Author Topic: voltage question  (Read 1682 times)

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powermiester

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voltage question
« on: May 25, 2006, 02:03:30 PM »
I have to mount my generator about two hundred feet from my house and battery bank which poses the problem of significant power loss because of the distance. Would it be more efficient to generate the voltage at 48, run it to the batteries through #8 wire and then convert for 12 volt usage or just generate 12 volts and suck up the significant power loss?
« Last Edit: May 25, 2006, 02:03:30 PM by (unknown) »

Flux

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Re: voltage question
« Reply #1 on: May 25, 2006, 11:04:04 AM »
Without knowing the size and type of generator you are thinking of it is not possible to form any idea.

Flux
« Last Edit: May 25, 2006, 11:04:04 AM by (unknown) »

scottsAI

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Re: voltage question
« Reply #2 on: May 25, 2006, 04:44:58 PM »
Hello Powermister,


You obviously have an understanding of the issue.


Several charts exist on the web of wire size vs power loss. Here is one:

http://www.powerstream.com/Wire_Size.htm


Depending on how much loss your willing to accept. Then the wire cost comes into play, 200 feet is a long run. Cost difference of 8awg vs 14awg is big. Look it up!


Yes, by boosting the voltage the current goes down. The boost could be 120 ac at the gen which is converted to 12 at the end. If the gen is DC, then you make the same choices, Remember to include the conversion efficiency. Transformers are not 100%.

Much less costly to convert AC!

Have fun,

Scott.

« Last Edit: May 25, 2006, 04:44:58 PM by (unknown) »

terry5732

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Re: voltage question
« Reply #3 on: May 25, 2006, 10:36:13 PM »
The worst transformers have efficiencies better than the line loss. Most transformers are in the 90s.

No sane person should be trying to transmit DC
« Last Edit: May 25, 2006, 10:36:13 PM by (unknown) »

scottsAI

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Re: voltage question
« Reply #4 on: May 26, 2006, 12:48:24 AM »
No argument. I use 95%, that still leaves 5% loss.

Most solar designs target 2% line loss...

Transformer loss are 2.5 time larger.


"No sane person should be trying to transmit DC"

Under some limited conditions that may be true.

Wind turbine is on my roof, many send down the power as DC.


Just so you know the largest power lines are DC. Bet you did. Just forgot.


The situation is the output of a generator.

I have no idea what power loss based on cost he is willing to live with.

If the generator is run for 4 hours each week all year. Or run 4 hours over the year. I think the acceptable power loss would change dramatically!

Have fun.

Scott.

« Last Edit: May 26, 2006, 12:48:24 AM by (unknown) »

Ungrounded Lightning Rod

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Re: voltage question
« Reply #5 on: May 26, 2006, 06:16:11 PM »
"No sane person should be trying to transmit DC"...


Just so you know the largest power lines are DC.


But do you really want to have an 800,000 volt battery bank in your power shed?  Get within a few feed and it will "reach out and touch you" (where touch = fry).  That might make checking the water level a bit problematic.

« Last Edit: May 26, 2006, 06:16:11 PM by (unknown) »

commanda

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Re: voltage question
« Reply #6 on: May 27, 2006, 02:37:56 AM »
No sane person should be trying to transmit DC


Pity how some people take things literally, rather than interpreting what the poster actually meant to say.


I think what you meant was more like "No sane person should be trying to transmit high power at low voltage". Both terms being relative, of course.


Amanda

« Last Edit: May 27, 2006, 02:37:56 AM by (unknown) »

scottsAI

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Re: voltage question
« Reply #7 on: May 27, 2006, 07:38:10 AM »
Hello commanda,

Based on the original question we are dealing with a novice.

We can not assume they will take a statement like that and interpret it correctly.

What does ASSUME stand for?


Back to what we all are making assumptions on.

Reading posts here, looks like DC is frequently sent.

This questions has come up before, it's a good thought full question nun-the-less.

I tried to answer the question helpfully. Without busting any body's chops.


Strongly worded, Broad statements are not helpful specially to a novice, more so when inaccurate at some or any level.


Your "what he mean" is just stating what the original poster understood. Else why would he be asking if boosting the voltage was worth the effort? The answer of course was it depends.

You did expect me to reply to this, I think lighting rod was going for it too.


After seeing all this riff-raff I wonder if he will let us know what choice he made?

Have fun,

Scott.

« Last Edit: May 27, 2006, 07:38:10 AM by (unknown) »

commanda

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Re: voltage question
« Reply #8 on: May 27, 2006, 05:41:42 PM »
Scott,


I was just trying to clarify Terry5732's statement "No sane person should be trying to transmit DC". Whilst this may be perfectly true with respect to electrolytic corrosion, the issue as far as powermeister, who started this thread is concerned, is more to do with power loss. Power loss is related to high power & low voltage, irrespective of whether it is AC or DC.


Strongly worded, Broad statements are not helpful specially to a novice, more so when inaccurate at some or any level.


Agreed. That's why I felt it necessary to correct it.


Amanda

« Last Edit: May 27, 2006, 05:41:42 PM by (unknown) »

Drives

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Re: voltage question
« Reply #9 on: May 27, 2006, 06:47:17 PM »
Scott:


The largest DC stuff I have worked with was low voltage, <600volts at 10,000Amps for induction furnaces.  The arc furnace at the steel mill I helped redesign was 3 phase AC 480Volts, 80,000amps.

I have looked at some of the largest power lines in the US (250KV+), and worked around Multi-Mega watt power generating stations.....I never saw any DC being generated, or transmitted.  I always saw 3 large wires, I thought it was 3 phase AC.....was Mr. Westinghouse wrong?

« Last Edit: May 27, 2006, 06:47:17 PM by (unknown) »

scottsAI

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Re: voltage question
« Reply #10 on: May 27, 2006, 07:53:32 PM »
Hello Drives,


You have me beat, only worked on 450vac, several MW of it.


http://en.wikipedia.org/wiki/Electric_power_transmission

Copied from above link:

HVDC


High voltage DC (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it can be more economical to transmit using direct current instead of alternating current. For a long transmission line, the value of the smaller losses, and reduced construction cost of a DC line, can offset the additional cost of converter stations at each end of the line. Also, at high AC voltages significant amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried. Since the power flow through an HVDC link is directly controllable, HVDC links are sometimes used within a grid to stabilize the grid against control problems with the AC energy flow. One prominent example of such a transmission line is the Pacific Intertie located in the Western United States.


Another link about HVDC (16,000 km line, try doing that with AC:-)

http://www.projectsmonitor.com/detailnews.asp?newsid=5400


"was Mr. Westinghouse wrong?" (Actually that was Tesla!-)

Well that depends. (Very interesting, earlier today I read about Edison and Westinghouse)

Most power lines will be high voltage 3 phase AC.

With the really long lines then DC is better!! So he is not:-)

The power lines become a LRC circuit when very long, Loses become larger than the conversion losses of using DC.


I hope you found this interesting, years ago I did.


Take a Look at a 500kv power switch with a problem: (movie is cool)

http://www.mikeholt.com/mojonewsarchive/USEI-HTML/HTML/High-Voltage-Power-Line-500-kV-Circuit-Switch
er-Testing~20031222.htm


Have fun,

Scott.

« Last Edit: May 27, 2006, 07:53:32 PM by (unknown) »

Drives

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Re: voltage question
« Reply #11 on: May 27, 2006, 08:22:01 PM »
Scott:


Thanks, I learn something new every day.

« Last Edit: May 27, 2006, 08:22:01 PM by (unknown) »

powermiester

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Re: voltage question
« Reply #12 on: June 02, 2006, 08:02:19 AM »
Thanks for your input Scott and for your patience with a novice. I began with the Dan's series of articles in BAck Home magazine and decided to build a wind generator using wheel rotor and hub. I also purchased Hugh Piggot's book on wind generation and discovered a chart which listed percentage of power loss from wind turbine to battery for 500 watt output to battery. Since I have 200 feet to run the wire to battery it seemed that the listed power loss of 48 volt battery voltage ( 5% using #8 wire) made more sense than the 47% loss for 12 volts using the same guage of wire. I thought it much more efficient to send the current to the battery @ 48 volts and then reconvert it to 12 volts to use in the workshop/home. Am I on the right train of thought or way off-base?
« Last Edit: June 02, 2006, 08:02:19 AM by (unknown) »

powermiester

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Re: voltage question
« Reply #13 on: June 02, 2006, 08:11:46 AM »
Thanks for your input. For clarification ,I am building a wind generator which should on average produce 500 watts of power ( range of 50 to 1500 ). I am not sure if I should mount the rectifiers near the generator or near the battery bank 200 feet away and the guage of wire is a concern as the smaller gauge leads to a much greater power loss, especially at 12 volts. My intention was to make a 3 phase generator , 48 volts. and sent through 8 guage wire to the battery bank of 4 12 volt batteries, then convert to 12 volt for load usage. I would think that this would minimize the power loss ( vs a 12 volt generator). Am I way off base?
« Last Edit: June 02, 2006, 08:11:46 AM by (unknown) »

scottsAI

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Re: voltage question
« Reply #14 on: June 09, 2006, 01:10:45 AM »
Hello powermiester,

Just noticed you posted another question.

Would have noticed earlier if you had replied to one of my posts.


In theory Yes to your question. But.

How are your going to convert the 48v back to 12v?


500w converter to do this is not cheap. Check eBay.

If the output is AC, this may be easier, but:

the wind gen output is variable voltage AC, the transformers do not work well bellow their rated frequency.


To my thinking, I would go for a 120vAC generator, can use a standard transformer to do the voltage conversion, help reduce line losses further and help make up for the transformers own losses.


PM generators output voltage is directly proportional to RPM.

With a cut in speed of 6mph, at 12v. At 12mph the output is now 24. and up.


This is the root cause of matching the gen to the blades.

You have many choices to solve this, read up and make your best guess! And go for it.

Have fun,

Scott.

« Last Edit: June 09, 2006, 01:10:45 AM by (unknown) »