Cabin System Help

[Steve_S]

Our battery bank is currently 190ah, but will eventually grow to approx. 300ah.
What would the optimal size charger be for our system?

No Answer.
The Battery Packs determine the max capacity the charger can push.
a 100AH Battery can take 50A charge. 280AH can take 140A.
Lowest Common denominator RULES because you cannot be 100% certain which pack will hit full first, if you hit a 100AH Battery with 140A when it is not rated for it... well, won't be pretty AND you'd be generating a Huge Cloud of BLUE AIR !

 

[HARG Hunter]

No Answer.
The Battery Packs determine the max capacity the charger can push.
a 100AH Battery can take 50A charge. 280AH can take 140A.
Lowest Common denominator RULES because you cannot be 100% certain which pack will hit full first, if you hit a 100AH Battery with 140A when it is not rated for it... well, won't be pretty AND you'd be generating a Huge Cloud of BLUE AIR !

Suggesting the batteries should be charged individually, and not as a full bank?

Bank: (1) 100ah Universal AGM, (3) 30ah Mighty Max AGM

 

[Steve_S]

Oh... AGM... I thought it was LFP.
Mismatched FLA ohhh man, that's another pile of trickery....
Tried that once, someone got a GREAT DEAL on slightly used batteries after a week.
Some may say I am wrong but you can't put mixed together like that and expect no issues.

The charge process (forget equalizing and all that, just the basics) reads voltage & amps being taken by the batteries collectively in the bank, The resistance & impedance readings are essential as there is no cell level watching.

The 100AH AGM is already derated due to usage & age, which starts the 1st time you start draining it.
the 3X 30AH AGM total 90AH but they are not as aged as the other. If you put all these into one bank parallel, the Lowest Common Denominator battery will pull the rest down to its level. Guess what that 100AH will do ?
Had you gotten another Universal 100AH AGM and put it in parallel it would have dropped to match the other and they would carry on without a blink. The 3x30AH can make one bank of 12V/90AH (45 useable) and the 100AH you have now is likely down to about that level "maybe" so it likely is best as it's own independent creature.

You can try to charge it all as one bank BUT be watchful, have your DVOM handy. Hopefully, you can watch the amperage during charge to see how it will decrease as they fill up and once the charger thinks it is done, then manually check the batteries.

 

[Hedges]

Suggesting the batteries should be charged individually, and not as a full bank?

Bank: (1) 100ah Universal AGM, (3) 30ah Mighty Max AGM

Not necessarily.
As they get full they will accept less current.
But during "bulk" charging they might take more current than they should. If all your batteries were the same size and wired symmetrically, current would be expected to divide evenly.

Each battery has an optimal charge current. See if you can find optimal or maximum in data sheets for those batteries. Some people say 0.1C for AGM (0.1 x 100 Ah = 10A charge current, 0.1 x 30 Ah = 3A charge current). My AGM specify 0.2A and say it can take an inrush that is higher.
50A charge current into a 100 Ah AGM battery is probably too much, would cook it. But possibly the battery can accept that for a while until voltage comes up, check the manual.

I think internal resistance of a 100 Ah battery is more than 3.33 times internal resistance of a 30 Ah battery. That means bulk charging current won't divide evenly. If charged together as a full bank it is desirable to avoid charging the 30 Ah batteries too fast, target maybe 3A to 6A per battery. Without being able to measure current in a single wire (and without introducing resistance of an ammeter which would affect current), difficult to determine precisely.

20A total charge current should be conservative.

If you put a battery disconnect on the 100 Ah, then you could run two battery chargers, each 10A or 20A depending on desired charge current.
I find cheap automotive battery chargers vary their current considerably depending on battery voltage.
Charge controllers maintain constant fixed current until voltage reaches target absorption voltage, so do the job in much less time.


If you had 190 Ah battery bank all one size battery, I would say 19A to 38A charge current (depending on battery specs) would be good.

 

[HARG Hunter]

Not necessarily.
As they get full they will accept less current.
But during "bulk" charging they might take more current than they should. If all your batteries were the same size and wired symmetrically, current would be expected to divide evenly.

Each battery has an optimal charge current. See if you can find optimal or maximum in data sheets for those batteries. Some people say 0.1C for AGM (0.1 x 100 Ah = 10A charge current, 0.1 x 30 Ah = 3A charge current). My AGM specify 0.2A and say it can take an inrush that is higher.
50A charge current into a 100 Ah AGM battery is probably too much, would cook it. But possibly the battery can accept that for a while until voltage comes up, check the manual.

I think internal resistance of a 100 Ah battery is more than 3.33 times internal resistance of a 30 Ah battery. That means bulk charging current won't divide evenly. If charged together as a full bank it is desirable to avoid charging the 30 Ah batteries too fast, target maybe 3A to 6A per battery. Without being able to measure current in a single wire (and without introducing resistance of an ammeter which would affect current), difficult to determine precisely.

20A total charge current should be conservative.

If you put a battery disconnect on the 100 Ah, then you could run two battery chargers, each 10A or 20A depending on desired charge current.
I find cheap automotive battery chargers vary their current considerably depending on battery voltage.
Charge controllers maintain constant fixed current until voltage reaches target absorption voltage, so do the job in much less time.


If you had 190 Ah battery bank all one size battery, I would say 19A to 38A charge current (depending on battery specs) would be good.

When I am running the generator during the day, it's typically to run a miter saw or table saw, and it's for a few hours.
The system is running fairly well right now, so I would only hook up a charger to give the batteries a boost IF there hasn't been much sun. Basically just to give us a little extra power to last through the night.

I know you've seen my recent pics regarding how I re-wired the battery bank and split the cables from the charge controller to try and balance the bank. Wondering if hooking up the battery charger the same way would help or if it wouldn't matter.

I will take a look at the specs for the batteries.
I will post them here shortly.

Hoclax8 - Sorry if it feels like I hijacked your thread. I find it helpful when similar situations are talked about so we can learn together. My situation is almost identical to yours.

 

[HARG Hunter]

Not necessarily.
As they get full they will accept less current.
But during "bulk" charging they might take more current than they should. If all your batteries were the same size and wired symmetrically, current would be expected to divide evenly.

Each battery has an optimal charge current. See if you can find optimal or maximum in data sheets for those batteries. Some people say 0.1C for AGM (0.1 x 100 Ah = 10A charge current, 0.1 x 30 Ah = 3A charge current). My AGM specify 0.2A and say it can take an inrush that is higher.
50A charge current into a 100 Ah AGM battery is probably too much, would cook it. But possibly the battery can accept that for a while until voltage comes up, check the manual.

I think internal resistance of a 100 Ah battery is more than 3.33 times internal resistance of a 30 Ah battery. That means bulk charging current won't divide evenly. If charged together as a full bank it is desirable to avoid charging the 30 Ah batteries too fast, target maybe 3A to 6A per battery. Without being able to measure current in a single wire (and without introducing resistance of an ammeter which would affect current), difficult to determine precisely.

20A total charge current should be conservative.

If you put a battery disconnect on the 100 Ah, then you could run two battery chargers, each 10A or 20A depending on desired charge current.
I find cheap automotive battery chargers vary their current considerably depending on battery voltage.
Charge controllers maintain constant fixed current until voltage reaches target absorption voltage, so do the job in much less time.


If you had 190 Ah battery bank all one size battery, I would say 19A to 38A charge current (depending on battery specs) would be good.

UPG #121000 - 100ah - 12v
Max Charge current is 0.3C

Might Max #ML35-12 - 35ah - 12v
Max Charge current is 10.5 A

The match charge current is listed a different way for each.
I just need to finish the math.

I assume this means Max Charge current for the UPG 100ah is 30A (0.3C x 100ah = 30 Amps correct?

 

[HARG Hunter]

Oh... AGM... I thought it was LFP.
Mismatched FLA ohhh man, that's another pile of trickery....
Tried that once, someone got a GREAT DEAL on slightly used batteries after a week.
Some may say I am wrong but you can't put mixed together like that and expect no issues.

The charge process (forget equalizing and all that, just the basics) reads voltage & amps being taken by the batteries collectively in the bank, The resistance & impedance readings are essential as there is no cell level watching.

The 100AH AGM is already derated due to usage & age, which starts the 1st time you start draining it.
the 3X 30AH AGM total 90AH but they are not as aged as the other. If you put all these into one bank parallel, the Lowest Common Denominator battery will pull the rest down to its level. Guess what that 100AH will do ?
Had you gotten another Universal 100AH AGM and put it in parallel it would have dropped to match the other and they would carry on without a blink. The 3x30AH can make one bank of 12V/90AH (45 useable) and the 100AH you have now is likely down to about that level "maybe" so it likely is best as it's own independent creature.

You can try to charge it all as one bank BUT be watchful, have your DVOM handy. Hopefully, you can watch the amperage during charge to see how it will decrease as they fill up and once the charger thinks it is done, then manually check the batteries.

Just to clarify, when you say the 100ah is derated due to age and usage....
It's actually the newest battery in the bank.

Age of the batteries:
UPG 100ah - (Nov 2, 2020 - 2 months old)
Might Max 35ah - (Oct 1, 2020 - 3 months old)

Just realized the Might Maxes are 35, so I actually have 205 ah total.

 

[Hedges]

30A charge current for the 100 Ah
10.5A x 3 = 30.15A charge current for 3, 35Ah in parallel.

Can't go wrong with a 30A charger (assuming the 35 Ah are wired in a manner that matches resistance of wire)
Up to 60A if split ideally, but can't be sure that would happen.

 

[Steve_S]

Just to clarify, when you say the 100ah is derated due to age and usage....
It's actually the newest battery in the bank.

Age of the batteries:
UPG 100ah - (Nov 2, 2020 - 2 months old)
Might Max 35ah - (Oct 1, 2020 - 3 months old)

Just realized the Might Maxes are 35, so I actually have 205 ah total.

Ohh, I somehow got the impression was older. No worries with that age.
As hedges put it, that works as long as your wiring is all up to snuff and nicely balanced out.

 

[BarkingSpider]

I have this great 120v fridge/freezer in my cabin, runs on 50W of power once its going, the startup surge is higher (around 300W).
Holds 24 cans of beer and all my icecream! Been going strong for 6 months now.

Amazon.com

I use it with this pure sign wave 1500W inverter that also runs my table saw. Its the only high frequency inverter I found that can handle surges up to 3000W as advertised.

https://www.amazon.com/gp/product/B074BQJH6M/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Merry Xmas!