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Old 11-13-2018, 01:06 PM   #1
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batteries for 24v thruster

Im looking for suggestions. I'm replacing my bow thruster batteries (2 12v=24v 288ah sweeper) flooded with Agm. No room for 6v so looking at two Northstar g31agm 102ah,1150cca. i realize that ill be losing some reserve capacity. Also no 24v recharge except from shore power or generator. Am i going wrong here? Any input appreciated.
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Old 11-13-2018, 01:16 PM   #2
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You are going to keep existing 24V setup right? Not considering changing that to a different voltage? If you want onboard recharging, look at Sterling DC-DC chargers.
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Old 11-13-2018, 01:19 PM   #3
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Why are you going to AGM?

Lots more expensive, especially $ per AH per year of lifetime.

Sure you can't make room for GCs?

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, around $400 per 200+AH (4x6V=24V) set

from BatteriesPlus or Sam's Club. Deka-labeled same batts also sold at Lowes.
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Old 11-13-2018, 01:24 PM   #4
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If you do really need AGM, besides Northstar check out Lifeline and Odyssey

Odyssey's PC-2150 is 100Ah G31 and terrific both for high-amp output and deep cycling longevity if cared for properly.

But pricey, no AGM can compete for value with the Duracell / Deka FLA GCs, nor

Trojan / Crown / Superior / US Battery FLA for that matter.

All these FLA makers can be trusted when they specify a given line is proper true deep cycling.

12V models included.

Rolls Surrette is tops in quality, but much pricier.
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Old 11-13-2018, 01:27 PM   #5
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For a thruster you want a starting battery.... Thin plates high current output.... what I did to charge my 24 volt system was to install a NOCO 24 volt marine smart charger and just powered by the inverter, not the most efficient way but it works well. by the way I used a couple of group 31 batteries.
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Old 11-13-2018, 01:31 PM   #6
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I think that AGM batteries are fine for powering a bow thruster. Two reasons:


As far as I have been able to determine, there is no difference between starting and deep cycle AGMs unlike FLA batteries.


Bow thruster use is a bit like starting and a bit like deep cycle.


Thus AGMs are perfect aside from the cost.


Look at Yandina's web site for ideas on how to charge your 24V batteries with 12V power.


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Old 11-13-2018, 01:46 PM   #7
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My thruster is only 12v, but in my analysis the batt duty cycle is much like a starting batt. You want lots of amps, but for brief moments (well mostly brief). I just use a normal marine starting FLA batt (I think it is Deka) and first one lasted like six years. Eventually volts got low when thrusting so new batt. New one has been ok for last five years.

No need for deep cycle or AGM in my mind, unless you want to spend extra money.

If you don't thrust a lot between periods when dock or genny power is available, a DC charge source is not really needed. The AC based charging should be ok.

I set up mine with a charge link from house batt as I do often run a lot without docking or starting Gennie. Not as easy to do with 24v thruster and a 12v boat.
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Old 11-13-2018, 02:44 PM   #8
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It seems to me that AGM or FLA is just a matter of convenience and access. If you have good access to the batteries where they are installed and don't mind watering them, a FLA battery is going to be a LOT cheaper and work just as well for that type of application. The high charge acceptance of an AGM wouldn't normally be an advantage for a thruster bank.
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Old 11-13-2018, 02:50 PM   #9
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The only reason for agm is poor location i have to use a mirror to see water levels. The DC to DC sound worth looking in to. It may be easer then changing out one of my alternators to 24v We do stay on anchor a lot. Ill have to price shop some of the other batteries.
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Old 11-13-2018, 03:09 PM   #10
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The only reason for agm is poor location i have to use a mirror to see water levels.
OK, valid reason for sure there.

Again, the Odyssey, Lifeline and Northstar AGMs are **far** superior for this usage than even good Starters or other-brand "dual use" like Optima. Take care of them well these can last a very long time.

Look for local distribution, don't pay shipping. Check the mfg dates.

Full River is also OK, but personally only if at least 20% cheaper than the top three.

Do not skimp on the amps throughput if you go with a Sterling 12-24V DCDC charger, AGM wants at least .2C, .4C would be healthier.

Yandina's Trollbridge can work OK, but not nearly as good as the DCDC approach IMO, not sure even that much cheaper?

Also note you don't need nearly as fat cable as you would without the DCDC, just look at temp / safety specs, don't worry about Voltage Drop,

that helps pay for the Sterling at least a bit, plus better longevity of the target bank getting its own staged charging profile.
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Old 11-13-2018, 03:09 PM   #11
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I have an Odyessy AGM for my 12 volt stern thruster. I wanted AGM since it is mounted under our aft cabin berth and I didnít want off gassing during charging. It has worked very well. It only gets charged on shore power but so far that has been fine.
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Old 11-13-2018, 03:16 PM   #12
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Be careful with selecting a DC-DC charger. You will overload it when thruster is running. Make sure that it can handle an overload or otherwise re-set itself after thruster run.

I solved this issue by putting a relay in my charge link that disconnects the link whenever thruster motor is energized.
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Old 11-13-2018, 03:21 PM   #13
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Im concerned about having the agm at a low state of charge for 7-10 days wile out and shorting life of battery between bring it up.
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Old 11-13-2018, 03:35 PM   #14
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Be careful with selecting a DC-DC charger. You will overload it when thruster is running.
Perhaps you were using a dinky unit under 40A?

Sterling goes up to 120A I believe, but obviously should not be bigger than the Alt output.

Also a big enough thruster bank will help. . .

> My thruster is only 12v, but in my analysis the batt duty cycle is much like a starting batt.

No, it is pretty easy to draw down to 10+% DoD, which really should get a batt with decent life cycle ratings as I reco above.
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Old 11-13-2018, 03:37 PM   #15
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Im concerned about having the agm at a low state of charge for 7-10 days wile out and shorting life of battery between bring it up.
Yes, that would really quickly murder even the best deep cycle batt, much less something cheaper.

Try to treat the thruster bank just as well as you do House. Have you got any solar?
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Old 11-13-2018, 04:30 PM   #16
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Perhaps you were using a dinky unit under 40A?

Sterling goes up to 120A I believe, but obviously should not be bigger than the Alt output.

Also a big enough thruster bank will help. . .

> My thruster is only 12v, but in my analysis the batt duty cycle is much like a starting batt.

No, it is pretty easy to draw down to 10+% DoD, which really should get a batt with decent life cycle ratings as I reco above.
When my thruster is running, batt volts go to 10.5. Whatever you use for charging will try to raise voltage up to the normal 13.8 or whatever. My charge link runs through a 10ga cable and 15A breaker from house bank. It trips the breaker if I did not use the relay scheme. It works.

And if you run your thruster enough to take batt down to 10% SOC, you are dogging that thing!! Or you batt is super undersized. I run mine just a few blips at a time to aid maneuvering. If I run it 30sec I did something wrong with my piloting!!
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Old 11-13-2018, 04:34 PM   #17
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24-Volt - Thruster Batteries -- AGM

FYI - I have both a 24-volt 10-HP bow thruster & 24-volt 13-HP stern thruster.

I use a serial / parallel set up with 4 AGM - Group 31 batteries at each thruster location. I have been VERY happy with them.

Batteries are mounted under the beds, so AGM in a group 31 size was the way to go for me.

I use a Sterling Battery to Battery Charger which works great.
Sterling Part # BB122470

I went with the "ACDelco" brand for the AGM's.

24 Month free replacement warranty.

Pricing is good & durability good.

NOTE: they have both Starting AGM's & Deep Cycle AGM's both. - they are not the same internally !

For the thrusters you usually want the starting type & I prefer a terminal rather than a post battery type hook up .

ACDelco Starting Thruster AGM Battery Part # is: 31 AGM CRT

31AGMCRT= Spec's: -- 110 Ah -- 925 CCA -- RC 190 -- 1140 MCA.

" Technology and Maintenance Council" - (TCM) standards as the benchmark for heavy duty group 31 battery performance - the 31AGMCRT has been tested @ over 850 + cycles of the SAE J2185 cycles operation parameter.
--------------------------------------------------------------------------------------------------------------------------------------------------------------
NOTE: the deep cycle 31AGMDCT is J2185 rated @ 950 + cycles.
Deep cycle AGM PT # is: 31 AGM DCT) - if you wanted deep cycle (31AGMDCT spec is: 700CCA - RC 200 - 100 Ah)

Certainly worth looking into.

Good luck.

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Old 11-13-2018, 04:58 PM   #18
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It sounds like a charge and the a relay would be a nice to have in line. The thruster say a minimum of 400cca or so and only room for two group 31s. So don't have much choice but to keep its use short. More practice on the back and full.
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Old 11-13-2018, 05:30 PM   #19
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We also have a 10 hp 24v bow thruster. It is mounted under the master v-berth so agm’s are required. Original owner had the thruster installed by Florida Bow Thruster in 2008. Current batteries were Sears AGM (no longer made). Saw FBT at the Annapolis Boat Show and they said they now use Odessy 31M-PC2150ST AGM batteries (x2) connected in series for 24 v. The batteries are next to the thruster motor so lead runs are very short. They installed a Promariner 20 battery charger (115vac). It can charge two banks at once, so it is connected to each battery for 12v. charging. All I can say is it works. Just waiting for spring to get the new batteries.

The Odessey 31M-PC2150ST are dual purpose crank and deep cycle (104 ah).
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Old 11-13-2018, 06:40 PM   #20
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When my thruster is running, batt volts go to 10.5
Then your bank is undersized, by definition. Likely not fully charged, maybe never fully charged.

Murderous conditions.

> My charge link runs through a 10ga cable and 15A breaker from house bank. It trips the breaker if I did not use the relay scheme.

Way too small to make a difference.

> And if you run your thruster enough to take batt down to 10% SOC, you are dogging that thing!!

Go back and look, 10% DoD means 90% SoC.

My point is such usage has nothing to do with Starter patterns, absolutely within deep cycling's definition, as your details make even more crystal clear.

Systems design is much better off defined by the worst case scenarios, ignoring the best-case ones.
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