Charge 18 volt tool battery from solar panel

 I would like to be able to charge my portable electric tools at a
remote construction site where there is no grid power or generator
available.  I seems that it would be reasonable to make a solar panel
charger for the purpose, but I have never done any work in this area.
Can anyone provide me with some ideas to get me going in the right
direction?

 
Check out this site... i believe there are chargers for larger
equipment as well.

http://solarlaptopcharger.com

 

You either have NIMH or Lion batteries. There are 4 options.

A) Inverter->charger
B) Modify existing battery charger. Can be as simple as feeding the charge
circuitry down stream of the existing transformer. For 18 volts you probably
need a 24v PV panel.
C) Procure a 12vdc operated charger. and get a 12v shunt regulator/charger
and a 12vdc panel.
D) Just plug the car charger into the truck ;)  Or even
Truck->Inverter->charger.

For the panel make sure its rated higher than the Battery capacity (C). eg:
3000mah Required current = 3A per 1 hour. I would pick 4A or greater.
You can go less than 3A but the batteries would take more than an hour to
charge.
If you want to charge 3 packs,  then its 3A X 3 = 9A or a panel rated >9A.
Thats if you have a sunny day.

FYI, most NIMH/Lion chargers charge at the C rate.

You could even have the PV charge a Deep Cycle battery that you would use to
charge the tool batteries. Great for rainy days. You would need a larger
battery (2 golf cart Batteries?) and a better charge controller. And a panel
sized for the batteries and days of autonomy.

For example: 12vdc car charger
 >>http://www.makita.com/menu.php?pg=accessory_tbl&tag=acc_chargers&cat_tag ‡&tbl=6&f=


Cheers

      Makita makes a charger that will plug into a cigarrette lighter
socket model DC1822. It is available from www.coastaltool.com for
about $60. Your best bet is to use a larger battery such as your
pickup battery that you charge with a solar panel. If that is not
convenient, you can get a portable batttery from www.xantrex.com that
can include an inverter to use your AC charger you already have. The
model Xpower Powerpack 1500 has a 60 AH battery, wheels and a handle
to make it easy to move. Several of the Xantrex models will accept
solar charging with built in charge controllers.

     To determine how much battery you need, check the AH (Amp-Hr)
rating on your electric tool battery. Now for some math! Multiply the
AH rating by the battery voltage to get Watt hours (for example 2.5 AH
and 18 volts = 45 watt-hr). Next determine how many times you need to
charge the battery on-site each day and multiply the previous result
by that number ( say you need to charge 4 times per day, 45 x 4 = 180
watt-hr). Next divide the total watt-hours per day by the voltage of
the Xantrex battery (12 volts) which results in 180 / 12 = 15 Amp-Hr
at the lower voltage. The Powerpack 1500 should be able to handle this
easily with its 60 AH rating. Keep in mind that no chargers or battery
packs are 100% efficient, so you should get at least twice the AH that
you need per day. This will prevent fully discharging the big power
pack battery which would shorten its life drastically. Now you can
just plug the Powerpack into the wall plug each night and forget the
solar!

     But since this website is all about solar, you can purchase a
solar panel to keep the Powerpack charged. The amount of solar energy
available varies from summer to winter, and from day to day due to
weather of course. On the average you can count on about 5 to 6 hours
of full sunlight per day. Remember that early morning and late
afternoon the sun is low in the sky and doesn't produce full power, so
even though it may be sunny for 10 hours a day, not all are full
power. So, a 3 Amp solar panel will deliver 3 Amps X 6 hours = 18 Amp-
Hr per day.
     Purchase a nominal 12 volt solar panel that can deliver at least
30% to 50% more Amp-Hours than you need to account for efficiency and
you are all set. For the above example I would select about a 3.5 Amp
rated panel that should deliver about 21 Amp-Hours per day. Solar
panels are often rated on power, so this would probably be about a 50
Watt panel.
     If you are using your pickup battery and don't want to walk home,
you can connect the solar panel to it using an inexpensive charge
controller, such as the Solar Controller from www.brunton.com for
about $29. Brunton sells a variety of solar panels as well including
flexible panels that can be folded for easy storage. The charge
controller is designed to prevent overcharging your battery, and it
should work with any lead acid battery including the ones by Xantrex
that do not have a built in charge controller.
     Have fun with this, and let us know how it works out.

Bob Butcher