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### Topic: U=R*I vs. Lightbulb with 40W pulls 40W no matter how high the voltage is (Read 1 time)previous topic - next topic

#### JohnRob

#15
##### May 26, 2018, 06:04 pm
I my have missed something in the earlier posts but I would approach the problem differently.

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If I have a lightbulb in my house with 230V and 40W
If we assume for a moment the lightbulb resistance does not change.

Power = E2 / Resistance

40 = 230*230 / R

R = 1322.5 Ohms

Power = E2 / Resistance

P = 24*24 /1322.5

P = 0.4355 Watts

One must remember for a  constant resistance power increases / decreases with the square of the voltage.

#### Grumpy_Mike

#16
##### May 26, 2018, 06:41 pm
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A guy who is into solar was telling me a water heater element designed for a 220 volt water heater could be used at 24 volts with solar pannels.   He's logic was the similar/same as the original poster.  I had my doubts, but he tells me it works for him.
Yes it will work, but as noted before the power produced will be 1/100th of the power, but sure it will work.
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Can't argue with a believer.
Sure you can argue with him, but in general walls are a tad more receptive.

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But then again over the years I've leaned the laws of Physice always seem to make an exception for some of his applications.
Sure yes. Thing is, that in the world of the blind the one eyed man is king, so all he needs is a few more brain cells than his moronic followers.

#### Doug101

#17
##### May 26, 2018, 07:36 pmLast Edit: May 26, 2018, 07:44 pm by Doug101
I agree.  And they make up scientific facts on the spot.

I had a California Certified Solar Design Engineer tell me that during the day the solar panels on my roof get charged-up during the day and then at night discharge and supply electricity to my home.  The guy then was trying to sell me four PowerWall battery banks.  I asked him why I needed the batteries if all of the energy is stored in the solar panels?

He said you know your right.  You don't need the batteries; all of the electricity is stored in the solar panels.

The other wonderful like I hear from the solar sales experts who just a few months ago were selling used cars is there is so much solar energy coming from the sun it would supply enough electricity to the world if only we had enough solar panels.

To which I reply, you know you are right, but you know, if all the suns energy striking the Earth were turned into electricity there wouldn't be any for planets, we would have no food, and it would be dark all of the item.

I hope you will join in my religion.  I am a science fundamentalist.   I M > HE  It is the oldest religion there is.  You will of course have to strictly obey the law of Physics and spread the good word of the knowledge of science to those who believe otherwise.

I hope you will join me and bring a friend.

#### Southpark

#18
##### May 27, 2018, 02:06 amLast Edit: May 27, 2018, 02:08 am by Southpark
I had a California Certified Solar Design Engineer tell me that during the day the solar panels on my roof get charged-up during the day and then at night discharge and supply electricity to my home.  The guy then was trying to sell me four PowerWall battery banks.  I asked him why I needed the batteries if all of the energy is stored in the solar panels? He said you know your right.  You don't need the batteries; all of the electricity is stored in the solar panels.
So, basically you're saying that ---- the particular solar 'design engineer' wasn't an electronic engineer (or someone that understands basic electronics), and doesn't know the basic functionality of solar panels etc.

#### wvmarle

#19
##### May 27, 2018, 02:25 am
He had probably just been trained to know very well "red goes here, white goes there, and green connects to that", for the electronics part, and a bit about how to safely install the panels themselves. That would mean he can install solar panels safely and properly, but has no clue on what's going on. A bit of a stretch of the word "engineer".
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

#### Doug101

#20
##### May 27, 2018, 02:53 pm
I just sharing my experiences.  I have spoken to well over 100 State of California state licensed professionals.  They had to pass some test to be a licensed professional.

You know what all of these solar professionals are connng customers to buy?  Battery packs.  These things are \$10k.  I think they are making a nice chunk of change from the sales of these things becaus they are all pushing them.  They know nothing about the things such as they are only 60% efficient.  The other 40% is lost as heat energy in charging and discharging the batteries.

#### Southpark

#21
##### May 28, 2018, 12:07 am
I just sharing my experiences.  I have spoken to well over 100 State of California state licensed professionals.  They had to pass some test to be a licensed professional.
But not all of them are like that, right? Just like any population or group.... a handful can be inadequate or bad. But not all are like that.

#### allanhurst

#22
##### May 28, 2018, 01:27 amLast Edit: May 28, 2018, 04:04 pm by allanhurst
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But not all of them are like that, right? Just like any population or group.... a handful can be inadequate or bad. But not all are like that.
I suspect the selling of snake oil attracts a certain sort of person...  mostly.

They're either technically illiterate, and so can be conned by even better salesmen, or know the deal and look at the bottom line - their pocket.

I have a friend who once sold 'better' electricity deals to people by knocking on their doors. Mostly old people.  He knew he was often selling them a poorer deal than the one they already had, but made a fat commission.

Eventually his conscience couldn't stand it, and he got out.

Many don't.

Allan

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