Aircraft inverter - what can I do with it?

[WB3JOK]

At a flea market I acquired for scrap prices a Bendix 1518-1 rotary inverter that had Repair and Serviceable tags on it from decades ago. The manual (which I refuse to buy, since $142 is ridiculous and multiple times what I paid for the inverter) has a 1949 copyright date!

It can turn 24-28VDC into 115V 400Hz, 1500 VA single phase or 2000 VA three-phase. Full load draw is 115 amps! (55% efficiency at best). So I set about cobbling up a hefty 28 volt supply to run it at least at no- and part-load. I rapidly learned that junkbox engineering doesn't work at multi-kilowatt levels   and 20-24 volt transformers at 2 or 3 kva are not cheap to acquire, nor to ship.

Anyway, I now have enough 28VDC to run it (1 KVA transformer, hefty bridge rectifier that requires heat sinking at these currents, and a 220,000 uf filter cap). I put new bearings in it (expensive for Timken, but cheap for Japanese ones from thebigbearingstore.com. I stayed far away from the $2 Chinese ones). Brushes look practically brand-new. There was a defective wirewound adjustable resistor in the output regulator circuitry that caused it to run wide-open, too fast and waaay too much draw. I fixed that and now it seems to behave normally.

The inrush is on the order of a couple of hundred amps   for a second or two which my transformer really struggles with, dropping to about 100 amps for another second as it spools up, and then the carbon pile regulator kicks in and you can hear it suddenly let off the gas pedal. It idles at "only" 20-25 amps. Still rather noisy, of course.

So - it has 115 volt three-phase. Aircraft use 115/200Y (probably now 120/208) and have for quite some time. BUT this one is a 115 delta (the neutral is not brought out), with one corner  grounded! That isn't useful for running anything 3-phase I can think of, since all three line-to-line voltages are 115 and there is no neutral.

I'd thought about using it to run a Collins 618T-2 that requires 115v 400Hz 3-phase. Although the power supply schematic shows a 115 delta primary on the HV transformer, the manual elsewhere says (and others have confirmed by actual measurement) that it needs 115/200Y. So that's no good unless I find another piece of large heavy iron, a delta-wye 115 volt transformer. I'm not even sure they exist since most are for higher voltages and I'd still need the 10 amp winding capability.

I'm wondering what, if anything, I can use it for besides a boat anchor (38 lbs) or gathering dust. And trying to figure out why Bendix would have designed it that way instead of 115/200Y... But I hated to see it just sitting and eventually scrapped. Thoughts?

[WB3JOK]

Having thought about this some more, I would need a three-phase delta-wye or isolation transformer at 2 KVA but with 115 volt windings (115 delta in, 115/208Y out). A 400 Hz transformer will be much smaller and lighter, of course. But they seem to be as rare as unicorns, or maybe hens' teeth  And almost all 60 Hz units, most of which are much larger than needed, have 240 or 480 delta primaries.

The delta-wye conversion can also use three separate single-phase isolation transformers. Some are rated at 50-400 Hz but obviously are bulkier than a 400 Hz unit... I assume that each would need to be capable of at least 667 VA since the full load is 2 KVA? Such a connection takes up more room and iron than a single three-phase transformer, although that is not a huge concern except for the equally huge shipping costs nowadays.

Anyone got some 400 Hz iron taking up space in their junkbox? 

[KD6VXI]

As you go up in CPS you need less and less iron.

I used an Sb220 filament xformer in the past to power 3 x 3-500Z tubes using a 120 CPS inverter in mobile use.

It ran that way for a couple decades until it was pulled from service.  At that point I put another sb220 fils xformer in parallel and made it able to be powered off 120 volts.

When you're at 400 CPS you are talking maybe 40 percent less iron needed.

Something to keep in mind sourcing xformers.

--Shane
WP2ASS / ex KD6VXI

[WB3JOK]

As you go up in CPS you need less and less iron.
<snip>
When you're at 400 CPS you are talking maybe 40 percent less iron needed.

Something to keep in mind sourcing xformers.

--Shane
WP2ASS / ex KD6VXI

Thanks, I'm well aware of that, Shane... that is why in my second post, I commented:

A 400 Hz transformer will be much smaller and lighter, of course

That's exactly why I am looking for 400Hz transformers, not 60 unless I get a bargain and don't have to ship them  Unfortunately all the old 400Hz stuff is probably long since scrapped since few hams have 400Hz power. I also have single-phase 115/400Hz at up to 1 KVA from my PP-7482/G!

[DMOD]

You might try contacting these firms:

https://lcmagnetics.com/transformers/400hz-transformer/

https://picoelectronics.com/power-transformers

https://abbott-tech.com/products/magnetics/400-hz-transformers/

https://www.surplussales.com/class/inductor/400_hz_transformers.html

https://www.agilemagco.com/50-60-400hz/

https://www.coilws.com/index.php?main_page=index&cPath=1_190

Phil - AC0OB

[WB3JOK]

Been there, done that  You forgot Fair Radio.

LC Magnetics will happily make me a 2 KVA 400 Hz 115D to 120/208Y transformer, for just $1452 
That would not be unusual for anything new or semi-custom.

I've browsed the $urplu$ $ale$ site too... nothing suitably large despite the high prices.
Shipping costs make it impractical to buy three single 700 VA isolation transformers and hook them up for delta-wye.

There is a possibility that there are actually three 115 volt windings in delta, and if I wanted to take the ENTIRE machine apart to get to the 400 Hz stator connections, I might be able to rewire them to 115/208Y.

But the schematic shows they are actually connected in wye with the neutral not brought out - which, if true, means each winding is only 67 volts and 67/115Y is not useful without a custom transformer either.

This design is very old (front page of the manual visible on ebay says Copyright 1949... looks like aircraft power was standardized to 115/200 some time after that.

[KA3EKH]

Have a similar dynamotor unit I picked up at Dayton a couple years back, 28 volts input and in my case just signal phase 120 60 cycles 1.0 kW out. Has small vacuum tube controlled regulator on top for controlling output and keeping it at 120 volts.
I have a slave cable connector and huge heavy cable that I can plug the thing into my M151 “mutt” and power it that way. That’s all zero gauge cable between the connector and the internal batteries so it can provide the huge inrush it takes to get the thing going and up to speed. With the crazy demands for starting current don’t think I would try to do a AC power supply and when you look at the efficiency of what its taking to generate that power its real questionable to use something like that for running anything in the house. Also, you will discover the mechanical noise is a issue after a while.
Would speculate that was once installed on a B-36 Bomber back in the day and was used to provide AC power until you got the engines up and running or if you needed power for something and did not want to run the APU. The B-36 was one of the first aircraft to use 120 volt 400 cycles everywhere being it provided a huge weight difference between DC powered radar and radios. They had a AN/ARC-21 1.0 kW AM transceiver that drew a couple thousand watts by itself that was all three phase and all the radar stuff was three phases. Huge advantages in weight and filtering by going three phase at 400 cycles and just about everything went that way afterwards.
On the 618T I would be more tempted to gut the three phase power supply and build an external power supply being you only need 250 volts for the receiver that was originally developed by a voltage doubler from one on the incoming AC lines and then build up a separate HV supply for when it’s in transmit.
Life will be much lighter and quitter then that inverter will be. You still need to provide 120/400 for the servo systems but that’s only around fifty watts or so provided you don’t intend that to provide the B+ for the receiver also.

[WB3JOK]

All good points... and the combination of the considerable noise and the inability to make 115/208Y without more transformers puts it back on the shelf.

I tried a 1 KVA transformer for a power supply and it wasn't near enough - sagged badly during start-up. So I found a deal on a 5 KVA toroid transformer (41 lbs, dual 120 volt primaries, and eight 20 volt@31 amp secondaries). Ran the primaries in series to a 240 volt outlet, paralleled all the secondaries to a 200 amp bridge rectifier on a big heat sink, and a milk-bottle-sized 220,000 uf computer-grade capacitor. 4 gauge cable everywhere. 250 amps RMS translates to 140-150 amps DC! Now I can run just about any mil-surplus that comes my way although I might want a bit more capacitance or even a choke if I can find one good for 150 amps... I'm going to build it into a rack-mount chassis with meters and breakers. Right now it's a tangled mess on the workbench.

The starting surge is about 420 amps on my Danfysik Ultrastab 867-700I transducer (which can read up to 700 amps from DC to 100 KHz). That pulls down even this beast of a supply. But the inverter really spins up fast now and the current drops quickly. Once it enters closed-loop, there's another sudden drop to the unloaded draw of "only" 40 amps... motor-generators of that vintage aren't the most efficient in the world!
Edit: my figures in the first post were estimates based on the transformer primary current. I forgot about the 1.6-1.8 factor from RMS to DC with a bridge...

Time to find some 400 Hz light bulbs and load 'er up!

[KA3EKH]

The AN/GRC-19 radio set was built around a T-195 100-watt AM transceiver that was intended to be used in the field in a M-38 or anywhere else from 24 volts. The early version had two dynamotors and when that tuned up if you did not have the engine in the M-38 running fast enough it would slow down or stall. Don’t know what the inrush draw was but it was big. They built solid state inverters that replaced the dynamotors in later service but still those old mechanical motor generators were never that efficient.
Cannot imagine the old WW2 stuff like the GPW “jeep” mounted BC-191 and the like that ran from six or twelve volts and their current draw.

Trivia- the receiver that was paired with the T-195 was a R-392 that had no B+, they used the incoming +24 for the plate voltage on all the tubes.

[WB3JOK]

Interesting trivia, thanks! I'm surprised they didn't use some kind of inverter to create more B+. Some of the later radios did... Fair sells the HV power supply from an AM-3349, their description:

• AM-3349/GRC-106 which contains the DC – DC supply for the High voltage power supply that powered two 4CX350F tubes to 400 watts PEP. Power input is 24VDC. This supply produced 500 VDC plate and screen grid supply for 8233 driver tube and screen grid for PA tubes. Also 2400 VDC plate voltage for PA tubes.
  

Sounds handy if I had to run a tube amp off 24 volts only

I know the ARC-5 receivers will run quite well on 24 volts but the audio power output is greatly reduced, naturally.
Tube car radios used space charge tubes that ran on 12 volts plate (12BE6?).

Earlier you referred to an M151 mutt... what is that? 

[KA3EKH]

My 1965 M151A1 Military Utility Tactical Truck (MUTT) or as most people call it a jeep although this was built by Ford. I do a lot of field opps and play radio with its onboard AN/GRC-106 400 watt SSB transceiver, RT-524 6 meter FM transceiver and URC-110 VHF/UHF AM/FM radio. My QSL card for opps from the mutt.

[AJ1G]

Float a pair of series connected 12V auto or  marine deep cycle batteries.  They will provide the extra grunt needed to spin up the inverter from parade rest.  Just keep an eye on the no ll
load supply output voltage so you don’t overcharge the batteries.  Floating the batteries across the output of the supply emulates the aircraft or vehicle electrical system where the AC to DC supply replaces the generator/alternator power source and supply’s normal running loads and charges the batteries and the batteries provide for short term load continuity in case of power source failure and support current surges when starting large loads such as the inverter

Been powering ART-13 Command Set and GRC-19 sets with big dynamotors this way for well over 30 years.

[WB3JOK]

That is the other high-current-starting option, of course, and I did consider it. But have you checked the price of sufficiently large batteries lately, plus the core charges and sales tax??  Not to mention the weight and space taken up.

I spent about the same amount on my entire BFPS and don't have to worry about maintaining or charging batteries. Whole thing weighs about 50 lb and fits in a 6U 19" rack chassis 

[WB3JOK]

A couple of pics of the finished BFPS. It handles the 400 amp starting surge, probably at least as well as a pair of batteries, and loafs at 35 amps (idling) and 75 amps (heating element load on the inverter).

[Opcom]

Plitron's a great manufacturer. I like their old logo better. The electric hedgehog. Looks like it's been given new life as they changed their name to Noratel?

[WD5JKO]

Speaking about Logos,  (off topic)

What ever happened to the Ohmite Girl?

I attended Powercon in Dallas back in 1981, and my memory recalls she was at the Ohmite booth.

What did she look like? Think about the Michelin man bound with color stripes instead of tires.

It seems that any images of her were pre-internet...

 

Jim
Wd5JKO

[Opcom]

I believe I have one of her refrigerator magnet business cards. (partial image of that with light background) and there was an Ohmite  promotional photo on the web. These are obviously from the web era. The early 2Ks I think.

[Opcom]

promo image. That was some time ago. I wonder if she still works for them. She was a fulltime employee IIRC an engineer as we discussed the technical merits of Ohmite components.

[WD5JKO]

Thanks Pat,

I will add those photos to my collection. My memory has many gaps, and distortion over time, but in 1981, I swear she was wearing a color stripped outfit.

I add a few from my list here.

Jim
Wd5JKO

[WB3JOK]

We seem to be experiencing thread drift   thanks for the nostalgia! I got my EE degree in 1981, and had been playing with electronics for years before that, but I never heard of the Ohmite Girl - learn something new every day.

Meanwhile, I hooked one of those oil-filled electric heaters up to the inverter (600/900/1500 watt selectable). Didn't feel like rigging up a three-phase load, but it's speced to run 1500 watts single-phase. And it does, very nicely although noisily. Draws the specified 115 amps at full load   Nothing got hot except the load after running for a while, too. However - the 150 amp DC breaker tended to trip on restart after 1 second and it takes 1.5 to spin up... I guess the breaker innards got warm and the oil of the hydraulic portion thinned out. May have to buy a 175 amp breaker. That starts to get expensive.

The supply can only muster 24 volts at 120 amps, although still within the typical 24-28 range. Ripple is 3 volts p-p at that draw. I don't know if rewiring for full-wave would help (four secondaries on each side). That eliminates one of the two diode drops, which would bring it up at least 1 volt, but then there's more I²R loss because only half the secondaries are providing current on each half-cycle.   Or maybe Schottky rectifiers (also expensive at this power level...)