Long DC Runs, Attentuation, and Transformation

Steven Lake
Steven Lake Solar Expert Posts: 402 ✭✭
in General Solar Power Topics #1
We have a project we're researching that would involve grabbing some hydro power off a local river. The catch however is that we don't know how much attenuation we'll have, or what voltages we'll need to step it up to in order to make the transition with the least amount of loss. This I was hoping someone had a few equations or a possible calculator app that would allow me to plug in distance numbers, voltages, etc and figure out if it's doable. IE, here's basically what I'm looking at getting.

Example 1: 24v input (100% power) => Stepped up to 1500v (0.05% loss per 100ft at this voltage) => volts lost over length of run => 24v output (82% final power minus all losses, including transformation)

Example 2: 24v input (100% power) => Stepped up to 5000v (0.02% loss per 100ft at this voltage) => volts lost over length of run => 24v output (92% final power minus all losses, including transformation)


Now that's not the actual equation, but that's just an example of what I'm looking for. I know there's a spreadsheet around here that does attenuation for non-transformed loads, but I figure at the distance this'll be traveling, it'll need to be stepped up in order to arrive with any degree of efficiency and any reasonably usable amount of the original input watts. Thus I'd need some kind of equation and/or calculator tool that would take that into account, including all losses from transformation.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Long DC Runs, Attentuation, and Transformation

    I must be getting stupid(er). :blush:

    Long DC runs? What are you using to change the Voltage?

    Normally you'd have 'X' Volts AC @ 'Y' Amps into a transformer (about 98% efficient) to 'FX' Volts AC @ 'Y/F' Amps over wire run (V-drop power loss calculation) into transformer (about 98% efficient) resulting in 'X' Volts AC @ 'E' Amps power.

    But since I just had to type "transformer" six times to get it right my brain has obviously already shut down for today. And it's only 7:30 AM. :cry:
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: Long DC Runs, Attentuation, and Transformation

    Don't worry Coot, go easy on yourself and use "xformer" :D
    On a more serious note, Steven, what wattage levels are you looking at, and how far distance from source to consumption? Give us something to think about :)
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #4
    Re: Long DC Runs, Attentuation, and Transformation

    Well, the generator is DC. It's an old 300w 24v hydro generator. Snagged it as a freebie from a friend who didn't want it anymore. He upgraded to something bigger and was just gonna pitch it. So I figure if I can get it to 100% capacity, (or as close as possible) and get at least 100w of power to the house, I might just add it to the other parts once I put them in place. If I'm gonna lose too much power over that long run then I won't bother. But if I can get at least 100w, then we're in business. It's not much, but it all adds up in the grand scheme of things. :)
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Long DC Runs, Attentuation, and Transformation

    How long is the run to the house?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Long DC Runs, Attentuation, and Transformation

    Problem is, you can't feed DC into a transformer and up the Voltage. That requires a lot of circuitry. At 24 VDC, power drops fairly quickly over a wire run. 50' would require 6 AWG to keep the Voltage drop below 3% @ 12.5 Amps (roughly 300 Watts on 24 Volts).

    Upping AC Voltage is easy. But converting DC to AC isn't. So if this is a long run, it probably isn't worth the trouble. Might be easier to pipe the water and take the mechanical losses (depending on terrain).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Long DC Runs, Attentuation, and Transformation

    Is this a three phase PMA alternator? Or a DC generator (bushed)? Could be a brushed AC alternator too...

    If AC, depending on the frequency, you might find some surplus transformers to step up/down the three phase AC (may be tough to justify 4-6 transformers for this job).

    Another suggestion, Most alternators/generators can efficiently output much higher voltage than the "24 volts" that is limited by the battery bank voltage. If you put an MPPT solar charge controller between the turbine and the battery bank, you may get quite a bit more output.

    Wayne (from Nova Scotia) has had very nice results with a couple MorningStar MPPT charge controllers. The TS MPPT family allows you to program the Vgen that you want (do some experiments with I*V=P and figure out what your optimum would be).

    If you can run double or triple the "DC voltage" -- You will gain both from more power and lower voltage drop as a percentage of operating voltage.

    The Midnite Classic probably would also be a good choice for this setup (they run wind with their systems too). They have been very helpful answering questions--give them a call or try their forum: http://midnitesolar.com/smf_forum/

    The only things to watch out for--What is the Voc-generator voltage (could exceed MPPT controller input voltage). And will the generator over-speed if unloaded (self destruct from over-speed). Not small issues--but if you can address those questions, MPPT may be the way to go.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #8
    Re: Long DC Runs, Attentuation, and Transformation

    My PMA sends 40 VDC through probably 300 ft cable (600 ft return), only loosing roughly a volt, then feeds TS-MPPT-60 which drops voltage to "12", and ups the amperage. I just have to be sure the PMA voltage never exceeds what the controller can handle - - which means soft starts of the turbine with lots of air let into the pipeline at first, otherwise, a fast moving freight train of water rushes down the pipe, strikes the turbine full force and drives the RPM and thus the voltage sky high till the surge of water calms down. Under normal operation, unloaded, the voltage from my low head turbine system does not exceed the controller's max input handling ability.
    My shutoff gate is up at the diversion dam, allowing the pipeline will drain and thus not freeze if shut down for any reason in winter.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Long DC Runs, Attentuation, and Transformation

    Looks like we're down to needing a few more details regarding the length between generation and use and exactly what type of generator it is.

    I'll point out that all generators produce AC by their nature. Some leave it as such, some convert it to DC via rectifiers, and some convert it to DC via a commutator. It's that last one that will cause a problem. The rectified generator can be "tampered with" if you're willing to have a go at it. Then you get AC out which can easily be increased in Voltage for the long run.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #10
    Re: Long DC Runs, Attentuation, and Transformation

    I can't tell you what the generator is. Given its age, I'm guessing it's a good old fashioned brushed DC generator. But I won't know until I actually look at it again. (it's still over at my friend's house) As for how far the run is, it's 3000ft. Running the water to the house wouldn't work because my house sits higher than the stream by a good 10 feet, and another 6ft to the river.

    Overall it's sounding like this project idea wouldn't fly, which is kinda what I was thinking. But I figured it was safer to ask and risk sounding stupid than build the thing and remove all doubt. :p
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Long DC Runs, Attentuation, and Transformation

    Just for fun, let's look at what you'd need to get that 300 Watts 3,000 feet.

    At 24 Volts ... looks like 4/0 will give you "only" 16% V-drop. :p
    Up the Voltage to 48 and it gives you 4%.

    But who can afford 3000 feet of 4/0 wire (times two)?

    What size wire could you afford that long? 8 AWG? That will give you 2% drop, providing you up the Voltage to 240.

    Of course you did say you'd be happy with 1/3 of the power. So if you're willing to take a 66% loss ... have I got an investment plan for you! :p

    Or 24 VDC on 2 AWG - about 50% loss.

    It's bad numbers any way you slice it.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #12
    Re: Long DC Runs, Attentuation, and Transformation

    I think many people install hydro without asking many questions. And some of them are even happy with the results. :p;)

    A couple of neat Hydro stories. The first one--Guy built "EVERYTHING":
    dwh wrote: »
    http://ludens.cl/paradise/turbine/turbine.html
    peakbagger wrote: »
    For anyone interested in hydro power (mostly very old equipment), theses folks seem to have a lot of fun

    http://frenchri.ipower.com/index.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #13
    Re: Long DC Runs, Attentuation, and Transformation
    Steven Lake wrote: »
    I can't tell you what the generator is. Given its age, I'm guessing it's a good old fashioned brushed DC generator. But I won't know until I actually look at it again. (it's still over at my friend's house) As for how far the run is, it's 3000ft. Running the water to the house wouldn't work because my house sits higher than the stream by a good 10 feet, and another 6ft to the river.

    Overall it's sounding like this project idea wouldn't fly, which is kinda what I was thinking. But I figured it was safer to ask and risk sounding stupid than build the thing and remove all doubt. :p
    Just invent that DC transformer and it would be a breeze! :D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Long DC Runs, Attentuation, and Transformation
    ggunn wrote: »
    Just invent that DC transformer and it would be a breeze! :D

    Let's see ... induction coil, triggering unit, send high Voltage pulses down the wire, accumulate at the other end, get electrocuted when you accidentally touch the output wire ..

    Nope; got to rethink it. :D
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #15
    Re: Long DC Runs, Attentuation, and Transformation

    Hydro is a HUGE wast of time, money and energy. There's no need of it, just check the thread on perpetual motion machines that produce far more energy than they consume! And if you don't see what you're looking for there, send me your credit card # and I'll forward plans so simple that anyone could build one. :D:D:D
    Signed:
    Get rich quick then go into hiding. lol
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
    Re: Long DC Runs, Attentuation, and Transformation

    rather than doing a dc approach, why not an ac approach? use an inverter modsine or sine and send the power to a charger that won't draw more power than is being produced and realized at the other end. you would have much better luck with wire gauges at 120v. there will still be losses even at 120vac for 240w would present a 12v drop (10% v drop) over that kind of distance with say #2, but it could bring it more inline with reality. use a transformer to up to 240vac and another to bring it back down and this could cut the loss even further by as much as 4x minus transforming losses. this is doable in theory. a smaller realized wattage would allow for an even lighter wire gauge, but it will still be somewhat thick if you opt for a good v drop percentage.

    theory aside and back to reality, just where are you getting all of this wire from as even that much of even a small wire size like #12 would be super expensive for that kind of a distance and my example showed what to expect using #2. maybe sell the hydro and put the proceeds towards investing in more pv?
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #17
    Re: Long DC Runs, Attentuation, and Transformation
    niel wrote: »
    rather than doing a dc approach, why not an ac approach? use an inverter modsine or sine and send the power to a charger that won't draw more power than is being produced and realized at the other end. you would have much better luck with wire gauges at 120v.

    I've often thought of trying that approach too Niel, even if it required a small battery at the generator go smooth out the bumps and surges. And for a really ling run, perhaps try a 220 VAC inverter. One day, just for the experience I may try that and let you all know how it turns out. Thing is, we'd need a voltage limiter at the generator to keep the smoke inside the inverter - - -
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
    Re: Long DC Runs, Attentuation, and Transformation
    waynefromnscanada wrote: »
    I've often thought of trying that approach too Niel, even if it required a small battery at the generator go smooth out the bumps and surges. And for a really ling run, perhaps try a 220 VAC inverter. One day, just for the experience I may try that and let you all know how it turns out. Thing is, we'd need a voltage limiter at the generator to keep the smoke inside the inverter - - -

    yes, there would be some sticky points in trying to do this. if you do it i'd be real curious of what you did and the end results.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #19
    Re: Long DC Runs, Attentuation, and Transformation

    If you put a 240 volt inverter on it at the turbine (with charge controller and battery, as mentioned), you'll only get a 3.8% voltage drop over 3000 feet with 10 gauge copper. 6.3% with 12 gauge. But also as mentioned, I would look into removing the rectifier from the turbine and see what AC voltage it produces when spun up. Loaded and unloaded. If it is high enough you may have an easy solution - physically remove the rectifier and put it on the other end of the line. But I doubt the AC output will be high enough voltage.

    Then there is the cost of all that copper (or aluminum)....
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    #20
    Re: Long DC Runs, Attentuation, and Transformation
    techntrek wrote: »

    Then there is the cost of all that copper (or aluminum)....

    Cut the copper cost in half. Drive a stake in the ground. Use (actual) ground return.

    Cal
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #21
    Re: Long DC Runs, Attentuation, and Transformation
    calbiker wrote: »
    Cut the copper cost in half. Drive a stake in the ground. Use (actual) ground return.

    Cal

    That has been used in the past by our provincial power company in very remote areas with light loads, and using voltages in the many tens of thousands, but it would be very difficult to get grounds good enough to work even fairly well with only 220 volts. I'm very much afraid the resistances involves would be a serious problem for anything but really tiny wattage levels. Friend of mine had a mis-wired grid panel in his home. It was drawing a couple hundred watts and kept a 10 foot circle of earth around his gnd rod snow free all winter. Geo-thermal heating anyone? lol
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #22
    Re: Long DC Runs, Attentuation, and Transformation

    If you do the "ground return" for DC, make sure there is no buried metal (water/gas pipes, metal structures/towers, etc.) in the ground--You may get lots of corrosion. AC is much less of an issue.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #23
    Re: Long DC Runs, Attentuation, and Transformation

    Here's a guy that sends 50 watts over 3200 feet with 20 gauge wire using 330 volts, using a ground return system.

    http://www.aprs.org/aprs-swer.html
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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