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12AX7
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Electrolysis power supply
The long awaited(?) design is here. 
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/H...
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/H...
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/H...
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/H...
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/H...
Over 90% efficiency, >0.99 power factor, 5V at up to 100A output. Adjustable and programmable voltage and current limits. Digital control,
timing, charge integration and so on.
Tim
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quicksilver
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DAMN! Bro' did you work up that schematic? That is a really well done job!
When you have something of high current, you really can't work that out on a breadboard (the little clips will fry, it seems) -- So how do you work
out prototypes?
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12AX7
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Easy, you build it. 
This is my senior project so I shall release it under GPL.
Funny thing about those little clips (alligator clips, that is), on one occasion I had the oscilloscope probe ground lead clipped to a capacitor.
Turns out it had been touching both leads of said capacitor, thus "shorting" the output. It cleared this fault quite effectively at around 0.2V and
50A, coincident with a little puff of smoke. Bye bye capacitor lead.
Tim
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quicksilver
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The large toroids catch the eye. Those are not "store bought" are they?
Have you begun to "light her up" and try for a week or so test?
I have a 5Vdc switching supply that I bought surplus. It needs two high end fans to draw the air over the contents. In your design I see no provision
was made for strong cooling. Does it not need it or has it not been presented in the initial design?
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watson.fawkes
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Quote: Originally posted by 12AX7  | | Over 90% efficiency, >0.99 power factor, 5V at up to 100A output. Adjustable and programmable voltage and current limits. Digital control,
timing, charge integration and so on. |
Good work. I have some questions. Naturally.
What kind of pulse frequency are you using on the PWM? I see you're using a gate drive transformer, so it must be reasonably high. What's the typical
duty cycle? What's the magnitude of your output ripple?
Your output filters are in the schematic as three turns and four turns, but I see a pair of five turn ones in the picture. Was this construction
tuning, or what? I assume that this must be related to the pulse frequency.
I have to admit I don't understand the power factor correction circuit, but I'm assuming that's because I don't have time this morning to read the
data sheet on the FAN7527 you're using.
You're taking OUT1 and OUT2 for the rectifier section from the first gate driver of its pair rather than from the PWM controller directly. Is this
just a matter of buffering the PWM output? Or is there some zero-crossing timing subtlety going on?
What are the decoder outputs for? If I had to guess, I'd say "for inspection during code development", but I can just ask you instead.
Is there an ICSP header on the prototype board? I don't see it. Or is it taken off as discrete wires? I mean, your microcontroller isn't socketed.
Brave man. Not even any optocouplers.
I assume that signals CFB and VFB are those for current and voltage sensing. But then what's VCOMP for that generates the actual analog signal into
the controller?
I don't see an analog crowbar circuit. How are you dealing with an output short condition?
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12AX7
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On closer inspection, you should also notice there's none of the familiar PFC parts on that board, nor a 40 pin DIP and its support hardware. That's
just the PWM board (drawings 2 and 3). 
This is the PFC board,
and this is the MCU board.
1. The TL598 oscillator runs around 240kHz, i.e. the output is 120kHz. Duty varies from 0 to 43% (per output), controlled by the voltage and current
error amps. I haven't measured output ripple yet but it should be small.
2. Turns out I could fit 5T on there, so I did. More inductance, the merrier!
3. FAN7527 is a typical PFC chip. It operates by turning on the MOSFET switch until inductor current reaches a certain peak value, then turns off
until current falls to zero, where it restarts. By varying the peak current, the average (= 1/2 peak, since current takes on a triangular shape) can
be varied. A multiplier circuit mixes supply voltage (i.e., humps of rectified line voltage) with the error signal, thus modulating currect draw by
voltage. Since voltage and current are proportional, the power factor is 0.99 or better. If a straight rectifier and filter capacitor were chosen,
PF might be 0.5 or less! Finally, the error amp, which must be slow enough that it doesn't react to line frequency, regulates the average output to
406-412VDC over all supply and load values.
4. OUT1 and OUT2 must be inverted -- analyze the circuit carefully to see why this is so. The first pairs of transistors accomplish this. The second
pair inverts it again, so the gate drive transformer is driven in phase. Hmm... I suppose the second stage isn't really necessary, due to the way the
GDT is wired. Oh well.
As for delay, ideally the GDT gets driven first, as it has more delay (20ns lost through the transformer, 50ns at the transistors, another 40ns or so
at the OPT). The total skew isn't too horrible as shown (~200ns), which may increase switching losses.
5. The decoder outputs are intended to control process equipment, for example if you programmed a sequence to drive 10 faraday of charge, then
activate a series of pumps to introduce a new batch of electrolyte. The PWM output is intended for higher frequency switching, like if you added a
phase reversal circuit in order to do high-throw electroplating.
The program is not currently setup for external inputs, but as you can see, a few ADC inputs are available which could be buffered to, say, a pH
probe. A secondary program might be setup to control pH via the decoder outputs, operating an acid pump for instance. In this way, a completely
automated chlorate cell could operate simply by adding raw materials and performing maintenence as required.
6. The ICSP header was changed to a 6 pin header, for use with the AVR ISP mk II.
7. Vcomp leads to a compensation capacitor, stabilizing the feedback loop. DC feedback is from the output (VFB).
8. No crowbar is provided to prevent voltage overshoot because in the intended use, this is not a problem. If you use this for digital logic supply,
it would be wise to add one, and also tweak the feedback loop to minimize overshoot.
The inverter is current protected (CFB and associated circuitry).
Tim
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watson.fawkes
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| Quote: Originally posted by 12AX7 | | On closer inspection, you should also notice there's none of the familiar PFC parts on that board, nor a 40 pin DIP and its support hardware. That's
just the PWM board (drawings 2 and 3). |
D'oh! I didn't even think to count parts.
Thanks for your responses.
I have a couple of comments, mostly about a device boundary for publication. First, I would recommend publishing with a crowbar circuit in place. This
is not for your personal benefit, or anybody else with enough experience to avoid shorting the output by accident, but there are plenty of folks
who'll want one of these and don't have that kind of experience and thus who, a fortiori, won't know how to design a crowbar or even know
what one is. If I build one, I'll put one in, just because I've got other folks around who aren't as experienced as I am.
Second, I'd recommend packaging the supply as just as supply and not as a supply-with-process-controller. Again, I'm sure this is just fine for you,
because you're intimately familiar with the control software and intuitively know what not to do in software. Other people won't know any of that.
Admittedly, this means you'd need a proper data interface, perhaps even USB, and some kind of protocol, and that's a chunk of extra work. But it would
improve resiliency of the supply as a separate unit that would just work and could be relied upon. What I'd do in this case would be to use a daughter
board as interface. That would allow for one board with buttons and a display and another microcontroller, and this board would be for completely
detached operation. Another daughter board would have a network interface. Etc.
I'd enjoy hearing from Swede here on how he'd integrate such a power supply into his existing rig, which already does a bunch of data capture.
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12AX7
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I still don't know what exactly you think "crowbar" means. A crowbar is NOT a short circuit protection device as you seem to imply. It is an
overvoltage protection device, which shorts the output brute-force, in order to protect any attached circuitry.
For example, a nominal 5V supply powering a bank of digital logic boards, which fail above 6V, would require a crowbar at about 5.5V to protect it
from surges. The fate of the power supply is of no interest because it's cheaper than the logic boards, though it would be useful to make the supply
handle such an overload gracefully.
This power supply is inherently current limited so it will handle a crowbar or other short-circuit fault gracefully.
As it is, the three boards stand alone and can be used effectively as such. For example, the PWM board can be used with a conventional line filter
and rectifier/doubler circuit for 120/240V operation, making it overall very similar indeed to a conventional ATX power supply. The downside is poor
power factor and two voltage input only (not universal input).
The PFC board can be added to improve power factor and accommodate any line voltage in the world.
The MCU board only provides voltage and current control signals to the PWM board, which can be supplied with potentiometers instead, thus making a
conventional regulated voltage supply with adjustable current limit. If programmable operation is not required, it can be omitted.
The power supply can be programmed on screen, no need for USB or whatever. The RS232 interface allows serial connection (which can be connected via
USB dongle, if you prefer USB) for control by remote computer. None of this requires knowledge of the internal programming, though the intrepid user
could reprogram his microcontroller using the internal ISP port. Microcontrollers can be programmed before installation, so the end user doesn't need
any knowledge of programming to use it.
Tim
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densest
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Very nice!
Are you going to publish PCB layouts or sell etched PCBs? They're the biggest
hurdle for most amateur builders. Getting 10 PCBs made is usually only a little
more expensive than getting 1 
How did you calculate loop stability over the 10:1 output voltage range? Or did you
do a worst case for the highest gain?
BTW I have a dozen or so pairs of TSF 8040 material 42-21-15 E ungapped cores and a hundred or so bobbins with pins to fit. I think they'd work for
this design. Electronic Goldmine was selling similar cores with a gapped center recently which could work for the PFC inductor.
[Edited on 24-4-2010 by densest]
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12AX7
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Calculate loop? Wazzat?
^ In fact, just last quarter I took a control system analysis class. Stuff like Routh-Hurwitz and root locus. Outdated, abstract and utterly
useless.
I haven't tested transient response yet. Adjustment entails substituting values for compensation capacitors, adding a zero (R+C), etc. I have tested
the PFC controller and discovered it is unstable with the PWM board as load, so it needs adjustment. I have the knowledge to evaluate a control loop,
but having learned to adjust them by the seat of my pants, I am quite satisfied to continue doing so.
Stability should be fine over the entire voltage range. Nothing in the system changes with respect to voltage. The inductances change slightly at
high currents (dropping by about half at 100A), causing the filter's cutoff frequency to rise by about 1.4x. No big deal. The only problem is the
discontinuity when duty approaches zero, which causes hysteretic behavior and oscillation. This is inevitable.
Your cores seem to be:
http://www.tscinternational.com/8040graphpage.pdf material
http://www.tscinternational.net/422115.html TSC store
which I guess is like a 3F3 or type 43 medium permeability ferrite.
Ewwww, the TSC store homepage has a rather annoying MIDI file on it. :-!
The 42-21-15 appears to have overall dimensions 42mm x 21 x 15.44 mm, a 30.32 x 9.13 mm winding window when assembled, with l_e = 97.23mm, A_e = 181.5
mm^2, V_e = 17.644 cm^3, W_a = 276.9 mm^2, m = 89.6 g and A_L = 6.57 uH/t^2.
The core I got is almost twice as thick, so you'll need to either ~double the number of turns (with copper strap, you don't want that), double up the
core (can't use the same bobbin), or double the frequency (unwise, although not impossible).
One thing you cannot do is use two transformers, because the secondary winding must have extremely low leakage inductance from end to end. As
constructed, a transmission line is formed between the circuit board ground plane, going up through the transformer, enclosing very little area =
generating very little inductance. Low inductance is necessary because, when one side of the synchronous rectifier turns off, stray inductance will
generate a flyback pulse, and when that stray inductance is charged to 100A or so, a lot of power will be dissipated by the snubber, trashing
efficiency.
Tim
[Edited on 4-24-2010 by 12AX7]
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Rosco Bodine
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For the cannibals amongst you, there may be a tasty morsel in this
http://cgi.ebay.com/NJE-5VDC-200A-Power-Supply-5-Volt-200-Am...
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chief
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At least in some countries you can't just market anything that runs on mains power ...; you would need permissions, need to be a person who can get
permissions, would need to have the design approved etc., at least in Germany ...
==> So for electric circuitry the only thing one can sell is something that runs on battery or incorporates a commercial power-supply ...
======================
But you might sell it as "functionable artwork", "only to be operated by qualified personnel" ...
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Mr. Wizard
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| Quote: Originally posted by chief | At least in some countries you can't just market anything that runs on mains power ...; you would need permissions, need to be a person who can get
permissions, would need to have the design approved etc., at least in Germany ...
==> So for electric circuitry the only thing one can sell is something that runs on battery or incorporates a commercial power-supply ...
======================
But you might sell it as "functionable artwork", "only to be operated by qualified personnel" ... |
Seriously? Here in the US, we barbarians are allowed to pull whatever we want out of the mains, as long as we don't pop our breakers, and pay the
bill. There are limits; if you start sending spikes back up the line or causing problems with radio interference, somebody will tell you to stop.
Wiring installation codes are followed, but nobody would ever think about asking for permission to install a damned electrolysis power supply, welder,
or even a kilowatt radio transmitter, provided you were licensed to operate one.
It's a different type of outlook I guess.
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12AX7
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In the E.U., you just slap a CE sticker on it. No one ever bothers to ask... just look at all the Chinese crap that obviously doesn't satisfy CE regs
yet has the hologrammed stickers and everything. In China, hologram stickers are a few bucks a roll.
Tim
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Contrabasso
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CE in reality means China Export, except for some curious people called Eurocrats!
You should have CE for when you place a product on the european market. Not a design for consideration.
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quicksilver
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Remember the TV shows that illustrated what Underwriter Labs did in tests? It was around the time we would watch Mutual of Omaha's Wild Kingdom.
If I do buy electronics I really make an effort to buy US, Japanese, or EU stuff. If anyone is interested I have some really good places for Lamda
Power Supplies (PM me). I've learned that I have a tough time getting a PC board as neat & clean as 12AX7: but I get better @ hiding my work in
boxes.
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watson.fawkes
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| Quote: Originally posted by 12AX7 | | I still don't know what exactly you think "crowbar" means. A crowbar is NOT a short circuit protection device as you seem to imply. [...] This power
supply is inherently current limited so it will handle a crowbar or other short-circuit fault gracefully. |
Well, OK. I use the term "crowbar" in my head to refer to both over-voltage and over-current conditions. I was indeed thinking
primarily of over-current.
Have you tried using the supply as a welder? This is the case I was most concerned about, that an inadvertent use of one in this mode would cause
something Horribly Wrong to happen. I mean, 5V @ 100A makes a good resistance welding supply.
More generally, I don't understand why it's inherently current limited, but then again I've not spend any significant time working with a synchronous
rectifier. I can see how the output filters give in an inherent impedance at f > 0, but not how it's limited at DC. Is it in the PFC circuit?
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12AX7
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The inverter is always switching, so it is always sending current into the OPT and therefore inducing current in the current transformer. This feeds
back to the current error amplifier, closing the loop in current.
Tim
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watson.fawkes
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| Quote: Originally posted by 12AX7 | | The inverter is always switching, so it is always sending current into the OPT and therefore inducing current in the current transformer. This feeds
back to the current error amplifier, closing the loop in current. |
OK, thanks. It helps to have time to read
the chip sheets. The piece I was missing is that it's the TL598 and its current fixed point that's preventing over-current. I had been looking for
something in the discrete part of the circuit.
[Edited on 28-4-2010 by watson.fawkes]
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densest
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I'm curious that you didn't use the OC pin on the half-bridge stage - the HV cap after the PFC holds 30+ J.
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chief
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How complicated ...
==> How much can you electrolyze with this ? 5V == 1 cell ... ... ; with the
100 A you can make 1kg of chlorate each day ...
=============
So my idea would be to construct some serious rectifier and have a big transformer ..., with enough voltage for several cells ... :
==> The rectifier, if capable of 100 A, will do it also for 20-30 Volts, which gives 4-6 cells, capable of electrolyzing 5 kg per day ... (chlorate
anyhow only as example ...)
==> or maybe a 100$-welding-supply, of the switching type, would do well: I has maybe 40-80 Volts at a lot of amperes ...
Anyhow a 10-liter cell with 80 A will be constantly sub-boiling, evaporate half of it's content per day, spray a lot of salt anywhere etc. ...
==> So more cells need to be run, in series ...
A good old transformer is much easier to setup with a rectification, also mor failsafe ...
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12AX7
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| Quote: Originally posted by densest | I'm curious that you didn't use the OC pin on the half-bridge stage - the HV cap after the PFC holds 30+ J.
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1. Output Control is a half wave / full wave toggle. When enabled, the outputs are driven in parallel. This is useful for buck, flyback and half
wave converters, but useless for full-wave (as this is).
2. Yes, the HV cap holds a substantial charge. I don't see where you were going with that...
| Quote: Originally posted by chief |
So my idea would be to construct some serious rectifier and have a big transformer ..., with enough voltage for several cells ... :
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Ah, but then you completely lose ALL controllability, plus your power factor is down in the sewer!
| Quote: | | ==> or maybe a 100$-welding-supply, of the switching type, would do well: I has maybe 40-80 Volts at a lot of amperes ... |
But it probably also has bad power factor (I don't actually know if inverter welders have PFC, but you will neither find a new inverter welder nor one
with PFC for the sum of $100!), a completely different controller (maybe current regulated to some extent), and none of the fancy schmancy features,
like automated setpoints, timering and charge integration.
Tim
[Edited on 4-28-2010 by 12AX7]
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densest
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Tim - sorry, I naively read "OC" as "overcurrent" which is how some manufacturers have labeled their chips.
My guess was that the cap is big enough to fry FETs. I'm painting my face very red since I overlooked the current transformer feedback  switching back and forth between diagrams. I'm assuming the time constant is small,
& the settings limit switch current to 5A or less, so all is copacetic. My apologies.
As for compensating the loops, I've used SPICE with some success. Some of the IC- manufacturer provided versions model the AC behavior of the
switching chips well enough so that all one has to do is break the feedback loop & get a Bode plot of the transfer function. Play with the
compensation components until it looks right. Without the IC model, it's a little trickier to model the loop gain & so on from the chip specs, but
still doable.
[Edited on 28-4-2010 by densest]
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chief
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Whats the big deal with the power-factor-correction ?
==> Any transformer can just be corrected with a capacitor ...
In the good old days they used mains-voltage, divided through a lot of cells ...
==> That's not even the worst idea, if it can be handled safely ...
==> because with a lousy 10-A-rectifier-bridge you can send those 10 A through 50 or more cells, giving 5+ kg of chlorate each day ..., on almost
no electrical equipment ...
Maybe on such small currents even carbon-electrodes would last a while ... : Does anyone know ?
[Edited on 28-4-2010 by chief]
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densest
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@chief - the PFC term is only partially correct - it's short for power factor & harmonic current correction. A motor, transformers, or any other
linear device (like a tungsten light bulb) draws a current which is exactly proportional to the line voltage. That only takes adding a capacitor or
inductor to make the current drawn from the mains exactly in phase with the mains voltage.
Anything nonlinear, like a rectifier, passes current nonlinearly with respect to the applied voltage. Typical "linear" power supplies with a
transformer, rectifiers, and filter capacitors draw current in spikes at the peak of the input voltage. Those spikes cause problems in a number of
ways. Mathematically, the current wave is equivalent to the line frequency with large amounts of harmonics at higher frequencies. The power system is
not, and never will be, designed to handle that current. The harmonic currents can cause transformers and wires to overheat, interfere with power
switching equipment, and cause other devices connected to the mains nearby to fail. Power providers have had to increase generating capacity to
ameliorate this a little at large cost and no return.
With these problems in mind, the EC requires that new electrical devices must draw essentially sinusoidal current from the mains. The "PFC" label is a
shorthand for fixing power factor & harmonic currents, and overlaps with RFI/EMI suppression.
Even if there is no capacitor after a transformer and rectifier, I'm not sure that current through electrolytic cells is linear. If an
energy-consuming reaction has a threshold voltage, then up to that voltage a current would flow proportional to the mobile ion density in solution,
but above that voltage current would also flow to power the reaction. This bump of current is what the so-called PFC circuits are supposed to prevent.
As I mentioned earlier, large amounts of this nonlinear current can cause transformer overheating.
One further point - rectified mains voltage is either half a sine wave or a sine wave "folded" so the pulses all go in one direction. That causes the
cell to see peaks and valleys of voltage. If there are multiple cell reactions with different voltages, the mix of reactions could surprise you if you
think that the cell is seeing a constant voltage, especially if there are reverse reactions which take place below a certain voltage - the cell would
see 0 volts 50/60/100/120 times a second. That could damage electrodes or reduce yield.
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