« first day (1713 days earlier)   

6:17 AM
@Asmyldof Looking into a different segment is not being a bastard. And the two example panels probably come with different quality, nothing wrong with that.
 
@jippie :-P You can make your own for about €0.7/Wp
just need some glue and something to stick the cells onto
bonus: you can decide the current & voltage
 
Physical things aren't my best
 
Ah, the great thing about solar is, worst thing that can happen is it doesn't work
no fire or such
 
I beg to differ
It wouldn't be your first solar panel that catches fire
 
I have not had any fires that weren't intended... see my discussion with @PlasmaHH
:-P
 
6:25 AM
too much scrolling back :-p
 
The silicon won't burn. It may glow
 
Did you see the solar power cycle path?
not the dutch one
but the
japanese or taiwanese or so?
the one where you cycle under the panels
 
the one with the panels in a roof over the path along a main road?
 
yeah
I want that in my garden to sit in the shade :-p
some day when I'm rich
 
Don't have to be rich anymore
Full installation should be possibly at € 2/Wp
 
6:28 AM
I first have to weed through my garden to get to the spot where I want to sit down.
 
lol
Just have to buy the right stuff at the right place
 
I need a contractor to remove the forest from my back yard
 
Or a flame thrower
@crasic sounds interesting. Two or three years ago I would have loved to see the progress or help. These days I use Eagle for stuff from others or for others and all the libraries they then have, etc, would probably add more overhead through your system.
 
hmmm, now there is an idea
 
How will you make Eagle load them, by the way?
I'll look for the black smoke and eventually burning house to see where you used to live
 
6:32 AM
@Asmyldof I wish I owned my roof :-/
 
@jippie you could have them mounted on a rack that folds over it from both sides
:-P
 
@Asmyldof I bet the neighbours wont mind
 
Of course not
Anyway, have to go. Have to return the bike in veldhoven after refueling :(
Had I not invested in new Rigols I might have asked them if I could keep it for €18k
 
enjoy
 
(And then made the Belastingdienst pay for half of it Jan 2016)
 
6:35 AM
:-|
 
 
1 hour later…
8:03 AM
good morning
 
 
4 hours later…
12:09 PM
They wanted 21k for it.
Too much
Can get it with <10km for that
 
12:46 PM
@Asmyldof you're probably right about the "shopping comment"
 
@Christoph it gets outdated so quickly
A chemistry and its behaviours is a valid topic, it'll be around for years
But beyond that
What you want, probably, is a simple $ 0.5 (bulk) chip that controls 2 internal or external MOSTs
 
my original thought was that knowing why a part works would benefit others, but you're right
 
Or a board, if you aren't designing in quantity that costs $1 or less for the chip, the board, the MOSTs and the capacitors and resistors
 
yes, I think the BQ29700 is more what you had in mind
 
That's exactly the line I'm thinking along
 
12:49 PM
I hoped to be able to create a PCB for the solar buck, the battery protection, and maybe a small MSP430
 
If you can CC/CV the buck regulator for highest charging efficiency, that chip is all you need, set at the right voltages of course
It is up to you
But I'd be lying if I said I hadn't just used a PCB in the middle of my own PCB before
:-)
Chinese Guy makes 100000 PCBs, sells me 10, I solder those in my design: done
No seeking MOSTs
 
is it safe to say that the smarter the buck regulator, the harder it will be to control it with a uC?
I hooked up a PWM output to an opamp to a buck regulator's FB input in LTspice, and that seemed to work, but real life will surely be different
 
@Christoph Not absolutely
It can very well be that you can force a regulator into low and high power peak behaviour, but how to best do that is always down to specific topologies
And some are harder than others, but it's not always just down to internal complexity
Your idea of FB manipulation is one that is not unheard of in the first "Digital Bench Top Powersupplies"
Or, "Switching Digital ..."
Saw one design with a pre-stage that was controlled by the chip with a capacitor barrier, PWM and op-amp smoothing, allowing the chip to regulate the incoming voltage to about 4V above linear output and then regulate the output linearly
pre-stage was a simple TDA type Flyback chip
Not the neatest solution, but it worked okay, if you accept some extra 15 ~ 50kHz noise levels
 
I think I have to accept that if I want to mess around in the regulator's feedback path
 
1:04 PM
If you want a robust solution you need to know about poles and zeroes and control theory and know what happens in bode plots when you do X or Y, so you can prove that your system will always work. If you're just designing something as a one-off or several-off, you can use a lot of common sense and a little insight about feedback loops to give yourself a better-than-90%-guarantee
 
is 90% pre- or post-simulation?
 
Post sim, pre-week(s)-of-testing
 
sounds good
 
simulations cannot give 100% ever, without re-doing some maths yourself
simulations are very good these days, but there's a reason many critical devices get tested in Autoclaves and damp-heat chambers, etc
I think in most DIY cases 90% is the best you're getting post-sim for any design
But, anyway, it should be possible, for a first try to use some Op-Amp sense applied to feedback and current sense loops on an out-of-the-box controller
If you have one with a current limit and a voltage limit, set by external resistors there's a much better than 50/50 shot you can control both domains with some evil trickery
Depending on the values of those resistors the trickery may take more or less tuning of components, but that will all be revealed once you know your requirements
As long as you have the patience to wait here you can always link some stuff here for me to look at, but if you have selected a device, thought of an idea and want to know if it would work and possibly how, you can always ask another question to get some more perspectives on that
(question as in on the ee.se site itself)
 
more specific questions is what I'm heading for, because now that I have an idea about the overall topology of the thing I can break it down into smaller domains and think about them (and I hope I don't forget about your argument about overall vs. local efficiency from yesterday)
 
1:14 PM
BTW, for the fun of it, I looked at the BQ29700 series datasheet again, the BQ29706 seems to be geared for LiFePO4 fixed current fast charge
It is a very important one. Never start optimising at the beginning, progress further and then forget to look back
It's okay to optimise locally, but always look around the schematic if what you are doing actually makes sense for it all
 
the bq29706 because of the 3.85 overvoltage level? IIRC the recommended maximum voltage for LiFePos is around 3.65 volt, so that looks ok
 
Many pre-produced boards actually specify 3.9V
LiFePO4 is a little more forgiving, as long as you don't keep it at that level for prolongued times
So, in fact, your system efficiency can benefit from you making the buck regulator 3.9V/3.5V settable. You could use PWM, but those two would be enough to keep the battery full but in shape
Or maybe 4V
Another thing, best safety is of course to have your BQ297##-type protector to be as close to the actual cell as possible in all regards
 
1:30 PM
I'm currently building a simulation for PWM-controlled switchable CC/CV.
 
I'd advise you in the final product to keep the system's long-term float voltage below 3.6V because of the flat plateau, keeping the cell at 3.5V or 3.55V won't cost you much of the capacity, but gives you some margin for error in your settings
Especially with thermal differences some set points may turn out to be very different in the real real-world.
If only for thermal gradients of the resistors used
 
1:57 PM
CC controlling a buck regulator with unknown-if-suitable OpAmps and the knowledge of a mechanical engineer is a pita. I'll go for something simpler like you suggested!
switching the buck regulator between 3.5/3.9V is a lot easier with a selectable voltage divider, which I can do with a simple transistor
 
:-)
Always go for solutions no more than 2 steps ahead of your knowledge, unless you have no other option
Next time you'll probably be more at ease using 3V to 4V ranging
 
so now my charging algorithm looks like
1) charge to 3.9V, current limited
2) let relax to 3.5V
3) CV charge at 3.5V
 
3.5V will not be charging, it will let your cell dictate untill it is discharged to 95% and keep it there until the cell gets really used
If you set it at 4V highest, your controller will see the "release" of the protection with a bigger margin
it will flop up to 4V at 3.85V
so to speak
 
2:17 PM
I understand the flopping up part, but why is 3.5V not charging? at some point the cell will be at those 3.5V (or 95%), and then it will be charged while the regulator charges the battery and supplies the application circuit
 
Assuming you charge up to the flopping point, your battery will be "fuller" than the 3.5V
But it's "risky" to try and keep it at full, since both the battery's full and your circuit's settings will be somewhat temperature dependant
So it's better to relax to 3.5V
It'll also keep the cell healthier for longer, most likely
But, probably at 10mA drain the "fuller" part may only be minutes
95% is just a number that tumbled out of my behind
 
thank you, I'll ask again when I have a schematic (when I'm sufficiently confident that I got it right I'll ask another question on the main site)
 
Feel free :-) Good luck
 
 
1 hour later…
3:39 PM
I am plorb
 
is that edible?
 
3:50 PM
bite
No
 
@Asmyldof, gotta design something with MOSTFETs now.
 
@ThePhoton It's Metal Oxide Silicon Transistor, it's completely valid
That we conveniently leave out the field effect is nobody's business but our own
 
@Asmyldof That stupid automotive networking thing was the stupidest project I ever worked on in my life.
 
....
I looked at the page for 5 seconds before deciding I was not going to invest serious life-seconds to further read text
Is that bad?
 
@Asmyldof Not unless you want to sell fiber optic transceivers to German auto companies.
 
4:00 PM
I don't, because they won't buy from me anyway
 
@Asmyldof Your fab is probably not big enough.
 
@ThePhoton My fab can be as large as need be if I have potential customers
No issues there
 
Also I'm pretty sure the environmental testing documentation has to weigh more than 1 year's production of parts to get a part qualified for the automotive market.
 
I have good contacts and my credit rating is platinum-plus-AAAA-triple-A-gold-plus
Testing can also be arranged.
With people who probably already know that document
 
@Asmyldof Unless your real name is actually Philips, I'm pretty sure you'd actually have trouble getting enough credit to build a fab.
 
4:04 PM
As I said, I have contacts
I don't need to build a fab
And if my name was Philips I'd have jumped of the roof of the Strijp S tower
 
@Asmyldof Then you'll have a lot harder time making money at it.
 
You don't need to make money on the first 10000
 
Making it harder to get funding.
 
You need to make name
 
@Asmyldof Nobody in the automotive business wants to buy just 10,000 of something.
Before they'll even talk to you they want you to show how many million per year you're prepared to supply.
 
4:12 PM
Good reason to not talk to them then
I'll stick to motorcycle-tive industry then
 
4:24 PM
frown most. annoying. project. ever.
Now that I have ordered nearly all components, the customer decides they'd rather not use batteries and stuff
Guess I'm going to be building a LiFePO4-equipped motorcycle sooner than I thought.
e-motorcycle*
 
4:46 PM
@Asmyldof Iiiiii ... don't want a pickle....
 

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