Is my SG current draw typical

[rmarquette]

I built my SG using the specifications outlined in Peter & Aaron's beginner book, with very little deviation. It is a single coil , 7 transistor device with a 24 magnet steel wheel with no Mods. It seems to be running fine and charging lead acid batteries as expected.

I am a bit concerned about the current draw. It seems a bit high. I wanted to see if my results are typical.

It draws 2.65 A from the primary battery at max RPM of 382.5. the RPM, was calculated using Aaron's method ( 153 Hz * 60 sec ) / 24 magnets)

The free wheel spin time is 9 min 30 sec. I recently balanced the wheel.



I also, upgraded the wire at the input and output terminals to the batteries to 12 awg.

[Tom C]

I built my SG using the specifications outlined in Peter & Aaron's beginner book, with very little deviation. It is a single coil , 7 transistor device with a 24 magnet steel wheel with no Mods. It seems to be running fine and charging lead acid batteries as expected.

I am a bit concerned about the current draw. It seems a bit high. I wanted to see if my results are typical.

It draws 2.65 A from the primary battery at max RPM of 382.5. the RPM, was calculated using Aaron's method ( 153 Hz * 60 sec ) / 24 magnets)

The free wheel spin time is 9 min 30 sec. I recently balanced the wheel.



I also, upgraded the wire at the input and output terminals to the batteries to 12 awg.

no that current draw is too hi, you should be at 1 amp with 470 ohm base resistors and a 12 ohm final resistor. make sure you did not put 47 ohm resistors in there.

tom C

[rmarquette]

no that current draw is too hi, you should be at 1 amp with 470 ohm base resistors and a 12 ohm final resistor. make sure you did not put 47 ohm resistors in there.

tom C

Tom,

I verified that all the base resistors are 470 ohms (1%). As for a 12 ohm final resistor, I don't recall that item at all. I looked at the schematics for the SSG and also the 7 wire SG and didnt see a final resistor. Could you please give more details. I included a pic of my final circuit layout.

There is a variable resistor modification on the trigger , it also changes the value of the base resistors, but this is , called out in the SG intermediate book.


Just a thought... I believe the original JB SG used an etched PC board as the circuit layout. I didn't use that, I cut PC board strips and glued them to a piece of aluminum sheet metal. Could this deviation be a problem? I figured it would be ok since it was non-magnetic.
Ray

[Aaron Murakami]

Hi Ray,

Your draw is too high, but 1 amp also seems too low.

I'm testing the kit extensively right now and the lowest it drew was 1.75 amps. Right now, I'm running it on 12v 35ah deep cycle AGM batts so that the draw is roughly about a C20 rate.

However, with a calibrated 0.05 ohm resistor on the input battery ground line - it is drawing 2.234 amps @ 12.83 volts right now for 28.66 watts.

It's running at 93Hz so * 60 = 5580 Hz / 21 magnets on the wheel = 266 RPM

382.5 is pretty fast! Is that with a battery on the output because without one, it will run quite a bit faster.

On the kit, the trigger is going through a 10 watt 12 ohm power resistor then the trigger goes to all 7 base resistors.

[Tom C]

Tom,

I verified that all the base resistors are 470 ohms (1%). As for a 12 ohm final resistor, I don't recall that item at all. I looked at the schematics for the SSG and also the 7 wire SG and didnt see a final resistor. Could you please give more details. I included a pic of my final circuit layout.

There is a variable resistor modification on the trigger , it also changes the value of the base resistors, but this is , called out in the SG intermediate book.


Just a thought... I believe the original JB SG used an etched PC board as the circuit layout. I didn't use that, I cut PC board strips and glued them to a piece of aluminum sheet metal. Could this deviation be a problem? I figured it would be ok since it was non-magnetic.
Ray

[ATTACH=CONFIG]1883[/ATTACH]

do you have insulators on all your transistors? the 12 0hm 5 watt resistor goes in series on the trigger wire before the individual base resistors.

Tom C

[rmarquette]

I didnt put insulators on the transistors.

I did a test with a mock up circuit with just one transistor , one coil wire and the trigger , but using my main wheel and coil. The current draw was only 150-200 mA. When multiplied by 7 that comes out to 1.40 A. My device pulls 2.65 amps So I have something pulling a lot of additional current when 7 transistors are in use. It may be the fact that I didn't use the insulators, which is causing the increase in current. I have some on order...

Thank for the advice...

[rmarquette]

Hi Ray,

Your draw is too high, but 1 amp also seems too low.

I'm testing the kit extensively right now and the lowest it drew was 1.75 amps. Right now, I'm running it on 12v 35ah deep cycle AGM batts so that the draw is roughly about a C20 rate.

Aaron,


However, with a calibrated 0.05 ohm resistor on the input battery ground line - it is drawing 2.234 amps @ 12.83 volts right now for 28.66 watts.

It's running at 93Hz so * 60 = 5580 Hz / 21 magnets on the wheel = 266 RPM

382.5 is pretty fast! Is that with a battery on the output because without one, it will run quite a bit faster.

On the kit, the trigger is going through a 10 watt 12 ohm power resistor then the trigger goes to all 7 base resistors.

That is with the secondary battery connected. I cant run my SG without a secondary battery connected, it burns up MJLs.

I tested my device with a 12 ohm 10W resistor and it had very little effect on the current draw.

Previously, Tom, asked about the insulators, so I am going to assume that the insulators are a necessary item at this point. This may be the cause of my higher current draw. Would you guys agree?

[Aaron Murakami]

The circuit in the kit doesn't have insulators on the transistors. The transistor are not connected to anything other than the 3 connections.

This is exactly what the transistors look like - when mounted on the SG's base, nothing is added to this.

[Tom C]

Never run your circuit without the charge battery connected it WILL destroy transistors eventually.

Tom C

[rmarquette]

Tom,

I installed the insulators and hooked it all back up. I am still pulling relatively high current, 2.50 A.

Prior to starting this thread, I suspected a bad MJL. I removed all the components resistors, diodes, lamps and MJLs and tested each one with a meter. I used the hFE function on the meter to check the MJLs and got a value of 96-106. I used a known good MJL as a reference. (Bad transistors typically register no value). I concluded that all items were good.

I am now wondering if I may in fact still have a bad MJL. When I first started to test my SG a while back I accidentally ran it without the battery. I know for a fact I destroyed a few MJLs. I tested them with a diode tester. I replaced the bad ones with new and assumed the others were good.

Is is possible that the hFE check would not reveal a defective MJL ?

[Tom C]

Tom,

I installed the insulators and hooked it all back up. I am still pulling relatively high current, 2.50 A.

Prior to starting this thread, I suspected a bad MJL. I removed all the components resistors, diodes, lamps and MJLs and tested each one with a meter. I used the hFE function on the meter to check the MJLs and got a value of 96-106. I used a known good MJL as a reference. (Bad transistors typically register no value). I concluded that all items were good.

I am now wondering if I may in fact still have a bad MJL. When I first started to test my SG a while back I accidentally ran it without the battery. I know for a fact I destroyed a few MJLs. I tested them with a diode tester. I replaced the bad ones with new and assumed the others were good.

Is is possible that the hFE check would not reveal a defective MJL ?

if you have a DC current clamp meter you can measure each individual strand to check for its individual draw, a hi strand will tell you something. if they are all close, then you need to increase your base resistance. there are variables here also, you may have a nicked strand in the coil causing an internal short, your transistors may be junk if they are not on semi some other known good brand... if you bought cheap ebay mjl's who knows.... I spend 4 bucks for each one of mine in batches of 100 to get beta matched sets. increasing the resistance of your large 5 watt resistor will reduce current draw, it that does not change it, then there is something wrong elsewhere in the circuit.

Tom C