House and crank battery setup

[Tai 2]

Hi all, first time poster here!

I have seen some great discussion and advice here and I'm hoping someone can help with my battery setup!

My newish to me Nova 28 is running a cranking battery as a house battery, obviously this is not great and I will add a deep cycle for the house.  I am thinking of keeping the extra  battery by connecting both crank batteries in parallel. They would also be used for the windlass.

I like the idea of having the extra capacity so are there any issues with running like this or should I just take the extra battery out? Also would I need to match the voltage before putting in parallel?

 

Any thoughts appreciated!

 

 

 

 

 

 

[aardvarkash10 846]

Hi Tai - welcome to the crew forums.

You can never have too much battery capacity.  However, keep an eye on the paralleled batteries to make sure they are in similar state of charge at all times - if one battery does die, it can lead to the charging system thinking the batteries are near full all the time, and so both batteries get under-charged.  There are very good bits of electronics that will do this for you and manage it, but they are not cheap and may require other changes to your charging system.

 

[harrytom 574]

use of windles make sure motor is running as the drain is a killer,should have a isolator from house/start battery

[Tai 2]

@harrytomYup, I always run the motor if I use the windlass (depends how strong I'm feeling) and the current setup uses the standard isolation switching and ability to put the house into parallel with the cranking battery.

@aardvarkash10

Im trying to keep things as simple as possible and cost down so don't want to spend loads.  I was hoping lead would be ok to monitor just the bank as a single battery, but your right that I should be keeping an eye on the voltage of each. Looks like I need to add another isolator / combiner switch other wise I'll be having to manually disconnect them to test.

 

 

[CarpeDiem 322]

While a simple question, the answer is quite complex with many options. 

One of the easiest, cheapest and safest way is to fit a VSR and an emergency parallel switch.  This is the full set, but you can buy the bits separately if you want to use existing switches. https://www.burnsco.co.nz/batt-switch-cluster-vert-w-vsr

There are a number of cons to this approach. But the pros are cheap and cheerful.

Assuming you're not on shore power, the best add on you could add to the above would be a solar panel and charger to keep the house battery topped up. This limits lots of the cons, but not all... 

If you are on shore power then a couple of cheap battery chargers will suffice. 

[Tai 2]

Those VSR switch sets look nice but I would probably be better off just getting a bigger capacity cranking battery if I was to spend that much.

I am going to be spending on a proper house battery and was hoping to keep both the exist cranking batteries without having to change the current setup much.

The isolation setup I have now is simple, effectively the two batteries are in parallel and each isolator switch removes a battery. 

Manually managing this is fine for two batteries but will probably become a PITA with 3.

Ideally I could just put both start batteries into permanent parallel so they are effectively a single battery, but as Aardvarkash pointed out I need keep an eye on each individual battery voltage.

I do have a small solar panel and charger however I need to test it as it's all old and not connected up. 

[CarpeDiem 322]

Oh I missed that. 

Effectively this is the standard 1/2/Both configuration found on most boats. 

I would replace one battery with a deep cycle and put a switch on the parallel for emergency only and whenever the engine is running. Of course you have to manage the parallel manually and this is a major con, because you will forget one day. That's where the dvsr comes in. 

If you want to have three batteries then leave the starts in permanent parallel and do the same with your third battery. 

I cannot see why you want two start batteries long term however, this is a recipe for a double failure due to cross charging and unless they are small you shouldn't need that much CCA unless your engine takes heaps of cranking. 

I would keep the starts as a parallel pair until they fail. (They will fail together). And then replace with a single start battery. 

 

 

[CarpeDiem 322]

1 hour ago, Tai Lockie said:

Ideally I could just put both start batteries into permanent parallel so they are effectively a single battery, but as Aardvarkash pointed out I need keep an eye on each individual battery Voltage. 

This is not a concern if they are in permanent parallel.  The batteries will eventually die as a pair and you'll be very unlikely to see it coming. 

[wheels 543]

DO NOT connect an old battery and a new battery together. Even if they are identical.
DO NOT connect two different types (deep cycle with start, or AGM with FLA etc) of battery together.
Do you have plenty of capacity with the current setup?
If yes, the best idea is to get a small deep cycle for House. You can either use a charge splitter to isolate the two (my prefered situation) or a VSR. I do not like VSR's because you are still charging two unlike batteries and the battery the VSR disconnects never gets fully charged. Not so much of a problem if you tend to be a weekend sailor, the boat gets connected to shore power when not sailing and a small charger brings everything back up to full. If you are on a swing mooring and you rely on just engine to charge, then that one battery will never perform and will die an early death.

[mattm 95]

1 hour ago, wheels said:

 the battery the VSR disconnects never gets fully charged.

I swear we had this conversation some 5+ years ago wheels, but a VSR does not disconnect one battery from anything. It just joins two banks together, exactly like an emergency parallel switch does.

[CarpeDiem 322]

Yeah, I see no difference between a vsr, a charge splitter or a correctly managed parallel switch.   (Not withstanding the fact that a parallel switch is a disaster waiting to happen - cause it is a question of "when" not "if" you forget it). 

They all have one supply, the alternator, it doesn't matter how you slice it or dice it, you can't optimally charge two different batteries from one supply, there will always be a compromise.

Comparing VSR to a Splitter:

A little bit of surface charge in the start battery could cause a vsr to hang on to the circuit for 30 seconds or so after the alternator turns off. I am not convinced this would be problematic as both batteries would need to be close to fully charged anyway for this to occur so there would be minimal current flow.

Other than that, what advantages does a splitter have over a vsr? 

[CarpeDiem 322]

19 hours ago, Tai Lockie said:

Ideally I could just put both start batteries into permanent parallel so they are effectively a single battery, but as Aardvarkash pointed out I need keep an eye on each individual battery voltage.

This is a simple three switch setup that a lot of boats have.

You will generally find this augmented with a VSR or a splitter so the parallel switch is never touched. 

To @wheels point. You should never join the start/house. (However, there's always an exception to every rule eg, while the alternator is running).

If you end up with a flat start battery, open the start isolator and close the house start.  Once the engine is running you could close the start... However if you're set up correctly, the start should never go flat unless it's dead, in which case leave it isolated and head home. 

[Psyche 480]

Whats your thoughts on the single switch?  Mine has house start and parallel but I've heard that it's a compromise over the three switch system.

[mattm 95]

The old 1/2/both ones aren’t that good in my opinion(and most others). With normal wiring configuration your picking which battery does all jobs, there’s no separation of loads (there are other ways to wire them if you have more than one 1/2/b switch, but I think it’s typically unnecessary complication).

The modern (3ish years old or less) Dual Battery Control (DBC) switches are good, operate similar to a 3 switch system but take less space. You’ll know the difference, the 1/2/b has 3 main studs on the back (some had 2 extra small ones for alternator field control), the DBC has 4. The Marinco DBC has the benefit of a house only on, the Blueseas one does not. 

For those who haven’t seen a DBC switch, they have an On position where house batt. is linked to panel, and start batt. to engine, a parallel position where the two banks are linked, and a house On only position, mostly in case you have an engine issue (ie alternator smoking) and want to radio for help without powering the engine. Down side would be you can’t have the house bank power the engine with the start bank off, without disconnecting a wire at the battery anyway. 

[CarpeDiem 322]

43 minutes ago, Psyche said:

Whats your thoughts on the single switch?  Mine has house start and parallel but I've heard that it's a compromise over the three switch system.

Assuming it's for your start/charge circuit?  And not your house loads? 

If you can avoid the both they are really fine.

Sometimes you can switch through the off to get to the house. But if you have to switch through both to get to the house then that's a compromise if you have a dead/flat start battery, particularly so if it has an internal short circuit. 

If you find yourself in a position where the start battery is dead, don't switch back to both go home and work out why the start battery has died.

The other issue with them is user error or accidental engagement. On CD the middle yellow switch is physically removed and lives in the chart table, that's cause once on a coastal classic at 2am I found we'd had amazing battery life - something wasn't right - after inspection I found someone or thing, maybe a thrown sail, had engaged the parallel.

And too what @mattmsaid above, I am assuming that this is just for your Start circuit and you have a separate house load isolator. 

Again, you'd still augment this with a VSR or splitter and only ever use start under normal conditions. 

[mattm 95]

CD, the DBC type is one physical switch, that effectively has 3 switches inside it, so it’s for both house, start and parallel functions.

https://www.bepmarine.com/en/p/772-dbc-ez

 

 

[wheels 543]

20 hours ago, mattm said:

I swear we had this conversation some 5+ years ago wheels, but a VSR does not disconnect one battery from anything. It just joins two banks together, exactly like an emergency parallel switch does.

Most likely we did.
It depends on the way the system is connected, which is determined by what the end goal is. All configurations have pros and cons.
Setup No1.
In the most common setup, there are usually two identical batteries. Usually start batteries. One battery was dedicated to start, the other was for running the stereo etc while out fishing. The Voltage drops to whatever the trigger point is and the Start battery is isolated from the "house" and protected from be discharged too far. When engine starts, the Voltage rises, the trigger voltage is reached and the Two batteries link to share the Charge Current.
Problem with that is, one Battery is often discharged far more than the other. When the two are reconnected, the charge current becomes unequal.
This is the most common set up found in small boats like trailer sailors and fizz nasties. IT was what the VSR was mainly designed for.

Setup No2.
This if for two different Battery types. Either size, chemistry or deep cycle House/Start. A more common set up for most slightly larger sailboats like Keelers, always in the water and usually on a mooring. ie no shore power available. No real room for Solar panels etc. 
This is to protect one bank over charging by taking the lions share of the charge current and the other remaining discharged, due to different charge current requirement of each. In this instance, the VSR is to isolate one bank when the Voltage reaches the trigger Point. Say 12.8V or whatever the VSR triggers at, as there are a few that can be voltage adjusted. The battery that is disconnected never never gets to be fully charged.
Not a huge biggy if the boat gets to sit on shore power at the end of the weekend and has a seperate charger for each bank when it does get to go on Shorepower

Setup No.3
A charge splitter is different from a VSR, in that one Battery does not "see" the other. They are completely isolated. When the engine starts, the Charge current is split to which ever battery requires whatever charge requirement. They are fully independant.  Well...to a point. There is a slight problem with large House and small start banks and Float voltages. But that's another discussion and not usually a major issue. The big plus is for an installation when a large House battery and smaller start battery is found. This is a slightly larger keeler that might be out for a week or more. The scenario of No2 above.

None of the above are of a huge issue. It is just my preference that I believe a splitter is by far the better and in most cases, the easiest to install. A VSR usually requires extra wiring on installation, but that does depend on setup of course.

 

[mattm 95]

What are you saying the issue is with the charge current to two seperate banks being unequal?

[Tai 2]

On 6/02/2022 at 5:05 PM, CarpeDiem said:

 

I cannot see why you want two start batteries long term however, this is a recipe for a double failure due to cross charging and unless they are small you shouldn't need that much CCA unless your engine takes heaps of cranking. 

I would keep the starts as a parallel pair until they fail. (They will fail together). And then replace with a single start battery. 

 

 

Mostly it was not wanting to lose any capacity and also that when running the windlass it seemed to loose some power after a short time, however that could be another problem I have that the engine controls currently wont let me adjust the revs while in neutral so I don't think the alternator is supplying a lot at idle.

 

[Tai 2]

On 7/02/2022 at 10:40 AM, CarpeDiem said:

This is a simple three switch setup that a lot of boats have.

You will generally find this augmented with a VSR or a splitter so the parallel switch is never touched. 

To @wheels point. You should never join the start/house. (However, there's always an exception to every rule eg, while the alternator is running).

If you end up with a flat start battery, open the start isolator and close the house start.  Once the engine is running you could close the start... However if you're set up correctly, the start should never go flat unless it's dead, in which case leave it isolated and head home. 

Right so this is almost what I have already except that I don't have a switch to put the house into parallel/start. I can see having the separate switch to bring them together would mean less chance of flattening the start.

Also when manually switching like this I'm thinking there is a risk of disconnecting a battery without the other being connected first and frying the rectifier diode.