Choice of converter for AGM batteries

Interesting info. So it looks like temperature compensation is indeed pretty important. With a 75 amp charger (like the Parallax 5475TC), and 3 batteries in my bank for 645 AH, I don't need to worry about the spec max amps on the converter, and it seems unlikely I'd every get there with the 100 Amp solar controller, so I'm covered there, right?

Direct Connection




As "Direct" As You Can Get. October test of 5-year old Lifeline, 104% capacity -- with attention paid to proper voltage for particular temperature.


The link below takes you to where you can download and store Lifeline maintenance information. A ton of it.

"Lifeline Sez" then becomes your salutation on the forum...




http://lifelinebatteries.com/knowledge-center/

Here is how I do it as learned from others on here with AGMs. Go camping run them down, do 50-90s same as with Wets, then go home.

Now you get to recharge the AGMs properly to their "real full" the specs for my AGMs say to recharge at 14.8ish and to float at 13.7ish

Everybody says the (only) way to tell if the AGMs are full so you can stop the recharge at the right time and not overcharge, is by watching the amps as they taper down to close to zip (under 1 percent of AH) and then drop to your Float voltage. After that the amps should be stable at near zero.

So how to do that? You need a charger that you can control the voltage yourself to keep it at the charging voltage and then \drop it to the spec float (adjusted for temp of course--you know the temp and there are tables for the adjustment to voltage)

And you need an ammeter to watch the amps as above. I use my Trimetric.

The other thing to watch is the spec max amps for the AGMs. Mine say 27amps per 100AH batts so with my pair of 100s that is 54 but I use my --Yes!--55 amp PowerMax ADJUSTABLE voltage charger. (so I do not use the 100 amper or I would be way over spec amps unless I had a bank of four of these things)

There is no way you can do the right thing without an adjustable voltage charger. If you do not do the right thing, your AGMs will not die in the first 5 minutes. So it is all about money--how often do you want to replace the AGMs vs how much to pay for a proper charger and an ammeter.

If your solar charger has temp compensation, use that for the final 20% of charge. The first 80% or bulk charge doesn't really require temp compensation.

You can use an adjustable power supply to manually bulk, or the cheaper Prog. Dyn. to get the batteries up to 80%; then let it drop out and leave the temp compensated solar to finish it properly.

JMO, but if I were investing this many $$$$ in a new set of AGMs I'd insist on a charger that offers temp compensation, which most converters don't. The Parallax ParaMode is one of those exceptions. :B

9280 gets my recommendation. Parallax TC is OK but a bit muted to really count. The daily boost of the PD should keep your batteries tip top all Winter.