I am looking for sources for workshop-type 400Hz supplies, both 26V and 115V, with power ratings from 25W to 300 or 400W. Either surplus, or even circuit diagrams.
Let me explain...
On the one hand, I have queries from people who are bringing 'old' aircraft instruments back to life, which need 26V 400Hz or 115V 400Hz, generally at something like 25 to 50W.
On the other hand I have queries from museums bringing entire simulators back to life, but where they are hampered by some of the bits and pieces (such as supply racks...) never having made the journey from site to museum..... In that case we're rather talking about several hundreds of Watts.
Neither 'category' can really afford the prices of new "aviation-certified" professional lab equipment. I've done some Internet searches without much success.
Hence my appeal to the TechLog community.
1) Does anybody have pointers/links to sources of surplus equipment of this kind? For the case of the instruments, even surplus aircraft 28V DC / 400Hz converters would do the job, of course. (DC supplies are cheap.) PMs are welcome, of course, if you do not want to 'advertise'.
2) If you have read this far... car battery to mains converter schematics (similar principles) are a dime a dozen on the internet. Unfortunately nearly all produce a somewhat rounded square wave and I don't think aircraft instruments would appreciate that very much. Schematics of circuits that produce something approximating a sine wave are few and far between. But if you know of one... yes please. Both of my 'categories' will gladly spend some time building a supply to save a lot of money.
Moderators, I thought this was the best place to ask the question. If you think I'll get a better response elsewhere, don't hesitate to move the post.
I don't think that your rounded square wave would cause any damage. Some standby inverters I have seen give a sawtooth output and are designed to operate the stby instruments such as ADI for at least an hour on battery power. (Can't remember the CAP number for this requirement)
I don't think that your rounded square wave would cause any damage. Some standby inverters I have seen give a sawtooth output and are designed to operate the stby instruments such as ADI for at least an hour on battery power.
When I said 'rounded' I meant just rounded at the corners... I don't know about damage, but it certainly makes a noise. When you say "sawtooth" it already 'starts looking' like a sinewave, and as long it's used to drive the motor in an emergency horizon or the power supply in a radio altimeter indicator, it would do the job!
Too big, really. Look at the ratings. It's the sort of equipment used at a base to supply all the workshops with 400Hz, like what we would have had at Fairford (50Hz primary).
If you have access to a workshop you could build a small scale motor-generator rig using a truck alternator. Commercial vehicles use 24v so I would imagine that the alternator output would be near 28v. As you're on a budget, you could probably find something suitable at your local scrappy. And an old washing machine motor will do the trick just fine. Remove the rectifier pack and run the the drive motor via a speed controller with a tuned circuit feedback loop from the AC output. You will just need to know how many pole pairs the alternator has to determine the motor speed.
Much more fun than just buying something off the shelf!
I am no expert on the conversion of DC to pseudo AC or vice versa but there may be an answer to be found in the marine or offshore world. The offshore people seem to have bastardised just about every single type of electrical generation equipment going, they also have a huge amount of retired aircraft engineers working for them.
winglit, sorry but I can't see your idea working, automotive alternators are all 3 phase machines and you'll get bugger all out of them if only using 2 of the 3 stator windings - I've tried! Further more they need to be running at several thousand rpm to give a decent output, and this would give a frequency way over 400Hz. You would still need to use the rectifier and regulator to control the voltage even if taking the AC direct from the windings.
In the olden days, an avionics workshop would indeed have a motor-generator, with the motor being 110V 60Hz or 240V 50Hz, or whatever the local mains was (or even a diesl engine), and the output being 115V 400Hz 3-phase, and where you 'borrowed' the 26V 400Hz via a transformer. Curses.... in those days they were just sockets on my workbench, and I didn't even ask where it came from.
Now I'm looking at trying to help out people who no longer have access to an avionics workshop, but who are still looking for 400 Hz supplies without paying a fortune...
I'm still hoping somebody has addresses for surplus equipment, or valid circuit diagrams.
As I mentioned, I don't think aircraft equipment will appreciate the near-square-wave output from the simplest of DC/AC converter circuits. Saw-tooth or distorted sine wave will do, I think, considering the mostly inductive loads.
Flying Pram, you're right about the rectifier pack, you would have to leave it in and tap off the stator windings for the AC output.
I've had a look at the theory and I reckon it could be done with the right kit.
If you could find an alternator with six salient pole pairs you would need to rotate it at 8000 rpm to get 400Hz, that's not outside the realms of normal operating speed for an automotive alternator. You could also expect an output of 70A which gives a power rating of nearly 2Kw which should be plenty.
You will also need a DC supply to energise the field. Maybe that's where you went wrong with regards to your low output current. Were you just running it with residual field excitation?
I made a homebuilt generator many moons ago in my uncle's workshop. It was made from an alternator off an old Volvo and a Suffolk Punch lawnmower. It worked a treat. My uncle ran a used car lot and he used it to jump start the old bangers with flat batteries. He also used to take it camping with him to charge up the battery in his caravan. Although this one was a 12vdc output.
... I suspect that your target market might be better found in the engineering forum ....
Thanks John. I wasn't sure so I tried TechLog first.
winglit and Flying Pram Thanks. I'll pass it on, in case somebody wants to go that way!
Quote:
Originally Posted by "Terraplaneblues
These are a start, nothing to write ohm about though
Not quite watt a chap with a vintage emergency standby horizon needs, watt? And the sim people I'm talking to don't need to run an entire aircraft either. The Le Bourget Concorde does have a Hoochin running outside the hall when the aircraft is being powered up, but the sims don't need quite the same power.
Many thanks for the links, though! If they have GPUs they may have other stuff. My "quest" is to find sources.
hedgester, Thanks for that link. Much the thing I was looking for, for the sim people. I'll be contacting them.
I'd be delighted if anybody else has something in that line.
John Hill, I agree... but determining the ratings of the components, and then finding those components, is not obvious for the cases I'm talking about.
NutLoose, Thanks! Since my "clients" (friends) are well aware of eBay, I didn't look yet. I'm sure they've already explored it, but maybe not necessarily in the right spots... I'll look at your links, and also set up a wider and longer-term search.
At work we use a Roband 3-phase inverter (P3333), variable anything between 60V and 160V AC and 300-600Hz. Obviously just runs off mains power. Not sure if they're still available or how much they'd cost? Weighs about 25-30Kg. The output is a bit noisy but it won't do any harm.
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