Powermax 75 amp converter/charger

He gave the correct answer......

The BS proofer

Hydrometer

The flooded battery polygraph

My ugly graph says starting at 70 amps, by 72% SOC he should be seeing 55 amps and tapering. He would not see 13 amps until around 88% SOC

So he is right that something is out of whack.

BFL13 wrote:

time2roll wrote:
13 amps is fine if you have 14.68 volts. This is why I recommend a smaller PowerMax with just two batteries. 35 amp would be fine.

That's if you don't mind another hour of gen time to do a 50-90 per my ugly graph above. And if the campground gen hours let you. Of course on shore power you don't care about the time it takes.

Then there is the dreaded 20% charging rate in Bulk for AGMs so a 35 amper being 20% means the bank is 175AH or less. The OP does not have AGMs though.

I did find that low and slow was how to recharge Marine/RV batts to true full, which don't like a high charging rate. But you have to maintain the low amps and keep charging till they reach 16v. Now the hydrometer says you are there and can drop to float. No wonder people have poor luck with those things using a 14.4v converter :(

OK and within a few minutes the OP is down to 13 AMPS into the FLOODED batteries. 75 might shave a few seconds.

Yes a battery with lower internal resistance such as AGM or Lithium will charge at a higher rate and charge faster on the 75 amp converter. Trying to relate to the OP's situation.

From above:

S Davis wrote:
The initial readings are within a min or two of hooking up the charger so I thought at 30% discharge the batteries would be accepting more amps.

A precision 10 ppm zener diode can be used as. A go no-go tester. Need an adjustable power supply and No Meaning Zero ripple

time2roll wrote:
13 amps is fine if you have 14.68 volts. This is why I recommend a smaller PowerMax with just two batteries. 35 amp would be fine.

That's if you don't mind another hour of gen time to do a 50-90 per my ugly graph above. And if the campground gen hours let you. Of course on shore power you don't care about the time it takes.

Then there is the dreaded 20% charging rate in Bulk for AGMs so a 35 amper being 20% means the bank is 175AH or less. The OP does not have AGMs though.

I did find that low and slow was how to recharge Marine/RV batts to true full, which don't like a high charging rate. But you have to maintain the low amps and keep charging till they reach 16v. Now the hydrometer says you are there and can drop to float. No wonder people have poor luck with those things using a 14.4v converter :(

time2roll wrote:
13 amps is fine if you have 14.68 volts. This is why I recommend a smaller PowerMax with just two batteries. 35 amp would be fine.

Ok thanks, I have a total of four but only use a pair at a time until I get the rest of the charging system done and the inverter installed.

Thermoguy wrote:
Just a point so you aren't chasing your tail. All meters are not 100% accurate. Even a Fluke Meter (often referred as the industry standard) can be off and need to be calibrated. Low batteries can cause inaccuracies, etc. So, most important for calibration is repeatability. That means if I take a measurement and I come back the next day, I should be within 2% or 3% or whatever the accuracy of the meter is. Just a point for anyone reading, cheap meters are just that, cheap. They can be off by 5% or more as standard accuracy. Each of my meters were $400 - $600, not cheap.

Good point, I am a HVAC/R tech and recalibrate my meters regularly.

13 amps is fine if you have 14.68 volts. This is why I recommend a smaller PowerMax with just two batteries. 35 amp would be fine.

Just a point so you aren't chasing your tail. All meters are not 100% accurate. Even a Fluke Meter (often referred as the industry standard) can be off and need to be calibrated. Low batteries can cause inaccuracies, etc. So, most important for calibration is repeatability. That means if I take a measurement and I come back the next day, I should be within 2% or 3% or whatever the accuracy of the meter is. Just a point for anyone reading, cheap meters are just that, cheap. They can be off by 5% or more as standard accuracy. Each of my meters were $400 - $600, not cheap.

BFL13 wrote:
Good that it is 14.68 :) so see my note above re the 13 amps.

You can run more 12v loads as a test. If the battery is still accepting 13 amps on the battery monitor, and those loads are running ok, then the converter must be putting out more than 13 amps which the loads are using.

There are no loads on the bank when charging and I am using fluke digital meters for my volt and amp values. Maybe you are right and the batteries were at a higher state of charge, I was going by the Trojan specs. I will get a meter and check specific gravity.