Modify Ryobi Charger for Li Battery

In this mod. we will take a P110 charger and allow it to charge the new Ryobi Lithium battery..

this will assume you are no longer using the older batteries and going with the Lithium batteries from this day forward.

This procedure involves removing the 4 screws from the bottom of the charger... flipping it over and adding 2 resistors... either 1/2 watt or 1/4 watt..

I tested this for over two weeks before releasing this to the community...

I fully discharged the battery before each test... When your one click on the battery, the Ryobi tool usually just shuts down abruptly.

OK time for the quick mod...

Step 1: Step 1. Make the Mod.

Lets unplug the charger from AC...

Get a 10K and a 39K resistor... 1/4 watt or 1/2 watt whatever is handy.

We are making a voltage divider to put Approx. 5 volts at the center connector.

Look at the charger opened up with the socket closest to you. Solder the 10K resistor from the left connector ( which is 0 volt side, black wire ) to the center connector ( white wire which goes to the SCR on the PCB) ... then take the 39K resistor and solder from the Center connector to the Right connector ( red wire + 28 volt ) .

Plug in the charger and measure to make sure you have a measurement of Approx.5.4 volts from left connector to the center pin. As long as it's at least 5 volts we're ok... over 6 and theirs something wrong... 10K and 39 K is close enough of a voltage divider to get you close to 5 volts, using common resistor values.

So now we're done... put the bottom back on with the 4 screws...

Step 2: Step 2 the Methodology Behind It

The battery has a patent number that I looked up to find the schematic. Basically the center pin when activated with +5 volts, turns the charge circuitry in the battery. The Battery sends pulses to that center connector which is connected to an scr. in the charger.. and the battery accepts the incoming voltage. Putting a meter across the Plus and minus of the connector will show the voltage changes during the charging process. The front panel green led will also blink during the charge signal given off by the battery signal to the charger.

Please note... this process to charge the battery will take at least 4 days, to get you to a full charge.

Measured current charging the battery is low, so the battery does not get warm...

Also... One more little caveat... IF you unplug the charger with the battery still in the charger, the battery which is still across the resistor will continue to blink... it still thinks its in the charger...

Pull out the battery and put in on the shelf... Ready for the weekend work.