Gray Tube Replication

[pranav2010]

hi crunner

i am not using permanent magnet on rotor because electromagnet is more powerful

i want to ask you what will happened if i use all material is mild steel.

i used 300mm long magnet core and its not wafer


i am very close to completion

[crunner40]

Magnet core material

Hi Pranav,

Mild steel is not suitable for electromagnet cores, especially in one piece! It will work ok for test purposes only, but will heat up quickly and will be inefficient. This is due to the magnetic flux which builds up in the core. See the comments from TV4FREE (magdude) in the GRAY MOTOR REPLICATION forum.

The most suitable magnetic metal for the core is electrical steel, or ductile iron, or a combination of both as Gray used in his cores. The magnet core must be built out of wafers of metal, all laminated together. Each wafer is coated with lacquer or varnish, so that when they are sandwiched together the lines of magnetic flux are isolated to each wafer. This allows the core to magnetize, and de-magnetize more quickly, and limits the heat build up. There can be electrical contact between each wafer, that is no problem, it is the magnetic continuity that we wish to disrupt.

Transformer cores are built using this method. they are normally laminated out of electrical steel which is the cheapest option, and is the easiest to work with. High quality ductile iron formed of sintered microbeads of iron suspended in a graphite matrix is probably the best option that I know of - but is very time consuming to work with, and requires a bit more thought.

Having magnet cores custom made by a transformer manufacturer should be very cheap in India. I would explore this option. India also has smelters producing products out of ductile iron, and locally you may be able to get the machining done very cheaply.

300mm long magnets will be difficult to wind. When Gray experimented with this he used two shorter magnets mounted close together in series to take the place of one large, long magnet. That makes a lot of sense.

To accommodate 300mm cores, your motor must be a MONSTER..!

Good luck..

[nat1971a]

Hi guys,

Thought i would report that i did a very quick test last night with adding more magnets to quench the gap. Surprisingly it took 5 ceramic magnets each side of the gap to finally quench the gap. I didnt notice any loud gun shot noises though Mind you i am still using the diode for safety reasons so i might relocate the spark gap to in front of the LV diode and retest.

Cheers
N.

[pranav2010]

core

hi crunner

thanks for the suggestion thank you very much

you are right i facing same problem what you mention

the core wont magnetize fast and strong

c1 capacitor will discharge very fast and only single time

now i am thinking cut 300mm into two part 150mm 150mm

and wind it separately

can i use transformer core ???

already i invest lots of money in motor. my motor is complete but i use all mild

steel material. i think there i mistaken

is your motor working ????? go for aaron sir's two point system

thank you

have a great day

[crunner40]

Hi Pranav,

Yes you can use transformer cores, but you will have to shape them to fit the casing/rotor of your motor, and you will also have to shape the faces to create an even air gap distance.

This would be a lot of work. And you will need access to engineering tools.

If you can you should speak to a transformer manufacturer near to where you live, and give him a dimensional drawing for your cores. He should be able to make them for you. Hopefully at a cost you can afford.

Rgds..

[pranav2010]

hi crunner

thank you once again

today i had been to the transformer manufacturer

there is E shape wafers are available

i will modify it in a proper shape

and one more think

i used all material is mild steel (body,shaft,end cover)

can you tell is this problematic ?????

you did not tell me is your motor is working or not ????????

have great day

[crunner40]

Hi Pranav,

I am glad that your transformer manufacturer can help you.

Regarding the iron housing, end covers and shaft - you will only know if the iron will give you a problem when you test it. Gray tried different configurations, and it seems that his goal was to keep the amount of "iron influence" near the coils to a minimum. For this reason i went for non-magnetic materials, SS and aluminium, and plastics where possible. Magdude experienced problems with iron brackets near to his coils.

The airgap distance between the electromagnets is critical. It must be as close as you can make it with your machinery. The effect of the magnets drops off very fast as the distance increases. I have made my gap 0.4mm (16 thou"), magdude used a gap of 0.5mm. However the gap must still be wide enough so that the magnets do not collide if there is any deflection of the magnets during rotation.

Re my motor: It is almost 100% fabricated, and only awaits testing before I make the final parts. I tested the initial coils, and am in the process of winding a second coil set with smaller gauge wire for further testing.

Once I can get the tube to fire, I will test it together with the new coils. If all goes well, I will wind and seal all 12 coils and assemble the motor for benchtop testing and measurement.

I am waiting for components at teh moment. It all takes a lot of time, and unfortunately I am busy with work at the moment, so dont have as much time as I would lke..

[Ghst]

Shaft Selection

crunner40
I thought that I should bring up the matter of shaft selection. Particularly, watch what material the shaft is made of. I started out using a 3/8" stainless steel shaft in my test motor. I am currently testing with two, 2 inch diameter, 1 inch thick, N50 neodymium magnets on the rotor. I ran into problems with the high voltage jumping from commutator thru the shaft and seeking ground that went to the automotive points on the other end of the shaft. I also noticed that the high voltage would also jump from magnets to the stator coils before the rotor had reached optimum position for the discharge. I know from earlier experiments with the coils on the rotor as Gray used, that its extremely difficult to maintain electrical isolation of the rotor coils when they are mounted on any type of metal shaft. for this reason I removed the 3/8 inch stainless steel shaft from my test motor and replaced it with a 3/8 inch oak (Wood) spindle. But Delrin shafts can be bought off of e-bay for fairly cheep. My wood spindle gives to much deflection. Commutation of these high voltage motors is proving to be a challenge to say the least. I hope this saves you some of the problems that I've had to deal with.

[pranav2010]

hi crunner

thanks

try this

3500v can jump 1mm gap so if you adjust gap with this proportion

you can solve your problem

have great day

[pranav2010]

hi crunner

where r u ???????

this is aaron sir's two point system

if you want detail of it go to page no 19 t0 23

you will find all the information

have great day

[pranav2010]

voltage

aaron sir

i want to ask you how much voltage you applying to high voltage side in two point system ???????????


thank you

[Aaron]

high voltage source

Hi Pranav,

I was using a Mallory Promaster ignition coil. It is somewhere between 50kv and 80kv.... 55k sounds about right. There are several versions of the promaster coil and I'm not sure exactly which one mine is.

That diagram you just posted works every time.

Triggering the high voltage front side with a capacitive discharge with the diode arrangement is the easiest way to make it work even though it will work without the capacitive discharge into the coil.

[pranav2010]

ignition coil

hi aaron sir,

in two point system you were used ignition coil

can you tell me how much voltage you were apply to it

if we want vary speed which side we should vary ????????

thank you

[Aaron]

ignition coil input

Hi Pranav,

No need to call me sir

I used a capacitor about 160 volts and up to 47uf and dumped that to the primary of the ignition coil. It will work with just a few uf's but you have to experiment with what works best. I would use the smallest capacitance necessary to get the effect.

[pranav2010]

hi aaron

thank you

your two point system is very much similar

to this patent us 6553981

and about "sir" your respective for me,thats why i am always calling you "sir"

please dont get any wrong meaning of it.

if your feeling somethink wrong

have a great day