MOSFET question for tactile switch

[Dougiestyle]

I'm planning on building a flashlight mod with a 18650 flashlight. I found this switch that I'd like to use at MV: Tactile Switch with Round actuator, 300g.. What I want to know is which MOSFET to use and how to wire it in. Where do I get a MOSFET? Please excuse the techtardedness. I'm by no means an electrician. I understand basics-only. My GF's son is an electrical engineer working on stuff for NASA, and I'm hoping to get him to hold my hand a little, but, well, it's a little embarrassing to ask for his help. The guy's pretty smart lol. I'd appreciate any help you have to offer!

3dit: I just brainstormed an idea... Could I use the circuits from an ego battery? The lighted switch from that would work great, too! I don't mind sacrificing an ego batt for what I want to build.

 

[Dougiestyle]

Bump. Anyone?

 

[Dougiestyle]

No replies? Where's the modders? It's a simple circuit question.

 

[AttyPops]

Well, MOSFET can depend on the circuit. For example, it is often pared with a voltage regulator, but doesn't have to be. There are a ton of threads suggesting them so a search should prove very fruitful.

I use em with regulators to get 5v devices, so I'm leaving stand-alone MOSFETs to be suggested in other posts. Look for power MOSFET. Check the datasheet and see what the activation current is and check the voltage drop. You probably want a LDO (Low voltage drop) MOSFET so you drop from 3.7 to 3.2 volts for example. Also, it won't regulate the voltage by itself, so you end up with the usual voltage/usage curve less the voltage drop across the MOSFET. That's why I use the regulator ones... as long as I'm going to the trouble of wiring it in, I may as well get regulated voltage out of it. You need 2 batteries for this tho. MV has them listed under regulators/ICs. http://www.madvapes.com/LDO-5-volt-30-amp-regulator-with-control-pin_p_2123.html

Of course, NASA may design them differently.....

 

[Dougiestyle]

Will this work?: RadioShack

 

[Mr.Self_Destruct]

I really wish I could help you. I have only used them with 5V regulators. I have been trying to find this info myself, but honestly haven't searched tooo hard and always come up with an N channel MOSFET, but have not seen anyone use it.

Good luck with your search, sorry I couldn't help.

 

[WillyB]

Will this work?: RadioShack

Nope.......

 

[McG]

Ive been using this mosfet switch in my puck for 4 months now with no problems. Works great for me but not sure if it will fit with your application.

Link to mosfet: Digi-Key - IRL3714ZPBF-ND (Manufacturer - IRL3714ZPBF)

Here is how I used it:

Link to thead: http://www.e-cigarette-forum.com/forum/battery-mods/105465-now-puck-cheap-parts-easy-24.html#post2493768

 

[Dougiestyle]

Ive been using this mosfet switch in my puck for 4 months now with no problems. Works great for me but not sure if it will fit with your application.

Link to mosfet: Digi-Key - IRL3714ZPBF-ND (Manufacturer - IRL3714ZPBF)

Here is how I used it: View attachment 34329

Link to thead: http://www.e-cigarette-forum.com/forum/battery-mods/105465-now-puck-cheap-parts-easy-24.html#post2493768

Thanks McG! I ordered the http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IRL3103PBF-ND last night. I had forgone the idea of building this simple circuit when I realized the circuit from my Ego/Riva batts would work for the application. Unfortunately, contacts got destroyed in the process of disassembly, and I didn't want to sacrifice any more working batteries for the sake of trial-and-error. I ordered the round actuator tactile switches last night, too. I'm stoked to be building a super dependable mod!

 

[McG]

Glad I could help. Hope it works for you as well as it has for me.

 

[Solder-Meister]

I'm using the CSD16325Q5C and I have it wired up according to this diagram. I'm getting 1.85V at the tactile switch (50mA) and I'm wondering if that is too much for it to handle.

 

[MickeyRat]

I'm using the CSD16325Q5C and I have it wired up according to this diagram. I'm getting 1.85V at the tactile switch (50mA) and I'm wondering if that is too much for it to handle.

How the heck do you solder that thing? Those terminals are tiny.

 

[Solder-Meister]

Pre-tinning, flux, and a steady hand. See this thread.

 

[CraigHB]

I know you've already gone another route, but I read of a guy that was making mods with his old eGo batteries. Though, it will be a regulated device which can be good or bad depending on what you're looking for. The cells in the eGo batteries don't last all that long anyway. They're supposed to be good for 300 cycles, but they seem to hit about 50% capacity after 100. You should have more opportunites to try it.

 

[WillyB]

I know you've already gone another route, but I read of a guy that was making mods with his old eGo batteries... The cells in the eGo batteries don't last all that long anyway. They're supposed to be good for 300 cycles, but they seem to hit about 50% capacity after 100.

That's interesting. Scottbee inferred that the eGo (the Joye ones at least) cells with their different chemistry, LiCoO3, were rather robust and could handle higher amp loads.

What do you think of Solder-Meister's choice of two 47k resistors in his circuit?

 

[breaktru]

I found this link for the eGo circuit board at GoodPhrophets. They are claiming that the Max Current is 2.2 amps which I think is an exaggeration.
eGo Circuit Board

 

[WillyB]

I found this link for the eGo circuit board at GoodPhrophets.

I think a more accurate description would be an eGoish circuit board.

This also sounds a bit bizarre.

Inhaling ?1500puffs after resetting: LED flashes for 50 times(200ms on/200ms off), totally 20s, it doesn't support inhaling during this time.It burns the e-liquid for 8S automatically to clean the atomizing chamber.

 

[CraigHB]

That's interesting. Scottbee inferred that the eGo (the Joye ones at least) cells with their different chemistry, LiCoO3, were rather robust and could handle higher amp loads.

It seems they handle high currents well. I actually took a cell out of one that died and did a full short test with a meter on it to see how fast it would vent. It actually did pretty well and took a lot current before it started gassing out, about 20A. The cells seem to have only about 50mΩ internal DC resistance which is pretty darn good for their size. However, they do not seem to have very good cycle life. I don't use them anymore but my wife does. In rotating three of them, all dropped down to less than 50% capacity in less than 6 months. That's about 100 cycles each. I bought a whole new set a few months ago and my wife is already complaining about shorter run times Not very happy with the short cycle life of these units. Once I get a compact single batt boost mod going for my wife I won't be using them anymore, working on that one now. Mine is too big for her, need to make a smaller version for the wife.

What do you think of Solder-Meister's choice of two 47k resistors in his circuit?

Don't really get that. Most POWER FETs achieve minumum Rdson with a Vgs of 10V. When using them as a switch, you're usually trying to find a way to increase Vgs to get the FET well into the saturated range and minimize Rdson. In some cases, I've used a charge pump to increase Vgs. Energizing the FET off a divider reduces gate voltage so you could be putting the FET into the active range, but it depends on the FET. If the FET goes active, that can result in a lot of extra heat and power losses. Not to mention you can burn out the FET that way. The only reason they can handle such high currents is because of their low "on" resistance. Putting them in the active range with a reduced gate voltage can greatly increase "on" resistance.

 

[WillyB]

Thanks for your input.

The whole charge cycle cycle thing can get rather confusing for standard Li-Ions. How high on the initial charge, how low on the discharge etc.

With my 18650 TrustFire flames I've noticed a bit of a drop off in initial loaded volts after about 100ish cycles (I'm kinda guessing here, about 4 months)). When I first bought them fresh off the charger with a 2Ω load I was getting about ~3.92V (that's a naked cell test). Now they are kicking at about ~3.71V. But at $10 for the pair that's fine.

I'm hoping that some of the folks keen on using mosfet touch switches on a single cell mod read your post. Too many folks look only look at the Gate Threshold voltage and treat them like OFF or ON switches not realizing how much time they actually spend in that wasteful semi-on region.

 

[CraigHB]

Li-Ions have the weird flare down from 4.2V at the beginning of the discharge curve. With lead-acid batteries you call that a surface charge, but I'm not sure if it's applicable for Li-Ions (do they have surface charge?), but I call it that anyway. Then the height of the curve in the flat part is different from battery to battery. The LiPo cells have the lowest internal DC resistance. The one I'm using in my mod has 20mΩ. When that one is powering an atomizer, the voltage sag is in the tens of millivolts and the curve is tall. The IMR batts I use in my production mod have higher internal DC resistance and sag a lot more, as much as a tenth of a volt and their curve is lower. So, the voltage you see under load is going to vary depending on the battery. I don't think the height and general shape of the curve changes a whole lot with wear, it mainly gets shorter in the flat part. It might get somewhat lower though. It stands to reason since the battery degrades conductively with wear as well. I don't know myself since I've never actually compared a worn battery with a new one.

It can be tough to try an jump into using these components with little knowledge of how they work. No offense to anyone, but sometimes I have to roll my eyes at some of the things people say. Just like being new to e-cigs in general, it's a learning process and people gain knowledge as they work with the stuff. I still remember when I had to research the term "atty" to see what it meant (that was before I ever saw the underliney things in the forum here). Though, it's quite easy to get in over your head on the electrical end of things and get discouraged. There's been a few posts I've seen already where my only response would be, "you're missing something, it should work." Hehe, there's been plenty of times I've said that to myself.