agm battery charge issue

[LittleBill]

what would cause a AGM battery to reduce its charging amperage, without the voltage reaching the set voltage cutoff in a CC mode stage of a charger

example, battery is at 13.6 yet a pd9245 in boost mode 14.4 confirmed, is tapering amperage

put a load on the battery down to 12.8 and its pulling the full 45 amps.


3 hours later its sitting at 14.4 doing 3 amps.

thoughts?

[LittleBill]

time2roll wrote:

LittleBill wrote:
yes but the v drop changes depending on amperage, it was doing 10 amps at 14.1. v drop doesn't remain static.

Yes that is the nature of resistance. The more amps the more voltage drop.

Eventually the amps will drop to zero and the converter output and battery will be equal voltage.

Need to address the resistance with an improved battery connection, fatter wire or move the converter close to the battery. Or all three.

Been through all this over the years.

yes but this is not the concern

v drop and resistance are the highest at low voltage yes?

at 12.8v at the battery it was putting out 46amps.

resistance goes down as amperage goes down right?

and on that same path voltage drop lessens. right?

so my problem should be going away as the battery comes up to charge, not making it worse.

my issue and my confusion, again is around 13.6v at the battery. PD is doing 14.4, but the amperage is going down around 20amps and still tapering, PD should be cranking the amperage up to get to 14, but its not doing it.

according to voltage drop calcs, v drop is cut in half during this.

I have never seen a charger cut its amperage before getting the voltage up to its cut off point. I can force and confirm the pd never left 14.4 at the converter.

[time2roll]

LittleBill wrote:
yes but the v drop changes depending on amperage, it was doing 10 amps at 14.1. v drop doesn't remain static.

Yes that is the nature of resistance. The more amps the more voltage drop.

Eventually the amps will drop to zero and the converter output and battery will be equal voltage.

Need to address the resistance with an improved battery connection, fatter wire or move the converter close to the battery. Or all three.

Been through all this over the years.

[BFL13]

LittleBill wrote:
i think you missed what i said. the voltage is not rising above 13.6 yet the amperage is tapering.

the meter output of the PD is confirmed 14.4 during this.

there are no other loads, everything is off.

You said it finally got to 14.4 at 3 amps in the OP, not being stuck at 13.6

But what was "it" ? Very confusing. Please take longer and provide a complete blow by blow on what you saw. At the converter and at the battery with meter readings vs converter settings if that comes up.

It is a mystery as it stands.

[LittleBill]

CA Traveler wrote:
As stated the wire is to small and/or to long for optimal charging. AND this can include the negative wire.

The 48A from the charger first goes to the loads which is 48-14A=34A and 14A into the battery from your numbers.

You can also check for the PD recommended wire size per the distance and compare that to your wire size. And as stated the connectors etc could also be part of the problem.

there are no loads. if voltage drop was the issue, wouldn't it would increase as the amperage goes up? thus somewhat limiting it?

it seems odd to me it can do full amperage at a lower charge. but then the voltage loss causes it not to correctly charge at like 90% full. IDK seems off to me. maybe i need to run some calculators.

at 5 amps the voltage is 14.4, the wiring has been replaced.

[CA_Traveler]

BTW If your OEM charger has been replaced the wiring should be a big red flag. :R :h

[CA_Traveler]

As stated the wire is to small and/or to long for optimal charging. AND this can include the negative wire.

The 48A from the charger first goes to the loads which is 48-14A=34A and 14A into the battery from your numbers.

You can also check for the PD recommended wire size per the distance and compare that to your wire size. And as stated the connectors etc could also be part of the problem.

[LittleBill]

time2roll wrote:

LittleBill wrote:
if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

Because the drop is 0.8 volts. When the battery is pushed down to 12.8 the converter is pushed down to 13.6 (or at least well below 14.4) and goes to full amps.

yes but the v drop changes depending on amperage, it was doing 10 amps at 14.1. v drop doesn't remain static.

[time2roll]

LittleBill wrote:
if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

Because the drop is 0.8 volts. When the battery is pushed down to 12.8 the converter is pushed down to 13.6 (or at least well below 14.4) and goes to full amps.

[LittleBill]

time2roll wrote:
If the PD output is 14.4 and the battery terminals are 13.6 as measured by the same voltmeter.... there is resistance in the connection between the two. Could be the wire, a connection, fuse, breaker, switch, relay etc. Keep poking along the path until the differential is found. Clean, replace, repair or adjust that item. Some difference might be normal but 0.8 volt seems big at less than 45 amps.

if that was the case how come when i put a load on it, it drops to 12.8 and the full 48 amps from the charger is going into the battery at 570w vs 198w at 13.6 plus whatever amps equals that

[time2roll]

If the PD output is 14.4 and the battery terminals are 13.6 as measured by the same voltmeter.... there is resistance in the connection between the two. Could be the wire, a connection, fuse, breaker, switch, relay etc. Keep poking along the path until the differential is found. Clean, replace, repair or adjust that item. Some difference might be normal but 0.8 volt seems big at less than 45 amps.

And yes if the voltage on the battery terminals is just 13.6 volts the amps will be tapering at about 70%+ charged.

[Skibane]

LittleBill wrote:
i think you missed what i said. the voltage is not the meter output of the PD is confirmed 14.4 during this.

Are you sure that it's measuring the actual output voltage right now, or is that just the voltage that your PD is set to terminate the charge at?

[wa8yxm]

AGM's are Lead Acid. same as Flooded wet. Only more expensive and a few other things I won't bother with.

The PD tapers off when recharging Lead Acid batteries..
Ideally a 9245 would push 45 amps till it's like 90% then taper off rapidly but many people have shown that's not how it works.. It tapers off almost from the instant it starts.. Now.. as it happens I know why it does that but. Beyond this post.. And the folks who did the testing explain it rather well.

Here is part of it
Charger (PD9245)------ Wire----(Also known as a low value resistor)------- Battery.

As the battery charges the difference in voltages between the PD-9245 and the battery is reduced. as current = Voltage/Resistance. the wire leads cause (both inside and outside the converter) cause the charge rate to slow.

NOTE that the only convrters that do not do this are very expensive with "Remote Sense" leads (two sets of leads that connect to the battery one heavy (Charge) and one light weight (Sense) the Sense leads read the voltage AT THE BATTERY.

I've never seen one save on paper.

Source: Other threads in this very collection of Forums.
I do not have links.

This is what the salesman says happens: https://www.progressivedyn.com/rv/charge-wizard/

Alas I could not quickly find a link to what does happen.
But it's not square corners. it's more a smooth curve.

As I said. it was heavily discussed on one of the boards here. a few years back.

[LittleBill]

i think you missed what i said. the voltage is not rising above 13.6 yet the amperage is tapering.

the meter output of the PD is confirmed 14.4 during this.

there are no other loads, everything is off.

[BFL13]

It is normal for the battery voltage to rise during the absorption stage while amps taper. This occurs at different SOCs depending on the charging rate. You could be seeing the Absorption Stage starting earlier than you expected.

If the charging rate is with high amps you can have voltage drop between charger and battery so the battery voltage is lower than the charger's. As amps taper this difference in voltage becomes less as battery voltage rises.

Some PDs are not very good at constant amps in the Bulk Stage for whatever reason (Salvo used to complain about that with graphs to show it---however one guy here showed his graph where his did constant amps ok)

And as you note, with chargers it is loads first battery gets what amps are left over, so you might have had a load come on for a while that you were not aware of.

Not likely anything wrong with the AGM without more evidence IMO.