Variable voltage with a three position slide switch?

[Solder-Meister]

It seems necessary to disclaim my circuitry experience as limited, so with that said I'll continue with my queries.

My goal is to create a mod that uses two 3.7v batteries and a three position slide switch to vary between 3.7v with the combined mAh of two batteries, and a 5v regulated output (and of course OFF). I'm trying to avoid using adjustable power modules like the PTR08060W, but would like to know if it would be necessary in this kind of setup. Any suggestions on the wiring is greatly appreciated.

Q1: Can this be done with an adjustable linear regulator, or is it absolutely necessary in this case to use a switching regulator?

Q2: What kind of regulator would you use? (Please include PN, Model#)

 

[Animeguy]

Oh this is a good question. I just bought a stuff from madvapes to make me a VV pv but if your question is answered, I might make that one too.

 

[asdaq]

With the batteries in parallel you would use a lot less wire if you used the ptn4050 booster, and had a switch that bypasses the booster circuit to get 3.7v.

 

[Solder-Meister]

Check out this diagram
http://www.e-cigarette-forum.com/fo...v-4-selectable-voltages-no-potentiometer.html

And this neat calculator tool
LM317 Voltage Calculator - Electric Circuit

Apparently it is possible to achieve voltage pre-sets with adjustable linear regulators.

 

[Solder-Meister]

That's a fantastic idea. How would I go about setting the voltage to, say, 5v for the second preset via the booster circuit?

 

[AttyPops]

Interesting approach (and link to o4_srt's mod). As mentioned, looks like you could use the switch to select the resistances for the v-adjust pin on the adjustable regulator. So just calculate what you need for 5v and for 3.7 v and those are the sub-circuits for the adj pin. Varies depending on what regulator you decide to use (you will find a formula in the datasheet). You'll have to do some research on that, but I'd shoot for a 3.0 amp regulator if you can find one, 2.0 amp otherwise. Of course, as long as you were at it, a 4 pos switch would give you a nice 4.x too if you wanted it.

 

[Dalton63841]

Granted my electronic skills are VERY rudamentary, but perhaps this is something that may work? Obviously it is missing resistors/led, but this is a quick rough drawing. Using a 3 position switch, it goes from 1 battery, to off in the middle of course, to 5v regulated on the other side. Is there any reason this would not work? I feel like I am looking over something very basic, but it should at least be a start.

EDIT: NVM, This is only for 2 batteries.

 

[asdaq]

The booster is 5v natively so you don't need to change anything. You said two batts to increase the mah, what size are you thinking?

 

[Solder-Meister]

Granted my electronic skills are VERY rudamentary, but perhaps this is something that may work? Obviously it is missing resistors/led, but this is a quick rough drawing. Using a 3 position switch, it goes from 1 battery, to off in the middle of course, to 5v regulated on the other side. Is there any reason this would not work? I feel like I am looking over something very basic, but it should at least be a start.

EDIT: NVM, This is only for 2 batteries.

I am actually planning to use two batteries, so you're on the right track. I assume the numbers on the main switch represent 3.7v and 5v respectively?

The booster is 5v natively so you don't need to change anything. You said two batts to increase the mah, what size are you thinking?

2x 14500 3.7v 900mAh

I am actually quite thrilled with this idea, never even thought to use a booster with a parallel battery setup. Any idea if batteries might drain unevenly? My samples should be here in a few days, I can't wait to try this out. Secondly, I would still like to find a cheaper solution something like Attypops was getting at by using an adjustable reg with the correct resistors on either position of the switch. Would a NCP630A work?

 

[Solder-Meister]

Interesting approach (and link to o4_srt's mod). As mentioned, looks like you could use the switch to select the resistances for the v-adjust pin on the adjustable regulator. So just calculate what you need for 5v and for 3.7 v and those are the sub-circuits for the adj pin. Varies depending on what regulator you decide to use (you will find a formula in the datasheet). You'll have to do some research on that, but I'd shoot for a 3.0 amp regulator if you can find one, 2.0 amp otherwise. Of course, as long as you were at it, a 4 pos switch would give you a nice 4.x too if you wanted it.

If I'm running two 3.7v batteries in a series for a total of 7.4v, regulating it down to five, then using a resistor to drop it even further to say about 4v, would I be wasting several volts into heat?

 

[Dalton63841]

I am actually planning to use two batteries, so you're on the right track. I assume the numbers on the main switch represent 3.7v and 5v respectively?

Yea the + and - represent the batteries and how they are connected, I, G, O is obviously input, ground, and output of the regulator, and 3, 0, and 5 represents 3.7v, OFF, and 5v.

So basically you want it to be something like batteries wired in series regulated to 5v, and be able to switch to being wired in parallel at 3.7v? In that case I have to second the idea of wiring in parallel, and using a booster.

 

[AttyPops]

If I'm running two 3.7v batteries in a series for a total of 7.4v, regulating it down to five, then using a resistor to drop it even further to say about 4v, would I be wasting several volts into heat?

Yes that would be a waste, but I don't (and didn't) suggest that.

I wasn't talking about a resistor on the output. The resistor is used for the adjustment pin on the regulator. In other words, the way you tell an adjustable voltage regulator what output voltage you desire is to vary the resistance on the adjustment pin. So your n-pos switch would have n-resistances (or n-1 actually due to the "off" setting) for adjustable voltage selection.

That way, you don't "regulate it down to 5" you regulate it to whatever you want! Thats why it's usually easier to just put a variable resistor (a POT) in, and make a vv with a wide range. But if you want discrete steps using a multi-pos switch, that works too.

Oh, and P.S. there's an argument that it's good to have a dedicated master "Off" switch, that disconnects the batteries from the rest of the device (either hot or ground). So, you would then have two switches, one that had the voltage selection, the other a master cut-off. Not absolutely necessary, but it ensures that off is off with less user error. Then, if you vape at the same voltage most of the time, you don't have to mess with the voltage switch all the time.

 

[asdaq]

If you regulate with a linear reg, you will waste a lot in heat. With the booster it is about 85% efficient and using two 14500's in parallel ensures also that the current is high enough for the booster. I can't find the link for someone who did this before but I think Sci or 48lowes did it. Essentially the booster circuit is wired as normal, and there is a switch in front of the booster that bypasses the + directly to the atty.

Ah, in series the battery in the back tends to get drained more, but in parallel it is quite balanced. Hope this helps.

 

[AttyPops]

@asdaq: Yeah, but in his original post, he didn't seem interested in a booster. I think he wants to keep it either 1) simple, and/or 2) low cost

A switching regular, although not required, is more efficient than the linear regulator. (Your Q1) If you use an adjustable regulator, you would put the batteries in series. Buck/Boost is a little more expensive/complex/experienced (but worth it if you want that sort of thing). IDK, from your OP, I assume that you wanted to keep it simple, even if you have to have charge a bit more often. Heck, I use a dedicated 5 volt linear regulator in my box mod and it lasts 3/4 to 1 day for me (2x14500's). Batteries charge in 2ish hours and are $10.00 per set USD. So, meh! If I went vv, tho, I'd probably use a POT rather than trying to build 2 or 3 different resistance circuits (since a POT only requires 1 circuit).

 

[Solder-Meister]

First off, I just want to thank you all for your useful advice as well as all the other technicians that make modding these devices possible to those without engineering experience. The reason I started this thread was because I'm dying to mod a 2x AA USB charger that comes with a three-position slide switch, one dedicated to 5v USB output and the other to an led flashlight. I was hoping to add better functionality to the third position, but with external access to a potentiometer, I don't see what better use I could make of it, except...... maybe a flashlight .

I was also hoping to build this for under $10, but the efficiency of the power modules is rather attractive, and the PTR08060WVD can be found just under $9 each. Now I may be wrong about this, but the PTN04050C appears to be most effective in a single battery setup, whereas the PTR08060WVD is best utilized regulating two in a series. I will have them both in my possession this Friday, so I'm looking forward to testing the booster/parallel vs evercool. I just hope they fit in the case...

I've read so many threads about people assembling the 5v mod kits from Madvapes, but the main on/off switch on those battery boxes don't seem rated very high. Why then, even in the absence of a mosfet, is it required to use a momentary switch at 3A, yet not to replace the vanilla slider switch?

 

[bstedh]

Why then, even in the absence of a mosfet, is it required to use a momentary switch at 3A, yet not to replace the vanilla slider switch?

With the slide switch your are not switching active current. There is no power draw when you turn it off or on. The power draw happens with the momentary switch which has to deal with the initial power surge as the contacts come together. Think back to the old points on non electronic ignition cars.

 

[AttyPops]

Yeah.... +1 bstedh post #16....button/switch bounce.... PLUS... the master switch happens to hold up most of the time (the physical switch). The wires, OTOH, are often replaced. Although, it is surprising how much that stock wire will take since vaping is intermittent draw and not constant current. So the wires don't heat up as fast as they would otherwise. And a 3x box is probably more robust than say a 2x box or 1x box (not sure about that one tho).

 

[Solder-Meister]

Thanks guys for clarifying that for me. Then I should be good with the stock switch that comes with the USB charger. I will find out this evening. Is 22AWG good for this application? Where in the circuit could I get away with smaller wire?

 

[AttyPops]

Then I should be good with the stock switch that comes with the USB charger.

I can't guarantee that....

Use stranded wire. 22 AWG is the thinnest I would go. 18 is even better. It depends..... you have to figure it out based on what you are doing.

 

[Solder-Meister]

I want a switch that has the center off, one side as the main ON, and the other to power a secondary LED as a flashlight function. Can I get away with a SPDT, or do I need a SPTT?