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Dave
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 Posted:
Fri Mar 11, 2005 1:42 am Post subject:
YOU THINK YOU KNOW, BUT DO YOU? |
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12V vehicle Inverter
200watt AC device @ 120v (do vehicle inverters push 110 or 120v?).
Is there an equation that will convert what an AC device draws on the
inverter to what in turn the inverter will draw on the car? Using the
above example..?
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Peter Bennett
Guest
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Fri Mar 11, 2005 2:24 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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On 10 Mar 2005 11:42:58 -0800, "Dave" <dmcomm_ads@yahoo.com> wrote:
| Quote: | 12V vehicle Inverter
200watt AC device @ 120v (do vehicle inverters push 110 or 120v?).
Is there an equation that will convert what an AC device draws on the
inverter to what in turn the inverter will draw on the car? Using the
above example..?
|
Power = Voltage times current.
Your 200 watt device will draw 1.7 amps at 120V, and the inverter will
draw 17 amps at 12 volts (roughly - the inverter will only be 80 - 90%
efficient, so will draw a little more power than it produces, but the
battery voltage would be over 13 if the engine is running, so it would
draw a little less current than the 12 volt calculation shows.)
--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq |
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Dave
Guest
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Fri Mar 11, 2005 3:24 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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Getting the 17 amps is what I was asking. What is this equation?
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Rich Grise
Guest
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Fri Mar 11, 2005 4:29 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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On Thu, 10 Mar 2005 13:24:34 -0800, Dave wrote:
| Quote: | Getting the 17 amps is what I was asking. What is this equation?
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Go back and reread your answer.
This should also be an object lesson in quoting context.
Good Luck!
Rich |
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JeffM
Guest
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| Posted:
Fri Mar 11, 2005 4:40 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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| Quote: | This should also be an object lesson in quoting context.
Rich Grise
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As a clueless Google Groups poster, Dave still won't get it.
All he has to do is scroll up the page.
He doesn't understand that the majority of folks use newsreaders
and don't visualize Usenet as he does. |
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Dave
Guest
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| Posted:
Fri Mar 11, 2005 4:42 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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One more time for the ubers...
Power= Voltage x current. Yeah, we learned that in grade school.
What was the equation used to arrive at the inverter drawing 17 amps?
There must be a correlation between what amps an AC device draws
compared to what amps this makes the inverter draw from the car.???? |
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Robert Monsen
Guest
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| Posted:
Fri Mar 11, 2005 4:45 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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Dave wrote:
| Quote: | Getting the 17 amps is what I was asking. What is this equation?
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The forumula is Power = DC current x DC voltage.
So,
200W/12V = 16.66A
However, that assumes your converter is 100% efficient, which it is not.
So, say it's 70% efficient, then
200W / 0.70 = 286W, so 286/12V = 23.8 A
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God. |
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Dave
Guest
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| Posted:
Fri Mar 11, 2005 4:46 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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| How did you arrive at 17 amps? |
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Dave
Guest
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| Posted:
Fri Mar 11, 2005 4:49 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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This should be an object lesson contributing something meaningful to a
discussion instead of an obviously nerdy, smartass, socially oblivious,
human contact lacking, left brain comment. |
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Peter Bennett
Guest
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| Posted:
Fri Mar 11, 2005 5:00 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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On 10 Mar 2005 13:24:34 -0800, "Dave" <dmcomm_ads@yahoo.com> wrote:
| Quote: | Getting the 17 amps is what I was asking. What is this equation?
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For a rough approximation, the power is constant through the inverter,
so VI at the inverter input equals VI at the inverter output.
--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq |
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Dave
Guest
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| Posted:
Fri Mar 11, 2005 5:07 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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Ah, true Usenet nerd police. I was waiting for your arrogant comments;
they always come, here goes the volley.
Clearly a case of a nerd who's little (although I'm sure intelligent)
one track mind puts meaning on what he thinks is fact.
What is actually so, is that I use a newsreader at home, but I can't at
work, so I use Google. I did scroll up son, but the equation was not
the one I was seeking. I always get what I need here. |
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Dave
Guest
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Fri Mar 11, 2005 5:29 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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Is the 70% used to factor in what the AC device draws on the inverter?
The 200W device is an AC device drawing on the inverter.
Pardon the novice. |
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Robert Monsen
Guest
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Fri Mar 11, 2005 6:10 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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Dave wrote:
| Quote: | Is the 70% used to factor in what the AC device draws on the inverter?
The 200W device is an AC device drawing on the inverter.
Pardon the novice.
|
No, it's losses in the conversion process, and it's just an estimate.
200W is what your plugged in AC device requires. I'm assuming that it
takes a bit more power to manufacture that 200W AC. Thus, I used a 70%
fudge factor, and used that to compute the power required of the battery.
From that, and the assumption that the battery is 12V, I calculated the
current draw of from the battery while a max load is plugged in.
Your converter will probably tell you how much current it needs in it's
product literature.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God. |
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Don Bruder
Guest
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| Posted:
Fri Mar 11, 2005 6:10 am Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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In article <1110483778.410642.278160@l41g2000cwc.googlegroups.com>,
"Dave" <dmcomm_ads@yahoo.com> wrote:
| Quote: | 12V vehicle Inverter
200watt AC device @ 120v (do vehicle inverters push 110 or 120v?).
Is there an equation that will convert what an AC device draws on the
inverter to what in turn the inverter will draw on the car? Using the
above example..?
|
Inverters can (theoretically - you'll almost certainly hit a wall due to
the limits of real-world materials) push any voltage the maker wants
them to, depending on how they're designed. You want 240 volts out of
it? Wire it right, and you'll get 240 out of it. You want 120 volts out
of it? Wire it right, it'll spit 120 volts. And so on for any desired
voltage from 0 to infinity. It's all about how it was designed.
To get the answer you want, you turn the 200 watts and 120 volts your
device wants into a "PIE" - the equation P = I * E (where P is power in
watts, I is current in amps, and E is voltage in - wait for it! - volts)
will give you that answer - and solve for I, like so:
Plug in the values we know:
200 (P, watts) = I (amps) * 120 (E, volts)
Transform the equation to make solving it give us current in amps by
applying basic algebraic principles:
200 / 120 = I
And do the math:
I = 1.666... = 1 and 2/3rds amps
Inverter output: 1 and 2/3rds amps at 120 volts.
But you want to know how much of a load that places on the car...
How do you do that?
You "make another PIE":
We already know that 1 and 2/3rds amps at 120 volts is 200 watts, so we
also know that the inverter is in turn drawing 200 watts (Note 1) from
the battery. We do exactly the same equation as when we calculated how
many amps the device draws from the inverter: Solve P = I * E. Only this
time, we're working with how much the inverter draws from the car's
power supply - 200 watts at 12 volts.
Plug in our known values:
200 = I * 12
Transform to make current (I) the unknown:
200 / 12 = I
And do the math:
I = 16.666... = 16 and 2/3rds amps
Your inverter needs to draw 16 and 2/3rds amps to power your 200 watt,
120 volt device when it's running from a 12 volt source (Note 2). Plug
it into a circuit with a 20 amp fuse, and you're good to go.
Note 1: This assumes the inverter is running at 100% efficiency - a
HIGHLY unrealistic assumption, but we'll ignore that factor for now
since there are too many unknown variables to say anything
that'saccurate.
Note 2: This ignores the fact that when the engine is spinning, the
voltage available to the inverter from the car's system is going to be
closer to 13.5 or 14 volts than 12 volts, which will change the actual
current being drawn from the car slightly - finding out exactly how
"slightly" is left as practice for you.
--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details. |
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Kitchen Man
Guest
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| Posted:
Fri Mar 11, 2005 1:26 pm Post subject:
Re: YOU THINK YOU KNOW, BUT DO YOU? |
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On 10 Mar 2005 14:42:24 -0800 in sci.electronics.basics, "Dave"
<dmcomm_ads@yahoo.com> wrote msg
<1110494544.568179.118660@f14g2000cwb.googlegroups.com>:
| Quote: | One more time for the ubers...
Power= Voltage x current. Yeah, we learned that in grade school.
What was the equation used to arrive at the inverter drawing 17 amps?
|
Power = voltage x current. Or, if you prefer, P = I * E. Yummy pie.
Two pieces of pie, one for each side of the converter. Both pieces of
pie are ideally the same volume, with different dimensions. P1 = P2.
You already know E1 and E2. The rest is a piece of cake.
| Quote: | There must be a correlation between what amps an AC device draws
compared to what amps this makes the inverter draw from the car.????
|
As others have mentioned, the efficiency of the inverter must be
factored, and you want to deal in rms units for the ac calculations.
Are you worried about power factor? Unless your load is heavily biased
capacitively or inductively, power factor shouldn't be an issue.
--
Al Brennan |
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