Author Topic: 12 volt - 24 volt - 48 volt  (Read 20057 times)

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harley1782000

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12 volt - 24 volt - 48 volt
« on: August 31, 2008, 08:27:16 PM »
Ok, You all know that I am new.  I am finally going to get started on a wind genny, and a solar panel or two.  The thing that is stoping me is do I go with 12 volt or 24 volt or 48 volt.  Now I understand if I start with 12 volt I can allways build up to somthing bigger.  What I wanna know witch one is the best to start and stay with.  I am not going to run my house off the grid, I want to run my work shop and some backup power just in case of a storm.  I have a 5500 watt back up genny with a serge power of 8000 watts.  So I can run a few things with that if I have too. So again witch is better 12, 24, 48.


Thanks

Jim

« Last Edit: August 31, 2008, 08:27:16 PM by (unknown) »

Muiller

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Re: 12 volt - 24 volt - 48 volt
« Reply #1 on: August 31, 2008, 03:10:03 PM »
I would go with a 24 volt system if your not going to spend a lot of money.

I started out with a 12v system last year and am changing to 24v at the minute.


  1. v you need large wire to carry the current,but you can get cheap modified sinewave inverters.
  2. v you dont need as large wire,and you can still get cheap modified sinewave inverters.
  3. v you can get away with thinner wire,so is good if you have long runs but you might have a hard time to find a low cost inverter for the system.


Just my 2 cents

Hope this help

 
« Last Edit: August 31, 2008, 03:10:03 PM by Muiller »

tsakach

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Re: 12 volt - 24 volt - 48 volt
« Reply #2 on: August 31, 2008, 04:35:35 PM »
If your goal is running an off-grid workshop, you may want to find out how many of your power tools use a universal motor which can operate on DC or AC sources. To run a universal motor on DC you generally need a voltage source of 48 volts or higher. See Run AC Tools on Batteries Directly, without an Inverter.


To determine if you have a universal motor, look for brushes inside the motor and windings on both stator and rotor. AC-only induction motors have windings only on the stator. See Why is a table saw quiet but a circular saw loud? for details.


I apologize if this seems too obvious or fundamental, but you will get more run time from DC if you can elmimate the inverter losses. Also, universal motors tend to run quieter and cooler on DC, especially when compared with performance obtained from a modified sine wave inverter.

« Last Edit: August 31, 2008, 04:35:35 PM by tsakach »

harley1782000

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Re: 12 volt - 24 volt - 48 volt
« Reply #3 on: August 31, 2008, 07:10:35 PM »
90% of my stuff will only run on ac, The rest runs on good old hand power.  So for me to run stuff on dc is just not an option for me.  But thank you for the two links, I read them both and gave me some more things to think about.  As for explain 12 to 48 volt, thank you.  Makes more sence to me now.  I think that I am going to go with the 24 volt system.  That was what I was leaning towards the first time.  Thank you for your help.


Jim

« Last Edit: August 31, 2008, 07:10:35 PM by harley1782000 »

richhagen

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Re: 12 volt - 24 volt - 48 volt
« Reply #4 on: August 31, 2008, 11:10:21 PM »
One of the main differences is the amount of power you can shove through a conductor, and your resistance losses associate with moving it if you are running from a limited  amount of renewable energy.


For example, if you have a 10 gauge conductor running 50 feet and you run 250 Watts through it, then at 12V, you would have to move 20.83 Amps of current, at 24V that would be reduced to 10.42 Amps, and at 48V that would be reduced to 5.21 Amps.  


All of those examples could be safely carried by a 10 gauge conductor of most common types, but the difference comes in your losses from resistance.  50 feet of 10 gauge wire has a resistance of about .05 Ohms.  Because of this resistance, power is lost as heat within the conductor at a rate equal to the square of the current times the resistance.  For 12V this would be 21.7 Watts of power, at 24V this would be 5.86 Watts and at 48V this would be 1.35 Watts.


Additionally, you have to have a complete circuit meaning that you have to move the power there and back, so if you were actually moving it batteries from your panels, or a wind turbine, or were moving it from your batteries to a point of use, your losses would actually be double.  The losses might be tolerable in terms of available power from your batteries and performance, but you have to generate the extra power to compensate for these losses as well and that will cost you money.


You can compensate by using larger wire, still costing you money, but if the distance from your turbine or panels to your battery, or the distance from your batteries to your inverter are larger, and you are moving large amounts of power, then higher voltages begin to gain significant economic advantage.  48V losses are 1/16th of those at 12V for the same conductor, and the losses at 24V are 1/4 those at 12V but 4 times those at 48V.  In other words you need conductors sized 16 times larger in cross sectional area for a 12V system to move the same amount of power with the same losses as a 48V system.  


What does all of that mean?  It means that you have to consider the power you will ultimately have to move through your system, and the availability of all of the parts that you need at the voltages, as well as local codes that may regulate more strictly systems with voltages above a specific voltage level - since shock hazards increase with voltage.  


If I were contemplating powering an entire workshop with several larger power tools that sees daily operation from Wind or solar, I would seriously consider higher voltages.  I have a 48V. system because that is the highest voltage for which I could order an off the shelf inverter, charge controller, and other parts.  A renewable energy powered computer lab I assisted BThumble with in Fiji runs on 12V in part because the laptop computers and printers (the first batch at least) could be powered directly from that voltage  without the need for an inverter.  You will have to evaluate your specific situation to find the best fit for your needs.    Rich

« Last Edit: August 31, 2008, 11:10:21 PM by richhagen »
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DanG

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Re: 12 volt - 24 volt - 48 volt
« Reply #5 on: September 01, 2008, 06:58:10 AM »
I would have loved to start with 12 or 24 volts - I would have had a system up and running a long time ago (as I attempt to piece together bits cheaply) and probably gotten the urge to have an RE system extinguished or at least my expectations lowered... And had more money to burn at the gas pumps etc...


48V not only reduces losses on wiring runs but also allows inverter circuits and chargers to operate more efficiently.


This may be my opinion only but it's also cheaper and easier to wire a series string of batteries than to make a parallel bus arrangement - and copper cable and lugs are not getting any cheaper.


The key idea is never have to buy twice - do not scrimp on cabling or fuse holders, circuit breakers etc. and keep an upgrade path in mind every step of the way...


 

« Last Edit: September 01, 2008, 06:58:10 AM by DanG »

jacobs

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Re: 12 volt - 24 volt - 48 volt
« Reply #6 on: September 01, 2008, 08:01:05 AM »
My opinion is a 144vdc battery voltage is the "Cadillac". Small wire sizes, economical off the shelf Home Depot disconnects, fuses & etc with inverter efficiencies exceeding 95%.
« Last Edit: September 01, 2008, 08:01:05 AM by jacobs »

phil b

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Re: 12 volt - 24 volt - 48 volt
« Reply #7 on: September 01, 2008, 10:22:38 AM »
Hi Jim

Just a few additional things to consider:


How comfortable are you in dealing with higher voltages? Do you have a friend that is an electrician?


Both of these factors should influence your decision.


I started off with a 12 volt system just to see how everything worked.

For 12 volt systems there are everything from coffee pots and ovens to cheap inverters...all off the shelf at the local truck stops.


However, I do like the 120 voltage systems now. Copper costs and the ease of transporting the electricity over distances weighed heavily in my decision. So, you can run your equipment from your generator or off your batteries. The drawback with higher voltage systems are the big strings of batteries.

« Last Edit: September 01, 2008, 10:22:38 AM by phil b »
Phil

harley1782000

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Re: 12 volt - 24 volt - 48 volt
« Reply #8 on: September 01, 2008, 11:47:01 AM »
Well the Higher Voltage dose not bother me.  I have been shocked so many times it is not funny.  I do all my own eletrical work myself.  I converted from 100 amp service too 200 amp service all by myself. New panel, Meter box, so on.  I am asuming right now that it would be better with 48 volt system. To get something up and running fast, 12 volt would be the way to go, But if you want "Cadilac of power" 48 volt is best. I am not too concerned about the money aspect of it.  Just the complexity of it.  I thank you all for your input.


Jim

"Hey dude, your shirt is on fire."

« Last Edit: September 01, 2008, 11:47:01 AM by harley1782000 »

methanolcat

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Re: 12 volt - 24 volt - 48 volt
« Reply #9 on: September 01, 2008, 06:10:38 PM »
who's shirt is on fire I don't get it?


   Matt

« Last Edit: September 01, 2008, 06:10:38 PM by methanolcat »

harley1782000

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Re: 12 volt - 24 volt - 48 volt
« Reply #10 on: September 01, 2008, 09:11:18 PM »
About two years ago I was welding and I told my cousin it was getting hot in here.  Well I went back to welding and I felt this tap on my shoulder I turned around and my cousin said "Hey dude, Your shirt is on fire!"  Some how a spark or somthing went over my helmet and caught my shirt tail on fire.  He has never let me live that down yet.


Jim

« Last Edit: September 01, 2008, 09:11:18 PM by harley1782000 »

veewee77

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Re: 12 volt - 24 volt - 48 volt
« Reply #11 on: September 02, 2008, 05:13:10 PM »
Being shocked by 120VAC is severely different than being shocked by 120VDC!  The AC tries to paralyze you, but DC just burns it's way through. You do not wnat to come in contact with 120VDC (or pretty much anything above about 36V especially if you are damp or sweaty.)


Even 12V can deliver a good burn if you are sweaty and get between the posts.


36 and higher is just dangerous!


Another thing to consider is that when you have a 120VAC circuit, like the one in your house or shop, it has likely a 15 or 20A fuse or circuit breaker. So, if you inadvertently get the wires crossed, you'll see a flash and the breaker will trip.


Strings of batteries are a different story. . . Unless you put a fuse in between every single battery (redundant and not really necessary) then the more batteries in your string, the higher the possibility of welding your tools and equipment to the battery posts or wiring. If there are no fuses in between the batteries, and let's say you have a 48 volt string and you are on the last one connecting them up. Now, these are 220amp-hour batteries, at 6 volts each. Now, you have 220amp-hours at 48V. Under short circuit conditions (dropped wrench ot etc.) there may potentially be thousands of immediate amps available current. You'll get HURT in other words.


Have Zen-like concentration and serious respect for the DC circuits.


NEVER, EVER attempt to use AC (household or otherwise) circuit breakers with DC circuits. Especially on voltages above about 24 or 36 max. They trip differently and when an AC breaker trips on a high-current circuit running on DC there is a nice little blue flame that could burn your whole operation down to a smoldering mass of CuAlFePbNi.


Don't let this scare you, just respect it and be diligent to use the right stuff in the right ways and you'll be fine. . .


Doug

« Last Edit: September 02, 2008, 05:13:10 PM by veewee77 »

jacobs

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Re: 12 volt - 24 volt - 48 volt
« Reply #12 on: September 02, 2008, 06:46:58 PM »
One positive aspect of using high voltage dc is you usually only need one string of batteries eliminating the troublesome series parallel setup. The big advantage of this is if one cell shorts out, it doesn't drain your other batteries that are in parallel. I personally have used 120 to 144 volt dc systems for 28 years now and would never consider anything else. Circuit breakers aren't needed, use fuses. They are very inexpensive, readily available at any hardware store and easily replaced. Yes, I've been shocked by 170 volts dc but it isn't any worse that 120 volts ac.
« Last Edit: September 02, 2008, 06:46:58 PM by jacobs »

spinningmagnets

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Re: 12 volt - 24 volt - 48 volt
« Reply #13 on: September 03, 2008, 05:22:20 AM »
jacobs, the system needs of 12,24,48 VDC have been well-documented here, but I am curious...How do you go about generating 144 or 170 volts? (diesel with a custom-wound generator, wind?)


What do you do with it? inverter-to-120 VAC?

« Last Edit: September 03, 2008, 05:22:20 AM by spinningmagnets »

jacobs

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Re: 12 volt - 24 volt - 48 volt
« Reply #14 on: September 03, 2008, 08:23:46 AM »
With PV's, I use eleven 12 volt panels wired in series for 144vdc. With wind, I use an old 1940's pre REA Jacobs 120 volt DC wind generator. The old Jacobs is a very dependable generator.


On high voltage systems like mine, It's real easy to charge batteries with a fossil fuel generator. Just wire from the 240 vac outlet of your generator, rectify the ac through a bridge rectifier, and then directly to the batteries. Then REDUCE the rpm's of the generator around 50% by installing a spring between the governor and the generator frame to decrease the 240 volts as necessary.


The 170 volts I referred to is battery charging voltage.


Inverter is a 3000 watt, 10,000 watt surge, modified sine wave, transformerless, H bridge custom made by Chad Lampkin of Michigan Energy Works. I've been using it for 8 years now and it has been flawless. It only weighs about 3 or 4 pounds and draws 2 watts no load.

« Last Edit: September 03, 2008, 08:23:46 AM by jacobs »

Slingshot

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Re: 12 volt - 24 volt - 48 volt
« Reply #15 on: September 09, 2008, 10:16:31 AM »
I've had trouble finding those "cheap modified-sinewave inverters" you mention for 24 volts.  Cheap 12V inverters (2KW for $100-$150) at Fry's (on sale) and at truck stops, but nothing in 24 volts without going to a higher-priced outlet.


Can you supply some links to the cheap ones?  I have a bunch of 24-V batteries that are presently going unused.

« Last Edit: September 09, 2008, 10:16:31 AM by Slingshot »

cylindar

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Re: 12 volt - 24 volt - 48 volt
« Reply #16 on: December 10, 2008, 11:26:23 PM »
The only advantage to a 24 or 48 system is when you have a longer run from your tower to your point of use. There is less voltage drop. Other than that a 12 system is the best if distance is not a concern. Look at your voltage drop tables to find out what you need.
« Last Edit: December 10, 2008, 11:26:23 PM by cylindar »