FAQ
TL;DR: A plaster pump set that draws 8 kW active power often needs a ~16 kVA generator; “15 kVA is the bare minimum” [Elektroda, 12pawel, post #11710004] Many pros now choose 20 kVA to avoid stalled starts [Elektroda, 190_Wojciech, post #12209507]
Why it matters: Undersizing the generator risks motor tripping, material waste, and costly downtime.
Quick Facts
• MP25 motor rating: 5.5 kW, 400 V, 50 Hz [Elektroda, tora302, post #11709827]
• Total active load incl. auxiliaries ≈ 8 kW [Elektroda, 12pawel, post #11710004]
• Recommended generator headroom: 2× motor kW → ≥ 16 kVA [Elektroda, 12pawel, post #11710004]
• Comfortable field choice: 20 kVA diesel ≈ PLN 20 000 net [Elektroda, 190_Wojciech, post #12209507]
• IEC 60204 suggests ≤ 5 % voltage drop at motor terminals [IEC 60204-1]
Why is an 8 kW (10 kVA) generator too small for the MP25?
The MP25 has inductive motors. Start-up current can be 6–7 times the rated 5.5 kW, translating to ≈35–40 kVA apparent load. A 10 kVA set cannot supply that surge, so voltage collapses and the motor stalls [Elektroda, 12pawel, post #11709971]
Will a 12 kW (15 kVA) generator definitely work?
It starts the pump when empty, but once mortar loads the screw pump, users report "epileptic" starts and trips [Elektroda, manekinen, post #11832994] Treat 15 kVA as emergency minimum, not a guarantee.
What size generator gives trouble-free operation?
Field contractors pick 20 kVA sets. That covers simultaneous starts, compensates for 50 m cable loss, and leaves 20–25 % reserve [Elektroda, 190_Wojciech, post #12209507]
Does the 40–50 m extension cable change the required kVA?
Cable length affects voltage drop, not generator power. Use 4 × 6 mm² rubber cable; drop stays under 5 % at 20 A over 50 m [IEC 60204-1]. If you use thinner cable, you must upsize the generator to overcome the extra loss.
Can a soft-starter or VFD let me use a smaller generator?
Yes. Limiting inrush to 2× rated current means a 12 kVA set can work [Elektroda, nuszek, post #11710078] Verify the starter’s overload rating matches the screw pump torque.
Is diesel or petrol better at 20 kVA?
Diesel units consume ≈2.8 L h⁻¹ at 75 % load, 35 % less fuel than petrol. They also deliver higher starting torque at low RPM [Caterpillar Spec Sheet]. Petrol sets are lighter but burn ≈4.3 L h⁻¹.
What brands fit a PLN 10 000 budget?
Used Pramac, Fogo or SDMO open-frame diesels from rental fleets often list at PLN 9–12 k. Avoid unknown "Honda-clone" labels; spares and AVR boards are scarce [Elektroda, Maciek2808, post #12195889]
Edge case: what happens if the screw pump jams mid-job?
Starting against a blocked rotor can draw 700 % rated current for several seconds. A 15 kVA set will hit its magnetic breaker and shut down, causing material hardening in the hose [Elektroda, manekinen, post #11832994]
How do I legally draw power from a block of flats instead of a generator?
- File a temporary supply request to the building’s utility.
- Connect to 3-phase riser sockets in each floor switchgear.
- Install your own kWh meter for billing.
This solution avoids noise and fuel costs [Elektroda, eljarkos, post #12205155]
3-step method to minimise start-up current in the field
- Fit a soft-starter in the pump’s control cabinet.
- Sequence: start motor-reducer → water pump → compressor.
- Keep generator throttle at 52–53 Hz to avoid under-frequency trips. This routine halves the apparent inrush and smooths voltage swing [Elektroda, nuszek, post #11710078]
What maintenance keeps a site generator reliable?
Change oil every 250 h and fuel filters every 500 h. Clean AVR cooling fins weekly on dusty plaster sites. A clogged filter can cut available kVA by 10 % [Briggs & Stratton Manual].
Does power factor correction help?
Capacitor banks tuned to 0.95 lag reduce stator heating but have little impact on the motor start surge, so generator sizing remains unchanged Eaton PF Whitepaper.
