Author Topic: My Scratch Pad  (Read 42827 times)

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Offline bj

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Re: My Scratch Pad
« Reply #465 on: May 03, 2017, 06:38:48 AM »
Green leaves--I'm envious
Few more days before they pop here.
"Even a blind squirrel will find an acorn once in a while"
bj

Offline MadScientist267

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Re: My Scratch Pad
« Reply #466 on: May 03, 2017, 10:50:45 PM »
LOL Yeah we've been in it for about a month I guess now. Just glad pollen season is basically done with.

Main thing with that pic was how bright our little neighbor there is... thought maybe my home planet had heard my cries and finally sent a rescue pod, but before I could get up on the roof with a flare gun, the interwebbythingy convinced me it was probably just Venus...  ::) ;D
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Offline MadScientist267

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Re: My Scratch Pad
« Reply #467 on: May 08, 2017, 03:59:52 PM »
ila_rendered
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Offline MadScientist267

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Re: My Scratch Pad
« Reply #468 on: May 11, 2017, 02:29:04 PM »
ila_rendered

Figured I haven't posted any good quality deadbug in a while... so here is... battery powered (for isolation) precision 2.5V reference using a TL431...

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Offline MadScientist267

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Re: My Scratch Pad
« Reply #469 on: May 11, 2017, 02:36:04 PM »
ila_rendered

... and a little "inside the ring" thinking involving filtering switching noise from hall sensors before it ever gets into them (the jury is still out on the results... will get revisited at some later date)
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Offline MadScientist267

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Re: My Scratch Pad
« Reply #470 on: May 11, 2017, 04:09:47 PM »
It keeps growing, and growing, and growing...

ila_rendered
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Offline lighthunter

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Re: My Scratch Pad
« Reply #471 on: May 13, 2017, 10:14:58 AM »
Hi Steve! Nice unit you built there. Its a solar charger right? 50v to 14v buck regulator? Good job on the display.

Not to change subject but was thinking about your fridge/energy storage ideas. I heat the DHW with solar but we also use distilled water a lot. Has anyone built a water heater that reclaims heat from distillation? Would take a bit of a piping exchanger apparatus but its not a difficult concept and "kill 2 birds".

Whats the specs on your converter? Thanks for the nice posts.
LH

Offline MadScientist267

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Re: My Scratch Pad
« Reply #472 on: May 14, 2017, 06:19:58 PM »
Hi Steve! Nice unit you built there. Its a solar charger right? 50v to 14v buck regulator? Good job on the display.

...

Whats the specs on your converter? Thanks for the nice posts.

Actually this one is for genset/grid, main converter is push-pull, can do 40A (schottkies being the limitation) at 15V, continuous.

That said, until I have an authoritative reference (pronounced "good DC clamp meter") to verify calibration, I have software CC limiting set to "32A" and hard CC set to 35 for the time being.

The pic above is only the brain, display, and control/protection sections, the grunt unit is out of frame.

It's fully active power factor corrected, and runs at approximately 83% efficiency (I of course won't be able to confirm this until I can do the final ammeter calibration).

I just recently completely redesigned 2 of the control and feedback sections, and it's running as it should at this stage of development... As soon as I get a little bit more done on it, I'm going to start a dedicated thread on it and give it the whole run down.

As far as reclaiming heat from distillation, I'm sure it's not incredibly complex, as you say, I couldn't offer up much more than theory on how to best implement it for highest efficiency. I'm sure someone has tho.

Steve
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Offline lighthunter

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Re: My Scratch Pad
« Reply #473 on: May 20, 2017, 12:58:34 PM »
Thanks for comments Steve, so your converter input comes from mains / genset driven transformer i presume? Or did you do the high freq stepdown with small hf transformer?

However you did it good job. Concepts seem simple on paper but always seems to be smoke where wasnt expected. I tried to connect a simple mosfet pair as a 400v. 10A switch the other day and it did not work. Stil dont know how i could screw that up. Maybe wrong choice of fet i dunno.,  5R140P. It seemed to work great up to 150v at a couple amps (relay contact driving 12v to gate). It would switch load on and off instantly. When supply voltage went up to 260v in full sun with 9 amps of current. It struggled to switch off and took a couple seconds to get to off. Needless to say mosfets dont do well in linear region even with heat sink. Gate to source pulldown resistor was 560ohm. I went with a 400dc rated relay with magnetic arc control instead.
LH

Offline MadScientist267

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Re: My Scratch Pad
« Reply #474 on: May 20, 2017, 01:21:49 PM »
Active PFC (at least as widely currently implemented) involves little more than what amounts to a specialized boost converter, which in this case is taking the rectified mains up to 380VDC, which then goes thru the push-pull step down via a HF transformer, and finally rectified back to LVDC by shottkies, yes.

I'm not sure what exactly to tell you on your switch issue, tho the knee-jerk reaction going on what's given is that it sounds like they were avalanching from inductance. You didn't specify whether you were using snubbing or not, but that would be my guess... it was either insufficient or not present at all. And you're right, they don't like that hehe

Steve
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Offline lighthunter

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Re: My Scratch Pad
« Reply #475 on: May 20, 2017, 04:19:41 PM »
You are right! i didnt think there was enough inductance in the wiring to make a difference. From the 1 minute i spent trying to come up with inductance of 200 feet of parallel 12awg conductor i came up with 460uH. While that may not be exact, i put it in circuit simulator and came up with these two screenshots. With/without snubber.
LH

Offline MadScientist267

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Re: My Scratch Pad
« Reply #476 on: May 20, 2017, 05:01:58 PM »
Hehe, yep that'll do it lol
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Offline lighthunter

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Re: My Scratch Pad
« Reply #477 on: May 20, 2017, 09:52:34 PM »
Ok now you have me curious about pfc. I've known about power factor for years but back when i learned what it was it referred to current out of phase with voltage causing something called apparant power and real power. A perfect power factor occurs with a resistive load where the voltage and current in load are in phase. A shift in the direction of capacitive or inductive involves apparant power such as connecting a capacitor directly across ac line. No real power is used, it is all apparant power therefore the power company will charge you for electricity used when you get no benefit. I can understand that. Now when it comes to an smps such as you have built...

Typically the 380v dc is arrived at by mains connected rectifier charging a bank of capacitors later used by a high frequency primary driver. So instead of mains current being sinusoidal over the full source voltage waveform, the mains current is more like a short duration pulse which the power company can charge you for the full duration and you are only using 50% of that.

So i get it that its a power factor problem but not inductive or capacitive ????   

Also how would you correct it ???

And why would you care??? Does it in reality waste power or does it just cause inaccurate billing? And dont the new smart meters compensate?

Just crazy thoughts, not necessary to ans all of it. Thanks in advance!

LH

Offline MadScientist267

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Re: My Scratch Pad
« Reply #478 on: May 21, 2017, 03:48:25 AM »
Haha All good questions... I'll do my best...

First, the older doubler method results in a no load voltage of about 320V across the caps, which dips quite a bit under heavy load, just as any unregulated supply does, only worse because of the "half wave nature" of a doubler fed by sine.

In active PFC, the 380V point however is a set point (regulated), and is typically chosen to be above the older doubler scheme, but presumably only by the necessary amount to accommodate the nature of boost converters, as this would make the PFC more or less a "drop in" replacement for the doublers in tried and true designs (which is exactly what happened in this case). If someone knows something to the contrary, by all means, as that's just speculation on my end.

The exact voltage isn't critical when it's used in this way, provided the MOSFETs used both for the boost converter and the main converter that follows are adequately rated/snubbed. It's usually in the 360-380 range (the charger actually reads something like 376V or so, sagging only slightly under load, down to around 372-374). Many times, the reservoir caps used (electrolytic) are rated for 400WV, so it will of course be below this.

The margin above 320 is to accommodate the 240V mains countries, without needing to manually select the voltage with a physical switch like on the old supplies. A boost circuit is not capable of producing a regulated output that is a lower voltage than it's input, because the DC path from input to output has no switching components in series in between (only an inductor separates them). To accomplish high PFC, it must always be regulating, so the target voltage is set higher than the peak AC voltage would normally reach (240 * 1.404 = 336.96V). Why is it called "320"? Nominal? Anyone? LOL Anyhow...

The boost converter is set up slightly differently for PFC than for typical DC usage, but for the most part, this is mostly at the cap used at the input. Instead of a relatively large electrolytic or tantalum, usually a much smaller value metal film cap of some variety is found in its place, immediately following the mains rectifier bridge. This is because it needs to be able to track the 100/120Hz rectified sine rather closely for the PFC to reach as close to unity PF as possible. Ideally, for phase distortion considerations (which counteract the active PFC with capacitance on an otherwise "resistive" load), it wouldn't be there at all, but the boost topology needs it to work correctly.

To accomplish the PFC, the boost converter more or less functions just like it's DC counterparts that you're (hopefully) already familiar with. It targets an output voltage, varying it's PWM as required to maintain regulation, as the input voltage rises and falls over the rectified sine, and load on the output changes. The overall pattern this results in is near maximum duty at the beginning and end of each sine pulse, with the lowest duty being seen at the crests of the waves. Load at the output causes the overall duty percentages to increase, with most of the difference being seen toward the crests.

The result is the entire wave produces output power, and not just the crests as in the doubler scheme. The loading effects this has, as I'll get to next... In a nutshell, the upstream source doesn't experience the disturbances that cause distortion of the sine.

Why is this important? Well, the problems that a simple doubler scheme cause are a little bit different in part from the voltage/current phase issues seen by things like directly mains powered transformers and motors... the main difference being that it introduces wild harmonics back into the source, that can't be controlled and compensated for by legacy L/C correction schemes. This is largely a "grid phenomenon" (meaning it is easier to "overlook" on smaller scales such as local generator feeds and the like). As SMPS gained popularity and presence on the grid, the distortions increased, and began posing problems to the infrastructure that again, passive PFC (within the grid) could not correct.

The other issue it causes, while different in originating nature, has the same end result - increased need for peak current handling. With SMPS (or countless, dozens at least) in every house on the planet pulling hard peaks at the crest of each wave, the impact on the grid is non-trivial. This is the more "visible" issue, in that the effects scale from single unit to the millions, with an even greater effect than the harmonics...

Let's take an SMPS that draws 1000W (for round number purposes) and ignore efficiency considerations for this example to keep the math cleaner, as it's a completely different concept.

It only *needs* 8.3A at 120V in doubler mode (or 4.15A at 240V in full bridge mode), but can, at the crest of the waves, draw current on the order of multiples of those during the peaks. Double, triple, quadruple even, and up. So let's play right down the middle and say the current spikes are hitting 3x average power used by the load... and rile the chip up... 1kW *average* power going in, 1kW coming out... but that's not what the upstream source needs to be capable of; it's seeing the need to provide a 3kW spike, even if only for a brief moment every cycle.

It is this spike of current multiplied by the instantaneous voltage within the "window" at the crest that becomes your "apparent power", and the upstream source, whether it be grid, generator,  or inverter, must be able to provide it while it's being drawn in order for the SMPS to feed it's load.

With PFC, the entire wave is supplying current to meet the actual power requirements of the load on the other side of the SMPS, the effective result is that the upstream source sees a mimicked resistive load, which has a perfect theoretical power factor (translates over to 100% "real power").

The harmonic distortion and behavior of the current spike are interdependent, in that the harmonic distortions induced in the upstream source are a result of the impedance of this source, and the distortions lead to further complexities that manifest as further disturbances in the current spikes, that result from the crests of the waves changing position, amplitude, and duration.

In the case of a smaller scale system, while the distortions still exist, the "round robin impact" is somewhat subdued, as the peak current demands can become the dominant problematic issue (by tripping fast acting overload protection schemes such as hiccup) before the distortions can cause problems, but not always. This is largely dependent on what types of other loads are also present within the system, and the impedance of the source. Generally speaking however, the main point is that "the grid will just keep on giving until something pops, and they'll just bill you for it, your generator and inverter will not".

(Ok, so generators and inverters can pop too, but that kind of popping is a massive PITA to "reset", and can come with a hefty "bill" of its own) :o

Hopefully, I've answered your questions with this, and didn't just add more confusion lol...

Steve
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Offline lighthunter

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Re: My Scratch Pad
« Reply #479 on: May 21, 2017, 10:11:49 PM »
Very good explanation, quite a few things i had not thought about. The Scientist part of your handle is accurate i'd say  :).   So is this why the newest miller welder line, (continuum) is using over 1000v in the power supply? This fact has puzzled me for a year or so now because the previous models were rectifying 3phase 480 to something like 640DC and then using igbt's at high freq to cntrol power. The newest line steps 480 3phase up well above 1000v before they use a very late technology igbt i cant remember who makes it but i know its 1400-1600v rated. I long for the days when you could flip the switch on and start welding. You can go get coffee before these are ready to go.

Anyways, i thought the reason for the high v was for efficiency improvements and "because they can" After reading your explanation i'm betting its all about pfc and the utility and of course more money from the customer.    These things really blow up hard when they crossfire. Though weve had some hardware failures its not miller's weak point, the power units are fairly solid for as much as is happening in them. Software is another matter, always updating...related to microsoft i guess :)   

Thanks again for explanation, good stuff!
LH