New battery to 2 existing ones

slawosz

slawosz

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Hi,
I am planning to add new battery to my Sadler 25 installation. Current batteries (two) have around 40 Ah and according to previous owner, never have a problem to start the engine. I am bit cautious and I will sail with rather inexperienced family, so in order to prevent any surprises, I think I will get a new battery.
After some consideration, I will get this battery: 812071 / 81270 Varta Hobby Leisure Battery A27 / LFS75 12V 75Ah
It will be plenty to start 1GM10.
As I have switch 1st/Both/2nd I am thinking about connecting 2 existing batteries into the bank. I wonder how much damage it could give to them? I realise that worse battery will drag the better one, but I don't see any other option - I don't think that installing yet another battery selector will be good idea. I am thinking about buying (or borrowing) this device: Battery Load Tester 100 Amp Load Type 6V - 12V Mechanics 6 12 Volt Car Truck UK 739904546245 | eBay but I am not sure if it would give me good results? In case when one of the older batteries is bad I will try to replace it with something used and for the time being use only one. Can I use 2 different batteries in a bank?
I would keep bank for year or two and then buy another Varta battery, or when it will start showing sign of dying.
Oh, and I don't have much amperage need - standard stuff (gps, vhf, autopilot).
 
If I've got this right you will have the 75Ah on position 1 and the two paralleled 40Ah on position 2.
Before spending money on a tester you could just charge up both existing batteries and monitor the voltage over a day or so. If they both maintain a healthy voltage of about 12.8V they are probably OK and you can parallel them. You could do a discharge test with a 5A load and try to measure their capacity or just use them as house batteries and see how it goes. As long as you keep the new battery for engine starting you will not have any problems if the house batteries go down as you can always run the engine for a while to charge them up.
If both the old batteries can start the engine, that is quite a good test and I would save the money for the Ebay tester and put it towards a new second battery when required.
I have started my 1GM10 quite easily with a 24Ah battery. If yours starts easily like mine it, only needs 80A for about 2 seconds so it doesn't need a battery with 600 cca.
 
Keep one of the 40ah for a start battery (if it is in good nick) and use it exclusively for starting the engine and buy a 100ah leisure battery for the house circuits. Junk the 1,2 both and fit a VSR (so the alternator charges both) and separate isolators for each bank. I am a fan of the BEP Marine switch cluster which does all of this for you and gives you a switch for combining the batteries for emergency start - although in reality you almost never need to use it as the chances of an engine start going flat are small given you only use it to start the engine and then it is immediately recharged - and never run down being used for house circuits.

There are other ways of achieving this simple idiot proof way of managing battery usage, but this is the idiots way of doing it and why I am using it on my project boat.
 
In an ideal world you would spend £160 on BEP switches, £40 on a Cyrix and £100 on a 100Ah battery. I have guessed that the OP is at the budget end of the boating spectrum (like me) and he could probably get sailing safely for much less. There is always a consideration of where to spend limited boat funds and maybe putting the money saved towards a new anchor or autopilot would give a better return for stress free family sailing.
 
Tranona said:
Keep one of the 40ah for a start battery (if it is in good nick) and use it exclusively for starting the engine and buy a 100ah leisure battery for the house circuits. Junk the 1,2 both and fit a VSR (so the alternator charges both) and separate isolators for each bank. I am a fan of the BEP Marine switch cluster which does all of this for you and gives you a switch for combining the batteries for emergency start - although in reality you almost never need to use it as the chances of an engine start going flat are small given you only use it to start the engine and then it is immediately recharged - and never run down being used for house circuits.

There are other ways of achieving this simple idiot proof way of managing battery usage, but this is the idiots way of doing it and why I am using it on my project boat.
Click to expand...

You have mentioned your liking for the BEP cluster a few times lately, i'd like to offer another method. Using Furneax Ridall as an example for prices:

The cluster is £176.70 BEP Square Battery Distribution Cluster for Single Engine with Two Battery Banks

Individual switches are £26.60 (£79.80 for the three) 404.html

Or a cluster without the VSR is £79.99 BEP Battery Distribution Cluster for Single Engine with Two Dedicated Battery Banks

A 120a Victron Cyrix VSR is £43 so £122.80/£122.99 for the switches and a VSR, over £50 less money.

There is also an issue with how BEP interconnect the switches/VSR. With the cluster that includes the VSR is is connected so the emergency switch parallels the batteries. This is a flawed method. There is no quick and simple way of isolating a dead battery and using the emergency switch to run everything from the good battery. For instance, if the engine battery has totally failed in some way you cannot use the emergency switch to start the engine, because you cannot parallel the good domestic battery to the dead battery because turning off the engine isolator has disconnected the engine from the system. If we parallel the load terminals of the two main isolators we can isolate the dead engine battery and parallel the loads, allowing the engine to be run from the domestic battery.

With the cluster without the VSR you can simply reverse the battery and load connections on the main isolator switches, ignoring the BEP fitting instructions. With the VSR cluster you also have to move the VSR connections to the same terminals as the load cables on the isolators and one (or possibly both, i can't remember) of the wires is too short to allow that without extending it.

So, my suggestion would be to fit the separate switches (or the cluster without the VSR) and a Victron Cyrix.
 
An alternative that worked well on Jissel was to have keep the 1-2-both switch, wired with the common to the starter, alternator output and starter battery to 1, domestics to 2 and a VSR* to link 1 & 2. Turn to off when you leave the boat, when you're on board leave it on 1 unless you have a problem, when you have the options of all in parallel or starting from the domestics. Don't leave it on both, though, you could run the starter battery down with domestic current.

* I used a cheap and cheerful cube relay, because VSRs were expensive when I did it, but I'd use a VSR now as the price difference is a lot less.
 
Slawosz, I wouldn't worry about adding another battery. I have had a similar set up with two 120ah batteries for over 16 years without any problems. Decide which one is for the engine and which is house. Try not to use them both together unless you need it to start the engine.
 
PaulRainbow said:
For instance, if the engine battery has totally failed ...
Click to expand...

Out of interest, how dead does a battery have to be before it mustn't be combined with a good one? Also -- assuming it still has a flicker of life in it -- is there any advantage to combining a bad engine battery with a good house battery, rather than just disconnecting it and using the house battery alone?

Things I ponder at night...
 
Stooriefit said:
Slawosz, I wouldn't worry about adding another battery. I have had a similar set up with two 120ah batteries for over 16 years without any problems. Decide which one is for the engine and which is house. Try not to use them both together unless you need it to start the engine.
Click to expand...

The problem with this traditional set-up is that your designated engine battery is required to provide a fraction of an amp hour to start the engine. This effectively means that you have 240ah of battery and only 60ah usable capacity on day one of a cruise (assuming brand new and fully charged) and less on subsequent days (given the difficulties in getting from 80-100% SOC) and progressively less with battery age. A small dedicated engine battery frees the unused potential of the second battery.
 
PaulRainbow said:
You have mentioned your liking for the BEP cluster a few times lately, i'd like to offer another method. Using Furneax Ridall as an example for prices:

The cluster is £176.70 BEP Square Battery Distribution Cluster for Single Engine with Two Battery Banks

Individual switches are £26.60 (£79.80 for the three) 404.html

Or a cluster without the VSR is £79.99 BEP Battery Distribution Cluster for Single Engine with Two Dedicated Battery Banks

A 120a Victron Cyrix VSR is £43 so £122.80/£122.99 for the switches and a VSR, over £50 less money.

There is also an issue with how BEP interconnect the switches/VSR. With the cluster that includes the VSR is is connected so the emergency switch parallels the batteries. This is a flawed method. There is no quick and simple way of isolating a dead battery and using the emergency switch to run everything from the good battery. For instance, if the engine battery has totally failed in some way you cannot use the emergency switch to start the engine, because you cannot parallel the good domestic battery to the dead battery because turning off the engine isolator has disconnected the engine from the system. If we parallel the load terminals of the two main isolators we can isolate the dead engine battery and parallel the loads, allowing the engine to be run from the domestic battery.

With the cluster without the VSR you can simply reverse the battery and load connections on the main isolator switches, ignoring the BEP fitting instructions. With the VSR cluster you also have to move the VSR connections to the same terminals as the load cables on the isolators and one (or possibly both, i can't remember) of the wires is too short to allow that without extending it.

So, my suggestion would be to fit the separate switches (or the cluster without the VSR) and a Victron Cyrix.
Click to expand...
I paid £150 for my switch cluster from Chas Newens (although it actually came direct from Aquafax!) - so less of a price difference. I know about the paralleling, but in all the years I had the last 2 I never actually needed it so in a sense it is a moot point. It would only be used in the highly unlikely event of having a dead engine start battery. As I am fitting a Red Flash doubt I shall ever need it, but I take your point that if the battery is totally dead it may not work.

I did say there are other ways of splitting banks, which is the main point I was trying to make.
 
Thanks, its a lot of option to consider.

One question: how long does it take for battery to recharge after starting the engine and what revs should I use? Never had inboard before.

Regarding so called `dual-purpose` batteries, what is your take?
 
Tranona said:
I paid £150 for my switch cluster from Chas Newens (although it actually came direct from Aquafax!) - so less of a price difference. I know about the paralleling, but in all the years I had the last 2 I never actually needed it so in a sense it is a moot point. It would only be used in the highly unlikely event of having a dead engine start battery. As I am fitting a Red Flash doubt I shall ever need it, but I take your point that if the battery is totally dead it may not work.

I did say there are other ways of splitting banks, which is the main point I was trying to make.
Click to expand...

If you want to use the BEP cluster (obviously you will as you already have it) you can still swap some wires around and have all of the benefits you get with using the cluster, plus the benefits i described. No downsides and no additional cost.
 
PaulRainbow said:
If you want to use the BEP cluster (obviously you will as you already have it) you can still swap some wires around and have all of the benefits you get with using the cluster, plus the benefits i described. No downsides and no additional cost.
Click to expand...
Thanks for that, Paul This is the wiring diagram bepmarine.com/-/media/inriver/716-SQ-140A-DVSR_TCHDAT_BEP1.pdf?modified=20191030113013

Would I be right to just swap the VSR links from A to B on the start switch and C to D on the house switch? Look like the cables are long enough - the start one might even be too long , although I think I can re-route it. Will the VSR still work OK like that?
 
Tranona said:
Thanks for that, Paul This is the wiring diagram bepmarine.com/-/media/inriver/716-SQ-140A-DVSR_TCHDAT_BEP1.pdf?modified=20191030113013

Would I be right to just swap the VSR links from A to B on the start switch and C to D on the house switch? Look like the cables are long enough - the start one might even be too long , although I think I can re-route it. Will the VSR still work OK like that?
Click to expand...

Yes, put the battery cables and the VSR on B and D with the load cables on A and C (y)
 
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