55 Amp Converter Charge Times

MNtundraRet wrote:

otrfun wrote:
Well, decided to run a realworld, worst-case test. Discharged the battery to approx. 11.90 volts with the converter OFF. Then, turned the converter ON.

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Zero Hour:
Converter (110 volt) input current: 9-10 amps
Battery voltage (at battery terminals): 13.02 v

1st hour:
Converter input current: 5 amps
Battery voltage: 13.38 v

2nd hour:
Converter input current: 3 amps
Battery voltage: 13.56 v

3rd hour:
Converter input current: 1 amp
Battery voltage: 13.64 v

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I've noticed I usually read approx. 13.70 - 13.75 volts at the battery when it's fully charged with the converter ON, and 12.75 volts with the converter OFF and no residual charge voltage remaining. Tried reading the battery voltage in a static state with the converter OFF, but I couldn't get the residual charge voltage to subside enough by the time I made this post (continued to hover above 13 volts).

Am I correct in assuming the above "3rd hour" battery voltage reading of 13.64 volts is very close to a 90% charge?

Thanks!

Did you get to 90% charge? NOT EVEN CLOSE!

First of all you bought the wrong type of battery. The marine battery you purchased is a hybrid between starting battery and deep-cycle battery. Worse than a starting battery and worse than a deep-cycle battery.

Your 55 amp 3-stage charger is gross overkill for your single battery. As you already saw your charger never went into "Bulk" stage charging at 55 amps. For an acid/lead battery a smart charger will limit the charge rate to around C/5 (15 amp-rate for 75AH battery).

If your group 24 battery was 75AH, charged fully, dropping voltage to 11.9 volts would be a 40% charge (30 amps left/ 45 amps used).

Since you used some sort of amp-meter you must realize that the reading is a rate similar to your speedometer. If you don't go 60 mph for the full hour, you did not drive 60 miles.

Your readings only total 19 amps charging. Since the amps tapered lower each hour deducting 25% will leave the real charge around 14 amps out of the 45 amps needed.

You should have purchased a larger AGM battery capable of faster charging rates, for your purpose.

For your testing you should have taken an amp reading about 10 to 15 minutes after starting the charge. The 3-stage charger will start in "Absorption" mode (10 to 15 amps) to test the battery-bank and then go into "Bulk" mode (55 amps) if the battery(s) can handle it. You may have missed the "bulk" mode if it happened at all.

MNtundraRet, I didn't purhcase this battery. It came with my brand new toy hauler. FWIW, nearly every RV center I visited in several states during my long search for a toy hauler install these Interstate Marine/RV batteries things as OEM. I'm sure they're on par with the choices a typical TT manufacturer makes for everything else they install--which isn't saying a whole lot--lol!!

The charging current you are quoting is the 120 volt INPUT CURRENT to the converter while it was charging my battery (with no parasitic loads). As I mentioned to Tenbear, even assuming terrible converter efficiency, I would assume my battery was seeing a whole lot more than 19 amps during those 3 hours.

Again, I'm not after fast charging times, just trying to get a rough idea of how much my battery charged in those 3 hours. With all the different perspectives in this thread so far, it looks like I'm probably going to have to do it by brute force. Just see how long my battery powers my 600 watt PSW inverter under full load :)