Graham,

I think we are on the same page - or at least in the same book lol - just coming at things a little differently.

for the peanut gallery:

(1) limit voltage to the lowest effective amount.
(2) Use a power supply appropriate for the task at hand - in this case, its merely to apply a field so, the smaller the current the better.

(3) If necessary - based upon power supply rating - employ series current limiting resistors to safely lower any possible short circuit current to a *safe* level.

(4) all HV sources / equipment should be put in an appropriate enclosure. If this is going to be outside, then it needs to be in the appropritae NEMA rated enclosure.

(5) Leads should be kept as short as possible. Longer leads, more capacitance, more leakage current especially at higher voltages and frequencies.

(6) HV parts should not be accesible to touch - either directly or indirectly. It would be best, if an interlock was installed that kills the HV supply when parts are made accessible. Additionally, provisions should be made to ground the system and drain any capacitively stored HV charge - this should be provided to both leads.


Insofar as square wave vs. sine wave - i think it all has to do with "jerk" i.e. da/dt (first derivative of acceleration with respect to time). A square wave is a more rapid change in polarity than a sine wave, this results in polar molecules being more rapidly accelerated which helps overcome their innate inertia to stay put where they currently reside within the bulk oil fluid.

Good thread, glad this all had a chance to air out.

Hi Wes,

That's a good summary. All agreed.

Yes, you're right, the soap seems to clump when harshly agitated.

I think this is true for mechanical agitation, too. If I spray the soap-laden BD forcefully into a container, I get soap clumping - a little like making butter, I recon.

Aha! There's my next experiment - see if I can make instant butter with 1000V square wave in a pint of milk!

This could also be why some folks have mentioned ultrasonics as being good for water separation - harsh agitation.

I'm off to bed - it's been a LOONNNGGG day today.

quote:

Originally posted by Dogma:
my preferance would NOT to be limiting short circuit current by resistors, my preference would be to employ a power supply that is properly spec'd and current limited for the application I was intending it to be used. i.e. if i want no more than 10mA, or 4mA or 1mA, that i should be able to control that at the source. Then, I can use a couple of resistors as my safety back up. But, in the course of the design and the construction, I'd make sure that the possibility of personnel exposure was as restricted as possible. Additionally, we've done alot of talking about redundant resistors etc. But, one thing that has NOT been considered is the insulation of the wire.

Well I plan to use neon lighting cable to leave the box to the electrodes with. Short ones at that.

As for the rest of it... How about doing that then? Design build and test a safe variable HT power supply that is intrinsicaly current limited? Possibly with some ability to vary current as well but maybe not. I'd build one if you did it first. I'm sure there are plenty of poeple here who would be grateful. They say the person who defines the problem is the best one to fix it...

That puts you square in the frame as well Graham...

quote:

Originally posted by GrahamLaming:
Let's not restrict our designs to what is easy and what is at a lethal limit. Let's design responsibly, safely and concientiously. If it needs something, it needs it. Full stop.

You can successfully use lower voltage in a bigger tank by interleaving electrodes.

Well I would suggest that includes voltage gradient if it really does need it as your trials suggest.

If you interleaved electrodes wouldn't you have a big three foot by four foot death capacitor disguised as an IBC full of bio?

On this point, just in case, what is a reliable and safe way to discharge any charge an IBC of bio may collect?

quote:

Originally posted by GrahamLaming:

If you use voltages much above 2kV, I believe you WILL find that you suffer from all kinds of leakage currents which will make the whole setup a nightmare to keep operating reliably.

There is so much likelihood for polar contaminants finding their way into your wiring, your insulation etc. I'd confidently predict you'll soon quit using extra high high voltages and venture down in the realms of 1000V or so.

Why cant I encapsulate or oil bath insulate most of the thing? Just neon grade wiring coming out directly to the electrodes? or that sulphur hexy something gas that makes sparks etc just about impossible.

quote:

Originally posted by GrahamLaming:
1 Instead of interleaving, you could use the simple close-spaced dedicated cell to process a flow of product - I think this has a lot going for it.

2 a square wave has more effect than a sine wave of same RMS value and frequency. My guess is around 50%, so a 650V square wave seems about as effective as a 1kV sine wave.


3 That device isn't intended to be used in a flammable vapour atmosphere, connected to a 1000 litre IBC, with wires running to a pair of humungous plates.

4 I'm no ego tripper,

5 Me too!

6 But we have seen mention of transformers with 15mA current rating. So, I proposed a safe way to limit that current to a more reasonable level.
.

Numbers in the quote are mine for easy reference.

1 yes you may be right but I am uncertain how that will work out in practice both for effective clumping of soap that doesnt get broken up again in the flow and for the time it might take. or indeed if it will work out at all for some yet unforseen consideration.

2 any easy way to chop a sine wave into a square wabve? If I go ahead with the transformer I will use a variac to start off with lower voltages.

3 I'm not planning to use the higher votages in a flammable atmosphere. They are for removing soap from demethalyted bio not glycerine from bio. I am convinced the lower AC voltage will work for that.

4 I never thought that for a second. I seriously doubt anyone did.

5 So you and or wes design the definitve variable HT power supply with intrinsic current limiting.

6 And I thank you for doing that. Thank you.

On this point, just in case, what is a reliable and safe way to discharge any charge an IBC of bio may collect?

I would shut off my Power Supply, then drain the IBC. Following that, I'd have a hefty switch through which i could shunt each terminal to ground. (in lieu of this, a shorting probe could be used, but, a properly rated switch would be "cleaner")

Insofar as designing something, well, I'd be up for it if Graham is. I have alot on my plate rate now, so, I don't think I could dedicate a ton of time.

Hi

I've made a start on a simple variable PSU which uses a Cockroft-Walton voltage multiplier.

It uses a 555 oscillator, driving a step up transformer intended for a switch-mode power supply and diode/capacitor multiplier chain.

This I think is a reasonably safe way to go for general purpose experimenting / tinkering, as it is inherently low powered and current limited.

It only creates DC.

As to square waves, this is not so easy to achieve in practise, as we have 2 enemies of a nice sharp rise/fall time ...

1. The electrode capacitance
2. The high source resistance of the power supply.

But, no sweat, sine waves are fine, so is DC.

As to discharging, the actual stored energy is going to be quite small if we use electrodes 30mm or more apart. I would expect even a damp piece of string between the electrodes to quickly leak off the charge.

And I don't think we need use a plate system at all. Plate area seems not to be the important feature, but instead, localised field intensity.

Even a coarse gauge chicken mesh works fine. This has very little area, very low capacitance, but can be extended over a wide tank area.

/agree.

yep, both of those things are going to add up to create a nasty RC time constant.

I'd like to see this taken a step beyond beaker sized experiments. How well will this work on something that has a substantial volume? My feeling is that it would be better to keep the ratio of the height of the column of oil fairly close to the distance between the plates. I think if that ratio gets too excessive, then this won't work as well.

Cool Look forward to building one. In the meantime I will try a 100lt plastic drum before I try anything larger.

I would have thought it works better in a tall thin container with electrodes extending to just above the glycering layer in the one case and down pretty much to the bottom in the demethed soap removal stage. Like the jam jar but bigger.

spacing and hight being the same might be Ok. bigger spacing than hight seems to be making things hard work for no good reason. Closest spacing gives lowest voltage gradient needs.

I am looking at some dc to dc conveerters as a safe meantime source of HV. 2KV-6KV each running on DC five to fifteen volts only 3W output which runs to 0.5mA if my decimal point is in the right place. Two can be chained back to back for 4KV-12KV variable still at 0.5mA as I understand it. here is the description.

Salvaged ex equipment type Astex/Brandenburg 568-409. Isolated tracking design, output varies 2 – 6Kv for input 5 to 15V. Output may be positive or negative or floating w.r.t. ground. Efficiency approx 60%. PCB mounted size 2.5 x 1.5 x 0.875 in. Tested working. Ideal for oscilloscope tube EHT, electrostatics etc. 125Mohm high voltage resistor included which can be used as a potential divider to measure the output, salvaged from the same piece of equipment

Safe enough Graham?

Mesh electrodes seem like a good idea. More room for the soap to plate.

I feel, rightly or wrongly, that clumping may or not work with KOH soap. I feel equally without real basis that plating onto the anode will work with KOH soap. This is my main interest in the whole process. Fast glyc seperation and oil dewatering are both way cool but can be done relatively cheaply and quickly with some energy and time. KOH soap settling for a dyed in the wool hydrophobic is time consuming no matter what else you do.

If this works on a resonable scale it is the answer to a problem for me. The alternative is a bowl centrifuge which as we all know is very expensive.

shameless bump because I like this thread a lot and it's heading off page 2.

Sorry folks.

No progress to report Graham? Anyone tried this on KOH? I' waiting for my low current 6KV supply to try it myself. Having taken the safty concerns to heart.

I'm in exactly the same boat as Ant...I want to remove soaps and glycerides, and I use KOH as the catalyst.

Ant, my one experiment was using a Ford coil (AC, probably about 15kV), and I saw no real effect. I am anxiously awaiting results from a DC supply on KOH soaps.

Hi George & Ant

I've been travelling all over UK these past few weeks, so haven't had much spare time to test.

George, the Ford coil will only give a brief pulse of high voltage.

If you were to draw a graph of voltage versus time, over let's say a 10 minute period, you'd see very little area under the graph, and it's that area under the graph which I believe is important in effecting separation.

How often were you pulsing it?

quote:

Originally posted by GrahamLaming:
Hi George & Ant

I've been travelling all over UK these past few weeks, so haven't had much spare time to test.

George, the Ford coil will only give a brief pulse of high voltage.

If you were to draw a graph of voltage versus time, over let's say a 10 minute period, you'd see very little area under the graph, and it's that area under the graph which I believe is important in effecting separation.

How often were you pulsing it?

Graham,

You've no need to account for your time here! We all really appreciate your contribution on this site. I just wish I were as capable of experimenting in this realm as you are.

The coil I have has a buzzer that makes and breaks at a really annoying (i.e. painful) frequency...somewhere around 15Hz, I believe. So it appears to be a nearly continuous spark when it crosses a gap. Someone earlier said that it was AC, but I would have guessed that it was just pulsed DC. Anyway, your point is a good one that the area under the curve of a sharply-pulsed DC or AC wouldn't give a continuous static gradient in the solution.

I just need to find a better HV source and do some small scale experiments to see if it works at all with KOH soaps.

Actually I think you should be locked in a dungeon workshop lab until you have perfected all the bio related things you are working on or think up while you are in there. What else could you be doing that even begins to compare in importance to the world? LOL

I was wondering if a cattle prod would give enough amperage and be used for a power source?

possibly too much amperage, certainly enough. Probably enough volts too although you would have to tell me what yours was rated at before i could really answer.

At first I thought you were going to ask if a cattle prod would give enough motivation to Graham in his dungeon workshop lab... Which I thought excesively harsh. He seems like a nice chap after all. Pity about his day job soaking up so much of his time is all. Probably has a social life and a family as well. They dont make mad hermit scientists like they used to...

Ant,

Take a look at this thread: http://biodiesel.infopop.cc/eve/forums/a/tpc/f/719605551/m/7301079961

My soap count after 9 hours is now 75ppm. I plan on letting it go for another hour and see where I am at.

I still do not know exactly why this is occurring, but I am doing more tests.

Possible reasons so far:
1. Prewash removed more methanol than I am used to and the KOH soaps are seperating from solution in the centrifuge?
2. Prewash + bubbling removed more methanol than I am used to and the KOH soaps are seperating from solution in the centrifuge?
3. I just never tried centrifuge only for an extended period of time?

I just made a "normal" batch without a prewash. I am removing the methanol now. I will then check the soap count and start it spinning to see if there are any results.

Sure would be nice to use KOH and no water or magnesol and produce clean fuel! I did it yesterday, I should be able to reproduce it again.

Here's a thought... what about an electric fence controller/chargebox?

I noticed while at the store that they're generally rated for between 3k and 12k volts, ultra-low amperage, DC and AC models available, already sealed against the weather... anyone know if they're continuous output, or just pulsed?