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  Simple Electrical Math
Posted by: Optimistic Paranoid - 10-12-2017, 06:38 PM - Forum: Solar/Electrical - No Replies

Simple Electrical Math
 
POWER is measured in WATTS.  It’s named after the Scottish inventor James Watt, and it originally was used for measuring the power of steam engines.
For Electrical Power, 1 watt is defined as the amount of work done by 1 ampere of current, driven by 1 volt of electrical pressure.
Or as we’d write it as a simple math expression, 1W = 1A x 1V.

(I will mention in passing, that there is no difference between AC and DC, as long as we are talking about simple electrical stuff like electric heaters and motors and light bulbs.  When dealing with electronics, something else called REACTANCE comes into play with AC electricity, and there they talk about Volt-Amps instead of Watts.  You might see volt-amps mentioned on computer power supply bricks, for example.  The difference between watts and volt-amps is something only electronics engineers need to worry about, and we can ignore it.)

Now, obviously, if W = A x V, then 12 volts x 1 amp = 12 watts.  And 6 volts x 2 amps also = 12 watts.  This explains why the battery cables on the old 6 volt cars were much thicker than the battery cables on 12 volt cars.  They need to carry twice the current to produce the same power.

This also explains why the wires carrying DC power going into an inverter have to be MUCH thicker than the AC wires coming out of it.  If you want 1,000 watts of power out of the inverter, you need to take 1,000 watts of power out of the battery.  The inverter merely changes the power from DC to AC, and from 12 volts to 120 volts.  (We’re ignoring real-world internal losses in the inverter due to resistance and other factors like that pesky reactance.)

Let’s run the numbers.  Back in 9th grade math class, we learned that we could manipulate a simple formula like W = A x V to make it easy to find the unknown quantity if we knew any two values.  If W = A x V, then A = W / V, or V = W / A.

So 1,000 watts / 12 volts = 83.33 amps.  Whereas 1,000 watts / 120 volts = 8.33 amps.  This tells us that the inverter is going to draw 83 amps of current out of the battery at 12 volts, in order to send 8.3 amps of current out at 120 volts.

Notice that there is a 10 to 1 relationship between 120 and 12?  That gives us a simple, handy rule of thumb.  If the power supply on a computer or television or anything else lists how many amps of 120 volt AC it is going to use, we know that it will take 10 times as much DC current from the battery to run it with an inverter.  We don't even have to reach for our calculator.

Now, both Amps and Watts are instantaneous values.  That inverter is drawing 83.33 Amps of current RIGHT NOW.  It’s drawing 1,000 Watts of power RIGHT NOW.  Turn the inverter off, and current and power immediately stop flowing.  Neither Amps nor Watts is a QUANTITY in the same way that Gallons is.  Take 1 gallon of gasoline out of a fuel tank, and we all understand what that means.  A little economy car puttering around town may use half a gallon per hour, and a Nascar racer screaming around Daytona at 200 mph may be burning 5 gallons per hour.  So gallons is a quantity, and gallons per hour (gph) is a RATE.

Likewise, Amps and Watts can be thought of as Rates.  We are removing power from our battery at a RATE of 1,000 Watts or 83.33 Amps. For Quantity, we need to be talking about Amp-Hours or Watt-Hours.

 As discussed in another post in this series, the Quantity of electricity “stored” in a battery is measured in Amp-Hours.  If we left that inverter running for an hour, drawing 83.33 Amps, we would use 83.33 Amp-Hours.  Or, since it’s drawing 1,000 Watts, 1,000 Watt-Hours.

But since battery capacity is almost always specified in Amp-Hours, we’ll mostly stick to using that here.  (But note that 1,000 Watt-Hours is also called a Kilo-Watt-Hour – from kilo being the metric term for 1,000 – and your utility charges you by the KWH for the AC electricity you buy from them.)

We rarely run something like a microwave oven for a whole hour.  Here’s a trick for calculating Amp-Hours when you are measuring time in minutes instead of hours.

Because 1 hour contains 60 minutes, if we divide 1 by 60, we get 0.016.  In other words, each minute is .016th of an hour.  If we put a cup of coffee in our microwave to reheat, and it draws 83.33 Amps of current, that’s 83.33 x .016 = 1.33.  In other words, even though the inverter was pulling 83.33 Amps of current out of the house battery to power a 1,000 Watt microwave, we only pulled 1.33 Amp-Hours out of our battery bank to re-heat that coffee.

I hope that sheds some light on Volts, Amps, Watts, and Amp-Hours; and how they relate to each other.  Once you understand them, it’s easy to use a calculator to juggle the numbers around to make sense or it all.

Of course, the real world is never as neat as the mathematical one.  There’s inverter efficiency and something called “Peukert’s Law”, which we’ll get to another time, which prevents us from actually getting these mathematical ideals.  But it’s usually close enough for government work, as they say. Especially if we are talking about small numbers, like lights or a fan would draw, instead of large numbers like an inverter would draw.

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  Simple Electrical Math
Posted by: Optimistic Paranoid - 10-12-2017, 06:38 PM - Forum: Useful Information - No Replies

Simple Electrical Math
 
POWER is measured in WATTS.  It’s named after the Scottish inventor James Watt, and it originally was used for measuring the power of steam engines.
For Electrical Power, 1 watt is defined as the amount of work done by 1 ampere of current, driven by 1 volt of electrical pressure.
Or as we’d write it as a simple math expression, 1W = 1A x 1V.

(I will mention in passing, that there is no difference between AC and DC, as long as we are talking about simple electrical stuff like electric heaters and motors and light bulbs.  When dealing with electronics, something else called REACTANCE comes into play with AC electricity, and there they talk about Volt-Amps instead of Watts.  You might see volt-amps mentioned on computer power supply bricks, for example.  The difference between watts and volt-amps is something only electronics engineers need to worry about, and we can ignore it.)

Now, obviously, if W = A x V, then 12 volts x 1 amp = 12 watts.  And 6 volts x 2 amps also = 12 watts.  This explains why the battery cables on the old 6 volt cars were much thicker than the battery cables on 12 volt cars.  They need to carry twice the current to produce the same power.

This also explains why the wires carrying DC power going into an inverter have to be MUCH thicker than the AC wires coming out of it.  If you want 1,000 watts of power out of the inverter, you need to take 1,000 watts of power out of the battery.  The inverter merely changes the power from DC to AC, and from 12 volts to 120 volts.  (We’re ignoring real-world internal losses in the inverter due to resistance and other factors like that pesky reactance.)

Let’s run the numbers.  Back in 9th grade math class, we learned that we could manipulate a simple formula like W = A x V to make it easy to find the unknown quantity if we knew any two values.  If W = A x V, then A = W / V, or V = W / A.

So 1,000 watts / 12 volts = 83.33 amps.  Whereas 1,000 watts / 120 volts = 8.33 amps.  This tells us that the inverter is going to draw 83 amps of current out of the battery at 12 volts, in order to send 8.3 amps of current out at 120 volts.

Notice that there is a 10 to 1 relationship between 120 and 12?  That gives us a simple, handy rule of thumb.  If the power supply on a computer or television or anything else lists how many amps of 120 volt AC it is going to use, we know that it will take 10 times as much DC current from the battery to run it with an inverter.  We don't even have to reach for our calculator.

Now, both Amps and Watts are instantaneous values.  That inverter is drawing 83.33 Amps of current RIGHT NOW.  It’s drawing 1,000 Watts of power RIGHT NOW.  Turn the inverter off, and current and power immediately stop flowing.  Neither Amps nor Watts is a QUANTITY in the same way that Gallons is.  Take 1 gallon of gasoline out of a fuel tank, and we all understand what that means.  A little economy car puttering around town may use half a gallon per hour, and a Nascar racer screaming around Daytona at 200 mph may be burning 5 gallons per hour.  So gallons is a quantity, and gallons per hour (gph) is a RATE.

Likewise, Amps and Watts can be thought of as Rates.  We are removing power from our battery at a RATE of 1,000 Watts or 83.33 Amps. For Quantity, we need to be talking about Amp-Hours or Watt-Hours.

 As discussed in another post in this series, the Quantity of electricity “stored” in a battery is measured in Amp-Hours.  If we left that inverter running for an hour, drawing 83.33 Amps, we would use 83.33 Amp-Hours.  Or, since it’s drawing 1,000 Watts, 1,000 Watt-Hours.

But since battery capacity is almost always specified in Amp-Hours, we’ll mostly stick to using that here.  (But note that 1,000 Watt-Hours is also called a Kilo-Watt-Hour – from kilo being the metric term for 1,000 – and your utility charges you by the KWH for the AC electricity you buy from them.)

We rarely run something like a microwave oven for a whole hour.  Here’s a trick for calculating Amp-Hours when you are measuring time in minutes instead of hours.

Because 1 hour contains 60 minutes, if we divide 1 by 60, we get 0.016.  In other words, each minute is .016th of an hour.  If we put a cup of coffee in our microwave to reheat, and it draws 83.33 Amps of current, that’s 83.33 x .016 = 1.33.  In other words, even though the inverter was pulling 83.33 Amps of current out of the house battery to power a 1,000 Watt microwave, we only pulled 1.33 Amp-Hours out of our battery bank to re-heat that coffee.

I hope that sheds some light on Volts, Amps, Watts, and Amp-Hours; and how they relate to each other.  Once you understand them, it’s easy to use a calculator to juggle the numbers around to make sense or it all.

Of course, the real world is never as neat as the mathematical one.  There’s inverter efficiency and something called “Peukert’s Law”, which we’ll get to another time, which prevents us from actually getting these mathematical ideals.  But it’s usually close enough for government work, as they say. Especially if we are talking about small numbers, like lights or a fan would draw, instead of large numbers like an inverter would draw.

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  20 lb blues....
Posted by: bLEEp - 10-12-2017, 06:08 PM - Forum: Heating/Air Conditioning - Replies (14)

Short and sweet.
Two different hoses, two different devices, brand new tank.
One pound bottle works on both, 20lb works on neither, with neither hose.
Thank gods I have a refil thingy for the one pounders....
Any ideas???

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  My STUPID RIDE
Posted by: Justacarsofar - 10-12-2017, 05:55 PM - Forum: Mechanical Problems - Replies (137)

Angry
I left the title vague so you can post YOUR own stupid vehicle stories.

MY STUPID RIDE  car..

This particular car I just picked up a month ago after ditching the last stupid car!

I went out to start it, completely dead, no clicking.
Got a jump from the nice maintenace man and drove it around enough to charge the battery.
Next day, the same damn thing happens.
I called my friend whom I got it from to ask the' questions: it was a good battery, 
no I didn't leave the lights on, no.. no.. not that  etc...

After the 3rd time, went and got a NEW battery - with install and exchange, over $120.
Yay, feelin almost good but not really cuz of the way the first battery seemed to drain juice..well..
Sure nuff!!  New battery, same frkn deal!!  I was ever so depressed.

This time, after the AAA guy came to jump it I drove it around a bit before heading to the shop'.
As I was slowly pulling out of a turn (no buddy around that ODIN) it stalled! just went dead!
Thankfully it started back up, but I could tell there was something hinky about it...

Got to the shop and explained Everything..
Got the call... nice mechanic explained how..(ok, can't remember the tech talk but)
the computer, sensor..whatever was totally F'd and it could not even be driven as is!
I had JUST made it to the place, and that was very lucky!

So, he had to order the junk and replace it.. so now the sensors and dummy lights work..
so maybe, just maybe this will also fix the mystery 'drain'??  Now we are not even sure that
there was a battery problem at all!

They kept it overnight to see if any weird draw was happening, but nope, it was normal!
They are keeping it one more night just to check again for any weird draw.. nice of em.

So, lookin like I replaced a perfectly good battery for no reason.  There went the first hundred bucks. 
........... ARRRRggggghhhhhh!
I'm lookin to spend at least $250 - 300 more to get it tomorrow.
There went my food money for the month!  bluddy HELLLL...(I have friends with food)
Will let ya know how it turns out.

STUPID CAR, stupid me... etc..... Angry

(just think, IF I had took off toward AZ before knowing)

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  One month anniversary
Posted by: Gary - 10-12-2017, 11:49 AM - Forum: Forum News - Replies (11)

And for the most part the damn thing is still running,further more there are people using it
the usual amount of computer bugs but computers suck like that 

contacted the host about bandwidth and such,they came back with this

'Hello Gary,

We do not have any pre-configured disk or bandwidth limits on your account. Having reviewed your account just now, you are well below the average disk usage of an account on our services. Your bandwidth usage is also fine.

Please let us know if you have any questions."

 

so it looks like we are good to go,if you have any issues or problem contact rvpopeye

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  Growing up
Posted by: Gunny - 10-12-2017, 11:38 AM - Forum: Heart to Heart Talk - Replies (7)

I thought I would post this here, it's off topic and sort of a look back at the past but what the hell.

I am a member of Mother Natures Network, they do good things but I am not the atypical member, My avatar is the Eagle, Globe and Anchor. I made a comment on one of their articles and I had put a lot of thought into my response and my comment was the highest rated, big deal right? So towards the end of the other comments the moderator compliments me and thanks me for my service. He got reamed by several members for acknowledging my military career. I didn't respond in typical Gunny fashion, I just asked them who made them the arbitrators of life. Anyway it bothered me. 

Now there is a new two part "history of Vietnam" series on PBS I think. I haven't watched it, I was there. 

http://www.pbs.org/kenburns/the-vietnam-war/home/

I can guess the slant without watching it.

There's a new book out Titled 'Hue'....Hue was my introduction to sustained contact. I haven't read it either. I may buy it just for shits and giggles so I can have someone tell me how I feel or should feel. 

I was 17 years and 9 months old when I got in-country. I grew up there. Fast. 

Bob Wells called me a "boy" once on the open forum...I let it slide for awhile until another issue popped up and I told him had I been standing in front of him when he called me a boy I would have broken his jaw. This was in emails exchanged and I still have copies should anyone want to read them. Fuck Him.

Some have met me, I am not a physically imposing person, old, fat and  out of shape. But as god as my witness very few people scare me and he ain't one.

Today is my oldest Daughters 42nd Birthday. Happy Birthday Heather.

Did I ramble?

Gunny.

   

And the opening video on We Are The Mighty is about Jane Fonda...

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  Whining again...
Posted by: TrainChaser - 10-12-2017, 11:07 AM - Forum: Forum Issues/Suggestions - Replies (18)

Is there some way that I can set my account so I DO NOT receive e-mail notifications?  Yes, I know I can click the box at the bottom when I post a response, but I almost always forget.  A.D.D., you know.  The other forum had it set so you automatically DIDN'T subscribe unless you marked it.  At least, when they had it -- I think it's turned off, now.

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  Training Videos
Posted by: Optimistic Paranoid - 10-12-2017, 10:25 AM - Forum: Member buy,sell and trade - No Replies

There is a company called RV Education 101.  They sell training books and videos related to the mainstream RVs.

http://rveducation101.com/

I have several of their dvds, specifically:

Drive Your Motor Home Like A Pro

Towing Behind Your Motor Home ( pulling a "toad" or "dingy" behind your rig)

Trailer Towing and Backing

Anyone interested in borrowing one or more of these should pm me and I will mail it/them out to you.  First come, first served.  I ask only that you come back to this thread when you are done and see who else wants to borrow one, and mail it on to them.

BTW, he's got a lot of other stuff on Youtube - not these complete dvds, of course - so check him out there.

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  Lunch or dinner Tucson to San Marcos, TX?
Posted by: TedOnWalkabout - 10-12-2017, 10:17 AM - Forum: Gatherings and Meetups - Replies (4)

As soon as I get my 2016 taxes done (one of my mottos is "Never do today what can be put off until tomorrow"), I'll be heading out to visit with #2 son in San Marcos.  I'll be going via I-10, Tucson to San Antonio, then up with I-35 to San Marcos. I'm thinking about going back through the Hill country.  

Anyone in the rough area wanna have a meal with me? My treat (unless the restaurant is Michelin rated!).
Ted

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  learning to back a tandem trailer
Posted by: Dean and buster - 10-12-2017, 03:41 AM - Forum: Recreational - Replies (26)

trailers are great and easy to pull forward but backing them in can be a challenge for some of us  so what I did yesterday is took the trailer and my van to a local bankrupt business parking lot .
while I was there doing my lessons on backing the van and trailer in a local police officer stopped me and asked me what I was doing and I told him that I was learning how to park a trailer by backing it in he was quite pleased that I was taking the responsebility for parking with a trailer on a van it .
if you are trying to learn this keep trying you will get it just takes time and you will get it so keep trying you will get it

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