Battery Charger Operation

Battery Charger Operation Electric Vehicle Battery Charger Notes

Battery Charger Notes

It is pretty much common knowledge that a 6-volt battery isn’t just 6-volts but rather closer the 6.75-volts. Each cell being 2.25-volts( 6 volt batteries have three cells). It stands to reason then, that the CitiCar or ComutaCar’s battery pack is not 48-volts but rather 54-volts in a fully charged condition. That is, fully charged and not over-charged, which is possible and reduces battery life. You’ve disconnected the charger from the pack, measured the voltage with your voltmeter and it reads only around 50-volts; what gives?

Amaze and impress your friends with what you are about to learn:

The power that comes from the wall is Alternating Current (AC). See picture 1. Note that the signal is both above and below the zero line. Inside the charger is a transformer that reduces the voltage and increases the current (a future article will describe how, for now, just trust me.). It is still AC at this point and must be converted to Direct Current (DC). This is accomplished with a rectifying scheme.


Picture of Charger output signal)


Picture 2 shows a Half Wave Rectified signal, note that it is pulses above the zero line for the most part. There is a reason that not all the bottom part is gone but that is too much for this writing. Notice that the signal is now a pulsed D.C. signal that utilizes half of the original A.C. signal. half wave signal


The CommutaCar charger uses a Full Wave Rectifier to better use the incoming power by flipping the power below zero to the top, making twice as many pulses. Picture 3 shows the signal, now using the entire original A.C. signal. full wave signal


The tops of all those pulses are well above 50-volts on the Sebring charger. Your voltmeter didn’t tell you that because it does not react fast enough to detect the Peak-Voltage but rather shows you Average voltage. Picture 4 show where the average voltage would be. So how does one find the peak-voltage and set the charger correctly? Average battery Charger Output

Batteries are like big capacitors in that they will take a charge and give it back again. Capacitors just do it faster. Batteries draw less and less current as they reach that peak-voltage but it takes a long time – too long to wait to make adjustments so let’s use a capacitor. Use CAUTION!!! There is still enough power from the charger to kill you! See the disclaimer at the end of this article. We need all the customers we have so again, USE CAUTION!

Nu-Kar E.V. (and other stores like Radio Shack) carries a very common 470uf (microfarad) capacitor with a voltage rating of at least 63-volts that will do nicely for this project. Connect the output of the charger to the capacitor and the voltmeter, minus to minus and plus to plus. Check for shorts. Switch the charger ON and watch the meter rise to a peak-voltage. Now turn the charger OFF and watch the meter indication slowly fall towards zero. Now you have a sense of how long it takes to charge the capacitor and how long it takes to discharge itself through the meter. Refer back to picture 4 for the results of adding the capacitor (battery) to circuit. Turn the charger back ON and make any needed adjustments to the charger. Again, there is wall power on that relay and charger power on the case, USE CAUTION and an insulated screwdriver.

One more helpful note: If you are working on a CitiCar or ComutaCar, Sebring used a cheap potentiometer to set the voltage, it may have corrosion on it that will make it difficult to adjust. See for replacements parts and circuit boards.


Our attorney tells us we must tell you that: this is for information only; we don’t recommend doing anything yourself that you can pay someone with less knowledge and attention to details to do; electricity kills; We’re not responsible for any damage you may do to anything or yourself; Use eye protection; don’t stand on the top rung of a ladder; fast food is fattening; smoking causes lung cancer;  breathing is dangerous; everybody is going to die sometime. In other words, be careful and if you do anything stupid, we are NOT to blame.


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©2003 & 2006


Posted by Glen Stevens


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