Batteries

[shrew]

I'm now looking at installing a windlass. This will require a dedicated battery. I already have a 40amp 3 bank charger, so that isn't an issue. I currently have 2 Group 31 AGM (Lifeline) batteries, 1 for the house and 1 for the starter. I'm considering taking the house battery and using it for the windlass. I'm considering replacing the house battery with a 4D AGM (Also lifeline because those batt's ROCK!!).

In looking at the specs, I'm a bit confused.

http://www.lifelinebatteries.com/marinedeepcycle.php


MOD = Minutes of Discharge

Group 31 (12V)
Rated Cap.Amp. Hrs20 Hr Rate = 105
25 Amp Draw = 195 (mod)
15 Amp Draw = 340 (mod)
8 Amp Draw = 688 (mod)

4D (12v)
Rated Cap.Amp. Hrs20 Hr Rate = 210
25 Amp Draw = 390 (mod)
15 Amp Draw = 680 (mod)
8 Amp Draw = 1375(mod)

8D (12V)
Rated Cap.Amp. Hrs20 Hr Rate = 255
25 Amp Draw = 475 (mod)
15 Amp Draw = 825 (mod)
8 Amp Draw = 1670 (mod)

Now when I look at the 6V batteries, the capacity seems much larger:

4CT (6V)
Rated Cap.Amp. Hrs20 Hr Rate = 220
25 Amp Draw = 492 (mod)
15 Amp Draw = 856 (mod)
8 Amp Draw = 1692 (mod)

It would seem a single 6v battery has more capacity and Amp Hours (AH) than the 8D in 12V. So here is what I'm tryign to figure out.

1) If I wire two 6V in Serias, does that give me the same Amp Hrs? (Does it double the AH the same as it would in parrallel, or does it cut the AH in half because you're doubling the voltage?

2) Would I have complications trying to connect 2 6v batteries in serias to the battery charger? (Any considerations?)

3) Would it simply be easier, better, faster to go with a 4d (12v) instead?

[Tommyfmu]

I am not well educated on this topic but since no one has 2-cent'ed up yet, I can tell you what is installed on my Carver which has 5 batteries. I have 2 main 12 volt batt's which provide for starting, windlass and 12 volt systems; they are on a 2 batt switch and charge by either the dual bank or engine alternators. I then have 2 golf cart 6 volt batt's in series (which makes 12 volts) on one switch which provides solely for a 1000 watt inverter which powers media i.e. 32" flat panel tv, dvd, wifi router, laptops and cellphone chargers. These 2 batt's, even after extended use have never run down even with full load (which I find incredible, so maybe the hours are double per your original question (?) ). Our fifth 12 volt battery on it's own switch is dedicated solely to start the generator.

While I do not know what would be best for your windlass question, perhaps I can extrapolate that (2) 6 volt's may give you more usage hours of lower power items, rather than the higher cranking amps needed out of a 12 volt to power a windlass or starter, especially considering the heavy AWG cable that's necessary to power a windlass (through the solenoid).

[seapuppy]

well..the windlass is usually used to pull or deploy an anchor..most of the amperage load comes on startup.....that being said..that's why it has a 50amp breaker...
now for a batt....when you deplot/recover an anchor...the batt. should be robust enough that if you use it for house and the windlass..it will work properly with enough left over for safety...so..a deep cycle batt is needed....now with that thinking...2 6vdc batts will give you with your numbers ..220ampsx2=440cch's ..and yes they need to be in series....
but..here's something else to think of ...we had a large gp 27 batt that has something like 800 cch that is quite definitely able to do the work...again..your not running that thing for long periods of time...just occasionally...plus while deploying the anchor..your not using the batt's per se...the engine is running...the rode is feeding out from batt pwr yet the alt. is charging the batt.s as it's working...

then when your recovering the anchor...you start the engine...start pulling the anchor...the engine is running to recharge....while the anchor is recovering.......

SP

[rtw_ca]

I have to differ with Seapuppy. Batteries in series doubles the voltage but the current remains the same. So if you have the 6V batteries with 220 Amp-Hrs, you'll still only get 220 amp-Hrs witht 2 in series but at 12V. So it'sa about the same as the 4D battery.

[shrew]

Originally Posted by rtw_ca

I have to differ with Seapuppy. Batteries in series doubles the voltage but the current remains the same. So if you have the 6V batteries with 220 Amp-Hrs, you'll still only get 220 amp-Hrs witht 2 in series but at 12V. So it'sa about the same as the 4D battery.

Ok this makes a bit more sense. So wired in Series will double the voltage but leave the amp hours the same? Wired in Parallel will double the amp hours but leave the voltage the same?

The only reason I was contemplating moving the Group 31 AGM from the house to the windlass would be because I've been toying with buying a second house an putting it in parallel with existing Group 31 house battery. The cheapest path to me seemed to be to move the house battery to the windlass and replace the house battery with a 4D ADM instead to increase amp hours on the house side. So with these calrifications it would seem I could get a bunch of 6v in series, or even 4 6v; 2 in series connected in parallel to another 2 in series. 2 g31's in parallel or a 4d. 4d sounds like the simplest to install and troubleshoot.

Unless I've understood incorrectly (please correct me if I'm wrong), then I think I have a plan. It looks like move the group 31 to the windlass and replace the house with a 4d, then wait until spring to go drop the hook and kick back.