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Forum Index : Electronics : 48V F&P’s
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KarlJ Guru  Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
I found this on fieldlines Voltage Smart Drive Stator Type 12. 60P delta, 80P star, 80SP delta 24. 80SP star, 60SP delta 48. 100S delta This got me to thinking as obviously they are talking stock rewire job of 7X2C (SP)for the 60's and 80's but these days we're doing the 2x7C as the 100S is rare. Additionally Cameron said 24V had more potential than 48V due to stock wiring limitations ie 7X2C in 80S works well for 24V so 48V should be 3.5X4C which we cant do for obvious reasons so were stuck at the low end with 2X7C, sacrificing precious AMPS to resistance of the windings.....or so I concluded now got to reading some more on imsmooth's addition of a few more turns on the 100S to make it work a bit better (24V), he got about 20% more out of it than stock at 24V Stock stators have on each finger 100S has 44 turns 80S has 115 turns 60S has 170 turns My way of thinking is that if the 80s wired for 2X7C = 805 turns total of wire to get what you need at the rpm 500odd (48V+)(5.5A or so for 300W)or 2.75A from each set of 1x7C ----not very much. UN-modified 100S has 616 turns stock, hence slightly higher cutin (30% or so), but lower coil resistance hence more potential -may be too late in the rpm range. But with 70 turns on each instead on the factory 44 turns gives 980 turns total hence should have a lower cutin than the 80S wired as 2X7C but still have the potential to deliver more amps as wire resistance is lower now the resistance of stock 100S is 1.0 Ohm and rewired should be 1.59Ohms and the 80S is 5.8 Ohms split into two (2X7C)is 2.9 Ohms. Thus I propose that adding the extra turns to a 100S in 1.0mm and wired as star 1X14C would not only yield a lower cutin than the 80S wired as 2X7C but would have the potential for 1.8X more power. Thus instead of getting for arguements sake 300W at 500rpm you would get 365W AND -it wouldnt fall over until 900rpm (where it would make 657W)unlike the 80S 2x7C which falls over at 750rpm giving you more control and better brakes to shut down. so....please knock some holes in the idea before I waste half a day stripping one stator to add to the other one! I make this mod at $15 in parts and few hours in labour, as opposed to the alternative Neo's which appear to have had mixed results and is even more time consuming and expensive. Phillm, say the word and i'll do the work and send it to you for a test, if it works you can have it, if it doesnt, you can have it too. (have to pay back the free advise somehow!) 
Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl I read on a forum in the states of a guy that replaced the magnets with stronger ones and canted them to reduce cogging and had an impressive increase in power out at any given revs, I cant find it again but it was intereasting but the cost of the magnets was prohibitive I think, got away from the spirit of the FP recycling. I was thinking with this VS I want to build by putting the mechanical position of the poles half a pole out would that reduce the cogging problem. All the best Bob Foolin Around |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
i decogged all three stators I sent you Bob. twisted the poles with the tool anthony loaned me Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Neo's are interesting and i'm sure I'll go down that path one of these days, just cant get my head around $100+ in magnets for something which is only worth that. One day I buy a Shedload and do a few, flog them for a fortune! I prefer the yards vs $$ methods Karl Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl I read this with interest and I didnt realise that there was so much difference in the motors it seems to me that rewinding as some propose, is getting away from the KISS principal with this range of turns on the windings and the ability to interconnect as required it should do most things without rewinding. Alot of work for a small watt return, the stronger magnet apart from the cost seemed a better alternative. As the volts go higher the amps get less so is less effect from increased winding resistance A X V = watts In my mind the resistive losses stay much the same. 
All the best Bob Foolin Around |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Ah yes Bob but the 48V solutions are not ideal EG the 80S 2x7C and as such become current limited due to the wire resistance sacrificing output to heat. HerbNZ, where are you when I need you! Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl Heat is my ememy up here too so I suppose it would be less loss in antartica good spot for mills bad for people. In my old slow speed alternator that I made for VSM it had 15 pole and I could rectify each one seperatly and series or parallel the output from 24V to 110 and switch them in or out to vary the load crude but it worked, I have asked my friends son to look out for FP up here to but he said not popular around here he has some other one that use a internal magnetic rotor but it needs high speed to get it going and produces three phases of 110 volts at 1200 rpm on his test bench, dont know what output but by the size I would say 500 watt plus I will make him a load tester when I get time. He said he gets a few with the power card blown and not worth repairing as all the parts on the board have no numbers you just gotta buy the new board. His test rig he made is of interest it is made of a 2400 watt brush type vac motor which he has fitted a small pulley and uses a large pully mounted on a old washing machine spindel bearing set he then uses a rubber hose as a drive to the motor under test ( which is clamped down] and meassures the coil voltages to find shorted or open coils a bit bushey but it works. he uses a variable speed controler out of the vac to vary speed and a strobe tacho for revs. Enough waffel for now must go and hunt provisions at the supermarket for the long weekend probably a lot of visitors All the best Bob Foolin Around |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl Dream Dream Dream Bob Foolin Around |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Hi Karl ... Where to start.... We'll ease into it as I say it's nice to see the water story gave you some pleasure... Now for the rough stuff. I had avoided commenting on this kind of story, as I don't have a F&P, and if I did, I would not use it. However, you are using it, so how does it really work, and what is the best thing to do with it. As I understand it, you are wishing to add more turns to a 100s stator, of thicker wire than the 80 stator, to end up with more turns, and lower resistance... thus getting higher voltages with lower resistance and so .. more watts..... then wire it in star, and get the extra 1.7 times the voltage... even better........no. Using ohms law, your idea is reasonable... but these things are iron cored long salient pole motors. These rules only vaguely apply. The synchronous impedance is the thing that will determine success here. These devices are governed at their limits from armature reaction.... not thin wire. You will never have heard of these things burning out..... or even getting very hot... why? It comes down to weak magnets, lots of turns and the effects of back MMF (magnetomotive force). When your permanent magnet passes your coils, it generates an EMF (voltage) in the coils, you then load it up, and amps flow in the coils. These amps now do what all amps in all wires do... they generate a magnetic field.... just like any electromagnet. This field will be oppose the ferrrite field in a amps/turn strength. You can see where this is going..... The more amps you can generate, the stronger the amp/turns generated magnetic field becomes..... and as it opposes the permanent magnet field, it neutralises the ferrite field at some point, and no more generation takes place.... no matter how fast you spin it.... it becomes current limited. It is now clear, that it is not just the ohms that limits these things, at a more serious level, the armature reactance is what stops it producing, and sets the scene for runaway. If it were just ohms law operating, the stators would burn up on their first outing in a good wind.... but they dont, they just stop producing anymore. Your problem.... if you could get the extra turns of 1mm wire in there, yes cut in would be lower, but with more turns, the amp/turns point where current limiting starts is lower. In star, you have twice the turns for .6 of the voltage of the two phase groups.... ie 1.7 times the voltage of one phase, but twice the turns, and twice the resistance and .6 of the added voltages (due to the 120 deg phase angle).... So if one coil group (delta? phase) had 100 turns and made 10 volts, if we use star, we use 200 turns, and get 10x1.7= 17v in star... and our R has doubled. This is not at all good, you have increased the resistance substantially (twice) and the ampere turns (twice) and have only 1.7times the volts to show for it. In an axial flux, we can juggle the wire diameter and turns to make star work very well, but where the amp turns make a significant (read major hurdle) contribution to the problems, sacrificing those out of phase volts for more turns for the same voltage is retrograde in my eyes. So because of the weak magnets, and salient pole design with small air gap, we are going to suffer armature reactance. To get the best out of your stator, you must first determine the turns/volt, your cut in rpm, and wind delta for that number of turns in 1x14c. Keep cut in later and use caps or a booster, and you can significantly lower your turns. Thicker wire can then be used to mitigate the R loss, but it is amp/turns that will still beat you.... Do whatever you can to get the turns down to the minimum. Happy to answer questions if I can John Tulloch Flinders Island Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
I posted oztules reply above as I PM'd him with the question, the answer gave me many more answers than I thought possible What I conclude is this, cutin speed Phillm tells me for his dual is approximately 100 and 150 rpm for an 80S in 2x7C with doublers and one in star the other in delta, thus a dual using an 80S 2X7C delta and a 100S in delta should provide for similar loading but starting at 150 and 170rpm. respectively Is this reasonable enough? The amp/turn limiting will be less and thus 600rpm will be a good safe point to furl it at This should make for an F&P dual capable of almost 1KW with anF&P efficiencyabout 80%+ Prior to the cap mod this idea would have been a flat out looser as cutins would have been 300 and 340 rpm, making quite a useless mill, but I think at half those speeds its more than acceptable. on to TSR's Thanks Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl That made me brush the cobwebs out of the head and go back over 40 years when I did all the theory and unfortunatly unless you are a designer you tend to forget it as not relievent which is true as most things are done for us now, we just put them together now. That is why the only way to go is delta for efficiency. We start a 3 phase motor in star to reduce its current draw and torque output therefore reducing its efficiency as a motor or a generator conversly. It saturates at a much lower amp input conversly in the FP a much lower amp output. My lathe has a 15 hp 3 phase motor which was star delta started at 15 amps and idle run current of 3 amps untill you load it up. due to a melt down in the star relays I have converted it to direct on line start {DOL} In this configuration it draws 60 amps for about a second and then drops back to its 3 amp idle current as before, not ideal but it works because it is unloaded when starting only spins up the pulley and belts as the lathe is clutch controlled. So what does this mean : that the internal resistance of the machine is very low untill the motor spins up to current limit point when the counter emf equals the line voltage it then settles down to use enough current to overcome the mechanical and electrical losses in the motor and drive system in my case 3 amps it is at this point saturated only increasing lhe load and slightly increasing the slip angle alters the balance and allows it todraw more current. From what I see we are seeing the same effect in reverse in an alternator. In the FP case the the stronger magnets mod increases the saturation point and lowerers the cutin rpm as the mod we where discussing to increase output but at a magnet cost that defeats the purpose of a simple conversion. The reason why the caps across the delta points dosnt work is that it induces a small dc current into the windings increasing their inductive reactence as the load increases and negates the effeect of the magnets on the windings as they saturate sooner due to this effect. You can use a 3 phase motor as an alternator by this effect by cnnecting caps to the delta points and with the right amount of capacitence you can induce a small dc component into the windings and causing it to excite from its ac windings as the load increases on the alternator it increases the self exitation until saturation is achieved then no extra power is generated a handy little trick if you have a few old style 3 phase motors laying around, it dosnt work so well on the newer motors as they are designed to opperate at a higher temperature so the internal resistance is lower and theren is less reactance from the windings. Enough Enough she cried All the best Bob Foolin Around |
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herbnz Senior Member  Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi Karl Received your pm To remove windings I find the coil that has been wound last usually at the star point the one that is two back. If that is not clear when you unwind the first coil if it gets to a point it crosses another coil you need to leave that set and start on another. I unwind each set of 14 before starting on another set. I hook the wire up and walk backwards down drive with the stator held horizontal with a slight movement as each coil unwinds moving around so the current coil is pointing to the hooked wire . my drive is 100metres on 80 series I have to go twice. 70 turns seems a lot turns ie 980 total this by my reckoning would cutin at about 200rpm but current limiting that depends on amp/turn would limit output. I would reduce turns and use a voltage doubler cct to get low wind output. Note on my Hydros that are have rpm about 1000 I some times only use 6 turns / coil Herb |
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