Converter 3 stage charger timeline

[cdoc83]

Hey all! Wondering how long I need to plugin my travel trailer before hitting the open road to reach the trickle charge stage. I have a Power Max PM55 converter charger and two 12 volt 82 amp hour batteries in parallel. From what I've researched, it seems the full 55 amp rate is available for charging the batteries if nothing else is running, so let's assume the batteries are at 50% charge with no other loads.

I'm assuming at 55 amps it will get through the bulk charge in less then 2 hours, but I haven't been able to find how long it hangs out in the absorption charge before it switches to the float charge.

Also... does it really charge the batteries at 55 amps? If so I'm afraid my battery cables are woefully undersized (8 gauge)...

I've helped my parents with general travel trailer stuff before, but am new to having my own. Thanks for your help!

[time2roll]

Now to figure out why the battery was allowed to get so low in storage.
OK and best to just leave it plugged in if you can. Otherwise disconnect a battery cable should prevent discharge from parasitic items. Give it a boost charge every 2 to 4 months. Or even better just get it out and camp.

[2oldman]

No less than would be good.

[cdoc83]

You folks are amazing, thank you very much!!! I feel much more confident now. At the very least, I'll plug in no less then 12 hours before heading out to make sure I have a full charge. Thanks again!!

[bobndot]

I have found even if deep cycle batteries are not 100% charged, they usually still show 12.6 volts at rest if you use a volt meter which is plenty good enough for me. I know it's going to get me through the day/night until the next day when I have the options of using my generator, solar or simply driving the rig if moving to a new site.

[BFL13]

55 amps on 164AH battery bank is 33% charging rate, so expect Bulk to end at just under 65% SOC (107AH)

So you do 82-107 = 25AH at the constant 55 amps for 30 minutes to get the bank to 14.4 volts and the converter drops to 13.6 volts for the Absorption stage to do the remaining 57AH. Allow at least 8 hours.

You only need the 13.2 stage if you are not using the RV. If camping on shore power it will stay at 13.6 where you want it.

That assumes you have the basic PowerMax 55 amper that does 14.4. There are other PM 55s that have different profiles. Some go to 14.6 and some go to 14.8. Some have adjustable voltages.

On shore power you have the time for your basic converter to get the job done, so no problem. The basic one is not so good for recharging with a generator since it takes so long at that 13.6v. For a generator recharge while camping you want a charger that gets to 14.8 and stays there until you shut off the generator at say 90% SOC. Few brands/models of any RV converter can do that. (The adjustable voltage one can)

[time2roll]

Bulk will probably end at 70% charged then the 13.6 could take half a day to get close to 100%. Not sure how long to get to float 13.2 but could be a couple days. No need to wait that long to get rolling.

#8 has adequate ampacity but will cause slower charging due to voltage drop at the higher initial ampere levels during the first hour of charging.

[cdoc83]

Awesome, thank you both! The manual indicates the voltages will be 14.3 for bulk, 13.6 for absorption, and 13.2 for float. If the voltage is reading 13.2 with nothing on, is it safe to say it's reached float?

[2oldman]

I'd give it more than 12 hours.

[ScottG]

The charge tapers rather quickly. So you won't get 55 amps for the entire 2 hours. It may only charge at that rate for 15~30 minutes. (I'm sure others have a more curve but you get the point)
8 awg is indeed on the puny side.