How the calculator works
The calculator above makes a first estimate in four steps:
- Running load —
installed kW × demand factor ÷ power factor (0.8)gives the kVA the plant draws while producing. - Starting peak — the largest motor (usually the exhaust fan) draws several times its running current while starting. The peak is the running load plus that extra surge.
- Required size — the generator must run the plant at no more than about 80% of its rating, and ride the starting peak with an acceptable voltage dip. The larger of the two decides.
- Derating — altitude above about 1,000 m and heat above 40 °C reduce a generator’s output, so the nameplate size goes up.
Installed power of Roadmixa models
| Series | Models and installed power |
|---|---|
| RMX-D drum mix | D60 105 kW · D80 135 kW · D120 200 kW · D160 300 kW |
| RMX-M mobile | M60 157 kW · M80 241 kW · M120 330 kW · M160 412 kW |
| RMX-C containerized | C80 245 kW · C120 305 kW · C160 345 kW · C240 505 kW · C320 660 kW · C400 810 kW |
| RMX-B stationary | B60 178 kW · B80 285 kW · B120 380 kW · B160 470 kW · B240 700 kW · B400 960 kW |
Full figures are in each product’s parameter table.
Ways to need a smaller generator
| Measure | Effect |
|---|---|
| Soft starters on the exhaust fan and drum motors | Cuts starting surge to roughly half of direct-on-line |
| Variable frequency drive on the exhaust fan | Smallest surge; also saves fuel at part load |
| Start motors in sequence, largest first | Avoids several surges at once |
| Separate small generator for bitumen heating overnight | Main set stays off when the plant is idle |
Generator choices for plant sites
- Prime-rated sets, not standby-rated: asphalt plants run long hours at high load
- Containerized, sound-attenuated sets for sites near villages or towns
- Two sets in parallel for redundancy on remote sites
- Day tank and bulk fuel storage sized for several days of plant and generator fuel
- Earthing and protection coordinated with the plant’s electrical system
What the calculator cannot know
The exact motor list, actual demand factor, harmonics from drives, and the generator’s own transient performance all affect the final size. Our quotation includes the plant’s electrical load list; give it to your generator supplier, or ask our engineers to size it with you.
