What's the "minimum Ah input during initial charge" of a lead acid battery

[Veek M]

http://www.agnesbattery.com/sfindustrial/stanqueen.html

For a 12V 150AhC10 battery - we charge at 10%, 15A till the voltage/cell
reaches 2.36V.

So why do we have this 'Minimum Ah input During Initial Charge' setting?
In another spec it says:

"Minimum Ah input 450% of C10 capacity" for a 200Ah C10 battery.
----
450% is something like 900Ah or 4.5 times the base Ah.. wth?

[Veek M]

Assuming he means some kind of absolute minimum charging current.. how
would that make sense because the battery starts charging at 10% of C10Ah
which is huge.. 15A..

Also, if the battery is comprised of numerous cells (12V-nominal/2.36Vpc
gives the total cells - 5 cells in series.) So 15A is the charge current
to all the cells.. ergo..

(and another Q, how does he check the per-cell voltage is 2.36V because
if they are in series.. does he just assume when he sees 12V across all
of them?)

[peterw...@gmail.com]

You need a basic lesson in Lead Acid Battery chemistry:

Terms:

Amps - the amount of current a battery can put out at a given voltage.
Volt - the energy behind those Amps above.
Amp-Hour - How much energy that battery can produce for one hour at a given voltage.
Self-Discharge - the amount of potential energy the battery loses while sitting inert.

Now, a battery is a chemical engine, in this case using lead and lead dioxide plates submerged in diluted sulphuric acid, separated into cells. The chemical reaction (exactly what that is not important) is limited by the surface area available for the reaction and the strength of the electrolyte (acid).

So, a 450AH battery is one that will deliver 450 amps for one hour before complete discharge. Such a battery will self-discharge at 22.5 AH per month. For ease-of-math, let's use one (1) AH per day. That is 42 ma per hour. So a maintenance charger would have to make at least 42 ma per hour to overcome self-discharge.

Anything more than that will (theoretically) 'charge' the battery, assuming a (partially) discharged state initially. A fully charged battery subject to additional charging (overcharge) will 'sulphate' - break down the water in the electrolyte into Oxygen and Hydrogen, increasing the acid concentration. Actual voltages are greater than 2.1 V per cell in order to initiate and maintain the chemical reaction required to reverse discharge.

Meaning that charging a battery is a balancing act.

Going through your questions:
a) Absolute minimum charging current: That which will overcome self-discharge.
b & c) Some industrial batteries have the individual cell anodes and cathodes accessible for just that purpose. Otherwise, one takes the total divided by six (6) for a nominal 12V battery. The resting voltage for a lead-acid battery is very roughly 2.1 V per cell.

Temperature Charging Voltage/Cell Charging Voltage (12V) Gassing Voltages
20 °C 2.43 to 2.53 14.58 to 15.18 2.415 14.49

Temperature: Chemistry, remember. Reactions are affected by temperature.
Charging Voltage per Cell: What it takes to initiate and maintain the chemical reaction for charging. NOT equivalent to resting voltage.
Gassing Voltage: what will initiate electrolysis in a fully discharged battery, and cause some electrolysis during the charging process. WHAT THIS MEANS: why it is that lead-acid batteries need to be checked for electrolyte status water is lost during the charging process, always, to some degree.

Lead acid batteries are not complicated, but they are also prone to abuse and failure if the basic chemistry is not understood.

Peter Wieck
Melrose Park, PA

[Jeff Urban]

Pretty good post on that Peter.

There are a few more things though. When the battery is bad it is usually a near open circuit. To restore it you need a much higher voltage and you have to babysit it unless you build a cool circuit for that. When it does not pull any charging current how can it charge ? And then sometimes you get a shorted cell.

Another thing is if it a not a gel cell you need to agitate it. Proof ? Charging a battery I kick it around a little and the ammeter on the charger goes up. That means I knocked the bubbles off the plates.

And then if you really can't get it to take a charge, (pull current) put epsom salt in it. That will restore almost any of them BUT, for one you can only do it once. If you do it again you risk a shorted cell and actually the thing might blow up. That is rare but it happens.

Another thing is the desulfater. You take 120 AC, put a light bulb in series like a DBT and hook that up for a while. A 100 watt bulb on 120 only lets a little more than one amp through, so it is safe.

The AC washes the plates, gets the nonconducting coating off them so they can work. It has to conduct or you get nothing. They actually sell desulfaters but you can do it with a light bulb. Some of the ones they sell use a higher frequency and I don't even know who to ask if that is better.

Anyway, there is no minimum charging current, it is all in how long it will take. Just to do not exceed the maximum. Charge it at 50 amps and the plates get all bent out of shape. And the thing could blow up, you know even if it can supply 50 amps it is not meant to do it all day. It can't. By the same token you cannot charge it all day at that rate.

Know what, just go to the boneyard and get an alternator from a 1970 luxury car. Get a motor and a belt. Those things look at the circuit and try to understand why the made them that way. They knew how to charge a battery.