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Old 10-25-2016, 09:29 AM   #1
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looking for a battery charger

I have installed 300 watts worth of solar panels on my rockwood minilite 2306 trailer . They work well ... when the sun shines or when we actually park in the sun . We just returned home from a six week trip , all around the northeast area of the country . I was confident that we could boondock at least half of the time and we did . I did not bring the generator because we would have plenty of battery power (two 6v interstate golf cart batteries, about 220 ah ) I assumed ...

What I learned ... Solar works fine , when the sun shines and when you don't park in the shade . If you don't park in the shade , you are out in the open and exposed, the dw does not like that . So we parked in the shade, and as it turned out when we parked in the sun we had full hookups or the sun refused to shine . It was kind of funny ! As I have read, here, the charge we get from the power converter on the trailer only gets the batteries to about 80% . Our biggest draw on the batteries is the fridge, my cpap machine and the water pump . We could go three days with no problem, without power, after that I would start to get power paranoid ( didn't want to run batteries down below 11.7v). I should have brought the generator to help charge the batteries .

Here are my questions.
While running my generator (3100w champion inverter), can I hook it up to the normal rv 30amp plug AND attach a battery charger directly to the batteries ... will I damage anything? (would it be any faster or safe )

I have read that a battery charger will do a better job of charging the batteries . The mfg of my batteries indicates that they should be charged at 15v . If I get a charger that will do that ... is 15v too much voltage for my converter (in theory ,I could pull the battery disconnect while charging the batteries )

I would prefer to use the generator as little as possible... we like to go do things and not hang around babysitting the camper while the batteries charge .
Am I asking too much ? Some suggestions would be appreciated .
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Old 10-25-2016, 09:39 AM   #2
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Good experience. I don't know where you got the impression that your converter would only charge to 80%. In fact, it will take the bank all the way up to 100%, it just takes a lot more time to get the last 15% or so since the battery fights back and the charge profile is much slower. Good converters will work fine.

You are correct in that most converters won't put out the 15 volts that deep cycle vendors specify. Trojan even quotes voltages higher than that. The problem is that most converter vendors don't want to risk damage to all of the systems that are connected to the batteries with all that voltage. My alternator is consistently over 14.3 or so, but never that high.

The best solution when you are short of sun is to run the generator to get back to 80% and then let the solar get you the rest of the way. Most good solar controllers will pulse voltages at 15 volts or so when in maintain mode. Who knows if this works?
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Old 10-25-2016, 09:44 AM   #3
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If you are plugged in or running the generator the converter should charge the batteries. With that said you can use a stand alone charger to ensure your batteries get topped off.

when on shore power or generator this is what I would do
1. Disconnect the batteries hookup your charger connect it to the outside outlet or generator 15amp 110V connection via extension cord.
2. Charge the batteries until full charge unplug the charger and reconnect the batteries to the trailer.

doing it this way the converter is powering your 12V in the rig and the charger is charging the batteries.
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Old 10-25-2016, 11:27 AM   #4
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Why does everybody think that an off the shelf battery charger is better than a 3 or 4 level converter with charge and voltage intelligence? True they are designed to be connected for days or months at a time and FR often uses wiring that is too small for the full amperage at the distance installed, but that can be fixed and it improves not only charging but 12 volt supply to the rig.
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Old 10-25-2016, 06:39 PM   #5
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Quote:
Originally Posted by ScottBrownstein View Post
Why does everybody think that an off the shelf battery charger is better than a 3 or 4 level converter with charge and voltage intelligence? True they are designed to be connected for days or months at a time and FR often uses wiring that is too small for the full amperage at the distance installed, but that can be fixed and it improves not only charging but 12 volt supply to the rig.
That is kind of one of the questions I have... Since I am only two years into this activity , I have allot to learn , thus i ask questions of people who are more experienced , of which you seem to be one . Would it be better (faster) to let my converter charge the batteries at 13.6 volts at 10 amps , or a charger at 20 or 30 amps at 14.5 volts . My thought is that the latter would be faster ... what am I missing? If this is correct , then my original question ... does anybody have any suggestion as to what kind/brand of charger should I use . If not , then your suggestion of improving the wiring is of interest to me ??? My thought is that my smallish travel trailer does not have a fancy converter and I wonder how expensive that might be .
Thanks for your input
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Old 10-25-2016, 08:45 PM   #6
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In 10 years of ownership, I've never needed a separate battery charger.
The WFCO converter has done a perfectly good job of keeping the two batteries charged up.
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Old 10-26-2016, 08:49 AM   #7
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Quote:
Originally Posted by lbmaples View Post
Would it be better (faster) to let my converter charge the batteries at 13.6 volts at 10 amps , or a charger at 20 or 30 amps at 14.5 volts .
A good (modern) 3 stage converter will charge at 14.4 volts in boost mode, dropping to 13.6 after it detects an 80% SOC back voltage until it fully charges the batteries and then drops to 13.2 (storage or trickle) from there. Some have a 4th stage that bumps the voltage back to 14.4 volts for 15 minutes every day or so to attempt to keep the battery electrolyte mixed.

Frankly, this is as good as you are going to do. Most battery chargers are more poorly filtered and will effectively give you boost and trickle stages, but they are no better than a good converter, although some might hit your system with more than 14.5 volts which can be dangerous for the loads that are connected. (Trojan specifies an occasional equalization voltage of 15.5 volts, but warns that the batteries should be disconnected from the loads during this process, which also tends to boil off a lot of electrolyte and should be closely monitored.) The converter has the 13.6 volt mode to both finish charging the batteries and to supply power to the loads in your RV while plugged into shore power.

The actual limitation is that many converters are located too distant from the batteries and wired with less that optimal gauge wire (mine are #6 or #8 at 22 feet from the bank) Since the converter only outputs these voltages on its terminals, the batteries see that voltage (and charge current) minus the voltage drop of the cabling. I have a Progressive Dynamics 9270, which will output 70 amps but with the voltage drop of the cables would only hit the batteries with 13.1 volts at 70 amps. This actually drops the maximum charge current well below 70 amps and lengthens recharge times. I have thought of using a chassis ground which would cut the loss in half, or rewiring the feed with much bigger cable.

Frankly, RV manufacturers are stuck trying to build for a given use and they assume that most RVs will remain connected to shore power for most uses. Frankly, I believe that they are correct.
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