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AC direct No Batteries but condition the AC how?  RSS feed

 
E Saponara
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Hi everyone,

I am planning a micro hydro system, and one detail that is hard to parse is when you do AC direct, you can have the load controller maintain the frequency, but how do you get clean power?

Most systems I see discussed still have some batteries and tap their power from inverted DC, which will be much cleaner than the AC direct from the generator.

some details, 2 x 4000w 240v triphase output, I'd like to just condition these lines and use that in the house, but I don't see much of this looking around, and the conditioners I have found seem rather expensive compared to inverters.

So how can I run clean power AC direct without batteries?

Will a rectifier and inverter essentially do the same thing for less with no battery or a small battery?

Thanks for any ideas.

ed

 
Joseph Lofthouse
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I think that most people use power conditioners every day and don't realize that they are doing it: They are called surge supressors, and uninterruptible power supplies.

A surge supressor gets rid of voltage spikes.

An uninterruptible power supply does that as well, but also stores energy in a battery to supply extra power during momentary voltage drops.
 
Dillon Nichols
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The MOVs (Metal Oxide Varistors) in the vast majority of surge suppressors are only good for suppressing surges; not sufficient for conditioning dirty power. They also wear out over time, and can be overloaded by an excessively high voltage surge. Many UPSes also rely on these for surge protection. Basic info here: http://www.circuitstoday.com/metal-oxide-varistor-mov

To get any sort of reasonable line conditioning out of cheapish devices like these, you'd need an AVR (Automatic Voltage Regulator), or a UPS with that feature. An Online UPS/double conversion UPS would be ideal from a protection standpoint, which is basically just moving the battery/inverter portion of the system down the line... as you say, much cleaner. A line interactive UPS might be good enough.

I don't have any real idea how dirty the power from your microhydro will be, so not sure if this sort of equipment would be adequate, or if you would need something more industrial. Is 240V triphase what you want to use, or do you need to convert that to something else?

I'm not sure how well an inverter will behave with no batteries; may have issues with input sag when loads are applied. I'd expect you'd do better with an abnormally small battery system to keep the DC input to the inverter stable; this would need to be something capable of an unusually high rate of discharge, like LiFePO4. You're dealing with quite a bit more available input power than I'm used to in DC systems, though, so depending on the rectification config I could be wrong about the need for this buffer...
 
E Saponara
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Well It would be nice to have 3 phase 240 from the jump, I have step up / step down transformers so easier than anything. plus the generators are rated at more watts at 240v.

the power conditioners I saw were rather expensive, it might be cheaper to rectify and have a small battery. Question, if I have say a single battery (say car battery sized) and tap my power from there will I be able to use the full 8000w? all coming through the battery? is it gonna dry up on me alot? It seems like the battery could be a choke point and cause problems. The soak load will be a water heater 8000 or 10,000w to handle the full load.

So no one conditions the AC from a generator direct? Rectifying then inverting seems a waste but if it's cheaper than conditioning it might have to do. If the rectfier and the inverter can handle the wattage, how small can the battery be without causing problems?

 
Joseph Lofthouse
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What's the nature of the power line noise you are expecting to have to deal with? Brown outs? RFI? Voltage Spikes? Intermittent? Consistent? What intended uses does that sort of noise interfere with? Don't you trust the generator? Perhaps consider a generator that isn't so dirty? Perhaps consider a generator with built in conditioning...

8000 Watts divided by 12 volts ==> ~700 Amps. Yikes!!! The copper wire necessary to handle that kind of amperage isn't going to come cheap. I think that's about 7 times the amperage that is optimal for charging a car battery sized lead acid battery.

When I was using a generator while working construction, the power was never conditioned. We used it just as it came out of the generator. We were only running motors, lights, and heaters, but not electronics. They didn't care at all if the power was dirty. Perhaps you don't need to condition the entire output of the generator. Perhaps only certain circuits need conditioning.

20 Amp 115/240 volt power-line filters cost about $10 on eBay. Install one for each circuit in your house/barn wiring. If you have 20 circuits then you are into it $200.


 
Dillon Nichols
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I haven't built or seen a system at all similar to this one; I would expect that there are people running microhydro and simply conditioning the power rather than rectifying and inverting, I just don't happen to have either hands on experience or a handy reference system for this config.

The handful of systems I have read about which incorporated microhydro were doing so as part of a mixed source setup, and I would expect that they found it advantageous to rectify and invert since they were getting DC power from solar arrays, so they needed the batteries/inverter portion anyhow.


12V? Did I miss something? I definitely wouldn't want to rectify to 12V. I would have expected 48V would be a more reasonable target voltage for a system of this high a capacity.


How dirty the power is, seems like a pretty key metric. Usage patterns also... As Joseph says, you might not need to condition all the power, maybe it's good enough for some uses as is.


As far as how small the battery can be, I expect it would be less about amp-hours, and more about discharge rate. Assuming that you wouldn't be expecting to continuously draw more power than is provided from the rectifier side, all you're looking for is something to buffer startup surges and keep the voltage available to the inverter nice and stable. A small bank of lithium ion or LiFePO4 cells would seem better suited to this than lead-acid. Putting a solid number on minimum size would require some idea of what sort of loads will be applied and what sort of sag can be tolerated...
 
E Saponara
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Thank you Joseph and Dillon,

It's for a home and i want to run audio electronics off it that would be hard to replace, the voltage in the country is 240 and that's what my 2 little generators will spit out at the highest RPMs which I should be able to reach easily.

I will need a load controller to keep soaking up the juice to keep it at 50 or 60 Hz from what I understand, as I said a water heater or 2 will be the soaks.

I am not sure how stable the voltage will be compared to rectified stored and inverted back to 240. I basically need 3rd world standard 220/240 and nothing too sensative, but I want to protect anything that gets plugged in from swinging voltages.

I guess the best thing is to set it up and measure it and then see thanks for the tip on power line filters, will definitely install those. I may very well be able to use it stright.

Since all systems I see have a charge controller and a lot of peripherals for the battery, I was hoping there was a load /charge controller that would run the AC system but it seems they all require rectification. The generators have a single winding 12v tap each which I can use to run the controller rectified and to charge a small battery.

It just seems like the controllers need it rectified to do their controlling, whereas I just want it to read the AC and keep the cycles even at 50/60Hz.

Looking at this http://www.homepower.ca/ac_hydro.htm I seem to only need a Load control governor and filtering /fuses plus the additional meters I want. Does it appear that way to you guys?

Thanks a lot for your guidance.
 
Troy Rhodes
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It would help if we could see some more specific specifications on your micro hydro generator or alternator.

If it really does produce 3 phase AC, you are going to have a very difficult time producing clean single phase 220/120 V.

Also, unless your flow rate and head are extremely stable, you will get wild variations in the voltage.

This is referred to as "wild" AC. There is no simple and inexpensive way to make clean stable single phase 220/120 out of that.
 
E Saponara
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http://ep.yimg.com/ty/cdn/yhst-129399866319704/ME1112.pdf

http://www.motenergy.com/mepmge1.html

2 of these.

I have plenty of head and water flow to spin these stabilly, so i guess i'll start there and see if rectification and a battery bank is necessary, if the AC is too wild. What is the expensive way? if it weighs less than batteries it could be the move.
 
Joseph Lofthouse
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E Saponara wrote:Looking at this http://www.homepower.ca/ac_hydro.htm I seem to only need a Load control governor and filtering /fuses plus the additional meters I want.


Home Power System # 1: the frequency of the generator is kept constant by diverting all excess power to heaters. Enough excess load has to be in place to use up more than the possible power output of the generator. 8000 Watts generates a tremendous amount of heat. More than a couple of water heaters would be able to handle. I suppose that you would have to plan on simply throwing away most of the heat generated by such a powerful generator. Or use it to heat a pond...

Home Power System # 2: The controller opens/closes valves to control how much water hits the turbine blades. The frequency of the turbine is kept constant by varying the amount of water flowing through the system.

Home Power System # 4: Uses a combination of an adjustable-flow valve and a deflector to control how much water hits the turbine. Thus controlling the frequency of the power.




 
E Saponara
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I have enough to use 7000/8000 watts easy, but I am going to start with one at 4000 and heat water tanks and yes a pond/ pool to absorb any extra load. don't want to mess with adjusting water flow, the Electronic Load Controller or the THES A2 below seem like the way.

something like this http://www.alibaba.com/product-detail/Electronic-Load-Controller-ELC-_116357027.html

or this at 3k plus 4 relays http://www.smallhydropower.com/A2_%20Version_%200.3.htm

OK, I think I know enough to check what's available locally before importing anything.
 
Troy Rhodes
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That looks like a very competitive price for a fairly sophisticated electronic load control (to dump excess load rapidly and in real time.)

It looks like it can handle 3 phase OR single phase input, but I believe it does not change the phase. 3 phase in = 3 phase out.

None of your consumer goods or electronics can use 3 phase.

I could be mistaken, as I'm not that familiar with that particular electronic load control. But I'm pretty sure it just diverts the excess load, it doesn't change the phase.

 
E Saponara
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It looks like 3 lines out of each box, but yes I will need to convert them to 3 single phase 240v lines if this box doesn't do it.


I really don't want to carry batteries up this hill, mules can nly handle so much.
 
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