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hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 05:40pm 05 Jun 2019
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The reference pin of the TL431 is on the left as the flat side faces up. It is high impedance till you get a little over 2.6V and never get higher. Then it turns into a zener and can sink lots of current, but not for long. I wouldn't subject it to more than that it will burn up quickly. There are many voltage divider calculators on the internet.
NEVER use just a pot as the voltage divider on the TL431(unless you are making a reference). The pot must always have a resistor in series to the higher voltage to limit current to the reference pin.
LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 06:00pm 05 Jun 2019
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I believed the spec'd current is 100mA continuous?
Solid advice.
There are no dumb questions.
I will (and am) walking away with a better and more refined understanding about this after you have asked all the questions, so please continue and the pleasure is all mine!
See, Andrew, Tinker dropped by and taught me a few more things I had never thought of before - critical safety features.
... and I wont have even known if you had not asked!
So you see why I told you that you need to run everything I say by a qualified electrician.
That's because I should have used the term "junction" instead of "middle pin".
By "middle pin" I meant the junction or the "middle point" of the two resistors. My lapse of memory caused you confusion. I will think a bit better next time.
I do most of my work here while in class so I can't draw and upload. Phones are for emergencies only - I will see what I can do when I go home but dad is strict about family and homework time so I don't get to do much around dinner time. Sometimes I get to sneak in during homework time because it's still on the computer but if he sees me drawing circuits I will be in trouble!
Of course you can - you can use 100W or 1kW resistors if you wanted to, nothing's stopping you but economics.
The question would then be - WHY would I dissipate 100W of power ($$$$) to measure panel voltage if I could get away with dissipating a few milliwatts ($) and obtain the exact same information?
.. and if all I am dissipating a few milliwatts, why use higher power ($$$$) resistors?
That was my line of thinking until Andrew, Tinker dropped by - you see I had only considered the power rating of a resistor but not the voltage rating.
The voltage rating of a resistor is a critical safety feature that tells us upto what voltage the resistor can be expected to behave as expected.
This voltage rating can vary for the same power rating of a resistor depending on the construction, manufacturing and design of the resistor.
A 1W resistor designed to operate at 1kV will be different in construction from a 1W resistor designed to operate upto 200V.
In our case, if we could find a 1/4W power rated resistor designed to operate upto 400V, we would be set - have a look around and see what you get, could you?
If I am not mistaken, standard/typical 1/4W power rated resistors are designed to operate upto 200V (which is why Andrew recommend putting two in series to operate upto 400V)
An alternative is to use standard/typical higher power rated resistors because they were designed to be used at higher voltages to begin with.
I do not know what those higher voltages are though - if someone can provide some input, I would really appreciate it!
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 03:33am 06 Jun 2019
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Thanks. You are an incredibly gracious person!
I think very few electricians would know beans about this stuff. Electronics and electrics are very different things. I have spoken to a number of electrical fitters/ engineers/ maintenance people that have been in the game for years and play with very serious electrics, motors, switchgear and the like. I jump at asking them questions about induction motor setups but I have been told more than once, you know a lot more about this than I do. It's simply not something they spend any time on in their work so logically, they concentrate their knowledge and skills on what they do need. They always have some interesting stories to tell though. :0)
OK, not a problem. That did pass my Mind but the more I read it the more I thought there was a pin I was missing somewhere. If I was not so ignorant with this stuff I would have known what you meant.
You are still at school? Geez, younger people are getting smarter and more switched on ( excuse the pun) every day!
The drawing Circuits comment made me laugh. I instantly got a mental image of you being interviewed in the future after some discovery or becoming the CEO of a major tech company and saying " I used to get in trouble from my father for drawing circuits when I should have been doing my home work". Sounds like the makings of a great passion and future accomplishments to me.
Next time your Dad is annoyed you are drawing circuits, remind him he should be proud you are doing that and not playing video games or hanging round shopping centres wasting your time doing nothing.
Your schooling IS important but it's also important not to stifle your passion and creativity.... especially when it's something worth while like what you seem to be interested in. Balance is the key. I personaly know 3 Very wealthy people that are Multi millionaires. Only one of them finished school. The other 2 are completely self made from ideas, hard work and following their interests. I have long said, education is great but you either have it or you don't regardless.
Seems to me you have the qualities well and truly in life to go a very long way.
I did read about splitting the resistance when I was looking up things about high power DC. Pretty much what I do with things anyway. I like load sharing and under rating and have set up all my solar arrays like that.
Thanks again for your help.
hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 01:16pm 06 Jun 2019
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I think you should read that again. Somehow some things got edited out.
The reference pin of the TL431 is on the left as the flat side faces up. It is high impedance till you get a little over 2.6V and never get higher. Then the reference pin turns into a zener and can sink lots of current, but not for long. I wouldn't subject it to more than that 5ma, it will burn up quickly. There are many voltage divider calculators on the internet.
The actual spec is 10ma. Getting any more than 1ma is bad design
100ma is thru the collector near saturation. As these are often used at much higher collector voltage, heat dissipation can be enormous and destroy the chip.
Who says PWM can't be MPPT. MPPT has become a buzzword and is often used incorrectly. Even Texas Instruments does and I do. If I didn't no one would understand what I am doing. MPPC is constant fixed panel voltage is nearly as effective and sometimes more. PWM with a capacitor bank holds the panels at the panels power point within a fraction of a volt. Edited by hotwater 2019-06-07
hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 01:59pm 06 Jun 2019
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I just lost my entire post. As I stated ONLY ONE question at a time. If you can't figure out panel, capacitor bank, controller, FET, heating element, you sure as hell shouldn't be working with over 200V. Draw a schematic and I'll correct it.
LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 04:22pm 06 Jun 2019
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So you want me to guess how you've set your system up and then you will tell me if I did it right and if not, where I went wrong?
OK, I will take you up on the offer: I will draw the block diagrams first.
You tell me if I did it right and if not, where I went wrong
Are you comfortable with Google Document that you will be able to edit and update saving your some work or you just want me to give you an image?
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:02pm 21 Jun 2019
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Many of these self powered solar circuits can go through a kind of agony at sunrise and sunset.
They start to power up, then when the load comes on, the panel voltage falls, and the system dies. It then tries to power up again. It will cycle on and off until finally there is enough power for the poor thing to self sustain and keep on running.
All this may be quite harmless, or it may cause something to be stressed and have a shorter than expected life.
Its probably better to have a system that cannot start up until there is sufficient power available for it to work as intended. And to shut down at some point before it gets really sick and really starts to suffer.Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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