New thruster/windlass bank - Ah & CCA specs?

My existing thruster/windlass bank is 4 x 75Ah batteries, 2 x C&D Technologies DCS 75 HIT and 2 x Interstate DCM 0075. The last few times I have anchored the windlass has struggled to get the anchor up onto the bow. By the time it is near the surface the bank's capacity is pretty much exhausted. They all charge up again fine, resting voltages 12.8 or higher.

I have a conductance tester which would seem to be a reasonable way to test the batteries without doing a full load test. The C&D's test out really well - internal resistance of 3 m-ohm, 100% health. The Interstate's have internal resistance of 9-12 m-ohm, and a health reading of 31-39% depending on whether rest charge was 12.8 or 13.1 V. So they are basically shot. The interstate's are 4.5 years old, whereas the C&D's are older. The PO used the C&D with a long cable run for the windlass, but seldom anchored. I now have the batteries in the bow near the thruster. My cable length is about 12' in total (negative plus positive), and the cable is all 2/0 between batteries and thruster. The windlass cable length is probably 8' longer, and is a little smaller in size. My thruster has a 500A fuse and the windlass a 200A fuse.

I am trying to work out which way to go for a new bank. The Interstate's ought to have lasted longer IMHO, so what killed them? Is the current draw too high for too long, or is the total Ah insufficient? I would typically have 75-100' of chain out, but occasionally it is 200-250'. I think the windlass load is the greatest challenge for the bank as the high thruster amps are for short bursts only.

I am thinking that as well as a higher Ah bank I should also go for high max current draw batteries, or a high 'constant current discharge rating' spec in particular. This would favour using 6V batteries. But how much Ah would be enough? I could use a pair of Fullriver DC250-6 in series, or 4 x DC 224-6A in series-parallel. Any thoughts?

Can't you run them off the house rather than dedicated?

menzies said:

Can't you run them off the house rather than dedicated?

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The house bank is near the stern. So it would add about 90' total cable length, which I would need to run and I think there would be significant voltage drop. But it is an option for sure.

Insequent said:

The house bank is near the stern. So it would add about 90' total cable length, which I would need to run and I think there would be significant voltage drop. But it is an option for sure.

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I would think not, if you get your cable size right.

My thruster and windlass are run from the house, which are at the aft end of the ER, and I don't have any power issues (however I have 12 golf cart batteries as house).

Also remember that when you are using either of those the engine is running, with the batteries charging off the alternators.

Maybe look at it - it would sure make your life easier.

My house is 6 x Odyssey PC 1800FT, for 1284 AH. I have 2 more of the same batteries as engine starts. I could take those and add them to the house to increase its capacity, and get one or two new start batteries of a different brand. You are right, with the engines running, and 2 x 200A alternators, the net draw on the house would not be too severe even if the bank is somewhat depleted.

Do you know your cable size, and thruster/windlass fuse sizes?

Insequent said:

My house is 6 x Odyssey PC 1800FT, for 1284 AH. I have 2 more of the same batteries as engine starts. I could take those and add them to the house to increase its capacity, and get one or two new start batteries of a different brand. You are right, with the engines running, and 2 x 200A alternators, the net draw on the house would not be too severe even if the bank is somewhat depleted.

Do you know your cable size, and thruster/windlass fuse sizes?

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The cables are 2/0. Not sure about the fuses but will look next time on boat.

I also had disconnect switches installed for both the windlass and the thruster on one side of the forward guest cabin bunk. I had a thruster thermal protection failure and a runaway thruster last Christmas during the lighted boat parade which wasn't fun!

Thanks. I am guessing that you have 24V units for that cable size to be OK?

Your windlass and thruster manual should have information as to the recommended Ah for them as well as recommended cable sizes based on the length of the runs.

My bank for the thrusters and windlass is in the stern with 4/0 cables.

For batteries, if you want AGM I think the cheapest Ah/$ are the batteries I am putting in to replace my house bank. Two of these 6v AGM would give you 390 Ah.
https://www.metroplexbattery.com/co...-battery-part-no-usagml16?variant=14920434310

dhays said:

Your windlass and thruster manual should have information as to the recommended Ah for them as well as recommended cable sizes based on the length of the runs.

My bank for the thrusters and windlass is in the stern with 4/0 cables.

For batteries, if you want AGM I think the cheapest Ah/$ are the batteries I am putting in to replace my house bank. Two of these 6v AGM would give you 390 Ah.
https://www.metroplexbattery.com/co...-battery-part-no-usagml16?variant=14920434310

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Dave, do you use the house, or dedicated?

Still messing around with that. For now, I am putting these batteries in to replace my house bank and will leave the thruster bank (2 x Lifeline 8D AGMs) as a separate bank for the thrusters/crane/windlass.

I may combine them in the future if I can figure out how to avoid certain pitfalls.

For the OP, having the batteries in the bow seems great. Just find out what capacity you really need based on your equipment requirements instead of a WAG.

How are those batteries being charged?

My thinking, what percentage of boat time are you using thrusters and windlass, and even davit?

Why dedicate batteries to those causes?

Dave, what pitfalls do you foresee, other than depleted batteries not allowing you to run those items (again these seem to be things that you would use when the engine is running)?

menzies said:

My thinking, what percentage of boat time are you using thrusters and windlass, and even davit?

Why dedicate batteries to those causes?

Dave, what pitfalls do you foresee, other than depleted batteries not allowing you to run those items (again these seem to be things that you would use when the engine is running)?

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There are several issues.

-To combine the two banks properly I would need to use two rather long parallel links between the batteries. This would certainly be possible but would not be ideal

- The thruster bank are expensive batteries in good shape but are different than the new house batteries I am adding. This would be OK but it makes a lot of purists really uncomfortable to combine different age, size, and manufacturer of batteries.

- I would need to come up with another way to measure SOC for the batteries. The SOC meter I have maxes out at 1000 Ah. The combined bank would be 1190 Ah. I could install a Balmar SmartGuage but that would require a lot of very long wiring runs as well as cutting new holes in my Pilothouse dash. I'm lazy so that doesn't sound fun.

- I have Vetus 95kg thrusters. They recommend a battery bank of 165-286Ah. They specifically warn against using a battery bank that is significantly larger than recommended because that reduces the maximum operating time. They also warn that if the Ah capacity of the bank is 5x or greater than the recommended size that the increase in thrust can actually damage the connection between shaft and motor or shaft and propeller. 1180 is about 5x the recommended Ah capacity range they recommend.

- Can my alternator handle sending that much current to that large a bank with a controller?

Those are just some of my thoughts.

Brian,no thruster owner here, but do you not get charge flowing to those dedicated batts from the alternators while the windlass or thrusters are operating? If not, could that be the current and maybe underlying problem?

dhays said:

For the OP, having the batteries in the bow seems great. Just find out what capacity you really need based on your equipment requirements instead of a WAG.

How are those batteries being charged?

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My Windlass is Ideal Windlass - can't find info on battery capacity, just cable size.

My thruster is Lewmar, and once again there is cable size info but nothing else apart from 'CCA should be at least equal to thruster current'. It is rated at 97kg, basically same size rating as yours. So the Vetus recommendation for bank size is very useful for me, thanks. The Lewmar manual indicates I should use 2 x 4/0 cables were I to run it from the house bank in the stern! So as much as I would like to run the windlass and thruster from the house bank I don't think its all that practical.

Charging of the bank in the bow could be part of my problem. It is via a Victron Phoenix 12/50 when on shore power, and schematics I have show no other charge source. The bank does charge when the engines are running, and I need to determine whether this is via the Phoenix or some other way. But in any case, if I only run for a couple of hours after hauling anchor, and then re-anchor, the bow bank will likely not be fully charged. I anchored out a lot during a 3 month period last year, so the bank could have spent a long time under-charged.

I ought to add an SOC meter for the bow bank. I think there is a way of connecting a second bank into the Victron Blue Panel I have, I just can't remember what additional piece of kit is required. I could also add another Blues Seas ACR into the alternator charging circuit and run 2/0 cable to the bow for greater charging rate for the bow bank. That would give extra boost for windlass use when engines are running. A trip down to the Gold Coast City Marina and some brainstorming with Jim from Odyssey Marine Electrics is looking to be a good idea before any decisions. But some good suggestions from menzies and dhays is helping me think though all this.

I really wish I was still in the USA and able to source reasonably priced batteries, as they are rather expensively priced here in Australia.

BruceK said:

Brian,no thruster owner here, but do you not get charge flowing to those dedicated batts from the alternators while the windlass or thrusters are operating? If not, could that be the current and maybe underlying problem?

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There will be some as I described above, but perhaps not as much as I could get if I do some mods. I think you are right - I need to get more benefit from the alternators. Then the size bank I had would be about right.

Brian

We have the windlass powered from the house bank. When hoisting anchor we run the genset which then charges the house bank via the inverter charger. We've never had an issue with windlass running out of hoisting KW.

We too have a Lewmar thruster. Separate battery bank, q

Good luck Brian, wish I could be more help. My suggestion is to figure out how the thruster/windlass batteries are being charged while underway and see if that is adequate.

My NP43 has a 500 Ah bank that runs thrusters, crane and windlass. Despite the very long run from the stern to bow, I've never had any issues with not having enough power. Even when anchoring a lot last summer, using the crane, and the thrusters (holding correct orientation while setting a stern shore tie after setting bow anchor). That thruster/windlass bank is charged via a Duo Charger which has a max charge rate of 30 amps. This only charges when the house bank is seeing charge voltage, either plugged into shore power or with the alternator. The Duo Charge will actually cut out if the charge demand is greater than 30amps. That has yet to happen.

My point is that it doesn't take a lot of charge current to keep the thruster bank charged up. If you are running for a couple hours a day between anchoring that should be plenty of time to get the bank charged up. An ACR would be fine if your house and thruster banks are a similar type of battery.

I like the idea of getting a pro to help you out.

Ok, so a 30 A Duo charger does the job for you. I would not ave thought it would be enough!

Just back from the boat, and the Phoenix 50A charger is the only charging mechanism for the bow bank, but in a somewhat cumbersome manner when not on shore power. In that case the Phoenix AC input is from the Victron Inverter, coupled to the House Bank. When the bow bank is being depleted (thruster or windlass in use) the engines are running and with 2 x 200A alternators the house bank is not impacted very much. So, although not very elegant, it all works.

Back to my original issue - why did the Interstate Deep Cycle batteries die after just 4 years? Could still be that they don't like the extended period of relatively high current draw while raising anchor. In that case going to a bank based on 6V batteries would make a difference. For the brand that I've looked at the 6V ones have a constant current discharge rating double that of the 12V ones, and the 6V rating is pretty close to what the windlass is likely to be drawing.

Believe it or not I would select a pair of wet lead acid Start batts fwd. for the windlass.

The starts will create the highest voltage under short high loads , and even with a 10% voltage drop under heavy load should be able to have 13V to the motor.

14.4 V from engine 1.4V drop 13 still left for long windlass pull.

Discharging at heavy loads the Starts will protect them selves by covering the plates with gas , so a short wait could restore them to near full charged , a cpuple of times.

You could also "steal" them to use as main engine starts if there is an electrical problem,

Insequent said:

My existing thruster/windlass bank is 4 x 75Ah batteries,

I am thinking that as well as a higher Ah bank I should also go for high max current draw batteries, or a high 'constant current discharge rating' spec in particular.

Click to expand...

Don't know if you can get them there... but if you have space, 3x Odyssey Group 31 12V PC-2150 AGMs would give you the same Ah and huge cranking amps. Four would be even huger. AGMs useful to minimize off-gassing in forward locations, and there's not much in the way of service... aside from routine charging.

I'm just now replacing a bank of 3x in a combined main engine start/half of the house bank. After 12 years; not inexpensive, but we got our money's worth.

-Chris

Brian

Our Maxwell draws about 1200 watts. These watts according to house bank BMK are replaced by inverter charger in bulk mode with genset running. Do you still have genset?

As you mentioned, a BMK on windlass bank may prove helpful. Without, your information as to windlass battery health and amps in-out is a bit of a guess. BTW, my thruster batteries, AGMs, did not make it past 5 years.

I am amazed no one's pointed out, you should always match the batteries in a bank, same age and model, buy them all at once.

Otherwise, the bank will perform as per the lowest capacity members.

Peukert's law says combine all banks into one big one if practical for maximum capacity and also longest life.

This can be done and still isolate sub-banks for more critical purposes (cranking) through LVD cutoffs.

But if not, IMO a bank monitor is important, as is periodic load testing, starting with a benchmark when installed new.

FF said:

Believe it or not I would select a pair of wet lead acid Start batts fwd. for the windlass.

The starts will create the highest voltage under short high loads , and even with a 10% voltage drop under heavy load should be able to have 13V to the motor.

14.4 V from engine 1.4V drop 13 still left for long windlass pull.

Discharging at heavy loads the Starts will protect them selves by covering the plates with gas , so a short wait could restore them to near full charged , a cpuple of times.

You could also "steal" them to use as main engine starts if there is an electrical problem,

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Access to the bow bank is only fair, and checking water level would be a PITA. I'm not willing to install wet batteries, I'lll take the price hit for AGM.

ranger42c said:

Don't know if you can get them there... but if you have space, 3x Odyssey Group 31 12V PC-2150 AGMs would give you the same Ah and huge cranking amps. Four would be even huger. AGMs useful to minimize off-gassing in forward locations, and there's not much in the way of service... aside from routine charging.

I'm just now replacing a bank of 3x in a combined main engine start/half of the house bank. After 12 years; not inexpensive, but we got our money's worth.

-Chris

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Some Odyssey's are available, I'll need to check which ones, and the price. All batteries here are expensive and then Odyssey is a premium on top. But it might well be the best option. I really like the PC1800FT's I have for the house, but know they are nor available. A dual purpose battery or a 6V bank seems to be the best way to go.

sunchaser said:

Brian

Our Maxwell draws about 1200 watts. These watts according to house bank BMK are replaced by inverter charger in bulk mode with genset running. Do you still have genset?

As you mentioned, a BMK on windlass bank may prove helpful. Without, your information as to windlass battery health and amps in-out is a bit of a guess. BTW, my thruster batteries, AGMs, did not make it past 5 years.

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I removed the gensets, just have a little Honda for when the solar is a bit weak on cloudy days.

If 5 years is normal for thruster batteries, ok, I'll live with that. In 5 years time my house bank will need replacing as well. By then LFP's might be cost effective!

john61ct said:

I am amazed no one's pointed out, you should always match the batteries in a bank, same age and model, buy them all at once.

Otherwise, the bank will perform as per the lowest capacity members.

Peukert's law says combine all banks into one big one if practical for maximum capacity and also longest life.

This can be done and still isolate sub-banks for more critical purposes (cranking) through LVD cutoffs.

But if not, IMO a bank monitor is important, as is periodic load testing, starting with a benchmark when installed new.

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Yes, I am now aware of the points you make. But 5 years ago, when I installed the thruster just after buying the boat I was not aware of all of the problems. I did at least match types (AGM) and Ah capacity - a case of knowing just enough to be dangerous?

Insequent said:

I removed the gensets, just have a little Honda for when the solar is a bit weak on cloudy days.

If 5 years is normal for thruster batteries, ok, I'll live with that. In 5 years time my house bank will need replacing as well. By then LFP's might be cost effective!

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Top-notch batteries (expensive) very well cared for (not easy) can go double even triple that.

Cheapos treated badly can die in a season.

I advise going cheap, learning to treat them well and if they last say six - eight reward yourself with quality.

Part of that learning is such familiarity you know exactly how they are deteriorating, so no surprises.

john61ct said:

But if not, IMO a bank monitor is important, as is periodic load testing, starting with a benchmark when installed new.

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John, any suggestions for a practical way to do load testing for mere mortals? I think load testing is a great idea, I'm just not sure how and if I would ever have the amount of time required to do it right.

Brian, my venerable Lehmans run at 1000rpm while retrieving using a 1200 watt (updated) Muir, the charge level drops back quickly post retrieve suggesting the alternators keep the Muir well fed through the procedure. The early death of 2 batts could be the combination of heavy loads and less than optimal recharge, especially as the thrusters use the same source.
With sub optimal access, AGMs,though pricey,are the answer, as you suggest. Maybe with better replenishment,including under load, you may not need as much battery as you currently have.

dhays said:

John, any suggestions for a practical way to do load testing for mere mortals? I think load testing is a great idea, I'm just not sure how and if I would ever have the amount of time required to do it right.

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From Maine Sail's
http://www.pbase.com/mainecruising/programming_a_battery_monitor

#1 Fully charge battery then allow it to rest, disconnected, for 24 hours

#2 Make certain battery temperature is between 75F & 80F

#3 Apply a DC load that = Ah Capacity ÷ 20 (small light bulbs and/or resistors can work)

#4 Connect an accurate digital volt meter to the positive and negative battery terminals

#5 Start DC load and a stop watch at the same time

#6 As battery voltage drops, during discharge, adjust the DC load to maintain as close to the C÷20 rate as is humanly possible

#7 Immediately stop the discharge test when battery terminal voltage hits 10.499V

#8 Note the hours and minutes of run time on the stop watch and figure your percentage of 20 hours that it ran. This is your batteries Ah capacity or state of health as a percentage. For example if a 100Ah battery ran for 16 hours it is at 80% of its original rated capacity. Flooded lead acid batteries are considered “end of life” when they can no longer deliver 80% or more of their rating.

#9 Recharge the battery immediately at the 20 hour rate. Follow this up with equalization level voltage and measure specific gravity until all cells match. (not for non-Lifeline AGM or GEL). A long slow recharge can have a slight reforming effect on flooded batteries and can actually recover some lost capacity.

"But RC isn't 10.5V bad for my batteries?"

A once yearly discharge test, done correctly, is arguably less damaging than taking your battery to 50% SOC and leaving it in that range for a day or two or the continual PSOC cycling the average boater thinks nothing of. Regular PSOC cycling is more damaging than a once or twice yearly Ah capacity test done correctly. A capacity test, done correctly, simply counts as another deep cycle.

WARNING: The only time your batteries should regularly be taken below 12.1V is during a capacity test. For regular house use, at your average house loads, your deepest loaded voltage should ideally not dip below 12.1V or better yet 12.2V. Unless you are running short duration high load device such as an inverter, windlass, electric winches, thruster, water maker etc. don't let your bank voltage dip below 12.1V. For certain situations, such as an off-shore passage or open ocean racing discharging to 70-80% DOD is acceptable provided the batteries receive a proper charger as soon as you get to the destination. Regularly discharging below 50% SOC on a regular basis in a PSOC environment drastically shortens battery life when compared to 50%.

Firefly & some GEL batteries would be an exception for regularly discharging below 50% SOC.

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How do I conduct an approximate 20 hour capacity test?

#1 Allow battery to attain a steady 75-80F temperature

#2 Fully charge battery and equalize if it's capable

#3 Let the battery rest for 24 hours

#4 Apply a DC load for 2 hours that = Ah Capacity ÷ 20 (small light bulbs and/or resistors can work)

#5 Allow the battery to rest for at least 10 hours at 75-80F (24 hours is significantly more accurate)

#6 Check specific gravity or resting open circuit voltage and compare to manufacturers SOC tables

#7 Use basic math to determine the approximate Ah capacity. For example, a 100Ah rated battery has been discharged at 5A for 2 hours. This means so you removed 10Ah's of capacity. If the battery was in perfect health specific gravity readings or open circuit voltage readings should show the battery at 90% SOC. If SG and OCV only show the battery at 60% SOC then the battery has lost approx 30% of it's Ah capacity.

This is an approximation only and NOT an accurate Ah capacity test. Variances can be anywhere from 10-18% off an actual 20 hour capacity test depending upon your particular battery.

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Also:

http://www.cruisersforum.com/forums/showthread.php?p=2386436

https://forums.sailboatowners.com/index.php?threads/specific-gravity-vs-actual-ah-capacity.185414/