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Choosing the Right Generator: 8kW vs 12kW for Putzmeister MP25 Plastering Unit with 40-50m Cord

tora302 37620 21
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Can a Putzmeister MP25 plastering unit with a 40–50 m power cable run from an 8 kW or 12 kW generator, and which size is actually suitable?

The 8 kW generator is too small, and the 12 kW/15 kVA unit is only a borderline minimum; several replies say you should really look closer to a 20 kVA generator for comfortable operation [#11710004] [#11832994] [#12201524] [#12209507] The main issue is the inductive motor load and the fact that the machine’s motors can start together, so even a 15 kW set may struggle under load [#11710004] [#11832994] [#12201524] The 40–50 m cable does not change the generator power requirement itself; it mainly causes voltage-drop issues, so cable cross-section matters [#11709951] One reply noted that if a soft-start is used, about twice the largest motor rating may be enough, but that was presented as the optimistic case rather than the safest one [#11710078]
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  • #1 11709827
    tora302
    Level 2  
    Posts: 4
    Rate: 6
    Hello,

    I plan to connect the plastering unit to the power generator, but I'm not entirely sure what power the latter should provide.
    I need the generator to provide adequate power for start-up and continuous operation during plaster application.
    I will add that the power cord between the devices will be about 40-50m.
    I have 2 power generators to choose from: one with a power of 8kW (10kVa), the other with 12kW (15kVa).
    Which one will be suitable? Or is it still not enough power? I will be grateful for a hint.

    The plastering unit is Putzmeister MP25, which has the following specification:

    Pump - D6 Power
    Pumping pressure - 40 bar
    Compressor - 0.55 kW / 208 l / min
    Pump drive - 400V, 50Hz, 5.5 kW at 392 rpm
    Tank drive - 1.1 kW at 23 rpm
    Water pump - 0.78 kW at 3.4 m³/h
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  • #2 11709904
    12pawel
    Level 34  
    Posts: 2355
    Help: 207
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    The first one is rather out, the second one should be fine if it really has 15kVA
    tora302 wrote:
    I will add that the power cord between the devices will be about 40-50m.

    I don't understand this at all. A power generator is a mobile device, so why use such long power cords?
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  • #3 11709951
    kwantor
    Level 38  
    Posts: 4263
    Help: 352
    Rate: 1225
    Why is the first one too small?
    Turns out it's just one time.
    The power supply distance has nothing to do with the power of the generator - it's a matter of voltage drop and proper cross-section selection.
  • #4 11709971
    12pawel
    Level 34  
    Posts: 2355
    Help: 207
    Rate: 696
    kwantor wrote:
    Why is the first one too small?

    The loads are themselves inductive, so high apparent power is needed. The first one is too weak.
  • #5 11709987
    kwantor
    Level 38  
    Posts: 4263
    Help: 352
    Rate: 1225
    It depends on what the launch conditions are - but it can indeed be a problem.
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  • #6 11710004
    12pawel
    Level 34  
    Posts: 2355
    Help: 207
    Rate: 696
    The first is out of the question. With an inductive load (motors), the power of the generator is multiplied by two. The active power of the set is about 8kW, so the power of the aggregate is 16kVA then it will work efficiently. As you can see, even the second one is quite small, but once you have it, you can try with it.
  • #7 11710075
    tora302
    Level 2  
    Posts: 4
    Rate: 6
    12pawel wrote:
    The first one is rather out, the second one should be fine if it really has 15kVA
    tora302 wrote:
    I will add that the power cord between the devices will be about 40-50m.

    I don't understand this at all. A power generator is a mobile device, so why use such long power cords?


    An apartment in a block of flats on the 5th floor will be plastered. Unfortunately, there is no other way to connect the plastering unit (there is no power socket available in the block), but I guess that the power generator produces too much noise to stand on the balcony or in the apartment. Hence, this aggregate will be placed under the block, and we will lead the electricity to the apartment via a cable.

    So I understand that the other 12kW may not be enough either?
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  • #8 11710078
    nuszek
    Level 30  
    Posts: 1421
    Help: 123
    Rate: 388
    have a look here link

    Instead of an inverter, you can use a soft-start /a little cheaper/ and then the power of the generator is enough if it is twice as large as the largest motor, i.e. 12 kVA is enough.

    We have done this for a 55 kW motor and a 100 kVA generator, it starts without any problems on soft-start..
  • #10 11710599
    atlantel
    Automation specialist  
    Posts: 1379
    Help: 170
    Rate: 256
    The manufacturer states:
    power nom. 13.5KVA / 5.0KW
    The request will not work.
  • #11 11710965
    tora302
    Level 2  
    Posts: 4
    Rate: 6
    OK, so I guess there's nothing left but hand plaster.
    Thank you for your help!
  • #12 11710990
    kwantor
    Level 38  
    Posts: 4263
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    Rate: 1225
    The one from the last link has 15 kW so it will do.
  • #13 11832994
    manekinen
    Level 29  
    Posts: 1629
    Help: 76
    Rate: 2360
    I do not know if the question is still valid, but I will write from experience that even the second 12kW is not suitable. In plastering, all engines start at the same time, which already gives food for thought. At 15kW, if it starts smoothly "dry", then the start of a loaded plastering unit (loaded 5.5kW motoreducer) will look like an epileptic attack - and neither the unit nor the plasterers will be satisfied.
  • #14 12195889
    Maciek2808
    Level 10  
    Posts: 8
    Rate: 3
    hello. I admit that the topic interests me. I have the same problem as my colleague tora302. I have another machine. Pft Ritmo xl. with motor 5.5kw + compressor, etc. total about 7.5kw. I start the 5.5 kw motor separately and later I can turn on the rest. the machine works on 400 and 230. I called a few manufacturers of similar machines and they all talk about 15 or 16 kW. You also write about 15 kW. the matter is clear.
    Question: what brand? I want (it would be nice) to spend about PLN 10,000
    I can't afford a Honda. I know there are fake hondas. and I haven't heard about others, they are NONAME for me. do you have any opinions? what brand does the job?? I was thinking about a liquid-cooled diesel. Regards
  • #15 12201524
    manekinen
    Level 29  
    Posts: 1629
    Help: 76
    Rate: 2360
    In each aggregate, you can manually turn on the engines separately, but you won't do it when you release the mortar - they must start together, well at least the water pump with the mortar - then you can attach the compressor and basket if it has a separate engine. And I think you know very well what eggs are like, when the glass dries up and the motoreducer cannot move it, then even after a short downtime, these 15kW may not be enough (as with a long power cord). For comfortable work, it is really worth looking for a more powerful aggregate, because these 15kW is such a minimum, and more combinations will be at the machine itself, like robots.
  • #16 12201620
    Maciek2808
    Level 10  
    Posts: 8
    Rate: 3
    hmm. You know, if you're right, I'll listen to you. It sounds sesownie. How much would you propose. 18 is enough? It's probably not worth $10,000 then. What brand do you suggest?
  • #18 12204005
    vanobro
    Level 11  
    Posts: 17
    Help: 1
    when the water pressure is adequate, the pump is not needed. Always 0.7kV in "pocket" :)
  • #19 12204042
    Maciek2808
    Level 10  
    Posts: 8
    Rate: 3
    it so happens that I do not have a water pump in this model. But at some point, she'd rather have to be attached. otherwise, I'd rather not recommend a self-leveling screed. To be honest, I haven't used Ritmo yet. Still in PL. will be picked up in early May.
  • #20 12205155
    eljarkos
    Level 21  
    Posts: 462
    Help: 46
    Rate: 103
    tora302 wrote:
    An apartment in a block of flats on the 5th floor will be plastered. Unfortunately, there is no other way to connect the plastering unit (there is no power socket available in the block)

    There are never power sockets in the block, but there are 3-phase power strips in floor switchgears. You apply to the power company for a power supply permit for the duration of the work and connect the extension cord and that's it. That's what I did and that's what, for example, scrapers do.
  • #21 12209507
    190_Wojciech
    Level 20  
    Posts: 406
    Help: 13
    Rate: 115
    The friend's solution makes the most sense eljarkos

    For comfortable operation, a generator of about 20kVA
    Petrol prices of this capacity oscillate around PLN 20,000
    22kVA in the open version without housing costs about PLN 15,000 net
    Diesel 20 kVA is about PLN 20,000 net
  • #22 12477563
    Maciek2808
    Level 10  
    Posts: 8
    Rate: 3
    Thanks a lot for the info. So far, I can do it on 230. I only worked with clients who had 400. I bought a car and I don't have money for investments this year. I hope that in January the pradotworczy will appear. Regards
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Topic summary

✨ The discussion revolves around selecting an appropriate generator for the Putzmeister MP25 plastering unit, specifically whether to choose an 8kW or a 12kW generator. Key considerations include the power requirements for start-up and continuous operation, especially given the 40-50m power cord length. Responses indicate that the 8kW generator is insufficient due to the inductive nature of the loads, which require higher apparent power. The consensus suggests that a generator with at least 15kVA is necessary, with some recommending even higher capacities (around 20kVA) for optimal performance. Concerns about noise levels and the practicality of using a generator in a residential setting were also discussed, leading to suggestions for alternative power supply solutions.
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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?

  1. File a temporary supply request to the building’s utility.
  2. Connect to 3-phase riser sockets in each floor switchgear.
  3. 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

  1. Fit a soft-starter in the pump’s control cabinet.
  2. Sequence: start motor-reducer → water pump → compressor.
  3. 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.
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