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BFL13's avatar
BFL13
Explorer II
Aug 23, 2018

What is the AGM Wall?

Mex described the "wall" one way, and LY describes it another way.

LY quote:
"My TPPL agm responds so well to the high amp recharge from a well depleted state that when I notice performance loss I intentionally drain it deeper just so that I can hit it with higher amps for longer. Odyssey AGM reconditioning procedure is to drain it to 10 volts under a high amp load and then apply no less than 40% at the 10 hour rate, until 14.7 is reached and amps taper to near zero, then repeat.

That brick wall on the amperage tends to get less too. When new the battery would brick wall at 0.0x amps, a year ago it would brick wall at 0.1 amp, now that is at the 0.28 amp area, and many solar only recharges will have it brickwall at the 0.4 amp range.

0.4a @ 14.7 brick wall indicates to me it is time for a well below 50% discharge and 65 amps applied until 14.7 is held, and 14,7 held until new brick wall established, back in the 0.2 to 0.3 range.

Your battery will be different"

A time ago, Mex said it was (ISTR) that when the amps got down to whatever (0.5 per 100 eg) showing they are full, you can crank up the voltage and get a brief jump in amps, which will then fall right back down, indicating the batts are so full, even raising the voltage won't make them accept more amps. That is the "wall" his way if I got that right.

So what is it? What does it mean for instance if the amps taper nicely,but stall at 1 amp per 100AH instead of dropping to 0.5 per 100?

Is that the "wall" and it is too high, so you need a recondition? Extra amps usually means they are going to heat.

Sometimes after bottoming out, the amps will start to rise. That is heat, and should be stopped (turn off the charger!). But what if it just stalls and does not go up or down? What does it all mean Alphie?? :(

17 Replies

  • Discharge both batteries to 12.00 volts. Charge each battery back up using 14.4 volts as a limit and NO LESS THAN 20.0 amps charge rate to start off on. Leave voltage set at 14.40 the whole time. Now what do you see as the point where voltage is at 14.40 and amperage decrease seems to "stall"? When absorbsion is working amperage will decrease as time passes. Then it decreases rapidly to around .5 to 1.0 amp.

    Example, the batteries should not diddle for hours and hours between 10 and 5 amps. Or at 4 or three amps.

    Create a diagram profile Minutes Versus Amperes.
  • So later, amps at 15.4v had risen to 3.7 and climbing. Oops!

    Felt the two 100s in parallel and one felt warmer. IR gun said one was at 29C and the other was at 44C. Oops. Disconnected the warm one and dropped back to 14.8 in hopes that battery will taper down like it should. We'll see about the other 100 later :(
  • So still stalled at 2.0/2.1 amps at 14.8v, so I jacked up the voltage to 15.4. Amps rose slowly 0.1 at a time to stall out at 3.0/3.1, no tapering from there (yet?). I will check on that later.

    Does not act like what I understand Mex's "wall" to be.
  • MrWizard wrote:
    Today, my two 100AH still in parallel have stalled out at 2.0 volts. (Instead of keep going down to 1.0 volt (0.5 each) or less.) LY seems to say the lower the better.


    do you mean amps ? where you said volts !


    Fixed that, thanks! And here I was giving that other guy a hard time about volts vs amps. :(
  • Today, my two 100AH still in parallel have stalled out at 2.0 volts. (Instead of keep going down to 1.0 volt (0.5 each) or less.) LY seems to say the lower the better.


    do you mean amps ? where you said volts !
  • Yesterday my yardstick had the 8D 6GFM250 (250AH) tapered down to 0.7a at 14.4v before I dropped the voltage to Float. It might have gone lower with more time.

    Today, my two 100AH still in parallel have stalled out at 2.0 amps. (Instead of keep going down to 1.0 amp (0.5 each) or less.) LY seems to say the lower the better. Phil says he can get his AGMs down to zero. But he is at 13.8 vs my 14.8

    (There are no other 12v draws on the batts to account for the higher amps)

    For these 100s, I smell a rat! I want to know more about the "wall", but also will investigate ( tomorrow) how each 100 acts individually, before I panic.

    Earlier this year capacity testing (10 hours at the 20 hr rate ) showed capacity was up to "as rated" in AH. Nothing happened since then to cause any worries.
  • Junk meters can cause this. This is exactly why I do not trust at face value supermarket grade shunts and three for a dollar eBay ammeters.

    Verify your shunt and meter by using a decent hand held muti-meter set to millivolts and then comparing it by checking the voltage drop across the shunt, then verify voltage of your panel meter.

    I had a bunch of cruising sailboat customers freak out when they saw me totally discredit their very expensive Cruising Equipment Co. panel meters. That is exactly when their "E Meter" superseded the panel meter.

    Wall does not mean the armor belt off the USS Missouri. Especially when dealing with weirdo variants of AGM technology. If your NEW FrankenAGM likes to stop at .67 amperes at 14.40 volts then that's where the "wall" is.

    And correct about the heat. No heating should be allowed to take place once the battery reaches max charge resistance. Do tweak the voltage. If it bounces then you have verification # 2.

    Have you performed a capacity test? Or verified new versus old impedance values? Old batteries do not act like new batteries. There's the rub.

    The trick is to get the manufacturer to issue valid test and troubleshooting values for your particular AGM battery. This is like pulling teeth. They regress into used-car salesmen grade hyperbole.

    But first get your house in order by verifying your yardstick.

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