120v dc system help

[jondecker76]

Before winding my coils for my 16' dual rotor machine, i've been racking my brain trying to decide on the best voltage. I would like a 120v dc system. I would like to build my own equiptment to change the DC into AC using modified sine wave, or possibly even a more acurate sine wave representation. However, my experience and understanding are a bit lagging.

Here are my thoughts -

For a true grid power simulation, I would need about 170v peak to peak in my sine wave. Since this goes both positive and negative, would this mean I would need a 340 volt battery pack with some kind of center tap? (is a center tap even possible in a bank of series-wired batteries?)

Assuming this is true, and I had a 340v dc batter bank, with a center tapped at 170v then I would just have to design a type of "inverter" that went between + and centertap, and - and centertap at 60hz?

Am I missing something or is there anything I am not understanding?

I want a high voltage system for the following reasons:

1. My location for tower erection is at least 500' from the house
   
2. Would like to keep losses to minimum
   
3. Would like to have the option to decide between battery bank or grid tie inverter when I get to that stage.
   
4. DIY transformer-less "inverters" are more in my experience and price range.
   
   

Please, any pointers, tips or suggestions would help me out a lot!

thanks,

Jon

[commanda]

If you use a full H-bridge (4 active devices) you only need half the dc voltage.

Amanda

[freerj]

jondecker76,

You may want to search for some earlier replies/posts by, I think, Nando.  Several have discussed using a high volatage mill.  Some for water heating, and the other was a really interesting discussion about a high voltage mill for AC generation as you described.

IIRC, the discussion basically said that you could do square wave AC pretty easily with H-Bridges of sufficient current handling capacity.  But, to do true sine wave, i believe that Nando said you needed much higher voltage supplies, something like 600V.  I think the discussion went on to suggest using a Wal-Mart MSW inverter as the frequency source for the device.

I may have misquoted here, but the posts are definitely around for an easy search.

Good Luck.

[terry5732]

I applaud your desire for higher voltage.

Don't get hung up on "true sine wave' as you don'y have anything that requires it. All you sensitive electronic devices have built in regulating power supplies that are capable of rendering a wide variety of inputs.

Swithcing polarity of batteries would give a solid square. It is the transformer primarily which gives the waveform in an inverter. You may as well keep the battery bank voltage down. Run your mill output high for transmission, and drop with a tranformer for battery charging. With sufficiently high mill output you could use an off-the-shelf 120V or 240V charger as your transformer.

[Nando]

Oh Boy, here comes high dreams !!!

To be able to FEED power into the GRID, it is necessary to determine the GRID voltage variation, SPECIALLY toward the high voltage end.

Some places may have NOT 115 Volts AC, but up to 130 Volts AC this represents 184 Peak volts .

Then there is the need of a Voltage over head to be able to generate a NICE and CLEAN SINE WAVE form -- therefore at least 40 to ? higher volts. ( how are you designing this part of the CKT ? )

Since I do not know how you are dreaming the Circuit, then it is not possible for me to tell you what to do .

So you may need twice this voltage or around 184 + 40 volts = 224 volts * 2 = 450 volts center tap .

With a battery bank the voltage should be 38 - 12 volts battery bank .

You are now trying to design the equivalent of a high level UPS ( with this voltage, I designed one in the 1980's ) -- 25 to 100 KW capacity -- for equipment requiring high reliability power sources -- for computers that need to work 24/7 .

@@@@@@@@@@@@@@

Now your wind mill :  If your wind mill is 500 feet away, use high voltage generator like at peak wind velocity to produce around 300 VAC - this depends on the end equipment --

A bank of 14 - 12 volts batteries can be used to make a very simple 5 to 10 + KW MSW ( Modified Sine Wave) for local energy - ( transformerless converter) or

with this battery voltage a High frequency transformer CKT to convert to 460 volts center-tap for a GRID tied Power source

ENOUGH FOR NOW

Nando

[DanB]

I've read all the comments so far and I think I'll jump in and play devils advocate a bit.  If you enjoy making things complicated I'd say go for it.  These are some of my thoughts on the situation.

I'm all for the idea of efficient MPPT controllers that allow the machine to run at very high voltage and optimise the efficiency of the alternator.

I think transformers will be expensive and problematic (unless you have lots of poles in your alternator you'll be running at very low frequency)

Good 48V sine wave grid tie inverters are widely available for reasonable cost and they have other added features like powerful battery chargers which come in handy.

"I want a high voltage system for the following reasons:

   1. My location for tower erection is at least 500' from the house

   2. Would like to keep losses to minimum"

If you run 1000' of #6 gage wire you'd be under .5 ohm.  At 500 watts output @ 48 Volts you'll be losing less than 10% in the line.  With a 16' machine most of your energy will probably be coming in at less than 500 Watts so you'd still be fairly efficient.    

I expect the work in building a slightly larger machine would be less than the work of trying to improve efficiency by running at very high voltage.  Maybe not - I guess it depends on your abilities and resources, but if it were me I'd have no problem with a 48V machine 500' away from the batteries.

Perhaps not a big factor, but worth noting that a 48V system is probably a bit safer than a higher voltage system.

   "3. Would like to have the option to decide between battery bank or grid tie inverter when I get to that stage."

This came up recently.  While I'm sure that some folks have the ability to build a grid tie inverter, I doubt it makes sense in most cases.  You can buy a very good one that runs off 48V for around $2000.

I guess what you do really depends on what sort of work you enjoy and your abilities.    Simplicity has it's advantages.  Some of my neighbors  have built very basic 12V systems and some of these machines are nearly 500' away.  In higher winds (which are not common) they're dismally inefficient, but in lower/average winds when they're producing around 100 watts or so (which is where most of the energy comes in with a 10' diameter wind turbine) they're not bad.  Overall - they are reasonably efficient.  While I loath the idea of 12V machines at such great distances sometimes it's the best option when folks allready have a 12V system.  At 48V, 500' doesn't seem too intimidating.

[Ungrounded Lightning Rod]

Unfortunately, an H bridge also means your neutral wire is hot for half the cycle.

Cheap inverters do this.  But it's not recommended for a house - or for any load that's not double-insulated or otherwise designed so either 'prong' can be the 'hot' one.

[River Goat]

Hello Jon, I ran a 120vdc system for many years. Most of my loads, shop tools, lights, tv, coffee maker and a few others, use the 120vdc direct. Some things like, washers, dryers and stereo (things with induction motors or 60hz transformers) need 60hz ac. I used a 12vdc input msw inverter to supply ac (because that's what I had). I built several 120vdc input square wave inverters with varing degrees of sucess, but all failed one way or the other. I could build one that would last but last year I found out that an Exeltech 1100w sine wave inverter can be adjusted to run on 150vdc input and at a very good price. The circuit in switching power supplies made to run on 120vac are made to run on 150vdc, thats what you get when you rectify and filter 120vac. Most of my electrical loads use these supplies. I raised my battery voltage to 144vdc; my solar panels and wind generator were already at this voltage and I got rid of the 12vdc system.

This system is very powerful and effecient and uses inexpensive "off the shelf" equipment. I'm very happy with it. But it does require knowing what kind of input circuit is in the equipment you use.

Good luck,

Jerry

[Nando]

I WOULD like to "INSERT" a Warning here.

Those that are interested in making a DIY transformer-less DC AC MSW inverter should be AWARE that a high voltage battery bank ( like 120 - 140 volts bank) when used directly to generate the AC voltage without an isolation transformer the whole string ( let's say: the wind mill, the charger, the battery and of course the DIY inverter) will be FLIPPING at the AC frequency.

This is ONE of the DRAWBACKS of the transformer-less inverter.

TO limit this effect the power supply ( the 120 string) needs to be either doubled in voltage, to have a center tap at ground potential or an additional circuit is needed to take the 120 + volts bank to generate the opposite voltage ( 120 V).

This way the switches just connect the positive or the negative at the AC frequency rate and the equipment prior the inverter stays at Ground potential.

The transformer-less inverters that have been built using my design, have the grounding arrangement, or have a larger 50 or 60 HZ isolation transformer.

If somebody is really interested in building a transformer-less inverter, please contact me for assistance to make sure no electrical problems appear

Nando

[altosack]

Hi Jerry,

I'd like more information on what you said about the Exeltech inverter being able to run with 150 VDC input.  Are you talking about the ones Exeltech makes for 108 VDC, or does this apply to any of them ?

I have an 1100XP/24 that I've been thinking about retiring since I "need" to go to a higher voltage battery bank (at least 48V, but 120V would be nice). I'd love to continue using it, since it's all I need and then I wouldn't have to buy another.

Thanks,

Dave

[stevesteve]

Has anyone had any safety concerns about using 120V DC?

I understood that AC power was a lower risk at higher voltages as it tended to throw you off if you touched a live connection. Is 120V DC enough to cause muscle lock and burns?

[River Goat]

Hi Dave,

I am sure it is only the 108v model. I talked to an Exeltech engineer at MREA fair; he said the 108 could go as high as 200vdc max. by changing the set points.The 24v might be the same as the 48v, but I don't know that. Mine was set at the factory to my requested voltage. One issue is that it is UL approved only at 108v, that is not an issue for me.

I wanted to build an inverter mostly for the challenge, but I have plenty of other challenges to keep me busy.

It is surprising how many things will run on 120vdc direct. CF lights with electronic ballasts work great and can be bought for under $2. Most newer electronics will run on it with no modifications. Brush type motors work but need better swiches.

I am installing a 108vdc system for my neighbor; he has only motors and lights so that will work good for him. I have alot of electronic equipment and 144vdc works best for me; my shunt regulator is set at 170volts.

Jerry

[John II]

Hi Jon:

While 120vdc is considered dangerous and perhaps "cutting edge" by some, It also appeals to me. I'm also in the stages of setting up a 120vdc system for several reasons. First a lot of shop power hand tools that already have switches rated for 120vdc will run directly off of it.

There are commercial 120vdc input inverters readily available, but my research has so far yielded only $6,000 and up commercial units. These units are also so ultra complicated, you will have to send them to a service center for repairs. Because these inverters are not "home owner" rated, you are looking at very expensive service feels for them as well. They are definitely out of the reach of being practical for my needs both financially and from a servicing point of view.

River Goat... please tell us all more about Exeltech's ability to run at 120vdc ? You told me once, but I have forgotten much of it. I'd like to here more about this again if you can find the time... Thanks in advance.

Right now 120vdc systems are considered too dangerous for the average home owner. But that may eventually change who knows. 240vac isn't exactly something that your kid should play with either and yet you have that in your home (smile)

And yes wiring cost is much lower and transmission efficiencies much higher for longer runs.

River Goat in his response to you, may have a great idea ( 144vdc systems) , I may eventually give his ideas a try.

I know of one fellow that has built a very plain old fashioned 120vdc square wave inverter. It is ultra reliable and he has run his entire home and water well system off of it for 8 years or longer. He has made his schematics and detailed implementation and alignment information available to me. If I can find the time, I may clean up his notes and set his hand written notes to print and with his permission and blessings publish it here. This inverter accepts 120vdc input and is transformer-less and very reliable. The prime drawback is square wave causes some motors to heat slightly and it also has poor voltage regulation. But for most house hold items this is not a problem. The real nice thing about his inverter is that it would be homeowner friendly to service or repair should you ever need to do so, and the circuitry is very simple and very reliable.

Do a Google search ( within FieldLines.com ) which can be found at the top right hand corner of the page you are currently on for " ibedonc " This guy has perfected a pure sine wave high voltage inverter that can be made to operate from 120vdc or higher voltages. He has an operational unit right now. The only catch is.... he's very very busy. It's going to be a while before he get's the info out to anyone that is interested. I understand that he also wants to do more load testing before publishing his information. But current test right now are proving it to be a fantastic unit.

I do think you ought to consider the voltages just as lethal as you would 240vac grid power and treat it accordingly. It's nothing to play with and can easily kill you.

This will no doubt raise some controversy, but I don't see any problem with safety issues with a transformer-less inverter. If the entire system is run as an isolated system and you have good hvdc GFI's (ground fault interrupt detection shutdown ) on your system. Should any part of your isolated system from the wind genie to your batteries develop a leakage to the ground, then the whole system would shut down. And that would include if the leakage was detected though your own body. But if you wish to disagree and argue the point, then running high efficiency ferrite toroid output transformers would be an option as well. Either way I think it can be done quite safely. You really don't want any leakage from any of your system anyway.

I may be incorrect, but I believe that Ibedonc's inverter which as I said is already tested and operational does already have full isolation from the batteries do to its high frequency input dc to dc converter which drives the "H bridge" which produces full RMS regulated sine-wave output. So I think it'll be able to run in full proper grounding mode if I'm not mistaken.

Most CFL's (compact flourescent) lamps run on 120vdc just fine as well as most modern electronics that makes use of switching power supplies. So for many items, your efficiency is even higher because you can circumvent the inverter altogether. `River Goat' ( Jerry ) has told me that if you bottom out your 120vdc batteries a lot of switching power supplies will quit working because of too low of voltage. So to avoid that, this is the reason he has bumped his 120vdc system on up to 144 vdc : )

John II

[iFred]

Personally I love high voltage systems, the major drawback at this time is control of the mill more then anything else. I have built high voltage mills and like them, but control was the overlying problem. Another issue is that the batterys that you choose to charge should be all almost exactly the same. Putting them in series and charging them in series is a slight drawback because not all the batterys will charge at the same rate. somethings to consider. I wish you good luck!

[ghurd]

"the major drawback at this time is control of the mill more then anything else"

What is the control problem?

G-

[robl]

I was off-grid with a 112V (nominal) battery system for more than 10 years. Power came from solar (10 12V/40W panels in series) and a Dunlite 120VDC 2KW wind-gennie on a 60 foot tower. I agree with most of what's been said but would like to add a few comments...

A series battery system is generally a better setup than a parallel system due to better current-sharing in the string. Because of the high voltage/low current algorithm, I2R losses were also less of a problem.

Control and monitoring circuitry was powered through isolated pwm switchers. Many off the shelf "AC" units do drop out at low battery voltages, but "universal" industrial units from companies like Meanwell/Samlex will go down to 90VDC with no problems.

I also used an Excel XP1100 for more than five years with no problems. It put out a beautiful sine-wave but it hated motors, so I had to put pfc capacitors on my washing machine and fridge.  I also used twistlocks on all the dc only tools to avoid plugging AC only tools into the DC system. Although many tools and appliances use universal motors, they also often employ scr's to vary the speed. SCR's on DC is not a good a match.

The folks at Exeltech were not very customer-oriented and rarely returned my emails. Their unwillingness to communicate with end-users is what helped me move to the Outback system. I reconfigured my bank to 48V and haven't regretted it.

HTH

Rob

[iFred]

if your furling fails or becomes misaligned, there is no way to magnetically short the mill (to act as a magnetic break). So other forms of control are suggested just in case.

[River Goat]

iFred, I have a 1kw/3ph/pm/150volt mill and shorting the 3phases works good for a brake.

Jerry