What charge controller for a 12v 35ah AGM battery?

[DLorien]

Happy Holidays Everyone,

Ok, before anyone flames me for not reading other posts...I did read many of the posts. The discussions just weren't specific enough to my needs. BUT, if there was a discussion, by all means, point me to it and I'll read it over.

I just purchased an Instapark 50w solar panel and a Sunforce 60031 10a digital charge controller (they're on their way now). I'm planning on purchasing/upgrading to around 300w of solar panels but for now, 50w should do me fine. I will be using the battery to power a CPAP machine so I can sleep in my van when I go camping. Something I used to enjoy until I was diagnosed with sleep apnea. The machine doesn't say exactly how many amps are used because it varies with the needs of the user while they sleep. I tested my machine on the battery and got a good 5 days out of it before the battery voltage got too close to 12v for my comfort. I probably could have gone a few more days, but my guesstimate is that I consume about 4-5 ah per night, or roughly 0.5-0.7 ah.

I didn't find any info from Sunforce regarding this controller and AGM batteries. Then I found a random post somewhere that said not to use a regular charge controller with AGM batteries unless it specifically states it works with AGM batteries. Well, now I'm in a pickle.

When fully charged and rested, my battery reads 14.95v on my meter, which is a 12v 35ah AGM. The only charge controller I see people talking about are the Morningstar Sunstar MPPT. This seems like an overkill for my needs. Is there anything else I might look at? What are your recommendations?

[Sunking]

When fully charged and rested, my battery reads 14.95v on my meter, which is a 12v 35ah AGM.

That would be a severe over charge and almost impossible so I suspect your meter is way out of calibration or just entirely inaccurate. A rested AGM battery should read 12.7 to 12.8 volts for 100% full charged. At no time during the charge process should you ever reach 14.95 volts on an AGM battery. The highest voltage you should ever see during the Absorption Charge is 14.4 volts under normal operating temps. Only in extremely cold weather would you ever go above that.

As to the question of Charge Controllers any decent CC will have a switch option to select Flooded, AGM, or God forbid a Gel battery. Whoever you are getting your info from should be ignored as they do not know WTF they are talking about. For AGM you should be using a Temp Compensated controller. Any CC with temp compensation has an AGM setting.

[PNjunction]

The Sunforce 60031 is not agm specific, although mine when I started out hit absorb at 14.6v, and float at 13.5 during balmy 70-degree day. That wasn't too shabby considering that the specs on the 60031 are kind of loose: absorb 14.4 plus/minus 0.4v, and float 13.5 plus/minus 0.4v. I measured mine on a Fluke 85, and also used them to charge agm's. So yes it will work with the agm, but you are taking the chance that the unit you get might be at the end of the acceptable ranges, and may exceed the rating of your battery - especially without temperature compensation. Why not start out right and move up a notch in quality with a simple Morningstar.

While the 60031 has temperature overload protection, it does not have any sort of temperature compensation - I'd suggest starting out right with at least a unit that has ambient compensation, although terminal temp monitoring is the best. The digital display on the 60031 can also be inaccurate - my unit with plus 0.3v high so it only served as a rough indication of the process - I broke out the Fluke meter to do any real DOD determinations. Had I relied on the internal voltmeter, I might assume I had only drawn down to a 25% DOD, when in reality I was down to 50%. Big difference!

Sounds like you have a nice fresh agm. When at REST (ie, measured after 4 hours no charge/discharge) a previously charged agm would read about 12.9 to even 13.05 volts with a surface charge if it was recently manufactured. However, that voltage drops down immediately to about 12.8v or so when even the smallest little load was placed upon it or left alone for a few days when the surface charge went away. At least all my fresh ups-style agm's, Odysseys, and Cyclon agm's do that when charged with a variety of quality charging equipment.

I'll bet you meant 12.95 volts when at rest, and not 14.95 volts right?