long enough to recharge the battery. Then we switch to the other bank to divert the alternator charge to house (#1), and isolate the starter (#2)

Very occasionally I combine the banks (BOTH or ALL setting) to allow charging of both. But this is exceedingly rare. There's really not much reason to combine the banks.

In the decade of cruising like this I've never run into a problem. On the rare occasion I've forgotten to switch to start, it's really no big deal. But to answer the "why" have two banks question, I just prefer knowing that if all else fails, I can rely on being able to start my engine via the isolated starter battery bank.

On my previous boat I did connect the banks via an ACR. It worked fine as well. If I were to rewire my current boat I might use and ACR or an Echo Charger, but I'm very content with the more manual approach with our 3-way switch.
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