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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 07-06-2009
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Using a deep cycle battery for starting?

So I got a super deal on a Dyno group 27 deep cycle battery at a charity auction. I was about to go on a trip and all the batteries on the boat are dodgy. Starting is one group 24 car battery of old age. The house bank is 2 interstate 4Ds, one old, the other very very old. So I picked up the Dyno to have a reliable way to start the engine, installed it and isolated it from the other batteries. I didn't think it would be that big of a deal because I've seen many a large engine started with deep cycle 4d and 8d batteries.

Is there any fundamental problem with using a good quality deep cycle battery for starting? Seems to be man enough for the job so far. Will my battery die a premature death? Will I cook my starter for lack of available juice?

Aren't starting batteries built with thin plates because they're cheaper to make and "good enough", whereas a good deep cycle battery would be a better, longer lasting albet more expensive starting battery?

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  #2  
Old 07-06-2009
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A true starting battery has many small plates so that it can put out more amperage over a short period of time. A deep cycle battery has thicker plates and is designed to produce less amperage at any given time but is designed to be drained to 50% many times. While these are the design parameters you still can use a deep cycle battery for starting. The amperage required to start a modern diesel can be surprisingly low. Unless your engine is very hard to start you should have no problem.
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Old 07-06-2009
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As long as the deep cycle battery can safely supply the "impulse current" or surge current needed by your starter motor (which can be 1.5-2.5 kilowatts easily) without overheating and warping the plates or internals, it is perfectly safe.

I had a discussion about this with JCI (possibly the largest US battery maker) some time ago, for a starting battery that had to sit for long periods and would be better served by using a deep cycle. Their answer was that if the deep cycle had enough capacity--it was actually the better way to go.

So, depending on how much power your start draws, it can be perfectly good to do it this way. On a 41? Dunno, you'd need to find out how much power that is.
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Old 07-06-2009
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I have been using a group 27 deep cycle for a starting battery for 4 years and it is still going strong. This after learning my lesson using group 24 starting batteries and replacing them every 2 years.
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Old 07-06-2009
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I'm in at least year 6 using a Deep Cycle 4D to start a 75 hp Yanmar.
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Old 07-07-2009
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Quote:
Originally Posted by hellosailor View Post
As long as the deep cycle battery can safely supply the "impulse current" or surge current needed by your starter motor (which can be 1.5-2.5 kilowatts easily) without overheating and warping the plates or internals, it is perfectly safe.

I had a discussion about this with JCI (possibly the largest US battery maker) some time ago, for a starting battery that had to sit for long periods and would be better served by using a deep cycle. Their answer was that if the deep cycle had enough capacity--it was actually the better way to go.

So, depending on how much power your start draws, it can be perfectly good to do it this way. On a 41? Dunno, you'd need to find out how much power that is.
That's kind of what I was thinking. DYNOs are great batteries with an awesome reputation and I know first hand because I've abused some of them before in the most horrid ways. So I figured that would make a better starter than a regular starter with thin plates, as long as it was up to the "impulse current" though I didn't know the term.

So how do I go about finding how much impulse current my starter draws, or for that matter, how much the dyno can handle? Starting batteries give cranking amps, deep cycle amp hours, and the usually never give you the other number though that would be helpful wouldn't it?

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Old 07-07-2009
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Quote:
Originally Posted by hellosailor View Post
As long as the deep cycle battery can safely supply the "impulse current" or surge current needed by your starter motor (which can be 1.5-2.5 kilowatts easily) without overheating and warping the plates or internals, it is perfectly safe.

I had a discussion about this with JCI (possibly the largest US battery maker) some time ago, for a starting battery that had to sit for long periods and would be better served by using a deep cycle. Their answer was that if the deep cycle had enough capacity--it was actually the better way to go.

So, depending on how much power your start draws, it can be perfectly good to do it this way. On a 41? Dunno, you'd need to find out how much power that is.
that's just how I do it on Catalyst w/ a 15 hp Merc 4-stroke to start and only one battery.... no problems.
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Old 07-07-2009
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Med, you find out by looking it up. Your engine maker should have a manual and a part number for the starter--that should (nasty word) say how much power it consumes. If not, contact whoever makes the starter, they can tell you. If you had to make a blind guess you could look for the wire size leading ot the starter, or any fuse in the starter cable, and ballpark down from there but that's a rough way to do it. (There are ways to measure it with a meter but unlikely you'd have access to one in that power range.)

As to the battery, same thing. Call the maker or look to their web site, the information is usually available even if it isn't on the web.

And of course bear in mind that also depends on "fires right up" versus the higher load of "needs to crank for fifteen seconds" which will generate a whole lot more heat in everything powering it.
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Old 07-11-2009
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So I think I am experiencing the same problem as Bubb2 above has conquered. My first starting battery lasted 3 years, the second 2 years, and the 3rd 2 years. Wheras my deep cycle 6vx2 batteries have lasted 6 years. The starting batteries seem to be very hard to keep over the winter, despite using one of these impulse type devices.

So I am considering using a deep cycle or maybe a combined deep cycle/starting battery for starting. I am going to investigate my starter, but in the meantime, how many amp hours deep cycle battery do you think would be needed for starting a 25HP diesel engine ?

Thanks very much.
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Probably one of your best choices would be the Trojan SCS225 battery. While it is listed as a deep cycle and Trojan doesn't label any of their current models "start batteries", it is designed to be a dual purpose battery. I learned this after a friend called Trojan before purchasing 2 of these to parallel for a house bank - he's very pleased and they do the job well. An ideal battery for a small powerboat that needs both start capability and house capability but not enough to justify multiple banks. This was apparently the use it was designed for.
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