Adding Bow Thruster and Windlass . . . What to Do with Batteries

[RaySea Lady]

Originally Posted by CharlieJ

Have you considered using 24 volt equipment for these heavy, remote loads? Reduces the cable size significantly.

SidePower makes a 24 volt bow thruster with a very slick contactor box that places one battery in series with the rest of the bank when 24 volts is required. The remainder of the time that battery is in parallel with the rest of the house bank.

Just a thought.

Charlie

I have this on mine and am in the process of changing it. My thrusters are sidepower model 155, 10.7 HP 24V units.

my house bank is four 8D batteries with an additional 8D for the bow thruster and that slick contactor box and it all works very well at 24V.

The problem comes in the fact that it seriously drains the batteries relatively quickly. House batteries are deep cycle and not designed for the quick draw that a thruster demands, usually a cranking battery type of application.

I have two refrigerators on board that will work fine off of the inverter for up 8 to 10 hours of cruising as long as I don't use the thruster. If I use it, usually for not much more than 10 seconds, I am down to about 2 to 3 hours before having to start the genny.

So, I will be installing two cranking 12V batteries to make the 24V for the bow thruster and isolate it completely from the house bank with its own 24V trickle charger (identical setup at stern and it works very well). Leaving the five 8D batteries for inverter/house duty, 24V charger and windlass only.

[CharlieJ]

Ray-Sorry to hear about your dissatisfaction with the SidePower series/parallel contactor box but I think you are solving the wrong problem by removing this system.

First of all, the vast majority of 8D batteries are not deep cycle batteries. They are, in fact, heavy duty starting batteries with a cold cranking amp (CCA) rating as well as a reserve capacity (RC) rating. There are some notable exceptions, Rolls/Surrette being one of them.

I suspect that the reduced capacity you are experiencing after operating your thruster is caused by failing or compromised batteries. A capacity test with a carbon pile tester or a Midtronics conductance tester would determine if the batteries are healthy.

Are the batteries flooded, AGM or gel?

Since you are already changing out the system, this all may be moot but it would be educational to understand the troubleshooting steps and the reasoning that led you to this decision.

Charlie

[RaySea Lady]

Hi Charlie,

The batteries are wet and had been replaced in july 08 and again in march 10. I am told by the electrician that this is caused by the batteries being drained below the 50% threshold which is primarily done with the use of the thruster.

With my batteries fully charged and reading 13.3v, when I leave the dock and use the thruster for 5 to 10 seconds, my voltage drops to 10.2V, after which voltage returns to approximately 11.8v.

Batteries have been load tested, levels are checked and filled every month. My electrician feels that taking the thruster off the house batteries will solve the problem. And it has been proven out by running on house only at the dock for 12 hours and batteries only down to 11.7v WITHOUT using the thruster. The refrigerators draw 5.4 amps and 7.5 amps at 120v when they are on, and, they are very well insulated.

Originally Posted by CharlieJ

Ray-Sorry to hear about your dissatisfaction with the SidePower series/parallel contactor box but I think you are solving the wrong problem by removing this system.

First of all, the vast majority of 8D batteries are not deep cycle batteries. They are, in fact, heavy duty starting batteries with a cold cranking amp (CCA) rating as well as a reserve capacity (RC) rating. There are some notable exceptions, Rolls/Surrette being one of them.

I suspect that the reduced capacity you are experiencing after operating your thruster is caused by failing or compromised batteries. A capacity test with a carbon pile tester or a Midtronics conductance tester would determine if the batteries are healthy.

Are the batteries flooded, AGM or gel?

Since you are already changing out the system, this all may be moot but it would be educational to understand the troubleshooting steps and the reasoning that led you to this decision.

Charlie

[CharlieJ]

Ray-
Your original post stated "thrusters" so I am assuming that you have a stern thruster also. The following analysis is only for a single thruster.

Discharging your batteries to 11.7 VDC operating the refrigerators is badly degrading your batteries as you are going well below the 50% SOC (state of charge) that is the industry standard. With this kind of usage, you truly need to install a battery monitoring system that will provide you with the number of amp-hrs that you have remaining in your house bank.

I understand that changing out your system is a done deal so this is more academic than practical.

Doing the math and not taking into account any inefficiencies:

LOAD
10.7 hp x 746 watt/hp = 8 kW (rounding up)
8 kW x (10 seconds/ 3600 seconds/hour) = .022 kW-hr = 22 W-hr

8 kW/24 volts = 333 amps

SUPPLY
A nominal 8D battery will provide on the order of 1500 - 1900 MCA (Marine Cranking Amps) and has a 20 hr rating on the order of 220 amp-hrs.

220 amp-hrs x 12 volts = 2640 W-hrs

SUMMARY
Your thruster required an instantaneous supply of 333 amps or 22 W-hrs from a source that should provide a nominal instantaneous 1500 amps with a capacity of 2640 W-hrs. A load that the bank should have easily been able to meet.

I do not doubt the empirical results regarding your refrigeration operation at the dock. The calculations simply show me that the true root cause of the problem has not been identified.

Charlie

[motion30]

Thw thruster on my boat draws 360amps at 12 v and does not seem to flatten the 2 8ds to any large amount Mayb I use it for a shorter time then you

[RaySea Lady]

Originally Posted by CharlieJ

Ray-
Your original post stated "thrusters" so I am assuming that you have a stern thruster also. The following analysis is only for a single thruster.

Charlie

Thanks Charlie,

The stern thruster has its own batteries completely independent of the house batteries.

I have no clue what else it could be if this is not it. My electrician tells me my batteries are good, my inverter charger is perfect and this draw is the main culprit.

Yes, it is a plan to put two independent batteries for the bow thruster and take it off the house batteries but it is not done yet.

The other thing that we are doing and this is in the process of being done now is a sterling regulator that will allow my 130 amp alternator on my drive engine to charge my house batteries while cruising.

there is also a battery and alternator monitoring remote that will be installed at the helm.

[Unicorn Dreams]

I would put 2 t-105's as close as you can, it's a lot shorter cable run that, which means more power to the equipment, which means less heating of the cable.
Remember hat the cables to charge the batteries can be sized with about 12 gauge which is easier to route thru the boat. As these will be charging only, there won't be a heavy load on the wire, plus the cost will equal out by not having to run heavy gauge cables all the way to the bow...

[RaySea Lady]

Originally Posted by CharlieJ

Ray-

I do not doubt the empirical results regarding your refrigeration operation at the dock. The calculations simply show me that the true root cause of the problem has not been identified.

Charlie

Hi Charlie,

could you elaborate as to what you think it could be???

[FatBear]

If you are worried about the weight forward, why not install hydraulic equipment? The pump is on the engine, the reservoir nearby and you run hydraulic lines rather than gigantic copper cables to the lighter-than-an-electric hydraulic motor on the thruster and/or windlass. A fault is extremely unlikely if you have the lines professionally built. Worst case you will get oil in the bilges while worst case with electric you will burn your boat to the waterline (at which point it sinks and puts out the fire - not the best ending.)

[FatBear]

I should have added that while the hydraulics might (or might not) cost you more than electric, you won't have a battery bank to replace every few years.

[CharlieJ]

Ray-
Long distance troubleshooting is sketchy at best but your symptoms point to an under performing battery bank. Why six month old batteries are under performing is the main question.

Here are some questions/points that might lead to a solution:

1. How were the batteries tested?
2. What are the quantitative results of the battery testing?
3. Your refrigerators are drawing 12.9 amps @ 120 VAC which roughly translates to 130 amps @ 12 VDC. With a 70% duty cycle you will consume .7 x 130 amps = 91 amp-hrs for every hour of operation. With 5 8Ds available for house loads you have 5 x 220 amp-hrs = 1100 amp-hrs available of which 550 amp-hrs is usable (remember the 50% Rule!). So your batteries will only support your refrigeration for a nominal 6 hours.
4. You mention a new regulator for your 130 amp alternator. What was the alternator arrangement before this addition?
5. Is the bow thruster working correctly; e.g., no binding, current to operate within specs, etc.
6. When operating the bow thruster, what is the voltage reading at the bow thruster prior to, during and after operating the thruster?
7. How big is the stern thruster?
8. Is the thruster wiring sized to give <3% voltage drop?
9. Have you ever left the batteries in a discharged state for any period of time?
10. How long does it take to charge the batteries until the battery charge goes to float?
11. What is the make and model of your battery charger?
12. Has the electrician taken specific gravity readings of your house bank? If so, what are the readings?
13. Have you attempted to recover the bank by equalizing it?
14. How many engine hours have you accrued since installing the new house batteries in March, 2010?

Hope this helps.
Charlie

[RaySea Lady]

Thanks Charlie, This will definitely help.

The current alternator setup is that each alternator charges the starting battery only for each engine.

The way the sterling regulator works is that it applies charge current for up to 2 minutes to the starting battery and 15 minutes to the house battery depending on need. This will be installed on the port engine alternator only which is a 130 amp alternator. This will allow my house batteries to be charged while cruising without running the generator to operate the house charger, and should extend my run time. With this regulator installed, I expect to have to check my battery levels every two weeks or so because of this constant high level charging.

I will be equalizing the batteries within the next week or two, I usually do that just before putting it in the warehouse for the winter.

The house charger/inverter is a Xantrex 3000W with a 140 amp charger and two echo or trickle charging lines. One echo charger line is sent to the genny battery and the other goes to the stern for the dinghy battery.

Both thrusters are identical Side-power 155 for 10.7hp each. The stern has its own dedicated batteries and charger.

I will have the batteries checked again and jot down all the readings. Currently, once the batteries have been on charge overnight, my voltmeter shows 13.4V while on float. I have never checked how much time it takes to go to float.

Assuming the batteries are good, like my electrician told me, removing the bow thruster from the house batteries and adding the sterling regulator should allow me to run my refrigerators on the inverter while cruising without damaging the batteries and without running the genset.

thanks again.