Figuring power reqts. for portable generator?

Discussion in 'General Electronics Chat' started by Lindsaydoo, May 10, 2015.

  1. Lindsaydoo

    Thread Starter New Member

    May 10, 2015
    Howdy all,

    So happy to find you! I have a home-based food business that is scaling up right now but that I legally can't take to a commercial kitchen space unless I invest about $100k in new commercial equipment that doesn't work any differently from my current home-based equipment (yes, I really do know this...I'm a professional chef as well). On "paper", my equipment uses about 83 amps at full surge and probably 18% of that on average since all my equipment is cyclically pulling power. I am moving to a bit smaller place and an acquaintance suggested I get a portable generator if I needed an additional power source. I'd like to see how much I can expect to pull from such a generator since I haven't used one before.

    Here's what I know:
    1. My equipment is all 110V friendly.
    2. I have looked online for some definition explanation and am not quite clear on some definitions I am seeing.
    3. I've already had electricians review each property I've looked at, and ultimately they have been too conservative to give me a truly appropriate recommendation, which I didn't learn until I gave up my last apartment for the sake of a bigger power-loaded apartment and then my electrician admitted he had been being VERY conservative about his prior recommendations and that I didn't really need to move. That's when I stopped asking electricians for help and started investigating all this on my own.

    Some questions I have are:
    1. I've worked in amps and watts but not in power factors. How do I calculate power factor (like, in English, not in the equation and definitions I see online :))? Is the power factor the 18% I mentioned if I were to cycle every item on in spaced intervals?
    2. What is single versus three-phase? I most likely have single-phase equipment but would like to be sure.
    3. Are all portable generators based on fossil fuel or are there other kinds? For example, since I am only producing on weekends, is there a generator that I could keep plugged into a home outlet all week and have it store up the electricity and then I could use it as a supplemental electrical source on the weekends when I am producing?

    Thanks soooo much :)!
  2. Papabravo


    Feb 24, 2006
    1. Power factor is the result of AC power going into a reactive load, such as a motor. It measures the difference in phase between the AC voltage and the AC current. The English description of how to calculate this is to "take the cosine of the phase angle between the voltage and the current". Without some mathematics background that statement will be as useless to you as an equation. At this point in time, it is not worth your while to worry about this. Stick with what you know which is Amperes, Volts and Watts. Your 18% is called "duty cycle"; in other words how much of the time are you using the maximum power available.
    2. If it goes into a standard wall socket it is a single phase device. Three phase power is used for things like large electric motors and those appliances will have a different socket and plug arrangement.
    3. Generators generally use either gasoline or natural gas. Generators are not capable of storing electricity. Batteries can be charged and used to run an inverter which converts DC to AC, the process is not very efficient and you will be better off adapting you power panel to use mains power all the time. If it had 6 20A circuits that would be more than sufficient for you current needs.
    Just as an aside:
    Large motors have an easy time running when they are up to speed. Starting and stopping are different matters. The current requirement for starting a large motor can be several times the required running current. If you stall a large motor it will draw large currents. I have a 10" radial arm saw that requires some care to start, and great care in operation to avoid a stall which will pop the breaker on a 20A circuit.
    Last edited: May 10, 2015
  3. Brownout

    Well-Known Member

    Jan 10, 2012
    Assuming 83 amps refers to current draw when operating at 110v, you'll need a 10KW generator. That's not exactly portable. Alternatively, you can use two 5KW portable generators, and divide up the workload.

    Single phase is used in most residential services. three-phase is used in some commercial services. Technical details are probably not a concern of yours.

    Generators produce power on demand, and so they cannot store power. Best to think about spreading out the workload throughout the week instead of trying to save up power.
  4. ian field

    AAC Fanatic!

    Oct 27, 2012

    The TS said 83A at full surge - I'm guessing there's a few heating elements involved, with PTC that drops current draw as they heat up, most likely a few mixer motors that draw a fair bit to overcome inertia when first started. As long as the TS doesn't have a single master breaker to bang everything onto the generator at once, there's not such a big problem.
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Also, some high-power heaters and oven-type devices can sometimes be rewired for operation on 240V. A 5 to 10kW generator will have an easier time powering 240V loads.

    You will not like the noise or fumes that such a genny will produce. Has to be outside, and the neighbors will hate it.

    You will not like the fuel cost, either. A kWh produced from gasoline is about 10X the kWh cost of residential electricity.
    Gdrumm likes this.
  6. Reloadron

    Well-Known Member

    Jan 15, 2015
    Aside from gasoline larger generators usually run on either diesel fuel, LPG (Liquid Propane Gas) or NG (Natural Gas. I have an emergency whole house automatic transfer unit rated for 18 KW which we run on Natural Gas. Unless you are running plenty of inductive loads and have special needs I would just consider a simple retail generator from a home improvement retailer. Here in the US I would suggest Lowes or Home Depot if you are US located. Additionally you can contact the guys who make these things like Kohler, Generac, Centurion and others and spell out your specific needs to one of their engineering types who will make some suggestions. Mine obviously sits outside the house and runs pretty quiet and I have never had an issue with the exhaust fumes.
    If you plan this for emergency use when mains power fails make sure when reviewing generators that you include the automatic transfer switch. Some units include the switch and some don't so suddenly that $4,000 USD generator becomes a $5,000 USD generator. Just about any of the brands I mentioned make units for small business support beyond their residential units.