Tuesday, October 30, 2012

Ryobi wired

Time ago I bought some wireless tools from Ryobi .
Nice tools. The "kit" included a drill and and a hand-circular saw.
For a while they worked just fine, then as expected, the batteries died.
In order to use them I have to buy new battery.

The original ones were NiCd 18V, but now there are available also Lithium ones.

The problem of course is the cost !
The NiCd new are around 30/35$ each, the Lithium are around 50$ each.
In the case of the Lithium I have also to buy a new charger. So basically an investment of ~120$.

Since I'm not using often the tools, and when it happens usually I'm at home, I looked for  a different solution.

The first idea was to change the internal batteries with a new series.
However there are two problems to follow this idea :

  • the cost of the "raw" batteries is not so distant from the original or refurbished one
  • it's a quite mechanically challenge because the way the batteries are connected
So I decided to follow another way.
Simply to create a "wired" battery ! 
In other words, the idea is to use the battery holder emptied by the batteries and connect it to  a power supply capable to drive the tools.

This modification will avoid any kind of warranty and can be potentially lethal if you DON'T KNOW what you are doing !
If you decide to do this modification the responsibility is only YOURS !

Battery holder preparation

The first step is to prepare the battery holder.
To open it, there are 6 Philips screws to remove.
The yellow cap will simply come out, exposing the batteries.
Once opened, remove all the batteries, leaving the only one  attached  to the contacts, cutting out the piece of metal soldered to the batteries.
Don't throw in the landfill the batteries ! Recycle them !
I use the Battery Solutions services for that.
The battery left attached to the contacts it is needed for the mechanical support of the contacts, don't remove it.

Simply connect a wire for the positive (originally it is  the battery itself to be connected to the contact) and put back the contacts in it's place with some glue (I used hot glue).
Then do a hole in the battery holder and connected a power outlet.
I choose one  compatible with the first power supply attempt (see below).

Of course this modification is related only to the battery holder. It is still possible to use the tool with new batteries.

Power supply  - first attempt

The first attempt is based on some articles I found on internet.
Somebody claimed to use a 18V 2A power supply from an old printer, like this one :

On eBay I did find a similar power supply, a 18V, 3.5 A switching power supply.
It didn't work as expected though.
It can drive the drill but not at the maximum speed and as soon the drill starts to really work, the power is not enough.
This brought me to the ...

Power supply - second attempt 

The second attempt is to actually build a suitable power supply.
The word to use here is "electric current", so we need a good old simple linear power supply.
In the end we need to power motors, so I started to look around and I found an old battery broken UPS from APC, the APC 500.

A UPS can be very dangerous even if disconnected from the grid !!
If you don't know what to expect and how to operate safely, DON'T EVEN OPEN IT !!!

Strip out everything and leave only the main transformer in the unit.
I put it down a classic simple power supply schematic :

The first attempt is just to obtain a decent DC voltage, no regulators or fancy stuff, just a very brute force power supply.
I was unable to find the specifications for the APC transformer, so I don't know how much current is capable to give, but at least I was able to measure the voltage, around 16 V between the yellow and white wires.
After the rectification we should have around 22V (Vpk/1.4142 - 6/1.4142 = ~22V) without any load.
Applying a load the voltage should drop a little bit, going around 18-19V, i.e. what we actually need to drive the tools motor.
Also I decided to reuse the UPC box and accessories  to contains the power supply.
I just bought two fuse holder, the capacitors (actually they are 50V, not 35V but is OK) and the 35A bridge.
Here some pictures of the UPS unit .. refurbished :)

The power supply is just perfect and is working just fine.
With no load I have a 22 Volt as predicted, value that drops around 18-19 Volt when a tool is in use.
For a normal use I don't expect to have heat problems.

I can operate now my Ryobi tools with the same battery performance.
Eventually I'll remove from the battery holder the outlet and instead I'll wire it directly for a better mechanical coupling.

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