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Old 05-07-2014, 07:05 PM   #1
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Thruster Battery: Deep cycle or not??

It's time for a new thruster battery. This is on my 38, it has a Sidepower SE60 3.1kW 12v unit. I run a grp 24 batt and only get a few years out of it. I know the batt is pretty small for the thruster, but in my duty cycle I rarely have to run it more than 10-20sec. When batt is fresh, it does well and volts don't drop below 10.5 at batt terminals. When batt gets weak (now!!), when I spin the boat, volts start at 10.5 but right when boat has made its spin, its down to 8v and thruster is really losing it. Charge rig is three step, and charging still seems normal. Bulk at 14.6, float at 13.5, amps soon go to zero.

Since this is a planing boat, I do what I can to minimize weight, so I am going to stick with grp 24. If I only get two or three years, I am ok with that. But if changing to a better type batt increases that, great!

Last batt was West Marine dual purpose start/deep cycle. My thinking at the time was that the duty cycle was not that far different than cranking an engine for similar time, so a batt good for engine starting would be good here. But maybe not.

So here's my question: Should I get a starting batt, a deep cycle, or a dual purpose?

I figure amps under load are about 300. I've never run it over a minute without allowing it to charge back up. Not really a deep discharge, only about about 5Ah. Not going with a AGM.

I'm going to get a Deka in the AM tomorrow, my alt shop gives me decent prices, and Deka seems to be quality. I am skeptical of West batts, even if made by a good mfr, I suspect West has them made cheaply (dock talk there!!!).

What says the site?

Thanks.
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Old 05-07-2014, 07:12 PM   #2
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Greetings,
Mr. S. I'm gonna be jumped on all over here but I think the dual purpose batteries are like all season tires. A poor compromise. Go with the purpose built starting battery. Your thinking it is like cranking an engine is correct I believe. I know nothing about battery groups but could you get a starting battery with more "oomph'?
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Old 05-07-2014, 07:17 PM   #3
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Not going with a AGM.
I use AGMs for thrusters since in my vessel it is in a closed bilge/cabin space, Less or no gassing as compared to WA.
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Old 05-07-2014, 07:23 PM   #4
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WM AGM's are made by Mastervolt. As far as the thruster battery 1 group 24 seems awfully light. I have been running (3) 31 series Lifeline AGM's for 5 years on my Mainship 40 Sedan Bridge with an enclosed hardtop (lots of windage). It also serves as an aux house bank. I am running the largest 12VDC VETUS thruster made. A minute on the thruster draws some pretty heavy duty current. How do you get away with using FLA batteries in the bow of the boat? It's one of the reasons I run AGM's there, the front stateroom AC unit shares the same space I wouldn't want gassing inside the boat for obvious reasons.
DEKA makes high quality batteries. I have a bunch of their Unigy1 AGM's I'm installing in my Gulfstar for the house bank.
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Old 05-07-2014, 07:23 PM   #5
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The reason I am sticking with flooded is that all batts in the boat are charged with one charger, and I can set it to only one profile. So if I go with agm for the thruster, I really should change all the batts in the boat. I also have my main engine alt set for for flooded. I think AGM might work better here, but not a good use of funds to change all.

Thruster batt compartment is well ventilated, not concerned about H2 buildup there.
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Old 05-07-2014, 07:28 PM   #6
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Okay I have a dedicated 40 amp smart charger in the bow just for that battery bank. The main house bank gets charged via solar and a Xantrex Freedom charger 130 amps/ 2500watt inverter. My boat has numerous chargers but all AGM batteries.
If you are vented then everything should be fine stick with what's worked for you.
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Old 05-07-2014, 09:58 PM   #7
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My manual for my SE 55 calls for 350 CCA (DIN) which is ~665 CCA (SAE/BCI) SAE = (DIN x 1.5) + 40.

Seems to indicate they want a starting battery.

I'd go to Walmart or Costco and buy the highest CCA group 24 starting battery with a 3 year non-prorated warranty and swap it out every 2.99 years.

Note: This is a "Do as I say, not as I do" recommendation. My thruster is hooked up to my house bank. Little boat means short cable runs.
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Old 05-08-2014, 01:47 AM   #8
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A minute of thruster use? Doesn't a Mainship have a rudder? Just curious...
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Old 05-08-2014, 05:36 AM   #9
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A minute of thruster use? Doesn't a Mainship have a rudder? Just curious...
I was responding to the original post not saying I use my thruster much if at all lately. I have rudders and twins but I wanted the thruster when I was new to boating over 7 years ago.
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Old 05-08-2014, 05:41 AM   #10
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A minute of thruster use? Doesn't a Mainship have a rudder? Just curious...
Uh oh, next thing you know Coors will be called Urquell.
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Old 05-08-2014, 06:25 AM   #11
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Noticed the manual is on-line. They want a minimum of 665 CCA. I happen to have Deka's marine battery cut sheet here. The only group 24 flooded that meets that spec is something called the 24M7 @875. If you can make a group 27 fit (they are 2 inches longer than a 24) than a 27M6 would be better, it is heavier and has about the same CCA @ 840 but more reserve capacity (182 vs 125) and more Marine CA @ 1050.
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Old 05-08-2014, 06:27 AM   #12
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Uh oh, next thing you know Coors will be called Urquell.
Being new here what does this comment mean?
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Old 05-08-2014, 06:53 AM   #13
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DC motors are very voltage sensitive , the higher the V the more power output.

I would select a big LA start batt to hold up the V with the many plates and huge surface area of a start batt.

Your one min of operation might cause the plates to get covered with gas , but that would be fine as it goes away and the batt would be ready for another docking attempt.

300A for a min would not deplete the batt to the point where a deep cycle would be preferred.
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Old 05-08-2014, 07:01 AM   #14
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I might disagree it depends on the wind resistance in perfectly calm waters the thrusters current might be lower than say trying to do an emergency docking in 60 plus mph winds? I had this happen to us and it took quite a bit of thruster as well as engine and throttles. It got so bad I have 4/0 wire from the bank to the thruster less than 4 feet total return and I started to smell the insulation heating from the bridge. The thruster didn't fail me and we were able to safely dock the boat. I'll never ignore my weather alert again.
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Old 05-08-2014, 07:52 AM   #15
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Eric: here's a different approach. Consider an Optima spiral-wound 'Blue Top SpiralCell 34M'. Although AGM, being spiral-wound it is very accommodating of charging voltages--more so than other AGM forms--- and will live happily with a FLA profile. And the other advantage of spiral wound is that it delivers a heck of a cranking charge. Victron, who DON'T own Optima, specifically recommend these for thrusters, for another reason: the spiral-wound form is very shock resistant (so good if installed in a bow). My 'cranking bank' (serves to start propulsion engines, operates Sidepower 75 thruster and my davit) comprises two of these and is 7 years old and still sounds as strong as when new.
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Old 05-08-2014, 08:17 AM   #16
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The reason I am sticking with flooded is that all batts in the boat are charged with one charger, and I can set it to only one profile. So if I go with agm for the thruster, I really should change all the batts in the boat. I also have my main engine alt set for for flooded. I think AGM might work better here, but not a good use of funds to change all.

Thruster batt compartment is well ventilated, not concerned about H2 buildup there.

FWIW, our charger has two profile settings, one for flooded lead acid AND AGM, the other for gel. When we started switching from FLAs to AGMs, both battery and charger techs told us mixing AGM and FLA banks (as we were gradually replacing banks) would be fine.

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Old 05-08-2014, 12:21 PM   #17
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This is my experience. I have FLA's for my house and start banks, but for my Sidepower SC 100/185T-12V, 8.4 HP I have (2) Optima Part #SC3DM Bluetop, 1125 MCA, 12 VDC batteries wired with 4/0 wire. The Optima batteries are charged via the house bank with a Blueseas combiner.

I am starting my 6th season with this setup with no problems so my suggestion is replace your existing battery with my setup. Yes you can combine an Optima Bluetop with your existing FLA's.
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Old 05-08-2014, 01:54 PM   #18
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I picked up a Deka 24M7 starting batt, 1000MCA, 800CCA. The pan is big enough to fit a 27, but the idiot boatbuilder (me) framed the hatch an inch too small for the 27.

We'll see how it holds up.

Some interesting tidbits: I weighed the old West batt: 40.2lb. Weighed the new Deka: 43.6lb. More lead??

My alt shop guy and I engaged in quite a conversation about the batt industry. Apparently there are few actual batt mfrs, but they make the batts to their customer's specs. So Deka may make West Marine or Batteries Plus batts, but those will not be same as some other retailer's Deka. Since we don't know what the retailers specify, it's a crap shoot for us.

He made some comment about the M6, M7, etc indicating a quality level, but not sure I heard that right.

This was highlighted a few times when I was involved in boats that suffered battery explosions. Tops blown off batts, and inside you find the actual cell only occupied the case compartment partially: The cell could have been much bigger. Thus my trick about weighing batteries!!

This alternator shop is locally owned and well established, and caters to mostly industrial and commercial clients. Only a couple years ago I found out they sold batts, and they said it was more as a service to their customers, and really did not consider it a significant part of their business. These are folks that have no idea of what MBA stands for or what marketing or modern retail means!! So if they say they picked this batt line because it served their customers well, I tend to trust them. The MBA would say "hey we can make more money if we put grp 31 cells into a 4d box"!!!

I'm going to reconsider going with AGM next time. Getting six years is better than 3, and may be worth the additional cost.

In defense of the old batt, I remember a couple years ago being in a boat parade with a buddy piloting the boat. Due to a very slow parade, he was steering with the thruster, and ran the batt into the dirt- until it no longer worked at all. That had to take some serious life out of it.

I also dock in a narrow creek, and I have to back out about 300yrds to get to a place wide enough to turn around. Backing in a narrow creek with a single means steer with thruster. Then it is still pretty narrow where I turn, so instead of stitching with the main engine, I thruster around 180deg. So thruster batt gets hit pretty hard (about 15sec to steer, 15sec to rotate, so 30sec total) each time the boat leaves.

We'll see how it holds up.

Thanks for all the input.
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Old 05-08-2014, 05:27 PM   #19
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Ski it almost sounds like you would benefit from LI-Ion batteries with a small dedicated automatic smart charger. The LI units are said to have much longer life much faster charge rate and can deal with deep discharge.
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Old 05-08-2014, 05:34 PM   #20
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Ski it almost sounds like you would benefit from LI-Ion batteries with a small dedicated automatic smart charger. The LI units are said to have much longer life much faster charge rate and can deal with deep discharge.
Lithium Ion batteries are very expensive, need a special charger, and as Boeing has found out, can have very serious problems. I love them for power tools but I wouldn't use one on my boat. A company at a boat show was trying to sell me on the idea but they were about five times the cost of AGMs.

As for the thruster, that's closer to the load of a start battery than a deep cycle battery. I would go with a starting battery or a dual purpose battery. That's my opinion.
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