Bow Thruster w/Dedicated Battery Charging Via Combiner

[slowbutsteady]

I have a bow thruster with a dedicated group 31 115 AH full river AGM battery. The dedicated battery is recharged via a connection to the house batteries (600 AH of AGM northstar Batts) about 7 feet away via a blue seas ACR/Combiner with 80 amp thermal breakers at both ends.

Ive noticed when underway and the combiner engaged the engine will lug and voltage will drop when the thruster is used. My interim solution to reduce strain on my alternator from those momentary load spikes is to manually trip the breaker while docking/maneuvering thus severing the combiner from my house bank and then rearming the breaker while underway or back at the dock and connected to shore power to keep the thruster battery charged. The thruster seems to operate with the same force whether the combiner is activated or not. The house bank is brand new and I did a simple test (not a load test) on the dedicated thruster battery to find that its still reading around 650 CCA (Its rated for 720). The thruster battery is getting close to 6 years old so Im inclined to replace it but just want to understand if there are any other flaws with the installation I should look at too.

The thruster is a 12 v 10 HP thruster. I dont know its precise amp draw during operation (i'll test this with a ammeter next time I have a buddy on board) but if pressed to guess I would say somewhere in the 250-300 amp range in short bursts. I'm conservative with the thruster when docking too but do use it in short bursts when getting in to the slip. On a few occasions the breakers have tripped themselves even with relatively light use.

I know there are a variety of ways to wire in a thruster but my understanding is that having a large battery directly adjacent to the thruster itself with heavy cable is ideal.

 

[sunchaser]

I know there are a variety of ways to wire in a thruster but my understanding is that having a large battery directly adjacent to the thruster itself with heavy cable is ideal.

Yes, this is common. Our 24V thruster is about 5 feet from the dedicated batteries. Works fine. With your thruster being 12V, do you have room nearby to park the battery? A group 31 AGM should be ideal.

 

[Comodave]

Maybe get rid of the combiner and use a dedicated charger for the thruster battery. That is what I use for my stern thruster. It only charges via 120 volt but I have never had a problem of the battery running dead. It sure simplifies the system. The battery is about 1.5 feet away from the thruster and I used 4/0 battery cable. I could have used smaller cable but it is a one time cost and the benefits are ongoing for the life of the thruster.

 

[Kiwi.]

The Fullriver Group 31 battery (1100 CCAmps) is exactly the right battery for the job. At about 7500 watts (10hp) you could be using about 625 amps plus a 15% efficiency loss so call it about 700 amps. That needs your battery to be in top condition, super close to the thruster and your wiring to be mega sized. Even if the thruster battery is in top condition it will ask the house bank for help the moment its voltage drops below the voltage of the house bank, if your ACR allows it to ask the question of the house bank.
It will also ask the alternator on your motor for help if the house bank can't supply the amps. Sounds like you need a new battery.
The BlueSeas ACR I'm familiar with charges the thruster battery but does not allow the thruster battery to demand current from the charging source. You describe your model as an ACR/Combiner which implies it can automatically combine the two banks if it wants to. That's a new one on me as that's exactly what an stand alone ACR is designed not to do. Sounds like a good idea, however, as the thruster is important for safety reasons and I'd be happy to deplete my house bank rather than have my thruster stop just before I avoided a superyacht when docking.
Your own suggestion is a good one; a mate with an accurate modern DC ammeter will give you a lot of information. But if it all worked well in the past I'd budget on a new thruster battery.

 

[DavidM]

Given that the house battery is only 7 ft away from the thruster battery (which means the total distance to the thruster is maybe 10 ft), I would pull the whole mess out, wire the thruster directly to the house batteries with 2/0 cable and put a 200A fuse at the house battery end of the circuit. That would be a whole lot simpler than what you have now and should solve some of your problems. 200 amps through 20' round trip of 2/0 results in just a third of a volt drop and would cost about $120 from Genuinedealz.com

Yes thrusters are kind of like engine starters, they draw a lot of current for a short period, but with 600 Ah of house batteries, it should be fine running the thruster.

I suspect you also have a weak engine governor which is letting the rpm fall too much when loaded. I have had several boats with direct wired thrusters that didn't load the engine like you are describing.

David

 

[Ka_sea_ta]

On the ACR there should be a start isolation terminal, when activated it will disconnect the two batteries. The start isolation should be wired to the control side of the relays for the thruster... In short when the thruster is energized the relay in the ACR opens, isolating the thruster battery from the house bank.... This will prevent loading of engine alternator.

 

[slowbutsteady]

Thanks All, this is a lot of good information.

@Kiwi - I suspect if you are right about the fullriver being rated at 1150 cca then its simply a bad battery. My tests showed it at 650 cca which is almost half of its rating. This boat is new to me as of November so its entirely possible the PO wasn't as conservative with his bow thruster AND I wonder if he checked the combiner to ensure the battery was being charged properly after using it.

I do like having a separate battery for the thruster as that means I just have one more isolated power source on the boat. I might consider getting a ACR only (not combiner) to avoid the power draw and stress on my 90 amp leece neville dumb alternator (another item I need to upgrade). On the other hand, you bring up a good point about system redundancy making thruster failure less likely. Im pretty good at docking without it but its nice to have when the wind is up.

Engine is probably lugging because the alternator is only 90 amps and its a 120 horsepower single lehman. I suspect any spiking demand north of 30 amps at low RPM's would stress it. Im not sure there is a governor issue but that might be worth testing before I upgrade the alternator next year

The Fullriver Group 31 battery (1100 CCAmps) is exactly the right battery for the job. At about 7500 watts (10hp) you could be using about 625 amps plus a 15% efficiency loss so call it about 700 amps. That needs your battery to be in top condition, super close to the thruster and your wiring to be mega sized. Even if the thruster battery is in top condition it will ask the house bank for help the moment its voltage drops below the voltage of the house bank, if your ACR allows it to ask the question of the house bank.
It will also ask the alternator on your motor for help if the house bank can't supply the amps. Sounds like you need a new battery.
The BlueSeas ACR I'm familiar with charges the thruster battery but does not allow the thruster battery to demand current from the charging source. You describe your model as an ACR/Combiner which implies it can automatically combine the two banks if it wants to. That's a new one on me as that's exactly what an stand alone ACR is designed not to do. Sounds like a good idea, however, as the thruster is important for safety reasons and I'd be happy to deplete my house bank rather than have my thruster stop just before I avoided a superyacht when docking.
Your own suggestion is a good one; a mate with an accurate modern DC ammeter will give you a lot of information. But if it all worked well in the past I'd budget on a new thruster battery.

 

[Arc]

Last year I installed a dedicated battery for each ,the bow and stern thruster. They are 3’ away . I used #31 AGM . I then installed a 10 amp charger on each. This way there is no DC connection to anything else. They charge off shore power or generator while underway. I did leave the original dc wiring next to the batteries. Of for any reason something fails, I can always just connect the house back on for an emergency

 

[slowbutsteady]

Yeah, it occurred to me that I could simply use a 110 volt ac battery charger and run my inverter while underway to charge the thruster battery. I could also replace the combiner with a dc-dc echo charger (this is how I charge my start battery from my house bank).

I suspect the original installer was thinking the combiner would help in situations where the dedicated battery was failing. Sounds like it is, and probably the crux of the issue now. I'll start by getting a new battery, then if it persists I'll either wire up the combiner with a relay to disconnect when the thruster is in use OR replace it with an echo charger.

Im not so worried about the day trips, but rather more extended cruises to Canada where Im more off grid and shore power is a rare luxury. solar is the next addition but Ive got to keep my upgrades to one at a time otherwise I'll bankrupt myself in a hurry!

Last year I installed a dedicated battery for each ,the bow and stern thruster. They are 3’ away . I used #31 AGM . I then installed a 10 amp charger on each. This way there is no DC connection to anything else. They charge off shore power or generator while underway. I did leave the original dc wiring next to the batteries. Of for any reason something fails, I can always just connect the house back on for an emergency

 

[Bacchus]

slowbutsteady

Several yrs ago I wanted to eliminate the diode isolator Mainship installed on alternator charge to split charge between house and dedicated thruster banks (for bow & stern thrusters).
I did some research on best alternatives and originally looked at Promariner ProIsocharge relays. When I contacted them and raised the concern of possible hi amp "backflow" from house to thruster bank when connected and thrusters activated their response was this was not a good application and shared my concern.

I looked at the Sterling ACVR combiner relays.
When I contacted Sterling & RC at Compass Marine (a TF member, knowledgeable resource & supplied the CVSR) they confirmed that the CVSR would work fine for this application. I have had it installed for several years and been very satisfied as it performs exactly as I anticipated.

See my write-up for details on Bacchus website see Charging System Mods

I have recently moved my main engine start to the thruster bank to further isolate my house bank but haven't edited or added that upgrade to my Bacchus site. My current thruster bank is one 8D AGM but my plan is, when needed, to replace it with two AGM GP31s to serve start / thruster needs with the same Sterling CVSR providing charging while underway. The CVSR has many optional modes including manual, ignition activated & auto choices explained further in the Oper Manual.

If interested happy to share more info or answer questions.

 

[Jeff F]

10 hp is a big load at 12v. That's ~700a @12v, and you'll get significant voltage drop immediately, putting a big load on the ACR link.

My 7.5 hp thrusters both recommend two batteries in a dedicated bank.

I installed 30 amp dc-dc chargers between the house bank and thruster banks when I replaced my house bank. One big plus for me was to have different battery types in each bank with dedicated charge regulation. I use starting batteries for thrusters - no need for deep discharge capabilities under typical use, it's all about the cranking power.

 

[slowbutsteady]

Thanks - yeah, with that kind of amp draw the nuisance tripping on the 80 amp breakers between the acr and the house and on the other side at the bow thruster bank on the positive feed is totally unsurprising. Everything else about the install of the thruster looks like great work done by a reputable local yard, but Im not sure if they installed the charging system too.

a dc-dc charger is an option Im looking at - this is already how I charge my starting battery (my alternator is wired to my house bank).

I don't like putting that kind of spiking load on the ACR or my alternator when I'm at low rpms (or ever really). It just seems like a recipe for docking disaster (or fire, which is just about the worst thing that can happen). My initial solution of manually tripping both thermal breakers before operating the thruster seems like it will work in the meantime but its certainly not ideal.

10 hp is a big load at 12v. That's ~700a @12v, and you'll get significant voltage drop immediately, putting a big load on the ACR link.

My 7.5 hp thrusters both recommend two batteries in a dedicated bank.

I installed 30 amp dc-dc chargers between the house bank and thruster banks when I replaced my house bank. One big plus for me was to have different battery types in each bank with dedicated charge regulation. I use starting batteries for thrusters - no need for deep discharge capabilities under typical use, it's all about the cranking power.

 

[C lectric]

If your ACR does not have a dedicated disconnect terminal as described then the 12V negative wire can be used for the same purpose.

Lead the negative to a switch that you can access reasonably easily and the other side of the switch to a negative terminal/buss. That way when you want to use the thruster flip the sw. OFF. When you are finished flip it to ON and the ACR will do its intended job.

You could use a relay to do the switching but the ACR will likely will only wait so long before it reconnects, some seconds, which may not be good for the ACR or alternator if running hard.

 

[Delta Tango]

I'm always concerned when a battery that is rated in stored amps is used where a dedicated cranking battery is needed. The reality of these batteries is the inability of the cranking duty cycle to keep up with the thruster need. Having a large battery is useless if its not up to the task - for example, if its a 10Hp then most likely a 100KG thruster or bigger. The run current at 10.5v will be north of 500a with an inrush of + 700a.
In my opinion - if the battery is not described in CCA first then stay away from it.