Ether way the test goes I will put a milliamp meter in series with a thermopile and get the current reading and report back tomorrow

 

This is a good video explaining how to step down the voltages efficiently. Using a just resistor is probably not going to work too well.

 

You could also use a diode with a voltage drop of 1 volt.

 

I tested the resistor based project and as expected it did not work ( just proves Ohms law does)
The bright side is the current draw was 126 ma little short of what we expected, I could not get the voltage drop at the same time but expect it was inline with the current draw.

Is there any suggestions for a premade Buck converter or schematic for a buck converter with a adjustable millivolt output around 150ma??

Thanks
George

 

input 1.5V , output=500mV

 

Buck converter will create additional problems: there will be interference!

 

I will try and get to drawing up a op-amp transistor current source. Back to where I mentioned a current source I still see it as a viable option.

Ron

 

I would try something along these lines.


As shown V1 is just a voltage source I used to simulate a pot. I would use a 10 turn 10K pot in series with maybe a 3K resistor so the pot provides about 0 to 9 volts to the op-amp. A Google of terms like opamp current source will yield dozens of similar circuits. Just about any single supply op amp will work and I used a 2N2222 which is common. R1 is a 25 Ohm resistor and needs to be about 10 Watt. The twelve volt source can be a battery pack of AA batteries. Not much to the thing and it should deliver about 0 to 350 mA. When testing a solenoid just measure the voltage drop across the coil as current is increased.

Ron

 

Here's what I propose from reading the post. The 1K pot VR1 will adjust the output from 270 to about 950 mv into a 2 ohm load with a fixed 18 mv tap. Uses three 1.5 volt batteries, regulation good down to 3 volts.
Steve G

 

I found this circuit that appears to work??
Changed 5V+ to 9V result = 0- 60MV output
Changed 10K resistor with wire result 0 - 840MV output
didn't have a 3 ohm resistor to put across output to see voltage drop used 100 ohm dropped about half, will test on old gas valve tomorrow to see what happens??

Best part I had everything in my junk drawer

Thanks for all the help and support
George

 

George.
I stumbled across this forum, while looking to do exactly what you are doing!
How did the whole thing work out????

 

Here's what I propose from reading the post. The 1K pot VR1 will adjust the output from 270 to about 950 mv into a 2 ohm load with a fixed 18 mv tap. Uses three 1.5 volt batteries, regulation good down to 3 volts.
Steve G
View attachment 143052

Nice solution- but for a test device box- one should contemplate the inevitable short circuit.
The 2N2222 will fry.