Choosing a battery charger

[Scott T-Bird]

I'm making electrical system upgrades and am now considering a new A/C shore charger. Mounted on the boat is probably original equipment. It's a "Professional Mariner" model Flyback 20-3. So it is a 20 amp charger with 3 positive posts. There are 2 - 4 AWG positive cables leading directly to the house bank and auxiliary bank and 1 - 4 AWG negative cable. I'd say it is about 35' to 40' round trip run. The manual's chart stops at 30' with 6 AWG so I'd say 4 AWG is reasonable. The charger has a standard setting for FLA batts and an alternate setting for "Gel Cell". The P.O. kept the boat on a mooring and never relied on shore power. He relied on higher output alternator and solar to keep the batts topped off.

My house bank is a pair of 4D AGM's installed in 2015 and the auxiliary is Grp 31 AGM also installed in 2015. I rely on shore power charging primarily (took the solar off the bimini due to the poor condition of the panels). I didn't have any issues with the original shore charger but I want to make an upgrade. I was confused about the pair of positive cables because the boat also had an echo charger (that I have now removed) but I suppose the echo charger was for the alternator and solar output. I removed the echo charger and installed Blue Sea ACR late last summer.

So now I'm choosing a Sterling PCU 12v charger but with constraints built in by the original system. It makes most sense to install the new charger in the same location as the original because the cables and A/C wiring are already in place. But the cable size is too light for a higher capacity charger and the way Catalina has these cables bundled where accessibility is seemingly impossible makes it unlikely that I will try to replace the cables.

I'm considering limiting the charger size to 20 amp (PCU 1220) but that seems light for the house bank capacity (400 ah roughly), which I'm not likely to reduce when i replace batteries eventually. I know that AGM batts like to be charged at the highest rate feasible. At just 10%, a 40 amp charger is needed ... I was thinking 50 or 60 amp. but the cable would be too small. Since I only need one lead to a distribution buss, I thought about combining the 2 positive cables but that still leaves the negative cable too small. Thoughts? I don't have a good mounting location near the batteries, which would seem the most logical solution. It would be relatively easy to route A/C wiring from the panel. But I just don't have an appealing spot for a charger on that side of the boat.

 

[JoeWhite]

I am sometimes confused when I read a post as to what the subject is about. The confusion is the difference between AC and A/C. To me AC means alternating current and A/C means air conditioning. I welcome any comments, any experts here?

 

[Richard19068]

I'm not an expert at either AC or A/C but I believe you are right. That said, I think it is pretty clear here that when he says A/C he is talking about alternating current for his shore powered battery charger.

 

[dlochner]

Is the house bank two batteries in parallel? If not then the charger is wired to charge each battery independently.

What are your plans for upgrading the batteries? At 7 years old the AGMs are probably approaching EOL. It may be wise to install the charger you will need with the upgrade. I'd think about a 50-60 amp Sterline/ProNautic charger.

 

[Scott T-Bird]

I am sometimes confused when I read a post as to what the subject is about. The confusion is the difference between AC and A/C. To me AC means alternating current and A/C means air conditioning. I welcome any comments, any experts here?

My mistake ... obviously talking about alternating current for battery charger.

 

[Scott T-Bird]

Is the house bank two batteries in parallel? If not then the charger is wired to charge each battery independently.

What are your plans for upgrading the batteries? At 7 years old the AGMs are probably approaching EOL. It may be wise to install the charger you will need with the upgrade. I'd think about a 50-60 amp Sterline/ProNautic charger.

Yes, the batteries are probably near the end, although I've had no difficulties or issues with them yet. I would replace in kind, probably with AGM - approx 440 ah for house bank capacity. But I would not rule out 6 volt golf cart batts, I suppose with FLA. The nice thing about upgrading the charger to a Sterling PCU is that I don't have to think about what I might choose in the future. With a choice of presets and programmable, it will be adaptable.

My question is more about the logistics of installation. The cables previously went to 2 banks. House bank is parallel 4D batts. Aux bank is a single Grp 31, all AGM. I prefer to utilize the existing 4 AWG cables if I can. But the cables appear to be too small for a 50-60 amp charger because the round trip run is close to 40'. I would change the location of the charger if I had a good place for it, but I don't think that I do. I tried to explain everything in the first post, but it doesn't seem to clarify. The greatest difficulty I have is that running new cables appears to be extremely difficult under the circumstances due to access. I'm looking for ideas to make a good installation simpler.

 

[dlochner]

\The greatest difficulty I have is that running new cables appears to be extremely difficult under the circumstances due to access. I'm looking for ideas to make a good installation simpler.

Use the existing cable to pull a dacron or polypropylene line through the tight places and then pull the new cable with the line. Nylon will stretch, so don't use that. So long as there are not sharp bends it may be easier to pull the larger cable than a smaller wire because it is stiffer.

 

[Scott T-Bird]

I think I pretty much came up with my own answer. I have a locker under the v-berth on the stbd side, same side as the batts under the stbd saloon seats. The locker has stuff in there but it isn't all that useful so i will put the charger in there and move most of the stuff out. The run from the charger to the batteries will be less than 10' round trip so I can use small cables. Running new AC wires from the panel to the new location won't be difficult. I was fixated on putting a new charger in the same place as the old charger, but the new location will be more suitable.

 

[dlochner]

I think I pretty much came up with my own answer. I have a locker under the v-berth on the stbd side, same side as the batts under the stbd saloon seats. The locker has stuff in there but it isn't all that useful so i will put the charger in there and move most of the stuff out. The run from the charger to the batteries will be less than 10' round trip so I can use small cables. Running new AC wires from the panel to the new location won't be difficult. I was fixated on putting a new charger in the same place as the old charger, but the new location will be more suitable.

Since you have decided to move the charger, put it somewhere that is accessible. The charger is easy to program unless you are hanging upside down in a locker. Spring for the remote display. It is great to see what the charger is doing from the comfort of the cabin and upside down in the locker. I've found it really helpful to understand battery charging as I can watch the current and voltage change over time.

 

[Scott T-Bird]

So now I have the position sorted ... I can pretty much choose any size charger I want. Are you folks with at least 400 ah house bank capacity using a charger greater than 50 or 60 amp capacity? 20% would be at least 80 amp charger.

 

[Scott T-Bird]

Since you have decided to move the charger, put it somewhere that is accessible. The charger is easy to program unless you are hanging upside down in a locker. Spring for the remote display. It is great to see what the charger is doing from the comfort of the cabin and upside down in the locker. I've found it really helpful to understand battery charging as I can watch the current and voltage change over time.

Yes, I'll install the remote. I'm getting more sensitive to price as the capacity of the charger increases. I'm a little hesitant to spend so much money on a charger with greater than 50 or 60 amp capacity. Currently, I don't have a great need for rapid charging, but that may change soon as my retirement plans allow for more time on the water with more places to go.

 

[dlochner]

So now I have the position sorted ... I can pretty much choose any size charger I want. Are you folks with at least 400 ah house bank capacity using a charger greater than 50 or 60 amp capacity? 20% would be at least 80 amp charger.

When I had a 460 ah bank I went with a 50 amp charger using the old rule of thumb of 10% of ah capacity of the bank. If I was to do that again, I would go with 60 amp which I believe is/was the largest of the Sterling/Pronautic chargers. At the time, about 7 years ago, there was a significant price difference between the 50 and 60 amp chargers.

 

[heritage]

Your 4 awg cables are certainly robust enough to safely charge the batteries with up to 6o amps. The problem is that the voltage drop will be close to 10% which would lead to under charging the batteries. If the charger has a remote voltage sensor that can be mounted on the battery, then it could compensate for the voltage losses in the cable.

 

[Scott T-Bird]

Your 4 awg cables are certainly robust enough to safely charge the batteries with up to 6o amps. The problem is that the voltage drop will be close to 10% which would lead to under charging the batteries. If the charger has a remote voltage sensor that can be mounted on the battery, then it could compensate for the voltage losses in the cable.

Yes, I was concerned about voltage drop so I am looking at the charts with 3% drop. But now, by deciding on a new location it is a moot point. Besides that, I wondered about where the voltage is sensed. I'm assuming the charger doesn't compensate for voltage drop.

 

[jssailem]

Here is the Blue Sea link to their calculator.

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

I agree that the present 4awg cables are too small for a 3% or less voltage drop over a 40ft trip with 60 amp charger.

You will need 1awg cable. Check that your measurement of distance is accurate.

 

[Kingjim91]

I am sometimes confused when I read a post as to what the subject is about. The confusion is the difference between AC and A/C. To me AC means alternating current and A/C means air conditioning. I welcome any comments, any experts here?

It’s clear from the context that he means alternating current.

 

[Ward H]

Scott, don't cut costs now. You've done the boat right so far. Go with the 60.
Thinking back to when we brought the boat down from Buzzards Bay, 1 night in a slip out of what, 5 or 6 nights. You'll need the larger charger to bring that 400 Ahr bank back up on trips like that. You have more than just day sailing in your future.

 

[Mark Maulden]

How is the air flow with your new charger location?

 

[Scott T-Bird]

How is the air flow with your new charger location?

Under the v-berth is pretty much open underneath on all sides and to the bow. I think the space is good because it isn't tight, but there really isn't any ventilation built into it when the cabinet doors are closed. There may be some opening to the underside of the saloon seats where the batteries are located. I think it would be a relatively cool area no matter what ... in the bow away from galley and engine, near a water tank and at waterline. What would be the concern?

 

[Mark Maulden]

Under the v-berth is pretty much open underneath on all sides and to the bow. I think the space is good because it isn't tight, but there really isn't any ventilation built into it when the cabinet doors are closed. There may be some opening to the underside of the saloon seats where the batteries are located. I think it would be a relatively cool area no matter what ... in the bow away from galley and engine, near a water tank and at waterline. What would be the concern?

the charger needs to be installed in a ventilated area. I believe there are fans to move air through the chassis…