Should I combine my Start & House battery banks - bad idea ?

[affinite]

A faulty solar panel connection has trashed my house battery bank which currently comprises 5 x 100Ahr lead acid batteries.
I've also lost the 100Ahr start battery as well.
I am thinking of replacing the house bank with 4 x 130Ahr Hanooks (XL31S) for reduced weight and increased capacity, but I'm also wondering if now is the time to replace the start battery with another 130Ahr Hankook and combine the two banks. (The obvious benefit being the additional 130Ahr on the house bank)
I would then take the starter cable from the house bank.
OK, I hear the howls of protest about not being able to start the engine if I flatten the house bank but (despite ruining the whole bank over winter) I am usually quite careful about battery management and I don't allow the bank below 70%
I also have a separate independent bow thruster bank comprising 2 x 100Ahr batteries so if I ever managed to discharge the house bank to the point where I couldn't start the engine, I could disconnect & move one of the thruster batteries to get the engine started.

FWIW I have to admit that my charging setup is rather underspec - I charge with a 20A Shore Mains charger, Solar (220W) and Alternator (60A) Sterling A-B charger and charge splitter
I know this sort of battery arrangement is not uncommon in the USA but Im not aware of too many boats in the UK & Med with this arrangement.

What do the panel think ?

 

[Caer Urfa]

In a word NO, best practice is always to have a separate starter battery but like many other boats battery systems you can add by switching the domestic batteries into it for starting if needed.

Any bow thruster should have its own battery (near the bow area)

 

[Freedommachine]

Hi affinite,

I was having the same thoughts as yourself.
My take on it is this;
Providing inline fuses are correctly used and having an auxiliary battery for backup - ideally linked to an isolation switch for quick selection if we find ourselves in difficulty.
Your proposal seems sound.
I'd also be interested to hear others thoughts on this as I'm considering the same.
My batteries are able to handle both starting and deep cycling.
The only issue I'm running into is I run a 24v inverter and have my 4 batteries in series and parallel.
Which means I would need to find or make a switch to be able to go from 24v to 12v to start the engine.
That said if your running 12v I can't see a problem

 

[Spirit (of Glenans)]

You do not say what size engine you have. I feel that many starter batteries are overspecced for the size of the engine.

 

[Alex_Blackwood]

A faulty solar panel connection has trashed my house battery bank which currently comprises 5 x 100Ahr lead acid batteries.
I've also lost the 100Ahr start battery as well.
I am thinking of replacing the house bank with 4 x 130Ahr Hanooks (XL31S) for reduced weight and increased capacity, but I'm also wondering if now is the time to replace the start battery with another 130Ahr Hankook and combine the two banks. (The obvious benefit being the additional 130Ahr on the house bank)
I would then take the starter cable from the house bank.
OK, I hear the howls of protest about not being able to start the engine if I flatten the house bank but (despite ruining the whole bank over winter) I am usually quite careful about battery management and I don't allow the bank below 70%
I also have a separate independent bow thruster bank comprising 2 x 100Ahr batteries so if I ever managed to discharge the house bank to the point where I couldn't start the engine, I could disconnect & move one of the thruster batteries to get the engine started.

FWIW I have to admit that my charging setup is rather underspec - I charge with a 20A Shore Mains charger, Solar (220W) and Alternator (60A) Sterling A-B charger and charge splitter
I know this sort of battery arrangement is not uncommon in the USA but Im not aware of too many boats in the UK & Med with this arrangement.

What do the panel think ?

How did a faulty solar panel connection "Trash" all your batteries? Would be interesting to know.

 

[pvb]

I reckon there's some comfort in having a dedicated starter battery which doesn't supply anything else.

 

[Humblebee]

I don't see any advantage to having just the one bank for starter and house, as said above, keeping a separate starter battery makes sense. In any case, can you not connect them, in effect, through the one, two or both switch? Or whichever switching arrangement you use?

 

[Catalina36]

I've always understood that starter batteries with high CCA have a different construction to deep cycle house batteries - plate thickness etc. If the engine always starts easily, probably no problem but if you ever had to crank it a lot to get it started, how would that affect a deep cycle domestic battery?

 

[affinite]

Wow thanks for the quick replies
I suspect that I'm swimming against the tide but Im genuinely interested in reasons as to why its a bad idea so I'll try to answer some of the questions asked
I've always had separate Start and House banks on my boat(s) for 20+ years and agree that conventional wisdom has always been to keep them separate however combining the two would increase my house capacity by 25%
I dont allow the bank to drop below 70% before recharging so I should always have power to start the engine
That said, if Mr Sod applied his law and the house bank went flat over night, I have a separate Thruster bank (In the bow), which could be used to start the engine in an emergency
Engine is a 60Hp Perkins
The CCA on the new Deep Cycle batteries I intend to use for the house bank is actually higher than that of the old starter battery and Hankook describe it as a "Dual Purpose" battery so I think it is OK to use for both applications

 

[affinite]

How did a faulty solar panel connection "Trash" all your batteries? Would be interesting to know.

Alex
The solar panel was left trickle charging the batteries over the winter. The connecting cable appears to have corroded/broken in high winds but I don't know why the whole bank discharged completely - there must be something draining the batteries that I wasn't aware of. The boat has been unattended on the hard for over 8 months and I haven't been able to get there to investigate further.

 

[MarkCX]

I would just keep all those nice big batteries for house, with the benefit of a bigger bank, and just get a smaller dedicated starter battery. My starter battery takes up very little room, is only 26Ah, but more importantly has 700 cold-cranking amps. These are kept separate from the house with a dual-sensing VSR. In an emergency I can bring in my house bank, but I never have.

 

[lw395]

One day, when your batteries are getting close to being due for replacement, your house bank WILL get discharged and you will regret not having a separate engine battery.
It's easy to say you'll never discharge below 70%, but in that case you might as well set aside one battery as reserved for starting.

It happens that things get left switched on, or some other mishap flattens the batteries.

I think you raise an interesting point, because a lot of people have their batteries combined so much of the time, due to VSRs and dual solar charging and so forth that the engine battery is being worn out faster than the house batteries sometimes.

If you had some other means of starting the engine, that would perhaps be different.

 

[jac]

Bad idea IMHO.

as you said, something happened that trashed your domestic bank. Can you 100% guarantee that that will never happen again?

and whilst you say you could move a bowthruster battery, how quickly could you do that? You can guarantee by Sod’s law that your electrics will be fried one time when you have a ferry bearing down on you, a choppy sea and the wind dies leaving you lug a battery from one end of the boat to the other.

adding an extra battery to the domestic bank is probably a good idea, more capacity Is always a good thing but maybe just add one of the special dedicated engine start batteries such as Optima red top.