AC Regulation ideas? - Page 1
Forum section: electronics / general

author: innkeeper
author_rank: Unknown
timestamp: May 09, 2019, 04:41:02 am
content: i'm looking for a way to regulate AC line voltage into devices but martian an AC signwave. in the past i've used farroresonant transfomers for this.what i am looking to do is basically drop the voltage to a lower voltage then the lowest line voltage i would see and keep it constant with varying like voltage changes and with varying loads, though at no time will the load be zero, nor would i expect regulation at low loads.in the cases where i want to do this, regulating the voltage within the device being powered is not possible and, the devices use the ac signwave as part of its function.any ideas on ways this can be accomplished? I've searched around and have yet to find an existing solution, though i am hopeful there are others who have ideas on how to do this or may know an existing method.The one important aspect is the ac out must still be a signwave so no chopping the ac or triac type output. some distortion at crossover would likely be fine

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2019, 10:53:37 am
content: Just one question: why? Most devices use switched mode power supplies, which work off a wide range of voltages.Keeping the voltage on the low end of the tolerance band might also increase overall power consumption and reduce efficiency, as the current taken by constant power loads will increase, causing more I2R losses.The usual way to do this is with a variac and servomotor which adjusts the wiper position, to keep the output voltage constant.

author: digsys
author_rank: Unknown
timestamp: May 09, 2019, 11:13:49 am
content: Spent many many weeks trying to achieve this - magnetic amps / DC controlled anti-phase windings etc etc Way too much distortion.Check out Line-conditioner circuits, it's pretty much exactly what they do - just bulky though - huge caps required.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 09, 2019, 11:33:50 am
content: You can buy units where they have a servo driving a variac, feedback is from the output. Another uses a multi-tap transformer and they select the taps digitally, again using the output as feedback.I use a UPS to drive some of my old test gear. It converts the AC to DC then creates the pure AC sine. You can program the output line frequency and the voltage. This unit is currently using a bank of supercaps rather than lead acid batteries.For a test fixture, you could look at Techron, who make DC coupled audio amplifiers. The have some that will directly drive 220V. Again a variable gain stage with some feedback to excite it. At home, I made a low frequency power amp that I use for this.

author: innkeeper
author_rank: Unknown
timestamp: May 09, 2019, 01:17:18 pm
content: Quote from: Zero999 on May 09, 2019, 10:53:37 amvarious old test gear that is difficult if possible at all to add regulation, or utilizes the ac as part of its circuit and susceptible to line voltage changes.

author: tooki
author_rank: Super Contributor
timestamp: May 09, 2019, 01:49:28 pm
content: Quote from: innkeeper on May 09, 2019, 04:41:02 amjoeqsmith summarizes all the options really: an automatic variac, a line-interactive or double-conversion UPS, or a power amplifier.

author: David Hess
author_rank: Super Contributor
timestamp: May 09, 2019, 04:03:31 pm
content: Use an audio power amplifier with an output transformer. Wire the secondary of the transformer in *series* with the line input so the regulated AC output is the vector sum of the line input and a fraction of the audio power amplifier output. Drive the audio power amplifier with a reference sine wave phase locked to the line input and use feedback from the summed output.Noise within the bandwidth of the audio amplifier is removed. With a limited adjustment range, power dissipation of the linear amplifier is lower than if it supplied the entire output although this design would be especially suitable to a class-d switching amplifier.Someone used to make line conditioners which worked like this but I do not remember the name.

author: capt bullshot
author_rank: Super Contributor
timestamp: May 09, 2019, 04:37:36 pm
content: Quote from: David Hess on May 09, 2019, 04:03:31 pmElgar, for example:https://www.eevblog.com/forum/reviews/elgar-3000b-(ancient)-ac-line-conditioner-teardown/msg2307084/#msg2307084

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 09, 2019, 05:48:41 pm
content: Could build a pure sine inverter that runs off AC and have a small battery bank in between. Basically a dual conversion UPS. Have the output match the average input voltage, and have the battery compensate for the dips. Technically you could even make the voltage higher than input as you'd just draw more amps from input.

author: German_EE
author_rank: Super Contributor
timestamp: May 09, 2019, 06:02:09 pm
content: 1) Incoming mains is fed to the primary of a transformer with 9 taps to cover your range of 117 to 125 VAC in 1V steps, the 110V transformer secondary is connected to your load.2) A cpu and an ADC measure your P-P secondary voltage via a low voltage tap.and feed the result to a lookup table.3) The output of the lookup table selects the correct primary tap to give you 110V secondary voltage BUT switching is only done at the zero crossing point of the AC waveform to keep the waveform as pure as possible.Selecting the primary tap is the difficult bit, there are some SSRs that use back to back FETS and these can provide a reasonable AC waveform.An ADC that can measure fifty or sixty times a second is easy and so is the CPU, you could probably write the control program in BASIC and get away with it

author: ogden
author_rank: Super Contributor
timestamp: May 09, 2019, 06:42:33 pm
content: Quote from: innkeeper on May 09, 2019, 01:17:18 pmIf you want to stabilize AC mains out of your mind - look for "Static IGBT Voltage Stabilizer".

author: D Straney
author_rank: Frequent Contributor
timestamp: May 10, 2019, 01:29:31 am
content: Quote from: capt bullshot on May 09, 2019, 04:37:36 pmYeah, seeing this thread reminded me of exactly this teardown.Honestly, it depends how much effort you want to put into it - if you'd rather have fun doing some fully-custom electronics, either imitating the Elgar (linear power amp driving transformer in series with output), switched taps, or the homemade sine inverter sounds reasonable. If you'd rather get it done comparatively quickly by buying off-the-shelf equipment, to put your time in elsewhere, then I'd recommend looking for a used AC source - they're meant for exactly this kind of thing (producing clean, stable AC power). Ebay has a lot of expensive ones, but depending on your budget there are some which aren't as bad:https://www.ebay.com/sch/i.html?&_nkw=ac+source

author: innkeeper
author_rank: Unknown
timestamp: May 10, 2019, 02:18:17 pm
content: Quote from: ogden on May 09, 2019, 06:42:33 pmI like the concept, has anyone implemented this at the relatively small scale I am talking about?

author: soldar
author_rank: Super Contributor
timestamp: May 11, 2019, 04:01:05 pm
content: Quote from: innkeeper on May 09, 2019, 01:17:18 pmYou would need to put some numbers on your project. What is the input voltage range? And the output has to be kept at what voltage and with what tolerance?When I was a kid TV sets needed a well regulated voltage and we had a little autotransformer with a voltage meter sitting under the TV and it had a selector switch to adjust the voltage.If you don't mind adjusting the voltage manually this is simple and cheap. An autotransformer can be very small as most of the power comes direct from the line.

author: Benta
author_rank: Super Contributor
timestamp: May 11, 2019, 04:16:57 pm
content: If you have three-phase service, the electrically optimal solution is a synchronous motor driving a synchronous generator.You can even include power factor correction for your home.

author: ogden
author_rank: Super Contributor
timestamp: May 11, 2019, 06:13:01 pm
content: Quote from: innkeeper on May 10, 2019, 02:18:17 pmMost likely complexity & price of small scale static stabilizers approach price of AC source. I like concept of static stabilizers as well, yet for < 1KW would definitely go for (used) AC source. You get many important benefits - isolation, wide voltage range, 50/60/whatever Hz, voltage/current/power measurements, clean AC sine.

author: innkeeper
author_rank: Unknown
timestamp: May 11, 2019, 08:35:52 pm
content: Quote from: soldar on May 11, 2019, 04:01:05 pmvoltage in is line voltage so typically varies in the 117-125v range, out would be 110v, and I could get away with 100v. stability is more important the exact output voltage.id say the voltage tolerance should be +/- .5v or better the more stable the better for sure.An autotransformer is not regulation, as there are voltage variances on the input, the output voltage will follow suit and so will not fit the needs

author: David Hess
author_rank: Super Contributor
timestamp: May 12, 2019, 04:09:53 am
content: Quote from: innkeeper on May 10, 2019, 02:18:17 pmThe system I described and capt bullshot linked work that way. It has been done in sizes below the power of a single wall outlet.

author: innkeeper
author_rank: Unknown
timestamp: May 12, 2019, 09:35:48 pm
content: most of the dual conversion / IGBT type solutions are kidna bulky, certainly could not fit them inside an existing piece of equipment in most cases.I have to think this could be done in a fashion where there is feedback from the output voltage, that fed back a circuit that would change what amounts to a resistance inline with the input ac to compensate for line and load changes. similar to what had been described earlier using an inline transformer and audio amplifier or what happens with a servo and autotransformer, just much faster, and relatively simple in design. if anyone knows of sample circuits I could look at like that please post, even if they are not directly relevant.i did manage to get my hands on an ac-ac converter type a clary sp560 for a dirt cheap price of 40 bucks used, it is a purpose built stabilizer with a UPS option, seems to work as red squirrel described, though seems to use some DSP technology. I cant tell it it is PWM so its likely not IGBT, they just describe the output as a sine wave generator. ... should be here soon, but, not expecting miracles with it. it is certainly would still be something outboard. I'm curious if it does better then the ferroresonant transformer. it didn't have great specs for the crest factor ratio, however, i am hoping those crest factor ratio figures were the worst case with non-linear loads. I could combine it with the ferroresonant transfomer to get a crest ratio near 1.414. .. that is getting a bit rube goldberish though and not very compact.even if i haven't responded, i've been digging into the various technologies posted and learning how things are being done, I'm learning a lot by reading about the various methods in use.I'm still on the hunt for something more simplistic and effective one could build themselves. Again not looking to drive huge loads, or needing any voltage boost. this is simply to stabilize ac line voltage to a lower level to drive equipment sensitive to line voltage variances...it needs to deal with load variances too though, test equipment loads don't vary all that much..and typically the kind of things I am talking about draw under 1/2 amp.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2019, 09:41:19 pm
content: Does it need to account for rapid changes? Many older dental xray systems had a variac and meter on the side of the cabinet, you would read the meter and adjust the variac as needed prior to shooting some exposures. Obviously it wouldn't help with glitches but to compensate for day to day variations in the mains voltage it worked fine.Those ferroresonant regulators also work pretty well though they run hot. Yeah the output is not a clean sine but in most cases that doesn't matter, they give you a stable output.A true sine inverter connected to a cheaply available hot swap server PSU would get you a cleaner output at probably comparable efficiency.

author: ogden
author_rank: Super Contributor
timestamp: May 12, 2019, 10:17:31 pm
content: Quote from: innkeeper on May 12, 2019, 09:35:48 pmGood find, especially considering price. Decent on-line, double-conversion (48VDC) UPS. It provides isolation and programmable output freq (40-70Hz). Most likely uses MOSFTETs. 3% TDH is "clean enough" sine. Definitely PWM is there as well. I think your search is over

author: innkeeper
author_rank: Unknown
timestamp: May 12, 2019, 11:35:45 pm
content: Quote from: james_s on May 12, 2019, 09:41:19 pmyea, the rapid voltage changes are the issue, not so much the nominal voltage. and to be clear when i say rapid, i mean surges and sags, not spikes or emi etc, line noise is not a problem affecting the equipment. I get lots of sudden sags and serges were I am. I am right down the road from a solar farm. plus, anytime the ac kicks on in the house or the fridge kicks one I get sags.This totally messes with meter readings on some old test gear ......I'll give you one practical example, I have this high voltage cap tester that measures leakage down to the uA range on an analog meter. When the line voltage swings that needle bounces all over the place. just to illustrate, imagine that 2v line change translates to around 7v change at the 600v supplied to the cap under test so it can make it hard to get a reading as the cap charges or discharges due to the voltage change ..... Excellent piece of equipment but totally susceptible to line variations. Plus, Due to the design, it doesn't lend itself to adding any DC regulation.Don't get me wrong, the ferroresonant transformer helps, but even if it cuts down a surge / sag to 1/10th, a .2v change will still be a .7v change and in the uA range that change causes the current to flow to a cap under test.

author: David Hess
author_rank: Super Contributor
timestamp: May 13, 2019, 03:52:32 am
content: I suspect an on-line or double-conversion UPS would serve you better. They will happily ignore all line input variations while producing a clean output and are less expensive and have better availability. Some will operate without batteries as a very good line conditioner.Or string together a DC power supply, optional battery, and inverter.The step-down transformer and feedback system I and some others discussed removes line noise within the bandwidth of the feedback loop but only up to a limited compliance so it might only compensate for a line variation of 20 or 30 volts. Without the step-down transformer, it just becomes an inverter and you are back to the solution discussed above. The advantage of using the step-down transformer is that it allows a lower power system to correct a higher power waveform but over a more limited range which was more important in the past when high power inverters were more difficult and expensive to produce.

author: innkeeper
author_rank: Unknown
timestamp: May 13, 2019, 06:04:38 am
content: well, I'll see ... the one I have coming works without batteries. its actually kinda the reverse, its a purpose built dual conversion conditioner unit, that you can add batteries on to also provide ups functionality. The timing was perfect, it just fell into my lap at the right price when checking out what Ogden and others had suggested. I'll defiantly post the results.

author: james_s
author_rank: Super Contributor
timestamp: May 13, 2019, 03:41:34 pm
content: I would think that a piece of test gear that is sensitive to a 0.2V mains variation is defective, either due to a fault or inadequate design. Properly designed equipment ought to tolerate at least +/-5% without malfunction.

author: innkeeper
author_rank: Unknown
timestamp: May 13, 2019, 03:58:21 pm
content: Explain that to the engineers at Sprague circa 1964

author: james_s
author_rank: Super Contributor
timestamp: May 13, 2019, 04:08:01 pm
content: Are you sure it isn't defective? AC line voltage varied back in 1964 too and ferroresonant transformers were about the only thing available to stabilize it.

author: innkeeper
author_rank: Unknown
timestamp: May 13, 2019, 04:54:23 pm
content: I'm very sure it is not defective...Would we put up with that on modern test gear, well of course not, but this isn't about modern test gearactually, there is plenty of old test equipment that cant handle %5 line change without altering measurements, low leakage capacitor testers with no regulation, 99% of the mutual conductance tube testers ..Including the most sought after ones like the Hickok 539C which go for 1500 usd and up in today's market. heck, even a humble old oscilloscope like an eico 460 didn't have a regulated supply.It is fun to dig into the theory and history on how these devices work you will understand the details of why that is. many times, back in those days it came down to cost. it was the difference between a true laboratory instrument only a manufacturer could afford vs something the general population could afford (and even then quite costly). Just as a starting point as to why, some of the designs actually utilized the ac sine wave as part of the test circuit function like tube testers. others they cheaped out and didn't have regulation, to keep thing affordable.just to illustrate, in 1958 a factory wired eico 460 costs $129 dollars [$1,140 in 2019 dollars] or as a kit for $79 dollars [$698 in 2019 dollars] (4.5 mhz sweep) versus a Tektronix type 310 cost $595 [$5,261 in 2019 dollars] (4mhz sweep). regulated, sure, but not within the budget for small businesses or hobbyists.Frankly, I think the way they designed the tube testing circuits was pure genius( pun intended and a bit of acknowledgment of Job Barnhart ) How they could do what they do with low part count circuits that your average tech could afford is an amazing feat of engineering for the time.it does mean dealing with line voltage variations for some of this vintage test equipment.And yes I am trying to better what line regulation would have been available at the time. That is the point of all this.

author: bsdphk
author_rank: Regular Contributor
timestamp: May 13, 2019, 05:17:05 pm
content: How many watts of power do you need ?If it is just a low amount say up to 100W, I would absolutely go with the audio-amp + transformer solution since that decouples you entirely from the grid.If you really want to get fancy about it, or if the load varies a lot, you can modify the amplifier so a resitive voltage divider on the secondary is the reference/feedback signal.I have not tried higher powers myself, but would probably look for high quality inverters.

author: dietert1
author_rank: Super Contributor
timestamp: May 13, 2019, 05:37:06 pm
content: For high end audio there are extremely expensive line conditioners, that essentially consist of a 50 Hz bandpass filter and an audio amplifier module in series with mains to realize (usually small) voltage changes. If you know what you are doing, development of this is a little project that involves using a safety transformer, resettable fuses, clipping diodes and the like.Eventually it can all be done modding a used power amplifier from ebay, that outputs +/- 50 V or so. In your case the bandpass filter would include some zener diodes to fix the output amplitude.Regards, Dieter

author: innkeeper
author_rank: Unknown
timestamp: May 13, 2019, 05:52:33 pm
content: Quote from: bsdphk on May 13, 2019, 05:17:05 pmlikely ~60W max. least thas the criteria I set forward at the beginning of the thread.think what I posted was 110v out at 500ma max. mostly as a working concept.the exact output voltage isn't as critical as stability of the voltage.

author: bsdphk
author_rank: Regular Contributor
timestamp: May 13, 2019, 07:23:11 pm
content: Then start out by finding a cheap second hand power-amp around 200W.Since you only need one phase you can probably bridge a 50W stereo-amp to get there.

author: capt bullshot
author_rank: Super Contributor
timestamp: May 14, 2019, 05:37:19 am
content: Don't forget the heat sinking and component rating of a typical consumer audio amp isn't suitable for prolonged periods of constant output power above maybe 1/5 of the output power rating. Typical music has a quite high peak to average power ratio, and most amplifiers are built based on this. Better look for a professional amp, proposed to heavy duty use at a stage.

author: TERRA Operative
author_rank: Super Contributor
timestamp: May 14, 2019, 06:24:01 am
content: I have a servo driven variac unit that works well, I just never need to use it so it'll get sold when I get around to it.It is no good for transients, but any variation more than a few seconds long will be corrected.It's not so complex inside, so within the realm of DIY.Here's a video I made about it way back when.

author: dietert1
author_rank: Super Contributor
timestamp: May 14, 2019, 12:08:45 pm
content: We also have a transformer with automatic AC regulation, but realized with a binary DAC. It has various low voltage taps that get switched in and out with triacs. The transformer is built with complete shields for primary and secondary. The name is CEK 300, brand "CoNet". It is quite old, but appears to be working.Another solution is the magnetic regulator. We have one that works very well and keeps output voltage to about 1% with input variations of +/- 25 %, but it produces much heat and some acoustic noise. It always sounds like it will melt down soon.Regards, Dieter

author: innkeeper
author_rank: Unknown
timestamp: May 17, 2019, 07:47:44 am
content: Good News:So the Clary SP560 dual conversion unit arrived and seems to do the jobBad News:the bargain was not a bargain....still to good a deal to send back...Fans don't work so it overheats. Seems to be microprocessor controled so gawd knows ... the software has no settings for the threshold for the fans however temps are read correctly ..fans are 4 wire PWM with tachanother project, just what I needed lol.

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2019, 12:36:53 am
content: Wouldn't surprise me if the fans themselves were bad, either that or the transistor or IC that controls them. Should be pretty easy to work out what's going on. I just expect this sort of thing with any used gear I buy, it's one reason I typically look for bargains that are already known to have some issues.

author: innkeeper
author_rank: Unknown
timestamp: May 18, 2019, 05:45:44 am
content: James_s .. you hit it spot on.... both fans are dead. I was surprised, I mean they move freely, they're just dead, and id bet there dead due to exactly what you said..they are 4 pin PWM fans, easy enough to get a replacement. I am getting power to the headers the fans plug into, so, even if the pwm doesn't work, I can get a replacement fan to work without much hassle.headers are giving 13.6v with no load, and these fans have a max voltage of 13.2v .. think I'll opt for some replacements that are good to 13.8 just for the headroom, or maybe put in a series diode just to drop the voltage or both..it isn't readily apparent how to get the voltage down, no vrm in sight, and I wonder if maybe its not directly regulated, so it might even rise from that 13.6v... this could explain the death of the fans. the diode is a hack, but, I dont see myself digging into the power section without a schematic.the unit is very nicely built actually, everything is conformally coated and glued in place with like a clear silicone. Turns out these are designed to be able to sit out in a traffic signal control box, and to operate in extreme temperatures from -40°C to +74°C (-40°F to 165°F) and humidity of 0% to 95% non-condensing .. seriously that's the operating range .. I might consider doing a video on this thing since I have it apart anyway.A nice note about the folks at CLARY...SERIOUSLY!You don't see this kind of thing nearly enough these days so I want to give kudos when these kinds of things happen it speaks well of a good corporate culture ....I fired off a question last night on their website about controlling the fans through their serial/usb interface, thinking maybe the issue was a software setting of the thermal thresholds ...and I got a call from an engineer at clarygo figure .. I guess they don't sell many of this cause he knew right away I was not one of their customers and was curious how I came to have it and how I was using it. The conversation headed in the direction of "we can give you a RMA and ocne we look at it we will give you an estimate on what it will cost to get it repaired" ... I explained I got this for 40 bucks off ebay and was just using it for clean power on my electronics test bench for test equipment. .. so wasn't about to send it in for repair. I was expecting a "Sorry we can't help you" ... but ... As soon as he figured out I was someone who knew electronics and wasn't sending it in, nor a typical customer, he answered all my questions as best as he was allowed to, even explained some things about the unit like battery charge current limitations if I wanted to attach my own batteries ... their command set to the device the don't document and send out, however, gave me enough information so I could troubleshoot that area if needed. .. like APC .. They don't give out schematics, I wonder if this is a "thing" within that industry. At one point he said .. and I'm paraphrasing ... well it's pretty easy to open it up and get to the fans, just pull the plugs and test them off a power supply. if they're good and as long as it's working well otherwise, you could just wire them directly to the 12v or replace them if they are bad ... nice to actually get a call from an engineer when you ask a technical question that will actually talk to people at their level being supportive of hobbyist basically. ........... refreshing.they seem like the type that you would find on the form actually ...by the way, this thing retails for over 1200 bucks

author: D Straney
author_rank: Frequent Contributor
timestamp: May 18, 2019, 03:37:06 pm
content: Glad it worked out in the end!Quote from: innkeeper on May 18, 2019, 05:45:44 amI'd definitely be interested in seeing the inside, even if it's just a photo or two.

author: innkeeper
author_rank: Unknown
timestamp: May 19, 2019, 03:15:11 am
content: best on another thread

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 19, 2019, 04:25:36 am
content: I ‘ll second D Straney’s request of seeing a couple of pictures of the inside circuit.It doesn’t have to be a full, EEVblog-grade teardown. A couple of sharp photos will do.