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  #1  
Old 02-26-2012
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Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

I’m trying to decide on a charging technology that will automatically charge all my battery banks when a charging source is present. Right now I’m trying to choose between the respected Blue Sea SI 120 ACR and the newish Sterling Battery-to-Battery Charger. I like the simplicity and reputation of the ACR, but I like the fact that the Sterling Charger can do multistage charging appropriate to each individual isolated battery bank. I also like that the Sterling can do a targeted desulfation charge.

The boat has a starting battery and a 400Ah house bank of Trojan T-105s that live inside the engine room, and a 350Ah house bank of Trojan L16Hs that lives under the companionway.

The boat is a full-time live-aboard 42 foot sailboat. I’m in the planning phase of a project to address a number of energy management issues. Typically, when I am charging, the house banks will have different levels of charge: one usually near full, one usually 25%-50% depleted. In this situation, I ideally want the charged bank to get a float charge while the discharged bank needs an absorption charge. I’m concerned that the ACR would cause the charged bank to get a voltage that is higher than it needs and the discharged bank to get a voltage that is lower than it needs (Calder, p40). This is why I’m looking into the Sterling battery-to-battery charger.

Dear reader, do you have any experience with this battery-to-battery charger?
Is there any feedback you can share about it?
Have you had a good experience with a different series regulator?

The echo charger probably has too small a capacity for charging the large banks I have.

Since I’ve owned her (until the past month) the boat has been run with the two sets of house batteries joined together in a single house bank. But as I contemplate buying new batteries, I’m coming face-to-face with what I’ve already known and have been trying to ignore, Nigel Calder’s cautions about mixing different battery types in a single bank, and especially the dangers of mixing batteries in the wildly different temperature environments between the engine room and the companionway area (in general, though, Calder strongly advocates single large house battery banks). Charlie Wing, on the other hand, advocates an older practice using half-sized and alternated banks that has turned out to have been essential to me in analyzing the health of my various different batteries.

Any thoughts you can share?
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Old 03-01-2012
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Good questions you pose, and I'm monitoring the thread for informative answers as well. Unfortunately I have no experience to report on the products you list.

I note there is a majority of opinions that advise against splitting a house bank in two, partly because it causes each bank to suffer a deeper depth of discharge than would be the case for a combined bank. Depth of discharge having a bearing on the longevity of lead acid batteries.

It does occur to me that if, for whatever reason, I HAD to have two house banks, my first approach would be:

a) Monitor the state-of-charge of each bank with a batt monitor (with DOD alarms).
b) Based on monitor readouts, I would manually switch drawing betw banks
c) Based on monitor readouts, I would manually switch charging betw banks

Essentially, I would do (b) and (c) above in a way that controls the depth of discharge of each bank, while at the same time ensuring each bank does a substantial share of duty.

I am sure it is feasible to build a smart charge/discharge controller that can do this automatically for two banks. Such products probably exist for the super-yacht market, but I doubt they exist for the cruising sailboat market/budget. Still, you never know.
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Old 03-06-2012
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

Hello mmv, thank you for your comments. [. ..]

> [...] a majority of opinions that advise against splitting [...] it causes
> each bank to suffer a deeper [...] discharge [...which has] a bearing on the
> longevity of lead acid batteries.
Noted, and agreed. If I could avoid this I would, but I'm resigned that the boat simply is what it is.

> [...] if [...] I HAD to have two house banks, my first approach would be:

> a) Monitor [...] with a batt monitor
> b) Based on monitor readouts, I would manually switch drawing betw banks
> c) Based on monitor readouts, I would manually switch charging betw banks
I’m with you on (a) and (b), but I’m trying to have (c) happen automatically-ish. In my own experience I find that manual procedures fall apart in spite of the very best of intentions.

> [. ..] a smart charge/discharge controller that can do this [. ..] probably exist for
> the super-yacht market, but I doubt they exist for the cruising sailboat market/budget.

Many thanks for your thoughts. It looks like nobody has anything further to add. I’ll report back if I learn anything more about the Sterling product.
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Old 03-06-2012
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

Quote:
Originally Posted by djwindrifter View Post
I’m trying to decide on a charging technology that will automatically charge all my battery banks when a charging source is present. Right now I’m trying to choose between the respected Blue Sea SI 120 ACR and the newish Sterling Battery-to-Battery Charger. I like the simplicity and reputation of the ACR, but I like the fact that the Sterling Charger can do multistage charging appropriate to each individual isolated battery bank. I also like that the Sterling can do a targeted desulfation charge.
You'd need the bigger B2B from Sterling if your charge sources are up to it. It is a nice piece of gear, as is the very simple ACR..



Quote:
Originally Posted by djwindrifter View Post
I’m concerned that the ACR would cause the charged bank to get a voltage that is higher than it needs and the discharged bank to get a voltage that is lower than it needs (Calder, p40). This is why I’m looking into the Sterling battery-to-battery charger.
This physically can not happen with combined batteries and should be filed under "urban myth".. The voltage across all battery banks becomes the same and each bank will take the current it needs from the charge source. You can not over or under charge "combined" batteries as they charge at the same voltage and reach an equilibrium.



Quote:
Originally Posted by djwindrifter View Post
The echo charger probably has too small a capacity for charging the large banks I have.
The Echo is the wrong fit for this application and far too small.

Quote:
Originally Posted by djwindrifter View Post
Since I’ve owned her (until the past month) the boat has been run with the two sets of house batteries joined together in a single house bank. But as I contemplate buying new batteries, I’m coming face-to-face with what I’ve already known and have been trying to ignore, Nigel Calder’s cautions about mixing different battery types in a single bank, and especially the dangers of mixing batteries in the wildly different temperature environments between the engine room and the companionway area (in general, though, Calder strongly advocates single large house battery banks). Charlie Wing, on the other hand, advocates an older practice using half-sized and alternated banks that has turned out to have been essential to me in analyzing the health of my various different batteries.

Any thoughts you can share?
As you already discovered the engine room is a TERRIBLE location for any battery bank, but of you must keep them there your "charge source" should monitor temp of the hottest bank and reduce voltage accordingly. This means your battery charger and alternator regulator should have temp sensing capabilities.

Charlie's statements are based on the old model of a boat with equal sized battery banks and a 1/2/BOTH. You have three banks 2 house 1 start. Most boats today use a single larger house bank, this allows for shallower discharges and longer life, and then a single starting battery. Alternating house banks usually results in deeper discharges to each bank and thus a shorter cycle life. If the new bank can be fit so all the batteries are the same then you might consider making them one big bank. If you feel more comfortable you can put a safety switch in that keeps them with the potential to be isolated but normally they would remain as one bank..

For the engine room issue alone the Sterling B2B makes a lot more sense than the ACR IF you can deal with a max of 45A charging output. If you need more than the 45A capability then an ACR with temp sensing on the engine room bank can work though the cooler bank will be charging a tad slower due to the lower voltage/pressure.

The B2B has the ability to BOOST the voltage going to the second bank while the hot bank is seeing a lower voltage or you could use the B2B to feed the hot bank and it does its own temp sensing..

Sterling B2B Charger
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Last edited by Maine Sail; 03-06-2012 at 04:12 PM.
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Old 11-08-2012
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

I think the one-big-bank vs. switching-between-banks will be a never-ending debate, and one that I don't think is a slam-dunk. I've gotten incredible life out of batteries in separate banks (O.K., they *were* Surrettes), and that was flipping the old A-B switch back and forth every day or so. The argument for separate sets is that they will always charge at their natural rate, unaffected by the possibly sulfated/hot/cold/whatever other battery in their bank. I think when they're new, having them in parallel (one large bank) is fine, but as they age, it tends to give grief. (A good argument for sets of 2v cells that are always in serial!).

Then again, I wouldn't argue with the large-bank proponents, either.

My other two cents - I think the Sterling B2B is a really cool idea, just haven't gotten a chance to put one in yet. Hoping to hear some first-hand comments.
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

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Originally Posted by AlanF View Post
My other two cents - I think the Sterling B2B is a really cool idea, just haven't gotten a chance to put one in yet. Hoping to hear some first-hand comments.
They are great units though a tad on the bulky side. The smaller water proof version has all the pig tail wires already attached. I find this to be a PITA as I prefer to run my own wiring but in order for it to be water proof it is what it is.. The larger units, like a stand alone battery charger, allow for this. While more expensive than an ACR or Echo or Balmar Duo they also do more and are a true battery to battery charger. They also allow mixing a GEL house bank with an AGM or flooded start bank because they also have the ability to "boost" the output voltage. So you can feed a house bank of GEL's at the manufacturer suggested voltage, say 14.1V, then feed an AGM or wet at it's recommended voltage of say 14.6V via the B2B.
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Old 11-08-2012
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

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Originally Posted by AlanF View Post
I think the one-big-bank vs. switching-between-banks will be a never-ending debate, and one that I don't think is a slam-dunk. I've gotten incredible life out of batteries in separate banks (O.K., they *were* Surrettes), and that was flipping the old A-B switch back and forth every day or so. The argument for separate sets is that they will always charge at their natural rate, unaffected by the possibly sulfated/hot/cold/whatever other battery in their bank. I think when they're new, having them in parallel (one large bank) is fine, but as they age, it tends to give grief. (A good argument for sets of 2v cells that are always in serial!).

Then again, I wouldn't argue with the large-bank proponents, either.

My other two cents - I think the Sterling B2B is a really cool idea, just haven't gotten a chance to put one in yet. Hoping to hear some first-hand comments.
Just remember that there are two main advantages to the single large bank:

1) A single large bank means each battery sees a lighter load. Ah's are specified at certain load current (the 20 hour rate) - anything more and you get less Ah's, anything less you get more. So for any given load when you add batteries you always get 'extra' capacity as the load for each battery goes down and therefore it's effective capacity at the new lower discharge rate goes up. It's like 4 lightly loaded horses pulling a kart will take it more than twice as far as 2 heavily strained ones.

2) You're discharging each bank less. Discharging a single large bank to 20% every day is a lot better than discharging a half bank to 40% every other day because battery lifetime goes up exponentially as discharge depth goes down.

Note that 1) also helps with 2) because the 'extra' capacity further reduces the depth of discharge for a larger bank.
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Last edited by asdf38; 11-08-2012 at 06:58 PM.
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Re: Battery Bank Combining for Charging –Sterling B2B Charger or Blue Sea ACR?

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Originally Posted by asdf38 View Post
Just remember that there are two main advantages to the single large bank:

1) A single large bank means each battery sees a lighter load. Ah's are specified at certain load current (the 20 hour rate) - anything more and you get less Ah's, anything less you get more. So for any given load when you add batteries you always get 'extra' capacity as the load for each battery goes down and therefore it's effective capacity at the new lower discharge rate goes up. It's like 4 lightly loaded horses pulling a kart will take it more than twice as far as 2 heavily strained ones.
This is called the Peukert Effect.

Two smaller banks will always see more use and cycle depth than a single large bank.. You also have charge inefficiency issues too. It is more efficient to charge one bank than two unless using 100% free energy and even then "finishing" two banks is less efficient due to the longevity of the time acceptance limiting and "finishing" takes.. The larger bank will also not be as dramatically affected by Peukert and you'll actually get some more amp hours out of a larger bank with the same load than you do with a smaller bank with the same load.

For example a bank with a Peukert of 1.2 and a average load of 8A it looks like this..

100Ah bank, Peukert 1.2, load 8A = 91Ah's
200Ah bank, Peukert 1.2, load 8A = 209Ah's
400Ah bank, Peukert 1.2, load 8A = 480 Ah's
600Ah bank, Peukert 1.2, load 8A = 782Ah's
800Ah bank, Peukert 1.2, load 8A = 1104 Ah's

This means that your bank will have shallower discharges, not just because it is one large bank, but if the load stays the same and you increase bank size you will actually get more out of the larger bank due to Peukert.
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Last edited by Maine Sail; 11-08-2012 at 07:13 PM.
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