Solar, House, Starter, Troller - Worried about charging..

[PSteward]

Hello!

I thought I had my battery situation figured out and took my two older deep cycle and created the house set and purchased a dedicated starter battery better sized to my engine size (7.4L V8), I was planning to combine (manual combiner) the batteries once the engine is on to help top up the house but am worried that the starter (which will already be mostly charged) will get over charged. Is that true?
After I understand that I am looking to integrate solar direct to house, and how to interface a trolling battery into the mix so it can get topped up when on the go or on solar, in addition my engine starter and alternator connection is not separate at the moment (one wire to my starter only).
I had started going over planning earlier but now I finally have access to the boat so now the picture is getting clearer in addition to getting more additions.

Thanks,

--Phil

[smac999]

When you drive your car with a full battery for 8 hours does it over charge?

No different then charging the boat battery. It’s fine as long as the voltage is.

I would put an acr or something instead of the manual switch. . One day you will forget to turn the switch off and drain all the batteries at achor.

[PSteward]

I agree on that statement with one battery, but what will be the effect of introducing two deep cycle battery that are at 20-30% charge and a few years old with a 95% charged battery that's different and newer during the charge period.
Ultimately I want to leave my starter alone and would like after top up that it's removed from the charging equation completely....

[DefinitelyMe]

Originally Posted by smac999

When you drive your car with a full battery for 8 hours does it over charge?

No different then charging the boat battery. It’s fine as long as the voltage is.

No, this is a very different situation. Yes, it does matter. By simply combining the banks your starter bank will be overcharged, off-gas, shed plate material and die prematurely. Meanwhile your house bank will be under charged, sulphate and die prematurely. So it's not an ideal scenario and it's exacerbated by the thin plates / high acceptance rates of starter batteries compared to think plates / lower acceptance of house batteries.

That being said, it is more common to under-charge than over-charge, which generally translates as 'if in doubt, charge'. Furthermore the addition of solar (which you say you will do) will really help to mitigate the imbalance as it means both your house bank and starter bank will be more closely matched (at least in terms of state of charge).

If you're going to charge a third (trolling) bank from the same solar it will cost only marginally more to get separate charge controllers, or a charge controller that can handle two independent banks.

[smac999]

Originally Posted by DefinitelyMe

No, this is a very different situation. Yes, it does matter. By simply combining the banks your starter bank will be overcharged, off-gas, shed plate material and die prematurely. Meanwhile your house bank will be under charged, sulphate and die prematurely. So it's not an ideal scenario and it's exacerbated by the thin plates / high acceptance rates of starter batteries compared to think plates / lower acceptance of house batteries.

explain how having one battery by itself at 14.2v is different then having 2 or more batteries at 14.2v for the same period of time when. at any charge level.

it's not different. the start battery will take the exact same current and the exact same charge by itself or with the others when put at the same voltage. it's physics.

the difference is will take longer for the alt to reach its 14.2v setpoint with multiple batteries so it's actually better for the starter battery to be with the others then by itself in that situation with a single voltage internal reg alt. as the start battery will actually only be in the 13v range for the first while untill the voltage slowly hits absorption. by itself it will hit absorption right away.

now the best is for each battery to have it's own 3 stage control and float when full. but putting the start battery at ~14.4v for hours and hours is what every single car battery does and those batteries last 7+ years doing it. it's not a concern.

[skipmac]

Originally Posted by DefinitelyMe

No, this is a very different situation. Yes, it does matter. By simply combining the banks your starter bank will be overcharged, off-gas, shed plate material and die prematurely. Meanwhile your house bank will be under charged, sulphate and die prematurely. So it's not an ideal scenario and it's exacerbated by the thin plates / high acceptance rates of starter batteries compared to think plates / lower acceptance of house batteries.

Sorry but I have to agree with smac999 on this one.

In simplified terms when a battery is discharged it will accept a lot of amps. As the battery's state of charge increases the internal resistance of the battery will also increase so it will naturally accept fewer amps if the voltage stays the same.

With a house bank and a starting battery the most common situation is for the house bank to be lower state of charge than the starting battery. So the starting battery will have a higher internal resistance sending most of the charge to the house bank and will not overcharge the starting battery.

The best setup for charging in my experience is this.

All charging sources (alternator, shore powered battery charger, solar, etc) are connected directly to the house battery bank (but through a fuse). The starting battery is then charged automatically using your preferred model of automatic battery combiner. I use the Yandina autocombiner but there are several companies that make similar units

Then anytime you run the engine, connect the battery charger or other source the starting battery is automatically connected to the system and charged but automatically disconnected when the engines (or any other charging course) switch off so you never forget and accidentally discharge your starting battery.

You might use a switch on the house batteries that facilitates disconnecting the house batteries when working on the wiring but this does introduce the risk of frying the alternator if someone accidentally switches off the batteries while the engine is running.

[DefinitelyMe]

Originally Posted by smac999

explain how having one battery by itself at 14.2v is different then having 2 or more batteries at 14.2v for the same period of time when. at any charge level.

it's not different. the start battery will take the exact same current and the exact same charge by itself or with the others when put at the same voltage. it's physics.

the difference is will take longer for the alt to reach its 14.2v setpoint with multiple batteries so it's actually better for the starter battery to be with the others then by itself in that situation with a single voltage internal reg alt. as the start battery will actually only be in the 13v range for the first while untill the voltage slowly hits absorption. by itself it will hit absorption right away.

now the best is for each battery to have it's own 3 stage control and float when full. but putting the start battery at ~14.4v for hours and hours is what every single car battery does and those batteries last 7+ years doing it. it's not a concern.

Interesting. I defer to your apparently better understanding of the principles involved. My comment was based on an unsubstantiated understanding of a passage from Nigel Calder's book 'Boat owners Mechanical and Electrical Manual', page 38 of the 3rd edition under the section titled 'charging more than one battery bank from a common alternator'. In this section he says that in situations where there is an imbalance in chemistries, capacities etc. then 'one is likely to be chronically overcharged while the other will be chronically undercharged'.

[PSteward]

I've been checking around and will settle on a Renogy DCC30S as it manages all components involved (solar, alternator, starter batt, house batt).
The main issue is the difference in charging from an alternator with a voltage regulator vs solar controller.
The solar controller is made for deep cycle and will properly charge that type and adjust voltage levels, while the alternator doesn't do much more than just keep pumping the same voltage which is fine for the starter but not for the deep cycles.

[sailinglegend]

Originally Posted by smac999

When you drive your car with a full battery for 8 hours does it over charge?.......

This idea comes up quite often here but the comparison to a boat with two battery banks needs more understanding of what over-charging means - this is charging a battery at too high a voltage for its State of Charge (SoC). A starter battery will drop less than 1% of its SoC each time the car is started. All battery manufacturers state that a fully charged battery must be dropped down from its designed Boost voltage to its designed Float voltage.

You also have to look at a standard internally regulated car alternator on older cars that never charged at high enough voltages to cause gassing - at around 14.4v (temperature dependent).

Newer alternators, like many now fitted on boats, have temperature sensors to reduce the voltage the hotter they get. So they start at 14.4v or higher and quickly fall back to less than 14 volts - so battery gassing stops and so over-charging stops. Modern cars have vehicle Engine Control Units that regulate the charging voltage.

A starter battery recharges very very quickly compared to a 50% depleted high Ah capacity deep cycle battery service bank. So using a VCR to parallel the starter battery and service bank, using the alternator, mains charging, or Solar can mean the starter battery can be gassing too long because the service bank can be sitting at 14.4v for a long time before it drops to Float.

This can be a disaster for sealed starter batteries.

[Adelie]

If the house batts are at 20% they will draw dawn the Starter when combined in order to equalize voltages. So power will be flowing from the alternator AND starter Batt to charge the house. The discharged batts will have a lower acceptance voltage than the charged battery. As the house batts charge and start discharge the voltage they would each like to be at will converge and amps coming out of the start batt will taper off. Once the start and house batteries have the same acceptance voltage both will start charging.

The problems that will have occurred are
A. Very high sustained current out of start batt. Start batts like to do short bursts. There are heat management issues involved.
B. The start batt will have been significantly discharged, to somewhere around 50%. Depends on the relatives sizes of the batteries. They don’t like going below about 90%.
C. The house batts don’t like getting discharged to 20%. True deep cycle batts don’t like to go below 50% repeatedly.
D. You should figure out if you have real deep cycle batts for the house or marine batts which are really a hybrid of deep and starting batts.
E. Once you get all the batts near fully charged you run into the problem that the different batts have a different desired finishing voltage. An automotive alternator is probably the best charging source here as the regulator will be set to a lower voltage. Otherwise it would fry a battery that was charged for hours on end when already full. As long as the motor is running and the batts are near full there shouldn’t be a problem.
F. As soon as the motor is turned off the battery with the higher resting voltage will be trying to continue charging the other bank. You really need to immediately un-combine the banks when the motor is shut down.

What would I do?
1. Never discharge the house bank below 50% if deep cycle, 70% if marine/hybrid batts.
2. Run the alternator to the house bank
3. Get a cheap 20W panel and PWM controller and charge to start battery from that. Even a large V8 is only going to use less than 1Ahr per start unless it is very hard starting. A 20w panel can put 1Ahr back in about an hour for a fully charged battery and faster is it’s not full.