AGM Battery Bank Configuration

[btrayfors]

Originally Posted by SV Demeter

..... would he not be better off with a DC generator?

Not necessarily.

Anyway, he has what he has, presumably an AC genset.

Some folks have had very good luck in using two identical 90A Iota/DLS-IQ4 chargers in parallel, with an output of 180A. They make provision especially for this paralleling.

Works well. Won't break the piggy bank :-)

Bill

[Exile]

Originally Posted by btrayfors

Not necessarily.

Anyway, he has what he has, presumably an AC genset.

Some folks have had very good luck in using two identical 90A Iota/DLS-IQ4 chargers in parallel, with an output of 180A. They make provision especially for this paralleling.

Works well. Won't break the piggy bank :-)

Bill

Yes, it's an AC genset.

Hey Bill! We met in the Wash. Channel last year via the SSCA. You gave me a hand with my SSB set-up as you may recall. I'm headed back to the Chesapeake next month -- perhaps you should be the consultant you suggested I find to take a look at the system??? Hope all is well. Dan

[donradcliffe]

If you don't have one, install a cable and switch to combine the engine start battery and the house bank. Then turn it on and leave it on.

This give you three advantages--

you can use the capacity of all three 8D batteries to run your house loads, which will extend their lifetime considerably

you can use both alternators on your engine to charge up the combined bank, thus charging twice as fast

your engine will start more easily with 3 big batteries rolling it


There is only one caveat--you will have to keep an eye on the voltage, and start either the engine or the genset if it gets below 12v. However, with a 750 amp-hour capacity, this means looking at the voltage once a day.

I know there are a lot of 'experts' who will say that this is too risky, but you do have a way to recover from either a shorted cell or unintentional draining of the batteries--just start your genset on its separate battery. I have run my boat this way for over 15 years of living aboard, and haven't had any problems, even when a cell shorted.

[Pete7]

Originally Posted by btrayfors

Works well. Won't break the piggy bank :-)
Bill

Good point, it's very easy to spend someone else's hard earned dollars trying to create utopia.

Looking at his power usage it's tiny, perhaps 50AH a day. It might be better to sell the 3rd D8, its certainly not needed with the existing 500 AH bank.

Since AGMs like to be fully charged the smaller bank would be easier to top up using the Genset and say a 75AH battery charger. Even after several days at anchor the shortfall in amps isn't going to be a lot which the genny and a charger could make up in a couple of hours. Trying to fully top off a 750 AGM bank regularly to maintain a long life will just be that much more difficult, since the last 10% takes the time.

With the cash from the 8D some solar would be good.

Pete

[btrayfors]

Originally Posted by Exile

Yes, it's an AC genset.

Hey Bill! We met in the Wash. Channel last year via the SSCA. You gave me a hand with my SSB set-up as you may recall. I'm headed back to the Chesapeake next month -- perhaps you should be the consultant you suggested I find to take a look at the system??? Hope all is well. Dan

Hey, Dan! Yep, I remember.

Would be happy to help, and if I can't we have a couple of other extremely well qualified techies who could.

Let me know when you're coming up this way.

You can PM me or email: bill at wdsg dot com

Cheers,

Bill

[Exile]

Thanks Bill -- I still have all your contact info so I'll give you a heads up. The SSB seems to be working great, btw, but the operator still needs some help!

OK, so far I'm gathering that increasing the house bank to 750 would likely require a larger capacity a/c charger, a larger eng alt, and possibly a smart regulator. Sounds expensive for a system that's otherwise working well. Pete7 is probably right about my consumption based on what I've observed on the voltage meter -- one of these days I need to do the math & track it better. I know electronics don't typically consume much, but I thought the auto-pilot would use more. I looked at a table that suggested that 12.2V is approx. 50% batt. consumption and I know I never get near there before turning the genset on (mainly for the fridge). So maybe just swapping out the eng start 8D with a smaller batt. is the way to go? But then I won't have an excuse to anchor out in the Wash. Channel and drink a beer with Bill!

BTW, the PO had a watermaker on the boat at one time. That and the two a/c's probably explains the large capacity genset. Chose not to add yet another layer of complexity onboard by not replacing that one!

[Exile]

Originally Posted by donradcliffe

If you don't have one, install a cable and switch to combine the engine start battery and the house bank. Then turn it on and leave it on.

This give you three advantages--

you can use the capacity of all three 8D batteries to run your house loads, which will extend their lifetime considerably

you can use both alternators on your engine to charge up the combined bank, thus charging twice as fast

your engine will start more easily with 3 big batteries rolling it


There is only one caveat--you will have to keep an eye on the voltage, and start either the engine or the genset if it gets below 12v. However, with a 750 amp-hour capacity, this means looking at the voltage once a day.

I know there are a lot of 'experts' who will say that this is too risky, but you do have a way to recover from either a shorted cell or unintentional draining of the batteries--just start your genset on its separate battery. I have run my boat this way for over 15 years of living aboard, and haven't had any problems, even when a cell shorted.

I like the simplicity, and am also not overly concerned about the potential risk to starting the engine. I think it's basically what I was asking about, namely leaving the existing charging & monitoring system intact, but wiring in the 3rd 8D to the house bank. Not sure how or if it would work, though. I certainly appreciate the input -- thank you.

[cheoah]

Pete's got a pretty good idea here, particularly if the bank is over sized and charging sources are overwhelmed. You'll have one less big battery to replace when they go bad, and the two remaining may be more appropriately sized and poised for longer life due to typically fuller charge.

I realize you weren't looking to complicate things to much, but I'm a big proponent of the combined house bank, and a separate, smaller, cheaper, start battery that is charged with a simple xantrex echo charge. I love my Balmar AR5 smart regulator, too! I have a lot of good things to say about it now that I am familiar with it. You can monitor temps of battery and alt and manage things like belt load and battery types. If you have pricey batteries, this is a good investment.

Anyway, Bill can get it dialed in for you-

csh

[Bash]

Originally Posted by Pete7

Looking at his power usage it's tiny, perhaps 50AH a day. It might be better to sell the 3rd D8, its certainly not needed with the existing 500 AH bank.

Since AGMs like to be fully charged the smaller bank would be easier to top up using the Genset and say a 75AH battery charger. Even after several days at anchor the shortfall in amps isn't going to be a lot which the genny and a charger could make up in a couple of hours. Trying to fully top off a 750 AGM bank regularly to maintain a long life will just be that much more difficult, since the last 10% takes the time.

With the cash from the 8D some solar would be good.

Pete

Agreed. Overkill is not always a good thing, and it's going to be hard to keep a 750 AH bank fully charged.

Sell the third 8D, then get the solar.

[Exile]

Originally Posted by csh

Pete's got a pretty good idea here, particularly if the bank is over sized and charging sources are overwhelmed. You'll have one less big battery to replace when they go bad, and the two remaining may be more appropriately sized and poised for longer life due to typically fuller charge.

I realize you weren't looking to complicate things to much, but I'm a big proponent of the combined house bank, and a separate, smaller, cheaper, start battery that is charged with a simple xantrex echo charge. I love my Balmar AR5 smart regulator, too! I have a lot of good things to say about it now that I am familiar with it. You can monitor temps of battery and alt and manage things like belt load and battery types. If you have pricey batteries, this is a good investment.

Anyway, Bill can get it dialed in for you-

csh

Is the Xantrex Echo Charge you mention the same idea as my "BEP Voltage Sensitive Relay" that I use to charge my gen batt off one of the house batts?
I'll look into the Balmar regulator. Funny, I thought my "smart" charger was the device to prevent overcharging & other issues.

[Exile]

Originally Posted by Bash

Agreed. Overkill is not always a good thing, and it's going to be hard to keep a 750 AH bank fully charged.

Sell the third 8D, then get the solar.

Assuming 2 house 8D's and a smaller eng start batt, what am I looking for in terms of output for solar? (There's already probably a ton of threads on this).

[Pete7]

Originally Posted by Exile

Assuming 2 house 8D's and a smaller eng start batt, what am I looking for in terms of output for solar? (There's already probably a ton of threads on this).

There are you will need to hibernate in an igloo for a winter to read through them all.

However, it's not the size of the battery bank that's important here, but your daily useage. For example it doesn't matter if you use 50 AH a day from a 200 AH bank or a 500 AH bank, its the 50 AH daily useage you need to put back that is the key.

As a rough and ready rule you will get 1/3rd of the panel wattage in amps hours per day. A 45w panel will give about 15 AH, in good conditions. I am 50.N and achieve about 10AH a day in the summer from a 45w panel with some shading during the day from the boom, not bad given the high latitude.

So if you want to replace your 50 AH daily usage you will need say 200w of solar (to be safe for cloudy and rainy days) and an MPPT/PWM controller to boost the charging effficency (thats another long read).

Since you have a huge 500AH bank already the solar doesn't need to balance the usage if you are willing to top up every few days with the genny. This is what we do, we use 30AH a day and have 10 AH back from solar so our 220 AH bank slowly goes into deficit. Every few days we run the honda 20i to top up the bank.

The other thing is that solar will trickle charge your batteries when you are away from the boat. You have AGMs, these batteries really do need to be regularly topped up fully as apposed to ordinary flooded lead acid which will take a bit more abuse IMHO.

Pete

[Exile]

Originally Posted by Pete7

There are you will need to hibernate in an igloo for a winter to read through them all.

However, it's not the size of the battery bank that's important here, but your daily useage. For example it doesn't matter if you use 50 AH a day from a 200 AH bank or a 500 AH bank, its the 50 AH daily useage you need to put back that is the key.

As a rough and ready rule you will get 1/3rd of the panel wattage in amps hours per day. A 45w panel will give about 15 AH, in good conditions. I am 50.N and achieve about 10AH a day in the summer from a 45w panel with some shading during the day from the boom, not bad given the high latitude.

So if you want to replace your 50 AH daily usage you will need say 200w of solar (to be safe for cloudy and rainy days) and an MPPT/PWM controller to boost the charging effficency (thats another long read).

Since you have a huge 500AH bank already the solar doesn't need to balance the usage if you are willing to top up every few days with the genny. This is what we do, we use 30AH a day and have 10 AH back from solar so our 220 AH bank slowly goes into deficit. Every few days we run the honda 20i to top up the bank.

The other thing is that solar will trickle charge your batteries when you are away from the boat. You have AGMs, these batteries really do need to be regularly topped up fully as apposed to ordinary flooded lead acid which will take a bit more abuse IMHO.

Pete

Thanks for the clear & concise explanation! That's exactly the intro I needed to start looking into solar. With 3 separate ways of charging my batts (eng, gen, backup Honda), my primary reason for solar would be for top-off purposes so I hopefully wouldn't have to keep the boat plugged in when I'm away.

[witzgall]

Here is a scenario:

You sit at anchor for 4 days, enjoying the serenity. Then you need to move, and
It is a motorsail situation. So you run the motor for eight hours. Regular basis, maybe not, but it certainly will happen sometime, and that alternator will fry in short order if subjected to that kind of stress.

One other option, upgrade your alternator, move the 8D over to the house, and then get a simple echo charge unit to charge the starter battery. No more "1-2- both" situation. Make the starter battery an AGM or GEL, and it will be very happy for a long time.

Originally Posted by Pete7

If he has a 8kw genny on board why would he use the engine alternator to charge the house bank on a regular basis? surely that would be the more efficient route.

Pete

[cheoah]

Hi Exile, yes the Echo Charge will bleed some current to your start battery, insuring it gets charged. No reason you can't just start your motor with the house battery either, unless it affects your electronics. Others can comment on this as I'm, certainly no expert. This would allow you to just turn your battery to one of the battery positions then to "off" when you leave. You could add a new label to your current switch and keep using it as an on/off switch, and only switch to the other position if you need the emergency battery to start

Solar would be a great investment for long term battery care and downright sensible power generation. Replacing batteries is a pricey chore!

Take Care-

csh