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Old 02-03-2017, 09:57 PM   #1
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12 volt boat/24 volt thruster batteries/charger

Hi Guys:

My boat is 12 volt. My thruster is 24 volt powered by 2 separate 12 volt batteries wired in series. The charger that came with the boat for these batteries is 20 amps and is "whining" so I need to replace it.

I can only charge the batteries through the charger which is powered only by shore power or genset power, not from the alternator on either of the mains.

Question: What's the fastest charging batteries and what's the best charger to recharge them quickly, so I can leave the dock and recharge them quickly by running the gennie as little as possible? Thanks.

Jim
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Old 02-03-2017, 10:51 PM   #2
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this DC converter 12V to 24V have fonction of 3 step charger but only 10A

this is solution to charge with your main engine

Mastervolt - Innovative power systems<br>for autonomous use
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Old 02-03-2017, 11:29 PM   #3
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Sterling Power has good stuff

Sterling Power makes excellent DC->DC chargers. Use one of these and your thruster batteries will be happy whether you are running on shore power, the generator, or your engine alternator. I am very happy with my 24 volt -> 24 volt charger. It keeps my bow thruster batteries in excellent shape. This 12 volt -> 24 volt model:

Sterling Power DC input 12v to 24v battery charging, battery to battery charger, marine grade DC input charger

will give you 50 amps.

(These also have the serious advantage of having a separate voltage sense wire. With this, you will not need to run super heavy cable from the charger to the bow.)
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Old 02-04-2017, 01:15 AM   #4
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How about an old style series-parallel switch relay? Charges batteries in parallel at 12 volts, and starts at 24. Connect thruster to the starter terminals. They were common on heavy trucks a long time ago.
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Old 02-04-2017, 06:02 AM   #5
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Back to your original question:

AGM batteries allow faster charging than flooded cells. You can usually recharge them at 30-50% of the batteries amp hour capacity. Two Group 27 batteries will give you lots of amperage output and 70 amp hours of capacity. So a 20-30 amp charger would work well.

I doubt if you need more than that. If you use your thruster for 30 seconds and it draws 200 amps (a lot at 24 V) then you can replace that in 15 minutes of generator running.

But it also might be worthwhile to install a small capacity 12V to 24V converter/charger. A 5 amp unit (and I don't know if they make them that small) would allow the propulsion engine's alternator to slowly recharge them over an hour period.

David
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Old 02-04-2017, 06:10 AM   #6
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"Question: What's the fastest charging batteries and what's the best charger to recharge them quickly, so I can leave the dock and recharge them quickly by running the gennie as little as possible? Thanks."

Basically you cant.

Whike some batts can be charged more rapidly during the bulk phase all slow down for the last bit.

I do not think you will have a problem. Leaving a dock with a power pole you should be charged 100%

The usual non hyd thruster is very time limited , so a couple of min of operation will not have discharged them much at all.

IF the only 24v load is the thruster the 12-24 realay would be a simple method of operation.

Basically all charging will be 12V , the time will be determined by the amount of discharge .

IF the engine is charging the thruster bank , it shopuld not take much time for 2-3% to go back in.
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Old 02-04-2017, 06:19 AM   #7
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Simpler solution is to add a pure sine wave inverter. I have the same 24 volt thrustet / 12 volt boat wiring. Having an inverter on whenever the engine is running really has, no downside, allows small appliances to be used, and batteries to be recharged as they were meant to be.

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Old 02-04-2017, 07:29 AM   #8
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Quote:
Originally Posted by jfelds View Post
Question: What's the fastest charging batteries and what's the best charger to recharge them quickly, so I can leave the dock and recharge them quickly by running the gennie as little as possible? Thanks.

Generally speaking, I think AGMs would be fastest charging from normal-chemistry batteries. FWIW, one of the thruster-installation-specialty companies I've read about always uses Odyssey PC-2150s (Group 31s), partly because of specs -- big CCAs/MCAs, 100-Ah capacity each -- and partly because VRLA AGMs don't off-gas as much so can be better for installation under bow staterooms, etc.

If you go that way, you could ask Odyssey what's the fastest charging level they recommend -- 30A? 40? maybe even 50A? -- and then just buy whatever charger will crank out that much current. A C/20 charger on a 200-Ah bank would only need a 40A charger, C30 could use a 60A charger, etc.

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Old 02-04-2017, 08:18 AM   #9
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Guys:

Thanks for all the responses. I will do my due diligence on all of your suggestions and note that there is always more than one way to solve a problem, especially on a boat, and especially an electrical one.

I neglected to mention that I followed a suggestion and did install a 12/24 converter. It was a Trollbridge 2400. The problem is that although I use a crackerjack electrician, even he couldn't get it to perform as designed, and it was an expensive experiment. I removed it two days ago which was when we discovered the charger was headed South. Thanks again for all the suggestions.

All the best,

Jim
MV Kokomo
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Old 02-05-2017, 02:00 PM   #10
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The simplest solution might be a pair of 12V start batts for the engine.

The boats std alt should hold the voltage up in use and the multiple thin plate start pattern will not be harmed a bit by a few min of hard work.

The thrusters will be stronger with the higher voltage .

The cruise , or a night at the power pole will recharge that few percent used by the thruster.

"Having an inverter on whenever the engine is running really has, no downside,"

But it also has no upside if the boats alt is powering it.Except for Margureta making!!!

Many alts are 130+ amps and few batt chargers , shore or inverter powered are that strong.

Also with a proper 3 or 4 stage V regulator the charge profile is better than from most AC powered batt chargers
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