Should I Change My WFCO Converter?
Opinions have often been expressed, both on this and other RV forums, that most stock RV converters are inadequate to properly charge and maintain batteries and are often of poor quality. It is frequ...
Forum Discussion
"the Megawatt continues 14.8 volts with tapering amperage. What I did not know was about leaving the Megawatt set at 14.8 indefinitely, or until the generator power ceases. I had the perception that this would lead to overcooking the batteries, but apparently not if the amps do taper, which I did not know the Megawatt did."
Mike,
Amps will taper during absorption/cv stage, regardless of which charger you use. Amps taper as a result of the battery's inability to ACCEPT as many amps, as it becomes more and more charged up. So as battery soc rises, amps taper. It is not a special program in the megawatt, or in any other charger/power supply unit, for that matter. It is a matter of battery acceptance.
The reason amps stay steady during the boost/cc stage, is also a matter of battery acceptance. For example, your pair of 6's will accept much more than 40 amps when discharged down to 50% soc. (This is why you could use a 60a or even a 75a charger). Using a 40a, the 50% soc batteries can accept more than 40a, but the charger is limited to 40a, so it will remain at 40a output until such time as battery voltage reaches the Vabs setting. Then amps will begin to taper. Using a 75a, it's the same thing, but because the voltage must be higher to maintain the higher amperage, battery voltage will rise faster and reach the Vabs setting sooner, and amps will then taper.
So, let's say you can get the batteries from 50-80% with the 40a, before amps taper. The 75a will only get you to say 65% before amps taper, but you will still put more amps into the batteries, faster, because of the extra 35 amps from the start, both during boost/cc and abs/cv.
The amount of amps the batteries will accept is dependent on both battery soc AND the voltage applied. Voltage is like water pressure, and current is like water volume. Raise the pressure, and you get more volume, lower the pressure and you get less volume. Imagine if there was little to no water pressure at your house. How much water do you think would come out of the taps? Now, imagine how little current is going to flow at little to no voltage (pressure) when the converter drops from 14.4v to 13.6v. With my powermax pm4b-45, I have seen amps instantly drop more than 70% when it dropped from 14.6v to 13.6v.
Likewise, if you were to start charging when the batteries were only discharged to say 90% soc, they would not accept the full 40 amps. Rather, they would start out accepting amps somewhere below 40a, and taper from there. There would be no boost stage; unless, of course, the charger was programmed to do boost regardless of battery soc.
Once battery voltage reaches Vabs setting, amps will taper. The only way to keep amps from tapering, would be to keep raising the abs voltage setting. Once you charge a few times, and watch what happens, you will see this and understand.
The problem with converters is, they are preset/programmed to drop in voltage, once battery voltage reaches the 14.4v (or whatever) setting. So, imagine, you are charging with a 40a converter/charger, preset at 14.4v, and the batteries are accepting all 40 amps, because they are discharged enough to do so. Once their voltage rises close to the 14.4 setting, the converter/charger drops down to 13.6v, at which time, amps will drop from 40a to somewhere in the mid to low teens. So now you're charging at say 14 amps, and amps start tapering from there, instead of amps tapering from 40 amps. This is why charge time increases significantly.
Hope this helps.
Mike,
Amps will taper during absorption/cv stage, regardless of which charger you use. Amps taper as a result of the battery's inability to ACCEPT as many amps, as it becomes more and more charged up. So as battery soc rises, amps taper. It is not a special program in the megawatt, or in any other charger/power supply unit, for that matter. It is a matter of battery acceptance.
The reason amps stay steady during the boost/cc stage, is also a matter of battery acceptance. For example, your pair of 6's will accept much more than 40 amps when discharged down to 50% soc. (This is why you could use a 60a or even a 75a charger). Using a 40a, the 50% soc batteries can accept more than 40a, but the charger is limited to 40a, so it will remain at 40a output until such time as battery voltage reaches the Vabs setting. Then amps will begin to taper. Using a 75a, it's the same thing, but because the voltage must be higher to maintain the higher amperage, battery voltage will rise faster and reach the Vabs setting sooner, and amps will then taper.
So, let's say you can get the batteries from 50-80% with the 40a, before amps taper. The 75a will only get you to say 65% before amps taper, but you will still put more amps into the batteries, faster, because of the extra 35 amps from the start, both during boost/cc and abs/cv.
The amount of amps the batteries will accept is dependent on both battery soc AND the voltage applied. Voltage is like water pressure, and current is like water volume. Raise the pressure, and you get more volume, lower the pressure and you get less volume. Imagine if there was little to no water pressure at your house. How much water do you think would come out of the taps? Now, imagine how little current is going to flow at little to no voltage (pressure) when the converter drops from 14.4v to 13.6v. With my powermax pm4b-45, I have seen amps instantly drop more than 70% when it dropped from 14.6v to 13.6v.
Likewise, if you were to start charging when the batteries were only discharged to say 90% soc, they would not accept the full 40 amps. Rather, they would start out accepting amps somewhere below 40a, and taper from there. There would be no boost stage; unless, of course, the charger was programmed to do boost regardless of battery soc.
Once battery voltage reaches Vabs setting, amps will taper. The only way to keep amps from tapering, would be to keep raising the abs voltage setting. Once you charge a few times, and watch what happens, you will see this and understand.
The problem with converters is, they are preset/programmed to drop in voltage, once battery voltage reaches the 14.4v (or whatever) setting. So, imagine, you are charging with a 40a converter/charger, preset at 14.4v, and the batteries are accepting all 40 amps, because they are discharged enough to do so. Once their voltage rises close to the 14.4 setting, the converter/charger drops down to 13.6v, at which time, amps will drop from 40a to somewhere in the mid to low teens. So now you're charging at say 14 amps, and amps start tapering from there, instead of amps tapering from 40 amps. This is why charge time increases significantly.
Hope this helps.
