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Old 08-04-2013, 10:07 PM   #1
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Default 120 amp alt? Advice please......

On this weekends 2 night stay at Branched Oak, a local lake here in Lincoln I noticed the boat was not cranking well when starting last night, switched over to the other battery and got back to the site no problem. This morning, sober and in better light I learned it’s no longer charging at least according to the gauge that’s obviously correct and corresponds with the situation.

Little back ground on me for those that don’t know, haven’t been on here in a while… I built and installed the engine and outdrive. I’m not new and have a few skills

I’m running 2, 1 year old deep cycle batteries that are exactly the same. I have a Perko 4FW2287 installed and can run 1-2 or both.

I’m also running a DB Digital mono amp and 2-12’s which pulls a LOT of power.

Assuming the alternator is shot, haven’t slept much in 2 nights and don’t feel like getting to the bottom of it right now… Would it be better to replace with a high output 120 amp something like this http://www.ebay.com/itm/HIGH-OUTPUT-...972#vi-content

Or will that jack up the deep cycle batteries? Obviously won’t make any difference when sitting, not running, listening to music.. but will it help the batteries get back up to par faster after a run around the lake? I recall reading that you are supposed to slow charge deep cycle batteries is why I ask. Or is my line of thinking just way off base from lack of sleep?
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Old 08-04-2013, 10:25 PM   #2
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I bet you don't have the jumper in your battery charger switched to Gel cell, so your not charging them from shore.

The Gel like to have a fast charge, and then drop down before they charge again.

If you still have your charger manual you will see the jumper setting.

80 amps is plenty for an alternator, stick a car battery charger on them with a % charge gauge on it, and I bet your battery are at 50%.
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Old 08-04-2013, 11:20 PM   #3
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Thanks for the response but looking for any alternator solution, not trying to charge them from shore power or a battery charger at all….. Although I need to now
Maybe just a new stock alt and a stiffening cap for the amp… It pisses me off then the lights dim every time the bass hits. Stupid 46 year old kids (ME)
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Old 08-05-2013, 12:13 AM   #4
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You said you have deep cycle batteries (not gel?, 2 different animals). How long do you run the boat after a deep cycle is discharged? If you discharge 400 amps it will take ~ 4 hours to charge with either an 80 or 120 amp alternator. A litter longer with the 80 and a little less with the 120. If you run the batteries low often then a battery charger is the best solution.
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Old 08-05-2013, 01:10 AM   #5
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i guess my point is, unless your going to run the engine for 3 hours, the batteries will never fully charge to 100%, and will shorten their lives.

as a battery discharges, then current goes down, and allows the acid to react with the lead plates, and produce a charge... (think of it as burning lead)

a $100 battery charger/tender will top them off over night, which I don't think your allowing for recover time at this point, regardless of the jumpers.

other option is a 3 battery for your boom boom and hydraulics on each wheel......
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Old 08-05-2013, 01:24 AM   #6
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They were called marine batteries, guessing they are deep cycle and not gel…. About 110.00 each if I recall correctly, O’Reileys auto parts stuff (I can get the part number if it will help) …. Are Gel better? More punch? Longer lasting? I take my boat out about 4 times a summer they never get used…. but I do maintain them. Pisses me off this stuff can’t last more than 24 months with 20-30 hours use annually…. Maybe that’s why they go bad, need to use them more?

Regular car batteries last for 4/5 years.. what the hell…

Regardless of the battery state…. That would not affect the charging gauge….right?
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Old 08-05-2013, 08:05 AM   #7
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a battery likes to be used, charged and discharged, your car is doing that daily.

The deep cell, or RV batteries, are high storage, but lower spike cranking amps... for like a starter.

Its a slower lower voltage use, like your radio and pumps, opposed to your crash load of a starter.

750-850 cranking amps is normal.

Funny, I just went through this, as my batteries only lasted two years, and that was with a charger on them.

I ended up at walmart, for their return policy of free replacement for two years, and its done at the customer service counter, so They will never check the battery, and just give me a new one....

The charging gauge, is only what the alternator is pushing out while running, so it should show anything above 12v.... usually 13.8 means its pushing our 1.8 v more then 12v.

Amp is automatic, and the rate the battery will take it, so the old battery could only be taking 5 amp, over 12 hours.
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Old 08-05-2013, 11:41 AM   #8
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As Pas said batteries like to be used and charged properly. If your marine batteries don't say deep cycle on them then they are just starting batteries which are not designed for deep cycle so the long hours of discharging them will shorten their life. Also with only using a few times a summer you should get a trickle charger to keep them topped off.
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Old 08-05-2013, 01:28 PM   #9
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Excellent stuff, thanks guys!
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Old 08-05-2013, 03:38 PM   #10
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ORR,

The flooded cell (acid) "starting" battery (Batt 1) on my boat is now 4 years old, maybe 5. The AGM (Batt 2) is 3, maybe 4 years old. No on-board charger. Stock, original, alt. No heavy draw electrics. We don't use the boat as much as we'd like to, twice a month on average I'd say, engine hours per outing probably amount to only 2 or 3. Sometimes the boat will sit on the trailer, at the marina, for a month without use and without being hooked up to a charger.

I always start on #1 and have never had a slow crank situation. We make the run to where ever we're going on #1 to charge it up. If we sit some where on the hook for any length of time I switch to #2. I keep the GPS, the VHF, and the whimpy stereo running. Back to #1 for re-start, then to Both for the run back. The batteries on mine don't see an external charger for the entire season. Ever. Biggest diff between how you use yours and how I use mine is the deep draw on yours from the amp(s).

One thing to remember when you run on "both" is that you are creating one big 12V battery. If, say, #1 has been drawn down to 10V, and #2 is at 12V, switching to both gets you one 11V battery at their combined A/Hr capacity (or whatever remains of their capacity). Of course, if you draw one down to 6V and the other is at 12 you'll get 9V. Maybe ok if you don't have an ECM/FI but if you do it could be a problem. One other concern is that if you have one seriously discharged and the other is fully charged, switching to both creates an in-rush of current into the dis-charged battery. Make sure you've got tight connections and beefy cables.

So yeah, a higher output alt will charge/re-charge the battery(s) faster. Down side is that faster charging creates more heat in the battery, shortening it's life (but it does tend to burn off some of the calcification that an in-frequently used flooded cell battery tend to accumulate. As mentioned, lead acid (flooded cell) standard - AKA starting, batteries do not like to be discharged at all, they will last their longest if they are always fully charged. Deep cycle batts tollerate discharge/re-charge cycles far better, as do AGM's (probably gel's also).

Gel's have very specific charging requirements. AGM's have less specific requirements and are similar to flooded cell. AGM's also dis-charge at a far slower rate when not being used than do flooded cell.

IMO, for boat that's used in warm weather, a battery with massive CCA (cold cranking amps) is unnecessary. The starter is only going to draw what it needs. Reserve A/Hr capacity rating is more important, as is relative immunity to dis-charge/re-charge cycles. I've started my boat on the AGM (B2) many times and have never had even a hint of a problem doing so. The AGM in my old big block (489) Chevy is at least two years old. The carb goes dry after sitting for a week so the thing needs quite a bit of cranking to get it to fire. Again, never a problem with the AGM. I think the CCA's are maybe 650. And oh, it has a very manly 37A alt.

When I winterize the boat I pull the batteries, take them home and put them on a shelf. I use the same trickle charger for both the flooded cell and the AGM, just alternating between the two every 3 or 4 weeks (the AGM take noticably less time to reach full charge than does the FC). When the flooded cell dies I'll be replacing it with an AGM.

Good grief I'm long winded sometimes! As my wife would say - and has, "when I turn the faucet on I want water to come out. I do not care why or how it gets there".

I'd probably keep the stock alt rating and run everything off B2 when you're on the hook. Just get into the habit of putting a charger on #2 when you get it home. Or up grade the alt and accept the possibility of a shorter battery life, but also make sure the existing charging wire from the alt will support a higher output.

Dan
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