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Old 11-21-2019, 09:03 PM   #1
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Stern thruster battery setup/ help

Here is what I would like to do. I have a 31í with bow thruster. I am having a stern thruster installed during winter layup. Right now I have 2- 8d lead acid batteries. 1 engine and 1 house. The bow thruster runs off the house battery, but most of the time while running I am on both. All is good . With the addition of the stern thruster I would like to add a group 31 AGM in the stern compartment very near the thruster. This will allow the use of both thrusters at the same time while taking the load off the 8dís .
What would be the best way to link the batteries . Should I have them run heavy gauge back to the 8d house battery or should the stern battery be a stand alone and isolated with only a charging circuit .
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Old 11-21-2019, 09:26 PM   #2
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What main engine do you have? My Cummins craps out at about 10.3amps on one of my 4D engine battery. My solution was to add one more 4D and move both thrusters to the 3X4D batteries maintaining the ability to parallel the engine 4D battery. That would give me a total of 4X4D batteries, always mindful of the fact, my Cummins will shut down at approx 10.3amps.
Your 2 8D batteries are rated at? They can be put in parallel ?
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Old 11-21-2019, 09:34 PM   #3
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Do you have an inverter? I would put a battery in the bow and one in the stern for each thruster. Run #14 guage wire from each to a 2 bank 12 amp battery charger. Power the charger off the inverter while underway and shore power while at the dock. Short battery cable runs (<4') keep the voltage higher for better performance from the thruster. My bow thruster is wired that way and works extremely well.

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Old 11-21-2019, 09:34 PM   #4
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The main is a cummins QSB 380. It never ever crapped out while using the thruster. Not sure about the amps.
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Old 11-21-2019, 09:40 PM   #5
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I do have an inverter charger and also a 2 bank 20 amp charger that the generator runs the inverter charger runs from shore power and the 20 amp can run from Gen of shore
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Old 11-21-2019, 09:54 PM   #6
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My bow & stern thrusters both run from one 8D AGM but nothing else connected to it.
One problem running thrusters from house or start might be if electronics are also off them and the batty V dips the electronics can have negative results.
At min may lose position on GPS or worst case can sometimes lose custom set up on a MFD.
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Old 11-21-2019, 10:17 PM   #7
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I put in a stern thruster a couple of years ago. I put a group 31 AGM in the lazarette compartment about 2’ away from the thruster. I put a 15 amp charger under the master berth and use it to charge the thruster battery only. It has worked well for us so far. I would not try to run battery cables too far due to voltage drop. It is probably as cheap or cheaper to put in a small charger than run 4/0 battery cable very far. I ran 4/0 battery cable the 2’ to my charger because I want the most voltage ai can get.
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Old 11-21-2019, 10:36 PM   #8
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Quote:
Originally Posted by Comodave View Post
I put in a stern thruster a couple of years ago. I put a group 31 AGM in the lazarette compartment about 2í away from the thruster. I put a 15 amp charger under the master berth and use it to charge the thruster battery only. It has worked well for us so far. I would not try to run battery cables too far due to voltage drop. It is probably as cheap or cheaper to put in a small charger than run 4/0 battery cable very far. I ran 4/0 battery cable the 2í to my charger because I want the most voltage ai can get.
Then I assume the aft battery is never charged from the main engine. Has this ever been a problem or is it just not used enough to drain the battery before it gets charged again ?
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Old 11-21-2019, 10:55 PM   #9
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No it has never been a problem. We use the thruster frequently but not for too long at any time, usually a short burst for 5 to 10 seconds. If I ever have a problem with charging I can add an ACR to charge the thruster battery.
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Old 11-22-2019, 06:18 AM   #10
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I think this is the way to go. It not only leaves existing systems alone but offers a 3rd battery for emergency
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Old 11-22-2019, 06:38 AM   #11
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Quote:
Originally Posted by Arc View Post
The main is a cummins QSB 380. It never ever crapped out while using the thruster. Not sure about the amps.
Turns out, all the batteries were crapping out too. My desire was to keep the 380 running at all cost. Docking can be accomplished w/o thrusters assuming it is not blowing a gale.
A nice friendly dock hand to get a spring line over and then complete the docking exercise.
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Old 11-30-2019, 08:29 AM   #12
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Quote:
Originally Posted by Arc View Post
Here is what I would like to do. I have a 31í with bow thruster. I am having a stern thruster installed during winter layup. Right now I have 2- 8d lead acid batteries. 1 engine and 1 house. The bow thruster runs off the house battery, but most of the time while running I am on both. All is good . With the addition of the stern thruster I would like to add a group 31 AGM in the stern compartment very near the thruster. This will allow the use of both thrusters at the same time while taking the load off the 8dís .

What would be the best way to link the batteries . Should I have them run heavy gauge back to the 8d house battery or should the stern battery be a stand alone and isolated with only a charging circuit .


You can parallel your two, same size, batteries together for both power draw and for charging. But itís a bad idea to parallel unlike batteries for power draw and definitely not for charging.
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