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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Dual vs. Deep Cycle

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Jared
1st Mate

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USA
70 Posts

Initially Posted - 03/24/2004 : 12:49:33

I am going to replace my batteries over the next couple of days and I have been doing some reading over the past couple of days about what I should buy and was wondering how other folks solved the delima of dual vs. deep cycle.

I have an electric start on the boat, but can use the rope to start the boat and not be bothered much at all. I also have a 2 bank system with the 1-2-Both-Off system. My electric demands really are not too high until we anchor out and run the lights all night. And really I can only sail on the weekends and not every one at that.

I was wondering if other folks with the same scenario have gone with the system of 2 deep cycles or 1 deep cycle and 1 dual purpose? It seems for a small outboard that the starting demands may be able to be handled by the 2 deep cycles without buying the dual purpose and paying the price of less available amp-hours. If I have 2 deep cycles, will electric starting the motor a couple times a week kill them? If not, is it better to have the reserve capacity of 2 deep cycles? Anyone have any thoughts or experiences?

Jared Jamison
86 C25 #5354 FK/TR "Saba Rocks" Richmond, VA

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 03/24/2004 : 13:37:29

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Jared
 I am going to replace my batteries over the next couple of days and I have been doing some reading over the past couple of days about what I should buy and was wondering how other folks solved the delima of dual vs. deep cycle.

I have an electric start on the boat, but can use the rope to start the boat and not be bothered much at all. I also have a 2 bank system with the 1-2-Both-Off system. My electric demands really are not too high until we anchor out and run the lights all night. And really I can only sail on the weekends and not every one at that.

I was wondering if other folks with the same scenario have gone with the system of 2 deep cycles or 1 deep cycle and 1 dual purpose? It seems for a small outboard that the starting demands may be able to be handled by the 2 deep cycles without buying the dual purpose and paying the price of less available amp-hours. If I have 2 deep cycles, will electric starting the motor a couple times a week kill them? If not, is it better to have the reserve capacity of 2 deep cycles? Anyone have any thoughts or experiences?
<hr height="1" noshade id="quote"></blockquote id="quote">

Personally, I would use two regular deep cycle batteries for both the outboard starter and house instead of having one dual purpose battery to start your outboard and one deep cycle for everything else.

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 03/24/2004 : 15:41:01

Very astute questions, Jared.

I'd suggest either as many 12V deep cycles wired in parallel as you want, or two 6V golf cart batteries wired in series. With recoil start available, you only need one battery bank. A deep cycle house bank large enough to be useful should have no problem cranking a small outboard, and is unlikely to ever be damaged by trying.

Those big round [OFF/1/BOTH/2] selector switches are sort of obsolete now, particularly in your situation. Instead, I'd suggest high current (maybe 100A) SPST switches & fuses or circuit breakers, and maybe a battery combiner if you choose to have a separate cranking battery.

One high current circuit breaker (or SPST switch & fuse) would be used to isolate the electric starter from its power source. This provides a means of quickly disconnecting the high current starter circuit in the event of a short. It can also be used to prevent unauthorized cranking.

If you go with 6V golf cart batteries wired in series, I'd suggest a high current SPST switch & fuse (or circuit breaker) in series with the batteries to provide a means of quickly disconnecting that high current source in the event of a short or other problem.

If you go with two 12V deep cycles wired in parallel, they should each have a high current fuse (or circuit breakers if you're feeling rich) in the positive lead as close as practical to the battery terminal. If you're still looking for a way to include the old [OFF/1/BOTH/2] selector switch, it could be used to put the two 12V deep cycles in parallel by always switching from OFF to BOTH. (You could rationalize the use of this relic by convincing yourself, "If one of the 12V deep cycles ever quit on a trip, I could take it offline using the [OFF/1/BOTH/2] switch instead of disconnecting one of its leads." That's one of my excuses for still having that rotary switch around!

)

No matter what house bank configuration you choose, you will of course want a separate main 12V (maybe 30A) circuit breaker (or switch & fuse) at the power input to your distribution panel to turn it off and protect its wiring.

Here's one situation where a battery combiner might help: If you use a [OFF/1/BOTH/2] switch to isolate the 12V deep cycles while not in use and being recharged (at the dock during the work week), a battery combiner would see that they each received the optimum amount of whatever charging current was available from a solar panel, shore power trickle charger, etc.

By the way, one of the advantages of the dual purpose batteries is that they are supposed to be able to charge at a higher current than pure deep cycles. This is of no importance unless you have a charging source capable of putting out more current than a deep cycle bank would accept, and are in that much of a hurry to get recharged.

-- Leon Sisson

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aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 03/25/2004 : 13:11:18

Leon,

You seem to have some knowledge on this subject. I have the selector switch set up but also have an isolator which is not linked into the system. Is an islolator the same as a combiner? Can you post a wiring diagram that an eletronics novice can read and understand?

Al Eckhart
GALLIVANT #5801

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 03/25/2004 : 16:24:56

Al E.,
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Is an islolator the same as a combiner?<hr height="1" noshade id="quote"></blockquote id="quote">No. It's my undertanding that a battery islolator uses diodes to prevent the loads on one battery from discharging another battery. This imposes diode forward voltage drops in series with the charging current. As a result, any charging voltage regulating circuitry can't tell what's going on at the battery, and precious solar power is wasted overcoming the diodes during low light conditions.

A [url="http://www.yandina.com/c50Info.htm"]battery combiner[/url] contains a very low resistance sealed relay switched by a rather clever analog to digital control logic circuit.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Can you post a wiring diagram that an eletronics novice can read and understand?<hr height="1" noshade id="quote"></blockquote id="quote">I'm going to try to post a link to my C-25 charging system schematic under "[url="http://www.catalina25-250.org/forum/topic.asp?TOPIC_ID=6081"]General Forum | Charging System - too many choices![/url]" where it seems to be more on-topic. I make no promises about "...that an eletronics novice can read and understand...".

-- Leon Sisson

Edited by - Leon Sisson on 03/25/2004 16:43:17

oldsalt
Admiral

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USA
578 Posts

Response Posted - 03/25/2004 : 19:07:14

Leon your understanding of battery isolators is correct and they aren't recommended for low amperage charging systems since the losses are excessive in comparison to the available charging capacity.

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Ben
Master Marine Consultant

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USA
1234 Posts

Response Posted - 03/25/2004 : 20:04:20

As usual, I know just enough to be dangerous, but I have two dual purpose batteries. I used them all last summer without recharging them. Usage was minimal, lights now and then, radio now and then. What are the drawbacks to having two dual purpose batteries?

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Jared
1st Mate

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USA
70 Posts

Response Posted - 03/25/2004 : 22:06:22

Thanks for all the advise. I decided to buy 2 deep cell batteries and just use the pull start most all the times unless people are on board and I want to look fancy. I got two 105 Ah deep cell batteries at Sams Club for about $50 a piece. Man, that sure is one heck of a lot cheaper than West Marine...

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 03/25/2004 : 22:19:37

"What are the drawbacks to having two dual purpose batteries?"

IMHO follows:

For the usage you describe (and indeed, probably for most of us) the dual-purpose marine batteries will work just fine.

I had them in my previous boat.. they lasted for years and were completely up to the task of keeping the nav lights on for a few hours and a providing a couple hours of cabin lights a day over a 2 or 3 day outing. However, for 'serious' cruising with extended drawdowns, the deep cycles are the really the best way to go. But heck, if your batteries are meeting your needs, there's no sense in spending extra money.

For either type, leaving them in a discharged state for an extended period of time will really shorten their service life. Keep 'em charged and the fluid levels up and they last a long, long time.

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falco_esq
1st Mate

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USA
60 Posts

Response Posted - 04/04/2004 : 17:31:06

I have a 1/both/2 switch for my batteries. How should I set this up, and is there a purpose for this switch? I have an electric start motor.

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