Am not too familiar with petrol generators and how big a generator I would be need to power an electric cement mixer. Am about to start building a house and I hope to do the base myself. We don't have electricity yet so I was thinking about buying a generator. Can anyone give me advice. all replies will be appreciated.
And don't forget how useful it would be for the millions of other jobs apart from running the mixer. I would strongly recommend getting a 110V version and running 110V tools. You may find it an idea to get one cheap on eBay and sell it when you've finished. You may even make a profit!
Christian.
Look on the ratings plate on the mixer, tell us what the current consumption is in amps. Your gen will need to supply that plus a generous margin for starting.
But as was said, a more powerful 3kVA or even 5kVA machine will run a lot more besides.
I cant see the sense in going 110v though, maybe someone else will comment on that.
Regards, NT
Others have answered your genny question - but can I ask - why do you want to mix the base by hand? Buying ready mixed concrete is far more cost effective, even if you costed your time at nothing.
Yes, I find my 4kVA Honda will not restart my 2kW compressor unless the air tank is fully discharged first, runs fine once its going though even with 80psi in the tank.
AJH
I would suggest that there is something wrong with your compressor. Starting under load is a recognised problem with electric motors, so much so, that all the compressors that I have seen decompress the pump part of the unit after it cuts out, to alleviate it.
With many loads if youre caught short you can use a series load to start the motor at reduced power: but that wouldnt work for a compressor where you need the full power output at start.
Regards, NT
Most small gennies have 110/240 outlets anyway. As for any benefit it really depends on how the generator is wired and earthed. But I don't want to open *that* can of worms again...
In reply to grunff.... should have pointed out that it is the mortar for the dead work that I need to do by hand (Engineer isn't too gone on this bag of mortar that you can buy from the readymix companies). The deadwork is quite substantial.... i.e. in 1 corner I have to bring it up 1.75 metres. I will indeed be getting ready mixed concrete for the floor area and foundations.
I will check the plate on the mixer and get back with what it says. Have been told that a 3.5 KVA would be sufficient. There is a big difference in price betweeen 3.5 KVA and 5KVA.
This is a cheap, Italian made, one from Northern Tools. There is a direct connection from the cylinder to the combine pressure relief and connection to the reservoir. The outlet from the reservoir is a pressure reducing valve, ap and pressure sensed on/off switch. There appears to be no provision to dump cylinder pressure at start up.
One way to start up an induction motor at reduced power is to drop the frequency of the supply with an inverter, an expensive option in this case. In fact it is not a problem to me, I can start with an empty tank and if I am blowing up a tyre, its main use, it will run for
10mins without reaching its cut out pressure, as the output is nearly matching the input.This is more a problem with these little capacitor start induction motors than others, I suspect a 3ph set with a 3ph motor in the same ratings would not have this problem, as the rotating field of the 3ph produces a good torque from start up, the quasi phase introduced by the capacitor has a small effect so there is no great torque until the motor starts turning.
In fact if I need to restart it at pressure I have found over speeding the genset will do it, albeit only as a short term measure until the motor is running.
I mention this only because I wonder if the OP's cement mixer may start ok empty but not loaded if the genset is undersized, not that I know of any circumstance where a mixer should be started loaded.
AJH
It must be a big mixer if it's taking 3.5kVa, that's 5hp which sounds a lot to me for a concrete mixer. Maybe I'm wrong though. (OK, I know 3.5kVa isn't 3.5kW but the power factor can't be all that bad can it?)
It sounded right to me, although I always imagined house foundations being trench things, rather than rafts.
When I was considering concrete for my conservatory and shed base, I calculated it would need an entire truck. A house would need much more.
Christian.
I've lost the beginning of the thread but if you're not driving HGV's on them, no. Domestic floor slabs are generally 100mm.
A useful tip, which I found out too late, is that if you're not putting a polythene dpm under the slab put a polythene sheet (of any thickness) there anyway. It saves losing a lot of concrete and grout into the hardcore and makes finishing the slab a lot easier.
No 3.5KVA genny to start the mixer. Motors need significantly more power to start than to run. Rough rule of thumb: genny kVA = motor kVA
Would be fun alright mixing so much concrete by hand. Would worry about my sanity if I was doing that. Engineer is looking for 150mm floor over an area of 222sq m. I know its big but we wanted a 2 storey but planning said no way. Its just the mortar for alot of dead work. Good point on the hardcore taking extra concrete. Engineer wants a sand blinding bed.... must try and get some cheap crap sand for that.
Have a 1.2Kw generator that just doesn't seem to be driving the mixer as well as it should. Gets really mad at me if I fill it more than 3 quarters. If I was to buy a new generator I'd like it do be of use for other tools etc. Not much good with the power and voltages etc. Can someone explain the 110V Vs 230V
Thanks for all your replies..... very much appreciated
230V is obviously the same as household electrics, with a neutral (0V) and live (230V). 110V uses two lives at anti-phase to give a maximum of 55V to earth, making it fundamentally safer when working outdoors on a building site. You'll find the most building sites use 110V. You may find a generator with both 230V and 110V outputs, which is the best of both worlds. Most contractors used to working on building sites will have 110V tools, although some of the later indoor trades (such as plumbers) might be on 230V.
If you add an RCD theres no real safety difference (without one there is). 240v is compatible with far more kit than 110, unless you have a building co that kitted up with all 110 before 240 RCD'ed became permitted.
BTW Which complains, the gen or the mixer?
Regards, NT
Er not quite. On a generator you have two phases 180 deg apart and
230v between them. Only if one of the windings of the generator is bonded to earth (as in large copper stake hammered in to the ground) do you get the unbalanced system you describe.Only if there is a center tap to the windings that is bonded to earth. Other wise the two phases float, either can contact "earth" with no problem but if one does the other is at 110v wrt to earth.
I have a petrol cement mixer, old but works, I was going to eBay it for 100 quid and up, for 100 you can have it. It in corwen, north wales.
Rick
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