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Title: Autoformers, anyone?
Post by: Mike Sokol on October 16, 2017, 04:34:02 pm
OK, this is for the RV world, not pro-sound. But I need your input to help un-obfuscate the psycho-babble of the Hughes Autoformer marketing department. Of course, an autoformer is just a buck-boost transformer in "boost" mode with some sort of relay to add a 10% or so boost when the line voltage gets below some threshold. But the marketing language and video implies that the low-voltage of an RV park can damage ALL of your appliances including an Apple switch-mode computer power supply that's rated for 90 to 250 volts, plus it will make AC motors pull more amperage (true for AC-DC motors used in circular saws and drills, but not AC motors IIRC). Plus they dismiss the obvious problem of increasing the amperage coming though the pedestal circuit breakers which will cause them to trip long before rated power is getting into the RV. Please review their site for marketing babble and let me know what you find. It's a great lesson in really understanding how low voltage affects available power.

See the text and link below.
https://hughesautoformers.com/autoformer-university/why-do-you-need-an-autoformer/

Why Do You Need An Autoformer?

Hughes Autoformers are designed to increase voltage to your RV and help eliminate low voltage damage to your appliances. Unlike a boost transformer, the ‘sense circuit’ in the Autoformer will adjust the output based on the load demand. For this reason you can run additional appliances on a 30-amp input. For example, a coffee pot and microwave each draw 1200 watts. Add wattage for the converter and/or a refrigerator – about 800 additional watts – and now you have 3200 watt demand. If you are only getting 100 volts from the supply, the maximum wattage would be 3000 watts. In this case, the Hughes Autoformer will boost voltage to give you 3600 watts to your RV!

The Autoformer output will self-adjust depending on the demand. With the increase in the voltage to the RV (through the Autoformer) the amperage demand will be lower and the overall performance will be greater. Your appliances will operate smoothly and efficiently without premature wear and damage to motors and compressors. With an operation range of approximately 94 to 125 volts input, the Autoformer will boost your RV voltage to safe & efficient levels.

Appliance failure can be costly, as well as frustrating and inconvenient. Many AC motors burn out due to higher-than-rated current draw caused by low voltage. This wasted current could be better used to operate another appliance at the same time the AC is being used. With low voltage you generally can’t run anything else without risk of damage.
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 16, 2017, 05:45:34 pm
OK, this is for the RV world, not pro-sound. But I need your input to help un-obfuscate the psycho-babble of the Hughes Autoformer marketing department. Of course, an autoformer is just a buck-boost transformer in "buck" mode with some sort of relay to add a 10-volt or so boost when the line voltage gets below some threshold. But the marketing language and video implies that the low-voltage of an RV park can damage ALL of your appliances including an Apple switch-mode computer power supply that's rated for 90 to 250 volts, plus it will make AC motors pull more amperage (true for AC-DC motors used in circular saws and drills, but not AC motors IIRC). Plus they dismiss the obvious problem of increasing the amperage coming though the pedestal circuit breakers which will cause them to trip long before rated power is getting into the RV. Please review their site for marketing babble and let me know what you find. It's a great lesson in really understanding how low voltage affects available power.
Apparently extreme low (or extreme high) voltages can damage appliances, I do not know all the details besides the obvious.
Quote
See the text and link below.
https://hughesautoformers.com/autoformer-university/why-do-you-need-an-autoformer/

Why Do You Need An Autoformer?

Hughes Autoformers are designed to increase voltage to your RV and help eliminate low voltage damage to your appliances. Unlike a boost transformer, the ‘sense circuit’ in the Autoformer will adjust the output based on the load demand.
marketing babble... autoformers are a type of transformer. The only variable output is from adding boost winding in series, when a threshold voltage drop is detected.
Quote
For this reason you can run additional appliances on a 30-amp input. For example, a coffee pot and microwave each draw 1200 watts. Add wattage for the converter and/or a refrigerator – about 800 additional watts – and now you have 3200 watt demand. If you are only getting 100 volts from the supply, the maximum wattage would be 3000 watts. In this case, the Hughes Autoformer will boost voltage to give you 3600 watts to your RV!
Bad math? 100/120 x 3200 resistive load = 2666W   

If autoformer steps 100V up to 120V they should only get the 3200W nominal in the appliances.

3200W @ 120V is 2.66 A... The 100V autoformer primary while stepping up, will draw 3.2A (again 3200W load) No power is is created or destroyed by the transformer.  If anything autoformer will have lower resistive losses than a straight step up transformer but that difference should not be significant. (it will be significant to cost of the step up device).


Quote
The Autoformer output will self-adjust depending on the demand. With the increase in the voltage to the RV (through the Autoformer) the amperage demand will be lower and the overall performance will be greater. Your appliances will operate smoothly and efficiently without premature wear and damage to motors and compressors. With an operation range of approximately 94 to 125 volts input, the Autoformer will boost your RV voltage to safe & efficient levels.
as you noted the primary current will increase by the ratio of voltage step up. So 100V stepped up to 120V will draw 20% more current from 100V primary (all else equal).
Quote
Appliance failure can be costly, as well as frustrating and inconvenient. Many AC motors burn out due to higher-than-rated current draw caused by low voltage. This wasted current could be better used to operate another appliance at the same time the AC is being used. With low voltage you generally can’t run anything else without risk of damage.[/color]

Auto formers are smaller and cheaper (less copper and less iron for same output power). The only downside is that the secondary is not galvanically isolated from primary, but for this application who cares?

JR
Title: Re: Autoformers, anyone?
Post by: Kevin Graf on October 16, 2017, 05:46:31 pm
Their description is not what I think of as an autotransformer. I think of a single winding with several taps.
Title: Re: Autoformers, anyone?
Post by: Stephen Swaffer on October 16, 2017, 06:32:28 pm
Power = volts x amps that much is simple-pick your point in the circuit and that law will apply so....

If I have a 30 amp breaker in the pedastal and 100 volts at the pedestal, I can pull 3000 watts of energy from that pedestal-no matter what "magic" device I place after that pedestal.

If I have a resistive load, then yes, bumping the voltage to the load up will indeed increase it's wattage-simple ohms law.  That may indeed be a useful function-perhaps improving the function of a coffee maker, etc.

If voltage is too low on a motor, it may indeed increase the current draw since a motor depends on reverse induced EMF to limit current flow, so yes bumping the voltage up here may also be an improvement.

If the OCPD is located in the RV-say you feed the Autoformer from a 50 amp 120 volt nominal/100 volt actual supply, then indeed the Autoformer could allow you to use the full 3600 watts your RV can consume.

In practice, you can probably pull an extra amp or 3 from a 30 amp circuit-so you just might actually get 3200-3300 watts out of a 30 amp 100 volt measured circuit.
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 16, 2017, 07:11:09 pm
If voltage is too low on a motor, it may indeed increase the current draw since a motor depends on reverse induced EMF to limit current flow, so yes bumping the voltage up here may also be an improvement.

IIRC The increase in current from lack of Reverse EMF is a problem primarily with AC/DC motors with brushes, hence why you can burn up the brushes on a circular saw on a really long extension cord. I had always assumed that this effect was much less for AC only motors, and the low voltage was mostly a problem during startup when the starting cap is drawing a huge amount of current and the motor doesn't come up to speed quickly enough to open the centrifugal starter switch. Or am I missing something?   
Title: Re: Autoformers, anyone?
Post by: Frank Koenig on October 16, 2017, 10:31:19 pm
IIRC Reverse EMF is a problem primarily with AC/DC motors with brushes, hence why you can burn up the brushes on a circular saw on a really long extension cord. I always assumed that this effect was must reduced for AC only motors, and the low voltage was mostly a problem during startup when the starting cap is drawing a huge amount of current and the motor doesn't come up to speed quickly to open the centrifugal starter switch. Or am I missing something?

My recollection is that conventional induction motors suffer with under-voltage*. So called "universal" motors (inductance-matched, series wound, brush-commutated motors), as used in portable tools, vacuum cleaners, etc., do fine with low voltage. They just go slower.

*There are exceptions, such as "torque motors", as used to tension the tape in tape recorders back in the day, which are induction motors designed to run at variable voltage to supply variable (~velocity independent) torque.

 -F
Title: Re: Autoformers, anyone?
Post by: Marc Sibilia on October 17, 2017, 07:19:08 am
My recollection is that conventional induction motors suffer with under-voltage*. So called "universal" motors (inductance-matched, series wound, brush-commutated motors), as used in portable tools, vacuum cleaners, etc., do fine with low voltage. They just go slower.

*There are exceptions, such as "torque motors", as used to tension the tape in tape recorders back in the day, which are induction motors designed to run at variable voltage to supply variable (~velocity independent) torque.

 -F

Induction motors running a fixed mechanical load will draw more current on low voltage.  The speed of the motor (before accounting for slip) is determined by the frequency, not the voltage of the AC.  The mechanical power to the load doesn't change much because the speed doesn't change much.  When the voltage drops, the torque at the same exact speed drops, but since the mechanical load is essentially the same, the motor can't keep up and slows down just a little bit.  This increases the slip (the difference between the synchronous speed and the actual speed of the motor, e.g 3570 rpm on a nominal 3600 rpm 4 pole motor).

The current drawn by the motor is a very strong function of slip, so a slight reduction of speed causes a large increase in current.  It will slow down just enough to generate the torque it needs to match the load.  Electric motors are pretty efficient devices (except shaded pole motors), so if the mechanical load is constant power because of the relatively constant speed, the electrical input power needs to be constant.  When voltage goes down at nearly constant speed, current goes up.

With universal (AC/DC brush type motors) speed is proportional to voltage, so reducing voltage reduces speed, mechanical load, and current.
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 17, 2017, 08:19:05 am
Induction motors running a fixed mechanical load will draw more current on low voltage.  The speed of the motor (before accounting for slip) is determined by the frequency, not the voltage of the AC.  The mechanical power to the load doesn't change much because the speed doesn't change much.  When the voltage drops, the torque at the same exact speed drops, but since the mechanical load is essentially the same, the motor can't keep up and slows down just a little bit.  This increases the slip (the difference between the synchronous speed and the actual speed of the motor, e.g 3570 rpm on a nominal 3600 rpm 4 pole motor).

The current drawn by the motor is a very strong function of slip, so a slight reduction of speed causes a large increase in current.  It will slow down just enough to generate the torque it needs to match the load.  Electric motors are pretty efficient devices (except shaded pole motors), so if the mechanical load is constant power because of the relatively constant speed, the electrical input power needs to be constant.  When voltage goes down at nearly constant speed, current goes up.

With universal (AC/DC brush type motors) speed is proportional to voltage, so reducing voltage reduces speed, mechanical load, and current.

Interesting. So my understanding is that the reverse EMF caused by the self-generator action of the AC/DC (or DC) motor is what limits the winding current as the rotational speed reaches some maximum design limit. But I think you're saying that pure AC motors actually change their impedance based on the slip angle speed of the rotor as compared to the rotating magnetic field. So if you added another motor to spin the first motor in phase with the line frequency, then the winding impedance would increase, and thus draw significantly less current. Am I thinking about this correctly?   
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 17, 2017, 09:47:19 am
Their description is not what I think of as an autotransformer. I think of a single winding with several taps.
That description is what happens when a non-engineer marketing type gets involved. An engineer probably told him the design features, then he put lipstick on it.

JR
Title: Re: Autoformers, anyone?
Post by: Frank Koenig on October 17, 2017, 12:50:27 pm
Induction motors running a fixed mechanical load will draw more current on low voltage.  The speed of the motor (before accounting for slip) is determined by the frequency, not the voltage of the AC.

Marc, exactly right and nicely explained. Thanks. --Frank
Title: Re: Autoformers, anyone?
Post by: Jonathan Johnson on October 17, 2017, 02:27:43 pm
There's no need for an "autoformer" to monitor the current. All it really needs to do is monitor the voltage and switch to a different tap as changes in current load cause different degrees of voltage drop.

This sounds to me like a marketing schmuck asked an engineer what it does, and with absolutely no understanding of electricity, tried to translate what the engineer said in plain English. Epic fail.

* * * * *

My uncle was an autofarmer. At least that's my guess, based on the countless hulks rusting out behind his barn.

He would have told you every one of them "has a good motor" -- probably because every one ran when he parked it there, anywhere from 60 years ago to within a couple years of his death a few years ago.

Shortly before he died, he managed to sell some of them to people interested in restoring them as classics. Probably made more money selling the hulk than he ever paid for the car.

(Sorry for the diversion. It's just the word "autoformer" made me think of "autofarmer" and that made me think of my uncle.)
Title: Re: Autoformers, anyone?
Post by: Marc Sibilia on October 17, 2017, 08:32:39 pm
Interesting. So my understanding is that the reverse EMF caused by the self-generator action of the AC/DC (or DC) motor is what limits the winding current as the rotational speed reaches some maximum design limit. But I think you're saying that pure AC motors actually change their impedance based on the slip angle speed of the rotor as compared to the rotating magnetic field. So if you added another motor to spin the first motor in phase with the line frequency, then the winding impedance would increase, and thus draw significantly less current. Am I thinking about this correctly?

That is correct. You got it.

And the reason that universal motors don't like low voltage is that they are often used on devices like saws, drills and routers where the load (the work to be done by the motor) doesn't change with the voltage.  Who slows down their cut when the drill isn't running as fast? Most people will just push harder to try to make the same cut rate.  If a universal motor were running a fan, the load would go down with the voltage and the speed of the motor, and the motor would be perfectly happy (and cooler) running slower.
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 17, 2017, 08:38:21 pm
This sounds to me like a marketing schmuck asked an engineer what it does, and with absolutely no understanding of electricity, tried to translate what the engineer said in plain English. Epic fail.

Yup, I talked to the owner of the Autoformer company today, and that's exactly what happened. I told him it had to have been written by someone either misinformed or lying, and he admitted he had never read that page on his own website and assumed that the marketing guy wrote something appropriate. Since I'm doing a story about this technology for RVtravel.com next month, I gave him the option of rewriting his website to correct the inaccuracies, or I would list the errors line-by-line and detail why each statement was wrong. I don't think he's a bad guy, but he wasn't paying attention to his own marketing hype.
Title: Re: Autoformers, anyone?
Post by: Stephen Swaffer on October 17, 2017, 08:53:52 pm
Unfortunately, inaccurate marketing hype will drive some potential customers away-the ones that understand what is going on-because some will assume they are just selling a gimmick trying to make a quick buck.  Others will expect the product to deliver performance it simply cannot leading to bad word of mouth.

Sounds like a useful product in some situations-though certainly not a silver bullet for every situation.  Low voltage caused by long conductors that were not upsized properly is a relatively benign situation that this device would work well to correct.  Low voltage caused by bad connections caused by age or whatever, not so much.
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 18, 2017, 09:22:41 am
Unfortunately, inaccurate marketing hype will drive some potential customers away-the ones that understand what is going on-because some will assume they are just selling a gimmick trying to make a quick buck.  Others will expect the product to deliver performance it simply cannot leading to bad word of mouth.
In my experience the fraction of customers who understand even basic technology was minimal... For most of my career I have had the luxury of writing (or approving) my marketing copy. That did not stop a few over-enthusiastic selling machines from going off the reservation. I remember one (west coast) AES show where I had to literally follow around a new sales manager and correct his spiel... He memorized the right buzz words but had no clue what they meant.
Quote
Sounds like a useful product in some situations-though certainly not a silver bullet for every situation.  Low voltage caused by long conductors that were not upsized properly is a relatively benign situation that this device would work well to correct.  Low voltage caused by bad connections caused by age or whatever, not so much.
Bump windings are even used by utilities so they have their place.

JR

@Mike maybe offer the company your suggestions for a more accurate description, just telling him it's wrong doesn't fix it. I would be (I am) surprised he was so receptive, I probably wouldn't be, but i wouldn't be so wrong. 
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 18, 2017, 06:54:00 pm
@Mike maybe offer the company your suggestions for a more accurate description, just telling him it's wrong doesn't fix it. I would be (I am) surprised he was so receptive, I probably wouldn't be, but i wouldn't be so wrong.

JR, yes I did offer him a few suggestions, and he asked if he could run the changes by me before it goes live. I think he was so receptive because he's an engineer who bought the company, but didn't read the marketing bling and just assumed it was right. He seemed totally embarrassed as he kept reading the copy over and over to me on the phone, saying it made no sense and was probably wrong.

Also don't discount the fact that my RVtravel.com articles get emailed to 50,000 readers every Saturday. This is the primary product of a small company, so any bad press could really hurt them. I don't go bashing products unless they really deserve it. In the right application, I think the AutoFormer can do a good job. But it has obvious limitations and can't perform miracles. 
Title: Re: Autoformers, anyone?
Post by: Tim McCulloch on October 18, 2017, 07:28:24 pm
JR, yes I did offer him a few suggestions, and he asked if he could run the changes by me before it goes live. I think he was so receptive because he's an engineer who bought the company, but didn't read the marketing bling and just assumed it was right. He seemed totally embarrassed as he kept reading the copy over and over to me on the phone, saying it made no sense and was probably wrong.

Also don't discount the fact that my RVtravel.com articles get emailed to 50,000 readers every Saturday. This is the primary product of a small company, so any bad press could really hurt them. I don't go bashing products unless they really deserve it. In the right application, I think the AutoFormer can do a good job. But it has obvious limitations and can't perform miracles.

Q.  Do I *need* an autoformer?

A.  How sketchy is the power at that new campground you've never stayed at?

Q.  What will an autoformer do for me?

A.  It will make voltage-sensitive appliances and electronics work like they're supposed to, avoiding potentially shortening of service life.  It might also uncurve your spine, unwarp your mind and win the war for the Allies...
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 18, 2017, 11:21:14 pm
Q.  Do I *need* an autoformer?

Here's one thing that it will really do. Many RVers have some sort of "smart" surge protector in their shore power  line that monitors the incoming voltage and will open up a contactor relay if it goes below some threshold of around 102 volts or so. In order to save the air conditioner compressor from a hot-start which draws a huge amount of current with a locked rotor, there will be a significant delay of up to 2 or 3 minutes before turning the power back on to the RV. So in a campground with low voltage and a lot of RVs using air conditioners, these smart surge protectors can cycle the power on and off to the RV several times an hour, which doesn't make the owner of a $250,000 RV or $500,000 coach very happy. By boosting the low voltage from the pedestal by 10% with an "Autoformer" those power outages in the RV will be avoided.

With the exception of the microwave, and compressor/fan motor on the HVAC unit, practically everything else in a modern RV has some sort of universal switching power supply, rated for 90 to 250 volts.
Title: Re: Autoformers, anyone?
Post by: Steve M Smith on October 19, 2017, 06:00:56 am
Is autoformer a real word in the US?


Steve.
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 19, 2017, 07:05:10 am
Is autoformer a real word in the US?

Steve.

Nope... It's a registered trademark.
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 19, 2017, 10:20:40 am
Is autoformer a real word in the US?


Steve.
I always thought it was a word,  :-[ ?

Here's a TMI autoformer story...  Back when Peavey entered the fixed install market where most install power amps use output voltage step up transformers to hit the nominal 70V/100V constant voltage (misnomer) sound distribution. Substituting autoformers for those output transformers would not only reduce significant weight, size, power loss, and cost, but the audio frequency response and distortion would even be better.

While it should have been a win-win-win-win....., it was a lose when the customers rejected them. The primary downside to autoformer outputs is that they are not completely floating. Apparently inadvertent ground shorts to one side or the other of 70V audio lines is pretty common. With a transformer's floating output, the short is ignored and the beat goes on. With an autoformer if the hot side is shorted (50-50 chance), the music stops and a difficult (expensive) service call is required. Further an amp upgrade in an old install from a previous transformer output model might not work as expected, until wiring is fixed, and lastly the install technicians didn't need to pay any attention to which output wire was which.

The install market was (is?) conservative and resistant to change so Peavey had an uphill battle even with no identifiable differences to point to. Since the customer is always right, we re-engineered the entire line to use the larger, heavier, less efficient, transformers. (ouch   :o ). That is a lot of copper and iron that arguable wasn't really needed.

JR
Title: Re: Autoformers, anyone?
Post by: Kevin Graf on October 20, 2017, 07:28:32 am
Is autoformer a real word in the US?
Steve.
Nope, the real word is autotransformer.
But in the old days, we would call it an auto-xformer.
Title: Re: Autoformers, anyone?
Post by: Peter Morris on October 20, 2017, 09:31:52 pm

3200W @ 120V is 2.66 A...


 ???

Title: Re: Autoformers, anyone?
Post by: Andrew Broughton on October 21, 2017, 01:16:52 pm
I used a variable autotransformer in China that worked as a voltage regulator. Hadn't seen that before, seemed rather ingenious. Voltages were all over the place in China so it worked very well keeping the output voltage steady without the "jumps" of a standard autotransformer. You could hear it humming away as the wiper moved slightly one way or the other, keeping the output steady.
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 21, 2017, 03:09:42 pm
I used a variable autotransformer in China that worked as a voltage regulator. Hadn't seen that before, seemed rather ingenious. Voltages were all over the place in China so it worked very well keeping the output voltage steady without the "jumps" of a standard autotransformer. You could hear it humming away as the wiper moved slightly one way or the other, keeping the output steady.
Variable autoformers are AKA "Variacs" (trademarked by General Radio in 1934). But Variacs are generally manual with a big knob and sometimes a voltmeter for the user to vary. These are common on test benches to troubleshoot/repair equipment.

Making it automatic is clever, as I mentioned already utilities use similar bump windings (also automatic) to manage mains voltage at substations as load increases and drops off over the day.

An anecdote I've shared too many times, the bump winding at my local substation got stuck one night (probably a decade or two ago). When I got home from work, I noticed my lights were unusually bright and getting brighter as the night went on... I called the power company and the guy working that night didn't believe me (I measured my wall voltage at 135V and rising). But it was a slow night so he drove out the 25 miles to check it out.

When he confirmed my measurements on the drop coming into my house, he drove the couple miles to the substation and probably whacked the stuck stepping contactor with a big non-conductive hammer.

JR
Title: Re: Autoformers, anyone?
Post by: Andrew Broughton on October 21, 2017, 03:52:14 pm
Variable autoformers are AKA "Variacs" (trademarked by General Radio in 1934). But Variacs are generally manual with a big knob and sometimes a voltmeter for the user to vary. These are common on test benches to troubleshoot/repair equipment.

Making it automatic is clever

Yeah, it used a servo motor fed from some voltage measuring circuitry and quickly corrected any voltage changes in the buildings, which happened quite often. Also worked from about 240v down to less than 80v. No protection against spikes, but for what we needed, it was a relatively low-tech solution that worked very well.
Title: Re: Autoformers, anyone?
Post by: Peter Morris on October 21, 2017, 08:31:24 pm
You can also do this trick - http://www.powerqualityworld.com/2011/04/constant-voltage-ferroresonant.html
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 22, 2017, 09:01:44 am
I used to have a humongous Variac with a 240-volt input and variable output down to 0 volts. I think it was rated for 30 amps at 240 volts, so 6KW or more) and it easily weighed over 100 pounds, But I stupidly sold it for scrap 20 years ago while cleaning out my garage. Now I really want a BIG Variac for my voltage experiments, and I don't have one.

Never throw anything away!!!
Title: Re: Autoformers, anyone?
Post by: John Roberts {JR} on October 22, 2017, 11:35:27 am
You can also do this trick - http://www.powerqualityworld.com/2011/04/constant-voltage-ferroresonant.html
I first got exposed to magnetic amplifiers in the 60's (used inside an early switching power supply for current limiting). Pretty old school technology.

As your link notes a ferroresonant transformers is effectively running at (magnetic flux) saturation, so pretty inefficient for variable loads. Clever stuff for the very old days. 

I can't say that I ever saw one in the wild (that I recognized as one).

JR
Title: Re: Autoformers, anyone?
Post by: Peter Morris on October 22, 2017, 08:23:11 pm
I first got exposed to magnetic amplifiers in the 60's (used inside an early switching power supply for current limiting). Pretty old school technology.

As your link notes a ferroresonant transformers is effectively running at (magnetic flux) saturation, so pretty inefficient for variable loads. Clever stuff for the very old days. 

I can't say that I ever saw one in the wild (that I recognized as one).

JR

The efficiency is only about 75% to 85% - I often used them in automation projects within factories to supply the PLC's and other critical electronics. The electricity supply within a factory was often subject to voltage variations and noise because of all the large industrial equipment switching on and off.  They provided isolation, voltage regulation and filtering and would ride through short interruptions. They were also simple and robust and failure was rare.
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on October 22, 2017, 08:25:39 pm
The efficiency is only about 75% to 85% - I often used them in automation projects within factories to supply PLC's. The electricity supply within a factory was often subject to voltage variations and noise because of all the large industrial equipment switching on and off.  They provided isolation, voltage regulation and filtering and would ride through short interruptions. They were also simple and robust and failure was rare.

I installed a few of them back in the day (the 80's), and they ran very hot to the touch (so they were very inefficient) and they made a lot of physical noise.
Title: Re: Autoformers, anyone?
Post by: Tim McCulloch on October 22, 2017, 09:54:31 pm
I first got exposed to magnetic amplifiers in the 60's (used inside an early switching power supply for current limiting). Pretty old school technology.

As your link notes a ferroresonant transformers is effectively running at (magnetic flux) saturation, so pretty inefficient for variable loads. Clever stuff for the very old days. 

I can't say that I ever saw one in the wild (that I recognized as one).

JR

One of the lakes nearby has a permanent stage and the "friends of the lake" group installed a ferroresonant transformer for audio and stage power.  I remember it was noisy and heated up the switch gear shack.  It was nice having good audio power.  Lights are on a conventional step down transformer.
Title: Re: Autoformers, anyone?
Post by: Peter Morris on October 23, 2017, 03:06:05 am
I installed a few of them back in the day (the 80's), and they ran very hot to the touch (so they were very inefficient) and they made a lot of physical noise.

 ... for my application the noise didn't matter - you could never hear them above the background noise in the factories that we installed them in ... production lines that made things like washing machines, steel roofing, gutters, steel car parts etc. 
Title: Re: Autoformers, anyone?
Post by: Jeff Robinson on October 23, 2017, 04:45:35 am
... for my application the noise didn't matter - you could never hear them above the background noise in the factories that we installed them in ... production lines that made things like washing machines, steel roofing, gutters, steel car parts etc.

Two observations, never exceed a ferroresonant regulator's maximum rated amperage and if the tank circuit's capacitor fails you do not want expensive gear hooked up. I sold one to a hospital about 10 years ago. Every time I talked to their guy I emphasized that it had to be sized to his load's maximum inrush amperage (medical lab refrigerator needed stable voltage to maintain a precise temperature). He called the manufacturer to get the correct unit after delivery (he knew I would not warranty his sizing mistake). A few years later I sourced a special capacitor to replace one in a different ferroresonant regulator.

My history with this product.

http://www.emersonindustrial.com/en-US/documentcenter/EGSElectricalGroup/brochures-flyers-pdf/pwr-cond-prod-guide-solahd.pdf
Link to Sola's descriptive PDF, they patented them in 1938.

Jeff Robinson

Disclaimer: I sell this product at my work (just not recently).
Title: Re: Autoformers, anyone?
Post by: David Buckley on October 23, 2017, 06:59:59 pm
Autotransformers with automatic tap changers are a thing, which do keep a reasonably consistent output voltage.  A full transformer is, for some applications, even better:  The Salicru RE series was a really good example of this, an isolating multi-tapped transformer, with the tap selection done by triac, so it was really fast at following input voltage changes, no more flickering lights.

Underneath that marketing babble is, as ever, a grain of truth; for appliances that are resistive loads, like a kettle, if the voltage is low, then they will use less current, and heat up more slowly, Ohms Law tells us this.

So put two kettles on, or three, then the supply voltage will reduce due to voltage drop, and thus with the reduced supply voltage the wattage per appliance drops.

Marc covered motors, something I'm pretty hazy on!

Stuff with switch mode supplies doesn't care much about supply voltage, it adjusts the current draw to deliver the required output power.

Of course, adding an autotranny to a supply that is already voltage challenged by the load applied will increase the supply current, which will cause further voltage drop, which cannot go on forever, eventually the supply current must exceed the protection device to protect the supply wiring.
Title: Re: Autoformers, anyone?
Post by: shelley watreen on November 01, 2017, 02:34:55 am
Yeah...I also think that the description of autotransformer is awful...
Title: Re: Autoformers, anyone?
Post by: Mike Sokol on November 01, 2017, 07:49:40 am
Yeah...I also think that the description of autotransformer is awful...
ditto: please change your login to your name. I'm getting all kinds of notifications from the name police... ;)