Powermax 75 amp converter/charger

[S_Davis]

I am charging a pair of Trojan T-105 batteries, they were drawn down to 12.38 or 6.19 per battery which should be about a 30 percent discharge. The powermax is only putting out about 13 amps @ 14.68 volts, does this sound right for a 75 amp charger?


https://powermaxconverters.com/product/pm3-12v-series/

[otrfun]

S Davis wrote:

BFL13 wrote:
Have you cleared up the 13 amp mystery?

BTW, if not fitted now, the wires from the 75 amper should be #4 or you can choke off some amps. I saw that with a 55 amper that did 55 amps with #8 but did 60 amps with #4. Most converters can do a little better than their ratings given a chance.

No but I am using about 6’ of #8 which is the smallest recommended in the instructions so that could be part of it.

Agree, could be part of your problem. 6 ft. of 8 ga wiring to support 75a is certainly not ideal.

Northern Lite used 18 ft of 10 gauge wire between the converter and batteries in our camper and it dropped the max charge current of our 45a PD converter down to 18a (bulk mode with 2 GC2 6v batteries discharged to 12.15v). Installed 4/0 and 2/0 cable as part of our 2000w inverter installation. We now get the max rated charge current of 45a with the batteries discharged to 12.2v.

[S_Davis]

MEXICOWANDERER wrote:
A hydrometer dip would quickly end ouija board seance and crystal ball guesswork.

Unless you delight in "the Butler Did it" drama..

I got one and will check them, the other pair showed fully charged after sitting for a couple weeks. I am discharging them to about 50% then I will check them before and after the recharge.

[MEXICOWANDERER]

A hydrometer dip would quickly end ouija board seance and crystal ball guesswork.

Unless you delight in "the Butler Did it" drama..

[MrWizard]

My old abused (soon to be replaced GC pair)
Will take 38 amps easily
Even at 12.3 they will take 30+ amps
And the main wire run from converter to the BBC is no bigger than 8ga and might be only 10ga
I have a 1 Volt drop between converter and the GC pair up front behind the grill

[landyacht318]

I wouldn't think so.

Something's not right with the batteries or your measurement tools.

New Batteries do behave weird the first few cycles in my experience, but not that weird.

[S_Davis]

So can they be sulphated when they are new and only have 2 Charge cycles On them?

[landyacht318]

A pair of gc-2s at a rested 12.38v, which only require 13 amps to be nearly instantly brought to 14.68v, are sulfated.

If they were healthy, I'd expect it to take at least 45 minutes or more for amps to taper to that level with 75 amps of charger available seeking 14.68v.

The hydrometer will reveal the truth, and you can then ask about or search for recovery procedures which might or might not be effective, depending on how hard the sulfation is.

I've a newish healthy single group 31 TPPL AGM and 134 amps of plug in charging source, at 11.90v starting point, 134 amps was not enough to achieve 14.7v at battery terminals instantly. The breaker blew and then 'only' 94 amps still took nearly 10 minutes to bring the voltage to 14.7v at which point amps started tapering.

This is a powermax adjustable voltage 100 amp model, and low input voltage is responsible for 94 amps instead of 100. A new 12AWG extension cord and it made 98 amps. I had it in parallel with my 40 amp Meanwell for those 134 amps into a depleted but healthy group 31 TPPl AGM.

How many amps it takes to bring a battery to a certain voltage is indicative of state of charge and state of health of that battery, and the more experience with that charging source on that battery, the better.

[S_Davis]

BFL13 wrote:
Have you cleared up the 13 amp mystery?

BTW, if not fitted now, the wires from the 75 amper should be #4 or you can choke off some amps. I saw that with a 55 amper that did 55 amps with #8 but did 60 amps with #4. Most converters can do a little better than their ratings given a chance.

No but I am using about 6’ of #8 which is the smallest recommended in the instructions so that could be part of it.

[BFL13]

Have you cleared up the 13 amp mystery?

BTW, if not fitted now, the wires from the 75 amper should be #4 or you can choke off some amps. I saw that with a 55 amper that did 55 amps with #8 but did 60 amps with #4. Most converters can do a little better than their ratings given a chance.

[S_Davis]

Ok so I will give them a full charge and monitor them next week when I go back to the job site. Just for giggles I checked the other two T-105s that were charged and have been sitting for about two weeks. They where at 6.36 volts and a specific gravity of about 1.325.

[MEXICOWANDERER]

He gave the correct answer......

The BS proofer

Hydrometer

The flooded battery polygraph

[BFL13]

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.

[time2roll]

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.

[MEXICOWANDERER]

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