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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Topic: Low Battery Indicator
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Author Topic: Low Battery Indicator  (Read 47777 times)

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Offline blkbd

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Re: Low Battery Indicator
« Reply #50 on: May 10, 2014, 04:43:19 PM »
Finding someone that stocks those resistors in a through hole configuration is proving to be challenge, Digikey, mouser are pretty much a no go, all I'm finding from them is SMD's

Thanks for the heads up,  :rockin smiley: Yeah the ones at Radio Shack have a 5% tolerance. I'll Google SMD and put in a order later this weekend. Thank you!  :thumbsup:

I take it 1/4 Watt is OK as long as the Ohm and 1% tolerance is correct?
« Last Edit: May 10, 2014, 06:12:18 PM by blkbd »


Offline blkbd

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Offline Visus

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Re: Low Battery Indicator
« Reply #53 on: May 11, 2014, 05:18:41 PM »
I owe you a beer or a six pack for that matter as I would have had to order from  different places, If your in NH drop me a PM.  :beer-toast:

Hope you have a sister who's a cheerleader or supermodel, hot geek will do nicely as well   :laughing2:   :thumbsup:

Offline blkbd

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Re: Low Battery Indicator
« Reply #54 on: May 11, 2014, 06:54:28 PM »
Hope you have a sister who's a cheerleader or supermodel, hot geek will do nicely as well   :laughing2:   :thumbsup:

No hot supermodel cheerleader sisters but if you piss me off I can introduce you to my ex-wife.  :laughing2:

Offline Jasen

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Re: Low Battery Indicator
« Reply #55 on: May 12, 2014, 12:54:46 AM »
I was looking for 1/8W which were near impossible to find anywhere.

Offline Visus

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Re: Low Battery Indicator
« Reply #56 on: May 13, 2014, 12:08:36 PM »
No hot supermodel cheerleader sisters but if you piss me off I can introduce you to my ex-wife.  :laughing2:

Im really not very choosey, are we talking one or two bags here.   :whistle::  jk

Hows that circuit coming along..   :stirpot:

Offline CraigHB

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Re: Low Battery Indicator
« Reply #57 on: May 13, 2014, 02:25:46 PM »

Offline blkbd

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Re: Low Battery Indicator
« Reply #58 on: May 13, 2014, 05:22:02 PM »
Im really not very choosey, are we talking one or two bags here.   :whistle::  jk

Hows that circuit coming along..   :stirpot:

She's cute but turned into a shallow evil succubus who would not give you a ride or a bottle of water if she found you crawling on your stomach in Death Valley at high noon while she was driving a semi full of spring water, And parts are on order.

Offline Jasen

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Re: Low Battery Indicator
« Reply #59 on: May 13, 2014, 07:33:27 PM »
You must have been looking in the wrong place;

http://www.mouser.com/Passive-Components/Resistors/Film-Resistors/Metal-Film-Resistors-Through-Hole/_/N-7gz41Zscv7?P=1yzaok0Z1z0wljo


 ;bow;

Apparently so, I think I found 1 of them at mouser.


I have an arthritic search finger, yea that's it.


« Last Edit: May 13, 2014, 10:49:39 PM by Jasen »

Offline mamu

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Re: Low Battery Indicator
« Reply #60 on: May 15, 2014, 11:40:04 AM »
I've been working with this and my setup must be funky as I can't get it to work with one red LED and the 10K (the LED is lit above my 6.3v cutoff, although dimmer at higher voltage), but it does work when using 2 red LEDs (LEDs off >6.3v and clear on <6.4v) like this...



schematic modified from here... http://homepages.paradise.net.nz/bhabbott/lvw.html

I'm using the LM431 and red flashing LEDs so maybe that's the reason.

Maybe I'll just tuck one LED behind the scenes.  :laughing:

Online Breaktru

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Re: Low Battery Indicator
« Reply #61 on: May 15, 2014, 12:12:07 PM »
I've been working with this and my setup must be funky as I can't get it to work with one red LED and the 10K (the LED is lit above my 6.3v cutoff, although dimmer at higher voltage), but it does work when using 2 red LEDs (LEDs off >6.3v and clear on <6.4v) like this...

I'm using the LM431 and red flashing LEDs so maybe that's the reason.

Maybe I'll just tuck one LED behind the scenes.  :laughing:

I'm using a single standard red LED and set for 6.0V as shown in the O.P.
Check the forward voltage spec of your LED and the ma rating. I'm using 2.0v, 20ma
You will also need a limiting resistor if using one LED
« Last Edit: May 15, 2014, 05:23:40 PM by Breaktru »

Offline blkbd

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Re: Low Battery Indicator
« Reply #62 on: May 17, 2014, 12:45:00 AM »
Going off of Kortts diagram and comparing it to Breaktru's schematic is this correct for a dual battery setup?

The 15K will be replaced by the 10K
240 willbe replaced by the 2.2K
the 4.7K will stay the same
and the 22K will be replaced by the 3.3K

Here is a pic using Kortts diagram. http://i1262.photobucket.com/albums/ii617/blkbd/kortt-LVI-2cell_zps9803df59.jpg

Offline Jasen

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Re: Low Battery Indicator
« Reply #63 on: May 19, 2014, 01:34:57 AM »
So as usual I've learned some very useful info here which got me taking a second look at things.
I'm going to run the Panasonic NCR18650PD High drain 2900mAh 10A in my PTR08100 build. What I learned tonight is they have a max discharge of 2.5V I'd like to tweak the low batt indicator to say 2.7V is that a matter of changing one resistor up or down, which one, or is it more involved then that.  I could sort it out myself w/ a little direction on where to start.

Offline memoevapor

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Re: Low Battery Indicator
« Reply #64 on: May 19, 2014, 07:09:06 AM »
Jasen, I am curious as to how much vape time is gained by having the indicator come on .6 v below the one in the OP?

Offline tommygun

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Re: Low Battery Indicator
« Reply #65 on: May 19, 2014, 07:43:13 AM »
So as usual I've learned some very useful info here which got me taking a second look at things.
I'm going to run the Panasonic NCR18650PD High drain 2900mAh 10A in my PTR08100 build. What I learned tonight is they have a max discharge of 2.5V I'd like to tweak the low batt indicator to say 2.7V is that a matter of changing one resistor up or down, which one, or is it more involved then that.  I could sort it out myself w/ a little direction on where to start.

Jasen, use Breaktru's diagram for the single battery set for 3V: http://breaktru.com/smf/index.php?action=dlattach;topic=804.0;attach=1634;image
Running the battery down to near max discharge can't be good. You will be safe at 3v. What will you gain by running down to 2.7v? A few more puffs?

Offline blkbd

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Re: Low Battery Indicator
« Reply #66 on: May 19, 2014, 07:45:47 AM »
Going off of Kortts diagram and comparing it to Breaktru's schematic is this correct for a dual battery setup?

The 15K will be replaced by the 10K
240 willbe replaced by the 2.2K
the 4.7K will stay the same
and the 22K will be replaced by the 3.3K

Here is a pic using Kortts diagram. http://i1262.photobucket.com/albums/ii617/blkbd/kortt-LVI-2cell_zps9803df59.jpg

Can someone confirm the diagram is correct for a dual batteries?

Offline Visus

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Re: Low Battery Indicator
« Reply #67 on: May 19, 2014, 07:53:32 AM »
There has to be a way to toss in a trimmer to dial  this circuit..  I am not sure where to place it and what resistor value to change.  My guess would be add a 4.7 resistor in place of the 10k and a 10k trimmer.   :Thinking:

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Re: Low Battery Indicator
« Reply #68 on: May 19, 2014, 09:30:21 AM »
Can someone confirm the diagram is correct for a dual batteries?

Yes, that would work for two series batteries with an indication at 6.0V

Offline blkbd

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Re: Low Battery Indicator
« Reply #69 on: May 19, 2014, 09:33:59 AM »
Yes, that would work for two series batteries with an indication at 6.0V

Thank you very much you  :rockin smiley: I guess watching some of those tutorials is paying off.

Offline CraigHB

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Re: Low Battery Indicator
« Reply #70 on: May 19, 2014, 04:00:16 PM »
Running the battery down to near max discharge can't be good. You will be safe at 3v. What will you gain by running down to 2.7v? A few more puffs?

More wear occurs at the end of the discharge curve than anywhere else so you do gain some longevity by not taking a cell down to the minimum allowable discharge voltage.

However, how much capacity you leave behind depends on the battery and the load.  In general, the discharge limit applies under load.  If you look at a cell's discharge curves, you can see a big difference there.  So you have to consider the battery characteristics and the load it's under when a discharge condition is detected. 

A high drain battery does not dip in voltage as much under load as a standard battery and that can make a big difference in detection.  For any battery you'll find the voltage higher when you check open circuit voltage open after a discharged condition has been detected.  Voltage can be quite a bit lower when the battery is loaded.



Looking at the curves for the NCR18650PD, you can see that taking the battery to 3V with a maximal load leaves about 500mAh untapped.  However taking the cell to 3V with a 3A load only leaves about 100mAh untapped.

Panasonics cells are unusal in that they don't have as tall of a curve as other cells.  If you do the same check with a higher drain cell, you'll find the difference much smaller.



For this cell, there's a difference so small you can't even see it really.

Offline Visus

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Re: Low Battery Indicator
« Reply #71 on: May 19, 2014, 06:10:39 PM »
Noone answered my question, booo lol  I found another circuit that did.

Because some batts best at 3.2-3v some IMr ok at 2.9v and having a dialer option would be awesome when swapping out batts after old and not have to dig in there because specs are worse or better 6v is a little low for me on the series.  I swap mine out at 6.6-7v.

Heres another 2 LBI circuits..

The data sheet circuit figure 26 so many ways to skin a cat --uber fun,  I need some parts.. lol
http://www.ti.com/lit/ds/symlink/tl431a.pdf

.

« Last Edit: May 19, 2014, 06:35:41 PM by Visus »

Offline Jasen

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Re: Low Battery Indicator
« Reply #72 on: May 19, 2014, 08:37:51 PM »
Visus, I'm not going to answer your question either, because I don't know ;)

Just thought it might give me a bit more vape time, but it looks like it's pretty much a mute point.

Offline Visus

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Re: Low Battery Indicator
« Reply #73 on: May 19, 2014, 10:37:05 PM »
Thats why I loaded more circuits jasen, you can also dial down breaks origin circuits   more stuff for us to play with, the parts are so inexpensive its also fun learning how to do it another way and the professors way.  One good thing about electronics is, there's probably a hundreds ways to sunset to get there.

the formula is in mamu's post.
Quote
When the device is operating with two external resistors (see Figure 2), the total dynamic impedance of the circuit is given by:
which is approximately equal to .     (1+r2/r3)



 I wanted to intensify the led with very slight turn on if possible and have higher turn on so woot more stuff to play with.  My complements to having so many lessons learnable on here thought pattern, "Don't just copy visus blow some shiz up lol..."

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #74 on: May 28, 2014, 10:11:50 PM »
I found it!
That's what i was looking for...

Do you think this will work???

hi Pako....i was looking at your circuit diag and wondering why it didnt work.....so decided to try it myself ! :).....didnt work for ME either...

so i played about with the 2 resisters and finally got this

now...granted, i only had a BC547B available so i dont know if that was the difference....but now i get....

4.2V fresh battery = Strong green light

3.4V                       =Still Green but dimmer

3.3V                       =Green AND RED

3.2V                       =Red light dim (ish) but gets stronger as you drop to 3v

now i am no expert....so maybe someone can work out if other parts are stressed or not....or what the total power consumption would be....but i feel sure it can also be tied to the fire button to just display when your using the mod....
« Last Edit: May 28, 2014, 10:24:41 PM by SilenTDoGz »

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #75 on: May 29, 2014, 04:22:50 AM »
Oh...and  i Know this is an old Post now...but as i had the previous circuit set up for single cell, i decided to modify it for Dual cell tricolour leds...think this one May suit Visus's needs

8.4V  ~   6.6v     = LED shows Green

6.5V  ~   6.2V     =LED shows Orange

6.1V  ~   Down   =Led shows Red

Once again, NO expert, but had it breadboarded and seems to work fine. Check it out yourself before you glue together huh :)....

Offline CraigHB

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Re: Low Battery Indicator
« Reply #76 on: May 29, 2014, 05:35:57 PM »
now i am no expert....so maybe someone can work out if other parts are stressed or not....or what the total power consumption would be....but i feel sure it can also be tied to the fire button to just display when your using the mod....

The draw on that ciruit is always at least as much as the LEDs so you definitely would not want the circuit powered other than when the trigger button is pushed.  Since voltage is higher with series cells power consumption will also be higher.  As far as components being stressed, there should be no issue.

--------------------------------------

For anyone interested, here's how you would estimate power consumption for all the components in the single battery circuit;

Voltage at the 1k resistor will be that of the transistor base pin which is always about 700mV (the base-emitter junction of a bipolor transistor is like a diode).  Current through that resistor is 700mV divided by 1k which is 700uA.  Using I squared R, power consumption at the 1k resistor is small, about 500uW.

Voltage across the 340 Ohm resistor will be battery voltage minus the LED drop minus the diode drop minus the base drop.  For a worst case, that would be 4.2V minus 2V minus 700mV minus 700mV which is 800mV.  Current flow is 800mV divided by 340 Ohms which is 2.4 mA.  Using I squared R, power consumption at that resistor is small, about 200uW.

Power consumption at the diode would be LED current times the voltage drop which is 2.4mA times 700mV for 17mW, no problem for a 250mW diode.

Currents through the transistor base will be that of the LED less the current flow through the 1k resistor.  The 1K resistor is drawing 700uA so that's 2.4mA minus 700uA for 1.7mA through the base of the transistor.  Multiplying by the base voltage drop, it's 700mV times 1.7mA for 12mW on the transistor, no problem there.

When a bipolar transistor is biased and conducting, the voltage drop at the collector to emitter junction is small so there's negligible power considerations for the transistor on the opposite side of the circuit.  Though, for big currents in other applications it can be a consideration, but not here.

Power consumption at the 110 Ohm resistor has to be considered under under two cases, when the transistor is on and when it's off.  When the transistor is off, voltage across that resistor is battery voltage less the drop from the LED.  The LED part of the circuit does not fully conduct until the transistor shuts off around 3V battery voltage. 

So voltage on the 110 Ohm resistor would be 3V minus 2V.  Current flow through the resistor will be 1V divided by 110 Ohms which is about 9mA, Power consumption there is about 9mW, well within the 250mW limit of a typical through hole resistor.

The highest power consumption occurs when the transistor is on and the 110 Ohm resistor is carrying the full voltage drop of the battery.  The worst case is 4.2V divided by 110 Ohms for 38mA.  Power consumption for the resistor is 160mW.  That's a bit high, but still within tolerance of a 250mW through hole resistor.

You could add up all the nodal currents I pointed out to find total draw.  I'm not going to crunch the numbers, but it's not going to be hugely more than that of the LEDs.  These are not big currents, but they're also not currents you would want full time on a battery.

For the circuit with series cells, I'm not going to go over the nodal analysis there, but you get the idea if you want to try it as an exercise.


« Last Edit: May 29, 2014, 06:05:11 PM by CraigHB »

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #77 on: June 05, 2014, 07:40:58 AM »
hmmm....post is cocked up :)...wait, let me try this..


i was having a think about this, and if it was tied to the fire button, would there  not be a false voltage reading due to the load on the batteries?


The draw on that ciruit is always at least as much as the LEDs so you definitely would not want the circuit powered other than when the trigger button is pushed. 


« Last Edit: June 05, 2014, 07:49:34 AM by SilenTDoGz »

Offline blkbd

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Re: Low Battery Indicator
« Reply #78 on: June 05, 2014, 11:14:33 AM »
The circuit or battery indicator is always on there for always drawing power, No big deal but if you leave it for a week in a weakened condition could over discharge the batteries, That how I see it but then I'm definitely not a electrical engineer.   

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Re: Low Battery Indicator
« Reply #79 on: June 05, 2014, 11:28:25 AM »
I always use an on/off switch at the battery

Offline blkbd

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Re: Low Battery Indicator
« Reply #80 on: June 05, 2014, 11:44:39 AM »
While we are at it what is the specs or model number for the tricolor LED?

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #81 on: June 05, 2014, 01:35:19 PM »
ah well.....the exact model i cannot give you.....a box of these things.....sorted as 5mm standards....but i am sure they are very close to this or equivalent

http://www.rapidonline.com/electronic-components/kingbright-5mm-red-green-led-tricolour-clear-56-0685

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #82 on: June 05, 2014, 01:59:11 PM »
I always use an on/off switch at the battery


..and i agree with that also!....especially if you have many mods you use.....but if you did not want the circuit to be connected full time Mod is on, then maybe consider a small tactile switch just to make the circuit to check on occasion the state of charge. Many ways to do things i suppose

Offline Visus

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Re: Low Battery Indicator
« Reply #83 on: June 05, 2014, 05:41:48 PM »
Wow this post went for a run again I found what I was looking for haven't built the circuit yet.  Busy and its on the burner I know when I need to change batts except when outside the house cannot hear the darn thing pwm rattle lol I need the circuit after all..

Thanks heres where I found it, also super fun circuits to play with..
http://talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#BatteryLowBeeper

Thanks craig for the defining of it..

15 bucks and you get a lot of play with items..

Offline SilenTDoGz

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Re: Low Battery Indicator
« Reply #84 on: June 05, 2014, 06:06:30 PM »
$15......??? Jeez , you must be MADE of money...... oh_my:

Offline Jasen

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Re: Low Battery Indicator
« Reply #85 on: July 22, 2014, 09:47:38 PM »
Can someone take a look at this battery health set up.

 
I based it off of SilenTDoGz's set up here.





Offline blkbd

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Re: Low Battery Indicator
« Reply #86 on: July 22, 2014, 11:16:47 PM »
Not sure about the schematic but doesn't the DNA 30 already have a battery indicator?  But if you want it that schematic
by SilenTDoG requires two LED's, One green and one red. But I'm no expert and I know someone will check it out that can give you a proper reply to your post as this forum is the best I have been to.
« Last Edit: July 22, 2014, 11:31:49 PM by blkbd »

Offline Jasen

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Re: Low Battery Indicator
« Reply #87 on: July 22, 2014, 11:23:54 PM »
Yes, but I wanted something in my face. It would also make for a quick easy check w/o really looking to see if it's off or on before I toss it in my pocket,

Offline CraigHB

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Re: Low Battery Indicator
« Reply #88 on: July 22, 2014, 11:46:53 PM »
It should work, but you might have to tune it on the bench a bit, should be around 3V though.  Didn't someone already do that in this thread? (not going to go re-read the whole thread).

The one issue with that circuit is it draws Vin/110 plus the bias current for the green LED when the transistor is on and the red LED is off.  That's going to be about 40mA so it's not something you want to power all the time or it will drain the battery.  You'd have to set it up so it's powered only when the atomizer is triggered which will require another transistor slaved to the atomizer.

Offline Jasen

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Re: Low Battery Indicator
« Reply #89 on: July 23, 2014, 12:25:53 AM »
I was using the IPD mosfet based off Break's touch switch and using the fire switch as a trigger for the mosfet to initiate the LED.

I figured I could not wire it to the atty power because the V will not be a constant w/ the V/V V/W of the DNA.

Craig, this is the post I and I believe you are referring to.

Quote

SilenTDoGz
Jr. Member

hi Pako....i was looking at your circuit diag and wondering why it didnt work.....so decided to try it myself ! :).....didnt work for ME either...

so i played about with the 2 resisters and finally got this

now...granted, i only had a BC547B available so i dont know if that was the difference....but now i get....

4.2V fresh battery = Strong green light

3.4V                       =Still Green but dimmer

3.3V                       =Green AND RED

3.2V                       =Red light dim (ish) but gets stronger as you drop to 3v

now i am no expert....so maybe someone can work out if other parts are stressed or not....or what the total power consumption would be....but i feel sure it can also be tied to the fire button to just display when your using the mod....


Offline CraigHB

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Re: Low Battery Indicator
« Reply #90 on: July 23, 2014, 02:26:54 AM »
That's the post I was thinking of.

It's not a problem switching battery power to the monitor circuit with a mod that uses a main power switch to fire the atomizer, but if you want to run the detector with a controller board, the problem you run into is the board does not switch battery power.  It only switches atomizer power.  In that case you need to switch battery power to the monitor with a transistor slaved off the atomizer.


« Last Edit: July 23, 2014, 02:32:16 AM by CraigHB »

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Re: Low Battery Indicator
« Reply #91 on: July 23, 2014, 08:55:05 PM »
Chraig, so I'd do it like this and I just need to sort out what transistor to limit the power from the atty to the mosfet trigger lead?


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Re: Low Battery Indicator
« Reply #92 on: July 24, 2014, 01:34:10 AM »
Jasen I would email Brandon @ evolv there may be a way to do it off the dna board but of course tiny soldering but ya,  Mamu did a really awesome display led on a nivel chip direct off the board so I figure it may be possible to do it off the dna, I may be way out in left field but much less parts count is always the plan..

Other wise there a post is about using an ic comparator with one part and resistors not a mosfet and two trans etc. that will do exactly what you want.
Tinker Ray was making his do exactly what you want..---->
http://www.e-cigarette-forum.com/forum/battery-mods/509605-raptor-flip-top-vv-mod-20a-120w-dc-dc-converter-24.html#post13274740

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Re: Low Battery Indicator
« Reply #93 on: July 24, 2014, 01:52:31 PM »
Using a comparator would be the smarter way to set up a detector, but even so you still have the issue of access to battery power when using a controller board.  A comparator circuit would consume less power than the posted circuit, but you still would not want to power it full time. 

With a comparator based monitor and a controller board, you still need to slave the monitor power supply off the atomizer.  The DNA switches battery power to the converter, but you would need to solder a wire to a component pad on the PCB.  Not something I would not do myself, really sketchy, could rip up the pad pretty easy and I doubt Evolv would warranty damage like that.

It's not a complicated task to switch power to the battery monitor, just use a small power MOSFET in an SOT23 package which is not terribly small or hard to work with.  You don't need the transistor with the question mark.  Just the one MOSFET will do.  The MOSFET gate is driven by the atomizer.  The drain and source of the MOSFET switch the power supply to the monitor.

To work with the logic polarity of the atomizer (high = on, low = off) you need to use an N-channel MOSFET configured as a low side switch.  The low side (battery negative) for the monitor is switched, not the high side (battery positive).   The connection is as follows;

Ground for the detector connected to NMOS drain. 
Battery negative connected to NMOS source. 
A pull-down resistor connected from gate to source.
Atomizer positive connected to the gate.

You can reverse logic polarity by adding another transistor (the transistor with a ?) enabling you to use a high side PMOS switch instead of a low side NMOS switch, but there's really no need to do that.


« Last Edit: July 24, 2014, 02:18:24 PM by CraigHB »

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Re: Low Battery Indicator
« Reply #94 on: July 24, 2014, 08:05:37 PM »
Visus, Craig, thanx for the guidance, I'll do my research into both of your ideas this weekend.

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Re: Low Battery Indicator
« Reply #95 on: July 24, 2014, 10:15:38 PM »
I think this N-FET meet's my needs for a single 18650 and standard red/green LED 2V-2.2V, it's also the lowest resistance I could find at 23 mohm.

Infineon BSR802N L6327


Transistor Polarity:   N-Channel   
Vds - Drain-Source Breakdown Voltage:   20 V   
Vgs - Gate-Source Breakdown Voltage:   8 V   
Id - Continuous Drain Current:   3.7 A   
Rds On - Drain-Source Resistance:   23 mOhms   
Configuration:   Single


http://my.mouser.com/ProductDetail/Infineon-Technologies/BSR802N-L6327/?qs=sGAEpiMZZMshyDBzk1%2fWi4GEWCr0KJSEQWPFR6yCrBE%3d


I'm kinda clueless as far as  pull-down resistor though.


Trying to figure out LTspice but I can't for the life of me figure out how to add a new component and it's values to LT's component list.
« Last Edit: July 24, 2014, 10:47:28 PM by Jasen »

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Re: Low Battery Indicator
« Reply #96 on: July 25, 2014, 12:55:33 AM »
You have to use the stock components in LTSpice unless you import your model, which is not terribly hard to do, but rather involved.  What I usually do for a quick check on a transistor circuit is use a canned part with similar specs if I can't find the exact part number in the library. 

To add a transistor to the schematic in LTSpice, press F2 to get the parts list and then select the generic NMOS or PMOS as required.  Add the generic part to the schematic then right click on it to get the option box.  Click the "Pick New MOSFET" button and select your part number.  Don't use the generic ones in an actual simulation, they don't work right.  They're only placeholders to provide a way to call up proper part numbers.

That FET you selected should do the job just fine.  You could even go as high as a 1/2 Ohm "on" resistance since the currents required to power the monitor are pretty low reducing the effect of switch resistance on voltage drops.

Pull down resistor values are not critical, anything between 4.7k and 47k should be fine.  10k would be a typical value.

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Re: Low Battery Indicator
« Reply #97 on: July 25, 2014, 02:02:32 AM »
Craig, if you ever need some guidance in hanging a door, setting a window, installing some cabinet's, you just let me know and I'll be glad to talk you through it.

Thanx again

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low voltage indicator
« Reply #98 on: August 29, 2014, 11:06:44 PM »
I have a unregulated mod running with a mosfet and an led button that lights up and I'm working on some kind of low voltage indicator for it. My thought was adding a zener diode on the resistor so that if it reached the low point the button wouldn't light up when pressed. Does that sound like it would work?

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Re: Low Battery Indicator
« Reply #99 on: August 30, 2014, 06:58:29 PM »
People like to think Zener diodes are digital devices for some reason, either on or off.  They're not.  They're analog devices.  They gradually increase current with voltage then quickly increase current with voltage after their breakdown voltage.  What you'll get is a light that brightens as voltage changes which can work I suppose, but it's not going to give you any kind of pass/fail indication.  You need to use a comparator or voltage detector to fully light the led when voltage falls below a threshold.

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