AGM Battery Charger Size

[Juliet 15]

Would a 125 amp inverter/Charger be adequate to charge a 1400ah bank?


I'm considering a Magnum 3000w inverter/Charger that charges the batteries at 125 amps max. The bank is 12v, 1480ah.



What I've read is ideally you'd want 10%-15% of the 20-hr ah rating (100 ah, get a 10 amp charger).


It seems to me the down side might be longer charging times.


Thoughts?

 

[ksanders]

1400*.15 is 210

Take away from that the boats normal operating loads. My boat runs over 30 ams for example.

But...

The only charger I know of that will do that is the Victron Quattro, or you can parallel chargers on some brands.

 

[tiltrider1]

It is capable but you will need to use 4/0 gauge wire. You can’t afford any voltage drop or it will take for ever to recharge a bank that large.

Note, banks of that size require additional safety considerations such as T size fuses. That much power can arc right across standard fuses.

 

[Juliet 15]

Thanks. I currently use an ANL 300 amp fuse. You think the T-fuse is better?

 

[Shrew]

It seems to me the down side might be longer charging times.

Thoughts?

Correct. The question(s) in my mind would be:

How deeply do I intended to draw down the battery bank (on average) over a given discharge cycle?

How long to recharge the same bank over a charging cycle?

Can my AC circuit (shore power stanchion, shore power cord, and/or generator to charger breaker) handle the load of the inverter/charger during charging?

Can my DC circuit (charger to battery bank) handle the load while charging?

 

[ksanders]

Another thought comes into play.

If you are truly seeking independent operation vs weekend warrior life then your battery bank only needs to be what you can recharge the next day.

More than that is not accomplishing anything.

 

[Bmarler]

I was thinking the OP was asking because he was planning to use the genset to recharge daily or every two days depending on daily consumption. It’s a pretty good sized vessel, so using a third or close to half of a 1400 ah bank is pretty likely. It that’s the case, a second backup charger could be installed to bump up the amps going back in, or a solar installation can help offset the charging deficiency. Many people tend to have daily generator run time, maybe this is the case?

 

[O C Diver]

What chemistry of batteries? For open lead acid I think you're fine with the inverter's battery charger. For AGM I might parallel a second charger for the bulk phase. Keep in mind, once out of the bulk phase, amperage starts tailing off as in the absorption phase, the charger maintains voltage and reduces amperage to accomplish that.

Ted

 

[Bmarler]

What chemistry of batteries? For open lead acid I think you're fine with the inverter's battery charger. For AGM I might parallel a second charger for the bulk phase. Keep in mind, once out of the bulk phase, amperage starts tailing off as in the absorption phase, the charger maintains voltage and reduces amperage to accomplish that.

Ted

Batteries are stated to be agm from the subject line.

 

[O C Diver]

Batteries are stated to be agm from the subject line.

My bad.

Ted

 

[tiltrider1]

Thanks. I currently use an ANL 300 amp fuse. You think the T-fuse is better?

You need to use a fuse with a destructible value large enough to handle the 1400 amp bank. I do not believe ANL fuses have that ability.

 

[tiltrider1]

My bank was 1400A lead acid for the last 11 years. On average I would use 600A in 20 hours. This required 4 hours of generator time to recharge. I also had a 40A back up charger. Occasionally I ran both chargers to reduce generator time. My bank was FLA not AGM.

I have now replaced the bank with 1000A of LiFePO.

 

[O C Diver]

You need to use a fuse with a destructible value large enough to handle the 1400 amp bank.

Why?

If the total of all loads was 400 amps and the total of all charging equipment was 250 amps, why would you need more than say 500 amps? Obviously you need to protect the cabling to the distribution point. Maybe increase the amperage if the bank is used for starting the engine. What's the reason for not limiting the fuse to the draw capacity?

Ted

 

[Juliet 15]

Thanks for all the input. I shld have included my reasons.


I want to be able to sit on the hook for longer. Right now I can hang out for about 26-30 hours on 460ah of FLA batteries before hitting 50% (time to recharge). I want to be able to go for 3 to 5 days without running the Gen if I want. Hence the 1480ah of AGM batteries.

 

[rslifkin]

Why?

If the total of all loads was 400 amps and the total of all charging equipment was 250 amps, why would you need more than say 500 amps? Obviously you need to protect the cabling to the distribution point. Maybe increase the amperage if the bank is used for starting the engine. What's the reason for not limiting the fuse to the draw capacity?

Ted

I don't think he was referring to the fuse trip rating, but the amperage interrupt capacity rating. With a fuse that has too low an AIC rating and a big battery bank, if you get a dead short it's possible that the fuse won't actually be able to break the circuit as the batteries can supply enough power to just weld across the fuse.

 

[tiltrider1]

I don't think he was referring to the fuse trip rating, but the amperage interrupt capacity rating. With a fuse that has too low an AIC rating and a big battery bank, if you get a dead short it's possible that the fuse won't actually be able to break the circuit as the batteries can supply enough power to just weld across the fuse.

This is correct and not common knowledge. Not an issue with a 400A bank but when you get these bigger banks you introduce new safety concerns.

 

[ksanders]

Why?

If the total of all loads was 400 amps and the total of all charging equipment was 250 amps, why would you need more than say 500 amps? Obviously you need to protect the cabling to the distribution point. Maybe increase the amperage if the bank is used for starting the engine. What's the reason for not limiting the fuse to the draw capacity?

Ted

Ypou need a fuse with the ability to stop a fault up to the availability of the fault current available from the batteries.

This is regardless of the fuse operating rating.

 

[ksanders]

Thanks for all the input. I shld have included my reasons.


I want to be able to sit on the hook for longer. Right now I can hang out for about 26-30 hours on 460ah of FLA batteries before hitting 50% (time to recharge). I want to be able to go for 3 to 5 days without running the Gen if I want. Hence the 1480ah of AGM batteries.

OK, great reason!!!

 

[Bacchus]

I don't think he was referring to the fuse trip rating, but the amperage interrupt capacity rating. With a fuse that has too low an AIC rating and a big battery bank, if you get a dead short it's possible that the fuse won't actually be able to break the circuit as the batteries can supply enough power to just weld across the fuse.

AIC is a separate and important consideration with large batty banks. Many are only aware of the need to protect wiring for normal loads. AIC is anotherv/ different consideration.
See. https://pbase.com/mainecruising/battery_fusing
Steve DAntonio also has a good article on this.

Fuses not rated for AIC that a LG bank is capable of delivering can weld themselves closed instead of openning the circuit.

 

[CMS]

Thanks. I currently use an ANL 300 amp fuse. You think the T-fuse is better?

The AIC of an ANL is insufficient for 1400Ah of AGM’s

As to charger size most quality AGM batts require a min of 20% of Ah capacity (.2C)in charger size because charge current plays a role in state of health of the battery. Too little current and you kill them prematurely. Some AGM’s such as Northstar & Odyssey want to see a min current of .4C. You’re not even at .1C….

 

[Bmarler]

The AIC of an ANL is insufficient for 1400Ah of AGM’s

As to charger size most quality AGM batts require a min of 20% of Ah capacity (.2C)in charger size because charge current plays a role in state of health of the battery. Too little current and you kill them prematurely. Some AGM’s such as Northstar & Odyssey want to see a min current of .4C. You’re not even at .1C….

This is a good point, and something I forgot about. My fullrivers have .1c as a minimum charge rate, and recommend .25c. That’s a lot of amps for a bigger battery bank. I can’t imagine .4c..

 

[rslifkin]

On the AGM charge rate thing, my Fullrivers are happy charging with anything below 0.2C (and mine often get charged slower from solar). But once you get up to 0.2C or higher charge rates, the batteries start getting rather warm. I pushed them to 0.25C once and had to back the charge down as the battery temps were pushing 120+ degrees (F). I've seen other AGMs happily accept high currents though, so it seems to vary between manufacturers and such even within the AGM world.

 

[Bmarler]

On the AGM charge rate thing, my Fullrivers are happy charging with anything below 0.2C (and mine often get charged slower from solar). But once you get up to 0.2C or higher charge rates, the batteries start getting rather warm. I pushed them to 0.25C once and had to back the charge down as the battery temps were pushing 120+ degrees (F). I've seen other AGMs happily accept high currents though, so it seems to vary between manufacturers and such even within the AGM world.

interesting. i'm usually at .16 c with the engine, or .14c with the inverter. my 210 amp alternator gets hot before the batteries do, so i've never pushed even to .2c.
solar obviously is a much lower rate, and mine happily accept that as well.
i do think it's important to push high amps into them regularly though, to keep them working well. i've found that after floating all winter, it takes a couple of cycles to get them performing at their best again in the spring.

 

[rslifkin]

i've found that after floating all winter, it takes a couple of cycles to get them performing at their best again in the spring.

I've found the same with mine. After sitting for the winter with a few hours per week of shore power (but no loads in between) it takes a couple cycles and some significant time in float before the float current tapers off to its normal 0.1 amps or less. It spends quite a while around 0.5 amps in float before things settle back to normal. After a cycle or 2 things settle much faster at the end of charge.

 

[Juliet 15]

After reading all this, I started looking for inverter chargers in the 200amp range. No one seems to make one. Does anyone here have an inverter/Charger that charges at 200ish amps?

 

[tiltrider1]

Mine is only 150 amps. I do have a back up 60 amp charger that I can kick on for those times I have really hammered the bank.

 

[Juliet 15]

Titlrider1, what brand and model is your 150 amp inverter/charger?

 

[tiltrider1]

Titlrider1, what brand and model is your 150 amp inverter/charger?

I have a Magnum Hybrid 3000w pure sine wave Inverter/Charger. It is connected with 4/0 cable to my battery bank. My back up charger is a Victron Centurian.

 

[Bmarler]

My xantrex freedom XC pro has 150 amps as well. Plus a 50 amp transfer switch.
Interesting thing about the transfer switches, the 30 amp is only good for 24 continuous. The 50 is good for 40 continuous. For this model anyway.
I had to upgrade from a 2000 watt because my transfer switch would drop out from time to time from high amp draw. I didn’t know they’d do that.
Bonus on the 3000 watt was 150 amps charge rate.

 

[luna]

As ksanders mentioned upthread Victron's 12 V. 5kVA Quattro is said to charge at 200A.

https://www.victronenergy.com/upload/documents/Datasheet-Quattro-3-10kVA-120V-EN-.pdf

There is a school of thought that says that you may well be better served by using 2 smaller MultiPlus inv/chgrs. The 12 V. 3kVa units are rated at a combined charge capacity of 240 A.

When inverting, if you run them paralleled they would act as a progressively larger single 120 V inverter rated at 6kVA.

Or if you stacked them they would provide 3kVa of split phase 240 V power to run your oven, water heater, clothes dryer or other 240V loads. This would be predicated on the fact that you are underway and your alternators (or your large solar array) are delivering a substantial portion of the power the inverters are using, otherwise you flatten the batteries rather quickly.
Your ac load buss would need to be split to accept the 2 120V lines, but if you have 240 V consumers now, it is already split. You should also look to try to balance the frequently used loads onto each stacked inverter as to not overload one of them. Usually easily done on the ac load buss.

Two smaller inv/chgrs. also give you some redundancy once reconfigured, should one fail.