A workshop is different from a cabin lighting circuit because several loads can be electrically quiet most of the time and then become demanding at exactly the wrong moment.
A table saw may start while the dust collector is already running. The air compressor can cycle on in the middle of a cut. A welder can add a large, rapidly changing load that does not resemble a simple motor at all.
So the design should begin with real tools and real operating combinations, not a generic table of “typical” surge watts.
1. Build a tool inventory
For each major load, record:
| Item | What to collect |
|---|---|
| Table saw / planer / dust collector | Voltage, rated current, LRA or starting data if available |
| Air compressor | Motor data, starting method, unloaded-start controls if present |
| Welder | Input current / duty cycle from the welder manual |
| Chargers / lighting | Continuous watts and expected simultaneous use |
| Future tools | Allowance for realistic expansion |
If starting current is not published, a suitable inrush measurement can be more useful than guessing from horsepower.
2. Design around the worst realistic overlap
Suppose the dust collector is already running when the compressor starts. The inverter has to supply:
Then ask the same question on the DC side:
- Can the battery and BMS supply the peak current?
- Does battery voltage remain high enough?
- Are conductors and connections keeping voltage drop under control?
- Does the inverter support that overload for long enough?
This is more useful than choosing an inverter because its “peak watts” exceed one tool’s estimated surge.
3. Inverter topology is secondary to verified performance
Transformer-based low-frequency inverters are often associated with strong surge performance, but topology alone is not a specification.
For the candidate inverter, compare:
- continuous output at the expected temperature,
- surge power and duration,
- split-phase capability if 120/240V is required,
- leg limits,
- overload and low-voltage behavior,
- manufacturer guidance for motors and welders.
A capable high-frequency design may outperform a poorly matched transformer inverter for a particular shop. Use the published envelope, not the label.
4. Battery protection has to interrupt the fault safely
Large LiFePO4 banks can supply very high fault current.
The main battery protection therefore needs more than the correct ampere rating. Verify:
- DC voltage rating,
- interrupting rating,
- fuse/breaker family approved for the application,
- conductor protection requirements,
- battery and inverter manufacturer instructions,
- available fault current for the actual bank.
Class T fuses are common in high-current battery systems, but that does not make Class T a universal requirement or establish the correct rating by itself.
5. Treat 120V leg loading and 240V loads separately
In a split-phase system, a 240V load uses both legs, while a 120V load uses one leg and neutral.
That means total inverter wattage can look acceptable while one 120V leg is overloaded.
Distribute 120V circuits with realistic simultaneous use in mind and stay within the inverter and panel ratings. Where a tool is designed for 240V, the higher voltage reduces current for the same power, but conductor sizing and protection still follow the actual nameplate and applicable code.
6. A practical shop-design sequence
- Inventory the real tools.
- Identify the largest realistic simultaneous start/run combination.
- Match that event to the inverter’s surge duration, not just peak watts.
- Check the same event against battery/BMS current and DC voltage drop.
- Design DC fault protection for the real battery bank.
- Verify split-phase leg limits.
- Add generation and storage based on daily/weekly energy use.
A workshop system becomes much easier to design once the problem is expressed as specific loads and operating events rather than a collection of generic inverter rules.
When comparing off-grid workshop power against utility-supplied electricity, our energy price reference provides official national electricity-price averages for selected countries. These figures provide general comparative context rather than specific local utility tariffs.
Use our Battery Runtime Calculator for the storage side once the load profile is known.