Bedini SG

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Thanks! Hopefully some of those little screws and nuts I've pulled out of hard drives will fit.

[Dennisrhodes]

hi

I dont know where you are, but have you seen these bus board strips?

1/8th " is fine as far as thickness goes if you use your flattened copper tube idea. I assume you will cut the tube length ways and open it out and flatten it? Then you can cut it into strips.

Good on you for having a go at this.
Dennis
Here is my old hack job of the same. It works fine.

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Hey Dennis,

Thanks. I appreciate you clueing me in to the existence of bus board strips and for your circuit photo. I hadn't tried to look for circuit photos online so yours is the only one I've seen apart from the one in the handbook. It gives me more clues about how to do it.

I'm in Costa Rica, out in the boonies a few hours from the city - where whatever they have is.

Even there the selection is scant - no ceramic magnets, nor the type of transistors recommended, nor 1/16" welding rods nor the spool size needed for the coil, etc. so the bus board strips may or may not be available.
This time around I'll just slice a copper tube up the way you're thinking. I also appreciate you letting me know the thickness shouldn't be a problem.

One question about fastening the transistors to the heat sink. I got the right sized screws out of an old boombox today, but only 3 have nuts. Can I just secure the others with pieces of the same plastic tubes they were screwed into or would the plastic be likely to melt against the heat sink? If so, would cutting some metal washers to go between the plastic "nuts" and the heat sink make much difference?

I'm actually a little uncertain about the need for a heat sink in general. The version of the handbook I have explains how to design the SG in the attraction mode and calls for a heat sink. On the other hand, in the video of Peter assembling the kit he says that a heat sink isn't necessary since the attraction mode is being used, and it runs cool.

[Dennisrhodes]

on the back of each transistor there should be a bare metal face. the transistor should be isolated electrically from the heat sink otherwise the heat sink will be a shock hazard.I used some thin square plastic transistor insulator washers and white transistor thermal grease for good heat transfer. The grease goes on the back of the tranny then the insulating pad against the heat sink surface. But I agree with Peter, they should not get hot anyway. here's a pic from Google as an example...see the grease squeezing out the sides?

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Thanks, that all makes sense. I have the grease and thermal insulators for the transistor heat sink interface.

My question is about the other side of the heat sink, where each screw securing a transistor is normally held in place by a metal nut, which I assume heats up along with the sink.

I don't have enough nuts for all my screws (taken out of context that phrase could get me in trouble) so if instead of metal nuts I use a plastic equivalent on 4 screws, will that work, or will they overheat and melt or fail somehow?

I took Aaron's good advice of getting a 1k ohm pot and 100 ohm resistors to replace the 470 ohm'ers so I can do some tuning. Last night though, I finally started reading some older material on the SG and saw comments saying the pot needs to be wire wound as the standard carbon track pots often fry within an hour or so. Mine is probably carbon track as I didn't specify wire wound (if they even have them). Is wire wound essential for SG's running in the attraction mode too? If so, is it worth putting my current one in at all?

In your photo (just like the one of John's circuit) a bus board strip is on top of the transistors. Is it attached with some sort of hot glue/epoxy type stuff between the second and third ones from the left (if not, how is it held in place)? And though I realize they're encased in plastic, is there any risk of shorting the transistors by having it right up against them?

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Copper strip on top of the transistors

Good day Dennis,

Perhaps I had too many questions in my last email for you to answer. No worries, I've resolved most of them but still have the last one for you, if you have the time.

It was this - In your photo (just like the one of John's circuit) a bus board strip is on top of the transistors. Is it attached to them?

If so, how?

I realize they're encased in plastic, but don't want to do anything that might risk shorting them, or add more insulation to increase their heat retention.

Thanks.

[Dennisrhodes]

Hi, no risk of that as long as the strip is not touching the transistor legs or pins. You can glue it onto the transistors with whatever kind of glue you have.
There is another way to do it altogether, which is to use the same welding rods as a bus bar, but you dont have any do you.

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Thanks for the clarification about working with transistors.

Nice to know I can use a welding rod (copper coated at least) that way. I appreciate the picture. I didn't get any welding rods here because they were all too thick to use as core material.

I'll use sections of 1 cm copper tubing (1/8" turned out to be too small) I cut in half and hammered flat.

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Finally finished it

I finally got it done. Thanks to those of you who offered advice. I was only able to run it for a short while today because a magnet flew off as it was speeding up since I only had them taped on.

I'd read not to glue them on in the beginning to allow for making final adjustments. I have one magnet every other spoke for a total of 18. Is the final adjusting a matter of trying out more or fewer magnets, or just adjusting their positioning or what?

Also, I didn't have small batteries, so I'm using light truck batteries. Is there any problem with using them instead of smaller ones?

[Aaron]

final tuning

I finally got it done. Thanks to those of you who offered advice. I was only able to run it for a short while today because a magnet flew off as it was speeding up since I only had them taped on.

I'd read not to glue them on in the beginning to allow for making final adjustments. I have one magnet every other spoke for a total of 18. Is the final adjusting a matter of trying out more or fewer magnets, or just adjusting their positioning or what?

Also, I didn't have small batteries, so I'm using light truck batteries. Is there any problem with using them instead of smaller ones?

The bigger the batteries the better.

For "final adjusting" - I'd just get used to it running in your current setup and get a feel for it. You can tune the resistor going to the base. You want the fastest speed for the minimum current draw. You can put a pot-meter in series with a fixed resistor like 100 ohms and a couple k ohm variable resistor.

[wrtner]

... because a magnet flew off as it was speeding up since I only had them taped on.

This can be a serious problem. I plan to use two layers of duct tape with a layer in between of the green plastic shown in this picture of a pallet of bricks:
https://www.shutterstock.com/image-p...ting-109398953

It is very strong and is to be found lying around building sites and merchants. I'll give the surfaces to be glued with Araldite a good sanding first.

Don't ever stand in the plane of the rotating disc which should be up against a wall.

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Aaron,

That's great to hear about the bigger batteries. I want to use this to rejuvenate vehicle batteries (I just bought Peter's video yesterday from your site - using a friend's credit card in case you see the purchase).

I put in a 1k ohm pot and 100 ohm base resistors. Unfortunately, it was not a wire wound pot (it was probably standard carbon track) and burned out after about 10 minutes of use. I let it keep running a few minutes after the pot burned out, but it was at a slower speed. I then thought since it was originally adding resistance to limit the current through the emitter-base junction, having only the 100 ohm resistors there was probably letting a lot more current through risking damage to the transistors, so I stopped it.

I'm not sure I'll be able to buy a wire wound pot here in CR. If not, what should I do instead?

I wasn't able to tune with the pot as I haven't been able to get the tach to work right (it throws out widely varying numbers, some ridiculously high). So all I was able to use the pot for was to slow down or speed up the wheel.

Wrtner,

I couldn't buy strapping tape locally so I just used 2" scotch tape. I think the rubber liner that usually fits inside a bike rim (to keep the inner tube from being scratched by the rim) would be a good addition though. Or, half of a bike inner tube (the half without the valve) or even the whole tube minus the valve. All of those are strong, flexible single pieces with no ends to come undone and because they would be stretched over the magnets, they'd hold everything tightly in place.

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Wirewound pot specs

You can put a pot-meter in series with a fixed resistor like 100 ohms and a couple k ohm variable resistor.

Since the 1k pot I was using burned out so fast I want to replace it with a wirewound one. I haven't found a source here, so I'll order from US. Due to the shipping costs and time I want to make sure I get one with the right specs.

What wattage is best?
Since I've seen both listed, do you recommend one of 1k or 2k ohm's?
Any brands that are better or worse for this use?

[Aaron]

misc

Aaron,

That's great to hear about the bigger batteries. I want to use this to rejuvenate vehicle batteries (I just bought Peter's video yesterday from your site - using a friend's credit card in case you see the purchase).

I put in a 1k ohm pot and 100 ohm base resistors. Unfortunately, it was not a wire wound pot (it was probably standard carbon track) and burned out after about 10 minutes of use. I let it keep running a few minutes after the pot burned out, but it was at a slower speed. I then thought since it was originally adding resistance to limit the current through the emitter-base junction, having only the 100 ohm resistors there was probably letting a lot more current through risking damage to the transistors, so I stopped it.

I'm not sure I'll be able to buy a wire wound pot here in CR. If not, what should I do instead?

I wasn't able to tune with the pot as I haven't been able to get the tach to work right (it throws out widely varying numbers, some ridiculously high). So all I was able to use the pot for was to slow down or speed up the wheel.

Wrtner,

I couldn't buy strapping tape locally so I just used 2" scotch tape. I think the rubber liner that usually fits inside a bike rim (to keep the inner tube from being scratched by the rim) would be a good addition though. Or, half of a bike inner tube (the half without the valve) or even the whole tube minus the valve. All of those are strong, flexible single pieces with no ends to come undone and because they would be stretched over the magnets, they'd hold everything tightly in place.

Saw the magnet flying post - if you do use tape, at least use strapping tape - the kind with the embedded string. Like this https://www.amazon.com/gp/product/B0...SIN=B001NBR7BU

LOL, ok , just noticed strapping tape comment.

With big batteries, also use large cables and other connectors.

For my pot-meters, I use Bourne brand - I personally like the 20 turn ones so it is very precise. You could do 2k ohm. Not sure of the wattage rating right off.

You can put a bulb in series - 25ma bulb like a flashlight bulb or something. So trigger wire> 2k ohm potmeter > 100 ohm 1/2 watt resistor > bulb > gate of transistor.

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With big batteries, also use large cables and other connectors.

For my pot-meters, I use Bourne brand - I personally like the 20 turn ones so it is very precise. You could do 2k ohm. Not sure of the wattage rating right off.

You can put a bulb in series - 25ma bulb like a flashlight bulb or something. So trigger wire> 2k ohm potmeter > 100 ohm 1/2 watt resistor > bulb > gate of transistor.

I'm using 12 gauge stranded wire. Should I use bigger? Is stranded better or single strand?

The only connectors I have are the alligator clips to the batteries. I soldered everything else. Do the size of the clips make a difference?

I'll get a small bulb and add it to the circuit. As a novice all I can tell is that it will add a bit more resistance, but I suspect there's more to it. What it's purpose?

The 100 ohm resistors I have in are 1 watt. Should I change to 1/2 watt?

I finally found a place with wirewound pots here, but...the smallest is 5k ohms, .2 watts and 150 volts. Will that work?