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Old 07-30-2009, 07:27 AM   #1
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Cabin John , Maryland
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Low voltage... converter or battery problem?

First, thanks to everyone for the excellent help in my previous thread about battery types.

Now, here's what I've got:
'07 Interstate with Varta flooded group 27 100Ah that didn't see a lot of shoreline charge time for the first 2 years (my own fault, lesson learned) getting the occasional charge by running the generator or the engine alternator. 7355 parallax converter, no timer option that I know of. (panel says "option B", not sure what that is... spec sheet says option T is the float charge timer). I have used a 400W inverter (and hope to do so again in the future) for running a 15" LCD without running the generator, but stopped when my uinverter started regularly giving me low-voltage warnings.

Here are the symptoms:
- Battery voltage (measured on the terminals, disconnected via solenoid) was steady at ~8V even after several nights plugged in to a 15A circuit via shoreline.
- I recently topped off the battery water level, and it was never below the plates.
- Converter output voltage (measured from the panel front when connected to a shore line with just cabin lights turned on) is around 13V, not 13.5-14 as expected for charging.
- After a weekend connected to a shoreline, folllowed by a few more hours at home connected to AC I got the disconnected battery to measure 10.5V, but could watch it drop by 10 mV per second or two, presumably headed back to the 8V I measured previously.
- All systems/appliances work fine when connected to shoreline, 12V systems work fine off the engine alternator when the engine is running, but 12V systems suffer under the low battery voltage when the engine is off and shoreline not connected.

Here's what I'm trying to figure out:
- Is the battery salvagable, or is it trashed already? My prior lack of understanding of proper charging has lead to this for sure, but is it too late to save it?
- Is the converter outputting a proper voltage for charging?
- Since the battery is (very inconveniently) mounted under the passenger's seat, and an AGM would eliminate PITA electrolyte level checks that can require removal of the seat, does the 7355 converter without the timer option provide the appropriate output for the AGM type batteries?

Thanks in advance, this forum is nothing short of amazing!
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Old 07-30-2009, 07:34 AM   #2
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It sounds like the battery is bad. You could pull it and take it to a store with a tester to get that verified. AGM batteries have the same charging profile as your standard lead acid battery, so no changes should be required if you decide to go that route.
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Old 07-30-2009, 07:52 AM   #3
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Not sure about the converter but the 12v reading may be from the battery operating on the maintain rather than boost phase. If that's the case not sure why it is not charging at the high rate.

I suspect the main culprit is the battery though. At least that is what to check out first. A battery at 10.5 v is a fully discharged battery. Disconnect the battery and put a separate battery charger on it. Give it enough time to charge, then check it. Next put a load tester on the battery. If you don't have one auto supplies often will be able to test.

If you decide on going AGM make sure the battery is compatable with your converter.
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Old 07-30-2009, 08:39 AM   #4
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Quote:
Originally Posted by azflycaster View Post
AGM batteries have the same charging profile as your standard lead acid battery, so no changes should be required if you decide to go that route.
I had heard they are more "particular" about voltages and/or sensitive to overcharging? I'm concerned b/c my converter does not out have the timer that drops back the charge voltage after 13 hours, like the higher-end one does.

Quote:
Originally Posted by Lumatic View Post
Not sure about the converter but the 12v reading may be from the battery operating on the maintain rather than boost phase. If that's the case not sure why it is not charging at the high rate.
The spec sheet on my converter is here (pdf):
http://www.parallaxpower.com/7300/7300pwrcntr.pdf
It's the straight 7355 version. I'm not really clear about what voltages I should be seeing at the converter connection to the panel, with and without the battery connected, and whether or not I need to open the converter or disconnect it from the panel to accurately check its output.

I have an appointment at the AS dealer in two weeks to get the battery checked and maybe replaced, and the converter checked, but I'm trying to beef up my BS detector and be able to ask the right questions.

I'm seriously considering an AGM, since removing the seat is a rediculous PITA for regular checks of electrolyte level, but I'm a bit concerned that my converter is too "basic" to handle the battery, given what I've heard about higher risk of overcharging damage, etc.
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Old 07-30-2009, 10:14 AM   #5
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AGM batteries and 3 phase chargers

Quote:
Originally Posted by azflycaster View Post
AGM batteries have the same charging profile as your standard lead acid battery, so no changes should be required if you decide to go that route.
I only know what I have heard which is particular brand AGMs are more compatable with certain converters which has an effect on battery life. A good person to get it from the horse's mouth would be Randy at something or other Converter, I forget. He is a forums member and a vendor. Somebody jump in and post his contact info. I will probably remember as soon as I hit the reply button.
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Old 08-22-2009, 10:24 PM   #6
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Three weeks later:

You are referring to Randy at bestconverter.com
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