Battery Charger Advice

Commotion

Member II
Here I go, telling on myself. I asked for advice on replacing my Xantrex Freedom HF1800 combination charger and inverter on Facebook's Boat Electrical Systems and got an overwhelmingly consistent response. Basically said Xantrex has really gone down hill on lower priced chargers and to avoid them. Most everyone recommended Master Volt and Victron. I thought I would check them both out... EXPENSIVE! I have three Group 31 12V Firefly AGM's (also EXPENSIVE) that are less than two years old and I have to replace my group 31 Lifeline AGM start battery. I still have (and love) my Atomic 4 (Inexpensive) and it does not take much juice to get that running. I am going to install a small AGM start battery. So, I have been talking to acdcmarineinc.com in Torrance and they seem VERY helpful. I just bought a Cotek CX1235 35 amp dual bank charger. Not that expensive... less than $250. So, I am going to install it this weekend. It seems like a feature rich charger. Ramsey, the owner of acdcmarineinc spent a lot of time going over my system. He said the Cotek chargers are built by the guys that founded Mastervolt before it was sold. Gave me a great tour of his shop. I think they have every gauge, switch and boat electrical component a boater might need. I am not going back to combination units... that was advised against when I installed it 9 years ago... I didn't listen then either. :esad: The problem isn't that is lasted 9 years, though light use, it is that when the inverter goes, the charger has to go with it. The lower cost Xantrex units are not repairable and just go into the trash.
 

Teranodon

Member III
Here’s something that bugs me about battery chargers. The newest ones always claim that they are “intelligent”, and adapted to all different kinds of batteries and states of charge. However, in real life, most charging occurs while motoring, when all of the batteries are simply connected to 14 volts or so, regardless of anything. I think that is the situation on my boat, and all three of my West Marine 110 Ah batteries seem to support it well. I have DVMs on them, and monitor them pretty closely. I never let them go below 12.4V.

I’ve been using the charger that the boat came with 6 years ago. Not sure that I would spend money on anything fancy if I had to replace it.
 

footrope

Contributing Partner
Blogs Author
Some of us run 12v refrigeration 24/7/365.
Yes, we run the fridge all summer after our first cruise. So, our good but very old three stage AC charger is floating our batteries when we have shore power available.

I installed a three stage alternator charge controller a couple years ago (2-stage controller failed) and it does a better job of "topping off" the batteries, especially if we motor at least 4 hours. The longer the batteries can be floated at their proper float voltage the longer the charge lasts once we're on the hook. Since we have shore power available at my slip, we take advantage of the properly set three stage AC charger to maintain the batteries over the off-season. If you have expensive AGM batteries, it might cost more to maintain them properly. However, flooded batteries also have needs that a smart charger can meet, to prevent overcharging and boiling off the electrolyte.

For those times when I don't need or want to run the motor so long, I am installing solar with three-stage controllers.
 

Tin Kicker

Sustaining Member
Moderator
As I posted in a different thread about chargers, just make sure to fuse the battery end of the cable(s). There've been fires caused by a simple short in the transformer inside the box, which puts the full battery discharge into the charge cable, which is typically no heavier than 12 AWG. Even if there is no fire, the glowing red hot cable will destroy any other wires it touches and can ignite flammable fumes, paper, foam cushions, etc.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Bob has a good point. That was only one reason I added fused protection for all of the misc. wires going to the battery terminal.
The only high amperage one is the charger wire, I should note. The others are for voltage sensing devices.
This little terminal is one of Blue Seas' coolest inventions, IMHO.
 

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Tin Kicker

Sustaining Member
Moderator
I get comments like "Battery chargers have internal fuses," and "charger cables are meant to handle current," etc.

The image below is one of a series of slides I use to teach investigations with. I like to keep updating the course with current material and even though the class is for aviation systems investigations, this part of the class is based in a fire that happened earlier this year aboard another brand of sailboat (iirc 30 ft). Great example for my class since it has just the basics. The owner had his family aboard for vacation and fortunately, the fire didn't find any fuel sources to spread to so after the thick smoke cleared he was "just" left with no electrics, a very expensive repair bill, interrupted vacation, and heck of a scare for him and the family.

This slide from the middle of the series shows how the system is similar to ours and how damage from the internal failure of the transformer (upper center photo) put the full battery loads into wires (a few are in the bottom center photo) never meant to handle that much current. At this point battery 1 is involved and after the coil heated for long enough the current from battery 2 also shorted to ground. As Loren commented, the damage would have been prevented by simply putting a small fuse at each of the battery switch poles labeled 1a and 2a (right photo). Size the fuses to the charge being applied and thickness of the wires. (Ref: https://www.bluesea.com/resources/96)



(This looks pretty bleak here without the fancy original background.)
 

fool

Member III
Excellent point and terrific reference, thank you!

Blue Sea also has their Circuit Wizard (online and app for mobile devices) if help is needed with wire or fuse sizes, intuitive with a little practice. Circuit protection is mostly to keep the smoke in the wire, but also to keep expensive repairs out of the boat!

 

1911tex

Sustaining Member
As I posted in a different thread about chargers, just make sure to fuse the battery end of the cable(s). There've been fires caused by a simple short in the transformer inside the box, which puts the full battery discharge into the charge cable, which is typically no heavier than 12 AWG. Even if there is no fire, the glowing red hot cable will destroy any other wires it touches and can ignite flammable fumes, paper, foam cushions, etc.
Per your informative advice, I recently installed Blue Seas Marine rated battery fuses and fuse holders for both house batteries. Makes me feel much better...thanks Bob!
 

Kenneth K

Sustaining Member
Blogs Author
I'm in the market for a new charger too.

I run a house bank (2×85=170AmpHrs) + a starting battery. I have the original Motorola 50A alternator. I'm thinking about buying a Sterling charger from Compass Marine. Wondering whether the 20A or 30A charger would be more appropriate. The charger I am replacing is an old Newmar 25A relic.
 

bigd14

Sustaining Member
Blogs Author
If I remember correctly the 30 Amp Sterling has larger studs to connect the battery charging cables to than the 20 Amp version. I went with the 30 Amp for that reason, and no regrets.
 

fool

Member III
I run a house bank (2×85=170AmpHrs) + a starting battery. I have the original Motorola 50A alternator. I'm thinking about buying a Sterling charger from Compass Marine. Wondering whether the 20A or 30A charger would be more appropriate. The charger I am replacing is an old Newmar 25A relic.
You don't mention which battery chemistry, but with FLA at 30% of 170 AH capacity you could go as high as 50 amps. I'd suggest the 30A with larger cables if appropriate, more lanes on the freeway to handle the extra traffic.

Charging a battery is a bit like waiting for a stadium to fill under general seating. When the gates open it's pretty easy to find a good seat, but at about 70-80% full looking for an open seat slows things down just a bit. By the time the stadium is 90% full finding a seat takes a bit of time and some strategy to get there before someone else does. It might take as long to go from 80% full to 100% for a sold out event.

Batteries and chargers are like that too... not too difficult to get to 70-80% when things start to slow down a bit, and equally as long to get to 100%
 

Kenneth K

Sustaining Member
Blogs Author
If I remember correctly the 30 Amp Sterling has larger studs to connect the battery charging cables to than the 20 Amp version. I went with the 30 Amp for that reason, and no regrets.
Ok, didn't know that. Are 10ga wires sufficient for a 20A charger?
 

Kenneth K

Sustaining Member
Blogs Author
You don't mention which battery chemistry, but with FLA at 30% of 170 AH capacity you could go as high as 50 amps.

Charging a battery is a bit like waiting for a stadium to fill under general seating...
Is 30% of capacity seen as an upper limit? Is there a lower limit?

The stadium analogy is quite fitting!
 

fool

Member III
Is 30% of capacity seen as an upper limit? Is there a lower limit?

The stadium analogy is quite fitting!
30% is a good rule of thumb to avoid gassing Flooded Lead-Acid batteries. Other battery types can take a higher amperage (but not necessarily voltage). There isn't a lower limit that I'm aware of other than time...
 

fool

Member III
Are 10ga wires sufficient for a 30A charger?
Ran a few number through the Blue Sea Circuit Wizard app:


Voltage: 12v
Current: 30a
Length of conductor (out and back, a wild-a**-guess): 10'
Voltage Drop: 3% (3% is for critical circuits, 10% is for non-critical like interior lighting)
Insulation Temp Rating: 105 degrees C (printed on the intended marine rated wire, pick 105 degrees C rated wire if possible)
Installed in Engine Room: No (A charger should probably not be installed there, especially with a gasoline motor. Sparks from a short wouldn't be good.)
Wires in Bundle: 2-3 (More wires in a bundle, require a higher gauge wire due to potential heat.)
Duration in minutes: 600 (Suggesting 10 hours to get to a full charge. This input can be skipped and the calculation will still compute.)

And after punching calculate got a recommended AWG of 10.

Ran the same numbers for a fuse size and couldn't get a recommendation for 10 AWG, changing the wire gauge to 8 AWG recommended a 40 amp fuse, a terminal fuse might be the easiest to install. Fuses protect wire from melting and setting your boat afire. Don't neglect "over circuit protection" which is a fancy way of saying fuse or breaker.

If you can manage it go bigger on wire size. The bigger the wire size the less resistance and the more efficiently your system will operate. (More lanes on a crowded freeway speeds traffic along, except for the rubberneckers.)

If you don't have the tools to crimp larger terminals, your local West Marine or chandlery may have tools to loan. Search the interweb of things for any how-to information you might need.
 
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