Here's a re-post of the two main links for info and troubleshooting the PD 720Q:
PD720Q Manual
http://www.progressivedyn.com/service_d ... MANUAL.pdf
It has a troubleshooting section.
Lots of info here:
http://dave78chieftain.zxq.net/ConverterInfo.html
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That is very interesting and great that you solved the problem.
From the owner manual it seems that the charger is somewhat "smart".
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I'm posting the following for everyone who is not too sure about maintaining 12v batteries or whether they should replace their converter/charger. This is very general advice. Different batteries and different charging and maintenance profiles.
It is a good idea for all of us to periodically check the charging voltage of our chargers.
Use a good multi-meter set to DC volts and measure at the house battery when your charger is plugged in. Check with two different volt meters if you can. Sometimes they're off by quite a bit.
Take a few measurements over the course of a week.
Ideally the voltage will drop to around 13.2volts when your batteries are fully charged and your charger is plugged in. That can take a week or more. At 13.2 volts or less you can leave the charger plugged in as much as you want unless your are in a really hot climate.
If you consistently see 13.8 volts or more you run the risk of "boiling" the battery if you leave the charger on. Your battery will "gas" at that voltage. You'll have to check battery water levels often. Even more often if you are in a hot temperature climate. I would not suggest leaving your van plugged in for extended periods at that voltage unless your particular battery brand requires it. I'd use a battery maintainer instead of your on-board converter/charger for long term maintenance.
If you consistently see 13.6 volts you probably could leave your charger plugged in for extended periods if you are not in a place where the temperature is mostly over 80F. 13.6v is considered to be on the high side for maintaining most battery brands. You'll have to check battery water levels monthly probably. I think I'd use a battery maintainer instead of your on-board converter/charger for long term maintenance.
If you have a converter/charger that consistently outputs 12.8 to 13.2 volts you should be able to keep your van plugged in for long periods.
Older converter/chargers are often blamed for premature battery failure when in fact the proximate cause is lack of battery maintenance. Batteries that are left for extended periods in a discharged state lose capacity. Eventually, they'll "boil" at much lower voltages the the normal 14.4 charging voltage. I'd say it is too late for the battery then. Get a new one and take better care of it.
Often, batteries in RV's never actually get fully charged. They are charged up to about 80% and the simple battery meter in the RV says that they are "charged". That's when some people turn off the charger. At least with Class B vans we tend tend to drive more often and the batteries usually get to see 14 to 14.4 volts so they can charge.
I calculated that it will cost me $11.50 to keep my 4 batteries on a float charge of 13.2 volts for an entire year! That is much better than letting them sit for extended periods in a discharged state.
Just my opinion here. It got a little long and off topic..........