Parallax Converter

We're hit-and-run campers ... even on our long 8-10 week trips. This means that our AGM batteries are hit with 14.XX alternator voltages for several hours when driving between destinations - so they are often getting their high voltage fix if this is in fact even needed for certain AGM batteries. Read the C&D Technologies white paper I gave the link to above to understand why certain AGM (VRLA) batteries may be just fine charged long enough with only 13.6-13.8 fixed voltages - assuming that they are in fact being brought up to full charge enough times during their lifetimes.

However regardless of what any experts say, my RV's AGM batteries (both brands I've owned over the past 11 years) WILL NOT accept any more charging current from a cold (therefore 14.XX volts) alternator once I've left them long enough on only the ~13.6 volts RV converter until the ammeter reads zero. For my situation by picking just the right AGM batteries for our RV I saved myself from having to also buy another charger/converter for the RV.

I guess this will have to remain an AGM mystery to us all.

P.S. IMHO, the optimum RV charger model series for certain AGM batteries (batteries with a 13.5-13.8 volt float spec and a 14.XX volt cycle-service spec) - would be this one from Parallax Power Supply LLC:

https://bestconverter.3dcartstores.com/assets/images/Parallax/4400/ParaMode%20TempAssure%20lit.pdf

Mex just posted this in another thread, but it belongs here too IMO.

"Or to put it in inverse fashion - the AGM will not like a straight 13.6 volt regime especially if the batteries are cycled. I pop my Lifeline every few weeks with 14.4 volts from a 13.3 float @ 26c. The battery amperage climbs to 21.2 amps then over a period of 11-minutes drops to less then 1.0 This tells me the battery is benefitting but I only do this after several weeks at 13.3 the system I have remains at 13.3 volts even with a 30+ ampere house draw....."

It seems to contradict the other advice that Phil likes. Phil does use his alternator every so often though, which must at least start of in the 14s? So maybe he is doing what Mex says and that is why his AGMs do ok.

I don't have a clue so I am just going to do what my AGM battery spec says. 14.8 for charging, 13.7 Float with the 7445, and if on a long term Float, then a shot of 14.8 or even 15.x once in a while like Mex says, and also what Mr Wizard does with his AGMs

Phil, thanks. That reminded me of this, which I had forgotten already :( Confirms your notion, para C. He did say to give them a pulse type recondition once a year even so. (A Vector portable has that feature)

(from BFL13 last month.)

" I talked to the UPG tech support about their AGM 121 battery specs and got some good info. (Very up to speed guy to talk to! )

A. 30% charging limit is to prevent venting--you can have "overcharging" from over voltage and/or from over current

He suggested two batts with a 55 amp converter.

B. Discharge is safe up to say 80a area for the 100AH (20 hr rate) but short. He says better have two batteries. He said higher discharge amps like into the 100s would be really bad for it. Don't do that.

C. Lower voltage charging is ok as it will still charge up, just take longer. It will not result in an incomplete recharge like with flooded batts.

D. He said they will stratify on a long term float but that will clear up on a recharge. No equalizing with high voltage with AGMs! He likes the pulse chargers for that job. He mentioned the CTEK 7002 that does that pulse thing. (14.8, stop, 14.8, stop, 14.8, stop is how it pulses) He likes the Vector chargers too. Recondition mode on them is that pulse thing. Don't do the high voltage Equalize with them though on an AGM

He said where you would do a recondition once a month on your flooded batts, once a year would be enough for the AGM (but do that)

E. He said when full they will still be accepting a couple amps if the float voltage is too high, but did not really say zero amps meant you were full, I suppose because you would not see that (unless you have Phil's set-up I guess)

I did not ask about the slap in the face thing mentioned before when they won't recharge fully after a few cycles. I suppose that would be incomplete cycles."

My rig's previous two 12 volt AGM deep cycle batteries were branded as Interstates - but of course Interstate doesn't actually manufacture batteries. Interstate calls the particular battery that I used - a deep cycle 12V AGM battery, model DCM0100 - a "wheelchair" battery:

http://www.interstatebatteries.com/m/category/mobility/mobility-product-line

http://www.interstatebatteries.com/p/gaymar-retec-hirider-dcm0100?dsNav=N~2147384796-2147384903

I believe that C&D Technologies made the battery that I used previously and branded it for Interstate. Here's some links on the C&D Technologies "equivalent" AGM model (DCS-100HIT) - note in the 2nd link below that the specified Cycle Service Charging voltage is 14.4 to 14.8 volts (again, no mention of this as "maximum" or "required") and that the specified float voltage is 13.5 to 13.8 volts:

http://www.cdtechno.com/product/vrla/deep_cycle.html

http://www.batteryplex.com/sheets/DCS%2D100HIT.pdf

Here's a very interesting C&D technical paper (that is my go-to authority on how I take care of my RV's AGM battereis) on charging VRLA ("AGM") batteries. Especially note Figures 14, 15, and 16 on Pages 18 and 19, along with all the text talking about them. The verbage here and elsewhere in the paper seems to imply/support that charging exclusively at the lower value of 13.8 volts is no big deal - just maybe taking longer. But since AGMs charge faster anyway at all applied charging voltages, I've chosen to live with an otherwise perfectly good Parallax 7345 and instead put my money into AGM batteries that are designed to be safely floated at around 13.6 volts:

http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

Phil, did the previous set of AGMs that you had good success with have the same specs as these?

P.S. I'd probably respond back ... "the part that I don't understand is what did you LEAVE OFF AFTER THE 14.7":

1) "Volts maximum when trying to charge in the shortest time"

OR

2) "Volts required to keep from shortening battery life"

;)

Phil, you should ask Full River. The only risk there is that they will say, "Which part of 14.7 don't you understand?" (Tee hee.)

If they do, I know where you can get an adjustable voltage charger that you can set to 14.7 and it will stay there. :) (Mr Wizard uses one on his AGMs, but at their own spec voltage of course.)

Here's the specs for the two Fullrivers I"m using:

http://www.fullriverbattery.com/product/batteries/DC115-12

14.7 volts for both bulk and absorption, and 13.6 volts for float.

But as usual, they give no reason for specifying 14.7 volts. My assumption is that this is a maximum voltage that should be used for those who wish for fastest recharge - which the manufacturer thinks that users want.

There is no hint that 14.7 volts MUST be used. :h

Phil that is clear enough, no doubt. What do your particular batts say their recharging voltage should be vs the floating voltage? (as in mine say 14.8ish vs 13.7ish)

BFL13 wrote:
I know you get yours down to where they won't accept any amps at all, signalling that they are "full." What would happen if you could then raise the voltage to 14.8? I am thinking they would accept amps again, and taper those to a "true full." Unless your particular AGM specs say otherwise?

I do that all the time: I drive the coach's AGM batteries down to zero current acceptance using only the ~13.6 volt Parallax converter ... and then start the engine and see 14.XX volts from the alternator sitting on the coach's two 12V Group 31 deep cycle AGM batteries ... at this point the AGM batteries still will not accept any more current. I see all this happening via three meters that I have on the cab's dash - a four-place voltmeter monitoring the alternator output, a four-place voltmeter monitoring the coach batteries's terminal voltage, and an ammeter monitoring the current into/out-of the coach's AGM battery bank.

The AGM batteries will not accept any more current when exposed to the 14.XX voltage coming from the engine's 130 amp alternator ... once they have been driven down to zero current acceptance by the converter.

I've never received an engineering/scientific answer within these forums (or in white papers on batteries) saying why, technically, 14.XX volts is required ... OTHER THAN it makes getting to full charge fast enough for an improved camping experience and/or it makes for a longer battery life because folks (who don't use ammeters) never wind up getting their batteries to true full charge at whatever voltages being used due to them not applying those charging voltages long enough.

You're the first person to mention the voltage versus sulphur re-migration relationship. If true for AGM batteries - then I'm slowly ruining my batteries by only taking care of them with a converter and an alternator. I replaced my last set of AGMs after around eight years "just for good measure" ... even though they seemed to still be performig well enough for a decent camping experience.

As it stands so far, our hit-and-run camping style is not affected via using certain fast charging low internal resistance AGM batteries along with only a converter and an engine alternator.