Adding more batteries

So I bought a 75 amp boondocker drop-in for the 55 Amp WFCO that came with my trailer. It's been working fantastic, goes immediately to 75 amps and holds the voltage fine till almost fully charged with peak voltage at 14.6 and only 180AH of AGM battery it gets there pretty fast: now the 'but'.
I've had a couple people now tell me the Boondockers taper the voltage way too soon, so I'm reviewing threads to find people who have had problems to find out what's different that breaks it sonetimes. Hi there to this thread, ?? I'm going to increase the battery capacity and I'm nervous I'll break something if there is an inherent weakness somewhere so I'm trying to to father more data.
1)I notice most people in these threads are using flooded cell golf cart batteries. Is anyone using AGM batteries and still seeing early drop off boost?
2)I moved my batteries so they are like 2 feet from the converter as part of my upgrade. I see in some of these threads that less resistance is seen to lessen the problem of early dropout. I tried an experiment of moving the battery back to the front, so like 15? foot of #6. Of course the current is less and the charging takes longer, but it still seems to be doing what it can within its limits of a maximum of 14.6 volts. It loses a maximum of 0.4 volts in line loses early in the charging cycle, but holds maximum voltage well.
The reason I am interested is that there is not enough room near the convertor for the total battery capacity I want and I'm nervous when I move things the approximate 8 foot of wire will expose some weakness and I'll have to plan on more work than just moving the batteries. I'm lazy btw.
Any more detailed insight, or other thread links, appreciated on what specifically the problem is triggered by. I'm not interested in changing the converter, please no product placements.

jharrell wrote:

brulaz wrote:

CA Traveler wrote:
From the Magnum manual:

AFAIK The current part of that graph doesn't represent the normal charging amps going into a depleted battery. As mentioned in this thread, the amps should start high and decline until float.

But I guess the Magnum does something different in Bulk, where it increases its applied V to the final bulk voltage?
Odd that they call that phase "constant current" when the voltage and current is increasing in Bulk.
Really don't understand what's happening there.

The time scale on the chart is deceiving they seem to be exaggerating the ramp up time in bulk, my Magnum 3000 ramps up to max charge current very quickly and stays there in bulk until absorbs volts are reached then switches to absorb and current ramps down while voltage is held. The Magnum ARC remote manual has better charts and info on programming the charge profiles which are very customizable including CC/CV for Lithium.

Ah thanks. That makes a lot more sense.

So, ignore the bulk current part of the graph, most of bulk (except for a brief "soft-start") really is max constant current, as expected.

We did have one good example where the PD did act almost "properly" for its rating, but most accounts seems to have the PD under-performing somewhat in the bulk stage by not holding the rated amps.

The good example was credible, and I would like to have more samples like it in case PD has made some improvements from the 9100/9200 to the 4655 and I then would have to change my thinking.

The example was posted by ah64id in 2014, but he since removed all his tracks from the forum. I guess he got annoyed about something.
( I printed his graph at the time, so I still have his data)

In his case he did proper measurements and with good wiring between converter and batteries, his 4655 on a pair of AGMs (300AH) at 50% did 56.4 amps steady for 20 minutes then slid down a bit to 56 after another 25 minutes, then to 54 amps after another 45 minutes, when battery voltage reached 14.4. Amps then tapered in the usual way for the absorption stage. That is not quite the same as holding 56.4 constant all the way, and I don't know why it didn't do that, but that is much, much better than the usual PD reported performance.

Hi BFL13,

Taper is not the correct word. More like it never gets to 14.4 volts, until the amps have dropped to about 1/4 of the capacity of the PD.

I've never seen more than 30 amps from my 40 amp unit. (with wizard)

BFL13 wrote:
PDs will stay at 14.4 for four hours when you use the Charge Wizard, so that is much better, although the amps are not as high as you should get due to a weakness in the PD design which makes the amps taper more.

jeremywatco wrote:
Thanks for the input. When I get back I'll get the batteries on the charger for a week then Pull them and test with hydrometer. While out I'll test the voltages at the converter. The converter sounds like what you describe to be normal operation. I guess I was hoping for a more bulk charging operation so when parked in shade I don't need to run genset for 5-6 hrs.

The Boondocker/PowerMax standard charging profile is not best suited for generator recharging because it drops to 13.6 for its "absorption" time instead of staying at 14.6 for a while so the amps stay higher even while they are tapering. (it would be fine if the batts are low in the morning and you do a shot of generator then go to solar for the rest of the day. But usually on solar you only get down to maybe 75% SOC overnight, so you are already higher than where that converter will stay at 14.6)

Iota is the same except it only drops to 14.2 instead of 13.6, so the amps are higher than with the PowerMax in Absorption, but still lower than they would be at 14.6 or so.

PDs will stay at 14.4 for four hours when you use the Charge Wizard, so that is much better, although the amps are not as high as you should get due to a weakness in the PD design which makes the amps taper more.

The PowerMax Adjustable Voltage models are perfect for generator charging because you just set your voltage and it stays there till you change it, so now you stay at 14.8 (say) for the whole absorption stage (or on generator, for the whole time you leave that running doing a 50-80 or 50-90.) and get the fastest possible recharge.

However, if you don't want a manual system, you would be better off with the PD and Charge Wizard, but get a bigger amp size to make up for the lower amps they do for their rated amps size.

Other adjustable voltage chargers will work too, as well as many chargers in inverter/charger units of various brands. Vector portable chargers are good at this also.

There is no simple one solution that works for everyone. (I use an adjustable voltage PowerMax for generator 50-90s and the simple 13.8v Parallax 7355 that came with the trailer for when on shore power. I could also choose to just dial down the PowerMax to 13.6 when on shore power, and ignore the 7355.)

Each RVer has to pick his own way to handle the problem.

Thanks for the input. When I get back I'll get the batteries on the charger for a week then Pull them and test with hydrometer. While out I'll test the voltages at the converter. The converter sounds like what you describe to be normal operation. I guess I was hoping for a more bulk charging operation so when parked in shade I don't need to run genset for 5-6 hrs.

jeremywatco wrote:
Would solar trying to charge at same time trick the converter?

Yesterday what I did to get my bank charged (above the 4amps it tried to charge at) was to unplug Mt solar controller, then unplug the converter. Let batteries sit for a min and then plug back in converter. It would then charge at like 25ampa for an hour or so. Did that a few times with the amps gradually tapering off. Was a pain but did the trick.

Can't tell what is going on with the converter unless you tell us the voltages at the converter's terminals at the same time as you give the changes in amps. Also we don't know the actual state of your battery bank.

You are missing the basic point that if everything is working properly, then your 220AH battery bank will only accept the 60 amps until the bank reaches about 70% SOC, when amps then taper.

If the bank is actually smaller than 220AH (most likely after two years of under-charging) then it will accept 60 amps only to say 65% SOC or even lower in SOC.

-----If the smaller size bank that will only take 60a till 65% is already at 67% and you hit it with 60 amps, then amps will immediately be lower than 60----- and start at what the bank will actually accept and taper from there. *That might be what you are seeing*.

So your Boondocker, might be working properly, but your battery bank is not as many AH as you think.

OR, something might be wrong with the converter. No way to tell with the little information being provided.

If the Solar has the battery at 14.x already, then 15 min after starting, the converter will drop to 13.6 and do fewer amps than it would at its 14.6. If the bank is starting at 60% as reported, there is no way the solar will get it up near 14.x any time soon, so that is not likely the problem here.

After getting dizzy reading those smart charger characteristics I need three fingers of Single Malt Scotch* and "they" need a rubber room and a Rorsatch evaluation.

*I don't drink

jeremywatco wrote:
Would solar trying to charge at same time trick the converter?

Yesterday what I did to get my bank charged (above the 4amps it tried to charge at) was to unplug Mt solar controller, then unplug the converter. Let batteries sit for a min and then plug back in converter. It would then charge at like 25ampa for an hour or so. Did that a few times with the amps gradually tapering off. Was a pain but did the trick.

Maybe as there are many variables. But basically if the CC and converter have the same charging profiles they play together well IF they are compatible and well designed.

I've not had your problem with my Magnum and Morningstar equipment.

Would solar trying to charge at same time trick the converter?

Yesterday what I did to get my bank charged (above the 4amps it tried to charge at) was to unplug Mt solar controller, then unplug the converter. Let batteries sit for a min and then plug back in converter. It would then charge at like 25ampa for an hour or so. Did that a few times with the amps gradually tapering off. Was a pain but did the trick.