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Forum Index : Electronics : Mill to battery cable
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Pt w/field Matt Senior Member  Joined: 24/02/2006 Location: AustraliaPosts: 105 |
hi all would grey plastic mains wiring type 16 square mm double ended 2 scews per end cable joiners be able to do the job for the no crimp tool guys out there? matt down south |
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Yes Matt Perfect stuff, you can get what are called "line-connectors" ,they are like a brass bolt with a "channel" milled into the threaded portion. You lay the 16mm conductors into this channel and with two shifter spanners tighten the nut and it squashes down the conductors. Now,you're not finished yet. Wrap some "self-amalgamating" tape around the exposed conductors and this will give you an insulated waterproof joint. Or, you can simply solder the joint after you bind it with some thin wrapping wire-need a gas flame or at least a 200-300 watt soldering iron-the type the old plumbers used to use with the pump and white spirit-thats another story. Buying that stuff is like withdrawing a half bar of gold from you bank ---so ,go scrounge it from the electric line depot --Previous story will give you the drum. Gee, hope I'm boring you out there.. Bruce Bushboy |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I think what this discussion demonstrates is that the lessons learned more than 100 years ago still apply and one of them is that significant power reticulation at low voltage is very difficult and expensive in materials. Now is anyone brave enough to raise the matter of transformers again? We have been told that transformers are inefficient at other than their designed frequency. I have no argument with that in fact I have personal experience of what happens when even heavy duty stuff designed for 60Hz is used in the 50Hz environment, you loose a lot of energy in heating the transformer and burn outs are inevitable. Now, as far as I can determine, the limiting factor is 'iron losses' when a transformer is used at low Hertz but I have been unable to find the clear statement of what the limitations are when using transformers at higher frequencies (i.e. Hertz). I think the standard F&P has 28 cycles per revolution which is 14,000 cycles per minute when spinning at 500 RPM. Divide 14,000 by 60 = 233 Hertz (which is cycles per second). Obviously in our F&P systems the frequency will be mostly be more than 50Hz although at a leisurely 100 rpm (according to my calculations) the frequencey will be damn near 47 Hertz which is about as low as a 50Hz tranny would want to go. It is my opinion that mains transformers, although not ideal, would be practical for a windmill F&P where they would be at their peak efficiency where efficiency is needed most and that is in light wind conditions. The advantages of transformers is that bringing three high voltage wires direct from an unmodified stator right through to where the power is to be used means much saving in transmission wire gauges and resistance losses. Such voltages would be LETHAL but the materials and techniques to handle these safely are readily available. One more thing, as far as I can determine the transformer limitation in upper frequency is to do with resonance in the transformer and I have absolutely no idea how serious this may be as a problem. Maybe I should do some tests? How about I set up a system with one phase terminated in a resistance and another phase coupled via a transformer to a resistance of a value equal to the ratio of the first resistance multiplied by the transformer ratio? I should see the voltage across both resistors climb at the same rate as RPMs increase? Any kink in the graph would indicate transformer limitations. Is this a appropriate test? Comments and corrections accepted in good spirit appropriate to the season! 
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
KiwiJohn - your points are well made there, and something I've mentioned a few times. My initial thought was to use a transformer that wasn't simply wound on soft iron - eg, a toroidal ferrite core. One thing I've learned over the years, is to ask people not what they want, but what they want to achieve. For example, here you're talking about a 3-phase machine running nominally at 200+ volts, and wanting a transformer to drop it back down at the battery end. Obviously, in this configuration, a 3-phase transformer is required, or 3 single-phase. But stop! Stand back and ask the broader question, "What are you trying to achieve". If you answer "Transmit power from the F&P to my batteries, while losing the minimum in transmission and conversion losses".... then the answer becomes (to me, at least) much more straightforward and surprisingly efficient. 1. Run the 3-phase line whatever distance is required, at the maximum configurable voltage of the machine (lets say for the purpose of the argument, 200 odd volts) 2. At the battery end where you would have had a stepdown transformer and a rectifier, use a high-voltage 3-phase rectifier (most you can buy here in australia are 400V anyway) and stick the rectified DC straight into a switchmode supply. For the electronically-savvy folk, old computer powersupplies are a great building block, good for about 300W (some twice that). The inverter transformer probably needs re-winding to get the output at 12V or whatever your battery banks nominal voltage is, but it's not a huge task. You have immediately reduced the transmission losses substantially, WITHOUT adding the additional losses of transformers to convert up and/or down, without all the frequency/performance issues associated, and without huge engineering hurdles. You end up with a reasonably well regulated voltage (unlike a transformer+rectifier), reasonably high efficiency, quiet and cool-running system. If there were enough demand, we could probably get together and either get some cheap SMPS made, or do a decent batch of PC power supply conversions. My 2c worth... |
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| TomW Newbie  Joined: 21/11/2005 Location: United StatesPosts: 1 |
Ross; I like the idea of what is needed rather than what is wanted. I found it much easier to satisfy customers using that method rather than just going by their [mis]conceptions about gear and systems. Just an observation from decades in a customer service role. Cheers. TomW  |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I prefer to stick by the KISS princible ( Keep It Simple Stupid ). I do have a couple of concerns about using a high voltage F&P and transmission line to a transformer/switchmode PS, Maybe we should start a new thread with this topic. While a transformer or better still a switch mode power supply would work very well under normal conditions.... Concern 1. A 80 series F&P makes about 0.5 volts per RPM, so 100 rpm is 50vac, 500 rpm is 250vac. Our 240 volt transmission cables, transformer or PS can handle that ok, but what happens when things go bad? A wind gust, whilly whilly or storm. If the RPM goes up to 1000, we have 500vac to deal with. Our transmission line or transformer are on the edge of their break down voltage, and the PS is already toasted. Using a 60 series stator will be a lot worse, from memory it reaches 500 vac at 600rpm. Now this just means more complicated control systems to protect the windmill and PS during these conditions, but this is getting complicated, remember KISS. Concern 2. High voltage transmission lines are dangerous. While most of us have a healthy respect for high voltage, windmills are very DIY and I worry about Jo Smith wiring up or handling connectors that could cary several hundred volts. A F&P in standard form will kill you easily. At least by reconfiguring it as a low voltage generator it will just give you a bit of a bite. So thats just my reasons for staying with low volts. Its easy and safe to work with, but the thicker transmission lines are a bummer, especially over longer distances. I've always been over cautious and tend to over engineer everything I make to allow for the unexpected worse case senerio. I know I do dumb things some times, like unscrew live electrical connectors without checking it was turned off. I dont like high volts, spent too many years working with Telecom and getting booted by the ring tone, and thats only 75vac. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
I think you're missing one vital ingredient here, Glenn, and that is that the generator is not running under "no load" conditions. The SMPS will still present a load of however many *WATTS* - arguably much better than a transformer and rectifier will, by virtue of the output being fixed voltage (and presumably largely fixed current therefore), it becomes a "constant WATTAGE load". Yes, volts will climb - but I don't see it making 1000V under a 300+ watt load. Have to argue that one too. Low voltage can kill too. Especially if someone were standing out in the rain trying to fix the darn thing. It has been my experience that when people KNOW it's only low voltage, they take little or no care and fewer precautions. look at how people "twitch" wires when they're hooking up their trailer lights for example! Most of those same people won't try to mess with the wires when they pull them out the end of their power drill for example. (There are exceptions of course...) Generally, I think people take disproportionately MORE care as the voltages go up. There are lots of things that we, as a group, can do to encourage people to do things a little more safely. Like recommending specific (suitable) cables. Eg, in this scenario, going and getting some 415V/3ph extension cable or going to the electrical wholesalers etc to get it. Lets specify something like the orange-circular of 4mm^2 minimum, or neoprene 3-phase freezer-truck cable etc, for outside use. LOL. Your reasons are valid Glenn, but I think that with a little additional awareness and caution, and perhaps some sensible, practical advice on what people can/should use, it can be made a whole lot safer. Instead of letting people whack a couple of tomato stakes in the ground and run some fencing wire in a single-wire earth-return high voltage system, lets ENCOURAGE them to do it right while WARNING them the dangers of cutting too many corners? |
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| Pt w/field Matt Senior Member Joined: 24/02/2006 Location: AustraliaPosts: 105 |
hi all again did yous read the first part of my disscription about the double ended cable joiners, would they do? and there not the bolt type bruce disscribed matt down south |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Ross, I would love to have the technical skills required to design a SMPS that will operate in this environment and which would be achievable for the typical reader of this forum to construct but I am afraid I do not have that expertise. I do however have a trailer-load of various transformers under the bench and I know I can readily enough buy more at Duck Smuff's! Nonetheless I am not adverse to SMPS, it is just that they are unknown to me and they would cost me $$$ to experiment with. That is of course unless I were able to press some of these old computer SMPSs into service. Regarding safety, I agree that even low voltages can be lethal. One would have to bear in mind too that the high voltages from the F&P are not voltages with respect to ground unless part of the system is grounded. The use of transformers, and I use the plural thinking that three trannies are likely to be easier to find than a suitable 3 phase transformer, gives DC isolation between the high voltage and low voltage domains. Whatever, by far the greatest incentive to the use of higher rather than lower voltage cables is our old friend Mr Ohm and his law. Suppose we have cables of 1 ohm resistance and we have a 12 volt load of 120 watts. Thats 10 amps through all parts of the circuit. 10 amps through that 1 ohm resistance is 10 volts! Blimey we are wasting 100 watts in the 1 ohm resistance cable, 5/6 of our windmill output is being wasted warming the feet of the birds perching on the wires! Now if we used 120 volts for our 120watt load that is only one amp, one amp through everything including our 1 ohm resistance cable. One amp through one ohm is 1 watt or only 1/121 of our generated energy being wasted on the flaming crows! Transformers or SMPs, the case for high voltage transmission lines is pretty compelling! |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah your right Ross, but whenever I describe a project or method, I'm aware that some readers will have nill expierence or safety awareness. Thats why I wont publish any 240vac circuits or give specifications on making a tower, I dont know how skilled or carefull the reader will be. While I dable in the HV stuff myself, I cant be seen to give instructions on how to wire a HV circuit. But yes a HV transmission line does have its benefits. Matt I use those cable joiners a lot. A few tips though. Buy bigger than you need, and feed the wires in far enough so they overlap. That way each wire is held in by two screws and makes a stronger connection. Dont tin ( solder ) the wires used in screw or crimp connectors, and if its out side wrap in heat shrink or insulation tape. 
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
These two-screws-per-end (ie, 4 screws per conductor) are excellent for your DIY use, if you take a couple of simple precautions. If the wire is a substantial proportion of the size of the connector (2/3 or so of the bore) twist it with pliars to keep the copper all together. DO NOT TIN IT (Solder) - see my previous post about the problems this causes. Put the wire in half way only and do up the outermost screw HARD. Then do the inner screw the same. HARD. It should make a little "creak" sound when its good and tight. Then put the other wire in the other side and repeat. If the cables are LESS than half the diameter, strip them enough to run the cable throug the whole way if you can, and do all 4 screws up tight. When its all finished, run good electrical tape over the whole lot - start at least 2" away from the connector, wind the tape on in one continuous piece with at least 1/2 width overlap each time, over the connector and down the other side for at least 2". Then come back over it again from the other side. Ideally, some "self-amalgamating" or "bituminous" tape over the whole lot. This stuff is impossible to put on cold. Keep in in your inside pocket until you're ready to apply it if its not summertime! Same as the PVC tape, overlap it about 1/3 as you go, but with this tape, STRETCH IT to about 1/3 longer than it comes off the roll, as you go. You will feel it - don't stretch it enough to break! (If you do, don't panic, just back up an inch and keep going). This stuff will, over the next short period of time, all "merge" into one solid, air and water-tight seal. Its essential to have a clean base at your wire for it to seal to (you should completely cover the PVC tape, because it will break down over time anyway). I'm not proposing designing one... starting with a discarded PC supply. Most are 300W or more, have the rectifier, switcher, regulation etc all there for the taking. Only limitation is that most are designed to deliver the bulk of their power at 5V, so modifying the inverter transformer would probably be required. That said... and upon looking at my written words.... rather than a 3-phase bridge into one of these supplies, and the complexity of rewinding the inverter transformer, might be simpler and *SAFER* to use THREE PC supplies. One on each phase. Series the 5V outputs, you now have a 15V output at 40+ odd amps, no modifications to the supply at all - don't even have to open the bugger up, and could handle potentially close to the 300 watts PER PHASE. Thats the entire point. Computer supplies are a dime a dozen. And most of them will happily work from about 90V to 250V AC - and depending on output current drawn, will handle quite low frequencies (although, 3 phase would certainly make this better. PERHAPS running the 3 phase from the F&P through a full-wave bridge, then into the three PC supplied with the inputs in parallel and the outputs in series would help with the low frequency end) (Note: the only reason they don't work too well at low frequencies is the high-voltage side storage capacitors have to "carry through" the missing part of the cycle) Your concerns with peoples construction capabilities is probably prudent - especially with todays increasingly litagous environment. |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574 |
hi everyone just to know that l havent seen "bituminous" tape for years since around in 1970 are they still avivable at electrical shop? and in the old days we use to cut up plastic tube and place in jar of finger nail cleaner to make it expand the tube and place on wire connect and shrink back in half hour before the heat shrink plastic tube was invent arrive . Other things i would like to know anyone know about Australa made Merlin wire-wound resistor manfacturer that made in Melboune in around 1967 also some information or histroy about Dunlight windmill generator made in Australia l belive Can anyone some inqurie as l would be happy find apiece of imformation. 
dwyer the old bushman |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
I have a few rolls left from 20 years ago, but did buy a roll of thinner stuff, I think 3M brand, 2 or 3 years back. Its still the only thing I'll use to protect radio equipment connections outside, and power connections in the weather. I even used it on a submersible pump a few years back, and it's still working so it must be doing ok ! |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
On the subject of sealing cable connectors and joints--- There's a product out there called "DENSO" tape,sort of a cotton tape saturated in this mustard coloured greasy stuff. We used it on antenna feeder joints and even in underground pits on electrical cables and communication cables.-(Had to cover the joints in S/S stockings on some towers to stop the cockatoo's ripping it off). Anyhow ,it's more messy than heatshrink,or the self amalgating tape. Bruce Bushboy |
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Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
Well, reading this lot has been as interesting as it has been frightening. All I can say as an electrical safety practitioner is DON'T DO HIGH VOLTAGE AT HOME unless you are a sparkie, or you can have a sparkie do that part for you. It certainly does saves voltage drop and using three phase saves even more. There are some things of general interest though, that reading the thread raises. Aussie standards before a few years ago required cabling for permanent wiring in buildings to have insulation rated at 600/1000Volts. That meant it was designed and therefore could be used at 600 volts between phase and neutral (and earth) and 1000 volts between phases. So older cable would be OK for the 500 volts phase/neutral mentioned above. In recent years we have "harmonised" many of our electrical standards with our Kiwi mates, for reasons of mutual commercial success. They got by previously with 450/750 volts rated insulation, so all new cables in Oz and NZ are rated at the lower voltages and carry thinner insulation. You can tell just by looking at the cables, the new power cables look about the same size as the old lighting wire. Its all OK, you just need to be as careful as the Kiwis obviously were in installing the cables, no dragging it around corners of timber studs etc. Now about voltage drop and the basis of the calculations. The fact is that AC voltage drop is larger than DC voltage drop, because of the magnetic field interaction with the electric current causing them. Resistance in the cables cause a drop in voltage for both DC and AC, but the property called Inductance is responsible for an additional drop in AC voltage. Inductance is worse if the cables carrying the current are spread apart, like on poles. It is least if the cables carrying the current are as close as possible, like in fully insulated multicore cables. Even if you rectify the current at the mill head, the combined output current contains large proportions of AC - draw a picture of it and you'll see that it still has a ripply top. So use the tables for AC when calculating voltage drop even for those carrying rectified output of a mill. It won't be quite as bad as what the tables say, but its best to be a bit conservative. About copper versus aluminium cables, you need an additional 60 % area in an aluminium cable to get the same resistance as a copper cable, but the inductances are the same. About using iron cored transformers at frequencies much above mains frequencies, our old mate, eddy current starts to play harder, losses increase rapidly. The ferrite cores are much better, working well up to (I think) a few hundred Hertz) Megawatt Man |
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Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
For those still seeking some reference of what to use for a length of run, i'd refer you to the Tricky Dicky Catalogue page 350 (2005/2006) also viewable @ Choosing the Right Cable http://www.dse.com.au/cgi-bin/dse.storefront/en/catalog/SUP1 000030 Copper Cable Characteristics http://www.dse.com.au/cgi-bin/dse.storefront/en/catalog/SUP1 000032 Properties of Copper http://www.dse.com.au/cgi-bin/dse.storefront/en/catalog/SUP1 000033 Winding Wire Specifications http://www.dse.com.au/cgi-bin/dse.storefront/en/catalog/SUP1 000034 and all the best for 2007 folks. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
[quote]but the property called Inductance is responsible for an additional drop in AC voltage.[/quote] Hmmm... however Megawatt Man inductance is reactance and as such does not consume power so although higher frequency may require higher voltage for the same current this may not be such a cause for concern. As the mill speeds up for a wind gust or squall both the voltage and the frequency rise and inductance may actually prove to be a desirable characteristic for keeping thingswithin limits? Heck, judicious introduction of inductance may prove to be part of designing a reliable system, dont you think? |
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| Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
G'day KiwiJohn, Thanks for asking that question and making me investigate further. This is what I came up with. If we rectify the output of a three phase configured F&P at the mill, the ripple is at 6 times the fundamental frequency so at first glance you'd reckon on a large voltage drop due to inductive reactance of interconnecting cables. But the proportion of ripple voltage on a full wave rectified three phase system is only 4%. So the AC ripple current is small anyway compared to the DC current so will make not too much difference to the voltage at the output end of the interconnecting cable. In addition, the influence of cable reactance on impedance and therefore voltage drop is not great, because Resistance and Reactance are comparable in magnitudes and Mr Pythagoras shows us that Impedance is not too much larger than either Resistance or Reactance. If we use a small cable size, (say 2.5 sq mm) Resistance will be a problem and Reactance only makes it marginally worse. If we use a large cable, (say 16 sq mm) Resistance won’t be much of a problem and Reactance will not make a noticeable difference. It turns out that these factors won't have too great an influence because after all, we are talking about maybe 20 amps per phase, although I hope to see this rise to say 50 amps per phase. Megawatt Man |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Megawatt Man, well there we go, I was ignoring the obvious and was thinking that the transmission had to be 3 phase AC where of course as you have pointed out rectification at the source end reduces the AC component to very low levels. Dare I suggest that it could be reduced even more by smoothing at the source end, either by addition of L or C or both. The thought of high voltage DC transmission gives me the willies which leaves us with high current (i.e. low voltage) transmission and inevitable R losses unless short distances and big cables are used. If we were to use high voltage DC transmission then a SMP would be required to get lower voltage suitable for the battery bank. Just my thoughts. |
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