BFL13 wrote:
Let's not confuse charger voltage with battery voltage. You start off at battery voltage of say 12.1. It spikes to 13.x, then slowly rises until eventually hours later it (almost) reaches charger voltage and so there is no spread between them and so no more amps.
But at first, the charger is at its rated voltage such as 14.8 while the batt has spiked to 13.x. So you get lots of amps with that much spread.
(You can see during bulk stage with the battery still at 13.x that the charger is going full blast, by using a Kill-A -Watt. This shows the charger is pulling full rated watts as VA from the gen or other supply. Do not think the charger is also at 13.x but just a little higher.)
The charger is current limited, so the amps are clipped to that so you get constant amps at that limit until the battery voltage rises close enough to the charger's voltage, that the spread is too small to make that many amps, so amps taper.
The absorption constant voltage stage is mis-named because the charger is still at its 14.8 but now the amps are tapering but the battery voltage is still slowly rising--or no amps would flow.
Amps stop at the very end when battery voltage gets (almost) the same as charger voltage. Actually absorption can go to infinity, so you just have to cut it off and let the rest happen on Float.
The big thing is that the charger needs to be at 14.8 vs 13.8 right from the start, so there is lots of spread between it and the battery's voltage, AND to get the battery above "gassing voltage" for the absorption stage.
BTW, I have had my single stage 13.8v Parallax 7355 doing 56 amps at its 13.8v. I had it backing up the batts which were being drawn down by the inverter sucking 98 amps. Short fat wires so no issues about voltage sag and all that.
The converter was acting as a power supply and was able to do its rated amps no sweat. That is a completely different thing from using it as a battery charger, facing huge resistance and only able to do less than rated amps at first and tapering from there too.
So, don't get all confused.
do some voltage measuring AT the converter, in bulk mode, voltage will be the battery voltage plus line drop. the converter is in constant CURRENT mode. It supplies the current regardless of what the voltage is. (up to 14.xV) converter output voltage may be in the 13V range even with 60+A. with a single battery it may be that converter output voltage is near 14.x v due to battery internal resistance. But that is not necessarily the case with a large battery bank.
the problem with the WFCO is it often goes out of constant current mode very quickly into the constant voltage 13.6V mode which will not deliver much current.
now as the battery charges you want the current to remain constant till the battery is near 14.5V or so, then go into a constant VOLTAGE mode, and hold that voltage till the current drops to a few % of rated AH.
then drop down to the 13.6ish volts
