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Author: Subject: PC PSU to laboratory PSU
Xenoid
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[*] posted on 19-1-2008 at 10:53


@ Aqua_Fortis_100%

I have only wired up this circuit in an experimental fashion at the moment, just to "try it out". To increase the current, I used two 2N3055s wired in parallel (I just happened to have two mounted on a heatsink), and was able to control 0 to 8 amps into a "dummy load" of 0.4 ohms. To wire 2N3055s in parallel I believe you need to put a very low value resistor (say, .05 ohms) in each emitter circuit so they turn on evenly. The TIP41 got hot only at the very top of the setting (so hot, I burned my finger, it wasn't on a heatsink). I haven't got any further than this, at the moment. because I've been so busy with processing various solutions, and "tending" my cells. I will certainly go ahead with this, I think it only requires a little circuit "tweaking". It is a very useful, simple and cheap addition to a computer PSU.

Perhaps someone "more skilled in the art" could comment on the circuit (12AX7, Rosco, ....)
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[*] posted on 19-1-2008 at 11:54


Exactly what circuit are we talking about?



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[*] posted on 19-1-2008 at 12:12


@ 12AX7

The simple circuit for current control of computer PSU posted by Aqua... bottom page 8 of the "KClO3 by ...." thread.

Just below where you told me to "point my nose down away from the clouds"!

http://www.4shared.com/file/32991572/7dcdf563/Regulador_0_a_...

It needs a bit of a tweak !

Actually, I guess a MOSFET would be better in this application, and control it with a simple voltage divider network.

[Edited on 19-1-2008 by Xenoid]

[Edited on 19-1-2008 by Xenoid]
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[*] posted on 19-1-2008 at 14:07


Oh, that's on my page 14 (most recent). Just what posts/page settings does everyone think they use here?...

A .RAR wouldn't have been necessary if the originator had any minutae of sense with regards to photography. What a horribly sized photo, and a line drawing saved as JPG? Sheesh! I was able to salvage them:

http://webpages.charter.net/dawill/Images/Adjustable_Regulat...

Edit: big image made link.

Drawn with my circuit symbols,



Picture:



That power supply is operating, not only open frame without a fan, but has no RFI filtering as well?! :o Yeesh...

Anyway, a regulator it is NOT. It appears to be a nearly darlington emitter follower, which since the TIP41 is supplied from extra voltage, explains why it gets so hot. (A 2N3055 might need around 0.3A base current for an output around 4V, causing the TIP41 to dissipate >2.1W, definetly needing a heat sink.) The rheostatic control method sucks, especially if the pot goes open circuit (as pots are prone to -- ever had a stereo with a scratchy volume knob?), putting full voltage on the output. The 1k resistor makes for a whacky control curve -- why couldn't the designer (so to speak) settle for a single linear potentiometer?

Far too much current can be supplied from the 100 ohm resistor -- if the TIP41 base is at 5V and the pot is fully open, there's about 80mA base current, and respectively, about 2A collector current flowing, for a dissipation of 14W!

The circuit obviously doesn't regulate, it only adjusts. The output impedance is roughly Rin / hFE, which is about Rin/400 after both transistors. For a Thevenin resistance of 90 to 600 ohms (highest in the middle of travel), the output resistance ranges from about 0.23 to 1.5 ohms, which is on par with typical load resistance: hardly a regulator!

To use a MOSFET in the same circuit, you can certainly control a large power MOSFET from a potentiometer, using the extra voltage supply to counter the gate offset voltage. But remember that power dissipation is still a problem, parasitic oscillation becomes a concern (at the very least, put a gate resistor of say, 100 ohms, as close to the gate terminal as possible), and output resistance is still nonzero, in this case being roughly 1/Gm, which might be 1/10 ohm or less -- better, but still not good enough to call regulated. At least you can saturate it effectively (7V should be enough for most MOSFETs to saturate to near rated Rds(on) at the currents we're talking about).

Where paralleling is concerned, BJTs are better, given an emitter resistor per (0.1 ohm, 10W is typical for something like 2N3055). MOSFETs have much more dramatic differences in Vgs(threshold), as discussed earlier, the best solution being an op-amp per.

In regards to electrochemical control in general...I use a big honking resistor. I have these things. And they work. Quite well.

Tim

[Edited on 1-19-2008 by 12AX7]




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[*] posted on 19-1-2008 at 14:25


.......The 2N3055 isn't reliable because that is very weak comparing with others and gives less current range.. ...........

This is just the circuit I've been looking for but in the 20 amp range @ 12 volt.

IIRC the 2N3055 in the TO3 package is good for absolute maximum 15 amps or so.

I have a few of these laying around and it seems that on a decent heat sink with a fan that maybe 10A continuous, should be attainable, given a reasonable voltage drop.

Aqua Fortis....do you have a schematic of this circuit as well as the point to point
diagram which you so kindly provided? Not that it's any trouble to derive myself, just wondering because I noticed your 4shared folder has multitudes of files and my Spanish ain't any good, lol, more like non-existent exept for the similar words with the O's on the end, lol.
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[*] posted on 19-1-2008 at 15:12


@ bio2

Tim has reproduced the circuit, above, and a link to the point to point.

Tim, I realise it is not a constant current regulator, I pointed this out in another thread. But a simple circuit like this is ideal for use with a bunch of small chlorate cells where you want to manually adjust the current, from day to day, especially for testing purposes. It SAVES fiddling around with high wattage resistors to get the right current/current density for experiments!

BTW it is not Aqua's circuit, he only provided the link, don't blame him ... :)

Post/page settings? I haven't changed mine, so I guess they are default!
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[*] posted on 19-1-2008 at 16:29


It would probably work out better to use an LM334 three terminal constant current source with maybe a 5K pot across
it for adjustment of the current , which is used as the base current for the first transistor in a NPN Darlington pair . The LM334 would supply base current to a NPN Darlington pair , the LM334 and NPN Darlington pair being supplied from the +12V rail , and the emitter of the Darlington pair then driving the base of the NPN Output transistor whose emitter is connected to the load and whose collector is connected to any + supply rail . The load would be between the emitter
of the output NPN and ground .

The load current would simply be product of the hfe values , the transistor Betas of the three (or more) transistors in the stack multiplied by the set current for the LM334 .

Now that's current amplification :D via ye old stacked emitter follower .


[Edited on 19-1-2008 by Rosco Bodine]

Attachment: LM334 constant current source.pdf (759kB)
This file has been downloaded 677 times

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[*] posted on 19-1-2008 at 16:46


Quote:
Originally posted by bio2:
... your 4shared folder ...


Please , note , this is the thing I'm trying to say all times : This ISN'T my circuit , ISN'T my photo and ISN'T my 4shared folder.. I just don't have one.
Xenoid understood this and also has already replied your comment.

And yes, Tim, thanks by the comments.. Criticism is what is needed for that circuit and all other things, since almost nothing is improved without it .

Quote:
Originally posted by Tim :
A .RAR wouldn't have been necessary if the originator had any minutae of sense with regards to photography. What a horribly sized photo, and a line drawing saved as JPG? Sheesh! I was able to salvage them:

http://webpages.charter.net/dawill/Images/Adjustable_Regulat...


Tim , please, note , that image/circuit the original author just made quick & dirty , just to reply my doubt at local "orkut" eletronics community forum.. Not to post on this international forum :D Because of this it wasnt made in any fashion , is just simple. So anyway I just posted that link to see if is anything wrong with that circuit and ways to improve/change it.. And now as you and others give the viewpoints , I will be more carefull of what I'm doing with my cell suply/circuit , as seems that was quite controvertial..

Quote:

That power supply is operating, not only open frame without a fan, but has no RFI filtering as well?!


IIRC , as I said in "KClO3.." thread, this was a QUICK & dirty test , where the author just used things laying around him , not to made anything special like chlorates cell , but just to test that circuit , so you can note that the TIP wasnt on any heatsink , the 2N3773 was on a small and not proper heatsink , the small lamp that he used to test and also the poor open frame PC PSU , all that for a quick test..

Quote:
Originally posted by Xenoid :
BTW it is not Aqua's circuit, he only provided the link, don't blame him ... :)


Oh god.. Maybe was better if I just dont have posted that link.. :( I dont like bothering anyone in any discussion, even more that serious like this..

I just talked here because Dann2 asked what was written.

Again, please sorry guys.



[Edited on 19-1-2008 by Aqua_Fortis_100%]




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[*] posted on 19-1-2008 at 17:02


I've just had another look at this circuit, not sure what I was doing wrong last time!

I used 2 2N3055s in parallel and was able to supply 0 - 20 amps into a .15 ohm gazillion watt carbon gouging rod resistor (dummy load). At the 20 amp stage the TIP41 was pulling about 2 amps, needless to say I didn't leave it at this setting for more than a few seconds. I left out the .1 ohm equalising resistors in the emitter legs of the 2N3055s and they still seemed to be getting equally hot! You'll need a big heatsink for each 2N3055 or fan cooling. I changed the 100 ohm resistor to a 150 ohm.

Works well, just what I wanted!

Edit: Hmmm.. strange things happen at high currents .. :o

With the 100 ohm resistor replaced with a 680 ohm, and using a 5K pot. and a reasonable quality analogue 20 amp meter. I got about 0 - 20 amps full adjustment of the pot. with the gouging rod load. At 10 amps the two 2N3055s on the same heatsink were quite warm and the TIP41 was pulling 200 mA, at 15 amps the TIP41 was pulling 510 mA and at 20 amps the TIP41 was pulling 970 mA. The TIP41 was on a small heatsink and didn't seem to get overly warm!

[Edited on 19-1-2008 by Xenoid]
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[*] posted on 19-1-2008 at 17:27


Thanks AX7 for the schematic. I was also wondering how this circuit could function
as a CC regulator.

You said.

.......in regards to electrochemical control in general...I use a big honking resistor.........

I've been using a piece of NiCr wire with adjustment by a sliding alligator clip.
Crude yet effective high power pot. At 15-20 amps it glows pretty bright, melting
wire nuts and welding the copper to the spring, lol, in my cobbled together test rig.

Is there a simple (low parts count) way to drive some high current transistors
from a LM317 wired as a constant current regulator to achieve a CC output?

Maybe some type of SCR circuit would be preferable however as I want to scale this up to 40-60 amps eventually.

The circuits I have seen for doing this (National Semi AN) are a little complex.

They use paralleled PNP bipolars driven by an LM317 but the current is only about
5A in the one I can't seem to find right now on National Semiconductors site.

You probably know the circuit I mean it's been in their AN forever but seems they have revised the LM317 Application Notes layout.

The problem I have been having is that it takes hours for the cell to fully heat up with
a consequent rise in current. Then depending on the ambient temperature it
may trip out on a hot day as I am trying to max out the PS output.

So the goal is to limit the current to the maximum the PS can deliver continuously
so the cell current is independent of temperature fluctuations.
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[*] posted on 19-1-2008 at 18:40


Why obsess over the LM317? Not an appropriate choice here.

My cell rises to a temperature and current suitable for the ballast resistor (which is around 0.03 ohm) and supply voltage, which is just fine with me. You might preheat the solution, you might watch it more closely in the first couple of hours, you could even put a cooling bath around it, etc.

A purely electrical solution would certainly turn up a more or less constant-current supply. In that thread, I would go with a N channel MOSFET or PNP pass transistor with a series current sense resistor. An op-amp controls current, and the voltage drop can be quite small (especially with MOSFETs).

SCRs have no place here. You could build a phase controlled power supply (I've seen them before: quite beefy with the power transformer and filter choke!), but that's obviously no use after a low voltage DC supply. The only use an SCR finds in a DC supply is as a protection crowbar, to precisely blow a fuse, thereby protecting the sensitive, say, logic circuit which follows.

Edit: concerning my criticism, it was directed at whoever created said media. I don't particularly care for badly adjusted photos, and obviously, I'm not afraid to say so. If it was not yours (Fortis), you probably agree with my criticism; if it was yours, then I trust you got the message and will be more careful in the future. In either case, I thank you for accepting it. Criticism is one of those things that's ever so useful, but hard to apply, and even harder to accept!

Tim

[Edited on 1-19-2008 by 12AX7]




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[*] posted on 20-1-2008 at 00:32


I wonder why people do not want to experiment with simple (or simplified) switchmode circuits. Everything that goes switchmode ends always so damn complex that no one ever dares to repeat original design.

About constant current supplyes: LM317 is ideal to 1 amp. I have not tryed to expand it with transistor so i can not comment how good this is. I suppose it could also be paralleeled - not that mad idea considering its cost.

I have noticed that simple constant current supplyes with FET and resistor or with trans and zener do not hold current that constant. It seems to depend a lot from junction temperatures (or whatever) and if one goes to 5 amp or more changes with time are more than just noticeable.

Opamap and transistor based constant current supply is simple to build but these tend to oscillate at some currents and load impedances - especially if darlington is used.

Btw there are DC to DC converter circuits that use thyristor based oscillators but for some reason they are not widely used (or known).


[Edited on 20-1-2008 by chromium]




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[*] posted on 20-1-2008 at 06:03


Switchmode circuits can be very simple: all the complexity gets tied up in a chip. Take the UC3842 series for instance: current mode flyback converter. Just add MOSFET and a few resistors and capacitors and you have everything you need on the primary side. TL494s are very common in computer PSUs, which are only a step up in complexity -- though they do use a few more resistors in the process! Mostly it's that people are intimidated by the total complexity, not realizing the value of viewing it from a level of abstraction, a viewpoint which is valuable in reading any schematic.

The LM317 drops at least 1.25V, and more like 2.5V for any real application. That leaves only 2.5V from the 5V rail! Of course, the 5V rail needn't be used here, the 12V rail could be used at this current.

Constant voltage regulators do not parallel. Use a power transistor to bootstrap the extra current flow, as detailed in the data sheet. Constant current sources can be paralleled, though I don't know why you'd want to when the same premise can be applied.

Op-amp circuits only oscillate when the user doesn't realize the value of compensation -- something fundamental to any feedback circuit, which the user ought to already know!

Tim




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[*] posted on 20-1-2008 at 08:44


........Mostly it's that people are intimidated by the total complexity, not realizing the value of viewing it from a level of abstraction, a viewpoint which is valuable in reading any schematic..............

So true! I have often been originally intimidated by certain circuits I've built but when viewed as you say and taken piece by piece when assembling, they don't seem that complex after all.

Thank you 12AX7 for your input which I am considering for different applications and yes admittedly, I do tend to fixate on the LM317 due to it's extreme simplicity in CC control. They did used to make 3A and 5A units in the TO3 package in the past.

That being said, I recalled last night while considering how to control a 1200 watt cell I am starting to build ,what may well be the panacea for high output or otherwise
Constant Current control for electrolytic cells. The only simpler way would be the
series resistor but the method presented below is voltage independent, powers from the line and gives true CC control.

The old tried and true method of placing series capacitors in the AC feed to a bridge rectifier connected to the 120V or 240V house power is very simple and also bullet proof.

I use this method of CC control to charge batteries of any voltage at 6A from the line. It is reasonably accurate and is short circuit proof as well, with the voltage virtually collapsing under a shorted condition.

To prevent the voltage from going to peak without a load
another capacitor can be placed in parallel with the AC line downstream from the seriesed caps. Otherwise it's easy to get a very nasty zap if the load is lost
and accidental contact is made.

This method is elegant in its simplicity and the capacitors hardly get warm regardless of the voltage drop. The output is about 1A per 16 uF and I use some large motor run capacitors, the old oil filled type, that I have scavenged over the years. Old air conditioner carcasses are a good source for these with even a 1HP unit having 45uF caps or bigger. These old oil caps are very large compared to the more modern foil/polyester type and are virtually indestructible.

I have and excellent article from EDN that has all the calcs to analyze this type of set up and various improvements that can be made by simple modifications to the DC side of the bridge although it works just fine in it's simplest form using 1 cap (or bank) feeding a bridge. Unfortunately my disc drive is on the blink so I can't upload the article but if I am able to find it again on the net then I will provide the link.

I encourage every one to try this method. It is suitable from milliamps to many, many
amps. This method is often used to supply small consumer devices obviating the need
for a transformer. I suppose if one could get their hands on those large pole mounted power factor correction capacitors the sky is the limit!
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[*] posted on 20-1-2008 at 08:53


Don't use capacitors -- use inductors. Much more economical for large supplies, and capacitors make big current spikes when connected suddenly.

You can use Ls and Cs in a 60Hz resonant impedance match, with whatever characteristic you prefer (for instance, the output matching network on my induction heater goes from about 60VAC, 10A from the inverter to over 100V, 160A RMS resonant energy in the tank circuit), but without a transformer on the line, you will never have isolation. Line isolation is one of the primary reasons to use a transformer.

Incidentially, somewhere around here I have notes on putting "soft start" on a light bulb. You might figure a 1:1 match, since the 60W bulb wants 120V, and the thing operates from a 120V supply. Fair enough. It has to be resonant at 60Hz. It has to hold a lot of VARs, since the bulb takes about 60J per second, so you need to store about that much to get a time constant of around a half second. The Q needs to be around 120, so the tank's reactance needs to be around 2 ohms at 60Hz. We're talking big reactive components here! It's no suprise such a thing has never been built -- but it would be neat to see a true passive soft-start light, wouldn't it?

Tim




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[*] posted on 20-1-2008 at 10:52


Yes, good concept. Thinking that a microwave ovens transformers primary winding
would make a decent output inductor. I will have to play around with this, as there are several old micros laying around in my junk pile.

Am I the only one that can't bear to throw away old electrical junk, lol? Years ago my garbage man neighbor would bring me old thrown out appliances. One day he comes over and says, "Hey man look what I found today, it looks almost new" It was a big all SS Kenmore 1500W microwave with hardly a blemish. Turns out that a blown fuse was the only thing wrong because a new one got it functioning again. I was tempted
to return it to the owner but my friend said that "That grouchy old bitch is so rich
she probably already has a new one".

The lack of isolation doesn't concern me as no one else will be operating the equipment and a series resistor does a half decent job of suppressing start up spikes which don't seem to adversely affect batteries or electro cells anyway. I have noticed that a noisy 120Hz wave from the rectifier may have even beneficial effects on an
electrolytic cell using SS electrodes.

Would you happen to know what the approximate inductance is for a 1KW or 1.5KW
micro transformer? These are somewhat deficient in iron mass compared to the typical
transformer of equal KVA.

I also have a few decent sized battery charger transformers laying
around which would also suffice, maybe in combination with caps for this application.
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[*] posted on 20-1-2008 at 11:26


An MOT is good for up to, say, 10A primary current (with fan), which is 1200VA, but not 1200VAR. To get that, you need to gap the core. As-is, the core probably saturates right around 120V (at the peaks), at a reactive current of only a few amps. You need to increase saturation current and decrease inductance to get a useful power transfer to whatever's after it. Cutting off the "I" section and putting it on an adjustable spacing to the "E" section will work. The least inductance you'll get (which may not be small enough for your load, but that's to figure out) is with the I completely off. You should use something stocky (like heavy solid cardboard -- not corrugated!) to space the pieces, and hold it with a clamp.

I will never condone offline circuitry. Surely it has occurred to you that you're connecting a *bath* of liquid to 120V? Doesn't that seem the least bit stupid? Not to mention, by using a full wave rectifier, you *guarantee* that bath has full AC on it!

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[*] posted on 20-1-2008 at 13:56


OK, I will try the gapping at different spacings to see the effect.

BTW, I just tried it with a small MOT (maybe 800W) with the secondary winding removed and produced 2.6A. The cell voltage was 5.6V (4 series water electrolyser) I only left it run a few minutes so the ultimate
internal heating effect was not determined. It was barely warm after 5 minutes or so.

........I will never condone offline circuitry. Surely it has occurred to you that you're connecting a *bath* of liquid to 120V? Doesn't that seem the least bit stupid? Not to mention, by using a full wave rectifier, you *guarantee* that bath has full AC on it!.......

I hear you and I wouldn't expect an "electronics" guy to approve anyway.
However, there are various applications that run even thousands of AC volts into a liquid bath.

There would only be stupidity in the operator causing an accident
if adequate safety precautions are not observed. I have seen some pretty sharp
"electronics" guys do some pretty stupid things around line voltages as I am sure
you have as well. Ever close a 2KA 12KV breaker into a fault? That's very exciting
yet done all the time.

With a sealed tank, bubbler buffer, dual flame arrestors and good fusing my experimental rig is safe enough given constant observation by me.

Needless to say commercial units have multiple layers of safety devices for
the obvious reasons. Many of these units run line voltage into 60 or 120 cell
banks and industrially thousands of DC amps are run into electrolysers full of
very conductive electrolytes as the norm, I once worked on an 8KA unit and
that is a small one. So no I'm not worried.

I do appreciate your concern and to those youngsters out there or those without
relevant experience; please do not try this at home as it may kill you.

How's that?


[Edited on by bio2]

[Edited on by bio2]
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[*] posted on 20-1-2008 at 15:32


Quote:
Originally posted by bio2
How's that?


Still no excuse! ;)

I haven't been around 2kA breakers, but I've been around 480V, 1.6kA breakers. Big, warm and humming. Lots of power flowing there. Good thing they're safely behind panels!




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[*] posted on 20-1-2008 at 15:32


Quote:
Originally posted by 12AX7
Op-amp circuits only oscillate when the user doesn't realize the value of compensation -- something fundamental to any feedback circuit, which the user ought to already know!

Tim


A little knowledge is a dangerous thing .
Try harder not to be such a scary guy :P;)

Op amp circuits will oscillate when the frequency response of
their feedback loop doesn't rolloff to 0 dB before the phase shift in the feedback path is sufficient to become positive and regenerative as opposed to attenuating . You won't get a stable servo lock in a control loop unless the Bode plot of the frequency response for that loop shows that stable response envelope is present for the whole loop , and each element in the loop contributes it's own phase , not just the op amp or the way you have it compensated .

Controlling a hugely capacitive Mosfet with an op amp is
about like making a ten foot flyrod into a bow with a heavy
rubber band from tip to butt , and having a bamboo hoop
on the tip end of that lightweight bow , loosely equatoring
a bowling ball which you wish to push and pull across the
floor in a precise motion :D It presents similar difficulties
as would be seen with the grappling of the Hubble space telescope by the shuttles spindly robotic manipulator arm ,
where the mechanical forces involved with positioning become a complex mathematical calculation that is much more involved than may be apparent . I mean it's just
simply reaching out and grabbing something right :D

Controlling that big mosfet with an op amp is slippery business , like trying to push a catfish around by his whisker tips .
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bio2
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[*] posted on 21-1-2008 at 12:55


An update on incorporating 12 AX7's suggested improvements to an inductor
seriesed with a bridge rectifier for Constant Current electro cell control.

I took an about 1.2KVA MOT and cut a 1mm gap in the I of the core and
about 4mm of the laminations below the cut were removed on both sides (these fell out anyway). Connected to the 120V line this arrangement gave 7.2V
6.8A on the unfiltered DC output to the cell. Without modification this MOT only produced 1.8A at about 5V. The same electrolyte concentration and temperature
was present.

The winding quickly heated but no temp rise measurements have yet been taken although it seems that a cooling fan will probably be needed. The current and voltage are very steady and according to 12AX7 this is a better method than using capacitors alone so it should give reasonably accurate CC over a wide output voltage range as do caps.

The energy density (space required per amp) is much better than caps so this
method should serve well for the 15A @ 80-100V cell I am building.
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dann2
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[*] posted on 21-1-2008 at 13:59


Hello,

15A @ 80 to 100v?

Are you putting a number (say approx. 12 X 6v cells) in series or just one cell at 6 volts, the rest being dropped accross the inductor?
The biggest disadvantage/danger with this system is that if one of your connections gets dogy the voltage (and power dissapated) will start to increase accross the dodgy connection and it will go red.

A similar thing happens if you are using a welder (+ rectifier) to drive a cell.
You set the current with the welder controll (say 30 amps) and the voltage across the cell will be approx. 6 volts. The welder inductor drops the rest, approx. 74 volts. The open circuit voltage of the welder (a common mannual metal arc type welder) will be approx 80v ac.
If a connection gets dodgy, the voltage will start to rise and rise accross that connection untill its gets red hot and there will be melting/ignition.
If you had a variac in front of the welder you could bring the open ciruit voltage down to some sensible level, like 10 volts so that you will not get red hot/ignition problem.

This happened to me BTW, I used to run cells using a 120 amp welder. Make sure connection etc are top notch.

Hope I am not misreading what you are doing.

Dann2
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[*] posted on 21-1-2008 at 15:40


Yes, you are misunderstanding, please reread my previous
post on using capacitors as constant current control.

I have used this method for years and it works very well. The voltage will automatically change with the current remaining constant over a very wide range. Inductive Reactance is what determines the current.

I have charged batteries at constant current from 6V to 48V at 3.7A using 90uF capacitance connected as previously described.

12AX7 said inductors work even better in this application and I have no reason to disbelieve him but am now doing testing.

My water electrolysis unit is run at 2V per cell so 40-50
are needed for 80-100V derived from the 120V line thru
seriesed caps or inductors. As I already posted my test rig
is 4 cells in series.

I would run about a 60 cell but am short of stainless steel for the electrodes. I will expand it later when I find some more suitable SS scrap. Right now I am cutting up a large SS muffler and tailpipe scavenged from a boatyard.

Your bad connection warning is well advised and for this reason they are being welded to the electrodes. Good fusing
is also used to preclude unexpected failures. The connections
are also made at the bottom of the electrodes to prevent any possibility of a spark as they are submerged in the electrolyte.

Other safety devices needed are not being described at this time. I get real tired of repeating myself because the posts
haven't been read using any attention.

I suggest you try the capacitor method. About 1A is produced for each 24uF capacitance. My previous statement of 16uF
was in error. Just gang line rated caps with adequate current
capability to acheive the desired current.

I still haven't looked for the EDN article describing in detail the theory behind this method. It was entitled XXXX Rectifier
not much help, sorry. Although I have never seen one the article says commercial battery chargers have long used this method for current controlled charging and in my experience it works very well.

I have a 1320AH battery bank and use this to charge CC at 6,12,18 or 24V depending on how I have them connected. So you see the current staying the same means it is advantageous to charge at 24V due to the higher available wattage. Then I reconnect to 6 or 12V and use the same unit as a trickle charger.
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[*] posted on 21-1-2008 at 16:30


Hello,

Apologies, I though you were going to run a (Per)Chlorate cell.

If anyone else is thinking about running a (Per)Chlorate cell using this method the problem I outlined will apply. The bad connection can (will?) come at the top of the anode and or cathode if salts are getting to the connection.

Also if/when the coating falls of a Ti substrate anode a large voltage will appear accross the cell and eat away the Ti.
In my neck of the woods it's 24OV mains so that a bit too big a voltage for using this method for just about doing anything with.

I am not saying that the method will not work, just these's problems may and can occur with (Per)Chlorate cells.

Dann2

[Edited on 22-1-2008 by dann2]
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[*] posted on 21-1-2008 at 17:53


The max voltage produced can be limited by paralleling
another capacitor of appropriate size (much smaller) across the mains downstream of the seriesed caps. This is normally done to protect against peak voltage with loss of load and the voltage will collapse in a short circuit so it is self limiting.

Put the caps in the hot line preferably although it will work
in the neutral being AC of course.

So 240V should not be a problem. For example if the desired current produces say 12V it can easily be limited to say 18V or any other value.

I have done this and it works very well. To get a feel for it
just get a handful of small across the line rated caps and
a small bridge and experiment with maybe 100mA or so
into some little resistors..
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