Battery Banks - Usage Question

[abraxus]

Having now set up, connected and fused my battery banks, with the help of those on here (many thanks by the way), I now want to determine the best way to use them.

I have two banks. One is a single 125ah battery (nominally the start battery), and the other is 4 x 125ah batteries (the house bank). I also have a 1,2, both, off, battery selector switch. The smaller bank is connected to position 1, the larger to 2, and all loads, engine and alternator are connected to the common post, with the exception of the bilge pumps which are directly connected to the house bank. Both banks are charged by a dual output charger when on shorepower.

From various reading it seems that the norm is to switch to 1 to start, and then switch to 2 when stopped, with various combinations of 1,2 or both when running in order to recharge batteries on the move.

Rather than all that faffing about with the battery switch, I was thinking about just leaving the switch on 2 all the time when in use. This would mean that the larger bank would be used for both starting and running the house loads, and would be charged whilst the engine is running. Given that I assume starting doesn't take much from the batteries, and that would be replaced when underway, then this seems much easier to manage.

The smaller bank woud effectively just be a fall back starting battery if anything happened to the main bank. That said, I would probably switch back to the smaller bank when back at the marina and on shorepower, as I leave my fridge on permanently, so if the shorepower was ever to be cut off then the fridge could only ever fully drain one battery and not the larger bank.

Is this a sensible way to go or are there any flaws in this approach?

Many thanks.

 

[JSYmartini]

Have you looked at something like this?

http://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A

Simplifies the whole process greatly

 

[Tranona]

Having spent all that effort and money on battery capacity, maybe you should junk that old 1,2,both switch and replace it with VSR and separate the two banks completely and use one battery only as an engine start battery and then take all the other systems off the house battery bank with separate isolators and a means of paralelling the two banks for emergency engine start should that one battery fail.

That way you do not have to do anything - the VSR will automatically charge your start battery first and then switch the charge to the house bank. You will never run any systems from the start battery will will always be fully charged. Starts take very little and are recharged quickly. You can do all this with a BEP Marine battery switch cluster, but you can also buy all the components (switches and VSR) individually. However, if you are going to seriously use that house capacity you should really be looking at upgrading your charging capability - not suggesting anything in particular because you don't say how you propose to use them and keep them charged.

 

[abraxus]

Have you looked at something like this?

http://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A

Simplifies the whole process greatly

Yes, but I'm not sure how that simplifies what I was planning to do, which pretty much involves me doing nothing, so it just seems like adding another bit of kit. Maybe I'm misunderstanding?

 

[abraxus]

Having spent all that effort and money on battery capacity, maybe you should junk that old 1,2,both switch and replace it with VSR and separate the two banks completely and use one battery only as an engine start battery and then take all the other systems off the house battery bank with separate isolators and a means of paralelling the two banks for emergency engine start should that one battery fail.

Maybe. But how is that better/easier than just using one big bank for everything and having a single battery as a reserve? I'm not sure that it offers enough to warrant the hassle/expense. Again, maybe I don't understand it fully.

That way you do not have to do anything - the VSR will automatically charge your start battery first and then switch the charge to the house bank. You will never run any systems from the start battery will will always be fully charged. Starts take very little and are recharged quickly. You can do all this with a BEP Marine battery switch cluster, but you can also buy all the components (switches and VSR) individually. However, if you are going to seriously use that house capacity you should really be looking at upgrading your charging capability - not suggesting anything in particular because you don't say how you propose to use them and keep them charged.

Batteries are currently charged with a 40amp smart charger (Stirling) and a 50amp alternator. Capacity is enough to last me 2 or 3 days at a time, which is the most I tend to need away from shorepower. I'm mainly marina based, with short fishing trips.

I guess I could look at increased alternator charging but it's not really a necessity or priority right now.

I'm happy to look at adding things but only if there's a significant enough benefit in terms of simplicity and capability. Using just one large bank (with a spare in reserve), seems as simple as I can get, but not sure if there are any downsides.

 

[VicS]

I agree now is the time to ditch the 1,2,both,off switch in favour of separate isolators and a split charging system or some type or other for charging from the alternator

How do you split the charging between two banks from the alternator at present. Manual switching, diode splitter, VSR or some other system. Do you have any form of fancy alternator regulator, if so what?

 

[JSYmartini]

Yes, but I'm not sure how that simplifies what I was planning to do, which pretty much involves me doing nothing, so it just seems like adding another bit of kit. Maybe I'm misunderstanding?

Using the 1,2,both switch involves having to remember to switch over whenever you want it to do something different, you also need to know when to switch from one bank to the other when charging, ie when one is full etc.

The kit I linked to has an on off switch, turn it on when you're using the boat, turn it off when you go home. The ACR (automatic charging regulator) in the kit will charge your starting battery then charge your house battery. When not charging it will automatically isolate your house battery so the starting battery won't be run down. Literally fit and forget.

 

[abraxus]

How do you split the charging between two banks from the alternator at present. Manual switching, diode splitter, VSR or some other system. Do you have any form of fancy alternator regulator, if so what?

If I really wanted to I guess I would manually switch, but ordinarily I don't split the charging from the alternator, The way I see it I have no need to, but maybe I'm wrong. I leave with two fully charged battery banks. Only use bank 2 (500ah) for starting and house loads, which is enough to last me the 2 or 3 days I need without going below 50% capacity. No fancy alternator regulator.

Barring any problems bank 1 (125ah) never gets used and is fully charged in reserve.

I agree now is the time to ditch the 1,2,both,off switch in favour of separate isolators and a split charging system or some type or other for charging from the alternator

Granted I could ditch the switch and install various other components instead, but given that my main battery bank is sufficent for my needs then what would be the gain in return for the cost?

I suppose what I'm asking is am I missing anything?

 

[VicS]

I suppose what I'm asking is am I missing anything?

Not really .

using one large bank for all purposes and keeping the other as a reserve is the method favoured in the USA. You will find it described, I believe, in Calders book.

I dont have the book but I believe the suggestion there is to take the alternator a output directly to the main bank with a VSR used to automatically charge the reserve. The logic then is that there is no possibility of alternator damage as a result of incorrectly operating the selector switch.

 

[abraxus]

Using the 1,2,both switch involves having to remember to switch over whenever you want it to do something different, you also need to know when to switch from one bank to the other when charging, ie when one is full etc.

Not sure what you mean by "do something different". I only ever use one bank for everything so no need to remember anything or switch when charging.

The kit I linked to has an on off switch, turn it on when you're using the boat, turn it off when you go home. The ACR (automatic charging regulator) in the kit will charge your starting battery then charge your house battery. When not charging it will automatically isolate your house battery so the starting battery won't be run down. Literally fit and forget.

Currently I just switch to 2 when using the boat and 1 when I go home, so it seems no different in terms of ease of use than a system that I switch off and on.

To be honest, I could actually just leave it at 2 all the time, which is about as "fit and forget" as you can get, but prefer to switch to 1 when I go home as an extra precaution.

 

[abraxus]

Not really .

using one large bank for all purposes and keeping the other as a reserve is the method favoured in the USA. You will find it described, I believe, in Calders book.

I dont have the book but I believe the suggestion there is to take the alternator a output directly to the main bank with a VSR used to automatically charge the reserve. The logic then is that there is no possibility of alternator damage as a result of incorrectly operating the selector switch.

Thanks Vic.

The switch is a Cole Hersee, make before break type, which I believe allows switching in use. That said, I never have found the need to switch in use so am I ok as is?

 

[NormanS]

One disadvantage of using the one bank for everything is that when you start the engine, the brief high current required may mean a temporary low voltage. This can upset some sensitive electrics and electronics, possibly causing them to trip out.

 

[VicS]

One disadvantage of using the one bank for everything is that when you start the engine, the brief high current required may mean a temporary low voltage. This can upset some sensitive electrics and electronics, possibly causing them to trip out.

Yes on a boat with a simple system. ie one battery or the other selected we used to have to remember to switch the Decca off before starting the engine.

 

[abraxus]

One disadvantage of using the one bank for everything is that when you start the engine, the brief high current required may mean a temporary low voltage. This can upset some sensitive electrics and electronics, possibly causing them to trip out.

Thanks Norman, I'm on the Thames.

The only sensitive thing on board is my girlfriend and she doesn't need low voltage to trip out.

 

[NormanS]

Thanks Norman, I'm on the Thames.

The only sensitive thing on board is my girlfriend and she doesn't need low voltage to trip out.

I'm not sure if that's good or bad