My 76,000 rpm pulsed dc motor

[mnsman]

thought you were having trouble with the BEMF....

thought you were using 12v input...I must have missed something

No problem with 12V battery and 1000V fet. 24V-36V running from the batteries is where I blow 1000V fets. The power supply worked fine up until I started using the 1000V power mosfets. Now with as little as 9v from supply the kickback into the supply makes it go crazy. So with the 1000V fets I'm limited to 12V input from a battery. If I use a 200V or 500V fet I'm okay with a p.s. until the cap charges up to close to max voltage rating of cap then the bemf starts reflecting back to the supply.

[mnsman]

I believe using a bifilar pancake coil pickup you can make more wattage than your input. I have been trying to communicate this to Jorge.

Yes I've made a few suggestions to him too. I don't know if it's the language barrier or if he never saw them or he's his own man.

What amperage is your current driver using?

Depends. I've run on as little as 250ma to 3A. 3A is way to much for the wire I'm using in the coil but I like to push the limits.

Is it the high voltage spikes that are blowing the fets? The transistor in my circuit has never blown. The circuit was designed for this purpose. The fuse goes first.

Yes the spikes are the problem with blowing fets. I wasn't blowing any until I started using the 1000V power mosfets. The bemf spikes are over 1000V with 39Vdc input. One exception... I finally blew the original fet I was using prior to start of testing others. That fet performed very well and got me to 76000 rpm. My best performer in terms of speed but less bemf.

What kind of coil are you using? Ohms?
What kind of spikes are you seeing? What are you doing with the spikes? I don't see any recovery circuit.

[OrionLightShip]

This is my last one...promise and you dont have to respond
I'm giving you a link to circuit that creates nanosecond PWM pulses up to 1000 volts from a nine volt battery.

Not what you are looking for but pay attention to the capacitive decoupling from the power suppy to the mosfet driver.

I promised....I will leave you alone now

Orion

No problem with 12V battery and 1000V fet. 24V-36V running from the batteries is where I blow 1000V fets. The power supply worked fine up until I started using the 1000V power mosfets. Now with as little as 9v from supply the kickback into the supply makes it go crazy. So with the 1000V fets I'm limited to 12V input from a battery. If I use a 200V or 500V fet I'm okay with a p.s. until the cap charges up to close to max voltage rating of cap then the bemf starts reflecting back to the supply.

[mnsman]

This is my last one...promise and you dont have to respond
I'm giving you a link to circuit that creates nanosecond PWM pulses up to 1000 volts from a nine volt battery.

Not what you are looking for but pay attention to the capacitive decoupling from the power suppy to the mosfet driver.

I promised....I will leave you alone now

Orion

Thanks Orion... finally some peace. l You aren't any bother my friend.. quite the contrary I value your input that's why I'm here. The problem is that I can only think and type so fast with two of you coming at me with your ideas. It's a good problem to have. I will look at your suggestions later. Probably should be spending some time upstairs with my family for Christmas. Maybe a little research/building later.

[soundiceuk]

Yes I've made a few suggestions to him too. I don't know if it's the language barrier or if he never saw them or he's his own man.

Yes there is a definite language barrier. I think he likes to do his own thing. Would love to donate some money to him as I know he's out of work.

Depends. I've run on as little as 250ma to 3A. 3A is way to much for the wire I'm using in the coil but I like to push the limits.

Have you actually wound a bifilar pancake coil? My suggestion is to use the piece of plastic that you get on top of recordable cd stack as the base. An embroidery grid and some bifilar wire. This is what I intend on using for my coil. The wire can be held in the correct place using a needle and thread.

Yes the spikes are the problem with blowing fets. I wasn't blowing any until I started using the 1000V power mosfets. The bemf spikes are over 1000V with 39Vdc input. One exception... I finally blew the original fet I was using prior to start of testing others. That fet performed very well and got me to 76000 rpm. My best performer in terms of speed but less bemf.

What kind of coil are you using? Ohms?
What kind of spikes are you seeing? What are you doing with the spikes? I don't see any recovery circuit.

I am using two ignition coils. One is 3.5ohm primary and 7900ohm secondary. The other one is close in spec.

I haven't got any test equipment apart from a multimeter. I need a decent scope and signal generator.

I have done a number of things using the spikes.

Put them back into the positive side of the battery.

Earth them to earth ground (plug socket or metal rod)

Let them go to atmosphere.

Put them back to coil negative as the earth is common on ignition coils.

Wire the coils in anti parallel and let the HV meet inside the bulbs I have been lighting.


What is your current coils spec?

If you want to find something off the shelf to play with I have recently learnt that in the transformer industry flat coils are known as "Planar" coils.

Might save you some hassle.

I need some HV caps and diodes to further my experiments.

[mnsman]

Have you actually wound a bifilar pancake coil?

Nope. Only standard bifilar coils. If I decide to wind bifilar pancake I will attempt to use some stainless steel gears designed for 1/4" shaft. This should work. The gears have collars with set screws. The shaft will have a hole drilled into the end and another hole drilled through radius of shaft meeting the hole drilled through the end. The hole through radius is where the wire goes through and out end of shaft. Hole through radius is where the two gears meet. Thread wires through hole in shaft, adjust the spacing between flat faces of gears to the diameter of the wire, lock down set screws and wind away. Furthermore the gears need slots (2 each 180 degrees apart) from circumference toward center to allow gluing of wire prior to separation of the gears after bifilar is wound. Otherwise the wire will spring apart when gears are removed. Hard to describe with words.

I am using two ignition coils. One is 3.5ohm primary and 7900ohm secondary. The other one is close in spec.

I haven't got any test equipment apart from a multimeter. I need a decent scope and signal generator.

I have done a number of things using the spikes.

Put them back into the positive side of the battery.

Earth them to earth ground (plug socket or metal rod)

Let them go to atmosphere.

Put them back to coil negative as the earth is common on ignition coils.

Wire the coils in anti parallel and let the HV meet inside the bulbs I have been lighting.

Doesn't sound like a motor you're building. And it sounds like you are going to have to buy some more equipment in order to see whats going on. This hobby ain't cheap.

What is your current coils spec?

drive coil specs: 12 pancake coils wired in series; each pancake coil is 20 turns, 22 gauge magnet wire; air core. Total coil resistance 1.1 ohms and total inductance 1.06mH video describing: Drive coil specs and construction method - YouTube

[soundiceuk]

Hi, yeah difficult to explain indeed.

No, I'm not doing motors yet. Your'e thread has inspired me to though.

Definately need some test equipment.

Do you understand the pros of the Tesla bifilar just out of interest?

[mnsman]

I'm probably wrong about the spikes from a short pulse

One more stupid idea...use an rc integrator on the gate trigger input to ramp up to full on

Okay. My thinking on that.. Not sure what effect there would be to the operation of the coil. It would mean that I would need a longer on time to have the same result with respect to rotational speed. How much longer will depend on the ramp up. The turn off time will have to be immediate to get a strong and quick release of bemf. Even if that is taken care of I don't like the longer on time.

The best solution I can come up with is some kind of rc circuit that allows the source voltage to ramp up slowly over say 10 seconds. I'm not in favor of a rheostat but if one were found that was about 5 ohm high wattage (500W) I would consider trying that. I would install a switch in parallel and switch it on after the full source is applied.

New thought:
Would a n-chan fet or NPN trans in series with the source work? Again switch directly to source with manual switch after up to full source. Instead of potentiometer an rc circuit could be used. I'm sure there must be better circuits out there. This is the idea though.

[OrionLightShip]

funny, I had the same thought and dismissed it due to more parts but yeah, you could put a slow rise time in between a primary power switch and the main mosfet.


I don't know that it will solve the problem because you have the same condition occur for every pulse right? Or does it always blow up at the first power up???

I think I would just use the 1500w TVP's

[mnsman]

funny, I had the same thought and dismissed it due to more parts but yeah, you could put a slow rise time in between a primary power switch and the main mosfet.


I don't know that it will solve the problem because you have the same condition occur for every pulse right? Or does it always blow up at the first power up???

I think I would just use the 1500w TVP's

I think I have two different problems. The sudden application of the power source at turn on and the huge spike from collapsing magnetic field. The tvp sounds like a good solution for the spike, it's just a matter of finding the proper size. Not to mention I think part of the problem is that I haven't been loading the recovery cap side. I really think I have to load it. My recovery diodes may not be fast enough too. These have been my thoughts tonight. That's it for tonight. Will be out for most of the day at a party tomorrow.

FYI: I finally read your Farnsworth thread. Interesting. Must learn more.

Jim

[mnsman]

Another revision of driver circuit

Hello all,

Have a look at this revision of the proposed driver circuit and let me know how it can be improved.

[OrionLightShip]

It looks better than anything I could come up with!
I do think the 1500 watt TVP diodes are going to be your best solution against spikes....but I haven't looked for them and don't know it is cost prohibitive.

[willy96]

Hello all,

Have a look at this revision of the proposed driver circuit and let me know how it can be improved.

to beg is to loose !


beg some more you make me laugh !

W

why dont you work at it insted of begging for help !!
do i beg did i beg .. the answer is no .. so your intenctions are inpure .. as your begging .. if you were suspoto have it you would never begg!

you need to learn that you get only what you work for !

fact! i have what i do from the work i have done !

[mnsman]

It looks better than anything I could come up with!
I do think the 1500 watt TVP diodes are going to be your best solution against spikes....but I haven't looked for them and don't know it is cost prohibitive.

Yes. I have to research tvps more and find an appropriate candidate. The zener and diode coming off of the drain represent the external tvp.

Thanks for your collaboration Orion.
Jim

[mnsman]

Would you agree?

In my humble opinion it makes sense to be on a forum posting progress and failure and seeking input from others that may have knowledge outside your own and suggestions for improvement. In my judgement this is wise because as the old story goes... If I give you a dollar- you have one dollar and I have one less. In the same manner I can give you an idea and you have the idea and I still have the idea. The idea can be shared further and has the potential to be disproved or improved by others and fed back to the originator. It's a feedback loop. That my friends is the concept behind being on a forum like this- the sharing of knowledge for the improvement and benefit of all.

Would you agree?