Riva 510 charger: can I use it on other lipo's?

[interestingfellow]

ok, I've figured out that my mouth is screwing up the touch circuit. I will say that I didn't use two really close contacts under one finger; I use my thumb and index. anyway, here's my circuit layout.


I'm thinking I need to reduce the 47k resistor, to increase the voltage across the touch wires?
Even then, there would still be current bleeding from the extra skin contact on the atty? Right now it fires 1/4 power with the touch switch. if I just touch the wires, it fires great!

Please help?

 

[Java_Az]

I cant read your diagram that really light blue color is barely visible on my screen. Not sure where you have the 47k but if it is going from gate to source for a pull down or up resistor you are going to need to go way up. 2Mohms at least. Since your skin is not a great conductor you need a pulldown / pullup resistor that has more resistance then your skin. But really i am guessing since i cant see your schematic. Some folks will put a resistor in line/series with the gate to try to protect it from static discharges. If you can change your colors in the diagram I might can help more.

 

[interestingfellow]

sorry, autocad does that. I use cutePDF writer as a printer, and the colors jut never come out right with a white background.
Here it is again, but less sucky.
OH! the carto is 2ohm, and the led voltmeter assembly is 280 ohms


Also, I should point out (again) that the "touch sensor" is not just two points under 1 finger. I had originally hoped to make the touch sensor pads my finger, and lip. kind of like an automatic switch (kind of).

 

[Java_Az]

It might be that mosfet you have. It is rated @ 4.5 volts rds on. A single battery goes from 4.2 volts down to 2.75. Really the 47k shouldnt even be in there the proper way would be to add a TVS diode from gate to source for static discharge protection. The 100Mohms is pretty high. Surprised the mosfet doesn't stay latched. I would change it all really. Get a mosfet with a RDS on of 2.5 volts. Then add a TVS diode btween gate a source and go with a 4.7 Mohm to 10Mohm resistor between gate and source. Although what you have might work if you take the 47k out of the picture or maybe try a 10k. But with the low gate voltage the mosfet will more then likely run hot and not last as long as if you used one more suited for a single battery.

 

[interestingfellow]

I got that particular design from scubatdan on this thread. he had it riggd into a 5v PS, so that makes sense.
This has been a steeply shaped learning curve for me, btw. I also have some LM3103's, but don't know what I'm doing, so don't know what to look at. I know Vgs is 1v min.... but don't know what that means really. total noob.

So, it''s the cut on voltage then? huh.

 

[Java_Az]

You mean a irl3103 IF so those also have a low of RDS on 4.5 volts RDS on is what you want to look at that is when the Mosfet is fully closed. It will be on at a lower voltage but not fully closed or fully latched. IF it is not fully closed then you get heat issues. Most all data sheets of mosfets will have at the top a line saying Very low RDS on @ ?.? volts. If you look at the irf 8736 data sheet your using you will see. http://www.irf.com/product-info/datasheets/data/irf8736pbf.pdf You want to get you one around 2.5 volts. Although if you take the 47k out you might just get by with the one you have now. But it would not be ideal since it more then likely the gate voltage wont fully saturate or fully close the mosfet.

 

[interestingfellow]

yeah.... I know I'm about to the bottom of a bottle of merlot, but I wouldn't understand that without the alcohol thinning my blood....

Yes, I have both data sheets.
Yes, I see that the 8736 says "4.8m ohm @VGS = 10V". how the hell do you see 4.5v in there? vgs says +/-20v. I just don't getit.
Yes, the 8736 got quite warm while screwing around (but I'm a chain vaper, so that'll be important)
Yes, I meant IRL3103; sorry, and thank you. again, Rds is 12m ohm.
I don't understand how you get the lowest full on voltage from that. FYI: I don't really know what all the abbreviations mean (rds, vgs, etc). I'll google'm when I'm sober....er.

Straight up easy cheat answer: which mosfet do I want to use?
I'm trying to learn/teach myself basic electronics... that's kind of like a blind guy picking out his favorite porno, IMHO.

Thanks!!!!! (no, really)

 

[Java_Az]

This is what you want to look at not the ohms really( at least not for a simple touch switch)But for RDS on but the two voltages that i have underlined in green. You want your gate voltage to be between those two. Not the One underlined in red is just the gate threshold voltage. All that means is that is the voltage required to start turning the mosfet on. Basicly it just means you will get voltage/current flow from source to drain but it will be very weak. You need the 4.5 volts to let Current flow really strong between source and drain. If you look up how mosfet work it might help you. I had a few beers so i am not going to get into how they work tonight. But i will post a part better suited for your set up. Here is one that will work Dont really have more time to look more but it is not to bad a price @ $1.19 NDS8425 Fairchild Semiconductor MOSFET Power

 

[interestingfellow]

WOW! Sober, I can now more easily see what the abbreviations mean! DUH!!!
Thanks!

Also, I'm sure you could teach me more, but I get the basics about operation of mosfet. Now I'm learning the technical (like what Rds is, and why it's important).

I'll check that chip out,and report back!

 

[interestingfellow]

yeah. I still don't get it entirely.

but those nds8425's are $0.50 each? yeah, I'll get some of those in a bit.

for now I'm waiting on my free samples from Texas Instruments; I ordered 1 each of PTN04050CAZ, PTN04050CAH, PTN04050CAD, TPS43000, TPS43000PW, BQ25050, and BQ25050DQCR.

the firs three PTN04050's are variations (through hole, bga, smd) of a non isolated POL: I'm gonna do a vv single cell mod like another 18550 mod.
the other two chips are PWM controllers, just for fun, and since I got 5 free samples in 1 order.


EDIT:
Do I want to use a pnp mosfet with the 04050 chip?
what's the difference between a pnp and npn? pnp switches the positive lead and npn switches the negative? why would that be important?

...cool, thanks!

 

[Java_Az]

Mosfets would be P channel or Nchannel and yes one switches positive and one switches negative. PNP and NPN are usually in reference to transistors. They do act like a mosfet but they amplify the output voltage and cant handle lots of amps. As far as the 04050 chips people have been reporting problems using Nchannel mosfets on them. So you might want to go with a P channel.

The nds8425's are $1.19 a piece at mouser unless you buy 1000 of them then they cost 50 cents a piece. There are cheaper mosfets that would work out there but they are in smaller packages , like the super SOT 6 package. So they are more then twice as small as the SOIC 8 package. Not sure if you want to be soldering components that small.

 

[interestingfellow]

I've tried, and can't figure it out. How the hell do I search for the correct mosfet? Digikey doesn't seem to have it (if I searched right). Do I; go to a site, search for mosfet, and then filter in power rating, volts, package, etc? then just start checking the results? Digikey is my only base for comparison, btw.

Will a so-6 handle the 3amps required? I guess if it saturates fully, then it won't need to dissipate much heat, so it wouldn't matter.

Also, what difference does it make if it's n or p channel for the 04050 chip (the simple explanation, not necessarily technical)? I'm gonna try to look around here to see what i can see.

Thanks again!

 

[interestingfellow]

yeah, did a search for "04050 mosfet" and this thread is the only one to come up.
I hate sifting through hundreds of erroneous posts for 2 lines of pertinent info. Such is the evil of the internet...

EDIT:
after further consideration, I still don't see the difference between switching the neg or the pos.
How is it any different if you install the fet and switch the neg before it goes into the chip, as compared to after?
Did that q make sense?

 

[Java_Az]

This will work with the 04050 booster chip Digi-Key - FDS8433ACT-ND (Manufacturer - FDS8433A)
Pchannel will switch the positive going to the booster . a N channel would switch the negative. So Pchannel is short for Positive channel . But from what i have read in here if you use a Nchannel the booster will consume battery power when off .You could also use one of these with your other set up but your going to have to change it from switching the negative to switching the positive. Also A Pchannel would require a negative voltage applied to the gate to turn it on, where a Nchannel requires a Positive gate voltage.

This is about as simple as i can explain the difference in P& N channel mosfets
"N channel is used for switching negitive. P channel is used for switching Positive. The P channel uses a negitive voltage on the gate to turn it on and the Nchannel uses a Positive. Thats pretty much the difference in the two."

 

[interestingfellow]

I get the Posative switching vs the Negative switching difference as far as n or p channel. But I don't see what the difference is in these simple circuits, as far as where in the circuit you switch it.... here, check out the diagram, and you'll see what I'm having issues understanding, I think. Maybe I'm not getting it, because in my mind, I make it as simple as this.



Sidebar: For as smart as I am, I get stuck on stupid things: in grade school, it took 2 weeks for me to understand the difference between 2ft² and 2²ft. In middle school, I couldn't use the quadratic equation without understanding how we got it (my teacher had to dig through her college notes in order to show me), and then I understood it better than most. this n/p channel will be added to this list, once I understand it.

 

[Java_Az]

Looks like you got it. I edited it a bit , added the names of the pins and a gate and touch. Left out the resistor though wasn't a lot of room to work with.

 

[CraigHB]

But I don't see what the difference is in these simple circuits, as far as where in the circuit you switch it....

You're right, there isn't any difference functionally, similar to a mechanical switch. For a simple circuit, it doesn't matter whether you put your switch on the low side (battery negative) or the high side (battery positive). However, high side switches can be advantageous when working with more complex circuits. The conventional location for a switch is always on the high side since it facilitates an undisrupted path to ground (battery negative). Disruptions in the ground path can cause issues for more complex circuits with multiple ground connections. Even for complex circuits, you could still put your switches on the low side, but it's not worth the additional design considerations when you can use a high side switch freely without issue.

 

[interestingfellow]

LOW SIDE/HIGH SIDE!
That is exactly what I was asking about.

I can see your point (or at least just go with it); then why do people use n channel fets? I know in things like an audio amplifier in order to bridge the channels they have to be inverted, and you would need N for one side and P channel fets for the other side, in order deal with that type of situation.


Also, I'm still trying to understand why the irf8736 wasn't working on my touch sensor; is it that because it was operating at less than full open (4.5Vgs), it was more easily "grounding out" to the - of the atty through my lips? More so, I'm trying to figure out why others haven't had that problem. I can get the whole setup to work, but I gotta deep throat the atty (so i don't touch the metal edge under the sil plug)....not cool. I tried swapping out different reisistor values to see if I could get it to work (at least work better); nogo.



Anyway, thanks!

 

[CraigHB]

then why do people use n channel fets?

FETs have many uses besides high current switches. Not only are there N-channel and P-channel ones, but also enhancement mode and depletion mode which are opposites in that they shut off current rather than allow it to flow. Depletion mode FETs are fairly uncommon so ehancement mode is always assumed. Plus there are various types of FETs in terms of matarials and characteristics. "MOS" FETs are often used as switches, but are not limited to that use. That doesn't really address your question though. N-channels are often used for logic inverting or signal isolation. In my current mod I'm using 2 P-channel small signal FETs and 3 N-channel small signal fets for logic inverting and isolation for the MCU. On the power circuit, I'm using one P-channel for control and the DC-DC converter uses one N-channel and one P-channel, those three are high power. All in all, the P and N types are half and half.