Beginners Guide to Processing 18650 Cells | Cell Database


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Nano help...
#31
@Geek: that still comes to $2/Nano (with the link you posted).
What I was saying earlier that if you needed a nano/cell, then 1 14s string would cost you $28. Whereas the TI chip would only cost you $10 for the same string (plus a pcb and some other parts; but still cheaper overall)
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#32
The Bq76940 is a nice chip. I did a design earlier this year based on it and you can find designs on github with it predone if you want with balancing and all.
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#33
I'll check it out. Thanks. That'll help me narrow down bugs and such Smile
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#34
Here's an idea, not sure if it would work tho, so I toss it to you guys to get input.

So, as mentioned earlier, an optoisolator would allow a nano to sense higher voltages. Now, I know that the opto is either on or off. I don't know if they make variable output based on resistance. I'm going to guess no as it's like a photo-resistor on the sensing side.
Now, my question is, could you have a FET that would pulse at a frequency based on voltage? Example, say, at 1v the FET would pulse at 10Hz, and at 4v it would pulse at 100Hz (just throwing frequencies out there, nothing solid, just used for reference) Would the sensing side of the opto pick up on the pulses and transmit that to the nano via the PWM pins (or via some other translation whereas the pulses are converted to 0v-5v references for the analog pins). Then do the math and you could get what the input voltages are.

Not sure if this is kinda what Geek was referring to when he mentioned it earlier.
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#35
Voltage to hz is normal to sending it out to a master yes. But there are linear opto isolators too but they are expensive.
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#36
That will work, you need a voltage to pwm converter (ie LTC6992), there are also modules on ebay (look for voltage to pwm converter) a led-dimmer works at the same principle.
And a optocoupler fast enough to keep up with the converter... they are out there. Then read the pwm signal and converting it with the nano back to volt.
Thats a great idea.... Smile

like this?
https://www.maximintegrated.com/en/app-n...vp/id/4502
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#37
Or maybe pass the pwm output from the optocoupler into a simple filter circuit to convert it back into a stable analog signal and then read the result at the arduino analogue inputs.
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#38
And this is exactly why we have to collaborate on a project so that we all can benefit from it. We all can contribute to the ideas to help the knowledge of the forum grow. Smile

I like both ideas of wim and watts-on.
The pros about the LTC6992:
Frequency 3.81Hz ~ 1MHz
Voltage - Supply 2.25 V ~ 5.5 V
Current - Supply 365µA

The cons (from DigiKey):
Qty Unit Price Extended Price
1 3.83000 3.83
25 3.41720 85.43
100 2.16000 216.00
250 1.98000 495.00

Now, there is an eBay seller that as 5 for $25. But, that's more than DigiKey; so no go on that. The LTC6992 would be a good choice, however, it costs more than arduinos Undecided

Soooo, back to that drawing board, I suppose. We need cheap solutions! Tongue
Here's another voltage to pwm: https://goo.gl/vqwv39 (Jameco site). However, duty cycle is 50% max (not sure if that'd matter for our application), fall/rise time of 50ns, Switching Frequency 500KHz, max current 1000mA. However, it says output isn't adjustable. Not sure what that means. It costs about $1.25 @ 5 or more, or 25 @ $1.09, or 50+ @ $.99. So they are fairly cheap. Will they work?

The MP020-5GS looked good @ $.38, till I saw the voltages:
Voltage - Breakdown: 700V
Voltage - Start Up: 17.3V
Voltage - Supply (Vcc/Vdd): 6.6 V ~ 28 V
I suppose they'd work if they got their voltages from the string, as long as the string stayed top charged.

Would a flyback pwm chip work? Not sure what those do, just that they show up in the search for "voltage to pwm controller"

@watts-on: what kind of filter were you thinking?
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#39
Well thats why we're here for.. Wink

I do not think we going to find a "ready to use" solution cheap enough for you, you cheap **.....** Big Grin

An other idee,

If we first take a cheap micro controller like the attiny ( 10 for 10 Euro ) with a small program to convert volt to a very slow PWM signal (i am talking someting like 10 kHz ) take that signal to a cheap optocoupler like a 6N136 ( fast enough and only like 10 for 5 Euro ) and let a nano time the signal to convert to a voltage.
No need to convert te pwm signal to voltage first (is in essence the same what we do with te nano.)
Very little other components needed ( a few resitors and maybe some little caps ).
Calibrating throu the firmware, so it can be accurately.

Making any sense?

Only question, do you have a isp programmer?

(08-25-2017, 01:37 AM)Korishan Wrote: Where are you getting arduinos w/o bootloaders installed? How much?  Or even clones or non-duinos (same proc, but not made by them)

Fyi (if still relevant) Tongue

With bootloader ie
http://www.benl.ebay.be/itm/Atmel-ATMEGA...Sw-ldZX560

No bootloader ie
http://www.benl.ebay.be/itm/5x-ATmega328...SwGYVXA7bL

first hits on ebay, you will find them cheaper...
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10KW 3phase hybrid inverter. 25Kwh 18650 storage (for now)
My setup: http://www.diypowerwalls.com/t-Instant-powerwall
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#40
(08-26-2017, 07:01 PM)wim Wrote: I do not think we going to find a "ready to use" solution cheap enough for you, you cheap **.....** Big Grin

Hahah, yes, I am cheap. Well, not cheap, just super thrifty   Wink  I believe there's always a better and more economical way to accomplish a task.  Besides, I was just tryin to get away from an arduino per cell. that's just crazy as it's a lot of wasted power and pins.

(08-26-2017, 07:01 PM)wim Wrote: If we first take a cheap micro controller like the attiny ( 10 for 10 Euro ) with a small program to convert volt to a very slow PWM signal (i am talking someting like 10 kHz ) take that signal to a cheap optocoupler like a 6N136 ( fast enough and only like 10 for 5 Euro ) and let a nano time the signal to convert to a voltage.
No need to convert te pwm signal to voltage first (is in essence the same what we do with te nano.)
Very little other components needed ( a few resitors and maybe some little caps ).
Calibrating throu the firmware, so it can be accurately.

Making any sense? 

Only question, do you have a isp programmer?
Makes a bit more sense, yes Cool


I actually wasn't thinkin of the attiny. That'd be a nice little chip as you can get it with minimal stuff onboard. Altho, still a lot of i/o ports not used if it's per cell. 
But, if we go with the attiny as the string brains, and the optocoupler and the other tiny pieces, can probably come up with something super useful!  Smile
Uhh, I have an isp provider? Is that the same thing?  Tongue
The arduino programming interface with a few mods and communication board can program the attiny. I've seen a youtube vid on it, though I don't remember who did it. Showed like 3 different ways to program it.
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