What rheostat to choose for tuning base resistances?

[marvkaye]

First post here, so I apologize in advance if this has been covered elsewhere. I tried searching using multiple terms but never did find the proper thread, if it exists.

I'm slowly working my way through the project as outlined in the "Bedini SG - The Complete Beginner's Handbook" and am pleased with my progress thus far... my wheel is setup with its magnets and shaft, I've got my coil wound, and am putting the finishing touches on my circuit assembly (pictures coming... it looks really nice, if I do say so myself). And as soon as I relocate my little CNC router I'll get the stand done. But back to the subject....

I noticed from various YT videos that the SG kit includes a 12ohm 10w power resistor, a component that isn't shown in the "...Handbook". I've also seen suggested in several forum posts the use of a rheostat or pot to fine tune the operation which can then be removed and replaced with the appropriate sized power resistor once the optimal value is discovered. My question is what would be the best maximum recommended resistance for the rheostat to allow one to dial in that correct value? IE, when using the recommended 470ohm base resistors, is a typical value for that inline power resistor 50ohms or less, or 100ohms or less, or more??? I've got an order cooking at Mouser and was thinking about adding a 100ohm 12.5watt rheostat to it for this purpose, but since it's not a cheap part I'd rather insure that I get the one that will provide the proper range of adjustment. Any suggestions would be greatly appreciated... and thanks for a great forum, there's a HUGE amount of knowledge stored here. I hope that i can add something meaningful to it one day soon.

<marv>

[John_Koorn]

Hi marv, welcome aboard! I hope you enjoy the ride

A 100ohm 12.5W rheostat sounds fine, however if you build it just like the book you would only need the 12ohm 10W fixed resistor which is probably a bit cheaper.

Can't wait to see your pictures!

John K.

John K.

[marvkaye]

Thanx for the advice. Since I ultimately would like to build a multi-coiler I think I'll go ahead with the rheostat and use it for experimenting as I progress. I actually sort of started this project years ago, but life and other commitments kept getting in the way of actually digging into it. I've decided I can put it off no longer, so am finally moving forward at a pretty good pace. When I first got interested I laid in some supplies based on the state of things at that point in time. Fortunately the recommended magnets and wheel size have remained pretty constant, but way back then the wire recommendation was 22 and 24 gauge, which is what I purchased. Consequently, my first coil is 7 windings of 22ga and the 24ga trigger, so I'll get to start off slowly with smaller batteries until I get a feel for things. Now that the recommended main coil wire size is 20 gauge I spent some time today making up a new 130 foot cable with 7 twisted pairs of 22 and the one 24.... the area of a twisted pair of 22's is equal to AWG19, so when I'm ready to move up to larger batteries I'll have a coil waiting in the wings.

Anyway, thanks again for the help. I should be able to get some photos of the circuit portion on Tuesday, after my terminal blocks show up and get installed... they're the only parts I'm missing. I'll be back!

<marv>

[marvkaye]

Got my terminal strips today, put on a little paint, added the wires so I'm officially getting close. Pretty exciting. I promised some pictures, so here you go.



Thanks again... Hopefully I can get the stand built soon so I can get back with the completed unit. Ciao.........

<marv>

[rsargent52]

Just finishing up the board for my first unit and ready to put the motor together but had a couple questions.
1. Since Marv mentioned the 12ohm 10w resistor that I got in the SG kit, what is the function of that resistor? Not quite getting it between the wiring diagram and tracing the circuit board.
2. Also in the SG DVDs the diagrams all seemed to use a comparator but did not get that in the TeslagenX kit. Is that for a more advanced design?
3. Also noticed in the kit some rather large heat sinks. Again in the SG DVDs, the system was supposed to run cool. So just trying to understand what is right.
Thanks...
Randy

[Tom C]

Just finishing up the board for my first unit and ready to put the motor together but had a couple questions.
1. Since Marv mentioned the 12ohm 10w resistor that I got in the SG kit, what is the function of that resistor? Not quite getting it between the wiring diagram and tracing the circuit board.
2. Also in the SG DVDs the diagrams all seemed to use a comparator but did not get that in the TeslagenX kit. Is that for a more advanced design?
3. Also noticed in the kit some rather large heat sinks. Again in the SG DVDs, the system was supposed to run cool. So just trying to understand what is right.
Thanks...
Randy

1- the circuit board has the location for the 12 ohm resistor, this is per Johns kit shown at the conference, 470 ohm on each base and a final 12 ohm, brings the current draw in line with what JB wanted for the base resistance, it is A SERIES PARALLEL resistance.

2- the comparator is another part of Johns technology and is available separately as an add on, it is not necessary to get started, so yes it is an advanced modification and is not sold as part of the kit, it is an additional 500 dollars.

3- yes the kit will run cool, the heat sink was also based on Johns design, the plexiglass kits JB made had heat sinks on them so we made sure they were included. if you run in repulsion mode transistors can get a bit warm until you tune it correctly. they work great as place holders for soldering and help the transistors stay stabilized in the board.

Tom C

[rsargent52]

Thanks, Tom!

[AndBirch]

Hi marv, welcome aboard! I hope you enjoy the ride

A 100ohm 12.5W rheostat sounds fine, however if you build it just like the book you would only need the 12ohm 10W fixed resistor which is probably a bit cheaper.

Can't wait to see your pictures!

John K.

John K.

Hi John,
Where can I buy this "rheostat" and the resistor with such a power ? On Mouser site, I didn't find...
Thanks,
And.

[Tom C]

Got my terminal strips today, put on a little paint, added the wires so I'm officially getting close. Pretty exciting. I promised some pictures, so here you go.

[ATTACH=CONFIG]2744[/ATTACH][ATTACH=CONFIG]2745[/ATTACH][ATTACH=CONFIG]2746[/ATTACH][ATTACH=CONFIG]2747[/ATTACH][ATTACH=CONFIG]2748[/ATTACH]

Thanks again... Hopefully I can get the stand built soon so I can get back with the completed unit. Ciao.........

<marv>

Marv I dont see any insulators behind the transistors, are there any?

Tom C

[Silver9]

Looking at Marv's set up, where do you buy the copper strips from? Is there a particular place that i can find them online?
Paul

[Ed_Morbus]

AndBirch, Search on Mouser

Wirewound/Metal Film Resistors