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Old 08-13-2017, 04:18 PM   #1
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2017 25' Flying Cloud
Bushnell , Florida
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How long can I run generator to charge batteries?

We have 2000 watt Honda generator and 2 group 24 AGMs (Lifeline GPL 24T) provided by Airstream on our 2017 25 FB Flying Cloud twin. The 8355 Parallax converter appears to be 3 stage so is there a point in running the generator that could overcharge the batteries? I've run it on occasion for a couple of hours and after shutting it down the batteries settle back to the 12.6 volt range.

Thanks!
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Old 08-13-2017, 04:37 PM   #2
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Parallax does not specify the voltages for the 3 stages of charging. That said, you will not damage your batteries with several hours of charging every day, particularly if you monitor the water level weekly and top up with distilled water as needed.

The reference to damaging batteries refers to situations where the batteries are left on charge 24-7 for extended periods. If you charge your batteries and then let them rest for a couple of hours with no load on them and the voltage is 12.6 or a little higher, they are fully charged.

It sounds to me like what you are doing is just about right for your situation.

Al
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Old 08-13-2017, 05:50 PM   #3
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Hi

You have about 150 to 200 AH worth of batteries. The normal "stop point" is half those numbers. If you have a 30A converter, you would think that it all would be done in two hours. The gotcha is that you get to about 80% and then things slow down. Depending on a number of things, you might get to full charge in 10 hours, you might get there in more or less time.

Bottom line - 24 hours is a pretty good number to be "sure". That's impractical with a generator, but easy for shore power.

Bob
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Old 08-13-2017, 08:25 PM   #4
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With your parallax you won't hurt the batteries. With 2 batteries it can take well over 24 hours of charging them from 0-100 percent. Even going from 50-100 percent can take up to a day. So you've got plenty of room.
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Old 08-14-2017, 12:10 PM   #5
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My charger, progressive 4655 is charging at 14.2 volts,( shore power),,how long does it take to charge batteries? It's been 12 hrs and it's still at 14.2 volts
Also when using my Honda 2000, it charges at 14.2 volts and usually off shore power it charges at 13.8
Can someone explain why this is?
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Old 08-14-2017, 12:24 PM   #6
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Typically the RV chargers will not drop into float if there is any use of DC, any loads. You would need to know the exact specs for yours. But, that means that if you are charging with your charger and anything runs like a light, pump, refrigerator control power, etc. you will not see the voltage drop to float. I do not understand what you mean by two different voltages on your generator. You aren't running your generator while on shore power? Your PD should charge at the same voltage whether powered from shore power or the generator. Where and what are you using to measure the voltage?
Larry
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Old 08-14-2017, 01:06 PM   #7
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Quote:
Originally Posted by Spinonedad View Post
My charger, progressive 4655 is charging at 14.2 volts,( shore power),,how long does it take to charge batteries? It's been 12 hrs and it's still at 14.2 volts
Also when using my Honda 2000, it charges at 14.2 volts and usually off shore power it charges at 13.8
Can someone explain why this is?
It depends on the size of your batteries and how low they were discharged. The PD has a boost voltage of 14.4 volts IOT bring the batteries back up fairly quickly but it can take 20 hours for a single battery to go from zero to full charge in boost mode. It will take longer on 2 batteries but not double. The PD then drops down to 13.6 volts for a normal charge voltage.
It can take 12 hours to get from 50 to 100 percent in boost mode. A lead acid battery takes much longer to charge than discharge.
If you have the charge wizard dongle you can manually control the mode. So if you manually put it in boost mode you may have to change it back to normal mode manually.
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Old 08-14-2017, 01:49 PM   #8
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charging with gen and aux charger

After reading repeatedly how inefficient my '16 FC convertor is, I quit using it to keep the stock batteries charged when parked at my home.

I either:

1) take the batteries out and charge them individually with a boat/auto multi charger. This charger when charging shows voltages up to 15+ volts and can charge a 75-80% battery to 100% (according to the charger)in about 2-3 hours.

or

2)Leave them in the AS battery box and charge them both together with the same charger. It takes 4-5 hours to reach 100% with same state of discharge.

I am thinking that next time I am without hookups in a place I can run my gens (2 Honda 2000s), plug the gen(s) to the front AS port with the AS battery switch to "store" and connect the auxiliary battery charger to the batteries with the charger plugged into to the gen. If I need to run the AC, I would connect both generators and if not just use one gen.

How flawed is my logic here? The charger is a 10 amp unit at highest setting but does show charging as I said before over 15 volts as compared to 13.6 v. with stock convertor.

Thanks for any input!
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Old 08-14-2017, 02:21 PM   #9
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Whew.... lots of information to digest... best way to know when the bats are charged is to hook up a amp/voltmeter... and when it gets down to the maintenance charge.. of around 5 amps... quit... as the bats get older they won't recover as quick as they did when new... and they lose the current capability as they get older... We used to use the power drawn... times 1.5 equals the re-charge time.. but math is not some of the strong points for some... so the best advise.. get a amp/voltmeter and run the genset till you get to the maintenance charge level... which for most is about 5 amps... for each bat... once your their... done... and done
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Old 08-15-2017, 07:48 AM   #10
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Hi

Ok this is headed off in about ten different directions ....

Best way to maintain batteries in storage is a properly designed trickle charger. A Battery Tender is one, there are others. Do not ever use an automotive or boat battery charger that was designed for dead batteries. They will do far more damage than any charger in any RV. Yes, I have empirical data ....

If you are charging off a generator, gas costs something. Noise is a pain. Run the generator while you have big loads (breakfast / dinner maybe) and let it charge the batteries then. You will do better with two one hour runs, done that way than just letting it chug for two hours.

If you want to get the maximum charge into your batteries, use a temperature corrected charger. The "full" voltage varies a lot with temperature. You will fake yourself out when it's cold and cook the batteries when it's really hot.

Accept that batteries don't last forever and ever. A six year old battery probably isn't going to do a lot for you. That may be fine in one case and really bad in another case. Four years is also quite possible for a "use by" date. Batteries wear out due to charge cycles as well as age. The deeper you discharge them the fewer cycles you get. At a small discharge, you may get thousands of cycles (that's what your car does). At heavy discharge, you may get a a dozen cycles (like running them to 10 V).

Also understand that some batteries just plain are not as good as others. They vary lot to lot and manufacturer to manufacturer. Just because I get a good set from Big Bomb Batteries does not mean they will ship you a good set. Running batteries in parallel doubles your chances of a problem. If one goes bad, it'll probably take the other with it .....

Lots of variables.

Bob
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