The Solar Power Expert Blog

The Free Charge Controller v4 is Working!

by Chris - July 4th, 2012.
Filed under: Charge Controller.

My request for help to the Free Charge Controller mailing list was answered by many generous people. Donald H, a member of the group, pointed out that C2 was being overworked. Below are the results of trying different values for C2.

The gate droop issue that was plaguing the free charge controller turned out to be due to C2 being too small of a capacitance. Tim Nolan’s original design showed a C2 value of 0.1 uF, which I copied. You can see C2 in the drive circuit here:

Buck Converter composed of half H-bridge and Inductor in a buck configuration.

I want thank the many people in the group who contributed suggestions to help me fix this bug in the charge controller. A few of the people who offered suggestions were Karolina Lindqvist, Donald H, Boon, and Troy Benjegerdes.

After changing the values of C2, I took a scope image of the gate voltages on M2 and M3. Here you can see the gate droop on M2 with a 50 KHz signal:

The signal above should be a 50Khz square wave with a 75% duty cycle. However, the ‘square’ wave takes a nose dive right away.

Here is the signal again after upgrading C2 from 0.1 uF (micro farads) to 0.43 uF:

A significant improvement! There is still a significant droop on the square wave, but I was very encouraged by the improvement in the signal.

The capacitors I grabbed were ceramic capacitors. Luckily, I had another 0.33 uF cap on hand that I was able to put in parallel, to bring the capacitance of C2 up to 0.76 uF:

There is still a rounded corner on the edge, but this circuit now appears to be functional. In the future, I think the magic number for C2 is 1 uF.

This next screen shot shows the output of the charge controller. You can see that it’s outputting a steady 12.4 volts from an 18 volt input. Again, the drive PWM signal is 50Khz with a 75% duty cycle. Increasing the duty cycle would increase the output voltage.

Again, thank you to everyone who contributed to helping me debug this circuit. I know it’s difficult to help someone with a circuit when all you have is a schematic to go off of.

I’m going to continue to test the v4 prototype and report the results. I’m also working to finalize the BOM so that Jameco can begin to offer it as a kit.

5 Responses to The Free Charge Controller v4 is Working!

  1. amazing!I hope this kind of open hardware design will really drive product quality up, like OSS did with software.

  2. Hi,

    Congratulations for sorting out the problem.

    I have assembled the board with Tim Nolan’s parts but charger is always off when i connect battery and solar panel..whats wrong? Should I also use 1uF cap?

    Ashwani Sihag

  3. Hey Ashwani,

    It’s impossible to tell what the source of the problem could be for your board. I was only able to narrow down the issue with C2 with my oscilloscope and a lot of help from the group. I’d suggest posting some scope images to the group (if you have one handy).


    Chris Troutner

  4. Hi Chris,

    I have sorted off problem, it was because battery was not taking any charge. Now its fine and showing 5 amps average.

    I have modified the schematics with help of one of my friend good in charge design. Please see and suggest if I am doing something wrong. We have moved current measurement part at end of circuit and removed back current mosfets and coil(doubt on this coil removal).

    I want to send picture of schematics but no way to do that.

    Ashwani Sihag

  5. Hi Chris,

    Please find the pic at

    Ashwani SIhag

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