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Old 03-27-2016, 11:22 AM   #1
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How to determine startup wattage?

How does one determine the startup wattage for various appliances?
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Old 03-27-2016, 01:34 PM   #2
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How does one determine the startup wattage for various appliances?
FaithBowls
One of these will do that: "Kill A Watt"â„¢ Electric Monitor
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Old 03-27-2016, 01:51 PM   #3
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Just look at the nameplate that is required for all appliances. Motors are a bit different in that the motor will draw up to 125% of full load starting. Not so with microwaves and such.

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Old 03-27-2016, 07:21 PM   #4
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Just look at the nameplate that is required for all appliances.

Tim

Appliances that use nichrome heating elements such as convection only ovens and small space heaters, coffee makers use 6% more current on initial start up of each heat cycle. Not an excessive over draw.

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Old 03-27-2016, 08:29 PM   #5
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Inrush current is a complicated topic. Are you just trying to be sure your inverter or generator can handle the loads?

Check this link for a good discussion of the topic.....maybe more than you wanted to know

http://sound.westhost.com/articles/inrush.htm
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Old 03-27-2016, 08:36 PM   #6
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Yes I want to calculate my power needs for generator, solar, batteries, inverters. I think it's prudent to base the system on startup wattage so I can turn everything on. I have microwave convection oven, electric fireplace, TV and components plus other equipment. The startup requirements for the TV system and fireplace are high and I'd like to figure how high.
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Old 03-29-2016, 08:52 PM   #7
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Like it was aid uo above, every piece of equiptment has a nameplate on it. All the information you need is on there. You might have to do a little ohms law to get your watts but it's all there
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Old 03-29-2016, 09:27 PM   #8
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No - I want startup wattage. Running wattage is on the plate but not startup wattage. How many watts to start up heater, TV, sound, convection? It's more than running watts and not on the nameplate usually. Sometimes a manufacturer can tell you but how can I calculate it?
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Old 03-29-2016, 09:43 PM   #9
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Most appliances other than the microwave (magnetron), refrigerator (compressor) and AC (compressor) won't have much of a difference in startup current vs. max steady state current vs. inverter or generator capacity rating. If you tell us what you are trying to do one of us may have experience and be able to share knowledge.
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Old 03-30-2016, 07:00 AM   #10
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How to determine startup wattage?

That's not accurate. Many appliances with computer controls have drastically higher startup requirements. I've seen 1,200 watt convection stoves that require 3,000 watts to start. Once again, I want to figure startup wattage for all my equipment, especially electric fireplace, residential fridge, AC units, TV and sound system. Maybe someone will come along who knows what I'm asking.
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Old 03-30-2016, 08:09 AM   #11
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@ FAITHBOWLS, are you asking what kind of device can accurately measure
"inrush current" and where to obtain one . Your correct name plate information indicates running power consumption. The other factor to consider is the probability of equipment starting at the same time.
IMO I think researching the size of generator sets used in particular rv's would be a tried and true guide for what power source size is needed.
As a last resort you can contact every equipment manufacturer for the equipment you have and ask them what the start up power draw is.

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Old 03-30-2016, 09:58 AM   #12
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Yes how to measure or calculate actual wattage used. If I'm running the fireplace and start up the convection microwave, I want to know the actual wattage used to start the convection microwave and any other equipment I start.
Seems like a basic question to me:
How to know the actual startup wattage used, not just the stated running wattage on the nameplate? I have a microwave, fireplace, heater, 2 AC units, 3 TV's, sound system, other small appliances - I want to know how much power they require to start up. Then I know what I can run and in what combinations.
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Old 03-30-2016, 10:13 AM   #13
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It may seem like a simple question but it's really not (FYI, I design power systems for a living). First basic concept is that, when dealing with AC, Volts X Amps DOES NOT ALWAYS equal Power. Most devices when you turn them on pull additional current (Amps), not that much additional power (Watts). The worst culprits are motors because they can pull a lot of extra current on start up. In a motorhome that is going to be when the A/C compressors start and it is a function of how long it takes the motor to spool up. That can be up to a couple of seconds. The electronics will have a higher surge current, but it will be over in less than 0.1 seconds. Your generator will NOT even notice that surge, although the voltage may dip a bit. Heating devices (fireplace) will be slightly longer and could take up to a second to stabilize. If you want to measure the amount, buy a clamp on Ammeter (search Amazon for "ammeter") but you have to be able to get the clamp around one, and only one, of the AC wires going to the device you want to test. Hope this helps.
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Old 03-30-2016, 10:19 AM   #14
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Thanks. I'm sure an ammeter won't work as rv equipment is well wired in. I'm surprised other people don't have this question. If the TV, microwave are on and you turn on the AC, the TV may turn off if you don't have enough power. Say you're running a generator that isn't quite big enough - you won't be able to start everything. So how to know that you have enough power to start and run everything?
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