I have looked (albeit quickly) through some of the previous postings re battery charging. I am looking for a bit of explanation as to why these battery chargers go from super simple to super complex. (I am guessing just features, ie charging rate, charging shut off, although I struggle with this one...later coment) I have a few old battery chargers, typical automotive ones, 6 Amp and 10 Amp. The circuit board in one (10 Amp, 6v/12v) was removed several years ago (burned...given to me this way) It consists of a center tapped transformer and the primary is switched (to accomodate the slow current charge or 6v or 12 volt, I assume)
I have bypassed the cct board for testing so essentially, full wave CT rectifier and measured 12.6 volts with the primary taps I selected. I then connected a small lead acid battery (measured 9.6 volts before any charging) and the output then measured 15 volts. I expected it to increase gradually as battery charged....? Also, the ammeter in the charger indicated only about 2 amps....I expected more charging current due to differential so can someone give a brief explanation as to why voltage across battery increased immediately (meter averaging? ) and current is so low (is there a higher impedance in small batteries that limit current?)
The original cct bd was simple...cannot recall components and some were burnt beyond recognition but I am guessing a large SCR or transistor and a few small discrete components. Some of the circuits I see posted here ie Guleph cct (**broken link removed**), look quite complex. Any suggestions for a simple charging cct? Can I just switch (via Mosfet or transistor) the rectifier output to the battery till battery voltage comes up, assuming I have to stop charging to monitor voltage. This as a result of my tests today indicate that the battery voltage appears higher during charging than the actual battery voltage is? So, it becomes charge, stop and check voltage, if necessary, charge...repeat. If not necessary, just monitor voltage.....?
I have ventured into uControllers a little so thinking of using one but it seems overkill considering the original cct in this box.....and leads to including a +5 supply for it, etc, so simple gets complicated. I guess it is true that "simple problems bring complicated solutions" ....;-)
Why is overcharging protection needed?....I would think that if a charger put out say 13.8 volts, then the battery charging current would gradually decrease until virtually zero as the battery voltage approached the max of 13.8 that the charger put out....why does it overcharge? I know it does/can with out protection, but why? or is this only in the case of simpler chargers which may put out more voltage?
Looking forward to the comments.
Thanks
Cheers, Shawn
I have bypassed the cct board for testing so essentially, full wave CT rectifier and measured 12.6 volts with the primary taps I selected. I then connected a small lead acid battery (measured 9.6 volts before any charging) and the output then measured 15 volts. I expected it to increase gradually as battery charged....? Also, the ammeter in the charger indicated only about 2 amps....I expected more charging current due to differential so can someone give a brief explanation as to why voltage across battery increased immediately (meter averaging? ) and current is so low (is there a higher impedance in small batteries that limit current?)
The original cct bd was simple...cannot recall components and some were burnt beyond recognition but I am guessing a large SCR or transistor and a few small discrete components. Some of the circuits I see posted here ie Guleph cct (**broken link removed**), look quite complex. Any suggestions for a simple charging cct? Can I just switch (via Mosfet or transistor) the rectifier output to the battery till battery voltage comes up, assuming I have to stop charging to monitor voltage. This as a result of my tests today indicate that the battery voltage appears higher during charging than the actual battery voltage is? So, it becomes charge, stop and check voltage, if necessary, charge...repeat. If not necessary, just monitor voltage.....?
I have ventured into uControllers a little so thinking of using one but it seems overkill considering the original cct in this box.....and leads to including a +5 supply for it, etc, so simple gets complicated. I guess it is true that "simple problems bring complicated solutions" ....;-)
Why is overcharging protection needed?....I would think that if a charger put out say 13.8 volts, then the battery charging current would gradually decrease until virtually zero as the battery voltage approached the max of 13.8 that the charger put out....why does it overcharge? I know it does/can with out protection, but why? or is this only in the case of simpler chargers which may put out more voltage?
Looking forward to the comments.
Thanks
Cheers, Shawn
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