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Old 09-01-2015, 10:48   #61
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Re: Need dedicated starting battery?

Umm. in post 10, I suggested a Lithium starter battery.
The A123 M1 LifePo4 cells can put out 70amps, and weigh 76 grams (0.17 lbs).
Using 4 in parallel, 4 in series for 12v, you have 10ah, 300 amps, and it weighs a massive backbreaking 2.8 lbs.

Quote:
Originally Posted by sailinglegend View Post
55 posts so far and only #22 suggesting what I think us the best solution - fit a very small Red Flash AGM start battery.

Ours is 37Ah that starts our 56 HP Yanmar engine in one second, taking less than 1Ah. It has been lying on its side under the floor for ten years and is still working perfectly.

These units are so small there is always somewhere you can fit and forget.
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Old 09-01-2015, 10:57   #62
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Re: Need dedicated starting battery?

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Originally Posted by sailinglegend View Post
55 posts so far and only #22 suggesting what I think us the best solution - fit a very small Red Flash AGM start battery.

Ours is 37Ah that starts our 56 HP Yanmar engine in one second, taking less than 1Ah. It has been lying on its side under the floor for ten years and is still working perfectly.

These units are so small there is always somewhere you can fit and forget.
I agree, that seems like the ideal solution. I have 2 31's for house and a 27 for
starting. I would love to combine those 3 to have a bigger house and then add
a small Red Flash (or the one Maine pointed out). A very small engine battery
seems like it would suffice to start my easy-to-start 39hp Yanmar and it would
be so much easier to find a new place to install.
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Old 09-01-2015, 11:49   #63
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Re: Need dedicated starting battery?

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Originally Posted by DefinitelyMe View Post
Go for it. I've had a similar system for years and i like it very much. I don't have a generator either, just a solar system. If you're observant you will never run your batteries so low that you can't start your engine whenever you want. In the meantime you will have:
- More house bank capacity
- Longer battery life (because you won't be discharging your house bank so far on each cycle, and the battery voltages (assuming they are all the same age, make, capacity etc.) will all be the same at the beginning of a charge cycle)).
- Simpler electrics, because now you don't need an isolator or anything to charge your house bank separately from your starting bank.
I

+1....cruised for 15 years this way. I even recovered from a shorted cell which brought the voltage down to 10.5 volts--I disconnected the bad battery and still had enough power to start the main engine. The bigger the bank, the longer it lasts and the easier the engine starts.
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Old 09-01-2015, 11:55   #64
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Re: Need dedicated starting battery?

We have 2 batteries dedicated to starting and windlass use. We also have 6 T105s for our house bank. We also have a heart monitor. The rule is starting and house batteries remain seperate.

We also have a portable jump starting battery shared between our car and the boat. It's a useful spare power source and can also be used to start our engine / generator if needed. They are cheap and even come with a carrying handle, air compressor for inflating the dinghy, jumper leads and a work light.

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Old 09-01-2015, 12:16   #65
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Re: Need dedicated starting battery?

We have the same boat as the OP and understand the space issues. Ours came with 4XGr27's under the starboard settee -- 3 house and one start. We upped the house bank by switching to 4X6V golf cart batteries from Sam's Club. They fit after making some modifications to the tray that was holding the Gr27's. We put a Gr27 starting battery on a shelf in the aftmost storage area under the quarter berth. However, if you have a Gr24 or Gr27 starter for your genset, I don't see why that can't be wired to serve as your engine start as well.
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Old 11-01-2015, 14:36   #66
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Re: Need dedicated starting battery?

I think the only time i would ever consider separating my battery banks is if i wasn't living on board. Then, i could maybe see the benefit; the boat sits on a mooring, or in a berth or whatever for a few weeks, things run down, you get a load of friends together to go out for a sail and you can't get out of the berth because you can't get the engine started.

However I presume most of you, like me, glance at the battery voltage every time you walk past the switch board right? - maybe 10 or 20 times a day. It gets written down in the log every 6 hours. There's no way those batteries are going to get low before i notice it! If you don't have a voltage display on your panel, it a lot cheaper than a load of extra wiring, isolators, separate charging systems, separate batteries etc. etc.

$6.90 on amazon! RioRand LCD Digital Volt Voltage Panel Meter Voltmeter 7.5V-20V - Power Converters - Amazon.com
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Old 11-01-2015, 14:44   #67
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Re: Need dedicated starting battery?

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Originally Posted by DefinitelyMe View Post
I think the only time i would ever consider separating my battery banks is if i wasn't living on board. Then, i could maybe see the benefit; the boat sits on a mooring, or in a berth or whatever for a few weeks, things run down, you get a load of friends together to go out for a sail and you can't get out of the berth because you can't get the engine started.

However I presume most of you, like me, glance at the battery voltage every time you walk past the switch board right? - maybe 10 or 20 times a day. It gets written down in the log every 6 hours. There's no way those batteries are going to get low before i notice it! If you don't have a voltage display on your panel, it a lot cheaper than a load of extra wiring, isolators, separate charging systems, separate batteries etc. etc.

$6.90 on amazon! RioRand LCD Digital Volt Voltage Panel Meter Voltmeter 7.5V-20V - Power Converters - Amazon.com
Watching voltage does not mean a thing. Put a load on it and it goes to nothing.
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Old 11-01-2015, 15:16   #68
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Re: Need dedicated starting battery?

The scenario I'm most worried about is a stuck bilge pump switch.
I should do the math sometime to figure out how long it would
take drain my house bank.

Even a live-a-board might leave long enough to get burned by this.
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Old 11-01-2015, 18:11   #69
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Re: Need dedicated starting battery?

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Watching voltage does not mean a thing. Put a load on it and it goes to nothing.
Sure.

But how often when you're on the boat do you not have a load on your batteries?

I do recognize you may be distinguishing when your batteries actually die vs being drained. In the first, volts can be really misleading. In the second, with usual cycling loads while cruising, I think volts are a pretty good surrogate for battery state.


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Old 11-01-2015, 18:25   #70
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Re: Need dedicated starting battery?

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The scenario I'm most worried about is a stuck bilge pump switch.
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Old 12-01-2015, 08:16   #71
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Re: Need dedicated starting battery?

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Originally Posted by malbert73 View Post
Sure.

But how often when you're on the boat do you not have a load on your batteries?

I do recognize you may be distinguishing when your batteries actually die vs being drained. In the first, volts can be really misleading. In the second, with usual cycling loads while cruising, I think volts are a pretty good surrogate for battery state.


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By a load I was speaking of a load like a load tester has. Basically a direct short. I'm making the assumption we are talking about lead acid batteries. It is only used for a moment but will detect a dead cell which otherwise can drive you nuts.
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Old 19-01-2015, 19:46   #72
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Re: Need dedicated starting battery?

Great input by everyone. Found a good spot for a small AGM battery in battery compartment. Had to go in from other side. Am planning to install this:

WEST MARINE High Cranking Power AGM Battery | West Marine

As starting battery using battery selector 1 for engine. Selector 2 will be house bank, and ALL will be the 4 batteries (3 x group 31 AGMs + starting battery) combined.

Since I could find room for additional battery which only weighs 44 lbs, figured that adds redundancy. The arguments against using house bank for engine won out- my main reason being safety- I can start the engine using 2 isolated battery systems with the turn of a switch in my nav station, which makes me feel a bit safer. This is especially since we cruise with 2 small children so not being able to start the engine in emergency isn't an option.
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