PWM HELP

[Josh Kline]

So I built a dual series pwm mod using the diagram attached to this thread. I have quadrupal checked everything to make sure I have the right parts and everything is wired correctly. I made a few modifications to the diagram such as adding a led bolt meter with 2 tactile switches one reads the battery voltage when pushed and the other reads the voltage at the atomizer after the voltage is being pulsed. I did that so I could press the switch and see what voltage I'm operating at when I turn the potentiometer. My problem is when I have the pot turned up to 100 percent I'm only getting 3.34 volts and when I turn the pot all the way to zero it's reading at 0.64 volts. Shouldn't it read at 8.4 volts if the pot is turned to 100 and the batteries are fully charged? I double checked the voltage at the atomizer with my multimeter to make sure my led voltmeter wasn't faulty and my multimeter is reading the same thing. Only 3.34 volts when turned all the way up. Any clue as to why this would be doing this?

 

[Bunnykiller]

PWM with a 555 is tricky, sounds like you have the " off time" resistor set too high... you need to reduce the off time width of the pulse by about 50% from what you have. A resistor of a smaller value could be used to drain the cap that controls the off time duration. Do you know anyone with a O-Scope? if you do, get it scoped and "see" what the times are between on and off... also, you may have the trigger voltage set too low ( 3.4 etc) and its kicking it into off mode before it reaches the 8V... see if you can get a reading on the trigger pin ( #2)

what type of caps are you using? Ceramic or electrolytic?... I prefer tantilum for 555 timers.

 

[Bunnykiller]

BTW, any wire used from the batteries to the 510 base and MOSFET D & S should be of a substantial gage ( 14-12 on avg power wires), everything else can be 16-20 ( control/signal wires).

 

[Bunnykiller]

http://www.electronics-tutorials.ws/

Bowden's Hobby Circuits

 

[BrotherBob]

So I built a dual series pwm mod using the diagram attached to this thread. I have quadrupal checked everything to make sure I have the right parts and everything is wired correctly. I made a few modifications to the diagram such as adding a led bolt meter with 2 tactile switches one reads the battery voltage when pushed and the other reads the voltage at the atomizer after the voltage is being pulsed. I did that so I could press the switch and see what voltage I'm operating at when I turn the potentiometer. My problem is when I have the pot turned up to 100 percent I'm only getting 3.34 volts and when I turn the pot all the way to zero it's reading at 0.64 volts. Shouldn't it read at 8.4 volts if the pot is turned to 100 and the batteries are fully charged? I double checked the voltage at the atomizer with my multimeter to make sure my led voltmeter wasn't faulty and my multimeter is reading the same thing. Only 3.34 volts when turned all the way up. Any clue as to why this would be doing this?

Welcome and glad you joined.
Might like to check out:
Modding Forum

 

[Josh Kline]

BTW, any wire used from the batteries to the 510 base and MOSFET D & S should be of a substantial gage ( 14-12 on avg power wires), everything else can be 16-20 ( control/signal wires).

So after some further testing and not being able to figure it out, I decided to check the voltage at the 510 connector with the PWM disconnected. So now it's a basic unregulated mosfet mod. The problem now is that with two cells in series it's reading at about 4.5v at the 510 connector and 8.4v at the pos and neg battery sled with the battery fully charged. What in the world could cause that significant of a voltage drop when there's no components other than the mosfet. Which is irlb3034. I've built a few unregulated mosfet mods and always had the battery voltage straight to the 510. If battery was charged to 7.9v I would have 7.9v at the 510. I have no clue what would cause this to happen. Thought maybe I had a fake mosfet like a cheap eBay remake or something but I even tried the mosfet out of my old mod and it's still doing the same thing. And I know that mosfet is good because it works perfectly fine in my other box.

 

[Oomee]

Measure the voltage across the mosfet, probably find that is dropping the remainder of the volts.

It is possible the mosfet is bogus or simply knackered(or wired wrong!)
Have a look at this vid, it gives a guideline on a simple test of Mosfet with a multimeter.