Thought I understood LAB charging, guess I don't

[MakeMePower]

so this has got me perplex. i have a 3 stage pd92145 battery charger that can do 45 amps. it is connected to a single agm battery about 15+ feet away with roughly 6 gauge wire. there is a shunt wired in on the negative side.

chargers are cc to cv i understand this

my issue

after diagnosing a bad agm in parallel (prolly would have caught fire) it was removed leaving what seems to be a healthy agm.

charging the battery it started around 30 amps at 13.5v, this confused me as the charger was outputting 14.4, ok so it voltage drop over the wires.

but here is where im getting confused, the amperage kept dropping yet voltage was only slowing climbing. I would expect the voltage to climb to 14.4, then amperage taper by going to cv mode.

so right now its sitting at 14.1 but doing 10amps.


so to add a little more to this. i threw a 100amp load tester on the battery while it was charging. voltage dropped to 12.8 but amperage went to 46amps.

what am I missing? if it was a voltage drop due to thin wires, i should not have been able to do 46 amps.

please someone shed some light here.

 

[Browneye]

That's the internal resistance of the battery, and why they need an extended absorption time to reach full charge.
When you add a load more current flows.

The battery is never going to show the same voltage as your charge source - it might get close, but when/if it did current would stop - there's no place for it to flow then.

Seems normal to me.

Voltage drop calculator shows about a half a volt drop, or about three and a half percent:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

If you replaced your charge lead with a 2awg wire you would only lose about 200mV, or just over 1%. 13V would drop to 12.83V over 15 feet.

EDIT: Also, come to think of it, those converters are known to drop to float before you want them to. Not sure the specific charge logic, but it may well be doing that, but it seems you're able to put a DMM on it to check for output voltage. They do taper down quit a lot when the battery gets 80% - lead acid charging profile calls for a very slow charge current to reach the full 100%.

My noco charger will sit there for a day or more on the final leg.

 

[MakeMePower]

if it was the resistance, then why isn't the voltage shooting up then? I understand voltage will not match battery terminals, but why is the amperage dropping while the voltage is still low like at 13.6 volts?

i can force my charger modes, it was not dropping out of 14.4, had a meter on it the entire time.

 

[Browneye]

Because it's reaching full charge.
If you're not sure, disconnect it from the charger and let it rest overnight - measure voltage compared to this chart:

 

[MakeMePower]

Chris, I don't want to come off like I am fighting you,

but you need to help me here. the charger will push the voltage higher, if the battery doesn't want amperage the voltage will just climb. i have seen this multiple times with my other chargers, it goes to 14.4 etc then the amperage starts dropping when switching to cv mode etc?

i have never seen lower voltage and lower amperage. its now sitting at 14.2 10amp for a while now.

 

[MakeMePower]

this is what i understand

Battery charger basics | Chargetek.com

Our three and four stage chargers can satisfy your requirements. Click here or call us at (866) 482-7930.

chargetek.com

amperage goes maxxed out, until it hits voltage cutoff, then it tapers amperage, until it goes into float/storage mode. I have never seen a battery drop the amperage before the voltage reached the set point

 

[Browneye]

I understand - you don't think your battery is reaching full charge voltage, or your charger isn't putting out full charge current. My hunch is that your charger is fine and your battery may be due for replacement.

This is a PD9245 - Progressive Dynamics converter/charger, right? Some thoughts...
1. Various chargers will vary charge current, they all have a little different charge profile.
2. PD, IOTA, and PowerMax 12V converter/chargers all get owner complaints about slow charging - they all have a very mild charging profile that tapers current off to slowly charge a lead acid battery. The design concept is that the boat or RV is plugged in for the duration. It can take a very long time to reach absolute full charge, at just a trickle of current. My noco charger will run at half an amp for days before it shuts off/terminates charge. I have experience with Parrallax, IOTA, and PowerMax converter chargers, as well as a variety of 120V portable chargers, my favorite from NOCO.
3. 14.2 at 10A seems normal to me. Yes, I've seen them climb to 14.4, but I never had a meter to actually measure current. I just plugged in and let it go. Now with a lithium pack and solar charger, and smart shunt and meter, I'm a lot more conscious of all these factors.
4. As a battery ages it takes longer and longer to get it to full charge - it will sit in absorption for a longer time. Internal resistance increases. How old is this battery? It may well be due for replacement - AGM's are only good for four or five years on a good bet. A heavy FLA can go 7 to 10, like a crown, trojan, or rolls.
5. Is the charger new? Has it successfully charge other batteries or battery banks? Have you seen a degradation of charging capacity?

I still say, take it off the charger, no loads, overnight, and measure resting voltage. That will give you a pretty good gauge of your charge state.
I've lived with LAB's in boats and campers for over fifty years. They've always been a little sleepy. And if you put a heavy load on them they really sag.

 

[Browneye]

Have you read PD's charging tutorial?

Home 3 - Progressive Dynamics

The Mighty Mini Compact All-In-One System offers an AC/DC Power Distribution Panel and Inteli-Power Converter with Charge Wizard battery charging technology.

www.progressivedyn.com

 

[MakeMePower]

the agm battery is prolly 8+ years old at this point its a blue top optima. I may have saved it a bit. ( im struggling to buy another agm or go down the life path) not sure what to do yet.

I think i woke it up, from being hooked in parallel to another agm, which almost had thermal runaway. that one is being removed.

appreciate info so far. not even sure where to buy agm batteries at this point, reviews are terrible for battery's anymore. 2 years is nuts.

 

[Browneye]

I'm pretty sure that's your answer.
I've had batteries that charged fine, appeared to have full charge voltage, and as soon as you hook a load or try to start an engine you get click-click-click. LOL

Optimas are great for offroaders. Or racing boats. Otherwise they're no better than a standard flooded lead acid battery.

Autoparts stores still sell them, they're very proud of them - big $$. And for two? Ew boy.

What's the application?

My project was the Winnebago - it had two golf-cart batteries, second set in fifteen years. Put some solar panels up, then finally broke down and bought a battery tester - gravity meter. One of the six cells was reading a bit low. I pulled them out and put the NOCO on restore/equalize and it helped, but the writing was on the wall, date code was seven years. Worse, 210A lead acid is only good for half that at 50% discharge.

I was going to buy a top of the line Crown or Trojan set, then got talked into building a lifepo pack here. It's been fun.

House pack got moved inside, it's 230A, DIY with Eve prismatic cells, Overkill bms. New charger and inverter too, 600w of solar.

 

[MakeMePower]

its for an rv class c, one battery inside on out, so agm is easiest. the 230ah models with a bms are only about 100 more then the 2 agms, and it gives me the equivalent of 3 agms.

looking at Xantrex Freedom XC 2000, but also may need dc-dc charger for engine. IDK its a ton of work to reconfigure,

not sure what to do, the built in generator is on the opposite side, idk if 3 runs of 8gauge will spin the starter.

4 hundred vs 2k, idk i don't think we go enough.

 

[MisterSandals]

idk if 3 runs of 8gauge will spin the starter.

I'd be worried about whether the BMS(s) can provide enough amps to spin the starter.

 

[MakeMePower]

I'd be worried about whether the BMS(s) can provide enough amps to spin the starter.

im getting a 200 amp bms, i think they surge to 400, i doubt the starter comes past 100.

i am considering leaving in a crap 24 group flooded, and just isolate, also trying to decide if i care enough to get the alternator connected in the new place as well. we only camp for 4 days on average. if i buy a 304 size lipo, thats like 4 group 49's and i make its 2-3 days now without issue ( i do go into the 11's, but the batterys are shot)

 

[Browneye]

Lifepo not recommended for starting, build it for house loads, separate starting battery. Yes, isolate systems.

 

[MakeMePower]

how is that any different then a ac or microwave load?

 

[Browneye]

Could be twice as much current.
A 200A bms does not surge to 400-600A.

I even moved my onan 4kW over to the chassis batts.

 

[MakeMePower]

Could be twice as much current.
A 200A bms does not surge to 400-600A.

I even moved my onan 4kW over to the chassis batts.

I guess I will throw a clamp on meter on it and see what it says.

 

[Browneye]

Perhaps there's something here:

What amperage does a starter motor draw?

A good starter will normally draw 60 to 150 amps with no load on it, and up to 250 amps under load (while cranking the engine). The no-load amp draw will vary depending on the type of starter. If the amp draw is too high, the starter needs to be replaced.

findanyanswer.com

You could always drop them in there and see if your bms shuts the battery down from over-current.
In the RV circles it's been done for generator starting, but generally not recommended.

Lead-acid starting battery for the engine, and lifepo battery bank for the house loads.
Solves the alternator charging conundrum as well. Charge your lithium pack with a dc to dc charger and/or solar.

Yeah, it's all expensive. I've spent a couple of grand upgrading the motorhome systems. Everything does work just killer though.

 

[MakeMePower]

Perhaps there's something here:

What amperage does a starter motor draw?

A good starter will normally draw 60 to 150 amps with no load on it, and up to 250 amps under load (while cranking the engine). The no-load amp draw will vary depending on the type of starter. If the amp draw is too high, the starter needs to be replaced.

findanyanswer.com

You could always drop them in there and see if your bms shuts the battery down from over-current.
In the RV circles it's been done for generator starting, but generally not recommended.

Lead-acid starting battery for the engine, and lifepo battery bank for the house loads.
Solves the alternator charging conundrum as well. Charge your lithium pack with a dc to dc charger and/or solar.

Yeah, it's all expensive. I've spent a couple of grand upgrading the motorhome systems. Everything does work just killer though.

Yea it is, I had a bad mishap the other day, almost lost the rv to a fire, so this has been side barred for a bit.

yea its expensive, I spent over 500 just for a suppressor and autoformer for ac power so i hear ya.

i just don't know how much we will use some of this stuff. 6 times a year is about the most we go. and i put considerable time into the generator, so i would like to see that get run a bit as well. we have our first trip in april, with our reduced battery capacity, we shall see how it goes, although we do have ac power.