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Battery Configuration - Dual Purpose

sadbassa

New member
Joined
17 May 2012
Messages
1
Hi,

Just a quick query in relation to the configuration of batteries.

I am renovating a cabin cruiser and nearing completition. I am happy with setting up the batteries, but I have a random issue that someone may be able to advise.

I have installed a 110ah deep cell battery, which I am now going to add to inline, probably another 110ah. I have recently seen a dual purpose starter/leisure battery which look quite good. I know I shouldn't start the engine off the leisure battery so my question is...

If I install the dual purpose in line (i.e positive to positive etc...) with the standard lesiure battery, could this be used as the starter battery or,. as they are inline, would this damage the standard battery.

This may seem like an inane question, but if is preferrable to install a second 110ah deep cell with a dedicated starter battery it would handy to know.

Thanks

Steve
 

Richard10002

Well-known member
Joined
17 Mar 2006
Messages
18,395
Location
Manchester
Hi,

Just a quick query in relation to the configuration of batteries.

I am renovating a cabin cruiser and nearing completition. I am happy with setting up the batteries, but I have a random issue that someone may be able to advise.

I have installed a 110ah deep cell battery, which I am now going to add to inline, probably another 110ah. I have recently seen a dual purpose starter/leisure battery which look quite good. I know I shouldn't start the engine off the leisure battery so my question is...

If I install the dual purpose in line (i.e positive to positive etc...) with the standard lesiure battery, could this be used as the starter battery or,. as they are inline, would this damage the standard battery.

This may seem like an inane question, but if is preferrable to install a second 110ah deep cell with a dedicated starter battery it would handy to know.

Thanks

Steve
I think you mean Deep Cycle battery, rather than Deep Cell. If its truly deep cycle, it won't make a good starter battery. A leisure battery is better as a starter.

Not normally a good idea to have deep cycle and leisure in the same bank, and better to have domestic and starters in separate banks.

If none of that makes any sense, you need some help, or more education. Search batteries on here - there are loads of discussions.
 

Cheekybrat

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Joined
25 Aug 2010
Messages
73
Location
Nottinghamshire
I think you mean Deep Cycle battery, rather than Deep Cell. If its truly deep cycle, it won't make a good starter battery. A leisure battery is better as a starter.

Not normally a good idea to have deep cycle and leisure in the same bank, and better to have domestic and starters in separate banks.

If none of that makes any sense, you need some help, or more education. Search batteries on here - there are loads of discussions.
I think I must need educating, in my train of thought knowing that each lead (plate) acid battery cell produces 2.2 volts at full charge, I would have thought that a deep cycle battery is one with thicker lead plates that don't distort so easily when getting hot due to producing more current as the voltage reduces. but I have found over the years that younger people know more than me, maybe one day they will say what a good idea wars are :)
 
Last edited:

Tranona

New member
Joined
10 Nov 2007
Messages
32,180
Hi,

Just a quick query in relation to the configuration of batteries.

I am renovating a cabin cruiser and nearing completition. I am happy with setting up the batteries, but I have a random issue that someone may be able to advise.

I have installed a 110ah deep cell battery, which I am now going to add to inline, probably another 110ah. I have recently seen a dual purpose starter/leisure battery which look quite good. I know I shouldn't start the engine off the leisure battery so my question is...

If I install the dual purpose in line (i.e positive to positive etc...) with the standard lesiure battery, could this be used as the starter battery or,. as they are inline, would this damage the standard battery.

This may seem like an inane question, but if is preferrable to install a second 110ah deep cell with a dedicated starter battery it would handy to know.

Thanks

Steve
The most common setup is a dedicated starter battery - which does not have to be anything fancy, an ordinary vehicle battery for your size engine will do, and a separate "house" bank for evrything else. You then have a choice of different types, wet acid or gel batteries depending on your type of usage and depth of pocket. Youy also need to wire them so that you can isolate the two banks or parallel them if needed and a split charging device such as a VSR or a split diode to ensure both batteries are charged efficiently.
 

VicS

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Joined
13 Jul 2002
Messages
45,311
Location
Home: Kent. Boat: Chichester
If you connect two batteries in parallel the first requirement is that they should both be the same type. Flooded, gel or AGM.

Id not connect a leisure battery in parallel with a deep cycle battery. There would be point in one of them being deep cycle. You'd not be able to deep cycle it without also running the leisure battery below what would be an acceptable level

If you need a larger capacity deep cycle battery for non-engine starting purposes then fit another deep cycle battery in parallel with it.

As Tranona suggests fit a small engine starter battery specifically for engine starting.
You can charge the two banks as he suggests using a VSR or by manual switching using separate isolator switches or a 1, 2, both, off switch according to your preferences.
Diode splitters suffer from volts drop so to fully charge using a diode splitter you really need a battery sensed alternator.
 

Richard10002

Well-known member
Joined
17 Mar 2006
Messages
18,395
Location
Manchester
I think I must need educating, in my train of thought knowing that each lead (plate) acid battery cell produces 2.2 volts at full charge, I would have thought that a deep cycle battery is one with thicker lead plates that don't distort so easily when getting hot due to producing more current as the voltage reduces. but I have found over the years that younger people know more than me, maybe one day they will say what a good idea wars are :)
What you say is correct..... Deep cycle have thicker plates and can be depleted further, but slower, than leisure/starter batteries.

Thicker plates don't make for good Cold Cranking, and you will usually find that a true deep cycle battery won't have a CCA rating.
 

PaulGooch

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14 Feb 2009
Messages
4,493
Location
Home = Norfolk, Boat = The Wash
<snip>
Diode splitters suffer from volts drop so to fully charge using a diode splitter you really need a battery sensed alternator.
Not really. Millions of boats with diodes out there that charge the batteries just fine.

Yes, there is a volt drop. But, a decent diode won't have a huge drop. Do the sums between the alternator output voltage, minus the diode volt drop, and you'll be left with enough volts to fully charge a 12v battery. If there is a small shortfall, it's be so small that it'll be unnoticeable.

The VSR concept is flawed and potentially dangerous. All the time the engines are running the VSR is running the battery banks in parallel. Having the banks in parallel defeats the point of having multiple banks. A single battery failure could leave you with all the batteries flat.

There are also some potentially life threatening dangers involved in fitting a VSR how some manufacturers suggest. I've seen fitting instructions where there is no fuse between the VSR and either bank and the wiring sizes only take into account the maximum charging output. This can be very dangerous.

For instance, you've sat at anchor for some time and the domestic bank is very low on charge. You start the engine and the VSR activates, connecting the banks in parallel. You press the windlass up button to haul the anchor. The windlass is wired to the domestic bank, which has nowhere near enough charge to haul the anchor, so all the power is drawn from the engine battery, via the VSR and it's wiring.

Where'd you put that fire extinguisher ?
 

PaulGooch

Active member
Joined
14 Feb 2009
Messages
4,493
Location
Home = Norfolk, Boat = The Wash
Hi,

Just a quick query in relation to the configuration of batteries.

I am renovating a cabin cruiser and nearing completition. I am happy with setting up the batteries, but I have a random issue that someone may be able to advise.

I have installed a 110ah deep cell battery, which I am now going to add to inline, probably another 110ah. I have recently seen a dual purpose starter/leisure battery which look quite good. I know I shouldn't start the engine off the leisure battery so my question is...

If I install the dual purpose in line (i.e positive to positive etc...) with the standard lesiure battery, could this be used as the starter battery or,. as they are inline, would this damage the standard battery.

This may seem like an inane question, but if is preferrable to install a second 110ah deep cell with a dedicated starter battery it would handy to know.

Thanks

Steve
Go check exactly what batteries you have and where they are (what they are powering). Post back with that information, along with how many engines the boat has and how it currently charges the batteries.
 

VicS

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Joined
13 Jul 2002
Messages
45,311
Location
Home: Kent. Boat: Chichester
Not really. Millions of boats with diodes out there that charge the batteries just fine.

Yes, there is a volt drop. But, a decent diode won't have a huge drop. Do the sums between the alternator output voltage, minus the diode volt drop, and you'll be left with enough volts to fully charge a 12v battery. If there is a small shortfall, it's be so small that it'll be unnoticeable.
We are told that the volts drop across the diodes will typically be about 0.7 volt.
dropping the effective cahrging volts from say 14.2 to 13.5. That's going to have more than an unnoticeable effect I think you will find.

There are also some potentially life threatening dangers involved in fitting a VSR how some manufacturers suggest. I've seen fitting instructions where there is no fuse between the VSR and either bank and the wiring sizes only take into account the maximum charging output. This can be very dangerous.

For instance, you've sat at anchor for some time and the domestic bank is very low on charge. You start the engine and the VSR activates, connecting the banks in parallel. You press the windlass up button to haul the anchor. The windlass is wired to the domestic bank, which has nowhere near enough charge to haul the anchor, so all the power is drawn from the engine battery, via the VSR and it's wiring.
You would take this scenario into account when wiring the boat. Giving the battery supplying the windlass priority charging would solve the problem, even if you did not power the windlass from the starter battery anyway.
 

PaulGooch

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Home = Norfolk, Boat = The Wash
We are told that the volts drop across the diodes will typically be about 0.7 volt.
dropping the effective cahrging volts from say 14.2 to 13.5. That's going to have more than an unnoticeable effect I think you will find.
Modern alternator voltage is 14.4v. Millions of boats are running around with diodes and the battery systems work fine. My own boat will happily run for days with only alternator charging, no mains charge and i'm running all of the domestics from a single 110ah leisure battery. Never had it go flat yet.


You would take this scenario into account when wiring the boat. Giving the battery supplying the windlass priority charging would solve the problem, even if you did not power the windlass from the starter battery anyway.
Plenty of other scenarios where a VSR would give you problems. Notably the fact that a single battery failure could leave you stranded. Running a VSR with all banks in parallel makes having the separate banks pointless. Might just as well have one bank charged straight from the alternator.
 

ripvan1

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20 Jun 2011
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Pompey
part of the op's question was regarding dual purpose batteries - can-t see any comments on these yet - interested as i've just got one but not in water yet, so can't comment on performance
 

VicS

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Home: Kent. Boat: Chichester
Modern alternator voltage is 14.4v. Millions of boats are running around with diodes and the battery systems work fine. My own boat will happily run for days with only alternator charging, no mains charge and i'm running all of the domestics from a single 110ah leisure battery. Never had it go flat yet.
Even if the alternator is 14.4 V a diode splitter will drop it to 13.7v at which value the batteries will not be as well charged as they would be at 14.4. Hence the need for battery sensing.
An alternative of course is oversized batteries but that increases the cost every time the batteries are replaced and may affect boat speed due to the increased weight. Even a small fraction of a knot can make all the difference in a closely fought race



Plenty of other scenarios where a VSR would give you problems. Notably the fact that a single battery failure could leave you stranded. Running a VSR with all banks in parallel makes having the separate banks pointless. Might just as well have one bank charged straight from the alternator.
No it does not make separate banks pointless and even charging via a diode splitter could have the same result if one battery failed and was taking all the charging current to no effect.

Maybe something like an X-split is a better choice than either a diode splitter or a VSR. Or a Sterling A-B charger giving independent charging of two banks with enhanced charging of the domestic bank.
 

VicS

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part of the op's question was regarding dual purpose batteries - can-t see any comments on these yet - interested as i've just got one but not in water yet, so can't comment on performance
By dual purpose it has been assumed he means leisure batteries.

They seem to vary. For some you will find a CCA given so are presumably suitable for engine starting. For others no CCA is quoted presumably so the manufacturers do not consider them suitable for engine starting.

Leisure batteries are not deep cycle batteries so the same constraints will apply as apply to starter batteries. They are merely more able to sustain a continuous steady discharge than a starter battery.

I have a leisure battery. It is not used for engine starting but is a lot less expensive than a deep cycle battery which might actually be a better choice for my boat. Hopefully for powering lights, instruments, autopilot etc it is a slightly better choice than a starter battery.
 

PaulGooch

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part of the op's question was regarding dual purpose batteries - can-t see any comments on these yet - interested as i've just got one but not in water yet, so can't comment on performance
There is no such thing as "dual purpose" batteries, if by "dual purpose" you mean the things that are being sold as "hybrid" batteries.

http://www.ybw.com/forums/showthread.php?t=316263
 

PaulGooch

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Home = Norfolk, Boat = The Wash
No it does not make separate banks pointless and even charging via a diode splitter could have the same result if one battery failed and was taking all the charging current to no effect.
Based on personal experience, that isn't the case. In 2009 we left Wisbech for Wells Next the Sea, the first leg of a day day journey to Suffolk, moving the boat to a different marina. When we arrived at Wells and i turned the engine off, all of the electrics also went off. I checked the battery connections and found them to be OK, the domestic battery had completely failed and had zero charge in it. A night on shore power to give us some domestic power and try to charge the battery and it was still totally lifeless. Had we have been using a VSR, with the mains charger on the VSR would have activated and had the batteries in parallel all night, i'm not sure that the dead battery wouldn't have flattened the engine battery.

Next day we left Wells and made the 100 mile trip to Shotley, Suffolk, without incident. The diode kept the faulty battery isolated from the engine battery and the alternator kept the engine battery charged, despite charging current also going to the dead battery, to no effect.

So i can say with 100% certainty that the diode system worked exactly as it should have done. Had we have been using a VSR, there is a high risk that the dead battery would have discharged the engine battery whilst under way, leaving us stranded the first time we turned the engine off. That could have been during the first day, had we have stopped for an hours fishing on the way to Wells.

I want completely separate battery banks on my boat. Not banks that are only separate when i don't have the engine running and i'm not connected to shore power. With a VSR, my banks would be in parallel all the time the boat is on it's mooring and all the time the engine is running, the only time i'd have separate banks is if i was at anchor, or on a visitor berth with no shore power.

Maybe something like an X-split is a better choice than either a diode splitter or a VSR. Or a Sterling A-B charger giving independent charging of two banks with enhanced charging of the domestic bank.
IMO, for boats with lower output charging systems a £30 diode is a good solution.

For higher output systems, where the diode price rises to £70, it's not a big jump to something like a Pro Split R at just over £100 or the slightly more expensive X-Split.

There are obviously cases where power requirements and charging facilities mean that the cheaper solutions aren't suitable and more expensive systems need to be fitted.
 
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