240v Generator / Inverter

TobyToby Solar Expert Posts: 56 ✭✭✭✭
I'm not an electrician. I wasn't completely sure how to title this question. Hopefully this will make sense. The question is inverter related.

I just tested a generator which was connected to my house through a transfer switch. It's rated at 7500 watts. Is it common for the generator's 120v output to only supply 1/2 of the total wattage?

The generator has 240v output. It feeds 240v (2 lines @ 120v) to the transfer switch which goes to the main circuit breaker panel. I had an issue powering a 240v appliance. I looked in the cb panel and discovered that 240v is fed off the same 120v buss bar. I sort of knew this, but never thought of the implcations.

So, commercial power supplies 100 amps per 120v buss of a 200 amp service? Correct? Double pole circuit breakers for 240v have no problems supplying the needed amperage off one buss. However, generators (and probably inverters) only supply 1/2 the total wattage per 120v leg.

Is this the way it's always done?

Why isn't 240v supplied off both busses, 120v off each? Is the cb the problem?

If you need a 240v inverter, how do you work-around this?

Comments

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    I'm not an electrician. I wasn't completely sure how to title this question. Hopefully this will make sense. The question is inverter related.

    I just tested a generator which was connected to my house through a transfer switch. It's rated at 7500 watts. Is it common for the generator's 120v output to only supply 1/2 of the total wattage?

    The generator has 240v output. It feeds 240v (2 lines @ 120v) to the transfer switch which goes to the main circuit breaker panel. I had an issue powering a 240v appliance. I looked in the cb panel and discovered that 240v is fed off the same 120v buss bar. I sort of knew this, but never thought of the implcations.

    So, commercial power supplies 100 amps per 120v buss of a 200 amp service? Correct? Double pole circuit breakers for 240v have no problems supplying the needed amperage off one buss. However, generators (and probably inverters) only supply 1/2 the total wattage per 120v leg.

    Is this the way it's always done?

    Why isn't 240v supplied off both busses, 120v off each? Is the cb the problem?

    If you need a 240v inverter, how do you work-around this?

    Hmmm. Sounds like somebody miswired things somewhere.

    A 200 Amp 240 volt service to a site consists of two hot lines, each 200 Amps, and each 120 volts to ground but of opposite phase (so that one AC bus is + at the time the other is - and vice versa.)
    The CB panel will have two bus bars, one for each hot wire, and a neutral which is only used when feeding 120 volt loads.
    A 240 volt breaker is actually two 120 volt breakers linked together with each one fed from a different bus.

    In the UK and other 220 volt countries, the hot line is 220 volts with respect to the grounded line and so a breaker panel would only need one hot bus, unless fed with 440 in the form of two out-of-phase 220 volt lines.

    If your generator really is 240 volts, with a third wire for neutral, then the transfer switch should connect one hot line to one bus in the breaker panel and the other hot line to the other bus. Then any of the 240 volt breakers in the panel will really be delivering 240 volts.

    If your transfer switch is one which brings the individual circuits from the main panel into the transfer switch enclosure and each circuit is (individually?) switched between a feed from the main panel and a feed from the generator, then a 240 volt load will use up two positions in the transfer box, and it is up to you to make sure that the two are connected to opposite phases on the generator side.

    Can you provide a photo or a drawing of what you are talking about? That may clarify things.

    And, yes, it is common for the generator to be able to supply only half of its rated power (or maybe a bit more) on one of its two 120 volt outputs. Most will have two 120 volt outputs, each of which can supply half the power, and a second 240 volt output which can supply the full output to a 240 volt load. There are various combinations of 120 volt and 240 volt load which will total up to an amount within the generator's output rating.
    SMA SB 3000, old BP panels.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter

    I'll see if I can post a picture. What you have written is essentially what I stated, so we appear to agree. Thanks.

    The transfer switch is very large and sends either commercial power or generator power to the main circuit breaker panel. The generator outputs 240v through a 4-wire NEMA 14-50 plug to a twist lock recepticle.

    Both circuit breaker busses are powered so I have power to all the house outlets and switches. When using the generator, I switch off circuit breakers for the high amperage 240v units (water heater, dryer, range, HVAC). The only 240v device left powered is the 6 amp well pump. The generator hardly notices the well pump when it turns on.

    "And, yes, it is common for the generator to be able to supply only half of its rated power (or maybe a bit more) on one of its two 120 volt outputs. Most will have two 120 volt outputs, each of which can supply half the power, and a second 240 volt output which can supply the full output to a 240 volt load. There are various combinations of 120 volt and 240 volt load which will total up to an amount within the generator's output rating."

    That's the problem. Even though the generator (or inverter) outputs 240v, it's still two hot lines of 120v. For a 240v appliance, the circuit breaker panel has a two pole cb that feeds two 120v hots to make 240v. Correct? So, for commercial power that one buss is 120v @ 100 amps? The second buss is 120v @ 100 amps? Together it's 240v @ 200 amps? Or is each 120v buss 200 amps?

    The problem comes with the generator (or inverter). If it's rated at 7500 watts and 240v, 7500 divided by 240 is 31.5 amps total. However, that is split in half to supply both 120v hots. So the most I could power on each cb buss is a 240v at 15 amps or 3750 watts. Is this correct?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    So, for commercial power that one buss is 120v @ 100 amps? The second buss is 120v @ 100 amps? Together it's 240v @ 200 amps?
    No, its 240 v @ 100 amps

    Toby wrote: »
    The problem comes with the generator (or inverter). If it's rated at 7500 watts and 240v, 7500 divided by 240 is 31.5 amps total. However, that is split in half to supply both 120v hots. So the most I could power on each cb buss is a 240v at 15 amps or 3750 watts. Is this correct?

    No. You can do 240 @ 31.5 amps. Or you can do two 120 volts, each at 31.5 amps.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 240v Generator / Inverter

    "That's the problem. Even though the generator (or inverter) outputs 240v, it's still two hot lines of 120v. For a 240v appliance, the circuit breaker panel has a two pole cb that feeds two 120v hots to make 240v. Correct? So, for commercial power that one buss is 120v @ 100 amps? The second buss is 120v @ 100 amps? Together it's 240v @ 200 amps? Or is each 120v buss 200 amps?

    The problem comes with the generator (or inverter). If it's rated at 7500 watts and 240v, 7500 divided by 240 is 31.5 amps total. However, that is split in half to supply both 120v hots. So the most I could power on each cb buss is a 240v at 15 amps or 3750 watts. Is this correct?"

    by this it is quite clear you are confused.

    if one has 2 hot legs on 240vac, each at your example of 120vac and 100a, it totals 240vac at 100a.

    now in your 7500w example it creates the rough equivalent of 240vac at 31.25a. each leg will be able to carry 31.25a at 120vac. now if one taps a leg at say 20a then that leaves 11.25a on that leg that can be used. if one has both 120vac loads and 240vac loads then after seeing the 20a occupied by the one leg it means that one can still go to that same 20a on the other leg to balance the 240vac load making 11.25a x 240vac = 2700w available for the 240vac load. the other 120vac leg can have up to a 20a load applied to it when the 1st leg has a 20a load on it and seeing a 2700w 240 vac load. in other words if it isn't used on both legs it is semi-wasted and the remainder (current capacity - load capacity) of any single leg current draw available limits the 240vac current draw to that same current draw - the single leg's current draw.

    hope i didn't confuse you with this. try this overview example,

    7500w genny = 31.25a x 240vac
    each leg cuts the power in half by only cutting the voltage in half. each leg is 120vac x 31.25a = 3750w x 2 legs = 7500w
    if each 120vac leg has a 10a load on it then 21.25a is available at either 240vac or each 120vac leg. if only one leg is using 10a at 120vac then the other leg is still free to use all 31.25a at 120vac, but the 240vac is now limited as a portion of the current was taken from the first leg and now means only 21.25a at 240vac can be utilized.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter

    Yep, I'm really confused now.

    Let's try this. I have 240v commercial electrical service to a 200amp breaker panel. It's supplied by three wires, two hots and a ground/neutral. Correct? Measuring Leg1 to Neutral is 120v. Measuring L2 to neutral is 120v. Measuring L1 to L2 (have not tried this) is 240v. Correct?

    In the breaker panel is two buss bars. Each supplies 120v (L1 to neutral and L2 to neutral).

    If the commercial service was limited to exactly 200amps, how is that distributed? L1 has 100amps and L2 has 100amps? Now I'm guessing that amps of service is more a factor of the cb panel than the wires to it.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 240v Generator / Inverter

    no, as each 120vac leg will be at 200a.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter

    "no, as each 120vac leg will be at 200a."


    Ok, that I can understand. I do see where it was explained earlier.

    Thanks.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: 240v Generator / Inverter

    200 amp service means each of the incoming hot wires will support 200 amps. Assuming the main breaker is a 200 amp breaker. Greater then 200 amps+ on either leg will trip the main breaker. Each of these line are interdigitated within the breaker box to support loading of either side (referred to L1 and L2 lines). L1 or L2 to neutral is 120 vac.

    Easiest to view incoming AC as a 240vac center tapped transformer output where the center tap in the neutral. The attached diagram outlines a typical residential setup.

    Normally total 120 vac loads from either L1 or L2 lines will not come close to totalling 200 amps max. The heaviest loads are 240 vac. (Air conditioner, hot water heater, electric range, and clothes drier).

    A typical 240/120vac generator has four components that make up its rated output. Output rating is VA not watts. Amperage is what counts.

    First there is shaft power available from the engine ( rpms X torque)
    Second there is the amount of magnetic field intensity the laminated iron core will support.
    Third there is the amount of magnetic field the field winding will generate.
    Finally there is the wire size for the stator winding and its current handling capability.

    Loading single sided 120 vac will be limited by the last item, wire size of stator winding. Typically you can draw about 120% of maximum rated amperage. The first three items listed above do not care where the load is coming from single sided 120 vac or full 240 vac. It is all the same to those three items.

    Any transfer switch put on the incoming A.C. must support the full grid current rating, 200 amps in this example. This is the case even if a small generator is used and is because the transfer switch can be passing the full grid current in normal operation.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter

    Thanks for the drawing. That helped.

    To follow-up, the transfer switch is made by Midwest. 200amp on Utility (Switch Up), 100 amp on Generator (Switch Down).

    Circuit breaker panel main cb is rated at 200 amp.

    My concern was how many amps were available when on generator if the generator supplies 240v and 7500 watts through a NEMA 14-50 four blade plug. My inderstanding is the generator splits the available amperage in half for each 120v leg. In other words, even though I have one 240v generator, it's like having two 120v generators, each supplying 3750 watts. 3750 watts or 31.25 amps goes to cb panel L1 and 3750 watts, 31.25 amps to L2.

    Now, in the cb panel I have a 240v clothes dryer that conncets to L1 through a two pole 30 amp breaker. I tried to run the dryer with the generator. Wasn't enough amps to power the dryer since the best it can get is 31 amps off L1. If was running but not at as it should. Maybe I'm not getting 31 amps off the generator.

    208/230v 5 amp well pump ran ok. It's on L1 with a two pole 20 amp breaker.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 240v Generator / Inverter
    Toby wrote: »
    Now, in the cb panel I have a 240v clothes dryer that connects to L1 through a two pole 30 amp breaker. I tried to run the dryer with the generator. Wasn't enough amps to power the dryer since the best it can get is 31 amps off L1. If was running but not at as it should. Maybe I'm not getting 31 amps off the generator.

    Is this an electric drier? Mine uses a 30 amp 240 VAC branch circuit which would imply a 24 amp maximum load (30 amps * 0.80 NEC derating).

    If your generator is not supplying the load--There may be an issue with the generator or the wiring somewhere.
    208/230v 5 amp well pump ran ok. It's on L1 with a two pole 20 amp breaker.

    Technically, the well pump is tied to both L1 and L2 (to get 240 VAC).

    The generator output probably looks something like:
    
    L1/Neutral 120 VAC 31 amps
    L2/Neutral 120 VAC 31 amps
    L1/L2 240 VAC 31 amps
    [FONT=fixedsys]
    ||(=========o~o=== L1+breaker
    ||(
    ||(
    ||(==\
            \
             ===+======== Neutral (earth grounded)
            /    --+--
    ||(==/    / / / /
    ||(
    ||(
    ||(========[/FONT][FONT=fixedsys]o~o=== L2+breaker[/FONT]
    
    

    There are a few gensets that let you connect the two outputs together in parallel (in this case, for 62 amps @ 120 VAC).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    My inderstanding is the generator splits the available amperage in half for each 120v leg. In other words, even though I have one 240v generator, it's like having two 120v generators, each supplying 3750 watts. 3750 watts or 31.25 amps goes to cb panel L1 and 3750 watts, 31.25 amps to L2.

    No. A 240VAC 100A service or generator provides [email protected] Assuming maxxed out balanced loads, the current on each 120A bus is the same - 100A. What's cut in half for a single bus is the power (Watts), not the current. [email protected] is 24000W. Each 120V bus carries [email protected], or 12000W.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter
    BB. wrote: »
    Is this an electric drier? Mine uses a 30 amp 240 VAC branch circuit which would imply a 24 amp maximum load (30 amps * 0.80 NEC derating).

    If your generator is not supplying the load--There may be an issue with the generator or the wiring somewhere.



    Technically, the well pump is tied to both L1 and L2 (to get 240 VAC).

    The generator output probably looks something like:
    
    L1/Neutral 120 VAC 31 amps
    L2/Neutral 120 VAC 31 amps
    L1/L2 240 VAC 31 amps
    [FONT=fixedsys]
    ||(=========o~o=== L1+breaker
    ||(
    ||(
    ||(==\
            \
             ===+======== Neutral (earth grounded)
            /    --+--
    ||(==/    / / / /
    ||(
    ||(
    ||(========[/FONT][FONT=fixedsys]o~o=== L2+breaker[/FONT]
    
    

    There are a few gensets that let you connect the two outputs together in parallel (in this case, for 62 amps @ 120 VAC).

    -Bill


    Yes, it's an electrical dryer. Supplied by a two pole 30 amp breaker on L1. Tag states the power requirements at 120/240vac and 24 amps. Since the dryer was having trouble running, I suspect the generator isn't supplying the full rated capacity. Not an issue. It was just a test.

    I don't understand how the well pump could be tied to both L1 and L2 since it is wired to a two pole 20 amp breaker on L1 circuit breaker buss.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter
    ggunn wrote: »
    No. A 240VAC 100A service or generator provides [email protected] Assuming maxxed out balanced loads, the current on each 120A bus is the same - 100A. What's cut in half for a single bus is the power (Watts), not the current. [email protected] is 24000W. Each 120V bus carries [email protected], or 12000W.


    Sorry, but you have completely lost me.

    I don't have straight 240v commercial electrical service. I have commercial electrical service which provides 120vac to circuit breaker panel L1 buss and 120vac to circuit breaker panel L2 buss. So yes, you could say I have 240v service. Both go through a 200 amp main breaker. 240vac to appliances that need 240vac is supplied by a single two pole circuit breaker on either L1 buss or L2 buss. A single appliances is not supplied with 240vac by being connected to both L1 and L2 buss.

    Example of what I see in the breaker panel:

    L1 buss
    Two pole 30 amp breaker - 240v clothes dryer
    Two pole 20 amp breaker - 240v well pump
    Two pole 30 amp breaker - 240v water heater

    L2 buss
    Two pole 50 amp breaker - 240v cooktop/range

    ....... and on it goes for 120v and 240v electrical needs.

    I have no idea if this is right or wrong. I'm just stating what I see in the breaker panel.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 240v Generator / Inverter

    You have to look at the breakers and bus bar. You will find the ganged breakers are across L2 and L1 buses. This is the only way you will get 240 vac.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    Yes, it's an electrical dryer. Supplied by a two pole 30 amp breaker on L1. Tag states the power requirements at 120/240vac and 24 amps. Since the dryer was having trouble running, I suspect the generator isn't supplying the full rated capacity. Not an issue. It was just a test.

    I don't understand how the well pump could be tied to both L1 and L2 since it is wired to a two pole 20 amp breaker on L1 circuit breaker buss.
    A two pole breaker connects to two busses; unless both busses in the panel are tied to the same leg, anything on a two pole breaker is tied to L1 and L2. If the busses are tied to the same leg, a two pole breaker in the panel supplying a single load would be a code violation as well as a safety issue.

    Just for clarity, a two pole breaker has two switch handles tied together. Is that what you mean, or do the breakers you are talking about have two terminals? If a breaker has two terminals (one for the bus and one for the conductor supplying current to the load) and a single switch, it's a single pole breaker; a two pole breaker has four terminals.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter
    BB. wrote: »
    You have to look at the breakers and bus bar. You will find the ganged breakers are across L2 and L1 buses. This is the only way you will get 240 vac.

    -Bill


    Actually that occured to me and I was just looking for a diagram that showed that. I'm not pulling any breakers but I believe you are correct that the two pole breakers connect to both the buss bars. I guess they over lap somehow in the panel. Thanks for helping me understand that.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    Actually that occured to me and I was just looking for a diagram that showed that. I'm not pulling any breakers but I believe you are correct that the two pole breakers connect to both the buss bars. I guess they over lap somehow in the panel. Thanks for helping me understand that.
    The bus bars have fingers that interleave under the breaker supply terminals so that in a column of single pole breakers, they alternately connect to L1 and L2. A two pole breaker occupies two adjacent single slots and connects to both L1 and L2.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter
    ggunn wrote: »
    A two pole breaker connects to two busses; unless both busses in the panel are tied to the same leg, anything on a two pole breaker is tied to L1 and L2. If the busses are tied to the same leg, any two pole breaker in the panel supplying a single load would be a code violation as well as a safety issue.

    Just for clarity, a two pole breaker has two switch handles tied together. Is that what you mean, or do the breakers you are talking about have two terminals? If a breaker has two terminals (one for the bus and one for the conductor supplying current to the load) and a single switch, it's a single pole breaker; a two pole breaker has four terminals.


    Yes, you are correct. Two switch handles tied together and each has a wire connected. At the empty space on the bottom of the panel I did notice the off setting of the buss bars which allows the breaker to conncet to both L1 and L2 buss for 240v.

    That has finally sunk in my head. Now I need to check the generator to make sure its working correctly.

    Thanks for everyone input.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: 240v Generator / Inverter

    If you are connecting as 240v/120v into transfer switch assume the 7500 watt generator can produce 31 amps per leg. Depending on generator its voltage may sag down to 210v/105v at maximum loading.

    You should put a dual pole 240v 30 amp breaker between generator and transfer switch to make sure you don't overload the generator.
    Be sure you know the 7500 watts (actually magitude of V*I, not watts) is continuous rating and not just peak intermittant loading.
    Things like motors and pumps have a power factor less then one and generator are VA rated even though they say watts on their labels.

    My dryer draws 25 amps. The heater element which is most of the draw is intermittant cycling after it warms up. An electric motor may draw more current when voltage sags where a heating element in dryer or hot water heater will draw less current.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: 240v Generator / Inverter
    RCinFLA wrote: »
    If you are connecting as 240v/120v into transfer switch assume the 7500 watt generator can produce 31 amps per leg. Depending on generator its voltage may sag down to 210v/105v at maximum loading.

    You should put a dual pole 240v 30 amp breaker between generator and transfer switch to make sure you don't overload the generator.
    Be sure you know the 7500 watts (actually magitude of V*I, not watts) is continuous rating and not just peak intermittant loading.
    Things like motors and pumps have a power factor less then one and generator are VA rated even though they say watts on their labels.

    My dryer draws 25 amps. The heater element which is most of the draw is intermittant cycling after it warms up. An electric motor may draw more current when voltage sags where a heating element in dryer or hot water heater will draw less current.


    The generator claims it can surge to 13,500 watts. Maybe. Also, the generator NEMA 14-50 plug markings state it's 240v 50A, but has two pop-out breakers that are each rated at 35 amps. ?

    I could put a clamp-on amp meter on the wires and see what the current draw is but I try to stay away from un-covered breaker panels.

    Thanks.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 240v Generator / Inverter

    That would be ~56 amps 240 volts (13,500 watt surge).

    But, normally, the continuous output current should be (I would expect) 35 amps * 0.8 NEC derating = 28 amps

    The more you are above 80% of a breaker/fuse rating, the more likely the protection device is to open. At 100% load, the device may open in minutes to hours (fuses/breakers are frustratingly in-accurate devices).

    -Bill

    PS: Clamp on Amp Meters are very safe--You just need to get to a single insulated wire to measure the current (safely).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: 240v Generator / Inverter

    My own experience shows that electric dryers are very hard loads on a genset, so your genset may be just fine. Mine is rated for 12,000 watts (50 amps @ 240), while my dryer is like others mentioned here 24 amps @ 240 volts (30 amp breaker). When I first installed the genset I had the dryer as one of my loads. You need clean clothes during an extended outage, so why not. However, when I ran it from the genset, it caused a severe voltage sag. I was still using incandescent lights at the time and it felt like I was in a brownout. It shouldn't have had a problem running that load but it did, so after one trial I removed the dryer from my genset panel. I also have a 2-ton A/C on that panel (30 amp breaker). The compressor pumps are notorious for having large startup surges but it never had a problem starting it or running it. No brownout. Go figure.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 240v Generator / Inverter
    Toby wrote: »
    Maybe. Also, the generator NEMA 14-50 plug markings state it's 240v 50A, but has two pop-out breakers that are each rated at 35 amps. ?

    The rating stamped on the plug or socket is the maximum load the connector can safely handle (not an indication that you can plug and unplug it with that load present though.)
    Normally the connector will be chosen conservatively and a breaker is used to limit the actual current to what the source or wiring can handle. 35 amp breakers in each leg indicate that the 50 amp connector is a good conservative design. (The next smaller one readily available is probably 30 amps.)
    SMA SB 3000, old BP panels.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: 240v Generator / Inverter

    Dryers have two primary components drawing current, the motor and the heater. The motor likely has a starting surge of 15 amps or so with a run current less then 5 amps. The heating element is the largest draw and is pure resistive.

    Punchline is you should not be having any trouble with power factor with heating element the dominent load. If your dryer starts up with initial concurrent connection of motor and heating element the combined motor startup surge plus the heating element may add up to 35 to 40 amps until the motor comes to speed.

    I have a 15kW Generac and it runs my dryer without issue. Make sure you don't have other loads on that adds to the total (like water heater).
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 240v Generator / Inverter

    Also, Nichrome Wire's resistance increases with temperature--So, for the first few seconds it can draw 10-20% more current:


    Increase in resistance with temperature[2]
    [TH]DEG.F[/TH]
    [TH]DEG.C[/TH]
    [TH]NiCrA[/TH]
    [TH]NiCrC[/TH]


    68
    20
    0
    0


    600
    315
    3.3%
    5.2%


    1000
    538
    6.3%
    8.6%


    2000
    1093
    6.0%
    10.5%




    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 240v Generator / Inverter
    RCinFLA wrote: »
    Dryers have two primary components drawing current, the motor and the heater. The motor likely has a starting surge of 15 amps or so with a run current less then 5 amps. The heating element is the largest draw and is pure resistive.

    Punchline is you should not be having any trouble with power factor with heating element the dominent load. If your dryer starts up with initial concurrent connection of motor and heating element the combined motor startup surge plus the heating element may add up to 35 to 40 amps until the motor comes to speed.

    I have a 15kW Generac and it runs my dryer without issue. Make sure you don't have other loads on that adds to the total (like water heater).
    They oughta make dryers so that the heating element doesn't fire up until the motor is up to speed.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 240v Generator / Inverter
    ggunn wrote: »
    They oughta make dryers so that the heating element doesn't fire up until the motor is up to speed.

    They probably do, at least the newer ones with electronic controls. The old ones with mechanical time switches would have needed additional components (at least one TD relay) to do it, so SOL.
    SMA SB 3000, old BP panels.
  • LEDGuyLEDGuy Registered Users Posts: 6
    Re: 240v Generator / Inverter

    Hi All... new here - looking to fill the knowledge base (in my head) with a lot of this info as I'm in the process of 'testing' some of these things as well.
    techntrek wrote: »
    My own experience shows that electric dryers are very hard loads on a genset, so your genset may be just fine. Mine is rated for 12,000 watts (50 amps @ 240), while my dryer is like others mentioned here 24 amps @ 240 volts (30 amp breaker). When I first installed the genset I had the dryer as one of my loads. You need clean clothes during an extended outage, so why not. However, when I ran it from the genset, it caused a severe voltage sag. I was still using incandescent lights at the time and it felt like I was in a brownout. It shouldn't have had a problem running that load but it did, so after one trial I removed the dryer from my genset panel. I also have a 2-ton A/C on that panel (30 amp breaker). The compressor pumps are notorious for having large startup surges but it never had a problem starting it or running it. No brownout. Go figure.

    I would agree that any load that needs 240 (split phase) typically has motors, compressors, large resistive loads, etc. I'm almost positive that the reason you are not seeing any 'brown-outs' with the AC/heat pump is that these guys have big honkin startup capacitors (almost like stored energy) for the initial kick in of the compressor motor. No typically the case with indoor applicances as these large caps can fail and EXPLODE (had one go this summer in my outdoor AC/Pump) and sounded like someone lit off an H-100 right outside the home.

    So in short on the topic at hand, without intentionally trying to hijack the thread, I'm looking to do much of the same as what everyone is talking about.

    Outdoor Genset (5kw)
    > \
    \
    Indoor Juice bank / Inverter
    > > To 240/Split Man Xfer Panel ----> Grid Power (Dual 200A / Split Phase Panels & Branch)
    (charged by either Solar/wind or line power) /
    /
    Possiblity of Large DC UPS system (240/Split) ->/

    Actually spoke to APC on friday about a hardwire UPS for 240 AC in and 240 AC out... Shouldn't be a problem.

    So Also have a Xantrex 3000 / 120vac or hardwire 120ac, but thinking of either using the solar/batteries/inverter as suplimental (kinda of stand alone) or did a bit of research on an Auto transfer switch made for marine apps. This might work: http://www.escousa.net/Merchant2/merchant.mv?&Screen=PROD&Store_Code=E&Product_Code=ES50M-65N&Category_Code=EP5 (Esco ES50M-65N) Or for a staggering price, they have one that allows hookup of Gen, Inverter, and Shoreline (in my case, 240VAC UPS) - This would all be BEFORE the Gen MANUAL Transfer Switch BEFORE entering any of the main hardwired panels.... Thoughts?
    Thanks in advance!
    LED Guy
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 240v Generator / Inverter

    Welcome to the forum LEDGuy!
    LEDGuy wrote: »
    I would agree that any load that needs 240 (split phase) typically has motors, compressors, large resistive loads, etc. I'm almost positive that the reason you are not seeing any 'brown-outs' with the AC/heat pump is that these guys have big honkin startup capacitors (almost like stored energy) for the initial kick in of the compressor motor.

    Just to clarify--The starting capacitor(s) on electric motors are not to "store" energy for starting loads/reduction in surge. They are there to "shift" or create a second phase for the electric motor.

    Motors need a rotating field to "drag" the rotor around (create rotational motion). Three Phase Motors do not need starting capacitors because 3 phase power is already "rotating" phases a 120 degrees apart.

    120 and 120/240 VAC "split phase" power is either one phase (120 VAC) or two phases 180 degrees apart (240 VAC split phase). There is no "rotation" available that you could wire up two sets of windings offset by XX degrees to "drag" the rotor in circles.

    When you take a second winding and put a capacitor in series with it (starting winding plus switch to turn on for starting) creates a leading voltage which is somewhere around 45 to 90 degrees or so relative to the single main power connection. So now, you have a "rotating" field which can start the motor rotation.

    Once the motor is rotating near full speed, there is a set of mathematical equations you can use to show that the 180 degree "up/down" alternating magnetic field is actually two counter rotating fields--When the rotor is rotating, the inductance favors one of the rotating vectors (low impedance) and the other counter rotating vector "sees" high impedance and therefore the fields now look to be rotating.

    There are other motor types that can be self starting from single phase power... Brushed motors use mechanical commutation to create the offset fields to produce torque. Electronic commutation to create three phase power (DC computer fans, DC PM motors), and motors with "motor run" capacitors (usually fractional horse power), or shaded pole type motors (used for small fans, AC motors) which use a copper shunt to delay a part of the main magnetic field.

    http://en.wikipedia.org/wiki/AC_motor
    http://avstop.com/ac/apgeneral/typesofacmotors.html

    So--Long way around of saying that Starting Capacitors do not reduce starting surge current--Although, you can adjust surge current/starting torque by selecting larger or smaller motor start capacitors.

    Of course, there are external devices that can reduce/control starting surge (used frequently by A/C folks) and there are VFDs (variable frequency drives) which take AC (or DC) power in, and create variable frequency 2 or 3 phase output which can directly drive many types of AC induction motors (and even make them variable speed--adjust them for load requirements--such as pumping water more efficiently).
    No typically the case with indoor appliances as these large caps can fail and EXPLODE (had one go this summer in my outdoor AC/Pump) and sounded like someone lit off an H-100 right outside the home.

    In all my years--I don't think I every had one of these caps fail explosively--And probably have only seen one failed cap--It is rare.
    So in short on the topic at hand, without intentionally trying to hijack the thread, I'm looking to do much of the same as what everyone is talking about.

    Outdoor Genset (5kw)
    > \
    \
    Indoor Juice bank / Inverter
    > > To 240/Split Man Xfer Panel ----> Grid Power (Dual 200A / Split Phase Panels & Branch)
    (charged by either Solar/wind or line power) /
    /
    Possibilityof Large DC UPS system (240/Split) ->/

    Actually spoke to APC on friday about a hardwire UPS for 240 AC in and 240 AC out... Shouldn't be a problem.

    So Also have a Xantrex 3000 / 120vac or hardwire 120ac, but thinking of either using the solar/batteries/inverter as supplemental (kinda of stand alone) or did a bit of research on an Auto transfer switch made for marine apps. This might work: http://www.escousa.net/Merchant2/merchant.mv?&Screen=PROD&Store_Code=E&Product_Code=ES50M-65N&Category_Code=EP5 (Esco ES50M-65N) Or for a staggering price, they have one that allows hookup of Gen, Inverter, and Shoreline (in my case, 240VAC UPS) - This would all be BEFORE the Gen MANUAL Transfer Switch BEFORE entering any of the main hardwired panels.... Thoughts?
    Thanks in advance!
    LED Guy

    More or less--Suggest you measure and understand your loads/needs... Generating power is expensive, and almost any amount of money you spend on conservation will save you money overall (smaller backup power system, less emergency fuel storage, less maintenance, less batteries to replace every 3-8 years, etc.).

    Once you have a handle on your needs--Then we can talk about over all system design and equipment options. There are a few devices out there like the Schneider/Xantrex Hybrid (off grid + grid tie capable) 120/240 VAC inverter that has two AC inputs (AC Mains and AC Genset)... Can make the wiring/configuration much less complex. However, they are not cheap and require a fair bit of understanding to install/configure.

    Feel free to start a new thread to discuss your needs. Usually makes everything easier to have a thread focused on your set of questions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LEDGuyLEDGuy Registered Users Posts: 6
    Re: 240v Generator / Inverter

    Wow, you're a wealth of info Bill.... Thanks for the input and new thread coming up!
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