Thread: Finding out motor power requirement.

You could get one of those plug in power meters. I am sure I have seen one that you plug into the power point, and then plug your load into it, and it tells you what power it is drawing.

Something like this: Power Consumption Meter – Find Your Energy Guzzlers « Steplight: sustainability programs and education

There may be others at different price points available.

Peter I think he wants to know the power before he plugs it in.

There is no easy way to do this since the current will depend on the load eg I can make the current drawn from my TS go from around 6A up to 18 A (before it trips).

Those 140L 240V mixers typically run a 0.5 to 1HP (750W) motor so a basic genny should be able to run it. I have not seen one that was more than 1.5HP.

Thanks chaps.

It sounds like I'll be safe with the size genny I'm thinking of (>=2400w).

Mud bricks, here I come

Most cement mixers that I have dealt with have had motors of about .5HP, and I dropped an old ebay .5HP into a mixer for a neighbour and it works as well as the original chinese motor did.

Even if the motor was rated it higher power, the current draw is controlled by the load placed on the motor, not by the rating plate stuck (or not stiuck) to it. The rating plate gives an indication of what the motor can be expected to endure, in terms of current, heat disipation etc. Similar to a car engine, it might be rated at 200KW, but most of it's time is hovering around the 30-40KW zone, depending on load, road conditions, and right foot weight.

It takes a certain amount of power for the motor to run naked (no load including drive belts etc) and then as you supply energy to the task in hand, the power consumption increases at about 1.2 times the power supplied as work.

So, as long as it is not permanently overloaded, a .5HP motor on a mixer would draw similar current to a 1.5HP motor on the same mixer for similar RPM and mix volume.

With regard to running from a generator, you need to have a high degree of peak overload capacity to start the motor in the first place, and I suspect that 2400W might be cutting it fine.

My father was a rural area builder and ran a mixer with a 1HP Villiers 4 stroke for 30 years or more. Check the oil, top up the fuel tank, give the mixer bowl a manual spin to start and let it chug away all day, about a quart of regular petrol for a days work. Most gennies in the size you are considering are 2 stroke and would burn that in a couple of hours, so you might be better to consider small second hand B&S or similar for the mixer.

Thanks Malb. A secondhand petrol mixer with a bigger tub is certainly another avenue to consider. I'll go have a squiz around eBay and gumtree and see what they're going for.

A friend of mine did mud brick house.
They filled a trailer with the mud and straw etc and then went over it with a rotary hoe (5hp) .
I would have thought a box former on the ground would have worked as well.
Good for me cos hoe died with 300 bricks to go. They got a new one for the 300 and then sold it to me.
Cement mixer sounds like small loads?? ) 20 bricks at a time?

Originally Posted by RedShirtGuy

Thanks chaps.

It sounds like I'll be safe with the size genny I'm thinking of (>=2400w).

Mud bricks, here I come

Originally Posted by _fly_

Cement mixer sounds like small loads?? ) 20 bricks at a time?

There are rare moments in time that I can be very patient

Malb is on the money as usual but I differ on one single point. Forget the BS. Briggs N Friggin' Nogo have never been on my party list and in an isolated rural setting you will want this thing to start when you pull the rope, not when it wants to. Get a trusted brand of engine, even secondhand, something you can rely on. As an aside, my father had an old side valve Villiers for decades running all sorts of different things and I don't remember it ever missing a beat.



I think the article below came from elsewhere on this forum:

SIZING A GENERATOR.

Formulas - W (power) = E (volts) x I (current) x P.F. (Power Factor). We need to find the current (I) so;

I = W divided by (E x P.F.)

Power Factor is used if you can't find the FLA &/or LRA of the fridge/freezer & only the wattage is known. Note - I have assumed that the fridge & the freezer have a P.F. of 0.8.
FLA - Full Load Current (run current).
LRA - Locked Rotor Current (start current).

Continuous Load calculation.
4 x 60 Watt incandescent lights - - - - - - - - - - 240 divided by 240 = 1 Amp.
1 x 300 Watt fridge - - - - - - - - - - - - - - - - - - - 300 divided by (240 x 0.8) = 1.5 Amps.
1 x 300 Watt freezer - - - - - - - - - - - - - - - - - - 300 divided by (240 x 0.8) = 1.5 Amps.
1 x 300 Watt TV - - - - - - - - - - - - - - - - - - - - - 300 divided by 240 = 1.25 Amps.
1 x 100W "printer" fax/phone - - - - - - - - - - - - 100 divided by 240 = 0.4 Amps.

Total continuous Watts as listed - 1240 Watts.
Total continuous current as calculated - approx 6 Amps.

Surge Load calculation.
The only items that will have a surge current are the fridge, freezer & TV.

1 x 300 Watt fridge - - - - - - - - - 1.5 Amps x 4 = 6 Amps.
Fridge surge - - - - - - - - - - - - - - 6 Amps - 1.5 Amps = 4.5 Amps.

1 x 300 Watt freezer - - - - - - - - 1.5 Amps x 4 = 6 Amps.
Freezer surge - - - - - - - - - - - - - 6 Amps - 1.5 Amps = 4.5 Amps.

1 x 300 Watt TV - - - - - - - - - - - TV surge is approx 0.5 Amps.

Total surge current - 9.5 Amps.

Your generator will need to supply a continuous current of 6 Amps.
Your generator will need to supply a total surge current of 6 Amps + 9.5 Amps = 16 Amps.
Converting these figures to "Power" (VA);
16 Amps x 240v = 3 840 VA surge.
6 Amps x 240v = 1 440 VA continuous.

Since you will not find a generator with these exact "continuous" & "surge" ratings, you must buy a generator that can accommodate the surge rating. ie you will need a generator with a surge rating of no less than 3 840 VA for the above situation.


Other notes.
1] My calculations are based on the fridge & freezer starting currents being 4 times their run currents. In some cases, the starting currents of these devices are smaller than 4 times their run currents or up to 8 times their run currents.

2] The sizes of the fridge/freezer used in the calculation are "typical" but you must still find the sizes of YOUR fridge/freezer.

3] "Portable" generators usually have a "duty cycle" rating, which must be strictly adhered to if you want maximum life from the them. It's a good idea to only load the generator to 80% of its maximum output.

Nice one dakota

Those calcs look familiar from when I was hunting out info a few years ago and it's good to "find" them again.