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Topic: ADC and a zener  (Read 1 time) previous topic - next topic

Wawa

#15
Sep 22, 2018, 09:11 am Last Edit: Sep 22, 2018, 09:15 am by Wawa
Sounds like a fun tool to have in a workshop  :o

Grumpy_Mike

Sounds like a fun tool to have in a workshop  :o
It is. It is like a miniature taser, sparks and everything. You apply it to the outside of a box at everything you can see sticking out. So that is socket ends on all connectors, plugs and even through ventilation holes and slots. The box under test is on a table standing on a huge sheet of aluminium, surrounded by a large space, barriers and traffic cones, and warning signs.

Paul__B

Simple version is a gas stove lighter.  :smiley-lol:  :smiley-lol:

Grumpy_Mike

Yes but one without its own gas supply. :smiley-eek-blue:

polymorph

Hang on, hang on.

My question is, would one clamp that input signal back to the negative side of the voltage divider or to battery neg.
The voltage divider does not share negative with the battery in my circuit.
So what is the common point of reference, then? Voltage is the measurement of potential difference between two points.

I skimmed the responses, I didn't notice if someone addressed this already.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

ReverseEMF

#20
Sep 22, 2018, 09:27 pm Last Edit: Sep 22, 2018, 09:27 pm by ReverseEMF
It is. It is like a miniature taser, sparks and everything. You apply it to the outside of a box at everything you can see sticking out. So that is socket ends on all connectors, plugs and even through ventilation holes and slots. The box under test is on a table standing on a huge sheet of aluminium, surrounded by a large space, barriers and traffic cones, and warning signs.
You mean, like this: https://youtu.be/_fTC_Ud_k3U?t=6m26s
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

Grumpy_Mike

Well a bit more low key.  :)

LandonW

400:1 means you're measuring >1000volt?
Give us the full picture.

Forget about zener diodes.

You could use a 2-stage voltage divider, and clamp to the unregulated supply (5volt, 12volt) of that 3.3volt processor, with normal diodes. That would take care of positive spikes, negative voltage, even when the Arduino is off (unlike a zener).
Leo..
I'm building a plug in horse power calculator for a 600 vdc system.  R1 in the voltage divider is 10M ohms and R2 is 26k ohms.


sorry I was late to respond. I've been busy at work.  I will post a full schematic and all component information ASAP.



Wawa

More than 10,000volt is needed to reach 1mA pin fault current with a 10Megohm resistor.
Don't worry about protecting the pin from that.

What is important is that that 10Megohm resistor.
Flash-over is a greater danger, so it needs to be able to handle several Kv.
You can buy high-voltage resistors, but they are easily made from a string of lower value resistors inside a piece of heatshrink. A 10-string of 1Meg resistors could work.

Don't forget a (10-100n) cap between pin and ground.
That not only helps the A/D during sampling, but also kills spikes.
Leo..

LandonW

I'm actually using four 10M resistors in series parallel.  The math with just one resistor put me at 1/8 watt. All the resistors I'm for that circuit are 1/4 watt rated.
I'm at work now.  I will make it a point to give specifics when I get home.

Wawa

I calculate 1/32 watt for a 10Megohm resistor with 600volt across.
600*600/10000000= 0.036watt. Not a problem for a single resistor.

Common resistors shouldn't have more than 100-200volt across.
Use at least four in series, and more if you're expecting high spikes.
Leo..

LandonW

I calculate 1/32 watt for a 10Megohm resistor with 600volt across.
600*600/10000000= 0.036watt. Not a problem for a single resistor.

Common resistors shouldn't have more than 100-200volt across.
Use at least four in series, and more if you're expecting high spikes.
Leo..
that is true but I scaled it to work up to 1200 vdc...

I attached the schematic and parts list.


Wawa

#27
Sep 25, 2018, 02:39 am Last Edit: Sep 25, 2018, 02:47 am by Wawa
Seems you're overthink things.
1200volt across 10Meg is 0.144watt. Perfectly fine for a 1/4watt resistor.
As said, the only worry is flashover.

The R5-8 with zener and diode setup doesn't make sense.
It should be a single resistor to Trinket ground (with smoothing cap across).
That resistor should max have the Trinket's internal reference across (~2.23volt?), so dissipates virtually nothing.

The opto circuit is not correct.
An indicator LED (Vf ~2volt) across an opto LED (Vf ~1.25volt) won't light up.
Should connect both LEDs in series, and one diode across both LEDs (for AC).
Not sure why you use 10Amp diodes there. A 100mA 1N4148 is big enough for this. 1N4004 if you must.

I'm sure an L358 won't be happy with 1000volt on it's inputs...
Better use some clip-on hall sensor there.

+1 for the neatly drawn diagram though.
Leo..

Edit: A trinket has a 3.3volt processor, so I2C pull up should go to 3.3volt, not to 5volt.

LandonW

I'm sure an L358 won't be happy with 1000volt on it's inputs...
Better use some clip-on hall sensor there.

+1 for the neatly drawn diagram though.
Leo..

Edit: A trinket has a 3.3volt processor, so I2C pull up should go to 3.3volt, not to 5volt.
yes I failed to put that the orange would be 3.3 instead of 5...  The L358 isnt seeing 1000 volts its on a shunt resistor and should be around 75mV max at normal conditions. 
and for the CR1 and CR2 i was aiming for safety

Wawa

#29
Sep 25, 2018, 03:15 am Last Edit: Sep 25, 2018, 03:19 am by Wawa
The L358 isnt seeing 1000 volts its on a shunt resistor and should be around 75mV max at normal conditions.

and for the CR1 and CR2 i was aiming for safety
Might be <=75mV between the inputs, but your diagram shown them connected to the +side of the motor.
Opamp inputs shouldn't normally have more than the supply voltage of the opamp on them.

Understood, but not needed, and creating more problems.
Forgot to add that R9 also must go, and R2 also must connect to 3.3volt.
R2 can actually be removed if the Trinket has internal pull up enabled.
Leo..

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