Jeff I think you are mixing up the AC and DC power formulas.
I am sure the impedance of the coil at 60 Hz is more than the DC resistance.
That would make the wattage less than what you have calculated using a DC equation.
A quick check of the Goyen catalog shows they draw about .05 to .07 Amps depending on the coil at 240 volts. That is around 10 to 16 watts. The DC resistance of the coils was not given. The coils on many of the valves can be changed to several voltages.
The DC resistance averages around 1600 ohms. According to my calcs there are around 4700 turns in the coil, so at 50Hz the impedance incorporates a significant reactance. The coil (obviously) has a ferrous valve plunger in its core.
They are marked 240VAC 50Hz (= our supply here in Oz) and the one I attacked with the Dremel is marked 5W.
No
Of course at 120V the wire would be twice the diameter. If it is corrosive flux at work, it would take longer to eat it away. If it is failing Pbfree solder bonds, who knows.
I am considering that. Meanwhile SWMBO is considering a replacement oven (which as you'd all know, means a complete new kitchen)
Oops. Y'er right. Big rush -> No time -> No brain -> No excuse.
Ok, that's better and less than the 5A fusing current for #34 awg.
10 - 16 watts might get the coil quite warm if energized continuously. Probably not enough to melt solder, but certainly will add a few degrees to the heat from the furnace.I don't think it's overheating from the furnace or the warm coil. It will get hot, but not enough to melt solder. Since various other solenoids have failed in the same manner, I don't think the failures are caused by some kind of soldering defect. The long time that it takes to fail might be the copper wire slowly dissolving in the solder. However, my limited experience indicates that most of the damage occurs immediately during soldering, not many months later. With a 5A fusing current and the rather large inductance of the solenoid, I don't see a high current "surge" fusing the #34 wire.
Offhand, I was thinking something else might be happening here. Something like a sharp edge on the solenoid terminal slowly cutting its way through the copper wire every time the solenoid is energized. It might be 50 Hz vibration work hardening of the wire causing embrittlement. However, these are unlikely to have also occurred in the other replacement solenoids, that also failed. It might be the difference in coefficient of thermal expansion between the epoxy and the copper wire. Usually, some paper or tape wrapping will provide room to expand, but again it would be an amazing coincidence if the same problem appeared in a competetors solenoid.
That leaves external influences, such as line voltage glitches and surges. Get your Dranetz power quality monitor/logger back, borrow something, or just setup a data logger on the AC line.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Sorry, that should be oven, not furnace (in multiple places).
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
WE had hundreds of that brand where I worked and some were pulsed every
30 seconds or so and some were almost always on. Hardly any problems with the coils. The ones that were on most of the time ran hot enough that you would almost burn your hand. Some of them were where the room temperature was over 100 deg F. The plant made polyester and the process required about 300 deg C of heat. I said room, but those areas were not occupied except to check on the equipment from time to time.Most problems were either the rubber disk wearing out or the plunger enlarging due to all the beating they take or the spring wearing out. The plunger is enclosed so no way for it to touch the coil form. While it could be something in the coil, I would think that as many that he changed out it must be something external.
One other thing, is the coil all the way seated on where the plunger is ? If not it could be drawing enough current to burn out the wire. We often left the coil hooked up to the conduit and just changed out the mechanical part. Mainly did that to keep from having to go to another floor and find the power source for the coil. Found that we needed to stick a large screwdriver or other item in the core of the coil or a fuse would blow or the coil would burn out.
I meant outside of the oven enclosure. Bypass the valves with plumbing in the enclosure and then put the valves somwhere else in the gas supply line. Eric
Yes that is a possibilty, but in our over-regulated environment it'd require all sorts of recertification, almost like the aviation/aerospace industries. Having been exposed to THAT industry it's a path I don't want to tread out of MY wallet.
Ralph, should I presume that was with pre-ROHS vintage coils? As I mentioned in my O/P, the original pair (which were pre-ROHS) both lasted two decades. Subsequent ones were 15-18 months AND the oven gets less use nowadays as the kids migrate outwards. Not a statistically significant sampling for some, but sufficiently damning from where I stand/sit.
We haven't had the moving parts show any issues, just coils.
Nothing external has changed, except our supply voltage has been "harmonised" with rest-of-Oz i.e. reduced from the original 254V rms down to 240V rms.
Appreciate the question. It is seated down properly. The frame which sits over the coil/valve assembly as part of it is actually a snug fit (you need to slide the coil into it and align the holes, it's a press fit) and then the frame is held down over the valve plunger "cylinder" and screwed down. No unintended magnetic/air gaps.
There is also a "spacer" pressed into each end of the coil bobbin the ensure it is located correctly (radially).
Pics of the valve assemblies in situ:
and of the coil post-Dremel (*):
(*) I needed effective bobbin length/diameters to calculate turns and hence deduce a credible wire gauge to match the known DC resistance.
Most of them were from days before the lead free junk.
When you pulse them about once every 60 seconds they do take a beating after 5 or 6 months. When they were first used in that application there were some complaints about how fast they were wearing out. However if you calculate the number of cycles , they lasted many more cycles than specified for by the manufactor.
You mentioned something about lowering the voltage from about 250 to 240 volts. Have you checked to see if the voltage is still around 240 ?
I didn't see any heat damage in the latest photos. Judge for thyself:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
It is.
Western Australia's grid voltage was 254(+/-6%) as a result of the move from 40hz to 50Hz a long time back. Actually the single phase voltage was never *defined*, rather it was 440V phase-phase (3-phase system).
Although it was/is not interconnected with the eastern states' grid (which was 240V as far back as the landing or the Ark), pressure to fall in line was brought to bear, particularly as appliances etc made for the 240V system suffered reduced lifetime at 254V, although there were incandescent lamps made for 250V if one hunted them down.
So the supply authority relented and cranked the grid back to 240V where it has been ever since as a statutory requirement.
Fine on the history of Australia's grid. Too bad all the coutries of the world did not set one standard to go by. Most of the US seems to be around a split system for the homes of 120 and 240 volts at 60 Hz. There are some places that may have other odd values.
I worked in a large plant and most of the larger equipment was 480 volts
3 phase. The smaller equipment and offices were set for 120 or 240 volts.Then we built a building of about 6 floors and while another and I were calibrating some 3 phase heaters we could only get about 380 volts out of the controler. Checked the incomming voltage and that was what we had. Seems that the engineer had bought some equipment from a country that required 380 volts. We were not told of this to start with and found out about it when we were checking out the equipment.
Years ago in the US it seems that the standard was 110 and 220 volts, then 115 and 230, now it is 120 and 240 volts. I hae a digital voltmeter on my ham radio desk that stays on all the time. It is usually around
122 volts, but I have seen it between 118 and 124 volts depending on the time of the year and day. I know it is accurate as I checked it against some meters at work that were calibrated by a lab to the government standrds.ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.