Automatic washing machines - peak VA

catkincatkin Registered Users Posts: 19
Hello :D

What's the peak VA for a 5 to 6 kg dry laundry weight front loading automatic washing machine without heater? I can't find this information locally or on the 'net for the brands of interest (IFB, Samsung and Siemens) and don't have any machines to measure.

IFB use 690 W motors and Siemens 400 W (Samsung don't say). Would it be OK to assume 3 times rated motor power for peak VA? Why might the IFB motors be nearly twice the power of Siemens to do essentially the same job?

What are the worst case power factors likely to be? This Australian Inverter and Washing Machine FAQ reports a measured PF of 0.13 but does not say if that coincides with peak VA. Should I worry about small PFs that do not coincide with large VAs?

The maximum wash cycle consumption for the machines of interest is 0.25 kWh so, even with 4 washes a day, the daily requirement is relatively low at 1 kVA. With a peak of, say, 2.1 kVA at maybe 0.13 PF the inverter would need to be generously sized, say 3 kVA. Assuming a 48 V battery bank to suit the inverter, 50% maximum discharge, 85% efficiency and storage for 2 dark days, the battery bank would have to be ~50 Ah. I guess that wouldn't provide enough current for the inverter without excessive voltage drop and we would have to add capacity beyond storage needs.

The washing machine will only be used between 8 AM and noon. If it was on its own PV system then that system would be under-utilised, lying idle for 20 hours out of 24 and with spare storage capacity. If my reasoning is correct then we could make better use of the kit (= increase the load factors) by mixing the washing machine load with an afternoon and night load - like events halls and public area lighting.

Just to paint the picture, I've got three possibly interrelated PV projects here. The first is the subject of NAWS thread "Panel mix and match - diodes?" The second is this washing machine project. The third is converting a 12 V DC two-house system, at the other end of site, to 220 V. The optimal solution might mean swapping existing components around, perhaps beefing up the "panel mix" system to take the washing machine.

Comments

  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic washing machines - peak VA

    Im not going to crunch figures with you but just let you know that I have a cheap 230v 50hz front loading washing machine and only ever run it on the inverter which is a 3kw 24v. It never breaks a sweat pulling around 4 amps ac max, around a 1000 watts. :cool:

    PS We have the heater function turned off !
  • BB.BB. Super Moderators, Administrators Posts: 32,009 admin
    Re: Automatic washing machines - peak VA

    I don't have any numbers for you... A good bet would be for you to contact your local supplier and see what they recommend for their products... Some will do better with short over loads than others (and make sure you wire your inverter DC wiring to be able to handle the large peak loads without causing the under voltage alarm to trip).

    And you are correct, you should watch the VA and ignore the bad Power Factor when the current (VA) is low.

    Next, you will also need to choose your washer/inverter pair carefully... An "inexpensive" inverter, called a Modified Sine Wave or Modified Square Wave design, outputs an AC wave form that is much closer to a square wave than a sine wave...

    These MSW inverter can play havoc with motors and electronics... A "simple" washer with mechanical timer may run better (and more accurately) than a high-tech electronically controlled washer on a MSW inverter... And for many motors, they will draw 20-25% more power (wasted as heat) on a MSW inverter.

    The better inverter to get for a permenant installation (one that you will use for years and need work well) is a "pure sine wave" inverter... The AC wave form they output is pretty much the same quality as you get from your power utility. And this is what everything is designed to run on--But they cost much more money to build/purchase.

    In the end, probably some 90% of your appliances will run OK (but a bit hot) on a MSW inverter. Problem is--you won't know which ones those are until you try them... Some will get hot and may fail a few years before their time--others may fail within a few minutes or an hour. Can't predict what will happen.

    Here is a quick FAQ that describes some of the inverter issue for (for US market--so some things will not apply to you).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic washing machines - peak VA

    Adding to BB comments dont even think of using a MSW inverter on a modern washing machine b4 I installed my SW304E (pure sine wave) I had a DR2424E modified unit, the washing machine was brand new and on the DR unit failed after 2 weeks, the motor mount cracked due to surge from the motor, it was repaired under guarantee and only ran from a generator (1600 watt inverter style) till I installed the SW unit. Been fine for last 2 years. In Spain with people living off grid the universal advice on washing machines is go basic with a mechanical timer and avoid digital type displays, even with sinewave inverters. Even the local electrical retailers offer this advice freely to us forgieners.
  • System2System2 Posts: 6,290 admin
    Re: Automatic washing machines - peak VA
    catkin wrote: »

    IFB use 690 W motors and Siemens 400 W (Samsung don't say).

    Be aware, seems like many motor manufacturers are no longer using the hugely inflated HP ratings, and instead have gone to rating the mechanical output power of the motor in watts. So, if the motor is 50% efficient, it will consume 800 watts, in order to output 400 watts on the shaft.
    Re the inflated HP ratings, a good example that's very common, is with compressors. Advertised as having a 5 HP motor, a quick check shows a consumption rating of 1/2 HP. Not bad eh? Is that the New Math being taught in our schools now?
    Just wondering
    Wayne
  • BB.BB. Super Moderators, Administrators Posts: 32,009 admin
    Re: Automatic washing machines - peak VA
    Be aware, seems like many motor manufacturers are no longer using the hugely inflated HP ratings...as having a 5 HP motor, a quick check shows a consumption rating of 1/2 HP.

    I thought I was the only one that every got ticked off by that... Even vacuum cleaners where doing the same thing... "2HP vacuum cleaner" drawing just over 1HP of power... How did they do that?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Automatic washing machines - peak VA

    Good question, and even better, how do they get away with it?
    Same thing with little portable stereos - - 1000 Watts plastered all over the box, yet it consumes perhaps 10 watts max. Perpetual motion with energy to spare?
    But I digress.
  • catkincatkin Registered Users Posts: 19
    Re: Automatic washing machines - peak VA

    On the subject of exaggeration, what's 2-and-a-half tons about a 2.5 ton air conditioner? (the question is genuine)

    Nice to know that at least one frontloader runs OK on a 24 V DC, 3 kW inverter.

    Maybe there's some exaggeration in the motor power figures but you have to dig deep to get them -- it's not upfront marketing data. Actually, very little data is used in the marketing! Most of it sounds good and means nothing concrete. Try getting some hard facts (or even meaning) out of "The surface of the drum has been sculpted into raindrop patterns that emulate the shape of the paddles to offer even more potent, yet gentle treatment." © Siemens.

    Nice FAQ. As Bill suspected the FAQ's brands aren't available here. One local supplier sometimes has [URL="http://www.steca-solar.com/en/art/uid_kategorien/0000581/id_matchcode/up_sinus_insel_wechselrichter/id_artikel/0000177/bop/0/chksum/d24387a47b3d5e3d9878659a7587b216/beetools.html
    "]Fronius Steca Solarix[/URL] (European, nice, too small) and one has Su-Kam (we would like to try something else). Digital Power Controllers may be interesting. Monitoring instrumentation and data logging is helpful on an inverter. Remote access to monitoring would be icing on the cake :D

    Regards local suppliers' recommendations, the Su-Kam supplier said just to connect a washing machine but I prefer to double check having blindly accepted their advice before!

    What about minimum battery Ah requirements for inverters? I'm sure I've read about it somewhere but cannot now find it.

    Mmm ... management is sometimes defined as the art of taking decisions without all the information. Does that mean designing a PV system for a washing machine is management?!
  • catkincatkin Registered Users Posts: 19
    Re: Automatic washing machines - peak VA
    catkin wrote: »
    What about minimum battery Ah requirements for inverters? I'm sure I've read about it somewhere but cannot now find it.
    From Real Goods Solar Living Sourcebook: A battery bank smaller than three-days capacity is going to get cycled fairly deeply on a regular basis. This isn't good for battery life. A larger battery bank cycled less deeply is going to cost less in the long run, because it lasts longer. Banks larger than five-days capacity start getting more expensive than a back-up power source (like a modest-sized generator). However, we occasionally run into situations with ¾ horsepower or larger submersible well pumps or stationary power tools requiring a larger battery bank simply to meet the surge load when starting.

    The weather patterns here are quite brisk; even in the depths of monsoon it's rare to go more than 2 days without sun; being in the tropics the sun is always high in the generating hours. For these reasons we design for only 2 dark days so we are more likely to require "a larger battery bank simply to meet the surge load".
  • System2System2 Posts: 6,290 admin
    Re: Automatic washing machines - peak VA
    catkin wrote: »
    On the subject of exaggeration, what's 2-and-a-half tons about a 2.5 ton air conditioner? (the question is genuine)

    I'm sure someone has the exact explanation, but in the meantime, my understanding is something along the following:

    A 2.5 ton AC unit has an ability to cool, that could in 24 hours, reduce the temperature by 1 degree F, of 2.5 tons of water.

    Wayne
  • DabblerDabbler Registered Users Posts: 22
    Re: Automatic washing machines - peak VA

    I believe one ton of air conditioning is equivalent to 12,000 BTU. It apparently has it's roots in the ice making business. Here's a useful description from http://www.onlineconversion.com/forum/forum_989421674.htm :

    Just wanted to provide background on the derivation for tons of refrigeration, and provide information on the similar SI standard.

    The latent heat of fusion for ice is 144 BTU/lb. For one ton, that is 2000 lb x 144 BTU/lb, or 288,000 BTU. Refrigeration's roots are in the ice making industry, and the ice guys wanted to convert this into ice production. If 288,000 BTU are required to make one ton of ice, divide this by 24 hours to get 12,000 BTU/Hr required to make one ton of ice in one day.

    This is simply the requirement for the phase change from liquid to solid -- to convert +32 deg F water into +32 deg F ice. As a practical matter, additional refrigeration is required to take city water and turn it into ice.

    One BTU is the heat removal required to lower the temperature of one pound of water by one degree F. In SI units, kilocaries are used. One kilocalorie is the heat removal required to lower the temperature of one kilogram of water by one degree C. One ton of refrigeration is equal to 3024 kilocaries per hour. It is basically the 12,000 BTU/Hr divided by pounds per kilogram divided by 1.8 (to get from degrees F to degrees C).
  • BB.BB. Super Moderators, Administrators Posts: 32,009 admin
    Re: Automatic washing machines - peak VA

    Regarding battery capacity... A few more details to move it out of the "management" category (and/or read the Battery FAQ--much of what I wrote here is in the FAQ--and probably better written too)...

    1. Assuming you are using good quality flooded/wet cell lead acid storage batteries, you should plan on discharging them a maximum of 50%. Discharging them further than 50% on a regular basis will dramatically reduce their life (so your 3 day storage really becomes 6 days of storage when calculating battery size). AGM batteries are supposed to allow 80% discharge (to 20% SOC--State of Charge). And car batteries (not recommended), should only be discharged by 15% (85% SOC). Some specialized storage batteries (like used by the telephone company for 20-40 year life) also have limited ability to take deep discharge (some are only rated to 85% SOC).

    2. Ideally, a standard flooded cell lead acid battery should never sit at less than 75% SOC for any longer than necessary. The lead sulfate converted in discharging the battery starts hardening after even a few hours when below 75% SOC. This hardened sulfate does not change back when the battery is recharged--eventually causing the battery to fail. So, if you discharge below 75% and it takes days (or weeks) for the bank to recharge back above 75% (over sized battery bank), your bank will not have a long life. AGM batteries (from at least one vendor) say that sulfates don't harden in their batteries so not an issue for them.

    3. When discharging or charging a battery, they have internal resistance and chemical conversion limitations... Basically, if you look at how much energy a battery can deliver (as Amp*Hours), and ideal 1,000 AH battery would deliver 10 amps for 100 hours or 100 amps for 10 hours. In real life, a battery that (made up example) delivers 10 amps for 100 hours (1,000 A*H) will deliver only 800 AH at 100 amps, or 500 AH at 1,000 amps... Typically, a battery will be rated at 20 Hour discharge (and perhaps some other discharge rates too)... If you discharge slower than 20 Hour rate, you will get slightly more power out of the battery--and if you discharge a lot faster than 20 hour rate, you will have significantly less capacity. Typically a minimum 20 hour rate to discharge or charge your Lead Acid bank is the ideal price point. When adding adding the 50% maximum discharge factor+3 day storage--you are also good for discharge rate (example, 4 hours of washing machine use per day times 3 days times 1/50% discharge level = 24 hour discharge rate). If you have specialized needs (use 1 hour per day or 24 hours per day, then you should look at each "parameter" of the battery's requirements). Also the 20 Hour rate usually limits battery heating issues (should have a battery temp sensor for charge controller). Some batteries, like AGM, have different strengths and weakness.

    4. If you will have a generator (diesel or equivalent) for emergency/backup use--the most efficient way to use the generator (say after days heavy storms or a lot of loads) is to start the generator at the beginning of the day and "bulk" charge the batteries up to the 90% or so SOC (batteries will accept large amounts of current below ~90% SOC), generator will be running with a good sized load--so it is fuel efficient and will run the minimum amount of time needed (keep noise/smoke down--and generators are very inefficient below ~25% load--depending on type). Once the batteries are above 90% SOC, they will naturally start to accept less current. At this point the sun is up and can supply the lower current for the next 5 hours and fully recharge the cells back to 100% SOC.

    5. Because battery life (and generator use) is very depending on use and State of Charge--knowing you battery's SOC is critical for managing load and charging. Most people will use an accurate DVM to measure voltage--but you need to have no load/charge current for a couple of hours (rest the battery), measure the battery temperature, and use the DVM to approximate the state of charge. If you have flooded cell batteries, the most accurate method is to use a hydrometer (and thermometer) to measure specific gravity... However this is messy--can contaminate the cells, and not possible to use for sealed type batteries. A Battery Monitor is worth the cost as it accurately gives you the SOC (and other information) because to tracks the current) into and out of the battery. You don't need to "rest" the battery--so you can instantly check your battery's state (look at the XBM--feature set is very well liked by several people here).

    6. If you are using flooded cell batteries, you may also look at new battery caps to help preserve water in your batteries (distilled water is not cheap to get or make in much of the world, and you can use several gallons per month for a large battery bank). There are several types and each has its advantages and disadvantages--likely a management decision as to which type you will purchase.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Automatic washing machines - peak VA

    Thanks Dabbler for the proper explanation on the Tons of AC.
    Cool.
    Wayne
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