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Thread: Using a relay to auto-power on HDD and power inverter

  1. #41
    What can I say? I like serial. Curiosity's Avatar
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    Mar 2004
    Florence Yall, BFKY
    Ah, I always wondered why it would need 120V since that's about 1% of the sine. So it's 80V peak in the square (modified) wave? I've never looked at one but it makes sense and understandable why appliances without transformers don't work. Still is the power supply in any appliance designed for the modified square wave to source it on a dialy basis? I just see these things as the spare tire where use is assumed and not exactly taken into account when appliances are designed.

  2. #42
    Raw Wave
    Join Date
    Nov 2009
    PRE-Posting-EDIT: It's not that I am committed - it's more a case of I should be committed. Or need to be.
    But I will split my insanity, er... ramble, over 2 posts. (I think the R-word was originally Reply. I know later, Rhetoric springs up.....) hic!
    /end PRE-Posting-EDIT/

    Yeah... I forget the trivials - or details.... We have 230VAC, but USA is 120V (if I recall....).

    So 120 VAC is 120V RMS which means things like 108V average (is it pi over root-8 or vice versa - I did this the other day...!) and 170V peak (120V / root-2?).
    And 170V peak means 340V p-p (peak to peak), or is it 170p-p with +/- 85V peak...
    Holly MadCow - this is so basic!
    I do know we needed battery banks of about 430 to 460VDC for 240 VAC...

    But forget the details...

    An AC supply is a sinewave which has an average value, a slightly different RMS value, and a reasonably higher peak value. From memory, the ratios are 63% & 71% with 100% being peak; ie - 2/pi, 1/root2 (= root-2 / 2) etc.

    For a squarewave, the average and RMS and peak are all the same.
    Hence for primitive square-wave inverters, what do you design for?
    Probably the RMS value - so for a 120VAC RMS, you have a 120V peak = 120V RMS square wave.
    But what if you are powering a switched-mode supply (SMPS), or something that requires a peak of 170V - maybe a starter for a fluorescent tube? It probably won't work on a mere peak of 120V - that's only ~70% of its required peak voltage.

    Fine - so we output a square wave of 170V instead. But now it's 170V RMS and that may fry the load.

    Enter the modified square wave - usually a two-level output that has a particular step timing to provide an RMS and peak voltage similar to a sinewave.
    It's average will not be the same as a sinewave, but average values have little relevance for loads (except... was it moving coil meters etc?).

    Note that the 2 voltage levels form 3 steps - like a winners podium - highest in the middle and flanked by the two lower levels. (Lets ignore the negative cycle - it's the same thing, just inverted....)

    So what are the two levels?
    Lets say the highest is 170V to give the 170V AC peak.
    The other level(s) will probably be half of that = 170/2 = 65V simply because 2:1 is easy to achieve.

    The timing of each level is calculated so it gives the same RMS & peak as the sinewave.

    The designs might vary - maybe the peak is dropped because whilst a sinewave is at its peak for an infinitesimal small period (of time), the modSquare has to be there longer. So instead of maybe 170V peak, we use 160V peak - say with duration the same as the sinewave is between 150V & 170V (ie, they both roughly average or RMS to 160V during that period).
    Then that 160V peak means 160/2 = 80V flanks, and they stay on long enough to provide the overall RMS value of 120V.
    Of course there is a 3rd level - namely off or 0V... Over a 90 degree 1/4 cycle, it might be 0V for 0-10 degrees, then 80V for 10-70 degrees, then 160V from 70 to 90 degrees; then the reverse from 90-180, and then the inverse (negative) from 180 to 360 degrees.

    Crikey mate - this is NOT easy in words. It is much easier pictorially!

    Anyhow, hopefully you can picture (oooh - bad pun?)..... you can picture the artificial "sinewave".
    (Designs could vary. If it's easier to have fixed 15 or 30-degree step intervals, you may vary the voltage levels.)

    So that's the cheap solution. A squarewave is easy, but unacceptable.
    [ I didn't mention the off time before - it can be +V, then 0V, then -V, then 0V etc. But intuitively, a full-on, zero, full(negative)-on is pretty doggone rough compared to a smooth sinusoid (like ripples/waves across water). ]
    The step or modified squarewave (aka pseudo sinewave) is better and generally acceptable, and most things work on it.

    Now to get to the catch!
    But I'll do that in the next post....

  3. #43
    Raw Wave
    Join Date
    Nov 2009
    Quote Originally Posted by Curiosity the power supply in any appliance designed for the modified square wave to source it on a daily basis?
    You know the answer don't you! You guys love goading me ..

    Yes - er, no....
    The square wave is harsh isn't it?
    Therefore it obviously damages equipment, right?

    Well, it can. But lets qualify the harshness. After all, car environments are VERY harsh, and they don't damage (properly designed) equipment. Vehicles can have transients of well over 100V, even 170V - so we have 12 Volt systems subjected to voltages higher than our 120VAC peak voltages!

    Mains (wall-socket?) powered AC equipment expects nice smooth sinusoid voltage as it comes out of those rotating generators.
    All loads were once linear - voltage and current were both sinusoid, although they may have been phase shifted (inductive or capacitive loads).
    The only distortions were due to faults - lighting strikes, cars hitting power poles, putting my son's tongue in a wall socket.
    Along come computers with their requirement for clean power.
    What do such demanders do? They give you the opposite in return.
    They want clean AC so they use SMPS which only conduct (take current) during part of the voltage/current cycle. That causes heaps of current distortion, hence harmonics, and eventually voltage distortion (ie - flattening of the once sinusoidal peaks).
    Worse than that, they cause the definition of Power Factor to include distortion factor and hence heaps of arguments. No longer is PF (Power Factor) - cos-phi (the cosine of the phase angle) as it was for linear supplies, it is now W/VA (Watts/Volt-Amps).
    You can have a PF = 0.6 and yet the voltage and currents are in phase (ie - cos-phi = 1, hence PF = 1, but it isn't - it is 0.6 because of crest factors way higher than the normal 1.414 (1/71% referred to above).

    Alas, I digress..... (but I have eaten lots of worms...)

    The problem with stepped-waves is usually overheating.
    A pure sinewave has no harmonics - it has only itself, eg - a 60Hz fundamental frequency.
    Any distortion adds harmonics. This can be seen mathematically, or observed on spectrum analysers that show the different frequencies - eg, they show music as being maybe 30Hz to 20kHz.
    They show a 60Hz square wave as a fundamental (60Hz) plus an infinite series of others. From memory, odd harmonics, hence from 60Hz, 1, 3, 5, 7 etc times 60Hz, so 60Hz, 180Hz, 300Hz, 420Hz etc. (I might be wrong - maybe a triangular wave is odds and square is evens, but trust me, such waves are made up of discrete frequencies. And ANY wave can be represented by a sequence of pure sinewaves. Oh the math! Oh the memories!)

    Anyhow, it's these other frequencies for which the circuit or loads were NOT designed that can be a problem.
    In effect, those resistors and capacitor and filters etc were not designed for those sharp square edges - they expected sinusoids in the frequency range for which they were designed.

    Now, as automotive loads have been hardened for their harsh electrical supply, many AC loads have been similarly hardened.
    It started with things like surges and car-pole & lightning spikes, then noisy computers and the increased abundance of (non-unity PF) noisy SMPS loads etc.

    Some AC loads now expect to be supplied by UPS and other systems, and even by cheap mod-Square inverters.
    Alternatively they have filters to filter out all those square-wave and SMPS distortions & harmonics. (Isn't that the same thing - hardening the PSU - albeit by absorbing the noise first, rather than beefing up the later components to handle (ie, absorb) the noise (ie - extra energy = heat)?)

    And now, on my 4th glass of xyz-OH, I realise how so many things add up to make sense.
    Yet again I feel like paraphrasing Ian Gillan (a hero way before the likes of Danny Crane) "I need to know everything before understanding anything else".

    So before I keel over backwards, did I answer Curiosity's question.

    Yes I did... ie - is the load designed to run on an inverter?
    Yes - maybe.
    See, that wasn't so hard was it?

    Oh crap - don't tell me it was rhetorical!

    The bottom line - if you have a sensitive load, or do not want noise (harmonic EMI/EMC etc), get a pure sinewave inverter. (What's cheaper - the load, or the sinewave inverter. It may be worth the risk - suck it and see. It's like over or under charging, or paralleling batteries,or over/under temperatures, vibration etc - it rarely kills the device, it merely shortens its life.

    BTW - where is that response to parallel batteries?

  4. #44
    What can I say? I like serial. Curiosity's Avatar
    Join Date
    Mar 2004
    Florence Yall, BFKY
    Yep. I think you answered it. But it's like anything you get made in China or wherever, it's kind of a gamble. The talk of harmonic frequencies always reminds me of the bridge that rips itself apart. Many possibilities are unforseen unless you have the equipment to monitor and compare differences such as heat and stress under artificially made conditions, and decide if a failure is going to happen.

    The one thing that does seem odd as that a 2 step can be much cheaper that just increasing the steps since multiple voltages can already be generated.

    I missed the parallel batteries question. lol

  5. #45
    Raw Wave
    Join Date
    Nov 2009
    Yeah - there is that risk of poor quality or inexperienced designers.
    And that's not just Chinese.... Volvo's recent recall of 8,000(?) new-gen cars; Ford's recall of cars that run away (cruise control).

    At least the days are gone where faults are deliberately engineered. I recall a local TV manufacturer that designed 17 points of failure in one model. (Along came the Japs and changed all that - they continued Henry Ford's work against the working class.... [lol].)
    Fine, there are still certain design flaws, but hey, that's our wasteful and inefficient commercial system.

    But 2-step is generally considered an easier and cheaper design.
    I far prefer the inverter that was designed many years ago... forget old ferro-resonant technology - it used a 50kHz or 100kHz dc-dc converter that produced a sinewave with 0.02% distortion! I was considering using it as a a 1kW audio amplifier!

    That however was to meet the spec that required sinewave (no noise nor distortions were allowed - load reliability was paramount!)
    But the point is the initial hurdle for its uPC etc design.
    Once achieved, it blew the ferros out of the market.
    [ My marketing spiel was "half the price, 1/10th the weight, 1/20th the volume, and half the inefficiency" (And I just omitted reliability - ha!).
    It was a 3RU 19" rack mounter (like a domestic receiver or amplifier) instead of a noisy 2 or 4 drawer filing cabinet weighing the equivalent of 3 people. (It also didn't "fail" monthly like the ferros, nor every ~2 years require a new ferro-core at half the cost of the original unit (and most of the weight). Designed for a 3 year MTBF, many were still operation well over a decade later. But enough .. ]

    After that initial hurdle, a change of frequency or behaviour was a mere program change. Even an input or output voltage change might not require hardware change....

    You'd think the same would apply for common dc-ac inverters, yet even ac-ac UPS tends to use modified-square wave outputs (excluding on-line systems - ie, not the common standby units).
    So I presume that despite the plethora of SMPS chips or DSPs etc, there is still no cheap way to manufacture sinewave inverters.
    Else the modSquares have recouped their R&D & production costs....

    And the same for multi-step conversions.
    As I recall, going above 2 (or maybe 3?) levels wasn't practicable - you would go the full PWM sinewave solution.

    But if you have some cheap design idea...
    Bearing in mind that input current is more than 10x the output current (for 120VAC) and over 20x for 230VAC - ie, 500VA out @120V is about 4A and hence 40A DC input. (Hence high frequency and probably high voltage intermediate conversion.)

    So I take it that there are no objections "continuing" this diverted-OP thread?

    And is there any interest, or is it just us ?
    Or me . Again.

    (The above are jest. When I finally face my higher priorities, this will will cease.)

    Ooops - how could forget the parallel battery...
    That's a reply that is expected at 139579-what-battery.
    I assume Jim's had a long weekend or yet to gathering the data.
    (I have a gross of people claiming how unreliable certain batteries are. Last week someone posted how their cheap AGMs were far superior to Jim's AGMs. I'm keen to offer evidence rather than repeating anecdotes and what I think was wrong - it is often NOT the battery that is at fault!)

  6. #46
    Constant Bitrate Startingline13's Avatar
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    Nov 2007
    Long Island, NY
    Hey I've got no problem with it going off topic - I got my problem solved thanks to you two. The rest of this stuff is waaaay over my head.

    BTW, the inverter does have a third pin in there. It was one of the reasons I got it, because the computer I originally had in there required it.

  7. #47
    Raw Wave
    Join Date
    Nov 2009
    So that 3rd pin is connected? (I didn't see the connection.)

    Is it connected to the 12V DC ground?
    Or connected to the chassis/case? (In which case it almost has to be connected to a ground!)
    Or something else - maybe (to the case and then...) to a capacitor or a capacitor to each 12V DC input?

    BTW - the "over the head" bit - yeah - I know! But if some of it makes sense, a lot more may become very clear and "simple". Just ignore the blah detail - there is a lot in there, we can only absorb so much at a time.
    Alas I still vividly recall my total d'oh (aka wtf?) when starting a new job and this tech mentioned "inductive coupling" due to "single-pole inverter switching". WTF? A year or two later I had the Regulating Authority not only approve but also endorse this "new" seemingly illegal dual-pole switching. But that was last millennium....
    It's thanks to the brilliant people I have met or read in forums like these, and several years, that I now know this stuff. And I'm still learning. And still being proved wrong.
    In fact just last week regarding car alternators.....

  8. #48
    What can I say? I like serial. Curiosity's Avatar
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    Mar 2004
    Florence Yall, BFKY
    Quote Originally Posted by OldSpark View Post
    Ooops - how could forget the parallel battery...
    That's a reply that is expected at 139579-what-battery.
    I assume Jim's had a long weekend or yet to gathering the data.
    Oh, I'm just going to stay away from that one. LOL

    I've seen too many plain lead acids with 5 good cells so paralleling something like that scares me. Optima is a totally different chemistry though, and I don't know too much about them.

  9. #49
    Raw Wave
    Join Date
    Nov 2009
    The data is twofold....
    Hopefully the testing that shows Optima's superiority to other batteries as Jim has claimed. I have seen similar from other reputable & quality manufacturers. For those that don't, the prove to be shysters - whether bragging about non-exiting testing or a known non-quality product is another issue. (Then there's the spotting of products that are suited to one application and environment only - but that's more relevant for other products.)

    But if for whatever reason Jim chooses not to supply the above, the at least we should be able to get the parallel data.
    After all, that only involves Optima batteries and is easier to test than tests involving other batteries.
    There would no doubt be "matched adjacent battery" tests - ie, both matched, sitting next to each other (same temperature etc) and cross-connected load (+ve from one battery, -ve from the other).
    But I'm hoping for the "matched separated" tests - ie, a matched pair at different temperatures as would be found in an engine bay and a boot/trunk. (They too should have a cross connected load even though this is RARELY done in practice.)

    Jim stated that it was ok to parallel Optima batteries and the impression given was without qualification.

    From my own experience, it is not worth paralleling batteries. That's assuming you are not monitoring them. (Parallel UPS strings were different - they are paralleled strings of f.ex 36 12-volt monoblocks/batteries.)
    Whilst many parallel batteries may be ok for a reasonable time, it's if one deteriorates before the other .... Apart from possible hazards, it simply kills the 2nd good battery. (And it get worse the more batteries that are in parallel - and four times the unreliability for 4 batteries etc.)
    It's fairly similar to the practice of tyre rotation. Once a tyre starts wearing the wrong way, it continues. Rotating tyres the means the lot are replaced quicker rather than just (continually?) replacing the faulty wheel's tyre.
    But in the battery case, they are cross connected so a bad battery brings down the others. It's like the other good tyre(s) start wearing like the bad tyre - ie, parallel batteries are like tyres AFTER rotation.
    (Or should I do some water-electricity analogy?)

    Anyhow, I'm hoping to get some data so that either I can just accept all the failures I've seen and head of with Optimas, else find out what is being done wrong to cause the failures.
    Some failures have been protentially dangerous - like the dude that insisted on uprating his alternator when it was an Optima will TWO collapsed cells. Of course the foolish owner didn't check the battery as advised - after all, it was only 3 months old. But when the Optima got too hot to touch - in his boot (next to his boot mounted fuel tank) - he figured out what his problem was. (Which amusingly enough was the 1st or 2nd reply to his post instead of the final solution being several pages later. And that's not including several pages of descriptive PMs from a colleague that also writes too much.)

    And Jim's comments were timely given that in an other "Kinetic" post, someone was going on about how unreliable Optima batteries were.
    Maybe I can reply later and offer an explanation for his experiences. (My experiences suggest little understanding by Optima users - they read the bling and fail to consult before DIY - hence undercharging in boots or excessive discharging etc - if only they read the voltmeter on their boot caps! lol)

    If Optimas do prove to be unreliable, their resellers can face hefty penalties here if they are found to make false or misleading claims. That should redress our national imbalance of payments - with people replacing Optimas as often as every 3 months....

    As to paralleling wet lead acids - its the same thing.
    Wets may be better matched that AGMs - or not. I can see AGMs as a tighter tolerance manufacturing process, but maybe the tech is less stable...
    Certainly AGMs a spec'd to last 10 years plus, whereas wet cells are usually 3 years.
    But that is irrelevant to parallelling.
    If the 10-year AGMs have greater variance, they will fail faster than wets.
    EG - if wets have negligible voltage difference but 2 matched AGMs don't (maybe 12.70V & 12.71V, or 11.70V vs 11.72V under load etc), then the deterioration cycles begins. (EG - LEDs produced in the same die can have very different parameters.)
    And then there are the temperature effects. Remember - AGMs can suffer thermal runaway. (I've seen a ~200V string of beautifully warped beige 12V AGMs. Beautiful, but scary!!)

    Anyhow, I know what you mean about staying away.....
    Alas I get little satisfaction from regurging the same crap and not solving issues. And whilst I have learnt not to tackle all, occasionally the right people come along that can crack the problem - in this case Jim.
    As to any flack - yeah, we all know.
    But we also know who is probably right simply by the way they are treated (no other knowledge required). Whilst some true-gurus can crack up, for the most part it's the shysters and bullshers that fling the mud and deflect the issues. Or suddenly have higher priorities. Or have their positions transferred.
    If only I had bigger boobs.....

  10. #50
    What can I say? I like serial. Curiosity's Avatar
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    Mar 2004
    Florence Yall, BFKY
    Well, personally I think they need to get the lead out (pun intended) and switch to a lithium based technology or something greener. AGM is an improvement of and old technology.

    But anyway, I don't see how any data will put your fears to rest because that's the nature of stored energy in a dense container. Think of a "safe" nuclear reactor. There's always the possibility of uh... releasing the energy too quickly, coupled with the intelligence of the end user makes the possibilities endless. Reports on the internet don't show all factors so I try not to judge based on user incidences because who knows? Proper venting, over/under safe temperatures, charging voltage, max discharge rate, dsicharging to 0V, physical stress, etc...

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