Question about 5v mod.

[basementcat]

So I just finessed My first 5v mod and I am having a mysterious issue. I wired it based off huffenheinz wiring diagram on madvapes. It seems to work fine but for some reason when I flip the on switch with an atty connected the led lights very faintly and you can kinda hear the carto sizzling. Then when you press the fire button the led lights all the way and it hits and sizzles like normal. I have looked at it over and over again making sure no crossed solder connections on the pcb etc and for the life of me can't figure out what I did wrong. You cab hit it as soon as the on/off switch I flipped on but it doesn't produce much vapor then web you hit the momentary it fires up normal. Also with no carto connected the led just stays on all the time when the on/off is turned on. So driving me nuts. What did I do wrong?

Here's the wrong diagram i used.

 

[5cardstud]

I always wire my pos from the batt to the switch, that means nothing gets through until I push the button. I never used that wiring before so I can't comment on why.

 

[basementcat]

Would a bad regulator cause this? I'm literally about to go insane trying to figure this out.

 

[Java_Az]

If your using the regulator i think you are you dont have the switch wired up right. Should go from ctrl to the switch then to ground i believe but it is really hard to say since you didnt post what regulator your using. If you post what you got wired up i could say for sure.

 

[basementcat]

I'm using the one sold at madvapes. The 5v 3a with control pin.

 

[basementcat]

I believe it's a fairchild

 

[Mentat Ix]

I used that wiring scheme to good effect twice now with that regulator.

I did test it once, mid-project, before I put the resistor on the pcb, and it did much what you're describing. Don't ask me why - I thought for sure I had messed something up... but then I put the resistor on and it started working right. Just food for thought.

 

[Java_Az]

That wiring diagram that you posted above is correct for that regulator. Thought you were using a TI reg. If you checked all your wiring could be bad regulator.

 

[basementcat]

Argh. Omg. Hours and hours of work and frustration to find out it was indeed a bad regulator. /cry

 

[WillyB]

That wiring diagram that you posted above is correct for that regulator. Thought you were using a TI reg. If you checked all your wiring could be bad regulator.

You sure? What's the deal with the 10uF output cap?

From the datasheet:

• Co improves stability and transient response.(Co > 47μF)

I did test it once, mid-project, before I put the resistor on the pcb, and it did much what you're describing. Don't ask me why - I thought for sure I had messed something up... but then I put the resistor on and it started working right. Just food for thought.

The reg/mosfet does the actual switching. You want it in one of 2 states, completely on or completely off (like a mechanical switch works, no in between). The pulldown resistor ensures that when you release the fire button the mosfet will go completely off (disable), it mkes sure the mosfet voltage is pulled down to .8V.

Without the resistor the mosfet can float in a semi open state letting some current seep through, like the OP experienced. The resistor pulls it shut (down) between firings.

 

[basementcat]

It was a ba regulator. I swapped it out and all was well. Thought it might have been a bad resistor but after swapping it I still had the problem. Just got back from frys with a bread board. Can we say I learned my lesson? Build and test before permanent gluing is my new mantra.

 

[Mentat Ix]

Without the resistor the mosfet can float in a semi open state letting some current seep through, like the OP experienced. The resistor pulls it shut (down) between firings.

Thanks for the explanation, WillyB. I still don't 100% get it, but a simple working knowledge is better than none. I've never messed with any kind of electronics before - taught myself how to solder a couple weeks ago specifically for this project. I like learning new things.

 

[Java_Az]

Originally Posted by Java_Az
That wiring diagram that you posted above is correct for that regulator. Thought you were using a TI reg. If you checked all your wiring could be bad regulator.

Originally Posted by WillyB . You sure? What's the deal with the 10uF output cap?

From the datasheet:
• Co improves stability and transient response.(Co > 47μF)

I went off the diagram they have posted on madvapes site. But yes if you Look at the datasheet it does recommend a 47uF

 

[WillyB]

does recommend a 47uF

Actually greater than 47uF.

Mentat Ix

Thanks for the explanation, WillyB. I still don't 100% get it, but a simple working knowledge is better than none. I've never messed with any kind of electronics before - taught myself how to solder a couple weeks ago specifically for this project. I like learning new things.

The problem with many of these guides is they are made by folks who just started. Everyone thinks they are a modder and goes about making a guide, without ever looking at the datasheet in most cases.

Following huffenheinz guide (and most others I've seen using the Fairchild chip) means you don't want to try and pull more than 2A (as with a Joye510/306) as it will usually go into thermal shutdown. If the recommendations of the datasheet are followed this is no longer an issue.

A 'modder' who builds his 5V boxes the same way, that are sold at some vendors site now posts a warning and calls this shortcoming of poor design a safety feature. Why not just fix it and do it right.