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Old 16-04-2021, 19:31   #1
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Deep cycle PLUS starting

Just when I thought for a second that I was getting it, (deep cycle vs starting). I decided to check what batteries I have (I know, should have known already...). Anyway, Dyno Gp 27 100 AH, combo deep cycle plus starting. I got two of ‘em on this Crealock I just inherited. Its an old boat with very little drawing off it. 55 amp alternator and a, ahem, Pisces engine.
What do you all think about this combo concept in one battery? They are essentially new from about 1 year ago. Note: I am adding a Tigris 1500 watt windlass. Will have engine on when using whenever I can.
Thoughts please, ( I am almost afraid to ask...).
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Old 16-04-2021, 21:56   #2
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Re: Deep cycle PLUS starting

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Originally Posted by AmzngGrace View Post
st inherited. Its an old boat with very little drawing off it. 55 amp alternator and a, ahem, Pisces engine.
What do you all think about this combo concept in one battery? They are essentially new from about 1 year ago. Note: I am adding a Tigris 1500 watt windlass. Will have engine on when using whenever I can.
Thoughts please, ( I am almost afraid to ask...).
I asked the same question when I installed my batteries and I was told "both". Here is an article that may help.

https://www.autobatteries.com/en-us/...ting-batteries
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Old 16-04-2021, 22:22   #3
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Re: Deep cycle PLUS starting

I general the combo thing is fine for small powerboats that run their engine regularly (daily or every other day) so the battery gets fully recharged and a significant portion of daily demand is directly met by alternator output. Batteries probably don’t go below 70% very often and with 2 of them there’s enough cranking amps to start a decent sized engine.

If you are running you engine regularly or have lots of solar they should be fine.

If you sail a lot and have a normal amount of solar and a normal amount of demand they will probably have a shorter life compared to real deep cycle batteries.

With 200Ahr of real deep cycle you should be able to start your motor no problem unless you have an old brute of an engine that is hard starting.

On the plus side they are Dyno which to me is the gold standard of batteries, they even publish their plate thicknesses.

My guess is that with very small loads and some solar you should do fine. In the PMW you will probably motor more than a lot of places.
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Old 17-04-2021, 04:36   #4
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Re: Deep cycle PLUS starting

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Originally Posted by AmzngGrace View Post
Anyway, Dyno Gp 27 100 AH, combo deep cycle plus starting. I got two of ‘em on this Crealock I just inherited.

What do you all think about this combo concept in one battery?
It's a common product. IOW, there are 3 common categories of lead-acid batteries: starting, dual-purpose, deep-cycle.

Whether a dual-purpose battery suits your needs -- some zenlike combination of your boat's DC architecture and your own typical DC power consumption -- depends.

Ref architecture: if your boat was designed to use a single battery bank to start your engine and to service house loads (many are designed this way), then dual-purpose batteries can be the cat's pajamas. And then if your current battery sizes are close but not quite a cigar... you can sometimes use the same architecture and just use "bigger" (more Ah capacity) versions of dual-purpose batteries. That starts depending on available space, but it otherwise not usually a difficult modification.

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Old 17-04-2021, 05:34   #5
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Re: Deep cycle PLUS starting

There is really no good reason for so-called dual purpose batteries. The name is clever marketing. Any decent deep cycle battery will start an engine with no problem while proving the capacity to be charged after drawn down by ‘house’ loads.
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Old 17-04-2021, 05:38   #6
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Re: Deep cycle PLUS starting

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There is really no good reason for so-called dual purpose batteries. The name is clever marketing. Any decent deep cycle battery will start an engine with no problem while proving the capacity to be charged after drawn down by ‘house’ loads.
I agree with this. Often someone posts "You need the cranking capacity". We have small, very small, engines on sailboats. They don't have big starters compared to large motor vehicles.
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Old 17-04-2021, 07:27   #7
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Re: Deep cycle PLUS starting

The overwhelming opinion on this forum is that you 'need' separate starting and house banks. I totally disagree. Thus far, the best argument for having that setup is "what if I run down the house bank by mistake?" which is, in my opinion, a very weak argument for a lot of extra stuff whose only purpose is to start a motor and sits there the rest of the time doing nothing. Maybe if they'd used that space for additional house capacity it wouldn't have run down in the first place?

We've operated on a single, large, deep-cycle bank ever since I've owned the boat. I've convinced several of my clients (I'm a marine contractor) to simplify by having a single bank and all of them are happier. One of them was worried about being stranded if he went out for a weekend so I installed a simple low-voltage alarm for him. Problem solved, very simply.

There are many genuine reasons why someone might need a dedicated starting bank but if you live aboard OR keep your boat in a marina there really is no need on the kinds of smaller, simpler boats that most of us are operating.

Even on larger boats there is usually no need for a main engine starting bank. A large boat will likely have a generator. OK, so have a separate starting battery for the generator, but start the main engine off the house (well, dual-purpose really) bank.
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Old 17-04-2021, 07:34   #8
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Re: Deep cycle PLUS starting

Oh, and in relation to your original question: when a battery is marketed as 'dual-purpose' all it really means is that it's not as good at cranking as a starting battery and not as good at cycling as a deep-cycle battery. They can be useful in applications where space is really limited and there isn't room for separate banks OR a decent-sized deep cycle bank. We had them in our camper van for example, where we couldn't physically fit a proper deep-cycle battery. But for most sailboats they really are unnecessary. Any decent deep-cycle battery will have oodles of cranking power for our little engines as another has already said. I'd say use your batteries until the end of their life and then replace them with deep cycle batteries. You'll get better performance all-round.
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Old 17-04-2021, 09:53   #9
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Re: Deep cycle PLUS starting

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Originally Posted by AmzngGrace View Post
...... Its an old boat with very little drawing off it. 55 amp alternator and a, ahem, Pisces engine.
What do you all think about this combo concept in one battery?
...............Note: I am adding a Tigris 1500 watt windlass. Will have engine on when using whenever I can.
I think your alternator is too small for your windlass, or your 1500 watt windlass will be WAY too big. At 12 volts you will be pulling 125 amps !! Even if you are 24 volt you will be pulling 62.5 amps on your 55 amp alternator - which wont be giving anywhere near to 55 amps anyway at low engine speeds. I suggest you stop & have a total rethink about all this. You can get a 700 watt windlass which should do the job you need...

Your batteries aren't really the issue by the way. Over here we call them leisure batteries, not dual purpose. I have 5 on my boat - 1 for starting, 4 for domestic power, all at 110 amp hours each. They cost me about £90 each & last me about 5 years. I junk & replace them all at once. So the average battery cost is £90 per season. They are NOT proper deep cycle batteries but they do the job, as long as you treat them right - but thats a whole other thread.
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Old 17-04-2021, 09:57   #10
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Re: Deep cycle PLUS starting

@Cliveon:
Quote:
or your 1500 watt windlass will be WAY too big. At 12 volts you will be pulling 125 amps
True, but only at stall, or max pull. It will be a fraction of that if he weighs anchor properly.
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Old 17-04-2021, 10:13   #11
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Re: Deep cycle PLUS starting

All the comments about 'duel purpose' batt are right, they are simply start batteries with slightly thicker plates not deep cycle.

The requirements for engine starting is not a/hr capacity but voltage. The start batt has to maintain 9-10v while cranking or the motor will turn slowly. That not only makes starting a problem but can also cause the motor to draw more current and overheat. A large capacity deep cycle batt will certainly start an engine when fully charged but can quickly struggle if partly charged. Quite often you may want to start the engine after a night or more at anchor when the house bank may be under 12v, that's when you may run into problems and is why separate start and house banks are always recommended. They also provide emergency backup for each other in case of a bank failure, remember you cant run the alternator without a battery connected. That means if you have an issue with your single bank and have to take it out of service you have no lights, engine, nav, instruments... Everything fails, things that are critical at sea need an emergency backup.
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Old 17-04-2021, 10:36   #12
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Re: Deep cycle PLUS starting

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@Cliveon:

True, but only at stall, or max pull. It will be a fraction of that if he weighs anchor properly.
So why pay for a 1500 watt windlass? Will his wiring be sized for that?

I have a 45 lb Delta on 50 metres of 10mm chain (+ 45 metres of nylon rode). My old (but rebuilt) SL Sea Wolf 520 has been bench tested as being able to pull in excess of 350 Kg - sorry - over 770 lbs but is rated at about 700 watts as far as I can see. My system is 12 volt but I have 440ah house batteries & a 120 amp alternator.
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Old 17-04-2021, 10:52   #13
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Re: Deep cycle PLUS starting

My 30hp Kubota tractor has a small battery by boat standards. Maybe 65AH.
The point is you don't need a big battery to start most sailboat engines.
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Old 17-04-2021, 11:05   #14
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Re: Deep cycle PLUS starting

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I agree with this. Often someone posts "You need the cranking capacity". We have small, very small, engines on sailboats. They don't have big starters compared to large motor vehicles.

Your comment may be germane for the OP, but not everyone here has "small, very small engines."

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Old 17-04-2021, 11:06   #15
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Re: Deep cycle PLUS starting

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Originally Posted by roland stockham View Post
All the comments about 'duel purpose' batt are right, they are simply start batteries with slightly thicker plates not deep cycle.

The requirements for engine starting is not a/hr capacity but voltage. The start batt has to maintain 9-10v while cranking or the motor will turn slowly. That not only makes starting a problem but can also cause the motor to draw more current and overheat. A large capacity deep cycle batt will certainly start an engine when fully charged but can quickly struggle if partly charged. Quite often you may want to start the engine after a night or more at anchor when the house bank may be under 12v, >>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>

If "under 12V" might this not be the case that the house bank is sized too small for the given loads?


If the house bank is enlarged, the voltage wouldn't drop so low after a night on the hook.
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