Charger for battery bank

MikeDamone

Not a Member
Researching
What kind of battery charger are you guys using for your battery bank? I have two vmax 12v 155ah agm batteries to charge from the alternator. Im just learning as I go with this so pardon my ignorance. So ive learned I need a dc to dc 12v to 12v charger. The batteries are rated at no more than a 35amp charge, ideally a 15amp charge. So when choosing an amp rating, do I go with the requirement of one battery, or the total system? Which, ideally, would be a 30amp charger. Ive found a few, but they all seem to have an equilazation charge, which from what ive read can be bad for agm batteries. I guess these dc dc chargers just aren't as common as ac dc chargers. Thanks.
 

Moot

Veteran Expediter
Owner/Operator
I'm using a Promariner DMC 12V to 24V Batt to Batt | ProMariner to charge two Full River 6 volt/224 AH batteries. The Promariner provides the correct charging profile for AGM batteries so it doesn't matter what type of starting battery your van has because the charger is only charging your house batteries.
 

Turtle

Administrator
Staff member
Retired Expediter
So when choosing an amp rating, do I go with the requirement of one battery, or the total system?
When you connect more than one battery together, it becomes one big battery. You have a 310 amp hour battery. So, the total system.
The batteries are rated at no more than a 35amp charge, ideally a 15amp charge.
The recommended charging current is between 10A and 35A. It's odd that they would recommend a range for AGM batteries, since the only number that matters is the maximum current, not any kind of minimum (you can charge an AGM battery with a 1 amp charger). With standard wet cell batteries the max charging current is 0.1c. That means 10 percent of the capacity. So, for a 100 amp hour wet cell, a 10 amp battery charger is what you want. The reason is, if you use higher current, the electrolyte will just boil and the chemical reaction required to fully recharge the battery doesn't properly occur.

AGM batteries do not have free-floating electrolyte, so there's really no boiling that can happen. They also have much less internal resistance than wet cell batteries, which means they can handle charging currents of much higher amperage. Theoretically, an AGM battery can handle 1.0c current, meaning a 100 amp hour AGM battery can be charged with a 100 amp charger. Concord Lifeline (the inventor of AGM batteries) places no upper limit in the charging current. Most AGM battery manufacturers nevertheless will state something like a 0.2c limit, or 20% of capacity. That's the safest, and most practical way to go (on some large installations you'd need a charger the size of a bulldozer and battery cables the thickness of telephone poles to put 1.0c amps back into the battery bank).

With the 155 Ah battery, it's in reality still the same 0.2c, or 20%. 155 times .2 = 31 amps. They list the upper limit as 35 amps, because you can do 2 or 3 or even 4 times that and still be fine.

But in your case, with two of the 155 Ah batteries, at 310 Ah, that's a 62 amp charger at 0.2c. You certainly could use a 100 amp charger, or a 200 amp charger. You can use a 10 amp or 15 amp charger, but it would take longer to charge. I would recommend anything between a 30 amp (for reasonable recharge times) and a 150 amp charger, it all just depends on how much you want to spend. You'll regret getting a smaller charger, like a 10 or 15 amp charger, but you won't go wrong at anything in the 30-150 amp range.
Ive found a few, but they all seem to have an equilazation charge, which from what ive read can be bad for agm batteries.
All decent battery chargers worth their salt will have an equalization charge, or have the ability to manually set the charging voltage high enough (usually in the 16volt range) to perform the equalization. Wet cell batteries need that. AGMs don't. A charger that has an equalization charge will rarely (of ever) engage the equalization function when set for AGM. Don't worry about it. But you can perform an equalization charge on AGM batteries, and they do benefit from it in certain installations, particular that of off-the-grid setups. But it's not really something we need to concern ourselves with out here if you have an AGM battery.
I guess these dc dc chargers just aren't as common as ac dc chargers.
Depends on where you look. They are ubiquitous in marine world where they are ubiquitous on boats.

I would recommend the one Moot is using (max output of 40 amps), or the Sterling Power charger (variable, user-selectable, up to 130 amps). They perform the same way, are similarly priced, and most importantly can be set for the correct charging regimen for AGM batteries, which allows you to mix battery types between the house bank and the cranking battery and charge them using the same alternator.

I would also highly, highly, highly recommend a battery monitor. With those batteries having only a one year warranty, and costing what they do, I'd want to make sure I monitored them carefully and correctly. If you won't monitor and charge them properly, they'll be doing good to last 18 months. Otherwise they could last 5-8 years out here, at least.
 

MikeDamone

Not a Member
Researching
Thanks for setting me straight, Turtle. I was looking at Sterling, but I couldn't find one under 50 amps, but I now see its a non issue. Something else I came across was something called a "variable voltage alternator", which, to save fuel, I guess, takes the alternator below the needed volts to run a charger. Its a newer technology put on mostly foreign vehicles. And seeing how I have a 2012 Nissan, im going to make sure before I purchase. My brother is a mechanic, so its no thing to have him hook up a volt meter and go driving around with me for a while, just to be sure.

I was also planning on getting a monitor. Any suggested brands?
 

Turtle

Administrator
Staff member
Retired Expediter
$102 is an excellent price for $30 worth of wiring, fuses and connectors. Don't you think?

The kit is handy, because the wires are color coded and it's got the fusable links and connectors already there. But really all you need is a two-wire twisted pair flexible connection cable (minimum AWG 24/0.2 mm) and a three-wire flexible connection cable (minimum AWG 21/0.4 mm). So, basically, telephone wire. And, two isolated inline fuse holders with 1 amp slow blow (AT) fuses and some crimp terminals. That's it.

You can literally use CAT-5 or CAT-6 cable. It has four twisted pairs.

The kit contains a roll of 12 conductor twisted pair cable, even though you only need the 5 wires (one twisted pair from the shunt, another wire from the shunt, and two from the positive terminal of the battery that contains the fuses). The reason is has 12 wires in the kit is so it can be used with the LinkPro for a second battery bank, and in case you want to connect wires to the alarm relay on the monitor.
 
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