making potassium (per) chlorate

[WSM]

A much easier option is propably to use an older atx power supply. They have the main output at 5 V. Normally from 20 to 40 A. And only 8 to 12 A at 12 V

 

For a chlorate cell, the modified computer power supplies seem to work. I'm not sure the output control needed for a perchlorate cell would be possible with one (I'm not experienced enough yet to be certain, but I suspect this is the case).

 

WSM

[schroedinger]

There are a couple ways to solve that problem:

1. Put a suited ammeter in series with the cell

2. Measure the ohm's of your cell and measure the voltage in front of your cell and behind it, then use I = U/R to calculate your used amps. (That would be an interesting project for an rpi).

3. Run your cell, and take a sample every day, titrate the chlorate content and add the missing ammount. This way you make sure the chlorate content stays high and the perc precipates.

After a week you should know the parameters of your cell, and be able to just add a certain ammount of chlorate and only need to check every couple days.

 

If you only want to determine the end of a run and got a constant voltage source, measuring the voltage behind the cell shoulb be enough. If the chlorate content lowers, the resistance raises quite fast and the voltage drop acros the cell increases. So you only need to shut down the cell if you got a certain e.g. 1 V variation in the Voltage.

[barzn]

 

Not really, i'm afraid. It's a weird problem to have, since you actually got a PSU that should be suited for this, rather then as most, try to make do with a power-source that has been scavenged from somewhere else.

B!

exactly. That's my frustration.. it was bought for this job in the first place, though i have other uses for it.

I'll try to get around this as best as possible soon, or look for an old pc psu

 

 

Hi barzn,

 

When you set it up does only the CC lamp light up? I'm wondering if the electrodes are too big for the PSU (peak demand ~23.22A)? One test would be to make an anode 25mm x 50mm (peak demand ~7.74A) with matching cathodes and try that with the PSU. Are you able to try that?

 

The worst case is that the PSU is incapable or running an electrochemical cell. Let's hope it's something else.

 

WSM

No, the CC light is on only when the configuration is as i described, once i "demand" more amperes by increasing with the knob, it goes to CV mode.

i also put a link to the PSU details from where i bought it few post below if it's of any help to tell how suitable it is.

It should be capable of putting 10A, the only problem is that the voltage will be about 20v or so.

Regarding smaller electrodes - i don't have the tools to reshape/resize the electrodes i have (without damaging them ofcourse). i would try though a carbon graphite rod with a stainless steel sheet to test it.

 

Here is a video i made to show the problem:

https://www.youtube.com/watch?v=5gx22kBbM70

 

Really thanks for your help!

[Arthur]

Are all the connections up to carrying the 10 amps you want to run. No croc clips,cables as short as needed olts done up tight, cables as fat as possible.

 

Can you read the volts and current at the cell by another means? Can you measure the volts from the +ve PSU connector to the Anode connector, same with the -ve terminal and the cathode connector.

 

I'm thinking that some resistance in the cables will lose all the current.

[barzn]

Are all the connections up to carrying the 10 amps you want to run. No croc clips,cables as short as needed olts done up tight, cables as fat as possible.

 

Can you read the volts and current at the cell by another means? Can you measure the volts from the +ve PSU connector to the Anode connector, same with the -ve terminal and the cathode connector.

 

I'm thinking that some resistance in the cables will lose all the current.

First, this is a test setup, all the firm connections, isolation, pH and Temp was set aside at this moment until solving this issue. much more cosmetics needs to be done.

I figured the volt&amp meter of the PSU are trustable, since the intensity of the bubbling suggest so.

Next step tomorrow morning will be to replace the connections as you suggested, and double check the readings.

one thing about the used wires - the were very warm after operating about a minute with 2A, and so was the anode (though less than the positive wire).

Thanks again.

[WSM]

First, this is a test setup, all the firm connections, isolation, pH and Temp was set aside at this moment until solving this issue. much more cosmetics needs to be done.

I figured the volt&amp meter of the PSU are trustable, since the intensity of the bubbling suggest so.

Next step tomorrow morning will be to replace the connections as you suggested, and double check the readings.

one thing about the used wires - the were very warm after operating about a minute with 2A, and so was the anode (though less than the positive wire).

Thanks again.

 

1) Larger diameter wires will carry more current with less heating. Try 14 or 12 gage wire (I'm referring to AWG, that is American Wire Gage sizes). Heating represents wasted power.

 

2) The anode is connected to the positive terminal of the power supply (the cathode is connected to the negative terminal). I hope I've misunderstood you and you wired it right!

 

WSM

[WSM]

e

Are all the connections up to carrying the 10 amps you want to run. No croc clips,cables as short as needed olts done up tight, cables as fat as possible.

Can you read the volts and current at the cell by another means? Can you measure the volts from the +ve PSU connector to the Anode connector, same with the -ve terminal and the cathode connector.

I'm thinking that some resistance in the cables will lose all the current.

 

To barzn,

 

I'm inclined to agree with Arthur; better to verify the voltage and amperage, and more importantly, do so at the electrode leads for an accurate measure of what your electrodes are really receiving.

 

If you use a digital multimeter, they usually have enough impedance to measure the power delivered without ill effects.

 

WSM

Edited April 21, 2015 by WSM

[pyrojig]

Wow you guys have really moved forward since the last time I checked!!!

 

 

My speculation would be in the lead wires , as suggested . Also verifying tight connections as Arthur said

. Warming wires are a sign of loss CE. power going up in heat. The proper sized electrodes will also play a role in the power consumption on the PS.

Great info you guys!! This topic is getting juicy again !

[Arthur]

Barzn, your cables should handle the operating current without heating. you must find (BUY IT) fat cable. If your cable is hot, that's where some of the lost power is going.

[THEONE]

The chlorate cells usually need to operate at 80-90°C. So you can not have a high current efficiency as long as some energy wasted with this way,that is correct ?

[MrB]

You can use tiny anode & cathodes, in a huge cell, and still get a high temperature. Just insulate it. Effectivity here isn't measured as "temperature of the cell" but how much product it produces over time.

B!

[Shunt]

As far as I know, you cannot defeat Ohm's law.

 

To keep a constant current through a variable resistance such as an electrolysis cell, voltage must increase as the cell resistance increases.

 

To keep a constant voltage measured across the electrode terminals, current must increase as cell resistance increases.

 

You cannot have your pie and eat it too as the saying goes.

 

I used to service and calibrate industrial control power supplys that weighed over 400 pounds. They were designed to deliver precision voltages to racks of circuit boards. The tolerance was +/- .010 volts and would go into 'crowbar' or 'shunt' mode ie short circuit the output if the voltage went out of tolerance to protect the devices downline. Each output also has a pair of 'sense' wires that went to the device or card in the rack that measured voltage at the device, which is not the same at the terminals on the supply itself.

 

That is the way most computer power supplys are designed, to keep the voltage within certain limits to prevent damage to the motherboard, CPU, etc. That is why they have so many wires sprouting out of the things

 

Sorry to ramble on, but as far as I know no power supply can deliver both constant current AND constant voltage to a variable resistance, certainly not a low buck E BAY unit. Ever bought a 100 amp battery charger and hooked it up thinking 'yeah that beast will charge my battery in no time' , but it only showed a charge rate of 5-10 amps? It was voltage regulated to prevent damage to electronics in the vehicle and the battery's internal resistance was too high.

 

Anyway, hope this was of use in your experiments, and now you know why 'shunt' is my username here, just a nickname I picked up back in the day...

[WSM]

The chlorate cells usually need to operate at 80-90°C. So you can not have a high current efficiency as long as some energy wasted with this way,that is correct ?

 

My chlorate cells usually ran between 45^oC and 55^oC, but that was before I used pH control. This was with MMO on titanium anodes and titanium cathodes.

 

WSM

[WSM]

You can use tiny anode & cathodes, in a huge cell, and still get a high temperature. Just insulate it. Effectivity here isn't measured as "temperature of the cell" but how much product it produces over time.

B!

 

No one cares about the temperature nearly as much as the production of oxidizers (Oh, you just said that...), the final product IS the point, after all.

 

I suppose watching the temperature can be a sort of bell weather, but none of the things we monitor mean near so much as the current over time (amp/hours). So the ammeter is probably the most important device to monitor.

 

WSM

Edited April 22, 2015 by WSM

[Arthur]

Electrochemical cells may not obey Ohm's law as they are not simple resistors, the reason why we use them is for the chemistry going on inside.

Rather like the battery you quote, -you can't drive current into a battery if the applied voltage is not sufficient.

 

IMO Barzn issue is that it's not the cell that's limiting the current, but a wire or a connector.

[MrB]

That is the way most computer power supplys are designed, to keep the voltage within certain limits to prevent damage to the motherboard, CPU, etc. That is why they have so many wires sprouting out of the things

 

Oh i wish. PC powersupply's only check voltages inside the PSU. Once it's gone outside, they don't care. On top of that, especially cheaper PSU's only really control one voltage, (generally 12v) which is a problem when you try and use the 5v line for something like a cell. You need a fairly equal load on the control lines, or the voltages may go way out of whack.

 

 

No one cares about the temperature nearly as much as the production of oxidizers (Oh, you just said that...), the final product IS the point, after all.

 

Yeah. And if someone actually would care, making the temperature anything special, it's easy to insulate it to reach a higher temperature. If it actually affects productivity, it's probably a good idea. But there are concerns, i read something about LD anodes falling apart in higher temperature environments, for example. I think 55c was the absolute highest recommended. But thats hearsay, at best.

 

IMO Barzn issue is that it's not the cell that's limiting the current, but a wire or a connector.

 

Since he states that the cable heats up, i agree. That shouldn't be happening.

B!

[barzn]

1) Larger diameter wires will carry more current with less heating. Try 14 or 12 gage wire (I'm referring to AWG, that is American Wire Gage sizes). Heating represents wasted power.

2) The anode is connected to the positive terminal of the power supply (the cathode is connected to the negative terminal). I hope I've misunderstood you and you wired it right!

WSM

It dawned on me how it didn't crossed my mind, because i do have pretty good knowledge in electronics. i replaced the connections with a 2.5mm2 (or ~13 AWG equivalent) and i will test the setup again soon.

The anode was always connected to the positive terminal of the PSU, or if connecting multiple ones in series with the PSU - where current direction goes (e.g to the negative of the previous cathode). I do undertand polarity

It's good to have you guys here with this extensive knowledge! you're the best WSM !

 

Barzn, your cables should handle the operating current without heating. you must find (BUY IT) fat cable. If your cable is hot, that's where some of the lost power is going.

It seems i trusted this chinese PSU too much. after i did some tests with the cables i found out that the cables were not retail ones, just a pair supplied with the PSU by the seller.. also i found that although thier outer diameter was o.k for delivering 10A (i'd say 11 AWG), the inner diameter (which has the dictating role here) was absurdicly thin.

The power supply itself is working flowlessly and very stable, so it seems the wires did all the trouble.

 

IMO Barzn issue is that it's not the cell that's limiting the current, but a wire or a connector.

I tend to agree, specially because neigther changing NaCl concentration, the anode-cathode distance and the temp. of the electrolyte made any change on the amperage that the PSU was putting out.

 

Thank you everyone for the help! will report back soon.

Edited April 22, 2015 by barzn

[barzn]

After modifing and replacing all connections, now the PSU delivers a constant current of 10A at 3.9Vdc, both PSU meters and testing with a multimeter on the anode confirm that.

After all the PSU seem to be a very good and reliable power source for the cells. after operating for 2 hrs, voltage dropped to 3.8Vdc and topping with little bit of (fully saturated) electrolyte got it back to 4V. Also, no excess heating of the cables or the PSU were observed.

Sure this is a 2 hrs test, so not that much can be said, but since electricity was good, and temp only raised from 30C to 42C within that 2 hours, it seems it is a viable setup to procceed with.

Now the finishing of the cells can go on, and other aspects of it (pH and temperature contol) can be dealt with. they will be running and kicking very soon - first this NaClO3 cell with the MMO, and after obtaining a good quantity of highly pure NaClO3, an LD cell and a Pt cell will be running also to make Perchlorate.

I will report back during the runtime of the cells, and share with you the results, the periodic logs of pH & temp and determination of ClO3/ClO4 with indicators.

much more work ahead!

 

WSM - wish to get more on how your experiments with the LD and Pt turned out. From what you posted, it seems very good i have to say!

Edited April 22, 2015 by barzn

[Arthur]

Barzn - I'm pleased that you have solved the problem. Electrolysis at a higher temperature is beneficial, so maybe you could stand the cell in a draught free place or even insulate it a little, when you have done a complete run, you will know how the temperature changes with current and time.

[WSM]

Barzn - I'm pleased that you have solved the problem. Electrolysis at a higher temperature is beneficial, so maybe you could stand the cell in a draught free place or even insulate it a little, when you have done a complete run, you will know how the temperature changes with current and time.

 

The photos from the power supply seller looked like the power leads had very small wires. I suppose that's why several of us suggested stepping up to larger gage wires. I, too, am glad it worked out for you. Congratulations.

 

WSM

[WSM]

WSM - wish to get more on how your experiments with the LD and Pt turned out. From what you posted, it seems very good i have to say!

 

Hi barzn,

 

My Pt and LD setups were "proof-of-concept" cells. I ran them with reagent grade sodium chlorate at a concentration of 600 grams per liter of distilled water.

 

Between the two, I'm most pleased and impressed with the LD anode. From my research, I expected better performance from LD over the Pt, but it ran even better than I expected it would. I'm not sure if the higher quality feed stock made the difference or it was the carefully controlled lower current density.

 

I need to set up a sodium chlorate cell (I've only run potassium chlorate before the sodium perchlorate cells) to make feed stock for the perchlorate cells, and compare runs with it to the reagent grade material. I'm running these experiments to expand the body of knowledge (and share it here), plus try to get to the point where we can make our own pyrotechnics grade potassium perchlorate from scratch. I love the sense of self sufficiency, making my own materials gives.

 

If you have any specific questions, feel free to ask here or send a PM. Your choice.

 

WSM

Edited April 23, 2015 by WSM

[THEONE]

If the temperature will be low enough, only hypochlorite will be generated and no chlorate at all. Edited April 23, 2015 by THEONE

[Mumbles]

If the temperature will be low enough, only hypochlorite will be generated and no chlorate at all.

 

That is a very incomplete statement.

 

Temperature only matters if you're also controlling pH. The temperature only affects reactions in the bulk solution. At uncontrolled pH, you're really only going to be generating chlorate at the electrodes. If you're not controlling pH to optimize the bulk reactions, the temperature of the cell is basically irrelevant. In any case, the difference between 30 and 80C is only 6%. Most cells I've seen run around 40-50 degrees as has already been mentioned. 80C is very much on the high end of things, and I suspect would lead to excessive salt creep and may lead to softening/deterioration of some cell materials.

[THEONE]

So, for best results, only Ph is the important reason, and the temperature not at all ?

[Arthur]

Optimised pH AND a suitable temperature both help having a good efficiency.