Saturday, January 12, 2013

70, Some flooring and Trimming.

During the past months, not all my time was wasted, tinkering with the Rotary convertor.
Two separate lots of decent secondhand chipboard flooring came up on eBay at reasonable "Buy it now" prices. It was just nicely enough to sheet the floor in the remaining ground floor rooms. It is only intended to be temporary and was lightly screwed to alternate joists. The permanent timber strip flooring, to avoid any possible damage, will not be fitted until all the major structural work is complete. There are thoughts, at the moment, going through my head of possibly laying some parquetry to the main areas, if this comes to fruition, the sheets will remain in those areas but will need to be further secured.

A couple of days was spent straightening the, now well seasoned, floor joists. The electric  planer found it pretty tough going and blades were replaced a few times owing to the hardness of the "Box" timber and the amount of ingrained dirt it contained. This was despite using brushes and compressed air to clean them as much as possible.


The Lounge room,on the East side was the first to be done and, with a good platform to work on, I was able to "Stud" the external walls. This framing is non load bearing and creates a cavity for power and communication cables as well as the plumbing. It also provides some space for insulation to be inserted, to prevent the stone sucking out the heat during winter. The extra wall thickness created, also improves the aesthetics of the window recesses.

The west wall, laid before the "saw" days, was constructed using formwork on the inside. Laying the stone against it caused the excess mortar to squeeze out and spread across the face. At the time, I couldn't see an issue with this "unseen" side. Subsequently, however, I found that much of it can break loose fairly easily and can cause problems when trimming the wall. Pieces would drop down behind the insulating paper, jamming behind the framing making it difficult to straighten.
The first hot day of the Summer, the Sunday 2 days before Christmas, was spent chipping off  the excess, in the relative coolness inside.


The wall, once cleaned, was much more pleasing to look at. In a way, it's a bit of a pity it will all be covered. The rows of bricks were placed to ensure a flat anchoring point for timber blocks, attached to the noggins for securing the framing. I wanted to get this done before the flooring was in place, cleaning up was easier, particularly along the edges around the bearers and the dust cleared better, falling to the ground.


Where it's at now. My current stocks of seasoned and dressed 70 x 45pine have been depleted, so the trimming of the Dining room, on the West side will have to wait for the time being.

With the fire season upon us, my attention has been diverted to the temporary roofing. I'm currently unable to fill the big hole in the front wall with the entrance door, but due to it facing south, it's not as concerning to me as all the gaps around the perimeter of the roof line. This may be the subject of my next post.

Wednesday, January 2, 2013

69, Rotary Convertor, part one.


I purchased my old thicknesser some 20 odd years ago, it was the first of my machines to be converted from 3 to single phase. Now that it had died, my timber machining couldn't proceed.
I unbolted the sickly 3hp motor and took it to the local "rewinds" for diagnosis. The news wasn't good, it had a short circuit in the run winding and the bill to repair it would exceed the replacement cost. An estimated $350 to $400 for a new motor was beyond me at the time and, as I had already been looking around for some time for similar sized second hand motors to no avail, some further options needed to be investigated.
Advice and a bunch of emailed links from a friend enlightened on the subject of rotary converters. These are a relatively simple way of converting single phase power to 3 phase.
The principle uses an "idle" 3 phase motor, of larger size than the machine motor that it is required to run. This is started and run by capacitors and generates a relatively smooth 3 phase supply.
Having accumulated numerous 3 phase motors over the years, mainly removed from machines being converted, my workbench was soon covered with them, along with the associated wiring. Some initial testing indicated that the system was feasible and a batch of various sized capacitors, as well as some volt and amp meters, were purchased from Hong Kong, via eBay.

Once the parcels had arrived  I delved into my stores of electrical bits and put together a switch panel to control the converter. For switching in and out the starting capacitors, I incorporated a timing relay.
Having a safer way of switching things, some more serious testing could be carried out.

A 7.5hp (5.6kw), motor, previously removed from the sanding machine was chosen as the most suitable for the Idler. Initially, all looked well with any number of subsequent unladen motors starting flawlessly, once the idler was in motion. Problems, however, were just starting....

The first issue to arise, (and the most enduring), was that, once the drive belts on the thicknesser were reattached and the motor had to start under load, the starting torque was unable to get the machine up to speed. The prolonged excessive current draw was then causing the main supply circuit breaker to trip. Reconfiguring the motors in either star or delta seemed to make no difference.
Dave, my mentor and researcher in this field, hit the Internet, looking for answers. The first thing that became apparent was that the design was gleaned from American sources, their power supply varies quite considerably from ours in Australia, theirs being more akin to a 2 phase supply. The Poms, whose mains supply is similar to ours, have found that a step up transformer is required to provide a 415volt input into the idle motor.
EBay came to the party again and a suitable 3 phase welder was purchased for $40.

We stripped the welder down and managed to tap onto an intermediate position on the main coil winding. Connecting the 240volt active wire at that point and the neutral wire to the end of the larger portion provided 440 volts across the whole winding, "near enough" for our application.

To reduce some of the bulk and weight I then set about cutting the transformer apart. The secondary coil was discarded and the laminated core was reduced down to a minimum height and rewelded. All being well, I'm hoping there is still plenty of metal to avoid any overheating issues.

With the voltage sorted, the next problem could be addressed, the starting capacitors. For this purpose I had purchased 5 x 100uF caps, trying different numbers of them until a suitable quantity was achieved. Using only 2, giving 200uF proved to be the most satisfactory, however, for reasons I have yet to determine, one by one, they failed. As entertaining as all the sparking and flashing was, the lot of them all ended up in the scrap bin. We figured, at first, that the higher voltage was too great for them, even though they were rated at 450v. I then ordered a further 2, at 400uF. These were arranged in series, to give a safer rating of 900v at 200uF, but the second time I used them to start the idler, they suffered the same fate as the originals. More head scratching was needed.
My simple solution came in the form of a two stage system. A smaller 1hp motor was added to the setup. I found that it was much easier to start, requiring only 5uF, and an equal amount to run. Once this motor was running, the larger motor, with it's separate capacitors, could then be started off it. A flywheel was, however, required to prevent the smaller motor stalling.
This setup also has the advantage that, if only a small, (less than 1hp), machine motor is required to be operated, the larger Idle motor can be left turned off. Current draw can then be minimised.

With all the preliminary testing taken care of, all the components could then be assembled. I calculated that most of the bits could be accommodated within the case of the trashed welder. For this I fabricated a frame, on to which the bits could be attached. This was then bolted to the base, along with the larger idle motor.
Now that everything was in place, the unit could then be properly wired. I have, at this stage completed all this with the exception of the wiring to the capacitors, as I am still waiting to purchase the 5uF ones, it's a bad time of the year for that!. For testing I have been using 4 larger caps, wired in series to achieve the correct values, but they can't all fit in the enclosure.
I have used the heaviest wire possible, right back to the distribution panel to minimise voltage drop, however there are still issues in starting the thicknesser motor, a 4hp, (3kw), 2900rpm, 3 phase job, under load, particularly when the bearings are cold. Some more research has revealed that this is apparently a common problem with rotary converters. I toyed with the idea using a clutch system, but are, at the moment, looking for a "soft starter" as a hopeful remedy. Initial testing shows that the machine torque is fine, once up to speed. Wood can be planed with no effort, although I have just had the blades sharpened.

Quite obviously it would have been much quicker and easier to simply replace the thicknesser's single phase motor. The theory is, however, that with this converter I will then be able to run any other 3 phase equipment as well. I already have a spindle moulder, a roller feeder for the same and a small drill press that, now, won't need conversion.

A few more helpful links on the subject;

http://www.nojolt.com/how-to-build-a-rotary-phase-converter.shtml
 
http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/415-volt-three-phase-converter-home-united-kingdom-102960/

http://www.electro-tech-online.com/re-projects/100563-3-phase-converter-schematic-miller-system.html

http://4.bp.blogspot.com/_vfmOyxDCru8/Sx3JO42TrII/AAAAAAAAGtE/crpJIGrAiDA/s1600-h/3_Phase_Converter_Schematic.png

http://hmin.tripod.com/als/andysm/pages/3phase02.html