I have a Go Power GP ISW 3000. Currently (no pun) set for 120 V output. Go Power states this uses more power to generate. What do you suggest 100, 110, 115 or 120 V?
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Actually, when voltage drops for a given load (resistance) of a device, current will increase. It's Ohm's law. A great example of this is when you're trying to run an air conditioner on an RV park's shore power during peak summer demand. As the voltage drops, the current goes up and when it hits around 104 volts, the breaker will trip due to excessive current demand.
The National Electrical code specifies 120 volts as the U.S. standard. That is where I'd set it.
JimJim and Ginnie
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Originally posted by TucsonJim View PostActually, when voltage drops for a given load (resistance) of a device, current will increase. It's Ohm's law. A great example of this is when you're trying to run an air conditioner on an RV park's shore power during peak summer demand. As the voltage drops, the current goes up and when it hits around 104 volts, the breaker will trip due to excessive current demand.
The National Electrical code specifies 120 volts as the U.S. standard. That is where I'd set it.
Jim
If you assume power demand is constant, then W = I^2 x R, then current and resistance vary inversely. But, power demand does not remain constant, except for maybe an ac motor with frequency trying to maintain rpm while voltage drops. Resistive loads are not constant power loads.Ted
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Originally posted by TedS View Post
I will disagree. Current will not increase as voltage drops. E = I x R Ohm's law. E and I are directly proportional.
If you assume power demand is constant, then W = I^2 x R, then current and resistance vary inversely. But, power demand does not remain constant, except for maybe an ac motor with frequency trying to maintain rpm while voltage drops. Resistive loads are not constant power loads.
Jim can certainly speak for himself, but I'll guess he is assuming the wattage demanded by the powered item remains constant. In that case the only possible result is higher current when voltage drops. The apparent resistance, or better term impedance, will change. Impedance is another leap beyond a simple resistive circuit where Ohm's Law is so easy to understand. ( Rudy , you should be able to speak to this now!)
A simple example from a purely resistive circuit: Put a 12v battery across a 12 ohm resistor and the amperage is 12 v / 12 ohms = 1 amp. If the voltage drops (say to 10v), the current drops. 10 v / 12 ohms = .83 amps. There are many examples of this we've witnessed in the "real world", like a flashlight. The bulb is going dim because the voltage is dropping, which pulls less amperage, so less overage wattage from the lamp.
Now let's calculate the wattage using the 12v and 12 ohm example. 12v (squared) / 12 ohms = 12 watts, or 12v * 1 amp = 12 watts. Doesn't matter how you slice it, the result is 12 watts.
So what happens if voltage drops but the device still pulls 12 watts to operate????
Current must go up when voltage goes down to keep the wattage constant.
Using the earlier example of a drop to 10v (from 12v) and a constant 12 watt demand, that means the amperage is now 12 W / 10 v = 1.2 amps. To accomplish this the impedance of the appliance has to less than it was when the voltage was 12. Otherwise the math doesn't work.
Howard
P.S. Sure hope that math is right...
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That's the key assumption howson . Fixed power. If a device has a fixed power requirement of say 1000 watts. 1000 watts/120 volts = 8.3 amps. 1000 watts/100 volts = 10 amps.
In the real world we were in an RV park and running our AC. When the park voltage dropped to 103 Volts, the breaker kicked due to high voltage.
But of course the type of load comes into play.
JimJim and Ginnie
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Ah, the mystery of electricity. Devices like heaters are resistive loads. So lower voltage results in lower current and less heat. Even though they are called 1500 watt devices, they are not constant, fixed power devices. 100 watt light bulbs will dim with lower voltage; not as much current going through to heat the filament. The resistance or impedance of the heat element will generally increase with temperature tending to limit current.
Air conditioner motors are a different animal. It draws high startup current at zero speed. The running speed is frquency dependent, voltage and current adjust to keep that speed. So lower voltage is accompanied by increased current trying to keep the frequency controlled speed.
DC motors are resistve devices, no frequency involved. Lower voltage results in lower speed, lower current. Also not a fixed, constant load device. If its load increases and voltage remains constant, the slide jams or drags, the current increases so that the increased torque tends to increase the speed back to where the voltage says it should be. DC motors have a stalled rotor current rating due to its resistive load characteristic.
It's a curse being interested in this stuff. I'll sit down.Ted
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Interesting discussion! This mechanical engineer now has a better understanding of things I thought I already understood .
RobCate & Rob
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..and this software developer has no idea what anybody in this thread was talking about. Well, except for the first couple of posts...Brian & Kellie
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The good old days of an IBM 360/370 main frame running off punch cards, Fortran, Watt5. Cmos, others, and machine code. I had to learn machine code on my own to finish my senior project. Nothing like going through 500 to 1000 pages of dump trying to find the one line of messed up code the someone else put in year earlier.
As for electricity - well lets say I know its working when I get bit or fry something. Transistors were new when I took electronics in High School. Funny I was a wiz at identifying resister color coding.
Speaking of punch cards and hanging chads , The punch card machines in College did not type what you punched as you typed. You had to go over to a compiling unit to do that, then go back through the cards and check for typing and spelling which I am great at..........NOT And heaven help you if you dropped your card box before you numbered your cards
It is great having the experts here - I have learned a lot and you folks have helped me not mess things up.......well yet
Keith2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.
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Originally posted by Yoda View PostSpeaking of punch cards and hanging chads , Keith
Where has all the time gone.
What I get a kick out of is when something is renamed and sold as the latest greatest idea, like the "Cloud". Ok Cloud sounds better than server.
How electrically challenged am I?
When I buy a new multi-meter I have to take a marker, look at the manual, and mark one side AC and the other DC.
I always set my multi-meter to the biggest number so it doesn't blow up in my hand. You don't know, could happen.
It took me about 4 times getting shocked before I figured out you could turn the power off before replacing an electrical outlet.
If you get zapped by a charge from the coil on the car it will knock you on your butt.
If you take a car battery, jumper cables and two rods, connect the rods/cables to the battery and shove the rods into the ground about 10 feet apart the worms come out of the ground real fast, particularly if it has rained recently.
If you are having trouble finding a short in an auto lighting system just start the engine and turn everything on, then watch for smoke.
See, I really do know a lot about electricity....
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