So there you are standing in the shade, next to a solar panel and a dead cordless drill. How do you solve this? Don’t do it: plugging the sun directly into your tool is a recipe for fried electronics.
On paper, it is a clean solution: quiet, renewable energy hovers above your head to charge your battery. Looks perfect. Real life is crueler.
To charge, power tools requires certain electrical conditions. The output of a solar panel are raw, varying direct current, which shifts in and out of shadow as clouds pass overhead. Eighteen-volt batteries in packs from companies like Milwaukee, DeWalt and Makita needs constant voltage.
Without a proper device between, mixing the two will fry electronics. The key, here, is to get your head around what’s happening between the unprocessed sun hitting a solar panel and then becoming a fully charged battery. Let’s examine this in terms of voltages and charging logic.
Power goes in. Battery holds it. Charger controls the process.
How To Safely Charge 18V Batteries With Solar Power
Why Direct Solar Charging Fails
Missing out on control step tends to be the breaking point for the battery. Most 18 volt tools uses lithium ion cells. Lithium ion cells are finicky.
They need a stable voltage, then a current taper. A simple solar panel doesn’t do that. It gives you whatever sun gives you.
Hooking it straight up to your battery runs risk of overcharging it. Chances are your battery management system kicks in to stop a fire. This is where a charge controller come in.
The Role of Charge Controllers
Do not skimp on this piece of equipment. This is your regulator between the pack and the sun. A maximum power point tracking controller adjust both the current and voltage to get most power in or out.
Don’t play Russian roulette with expensive tools. If there is no charge controller, the solar input fluctuate and the battery lack stable power. Another important thing is that the voltage must match.
Matching Voltage Requirements
When you charge an eighteen volt battery pack, it’s seldom dead-on eighteen volts. It tops out at a higher level; in a five-cell setup, it is probly closer to twenty-one volts. No way will a ten volt panel ever fill it.
Maybe with the right controller, a twenty four volt panel would of worked. Check your maximum charge voltage against the nominal voltage on the battery. If you get this wrong, the battery will not be filled up.
Size matter, Amperage equals speed. Solar panels is rated by watts, not amps. How much current does your panel produce?
Sizing Your Solar Panel
Is it sufficient to do the job? A five watt, little panel may run a light. If you trickle charge a drill battery, it will take days.
Realistically, go for something like a one hundred watt panel. That’s big enough to overcome internal resistance and push those electron along. There will be some efficiency loss.
There’s a resistance at every connection. Energy turn into heat. Twenty percent efficiency loss is typical.
Under perfect conditions a 100 watt panel may output only 80 watts. On cloudy days less. Size your system for the worst weather you expect to encounter.
Using Portable Power Stations
A unit like a Jackery or Bluetti take solar input. Output is via USB or a barrel plug, just like any other device. Sun charges the station.
Your tool charger plugs into the station. One more step. The station handle complex regulation.
Is Solar Charging Worth It
Clean energy is yours. Solar charging of 18 volt batteries are possible. But not directly.
You want an intermediate power bank or a proper charge controller. The sun is free. The hardware is expensive.
Think about how much the hardware costs and weigh it against your access to the grid. If you’re remote, it pays off. In the suburbs, it’s mainly a hobbyist project.