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Thread: Measuring whole house watts for generator

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    Measuring whole house watts for generator

    Will using a Redfish iDVM550 (on kw setting) at the main panel with the clamp around 1 incoming (main) hot leg and the leads on the 2 (main) hot legs give an accurate measure of how many watts are being consumed, and thus what size generator will suffice (assumes all appliances are running that one wishes to run on the generator)? I believe it will, but would like to verify.

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    Quote Originally Posted by vin lashon View Post
    Will using a Redfish iDVM550 (on kw setting) at the main panel with the clamp around 1 incoming (main) hot leg and the leads on the 2 (main) hot legs give an accurate measure of how many watts are being consumed, and thus what size generator will suffice (assumes all appliances are running that one wishes to run on the generator)? I believe it will, but would like to verify.
    The biggest concern is the inrush current of the inductive loads.

    I've only ever used an ammeter to check what I want/can run on the generator and basically come up with an amp "budget".

    The 120v loads should be balanced. Lights, ceiling fans, refrigerator. Be mindful of that.

    If you're trying to run a full-sized A/C, I can tell you from experience a 2.5 ton starts up nicely with my 9350 (starting) 7500 (running) watt generator and only draws about 8-9 amps Total while running.


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    Quote Originally Posted by shellkamp View Post
    The biggest concern is the inrush current of the inductive loads.

    I've only ever used an ammeter to check what I want/can run on the generator and basically come up with an amp "budget".

    The 120v loads should be balanced. Lights, ceiling fans, refrigerator. Be mindful of that.

    If you're trying to run a full-sized A/C, I can tell you from experience a 2.5 ton starts up nicely with my 9350 (starting) 7500 (running) watt generator and only draws about 8-9 amps Total while running.
    This morning I used the iDVM on my main panel and came up with about 6800 watts, which I think was about right with my 1.5 ton and 3 ton A/C's running, along with a couple of refrigerators and, a few lights and TVs. Even with long power outages, I could get by without the 3 ton. your comment regarding the 2.5 ton is helpful. This is for my house (hurricane season is back), but I began thinking about it (again) because a friend of mine is asking questions about a generator for his house. I guess to really be sure, I'd need to check the A/C's individually and see if it adds up to what I get at the panel with only the A/Cs running.

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    Quote Originally Posted by vin lashon View Post
    This morning I used the iDVM on my main panel and came up with about 6800 watts, which I think was about right with my 1.5 ton and 3 ton A/C's running, along with a couple of refrigerators and, a few lights and TVs. Even with long power outages, I could get by without the 3 ton. your comment regarding the 2.5 ton is helpful. This is for my house (hurricane season is back), but I began thinking about it (again) because a friend of mine is asking questions about a generator for his house. I guess to really be sure, I'd need to check the A/C's individually and see if it adds up to what I get at the panel with only the A/Cs running.
    With how much gas little portable generators burn, I'd be running the 1.5 ton only. The 7500 watt champion brand generator that I have would suite you well if so.

    If you want to run them both, you'll want to get something like a 12kw running with 15kw starting watts. Keep in mind the starting watts are what they advertise when you look at generators.

    Sent from my motorola one 5G UW using Tapatalk

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    Quote Originally Posted by shellkamp View Post
    With how much gas little portable generators burn, I'd be running the 1.5 ton only. The 7500 watt champion brand generator that I have would suite you well if so.

    If you want to run them both, you'll want to get something like a 12kw running with 15kw starting watts. Keep in mind the starting watts are what they advertise when you look at generators.

    Sent from my motorola one 5G UW using Tapatalk

    I'll probably get a Generac and run a gas line. I could get by with just the 1.5 ton. I think a 10kw would handle both A/C's fine, but I'd need to collect verifiable data before biting that particular bullet. The only reason I might want the ability to run both A/Cs is for those rare times when the power is out for days or weeks.

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    Just put them on a load shed device.
    "The only true wisdom is in knowing you know nothing" Socrates

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    Quote Originally Posted by mgenius33 View Post
    Just put them on a load shed device.
    Something like this?

    https://www.homedepot.com/p/Generac-...oduct-overview

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    Kohler has much better stuff. I wouldn’t use anything Generac.
    If I do a job in 30 minutes it's because I spent 30 years learning how to do that in 30 minutes. You owe me for the years, not the minutes.

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    Quote Originally Posted by vin lashon View Post
    I'll probably get a Generac and run a gas line. I could get by with just the 1.5 ton. I think a 10kw would handle both A/C's fine, but I'd need to collect verifiable data before biting that particular bullet. The only reason I might want the ability to run both A/Cs is for those rare times when the power is out for days or weeks.
    Vin, we have a 8kw with a manual transfer switch. We power the inside panel and pop in a W.U. where needed for long term.
    We play green acres with the stove and HW heater. My real concern is with the noise for long term use.
    The last "outage" we made coffee for the neighborhood...
    Life is too short, Behappy!
    TFMM

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    Quote Originally Posted by STEVEusaPA View Post
    Kohler has much better stuff. I wouldn’t use anything Generac.
    Yeah, I would agree. Kohler is more durable.
    "The only true wisdom is in knowing you know nothing" Socrates

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    Just tying up loose ends for a few of my old threads. I ended up buying a 10kw Generac from one of my supply houses, and the iDVM550 does indeed measure KW loads. This 'recording' is with 2 refrigerator/freezers running, various lights, TVs, the PCs in my office and 2 A/Cs. The spikes are the start up amps on the condensers.

    Name:  DVM kw load.PNG
Views: 221
Size:  156.2 KB

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    that seems low to me 10KW, remember the voltage does not drop when being powered by your utility company. when all you have is a generator, the loads will put strain on it and cause voltage drop and amperage increases.
    I have a 9000watt peak generator, with a v-twin engine, it barely starts my 1.5hp pump for my well..
    I'm not young enough, to know everything...

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  17. #13
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    Quote Originally Posted by dieseldude View Post
    that seems low to me 10KW, remember the voltage does not drop when being powered by your utility company. when all you have is a generator, the loads will put strain on it and cause voltage drop and amperage increases.
    I have a 9000watt peak generator, with a v-twin engine, it barely starts my 1.5hp pump for my well..
    Time will tell. I can always limit what the generator runs. I also plan on running a large enough gas line so that I can upsize if ever needed.

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    What are opinions on soft start vs HSK when using a generator?

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    Quote Originally Posted by vin lashon View Post
    What are opinions on soft start vs HSK when using a generator?
    Soft start would definitely be better than a hard start. I purchased a rebranded Emerson for about $250-275 I think it was.

    I put one on my 21K BTU nominal compressor. It didn't make an audible difference as far as the generator "bogging down", but it never had a problem starting it without the soft start kit, either. I didn't do in depth testing as far as inrush current, since I didn't have a meter with that function at the time of it getting installed.

    My generator is a champion brand 7500 running watts, 9375 starting watts

    Sent from my motorola one 5G UW using Tapatalk

  20. #16
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    Quote Originally Posted by vin lashon View Post
    What are opinions on soft start vs HSK when using a generator?
    If your generator handled as is, I wouldn’t bother.

    More stuff to break.

    Keep it as simple as possible

    Biggest thing would be to make sure both condensers dont start at the same time.

    Couple idec timing relays could make that happen if the furnaces or the condensers are close to each other.


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    Thanks for your comments, y'all. Both my condensers are close to the furnaces (15' give or take). Generac makes "smart connect modules" that do load shedding. They come in 50 amp and 100 amp. I think you have to get a separate module for each appliance whose startup you want to control.

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    Volts x amps = watts.

    You can do a quick add up for total wattage but pumps and motors spike amps on start up so you need to keep that in mind.

    Adding a 5-2-1 start kit drops the compressor amp spike and is friendly for your generator and compressor.

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    I put 5-2-1s in before I took the last KW load here. It made a huge difference. Before I put the HSKs in, it would spike over 12kw. With HSKs, hardly any spike. Here's a kw load I did today. Using the toaster oven or microwave puts me near 9, so I'd have to make sure one of the A/C systems was off if using. I'm planning on picking up a gas stove, which will eliminate the toaster oven load.

    Name:  KW Long Labeled.PNG
Views: 156
Size:  200.5 KB

  24. #20
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    Quote Originally Posted by vin lashon View Post
    I put 5-2-1s in before I took the last KW load here. It made a huge difference. Before I put the HSKs in, it would spike over 12kw. With HSKs, hardly any spike. Here's a kw load I did today. Using the toaster oven or microwave puts me near 9, so I'd have to make sure one of the A/C systems was off if using. I'm planning on picking up a gas stove, which will eliminate the toaster oven load.

    Name:  KW Long Labeled.PNG
Views: 156
Size:  200.5 KB
    How does the wattmeter account for imbalance between L1 and L2 - IE more 120v load on one line?

    I always thought watts for a split phase panel was

    Watts = volts x (L1 amps + L2 amps / 2)


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