Experiment - Fail !

[vereybowring]

Somebody asked me if it was possible to have a variable voltage pass through this week, so I thought I'd have a go at it since I thought it was a simple yes.

Tinkering about I found that it is possible, but to make it possible it kind of negates the ease of use a little.
USB supplies 5.2 ish volts which is fine, but as many people know it does not supply a great deal of current safely so people use mains adapters and powered hubs to use a PT on.
Due to this I found out rather quickly that my 2000mA powered hub doesn't have enough current to get the VV circuitry to fire properly.
The best I managed to get out of it was 2.86V no matter what the dial was set to or what control resistors I put in.

I know what the solution is, you need to have a large capacitor (like ones used in mainframe computers 5.5V 0.1Farads) or a battery to even out the power, and with a battery you need to put in circuitry to stop the constant loading blowing the battery (a charge circuit is ideal for this instance).
I think this is wasteful so won't be building a PT that works this way.

A better use of resources is to build a normal VV device that has a charge circuit built in so you can plug in at home and still use it while plugged in - in fact the devices I tend to build anyway.

Still every little experiment improves my knowledge and is good soldering practice (god knows I need to practice that) since you learn best by actually doing something rather than just reading about it - which is especially true for me since my health problems cause me concentration issues.

[jerryrm]

Keep at it Verey, you will succeed one of these times.

Thomas Edison tried many different types of filaments, when he invented the lightbulb and he failed many times, before he found the right one.

[Jemima]

*nodding like I understand what your talking about and goes to google what a farad is*

Yeah... erm ... what Jerry said

[Scylla]

Over my head too, Jem

Still, Verey, it wasn't a wasted exercise for your soldering skill, plus you've banked the experience

scylla

[clockworks]

Easiest way to build a VV "passthrough" is do what Christophe did - use a laptop PSU or similar to power a buck module.

[Clutter]

Easy ???

I don't even understand your post

[Perpetua]

Lol . . . me too Clutty.

Woosh over my head the vaping techmifications, but I'm in awe of those that can.

[Chrissie]

I'm in awe as well

Verey, I'm sure that when you feel up to it, you will succeed - just don't push yourself

[MIDIManNI]

Verey...

I understand exactly what you are saying (Physics at Uni helped a bit here...) but it is still beyond me.

Keep up the great work anyway.

Later...

[rawveg]

See, I would have thought that the obvious choice for VV in this situation would be a Buck/Boost module such as the PTN04050CAH. I know Christophe had success using a similar module, but something he did with his meant that the voltage was offset by .5v (not sure what he did there).

2000Mah is always going to be enough to power a VV mod. I've had VV mods that run on stacked 300Mah batteries, so that's not the issue. I think the biggest problem here is likely going to be the amperage draw... is the power supply you're using supplying usable Amperage? Many PSU's only supply 150-500 Milliamps which is just going to fail to fire the atomiser immediately...

[vereybowring]

It was a 04050CAD booster I used and I use a 2A powered USB hub (fires normal PT's fine) so was a bit surprised it didn't quite seem to have the strength to power the circuit - but I tried several times using different resistors.

I know I could use a mains power supply but that wasn't what the experiment was aiming for but thank you for your suggestions.

[johnnyjames]

Oct 3, 2011 8:57:24 GMT rawveg said:

See, I would have thought that the obvious choice for VV in this situation would be a Buck/Boost module such as the PTN04050CAH. I know Christophe had success using a similar module, but something he did with his meant that the voltage was offset by .5v (not sure what he did there).

2000Mah is always going to be enough to power a VV mod. I've had VV mods that run on stacked 300Mah batteries, so that's not the issue.

Don't confuse mA, a measure of current, with mAh a measure of battery capacity. And in general a cell in a booster has to provide about 25% more current to obtain the same watts as a step down regulator.

When feeding those 04050s (way under powered for today's atties with their 12W/2.4A rating) a battery can usually supply what is needed. It's current output is flexible. Larger cells and IMRs can supply 3+A if called for. With a 2A power supply (and you have to hope that's accurate) how much of that can actually get to the atty? In the real word those boosters are about 80% efficient, especially when a diode is involved to drop the final voltage plus of course the additional resistance a switch and the mod wiring adds.

A quick example.

Using Ohm's Law, 5V @ 2.5Ω we need 2A for 10W. But in this case we are boosting from a 3.7V source. So what do we need to get 10W from let's say 4V (a fresh cell). Ohm's Law tells us at 4V we need 2.5A for 10W. As the cell discharges at 3.6V it will have to now provide 2.8A to maintain that 10W. You'll note I haven't even figured in the efficiency loss of the booster/mod.

[garrydibley]

What VV board you using mate?
Could just be that the min input voltage on the regulator is above the USB 5v
Some need around 6v in to operate.
Could be the problem.