Deep cycle and dual purpose in same bank

[skipmac]

Originally Posted by Dougtiff

Your charging system should go to your STARTING batt. first then combine to the HOUSE bank [Nigel Calder].Use your DUAL purpose batt. for STARTING and the others for HOUSE bank, that way you can have different batts. this way the START is allways charged and also wire in a ON/OFF switch between the start and house bank, thatway you can combine if needed.

Hi Doug,

My edition of Calder shows the opposite. Charging connects directly to the house batteries with a paralleling circuit or battery switch connecting charging circuits to the start battery.

The logic behind this method. Unless you have a problem with the engine, normal starting uses very little of the charge from the start battery. For example if your starter draws 150 amps and it takes 15 seconds for the engine to start you have used less than 1 amp hour. The house batteries are typically drawn down a lot more. Depending on how your boat is equipped it could be 50-100-200 amp hours in a day. So the batteries that need charging are the house batteries where just a little top off and maintenance is sufficient for the starting battery, assuming it is not connected to the house bank.

[jeremiason]

Maybe I missed it...

Did someone mention the "Dual Purpose" Batteries will loose voltage faster than the heavier plated "Deep Cycle" Batteries...

I am guessing because of that, the Dual-Purpose batteries will start drawing off the Deep Cycle batteries to compensate for the voltage loss.

Also again a guess, but even with a smart charger, I don't think by combining the deep cycle and dual use batteries you will get a full charge on any of them....

These are guesses... Anyone can confirm or tell me different?

[sailorchic34]

The blonde engineers take is that if they are all 12V 6 cell lead acid batteries, it will make no practical difference. You can mix group 24's, group 28's and group 31's wet cells and the charge and discharge voltages will be the same. well close enough to make no difference. Internal resistance varies a tad, but not too bad.

I would wire the battery's so that the dual purpose and starting batteries were on separate branch circuits and not intermixed, but they could be then connected together for one big happy family.

It's far more important that the batteries are wired so they all see the same voltage drop across the wires. Generally that means + tied to one end and - tied to the far end, with parallel straps the same length and size.

[wesevans]

This will not work well as the batteries will have different capacities and different discharge characteristics.

[Stu Jackson]

Originally Posted by Dougtiff

Your charging system should go to your STARTING batt. first then combine to the HOUSE bank [Nigel Calder].Use your DUAL purpose batt. for STARTING and the others for HOUSE bank, that way you can have different batts. this way the START is allways charged and also wire in a ON/OFF switch between the start and house bank, thatway you can combine if needed.

This is SOOO a UK phenomenon. I believe it is because the skippers in the UK have Lucas starters, which never work. Maine Sail and I, both, had extensive discussions on ybw.com a few years ago about this and we simply gave up!

The "work" required of a start bank takes all of 2 ah to start an engine. There is NO need to recharge it immediately.

Charging should go to the house bank first, and an ACR/relay to charge the start/reserve bank is more than sufficient to recharge it. In fact, most folks could use the "start" bank to start their engines a couple of dozen times WITHOUT RECHARGING the start bank before that bank would even get close to 50% SOC.

And combining a dead bank with a full one is just nonsense.

Here's why, as if I haven't posted this tons of times before:

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries | SailboatOwners.com Forums

It has NOTHING to do with battery types.

I have seen this with our Link 2000 for the past 15 years.

[Terra Nova]

It makes sense to top up the start battery right away because it won't take long to replace what was just used. And the start battery will then be instantly available, with 100% power to the starter, whenever called upon.

The only drawback to this, that I can see, is the reliance on a fallible charge splitter for the house bank's charge.

[Stu Jackson]

Originally Posted by Terra Nova

It makes sense to top up the start battery right away because it won't take long to replace what was just used. And the start battery will then be instantly available, with 100% power to the starter, whenever called upon.

The only drawback to this, that I can see, is the reliance on a fallible charge splitter for the house bank's charge.

No it doesn't.

Consider being on the hook for a night.

Which battery bank NEEDS more charge?

Why not use the AO to the house bank first, with a relay to charge the start bank as the secondary bank?

Why run the current through the relay from the start bank to the house bank when you can go house bank first?

Oh, well, I've heard it all.

Still makes no sense.

[skipmac]

Originally Posted by Stu Jackson

In fact, most folks could use the "start" bank to start their engines a couple of dozen times WITHOUT RECHARGING the start bank before that bank would even get close to 50% SOC.

I have an old tractor with a Perkins 4-108 and no working charging system. I do crank it a dozen times or more without charging the battery. Even then I only hook it up to an charger because of self discharge and not the power used to start the engine.

[hd002e]

Thank you all for uour replies, the reason I wanted mix dual purpose with deep cycle 12V was to give the house battery bank some oomph in the marine cold cranking amps department if I needed to rely on the house bank after a starter battery failure. The engine is a small (18hp) diesel so maybe I am being overly cautious and possibly bringing my house banks life down. :/


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[Terra Nova]

Don't be silly.

[Tikka]

Answer to your question is Yes , you can use different 12 volts batteries.
Deep cycles are not designed to heavy starting current, simply they have higher
internal resistance and do not care to supply starting current , normal batteries
takes it over, no harm done.
The only problem become when no load or charge is present, than they are discharging
each other...irrelevant if they different type or even the same brand and date manufacture .

[a64pilot]

Originally Posted by sailorchic34

The blonde engineers take is that if they are all 12V 6 cell lead acid batteries, it will make no practical difference. You can mix group 24's, group 28's and group 31's wet cells and the charge and discharge voltages will be the same. well close enough to make no difference. Internal resistance varies a tad, but not too bad.

I would wire the battery's so that the dual purpose and starting batteries were on separate branch circuits and not intermixed, but they could be then connected together for one big happy family.

It's far more important that the batteries are wired so they all see the same voltage drop across the wires. Generally that means + tied to one end and - tied to the far end, with parallel straps the same length and size.

This, but I will take it one step further, if they are just regular sized 12V batteries and not a very high end battery, it is very likely the only difference between them is the sticker on the case. Identical batteries are often labeled "deep Cycle" or "Dual Purpose"
You may also be surprised to find the weight differences between different brands of the same group size battery. You can infer the significantly heavier one may have more lead in it.

[TurninTurtle]

You don't have to be measuring to ensure all the wires are the same length... over a couple of feet the resistance of adequately sized copper for the load will be negligible. We aren't dealing with the accuracy needed in nuclear physics. A few seconds of no load or low load and the bank will have all batteries at the same voltage after starting the engine.

As long as the batteries are the same basic chemistry and cell count its going to work. "deep cycle marine" + starter type batteries mix just fine when paralleled.
The deep cycle is actually already a combination starter and deep discharge battery. (not the best choice for either use)

The load usage is where you run into issues.
Deep discharging the starter battery will degrade it faster than the ones made to handle it. The starter batteries will fail early if you are discharging significantly on a regular basis.
Demanding high current from the deep discharge type will damage them. You are not really protecting them from that by adding the starter type to the bank.

Sure it can work a couple or 3 years. But you should get 5 to 10 years from deep discharge batteries. 5 to 7 from a typical automotive starter battery. (when used as designed) You are cutting the life of the most abused batteries.
Unless there's a system to automatically isolate the weak battery the first to fail will pull down the whole system.

For the small diesel engine, starting off the house bank may not actually be a high current demand. You need to know the starter current demand vs the house bank capacity.

[mitiempo]

If the house bank is composed of multiple batteries, even if deep cycle, their total cranking ability is greater than a dedicated starting battery. This is true even if the house bank is 6 volt true deep cycle batteries.

[leftbrainstuff]

Originally Posted by hd002e

Battery question: i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank without an isolater in between. Will it be OK or will I see a discharge between the two?


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Depends.

The bank will eventually see the steady voltage of the lowest individual battery. If you see heavy usage of your house battery then your start battery will not be fully charged when needed.

Your start battery may also see more high current charge cycling than it needs. This will gas it more and shorten its life through shedding.

I do not consider a combined bank good practice ever. Fitting an isolator and seperate charger / regulator also gives you redundancy. Yes it's more expensive but so is replacing batteries. An echostart or similar will allow you to limit the charge current to the start battery.

The house batteries have lower internal resistance so their voltage will always dominate the bank. You might see a difference in battery temps for long charge cycles. If you can fit a temp sensor and connect it as an input to your charger then place it on the start battery.

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