2 cranking batteries and 1 domestic?

[IC85]

Hi

My first post on the forum (actually… my first post in ANY online forum) so I’m hoping you’ll be kind to me!

We’ve recently bought a 10m sailing boat. On closer inspection of the battery bay today, I’ve discovered that the previous owner has installed 2x cranking type batteries and 1x leisure battery… which seems a bit odd - does anyone know why you might do this?

The plot thickens when you consider the single leisure battery is connected to the battery selector switch as “Battery 1 - engine start” and the 2 cranking types are connected to the switch as “Battery 2 - domestics”.

In terms of load, the auxiliary engine is a very standard VP MD2030C, and normal domestic electrical loads (water pump, fridge, plotter and few lights etc), so basically nothing exotic.

What’s going on?! Some sort of kerfuffle by the previous owner? Or is there a logic here that I’ve missed?

Thanks in advance!

 

[William_H]

I presume you have identified the battery types as deep cycle and cranking or high CCA rating. You are correct in identifying that the previous owner has fitted the wrong kind of batteries. The one connected and used as start or cranking battery should be the high CCA type as used in cars tricks etc. The deep cycle type are optimised for domestic low current long term load. Now that does not mean that either battery is no good for the present use. Just not optimised. If the deep cycle battery is large it will happily start the engine but deep cycle aspect is wasted in capability. Likewise the cranking batteries will have limited capability and life if deeply discharged in domestic role.
It may be that he got second hand batteries (or a good deal) were fitted when a need arose. Or he just got mistaken.
I would suggest move one cranking type battery to the engine crank position, either physically or change wiring. Then move the deep cycle battery to domestic use again by moving battery or wiring. The remaining cranking battery may be retained wired in parallel in domestic role. But will have far less contribution capability than the deep cycle one.
Of course this assumes that all batteries are "good". You may discover that the cranking battery will not supply enough current for cranking in which case try the other cranking battery as engine battery. You may also find that you have limited power available over time on the domestic battery set up. Try disconnecting one battery then the other in the parallel arrangement to see which one is failing first. Do this by charging all batteries then run domestic load until voltage falls.
My guess sit hat sooner lor later you will need to buy new battery(ies) ol'will

 

[Bouba]

Perhaps because the previous owner had a pair of cranking batteries and so he used them in parallel (they are in parallel ?)...or maybe the battery selector is wired wrongly

 

[Bouba]

Ps....welcome to the forum

 

[Tranona]

Sounds like he just bought the wrong batteries either through ignorance or maybe got a cheap deal. The actual selection is correct (assuming the capacity of the 2 cranking batteries are greater than the one leisure). If you hang around here long enough you will find there is not a lot of support for that type of arrangement but rather to split the 2 banks completely, switch them independently and charge from the alternator through a split charger such as a VSR. This ensures more efficient and reliable charging and avoids accidental running down of the engine start. Ideally new batteries. A small car type battery of maybe 65Ah for the engine and 2*110Ah either SLA or AGMs would be appropriate for a 10m yacht.

 

[B27]

These days, there's often not much difference between 'cranking' and 'leisure' batteries.
With most cars of the last 15 years or so being 'stop/start', modern cranking batteries have changed a bit and often perform very well as house batteries for a boat. And most leisure batteries are perfectly capable of starting an engine.
I'd suggest not worrying about it until the batteries show signs of not meeting your needs.
Your major need will probably be the fridge, you may find it helpful to understand how many Amp-hours that needs for a day and how that charge gets put back into your battery bank from engine/solar/shore power.

 

[IC85]

Morning all

Thanks v much for your replies. It seems like we have consensus that it’s a bit odd, but not a terrible set up.

Given the batteries are around 8 seasons old and struggling to hold voltage, I’ve taken them home for a jolly good charge and bit of drop testing. It might be time for a replacement set (and maybe with the right batteries for the job!)

Thanks again - it’s appreciated

 

[IC85]

Ps....welcome to the forum

Thanks!

 

[Neeves]

And when you have sorted out what you have and how good are there batteries - post again and you will receive sensible advice as to how to go forward.

But, there is always a but. Tell us the type of yacht, tell us what equipment you have, how the battery(ies) are charged - we are good (well in terms of batteries I'm no good) but we cannot guess.

And enjoy being a member - its useful - sorry, invaluable

Jonathan

 

[ChromeDome]

Some may even suggest you rework the setup.

Find the Amp sum of consumers, then fit a (true) deep cycle battery big enough to run them for the number of days you intend to use the boat between charges, without discharging below 50%
The Volvo probably needs 600+ CCA so get a suitable (e.g. AGM) battery for that.

Select a charger with two separate channels to keep the battery banks full & maintained. A charger that provides 10% of the nominal Amp of the batteries in theory will fill them in 10 hours, so getting the next size charger will leave you with a nice margin.

If you want to avoid the battery switching you can fit an automatic separator that will protect the starter battery so that you always can start the engine (and charge by its alternator).

 

[Refueler]

Morning all

Thanks v much for your replies. It seems like we have consensus that it’s a bit odd, but not a terrible set up.

Given the batteries are around 8 seasons old and struggling to hold voltage, I’ve taken them home for a jolly good charge and bit of drop testing. It might be time for a replacement set (and maybe with the right batteries for the job!)

Thanks again - it’s appreciated

OK ..... lets some info in the mix ...

a) There are 2 general forms of Leisure battery .... 1. is a compromise battery that can start small to moderate sized engines and also provide slightly more discharge than a cranking battery. 2. Deep Cycle battery with soft plates that should not be used for starting engines other than small ... the plates cannot take the high amp demand - if subjected to - the plates buckle and battery is then ruined. But provides deeper discharge ... but surprisingly still not advised to go further than 55 - 60% max.

Type 1 came about for RV camping etc. - where people wanted batterys capable of starting their 'van' but also capable of about 50% discharge. Prior - most of us ... yes I was a Caravanner !! - we used a starter CCA battery for vehicle use and a separate deep cycle battery for the caravan .. VW campers and so on had to decide - use the engine battery or add a second. The compromise leisure battery - type 2 solved that.

So now that's out in the mix ... your 2 + 1 setup. Personally I would change it ... and if the batts at 8yrs - you find one or two are past their goood life ... relegate them to some other job elsewhere.

Then make a decision on how much discharge you need on domestic. As for starter - use a proper CCA starter battery ... as it will usually never need to go low on charge - it will be topped up by engine etc etc. I would also make it a single battery to engine. You should not need two batterys.
For the domestic if you don't need deep discharge - then you can use a couple of CCA or a couple of leisure ....
Depending on what size engine - you can think of two deep cycle batterys - but only for emergency start if engine not small.

My 25ft Motor sailer has two 90A/hr CCA starter batterys via the old style 1 - Both - 2 - Off switch ... so either can start engine or both. Either can give me the limited domestic I need or both. That's been system for years and I get good life out the batterys. It has a 43HP Perkins 4 cyl diesel.

My 38ft Cruiser Racer has three 75A/hr CCA starter batterys (installation by previous owner) ... 1 for engine ... 2 for domestics. Somewhere on the boat is a VSR - yet to find it !! It also has solar. I have had two occasions where domestic fell very low after running fridge hard overnight ... so will look to improve - but swapping for leisure / deep cycle will not be enough. What we find hard to understand is that when the domestics fell low - it also dragged the starter battery down ... need to find out why. It has a Yanmar 20HP 2 cyl diesel.

I appreciate that there will be contrary posts to this ... but that's life. I can only post based on experiences and observations ....

Summary (my opinion)

Change engine to a single CCA starter battery such as used on a car.
Change domestics to two leisure compromise batterys - giving you increased capacity on house items and possibility as emergency start.

Change to VSR / split system ? That is where I will call off as I am not totally convinced of having extra switches etc. .... my 1-B-2-off has served me well for decades .... but I can also see its point.

 

[Alex_Blackwood]

Hi

My first post on the forum (actually… my first post in ANY online forum) so I’m hoping you’ll be kind to me!

We’ve recently bought a 10m sailing boat. On closer inspection of the battery bay today, I’ve discovered that the previous owner has installed 2x cranking type batteries and 1x leisure battery… which seems a bit odd - does anyone know why you might do this?

The plot thickens when you consider the single leisure battery is connected to the battery selector switch as “Battery 1 - engine start” and the 2 cranking types are connected to the switch as “Battery 2 - domestics”.

In terms of load, the auxiliary engine is a very standard VP MD2030C, and normal domestic electrical loads (water pump, fridge, plotter and few lights etc), so basically nothing exotic.

What’s going on?! Some sort of kerfuffle by the previous owner? Or is there a logic here that I’ve missed?

Thanks in advance!

You will probably never know why the setup is like that. If it is working, leave it alone, sort it out in slow time, find out exactly what your set up is, charging arrangements etc. and fix it when either the batteries start to fail or you have the time, money and inclination.

 

[jbweston]

A lot of good advice in previous posts.

One further point. Advice is generally not to wire dissimilar batteries in parallel - even batteries that were identical when new but are of different ages. That's because if ever one has a different voltage (maybe because it's deteriorated somewhat with age, or has a different charge/discharge profile because it's of different construction, the one with the higher voltage will try to level up the voltage by passing current to the other. As (if in the normal set up) they are close together there will be almost no resistance in the circuit from one terminal of the first battery throught the connection, then through the other battery and back through the other connection to the first. As current is voltage divided by resistance, even a small difference in voltage where there is almost no resistance will produce a large current and can produce excess and even dangerous heat.

I'm not an electrician, and am happy to be corrected if I'm wrong, but I believe this is why it's good practice to join only identical batteries in parallel. As far as I know, it isn't a problem to join non-identical batteries in series (e.g. two 6v to make a 12v supply), but I think we are all assuming that your two connected batteries are 12v connected in parallel.

Practically speaking that means if you replace batteries in a single bank joined in parrallel, you should replace all of them at the same time with batteries that are identical to each other.

 

[Kwik Decision]

As an additional point, if you have a "1, both, 2, off" type battery switch, you don't really have an engine battery and a domestic batteries, you have battery bank 1 and battery bank 2. With the switch on 1, battery 1 is powering everything; lights, instruments, engine etc, and with the switch on 2, battery bank 2 does everything. On both, all 3 batteries are linked together in parallel, and do everything.
This traditional system generally works fine provided you have a good memory, and remember to select the appropriate battery bank when starting or switching off the engine. It has the downside that the voltage drop when starting the engine may cause the instruments to switch off, particularly if your engine takes a while to start. If it were my boat, I'd leave the switch on 2 most of the time, and switch to 1 occasionally when the engine is running, to make sure it's charged, or switch to 1 if I've accidentally flattened 2.

If you're looking at longer term improvements, I'd replace the 1, both, 2, off switch with separate switches, a VSR, and link switch. This would separate the domestic and engine circuits, and remove both the voltage drop issue (if that is an issue on your boat) and the need to have a good memory.

 

[Refueler]

As an additional point, if you have a "1, both, 2, off" type battery switch, you don't really have an engine battery and a domestic batteries, you have battery bank 1 and battery bank 2. With the switch on 1, battery 1 is powering everything; lights, instruments, engine etc, and with the switch on 2, battery bank 2 does everything. On both, all 3 batteries are linked together in parallel, and do everything.
This traditional system generally works fine provided you have a good memory, and remember to select the appropriate battery bank when starting or switching off the engine. It has the downside that the voltage drop when starting the engine may cause the instruments to switch off, particularly if your engine takes a while to start. If it were my boat, I'd leave the switch on 2 most of the time, and switch to 1 occasionally when the engine is running, to make sure it's charged, or switch to 1 if I've accidentally flattened 2.

If you're looking at longer term improvements, I'd replace the 1, both, 2, off switch with separate switches, a VSR, and link switch. This would separate the domestic and engine circuits, and remove both the voltage drop issue (if that is an issue on your boat) and the need to have a good memory.

True .. but OP has said his switch is labelled ... so someone before him made decision which is which ...

But of course OP can ignore and use as he decides as the 1-B-2-Off switch doesn't care ...

I wouild suggest that OP may not be experienced in changing to VSR etc. ... just based on his questions. No disrespect intended to .OP.

 

[IC85]

True .. but OP has said his switch is labelled ... so someone before him made decision which is which ...

But of course OP can ignore and use as he decides as the 1-B-2-Off switch doesn't care ...

I wouild suggest that OP may not be experienced in changing to VSR etc. ... just based on his questions. No disrespect intended to .OP.

Thanks - no disrespect taken. Just appreciating the ‘group wisdom’

I reckon I can swop in a DVSR and it’s on the winter job list. Agreed with you tho - this is just an exercise in second guessing the wisdom of a previous owner!

 

[IC85]

As an additional point, if you have a "1, both, 2, off" type battery switch, you don't really have an engine battery and a domestic batteries, you have battery bank 1 and battery bank 2. With the switch on 1, battery 1 is powering everything; lights, instruments, engine etc, and with the switch on 2, battery bank 2 does everything. On both, all 3 batteries are linked together in parallel, and do everything.
This traditional system generally works fine provided you have a good memory, and remember to select the appropriate battery bank when starting or switching off the engine. It has the downside that the voltage drop when starting the engine may cause the instruments to switch off, particularly if your engine takes a while to start. If it were my boat, I'd leave the switch on 2 most of the time, and switch to 1 occasionally when the engine is running, to make sure it's charged, or switch to 1 if I've accidentally flattened 2.

If you're looking at longer term improvements, I'd replace the 1, both, 2, off switch with separate switches, a VSR, and link switch. This would separate the domestic and engine circuits, and remove both the voltage drop issue (if that is an issue on your boat) and the need to have a good memory.

Thanks - v helpful nice post

 

[PaulRainbow]

If you're looking at longer term improvements, I'd replace the 1, both, 2, off switch with separate switches, a VSR, and link switch. This would separate the domestic and engine circuits, and remove both the voltage drop issue (if that is an issue on your boat) and the need to have a good memory.

Good advice

 

[William_H]

To OP beware of the temptation to start engine on both. This gives a good cranking power with all batteries in parallel and of course is ready to be charged by the alternator. Problem is that you have 2 battery systems for redundancy so if one is discharged you can use the other to start the engine. You need each one of the battery systems to be able to start the engine (alone) As common failure mode for an engine start battery is that it won't provide the cranking amps, by using both batteries for cranking you can mask a failure. So ideally start on B1 on one day and B2 on next day. But then once engine is running you have to switch to "both" to charge both. Hence discipline is needed for proper use of 1,2,b switch system. While VSR arrangement becomes foolproof.
Nigel might be right about engine cranking on a deep cycle battery causing internal damage. However I suspect that usually with large deep cycle. (especially 2 in parallel) you do not have so much concern for a small engine.
Agaimn jkbweston says don't connect dissimilar batteries in parallel. Of course there may be a large current when batteries are connected together due to dissimilar voltage. However this will always be the case with the 1,2,b switch or indeed VSR when you go to charge from alternator. I don't think much real problem in permanent paralleling dissimilar batteries except the combined total may be reduced to that of the worst battery. But of course theoretically jb is correct. ol'will

 

[Daydream believer]

Sounds like he just bought the wrong batteries either through ignorance or maybe got a cheap deal. The actual selection is correct (assuming the capacity of the 2 cranking batteries are greater than the one leisure). If you hang around here long enough you will find there is not a lot of support for that type of arrangement but rather to split the 2 banks completely, switch them independently and charge from the alternator through a split charger such as a VSR. This ensures more efficient and reliable charging and avoids accidental running down of the engine start. Ideally new batteries. A small car type battery of maybe 65Ah for the engine and 2*110Ah either SLA or AGMs would be appropriate for a 10m yacht.

Definitely do away with the single switch & have 2 singles. If the VSR does not have a battery coupling device ( to couple all batteries in event of starter being low) then wire in a link with a third switch. However, the VictronConnect version does have an emergency link that cuts out after a few seconds. This can be useful if one can get the engine started in time, annoying if not, as one has to keep pressing it, then get back to the engine start sequence. i have a link switch, but if I forget to disconnect it I can flatten the lot which can cause some problems.

Of course, you could leave the whole lot ”as is” for now & wait until you actually need new batteries. You have recently bought a new, to you, boat & there will be plenty to splash the spare cash on