Will this work? (passthrough)

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Laredo7mm

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Mar 20, 2009
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Lets assume for a moment (since neither of us know if the 3.7v protected batteries have overcurrent protection) that these batteries do indeed cap output at 1.35a, how would that effect a voltage boost converter? As I understand it, boost converters essentially trade amperage for voltage, but if the amperage output is capped at 1.35a, would your available amperage actually decrease to the atomizer while increasing voltage, but for a net wattage gain of 0?

I am not sure since I don't know what happens with the boost converter output when the load is applied. If you hook up your boost converter and measure its output, it will read 5V. Now apply your load, and you get a voltage drop. Does the boost converter then compensate and try to boost that voltage back up to 5V?

Lets say the boost converter does not do that, it just puts out the 5V and doesn't compensate for the voltage drop. Your battery is going to max out at 1.35 amps and sustain that draw. I think the boost circuit would just be able to give the 5V at 1.35 if you don't factore in its effciency. As the battery voltage drops more, then your wattage will start to drop.
 

Kewtsquirrel

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I am not sure since I don't know what happens with the boost converter output when the load is applied. If you hook up your boost converter and measure its output, it will read 5V. Now apply your load, and you get a voltage drop. Does the boost converter then compensate and try to boost that voltage back up to 5V?

Lets say the boost converter does not do that, it just puts out the 5V and doesn't compensate for the voltage drop. Your battery is going to max out at 1.35 amps and sustain that draw. I think the boost circuit would just be able to give the 5V at 1.35 if you don't factore in its effciency. As the battery voltage drops more, then your wattage will start to drop.

I've got a 5v boost converter PCB that should be here sometime next week, I'll post up a thread with some tests once I get my new voltmeter in.

To measure the current under load, I just need to attach my probes on other side of the atomizer while its active, correct?
 

Laredo7mm

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Gotcha, quick question though, you said you were using li-polys and I know that you've been experimenting with some ldo vregs, most of the li-polys I've seen that are reasonably priced are 3.7v cellphone batteries, are you running 2 of these in series?

The single LI-Poly I am using is with a boost converter. I am working on finding parts for my next version which will use two in series with a voltage regulator. It will make the circuit alot more simple, plus then I should be able to get my touch switch working since I can tap into a higher voltage source for my mosfet.

The draw back is the mod will probably be bigger if I want the large capacity 2500mah, or else sacrifice capacity for size and only go with 1100 mah.
 

mogur

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I just ran my new, fully charged 14500 li-ion cell through a 3 ohm power resistor and drew 1.13 amps. Then I short circuited it (just for science, it's only 2 bucks), and drew 13 amps before I chickened out. Li-ions are only rated for 2C or 3C max draw, but that means for 'reasonable service life' you should not subject it regularly to huge draws. But, like most cells, they will put out almost any current you demand of them, for awhile. Ask my nephew, he jumped up and started hopping around while we were camping a few years ago. Turns out, a quarter shorted out the 9 volt battery in his pocket and got quite toasty. We still call him 'Eveready'.
 

Kewtsquirrel

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I just ran my new, fully charged 14500 li-ion cell through a 3 ohm power resistor and drew 1.13 amps. Then I short circuited it (just for science, it's only 2 bucks), and drew 13 amps before I chickened out. Li-ions are only rated for 2C or 3C max draw, but that means for 'reasonable service life' you should not subject it regularly to huge draws. But, like most cells, they will put out almost any current you demand of them, for awhile. Ask my nephew, he jumped up and started hopping around while we were camping a few years ago. Turns out, a quarter shorted out the 9 volt battery in his pocket and got quite toasty. We still call him 'Eveready'.

Was it a protected 14500, mogur?
 

Laredo7mm

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Mar 20, 2009
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I've got a 5v boost converter PCB that should be here sometime next week, I'll post up a thread with some tests once I get my new voltmeter in.

To measure the current under load, I just need to attach my probes on other side of the atomizer while its active, correct?

IIRC, you would wire your probes in series with the positive wire going to the atomizer. There should be three places on the multimeter to plug in the leads, one for common/ground, one for voltage/low current, and one for high current.

I am assuming that your 5v boost converter is designed for running LED flashlights. Is it the one on DX that is rated at 700ma? If yes, are you going to put two in parallel to boost the amperage capacity? I had some on order from DX, but waited for over a month for them to come off backorder. I got tired of waiting and canceled my order. I will be interested to see your results.

The ones I ordered could be modded to put out about 9 watts. Would have ben about perfect, but I am too impatient. :D
 
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Kewtsquirrel

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IIRC, you would wire your probes in series with the positive wire going to the atomizer. There should be three places on the multimeter to plug in the leads, one for common/ground, one for voltage/low current, and one for high current.

I am assuming that you 5v boost converter is designed for running LED flashlights. Is it the one on DX that is rated at 700ma? If yes, are you going to put two in parallel to boost the amperage capacity? I had some on order from DX, but waited for over a month for them to come off backorder. I got tired of waiting and canceled my order. I will be interested to see your results.

The ones I ordered could be modded to put out about 9 watts. Would have ben about perfect, but I am too impatient. :D

Negative, these are from a US supplier who does stuff for hobby work, robots I think. There are 2 options available right now: .8"x.8" or .5"x1.2", I ordered the rectangular version. The guy who made them was pretty sure they'd work with lithium ions, they have an overheat shutoff either way, so I should be fine. Maybe.
 
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