AGM Battery Charger Size

[Juliet 15]

I must be misreading something.



I looked at the Magnum hybrid 3000w. They advertise 125 charging amps (my focus is the abiloty to recharge the house batteries).


I looked at that same Victron Quattro, and it doesn't appear to me to clearly say what it charges the house batteries at (it lists 52v under "charge house batteries"- wha...?). The Quattro seems to indicate it provides 3-5000w at up to 220 inverted amps. But I'm missing seeing its ability to charge large banks at 200 or so amps.

 

[luna]

The data sheet that I linked is a bit difficult to read.

First you need to find the inv/chgr that interests you. They are listed across the top of the page. Your's would be the 12/5000/220-100/100 120V, listed in the middle column. It's important to recognize that this is the first inv/chgr. listed in this grouping.

Now go down the to the Charger portion of the data, about 1/3 down the page. 4 lines down is the "Charge current house battery (A)". The first number listed, 200 is the current in Amps that this charger delivers. The 2nd number, 120 pertains to the 2nd model listed at the top in this column, which is the 24/5000/120-100/100 120 V, which would be used if your bank is 24V.

The rest of the data in this middle column reads the same way as there are 3 inv/chrgs in this grouping.

Got it?

 

[Juliet 15]

Lol, got it. Thanks! I wasn't decrypting it right. I like this I/C, and am leaning toward it. It cuts the charge time literally in half (from slightly over 10 hrs at 125 amps to just over 5 hrs at 200 amps).

 

[luna]

For the reasons cited in my earlier post, plus the price of these beasts, the wind will likely blow you in the direction of a pair of Multipluses.

Also, remember that with AGMs you need to full charge them often. A partial state of charge even at 90%, if often, is not good for longevity.

Fully charging will take longer than 5 hours even if you had 300 Amps of charging capacity to start with as you have to get well through the absorption stage.

 

[Juliet 15]

Thanks, every one of you. I learned a lot. I'm going with a Victron Quattro 220 amp inv/cheer for ease of installation. So many people helped me make an informed decision - thank you!

 

[mvweebles]

That's a pretty large bank to charge. What type of boat and do you have alternators capable of charging underway?

From experience, cabling a large bank is challenging and expensive. And you're adding quite a bit of weight.

If you're really needing 4-5 days of dwell time, given the expense of batteries and cabling, would it make sense to augment your system with solar? Are AGM batteries your best option? A pair of 300AH LFP batteries would give you almost the same useable capacity at an affordable price (when cabling is included), though some changes in your base system might be needed.

Peter

 

[Bmarler]

Peter,
He’s in a hatteras 58 according to his profile. I could see a 1400 ah agm bank being appropriate for 3-4 days without genset.
From what I’ve seen on hattaras electrical systems is that genset use would be primary charging source, the engines usually have fairly small alternators, many times 32 volt. The 12 volt system is either tapped off that, or stand alone, or a hybrid of both, with systems for running the boat tapped off the 32 volt bank, and house loads on a stand alone bank.
I have a large agm house bank too, at 1125 ah I could sit for two days easily, without conserving power at all. I installed .75 kw solar this year and it makes my daily electricity easily. So your suggestion of the OP looking at solar is a very good one. I can sit indefinitely without having to fire up an engine. (In summer anyway)

 

[RickyD]

This is interesting as I have a 1300 ahr set up with FLA 6v L16's and a 120 amp Victron Multi-Plus inverter charger. I run my genset twice a day to stay above the 50% area. Once in the morning and once before bed. With a full sized refrigerator freezer with ice maker in the galley and a small refrigerator/freezer in the sun deck I run the genset as soon as I wake up as the batteries are down a bit. Maybe 12.3. It takes hours to get them back up. Now an associated question is, do I charge till I get to float or just till I get over 13 volts? If I did more offshore I'd put solar up on my hardtop. Right now, even at California diesel prices, running the gensets a few hours is cheap enough. I have a 16kw that uses max 1 gph and a 4k at half that. I mostly run the 4k unless I'm making water. Maybe I could add another Multi-plus and cut the charge time.

 

[Bmarler]

This is interesting as I have a 1300 ahr set up with FLA 6v L16's and a 120 amp Victron Multi-Plus inverter charger. I run my genset twice a day to stay above the 50% area. Once in the morning and once before bed. With a full sized refrigerator freezer with ice maker in the galley and a small refrigerator/freezer in the sun deck I run the genset as soon as I wake up as the batteries are down a bit. Maybe 12.3. It takes hours to get them back up. Now an associated question is, do I charge till I get to float or just till I get over 13 volts? If I did more offshore I'd put solar up on my hardtop. Right now, even at California diesel prices, running the gensets a few hours is cheap enough. I have a 16kw that uses max 1 gph and a 4k at half that. I mostly run the 4k unless I'm making water. Maybe I could add another Multi-plus and cut the charge time.

With flooded batteries I’d prefer to charge till I hit the end of bulk. 14.6 or thereabouts.
That would put you at 90%ish? With only 120 amp charger it would take a while. In your case, since you don’t have any plans for solar, I’d definitely install another charger, maybe a 150 or 200 amp unit to cut my charge time down and get to a higher state of charge.

 

[Juliet 15]

Bmarler, you're spot on. It's a Hat58 LRC, and the 12v system is a separate system from the 32v system. I've slowly moved most house items to the 12v system and that's what the large bank is for. I can't completely get rid of the 32v system as the engine start system is 32v.



Also, yes, the alternators are only 60 amp/32v (1 per engine). I added a 105 amp 12v alternator to charge the 8D batteries that start my generators, but that's too small for the house bank.


Last, yes, I'm planning to add a smaller solar charging system to the house bank. I dont want a huge one, just one like your setup that can charge enough to replenish one days' worth of usage. That could, in theory, extend my hook time.indefinitely.

 

[Don L]

I don't really understand how and why this thread is so long. The only battery I have ever seen that said it "needed" a fast charge was FireFly carbon foam (mine still only lasted 2.5 years). There really isn't such a thing as a too small charger except that it will take a longer time.

I am mostly solar, but run the generator and charger sometime when it is cloudy out . On those days I assume I am not going to get fully charged and it more about listening to the generator for 1 hour/day for 2 days, or run it for 2 hours on 1 day.

My understanding is that most trawlers etc have electric stoves, are you not going to have to run the generator to cook anyway and would run the charger at same time?

 

[rslifkin]

My understanding is that most trawlers etc have electric stoves, are you not going to have to run the generator to cook anyway and would run the charger at same time?

That's common and how my boat is currently set up, although on a decent solar day the batteries are typically full when I crank up the generator to make dinner. However, as battery technology has improved and large inverters, battery banks, and solar setups have become more common, it's become more common to run an electric stove (typically induction) on battery power vs relying on a generator or shore power to run it.

 

[Bmarler]

Bmarler, you're spot on. It's a Hat58 LRC, and the 12v system is a separate system from the 32v system. I've slowly moved most house items to the 12v system and that's what the large bank is for. I can't completely get rid of the 32v system as the engine start system is 32v.



Also, yes, the alternators are only 60 amp/32v (1 per engine). I added a 105 amp 12v alternator to charge the 8D batteries that start my generators, but that's too small for the house bank.


Last, yes, I'm planning to add a smaller solar charging system to the house bank. I dont want a huge one, just one like your setup that can charge enough to replenish one days' worth of usage. That could, in theory, extend my hook time.indefinitely.

i'd say you've got a pretty good handle on what's needed, and what your options are. you could replace one of the 60 amp 32 volt alternators with a big 12 volt one, but then you'd need a separate source of 32 volt in case of alternator failure. so, in your case, it probably makes more sense to just add another 12 volt charger to run off the generator power to speed up the house bank charging, or i think you may have posted already, a bigger inverter/charger.
the plan for solar can be a real game changer. i know it was for me. with agm's, it's important to charge to completion regularly, and solar can be the source to do that. you're topping off the batteries without having to run an engine.
the only downside to not having a big 12 volt alternator on the mains is that in order to arrive at anchorage with full batteries, you need to run a generator to top them up so the solar can keep them charged.

 

[Don L]

That's common and how my boat is currently set up, although on a decent solar day the batteries are typically full when I crank up the generator to make dinner. However, as battery technology has improved and large inverters, battery banks, and solar setups have become more common, it's become more common to run an electric stove (typically induction) on battery power vs relying on a generator or shore power to run it.

Then you shouldn't worry about the battery drain and it is something to be made up later. I do the same now when I run the inverter off the batteries to use my microwave or make hot water instead of running the generator.

 

[Bmarler]

I don't really understand how and why this thread is so long. The only battery I have ever seen that said it "needed" a fast charge was FireFly carbon foam (mine still only lasted 2.5 years). There really isn't such a thing as a too small charger except that it will take a longer time.

I am mostly solar, but run the generator and charger sometime when it is cloudy out . On those days I assume I am not going to get fully charged and it more about listening to the generator for 1 hour/day for 2 days, or run it for 2 hours on 1 day.

My understanding is that most trawlers etc have electric stoves, are you not going to have to run the generator to cook anyway and would run the charger at same time?

running a slow charge rate with agm's is less than ideal. yes, it can be done, but my experience with them has been that they don't perform as well if you can't give them a good dose of amps regularly. i've been using agm's for decades, many different brands, and this has held true for all of them i've owned.
although a lot of trawler owners prefer electric stoves, i think you're mistaken to think most trawlers have electric. there are a good many cruising boats that use propane. i'd hate to have to fire up a genset just to have a meal.

 

[Don L]

Never have ever read anything about needing a big charger for AGMs. All I have ever read is that charger sizing ideally is 25% of capacity (amps/AH) for a acid battery because that allows it to charge at it's fastest rate. But of course that only does those amps during bulk and even an AGM is only doing a small part of that the last 10%. Lots of boats, sailboats especially probably, are out there with a solar system doing 90% of their charging and it is only 10% of capacity.

 

[ranger58sb]

Never have ever read anything about needing a big charger for AGMs.

From the Lifeline manual:

For repetitive deep cycling applications (deeper than 50% DOD), chargers should have an output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than this value, the life cycle of the battery may be negatively affected.​

From the Odyssey manual:

To fully charge a 31-PC2150 battery that is reoutinely discharged deeply, a minimum of 40 amps are required with charger voltage within the range of 14.1V to 14.7V.​

(Note: A PC-2150 is the old name for their Extreme Group 31 100-Ah battery, so they're saying a minimum of .4C.)

-Chris

 

[Don L]

so 20% to 40%, such a well established rule.

I have no bone in this fight other to say it is a lot of worry I believe about nothing. Way more important than how fast you charge (take 5 hours pretty much regardless) is you get those AGMs to 100%. The whole reason I got away from acid batteries.

 

[Jelliott]

Magnum problems

I would add a caution to this discussion. My Magnum 2812 was purchased new in February of 2021. By January 2022 it stopped working. I was in Texas and Magnum told me to go with their certified repair facility in Houston. For over a years time they never could get the part it needed. And as of this October the repair place is gone. So is my inverter. Magnum has been unsympathetic. I would caution against purchasing a magnum. I’m sparing you the details.

 

[Reba]

Consider a extra high capacity alternator

The bank size you are quoting is not massive but if you are drawing it down overnight and cruising the next day why not also instal an extra alternator on 1 or both engines use a balmar or other external regulator and you can easily cut a lot of generator hours. The inverter charger you mentioned should be fine for bank use when you don’t want the gen set on when you leave the boat at anchor to explore for a few hours or quite sunset drinks

 

[klee wyck]

From the Lifeline manual:

For repetitive deep cycling applications (deeper than 50% DOD), chargers should have an output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than this value, the life cycle of the battery may be negatively affected.​

From the Odyssey manual:

To fully charge a 31-PC2150 battery that is reoutinely discharged deeply, a minimum of 40 amps are required with charger voltage within the range of 14.1V to 14.7V.​

(Note: A PC-2150 is the old name for their Extreme Group 31 100-Ah battery, so they're saying a minimum of .4C.)

-Chris

Hmmmm…
I am hoping that this is only important if you routinely discharge deeply as the qualifier above suggests. I have 6 PC1800 extremes wired in parallel to make 642 amp hours at 24v from these 214 amp hour 12 volt agm batteries. I only charge at 100 amps generally but am never purposely below 25 volts on the system. I get them to near 29v at end of bulk.

Am I being hard on them?

 

[ranger58sb]

so 20% to 40%, such a well established rule.

Not exactly a "rule" I think... since so much varies by specific manufacturer. Voltage recommendations, for example, are also much different between Lifeline and Odyssey batteries... and I'd guess everything varies with other makers, too.

I dunno what other AGM makers suggest, recommend, or mandate... but from what other folks have said here, maybe they're all consistently .2C or above?

Hmmmm…
I am hoping that this is only important if you routinely discharge deeply as the qualifier above suggests. I have 6 PC1800 extremes wired in parallel to make 642 amp hours at 24v from these 214 amp hour 12 volt agm batteries. I only charge at 100 amps generally but am never purposely below 25 volts on the system. I get them to near 29v at end of bulk.

Am I being hard on them?

Odyssey does at least say "discharge deeply" in their guidance... and it sound like you're not.

-Chris

 

[Don L]

Not exactly a "rule" I think... since so much varies by specific manufacturer. Voltage recommendations, for example, are also much different between Lifeline and Odyssey batteries... and I'd guess everything varies with other makers, too.

But why should they vary for a given construction type of battery. My point is that this whole thread is about charger sizing when after all these years there isn't industry agreement.

Testing I have seen shows that you can not even charge an AGM at 0.4C except for a small area on the charge curve because the battery just can not accept it. So having a big charger is mostly just a waste of money.

 

[ranger58sb]

But why should they vary for a given construction type of battery. My point is that this whole thread is about charger sizing when after all these years there isn't industry agreement.

Testing I have seen shows that you can not even charge an AGM at 0.4C except for a small area on the charge curve because the battery just can not accept it. So having a big charger is mostly just a waste of money.

I expect a "given battery type" isn't sufficiently detailed enough, and AGM is only a generic term. IOW, an AGM by Maker X isn't the same as an AGM by Maker Y.

??

And/or maybe the testing you saw wasn't from Odyssey or specific to Odyssey batteries? (For example.)

??

Reading suggests folks with various brands of AGMs see different longevity results... although anecdotal yakking on the 'net certainly doesn't mean there's any sort of standardization involved in those various result reports.

-Chris

 

[Don L]

Far as I am concerned an agm battery is pretty much an agm battery, people think their agm is "special" but that is mostly just marketing.

 

[cafesport]

Juliette,
I think your expectations are a little too much on the high side as far as what to expect for charging and real world results on your agm bank. Check out the lifeline manual and the marine how to website for more realistic charging and discharging data.

Fwiw we have run over ten years on a larger bank than you plan but we isolate our banks to use exactly what you have, and have used a variety of of chargers and inverters including the magnum for maintenance over the years.

Without solar aid you can plan on running the generator at least ten hours a day to get to full charge when you charge with ever diminishing loads ie four hours outputting less than 1000 watt.

Bottom line as long as you have another charger and program it it to work with the magnum and limit the magnum to limit charging to 70 percent and you recharge to 100 percent every day you will be fine. If not then all will go pear shaped soon and the magnum will be first to go.

Currently we are outputting 650 watts charging to our agm bank discharged to 95 percent depleted by 38 amps@24 v 918 watts. At this rate it will be more than four hours to full charge. Guess what is not going to happen tonight. Oh and we also have more than 14.4 kw of charging capacity available. Fortunately our lithium bank will handle the rest overnight.

 

[SteveK]

Without solar aid you can plan on running the generator at least ten hours a day to get to full charge when you charge with ever diminishing loads ie four hours outputting less than 1000 watt.

Ten hours of generator? Are you basing that on the Magnum charger averaging 1/2 of the 1480Ah bank to recharge 740Amps back into the bank at 74A per hour.
This was my concern as well installing 800Ah bank of LFP if I used it all. Right now I can do 200A per hour and I am working on adding another 100A for total 300A charge when the genny is running. My bank can take up to 400A so we shall see if I need more than 300A

 

[ranger58sb]

Far as I am concerned an agm battery is pretty much an agm battery, people think their agm is "special" but that is mostly just marketing.

I'd guess if they were all equal, all AGMs in a given BCI group would weigh the same... but apparently they don't... with maybe even a 20-lb difference in G31s and larger.

And makers would all recommend the same bulk, absorption, and float charge voltages... but they don't.

I think Rod Collins (CMT, here) might have done some comparison testing, and if so it'd likely be published on his marinehowto site...

-Chris

 

[Bmarler]

Far as I am concerned an agm battery is pretty much an agm battery, people think their agm is "special" but that is mostly just marketing.

You are certainly welcome to hold your own opinion on that. I know that before I had such a large investment in batteries I didn’t give charge rate a single thought. Replacing 4 isn’t a huge deal. But now I’m working with 16, so I pay attention ant try to get every amp hour I can out of them.

 

[Don L]

I am sure the people who buy $1000 Battleborn LFPs will always get up in arms about those that paid $300 for the same spec batteries.

In 15 years of reading about boat batteries from users I have seen no difference is their life for a brand really. The most expensive batteries I even have had, they were 3 times the price, last the shortest amount of time.