Hey sarge, tried to send some photos of the story so far but satelite not playing too well today. Will all the different north and south poles on the same plate not cancel each other out?

Not really - there will be "weak" areas of magnetism between the N and S poles. Small items will likely tend to concentrate around one of the pole areas. Larger items may try to align themselves between two of the poles.

I've got a 28v alternator good for 24A to play with or some 12v 65A ones. I'm gonna make a DC magnet from the 28v one and try to make an AC magnet from the 12v one.

You might try using all 12v alternators instead. That would give a much better idea of how they perform in comparison. The 24v alternator may require too much torque for a strimmer to drive.

From the schematics you sent would I be correct in saying I would for a wye join three ends together then simultaneously wrap arround the offending object say a bar at this stage with each of the other ends connected directly to each of the stator windings directly?

I'm afraid that a single bar would not work well if you attempted to put three phase windings on it. The three phases are 120° apart, and if you tried winding them on a single bar, they would effectively cancel each other out.

How about just trying to make a DC magnet for now? You will need to wrap quite a few turns on a bar.

If you wanted to try a 3-phase version, you might try three bars connected in a triangular shape. It would be easier to wind the turns of wire on before joining them at the ends. A Delta configuration would be somewhat easier to connect up.

For the delta configuration it looks like we just have three coils joined in a delta shape with each of these connected directly to the stator windings.
For the 28V alternator I have, what size of capacitor does C1 want to be?

Preferably an electrolytic capacitor with at least a 50v rating, as many uF's as you can find! A "rule of thumb" for electrolytic capacitors is to use a voltage rating of at least twice that of what you expect to find in the circuit, in this case you would really want a capacitor rated for 60v - but you'll have to use what you can find. Electrolytic capacitors tend to "leak" more current as you approach their voltage rating. The "leak" is actually a resistive short inside the capacitor. If the leakage current gets too high, the capacitor will overheat, and may rupture or explode. While not generally hazardous, having a piece of equipment blow up like that might be stressful for those already involved in stressful and dangerous work.

It's all happening very slowly I'm afraid because I want my local staff to be involved.
Regards,
Jamie.

That's perfectly fine. I think it's important for everyone to be involved in what's going on, and thinking about how to make such a dangerous job less hazardous and more rapid.

Be safe over there!

 

Something like this can ruin part of the day...

 

On a more serious note, I have recalled an attempt to partly mechanize agriculture in poorer countries back in the 1960's. The idea was to speed the tilling of fields ith engine power, but without the expense of tractors.

The plow was supposed to shuttle back and forth across a field drawn by a cable. There was a gas engine on one side that pulled an endless cable. The other side was an anchor for the pulley. The plow could be attached to the cable so it would go both ways. The awkward part was in the many small movements of the anchor and engine co cover the field.

This is another idea that may be too difficult. But the mines can't be too deep, so arranging for a gang plow to go down perhaps a half meter might turn up mines with minimal danger to the operator?

 

Thanks again guys,
we've made a few magnets now but nothing really doing the bussiness. Our first attempt was making a bar magnet and putting it in the crown wheel of a differential but although the magnet could lift about 3.5Kg on its own when we stuck it in the crownwheel it would hardly lift a spanner. We made a few of these bar magnets in various configurations but they also got too hot to hold after about 6mins. The resistance of the windings was 3.1 ohms and we used a 12V battery. I don't know the current because I only have a small multimeter I didn't want to risk but there wasn't so much for sure. Less than 10 amps probably because it wouldn't register on a battery tester.We got a few shocks when disconnecting the coil which put a few of them off. Is there a better way of doing this?
I've got the guys scavenging around for old speaker magnets now and the solenoids from old starter motors. I'm gonna try the solenoids as a last ditch attempt at electromagnets by putting them around an annulus cut out from 12mm mild steel instead of a crown wheel. The strimmer to alternator interface is no probblem now.
The speaker magnets might be the way to go with having a cloth in front of them to get rid of the contamination.
Still not happening on the photo front. I think my computer has a virus because I cant use video such as youtube and when I upload something the whole thing freezes and I have to restart. It's also all in portuguese which dosen't help!
Regards,
Jamie.

 

OK, a crown wheel is a pretty massive object, hard to get to, and messy (covered with 90w oil!) Why not use a disk brake rotor instead? They would be easier to get off the vehicle, as well. Actually, you might consider a brake drum, too. Wind the wire around the outside of the drum.

P(Watts) = EE/R
P = 12.7*12.7/3.1
P = 52 Watts
I = E/R
I = 12.7/3.1
I = 4.1 Amperes
P = EI
P = 52 Watts
Not surprising that it's getting warm.

Shocks:
I didn't know that you were going to try battery-powered coils. You need to have a rectifier diode connected across the coil in reverse polarity when you're powering by DC.

What's happening is that when current starts flowing through the coil (a large inductor) it causes a magnetic field to expand around it. When current stops flowing in the coil, the magnetic field starts collapsing. The current tries to continue to flow in the same direction, but since the circuit is now open, the voltage polarity across the coil reverses, and can become extremely high for a short duration. If there is a diode in place, this high reverse voltage is shorted through the rectifier diode, eliminating this problem. As mentioned before, there are some large rectifiers in alternators.

Language in Windows:
Open the Control Panel, and find the Regional and Language Options icon, which looks like a globe on a stand. Double-click the globe, then select English, and the Apply button. Re-boot. Your life will get a bit easier.

Virus:
Download AVG Free at this address:
http://www.download.com/AVG-Anti-Vi...42.html?part=dl-AVGAntiVir&subj=dl&tag=button
You may have to re-boot to Safe Mode with Networking in order to download things.
To accomplish this:
1) Power down your computer. When it finally turns OFF, wait at least 10 seconds.
2) Power the computer ON. Press the F8 key repeatedly at 1/2 second intervals.
3) Within about 30 seconds, you should see a "Windows Startup" screen.
4) Select "Safe Mode with Networking"

If you can't download AVG Free, try downloading System Mechanic Professional 7 trial here:
http://www.iolo.com/SM/7/pro/download.aspx