Running Power Tools Off Solar: Inverter Size and Surge

Running a workshop off solar is very doable, but power tools ask a lot of an inverter and battery for short bursts. The trick is planning for the start-up surge, not just the running watts.

1. Running watts vs starting surge

Every tool has a running power, usually on its label. Many tools also draw a much bigger burst of current for a moment as the motor starts.

• Easy loads: lights, phone and laptop chargers, cordless tool battery chargers, soldering irons and radios.
• Medium loads: drills, jigsaws, angle grinders and orbital sanders. These motors start fairly gently.
• Hard loads: air compressors, bench grinders, table saws, drop saws and pumps. Motors like these can draw several times their running power for a moment at start-up.

2. Sizing the inverter

1. Add up the running watts of everything you'll use at the same time. Size the inverter's continuous rating above that total, with some margin.
2. Find your hardest-starting tool. The inverter's surge rating needs to cover its start-up, on top of anything else already running.
3. If an inverter trips every time a tool starts, its surge rating is too low for that tool.

A pure sine inverter is the right choice for a workshop. See Pure Sine vs Modified Sine Inverters.

3. The battery has to keep up

A big inverter is no use if the battery can't supply the current. A 2,000W load on a 12V battery draws roughly 170 to 190A once inverter losses are counted. Check that the battery's maximum continuous discharge current, its BMS and the cables can all handle it. This is a big reason workshops often use 24V or 48V. See 12V, 24V or 48V? Picking Your System Voltage.

4. How long will it run?

Most workshop tools run in short bursts, so their daily energy use is often smaller than you'd expect. Estimate each tool's running watts times the hours you actually use it in a day, then add them up. That daily total is what your panels and battery have to supply.

5. Easy wins for a solar workshop

• Use cordless tools where you can, and charge the batteries in the middle of the day when the sun is strongest.
• Run heavy tools like the compressor in the middle of the day.
• Switch the inverter off when you're not using it, to save its idle draw.
• Use LED lighting.

Looking after the cordless batteries themselves? See Cordless Revival.

Safety: in Australia, any work on 240V AC wiring, including connecting an inverter, battery or solar system to a home's switchboard or fixed wiring, must be done by a licensed electrician. Grid-connected systems also need approval from your electricity network.

Handy gear

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