Usually, yes — and not for the reason the spec sheets imply. Pure sine used to cost two or three times what modified sine cost, and the question was worth agonising over. That gap has collapsed: a documented 2,200W pure sine unit now sells in the same conversation as a 2,000W modified sine one. When the discount is modest, the waveform question stops being a budget decision and becomes a load-list one — and most RV load lists include at least one thing that genuinely prefers pure sine.
The honest exception exists, and it is narrower than it was: if your inverter runs chargers, a TV and things that get hot — and nothing with a motor, a compressor or a medical purpose — modified sine still works, and the savings are real. The rest of this page is about knowing which side of that line your rig sits on.
What the two waveforms actually are
An inverter’s job is turning your battery’s DC into the alternating current your appliances were built for. Pure sine units reproduce the smooth wave the utility grid delivers. Modified sine units approximate it with steps — jump to a positive voltage, hold, drop to zero, hold, jump negative, repeat.
Pure sine wave
GIANDEL publishes ≤3% THD for the PS-2200KAR — comparable to utility supply.
Modified sine wave
Krieger publishes 10–45% THD for the KR2000 — an honest number most modified sine makers omit entirely.
Those two THD figures are worth pausing on, because they are published by the manufacturers themselves and they quantify the entire debate. Three percent is grid-quality power. Ten to forty-five percent is a supply that resistive loads shrug at and rotating machinery objects to — and credit to Krieger for printing it, which is more than most of its competitors manage.
What runs fine on modified sine
- Anything that just gets hot. Toasters, coffee makers, electric kettles, hair dryers on heat. A heating element does not care what shape its power is.
- Modern chargers. Laptop bricks, phone chargers, tool battery chargers — switch-mode supplies rectify the AC immediately, so the waveform barely matters.
- Most TVs and LED lighting, for the same switch-mode reason.
If that is genuinely your whole list, the Krieger KR2000’s discount is yours to keep — and its published idle draw, under 10W, is the lowest of any unit we compared.
What suffers, and how it tells you
- AC motors — fans, some older fridge compressors, power tools with brushed motors. They run on modified sine, but hotter and louder: the buzz is the stepped waveform made audible, and the extra heat shortens motor life. Krieger’s own manual carries the list of what it advises against.
- Microwaves cook more slowly and run warmer — a cost both sides of the category acknowledge. Slower cooking also means more minutes of the heaviest load your inverter carries, which eats back part of the purchase saving.
- CPAPs and medical equipment. Most makers specify pure sine, particularly with heated humidifiers. Follow the device maker’s power specification — this is the one category where “it seems to work” is not a standard.
- Sensitive electronics with audio or measurement stages — the harmonics show up as hum in amplifiers and noise in anything precise.
The price collapse that settled the argument
The old advice — buy modified sine unless something on your list demands better — was written when pure sine carried a heavy premium. On today’s prices the gap between a documented budget pure sine unit and a documented modified sine one is modest, and it buys the waveform question permanently closed: nothing you plug in, now or in five years of ownership, needs checking against a compatibility list.
That is why our inverter roundup puts it plainly: modified sine is only worth buying when the budget is genuinely fixed and the load list is genuinely simple. Both conditions are real — they are just rarer than they were.
Deciding in one pass
- Any motor, compressor, microwave or medical device on the list? Pure sine. Done.
- Genuinely just heat and chargers? Modified sine works — take the saving, and keep the load list true when new gear comes aboard.
- Not sure what the future holds? Pure sine. The premium is the cost of never re-asking the question — cheaper than replacing a motor or a night’s sleep.
Whichever side you land on, the wattage question comes next and it is decided by your battery bank, not your appliances — that arithmetic is in what size inverter do I need.
The picks
Pure sine on a budget
GIANDEL 2200W
2,200W at ≤3% THD with a published spec table and a 3-year warranty — the price that ended the debate.
Pure sine with GFCI and hardwire
Renogy 2000W P2
The documented 2,000W unit with battery cables included and a remote in the box.
If modified sine fits your loads
Krieger KR2000
The honest version of the cheap option — it publishes its 10–45% THD instead of hiding it.
All seven units we compared — including the inverter/chargers and the dealer-network brands — are reviewed in the best RV inverters. And if you are replacing your converter at the same time, read inverter vs inverter/charger before buying either box.
Related guides
- Best RV inverters — the full comparison, with published THD, idle draw and warranty terms.
- What size inverter do I need? — the wattage half of the decision, sized from the battery bank up.
- Best RV lithium batteries — the bank that feeds whichever waveform you choose.
- 30 amp vs 50 amp RV — what shore power delivers when you are not on the inverter at all.
- The electrical section collects everything published so far.
For how products on this site are selected and what we do not claim about them, see the editorial policy.
Questions worth answering
Will a CPAP run on a modified sine wave inverter?
The machine will usually power on, but most CPAP manufacturers direct you to a pure sine supply, and heated humidifiers are the component most likely to misbehave. This is medical equipment — follow your device maker's power specification rather than a forum's experience, and when in doubt, pure sine removes the question entirely.
Will a microwave work on modified sine?
Yes, with a caveat both sides acknowledge: it cooks more slowly and runs hotter, because a microwave's transformer takes less usable energy from the stepped waveform. Add the longer cooking time to the battery bill and the modified sine saving shrinks in daily use.
Why does my fan buzz on the inverter but not on shore power?
The buzz is the waveform made audible. An AC motor fed a stepped approximation instead of a smooth sine responds to every jagged transition — heard as hum or buzz, felt as extra heat in the motor winding. It is the signature symptom of modified sine power, and it is the motor telling you it is working harder than it was designed to.
Are laptop and phone chargers safe on modified sine?
Almost always. Modern chargers are switch-mode power supplies that rectify the incoming AC immediately, so the waveform shape matters little to them. The exceptions are chargers with AC motors or transformer-input designs, which have mostly left the market. This is why a charging-and-lights load list is the one place modified sine remains a defensible buy.
Is the power from a pure sine inverter as good as shore power?
In waveform terms, often better. GIANDEL publishes 3% or less total harmonic distortion for the PS-2200KAR, and utility supply commonly carries a few percent of its own. Anything that runs correctly at a campground pedestal will run correctly on a decent pure sine inverter, sized per the bank's limits.