I've been handling generator service and sales orders for eleven years. In that time, I've personally made and documented 12 significant mistakes, totaling roughly $47,000 in wasted budget. The first big one involved an 800 kva SDMO generator that should have never left the dealer lot. The most embarrassing one involved an Onan generator fuel filter that I ordered entirely from memory. Both taught me the same lesson: assume less, verify more.
This isn't a sales pitch. It's a confession with a checklist at the end. If it saves you one service call, the story was worth telling.
It Started With an 800 kva SDMO Generator Quote
In March 2023, a cold-storage client was expanding their facility. The electrical contractor said they needed a serious standby plant. Within a week, I had a quote on my desk for an 800 kva SDMO generator—a 640 kW-class unit, roughly the size of a small delivery van. It looked impressive. It wasn't.
Something felt off. My gut said the contractor had multiplied the calculated demand by 2.5 just to be safe. The numbers, however, came from the contractor's spreadsheet, and I chose to believe them. So I sent the proposal. That was the mistake.
The 800 kVA unit arrived on a flatbed. It needed a bigger concrete pad, a 2,000-gallon fuel tank, and a crane lift. The delivery alone took two days. Then the commissioning test failed. Not because the generator was bad, but because it was too big for the actual load. The engine couldn't reach operating temperature under a 4% load. We spent three weeks fighting warning codes and wet-stacking symptoms.
The 'bigger is safer' thinking comes from an era when diesel was cheap, loads were simpler, and a lightly loaded engine could be cleaned out with a monthly full-load test. Today, with EPA Tier 4 emissions systems and electronic controllers, an oversized diesel can fault out before it ever helps you.
Why does this matter? Because oversizing isn't harmless. It increases purchase cost, floor space, fuel consumption, and maintenance. It also makes the unit less reliable exactly when you need it most.
I finally called in an electrical engineer. The steady-state load was 41 kW. With the new compressor's starting surge, it hit 62 kW for about ten seconds. We didn't need 800 kVA. We didn't need 100 kW. Actually, we needed a 45 kw SDMO generator with some margin. Right-sizing meant a 45 kw SDMO generator with a temporary load bank test.
The 45 kw SDMO generator was about a third of the footprint and burned a fraction of the fuel. It handled the load. It still does today. The 800 kVA unit went back to the rental fleet, and the client paid a restock fee that I swallowed on the job's profit. That's where my $47,000 number starts.
The Fuel Filter That Made Me Look Stupid
A month later, I was back in the shop when a tech called about a small generator at a telecom site. It was a 15kw inverter generator—an engine-driven unit with an inverter module that produces clean power for sensitive radios. It kept stalling. I told him I'd bring a fuel filter.
I checked the engine model, remembered an Onan generator fuel filter we'd stocked for years, and grabbed one by memory. The tech installed it. Fifteen hours later, it stalled again. The filter had clogged. Turned out the thread pitch was close, but the micron rating was wrong. There are at least three Onan filter part numbers that look identical on the shelf.
I assumed 'same brand' meant 'same part.' Didn't verify. That $18 filter cost about $900 in labor, a rental thermal camera, and an after-hours site visit. The comment that stung: 'Did you even look at the nameplate?'
Here's the thing: every part number needs to be verified against the generator nameplate. The engine model is not enough. The gen-set model is not enough. You need the part number for that specific build. It was a simple, expensive lesson.
Then a Customer Asked: What Is a Solar Generator?
The same week, a different customer asked a question I get a lot now: 'what is a solar generator?' They were considering one instead of the diesel unit we'd recommended. I had to explain—without making them feel silly—that 'solar generator' is marketing shorthand for a battery, an inverter, and solar panels in one box.
A solar generator stores energy and converts it to AC power. It has no engine, no alternator, and no fuel system. For a small office or a single server rack, it can be a reasonable choice. For a pump, a chiller, or any motor-starting load? Not so much. The energy math doesn't work: a 45 kw SDMO generator can deliver 45 kW all night on a fuel tank. A solar generator with a 10 kWh battery delivers about 5 kW for two hours before it needs sun.
A 15kw inverter generator is also not a solar generator. It burns fuel, and—as I'd just learned—it has a fuel filter. A solar generator is a completely different animal. The question isn't 'which is better?' It's 'what is the job?'
I'd rather spend ten minutes explaining that than deal with a system that fails at 2 a.m. An informed customer asks better questions and makes faster decisions. Education is not a sales technique; it's the product.
The Checklist I Now Use on Every Site
After the 800 kVA disaster and the fuel filter embarrassment, I built a one-page checklist. We've caught 47 potential errors using it in the past 18 months. That's not a brag. It's proof that my memory is not a reliable source.
- Get a real load study from a licensed engineer. Do not size from a contractor's 'rule of thumb.'
- Target 60-80% average load for a diesel standby set. Oversizing is a maintenance problem.
- Verify every filter, belt, and part number against the generator nameplate. If you need an Onan generator fuel filter, look up the exact part number. Do not trust memory.
- Test under an actual load for at least 30 minutes. NFPA 110 requires it for emergency systems; your equipment deserves it too.
- If someone asks 'what is a solar generator,' explain the energy math before you talk about price. Solar may be a good supplement, but it is not a drop-in replacement for a diesel generator on a mission-critical load.
I'm not an engineer. The load studies are done by licensed people, and I follow their numbers. NFPA 110 and EPA diesel emissions rules are where I send customers who want the technical details. (Source: NFPA 110, 2023 edition; EPA standards for nonroad diesel engines.)
What I'd Do Differently
If I could go back to the cold-storage project, I'd thank the electrical contractor for the recommendation, then ask to see the load study before ordering anything. That 800 kva SDMO generator would have looked great in a brochure. It would have made a terrible everyday machine. The 45 kw SDMO generator we installed is less impressive on paper, but it starts clean, runs under load, and doesn't eat its own maintenance budget.
SDMO's line, now marketed as Kohler-SDMO, covers a huge range—from portable rental units to 1250 kVA industrial sets. The problem was never SDMO. The problem was my sizing. And the fuel filter? The problem was my assumption.
Leaving the cold-storage site the night of the first successful full-load test, the customer asked, 'So this smaller unit is really enough?' I watched the lights hold steady while the compressor started. 'Yes,' I said. 'Enough is enough.'
