Cheap vaping -- the Low Cost Mod

[Seebs]

I found a US seller that carries a few different flavors of the Buck Converter (LM2596 and LM2587), they also have the 3-wire voltmeters and a bunch of other goodies. Just search NYPlatform over at ebayworld and you should find the store in question.

The LM2596 units they carry come in two flavors:

1- LM2596 DC-DC Step-Down Module 1.25V-30V 5mV --> This one has R1 with a value of 430 Ohms (SMD resistor marked 431).
2- LM2596 DC-DC Step-Down Module 1.23V-35V --> This one has R1 with a value of 470 Ohms (SMD resistor marked 471).

Going by the chart that Rader2146 made over at the Just LM2596 Users thread. I can't find the post where he showed the formulas for finding the "target" trimmer resistance so I can't calculate it for the 430 Ohm unit (he only listed the values for 330 Ohm units and 470 Ohm units).

They also carry the mini volt meters in two flavors:
1- Mini LED Volt meter 0V to 99.9V.
2- Mini LED Volt meter 3.3 to 30V.

They carry lots of other goodies as well...

These caught my eye: 5mm Photoresistors. They have them in different values for resistance while lit and obscured... And also different sensitivity values. I'm wondering if it would be possible to use one of them as a "poor-man's" touch sensitive fire button. Maybe a variation of the "Reisistor to Pin 5 on the IC to turn the unit ON/OFF".
Am I right on this, or am I just blowing hot air out my .... ?

The prices on all the stuff they sell are a bit higher than what the "overseas" vendors are offering. Think $5 -$6 for the LM2596 units versus the $1 - $3 for the same units coming from the other side of the world. I think the price difference is worth it if only for the convenience of having your purchased items delivered to your door in 3 to 5 business days instead of 3 to 5 weeks.

PS: If one were to use the LM2596 unit that comes with the 470 Ohm resistor at R1; Rader's chart indicates that the best option for replacing the 10K ohm trimmer would be a single turn, linear trimmer in the 3K ohm range. This would yield a max output voltage of 6.6 give or take a few ticks. I've looked at every site I know that sells these things and have not been able to find a suitable trimmer; the ones in 3K Ohm rating are multi-turn units. If someone knows of a place where a 3K Ohm, single turn trimmer that can easily be soldered to the unit; please let me know.

One more question. I have space in the project box I'll be using for this mod (4" x 2" x 1") from the ratshack. So I'll probably be adding one of these batteries to the mod: Protected 3400mAh 18650 Li-ion Battery - Cell Panasonic NCR18650B. I've looked at that page a few times and can't figure out if that version is high drain or not.
So if any of you know the answer to this; please do let me know.

And one last question.
Can the unit, as it is built, function as a charger to the battery while the mod is plugged to the external power source? Or do I just make the mod into a "pass-through" that uses external the external power source when it is connected to it and then switches over to "battery mode" once the external power source is unplugged?


Thanks

Seebs.

 

[daPorkchop]

From what I've read around the interweb, you can vape and charge at the same time, but when you press the button the battery doesn't charge until you let go of the battery, no big deal really. The Battery University says you shouldn't charge and use it at the same time.

Some portable devices sit in a charge cradle in the on position. The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic load because it induces mini-cycles. The battery is continuously being discharged to 4.20V/cell and then charged by the device. The stress level on the battery is especially high because the cycles occur at the 4.20V/cell threshold.
A portable device must be turned off during charge. This allows the battery to reach the set threshold voltage unhindered, and enables terminating charge on low current. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low. A battery may be fully charged, but the prevailing conditions prompt a continued charge. This causes undue battery stress and compromises safety.

With that said, I'm pretty sure you don't want to charge your battery with a 12v charger either. Or if it would even charge or work since the battery is protected it will stop getting voltage at 4.2v. If im understanding that right. Though, I guess the battery will take what it can til it hits 4.2v. Then the PCB will stop taking it?

So with this wall of text, I have pretty much confirmed nothing 100%. Though I would like to know if I'm wrong here. Especially with charging a 3.7v battery with a 12v power source.

 

[WillyB]

@seebs.. you need 2.5 volts more in than out on the LM2596. So 5.4V will only put out 2.9V..
I know yours says 1.5v but in my experience with a lot of Lm2596, that figure is not under load.

Mine was ~2V.

Top pic wide open, no load with a pair of 14500s. Bottom with a 1.6Ω DC, under load, with an added heat sink.