What Size Do I Need?
Most returns in this category are not defects. They are sizing mistakes. Five minutes here saves you a return.
1. Continuous power is the only number that matters
Every inverter carries two ratings. Continuous is what it delivers all day. Surge is what it delivers for a second or two while a motor starts. Marketing quotes surge; your appliances need continuous. Size on continuous, then check that surge covers your startup.
2. Motors need two to three times their running watts to start
A fridge compressor, a well pump, an air conditioner and a power tool all draw a brief spike far above their rated wattage. A 1,000W microwave actually draws around 1,500W running and can ask for 2,400W at startup. The common rule in the field: pick an inverter rated about twice your microwave's wattage.
3. If your RV is "inverter prepped", 2000W is usually the ceiling
Factory inverter-ready RVs feed a branch circuit wired in 14 AWG for 15 amps. That circuit tops out around 1,800W no matter what you bolt to it. A 3000W inverter on that wiring buys you nothing unless you rewire. Check the gauge before you buy the bigger unit.
4. 12V or 24V is decided by your battery bank, not by you
A 24V inverter will not run on a 12V bank, and no adapter fixes it. Read the input voltage on the product page and match it to the bank you already have. This single mismatch is one of the most common returns in the category.
5. Above 2000W, 12V starts fighting you
Power equals volts times amps. A 2000W load at 12V pulls over 165 amps from the battery; the same load at 24V pulls half that. That is why high-wattage builds move to 24V — thinner cable, less heat, less voltage drop.
6. Size the charge controller on array watts, not on hope
Controller amps × battery voltage = the maximum solar wattage it can take. A 60A controller on a 12V bank handles roughly 720W of panels; the same controller on a 24V bank handles roughly 1,440W. Doubling your battery voltage doubles the array the same controller can carry.
7. Watch the PV voltage window
Your panel string has to sit inside the controller's input range, minimum and maximum. Below the minimum it will not start. Above the maximum you damage it. Panel voltage rises as temperature drops, so check your string against the coldest morning of the year, not today's weather.
8. Cable and fuse are part of the install, not an afterthought
Undersized battery cable is the single most common installation problem in this category, and it is what turns a working inverter into a heat source. Use the gauge the manual specifies for your run length, and fit the fuse. If you are unsure what your run needs, email us before you wire it.
Still not sure? Send us your battery bank, your panel array and the appliances you want to run, at support@prestonsupply.com. We will tell you which unit fits — including when the cheaper one is the right answer.