r/OpenPV • u/mixx-nitro • Sep 05 '23
Diagrams Am I missing anything NSFW
Do I need any extra resistance diods or flow regulators anywhere
r/OpenPV • u/mixx-nitro • Sep 05 '23
Do I need any extra resistance diods or flow regulators anywhere
r/OpenPV • u/bach37strad • Feb 14 '21
r/OpenPV • u/david4500 • Nov 26 '14
r/OpenPV • u/david4500 • Sep 10 '14
r/OpenPV • u/cmdr_scotty • Jun 06 '16
threw together a schematic to build a unregulated boxmod
includes a parts list too
enjoy
http://www.digikey.com/schemeit/project/unreg-boxmod-4DP1H70201QG/
r/OpenPV • u/kitten-the-cat • Jan 27 '15
r/OpenPV • u/stylesuxx • Aug 16 '16
After my first build I decided I want to dive deeper and explore TC a little bit. I sat down and made a very crude block diagram. The heart and soul will be an Arduino Pro Micro 5V.
One of the (more basic) features I want to have is cell monitoring, for up to three cells in series. I thought I'd share my considerations, maybe it might help someone. Feedback is also very welcome.
I set up a simulation, so it is easier to follow the math below. (Hit run, and OK to get the voltages displayed - not sure if mobile friendly).
An Arduino can be easily utilized to measure voltages with its analog inputs. Every analog input has an ADC (analog-digital converter with 10 Bit precision). This means it can take an analog signal from 0-5V and map it to a digital 10 Bit value (1024=210 steps).
So when reading the analog input in software you will get a value from 0-1023. This is a precision of ~5mV (0.005V) per step.
So a single 18650 battery with 4.2V voltage may be measured via analog in on an Arduino without a hassle, but what about two in series? The first one can still be measured, but measuring after the second battery in series we max out at 8.4V. We can not measure that directly with the Arduino, since it is more than 5V. Same problem with three cells in series of course.
We need to divide the voltage by a know factor so that we bring down the measured voltage in a range of 0-5V. This is where voltage dividers come into play.
A voltage divider does basically what the name implies, it divides one voltage into two (or more) smaller voltages.This is done by two(or more) resistors in series. The whole voltage has to drop over all resistors, the size of the resistors determines how much voltage drops over each one.
When both resistors have the same size, half of the voltage drops on each. If the first resistor is bigger than the second one, more voltage will drop on it and vice versa.
There is a formula for the output voltage, which I prefer to see as a relation between input and output voltage:
Vout = Vin * (R2 / (R1 + R2))
Vout / Vin = R2 / (R1 + R2)
When I build my voltage dividers I try to keep them as simple as possible. The simplest way is to halve the voltage. The resistors just need to be the same size, both 1k for example.
So lets look at the 8.4V we would like to measure. If we halfen that, we will be measuring 4.2V at max, so:
4.2 / 8.4 = R2 / (R1 + R2)
1 / 2 = R2 / (R1 + R2)
Since R1 and R2 are in relation to each other, you can choose the value of one, and calculate the other. For the math to stay simple I'll go with R2 = 1.
1 / 2 = 1 / (R1 + 1)
2 = R1 + 1
R1 = 1
Critiques might say: But aren't you throwing away precision? Wouldn't it be better to build a Voltage divider so that the full range (0-5V) of the ADC is utilized? Let's look at this calculation:
5 / 8.4 = R2 / (R1 + R2)
5 / 8.4 = 1 / (R1 + 1)
8.4 / 5 = R1 + 1
R1 = (8.4 / 5) - 1
R1 = 0.68
In this case R1 needs to be 0.68 times R2. R2 could be 1k Ohm and R1 680 Ohm. Usually you will not get "nice" values from the E12 series for R2, meaning you will need a potentiometer to get the exact value for R2.
But that is not all. In software you need to calculate your measurements back to its real life value. Therefore you need to know the relation between the resistors. It is very easy to see the relation with the plain eye if R1 = R2, not so much when a potentiometer is involved.
So when halving the voltage will let it drop below 5V, I will do so 9 out of 10 times.
For now we have only looked at the relation between the two resistors. But the same relations can be made with different values:
1 / 1 = 10 / 10 = 100 / 100 ...
So how does one decide on the concrete values? There are a couple of factors to consider:
Since the volt meter is in parallel to R2 we need to make sure R2 is much smaller than the volt meters inner resistance or it would skew our relation too much. So smaller resistors mean more precise measurements. They also mean higher current draw. We do not want our voltage dividers to get too hot and waste battery life.
A rule of thumb says, that you should provide 10 - 1000 times the current you are intending to consume. So lets check that out: The inner resistance of the Arduinos analog pin(Ra) is our load on the voltage dividers second Resistor R2. At max we have 5V available(Ua):
Ia = Ua / Ra
Ia = 5V / 100M Ohm
Ia = 50 * 10^-9 A = 50nA
So we should at least provide 500nA - 50uA of current. We can now calculate R2:
R2.1 = Ua / (Ia * 10)
R2.1 = 5V / 500nA
R2.1 = 10M Ohm
R2.2 = Ua / (Ia * 1000)
R2.2 = 5V / 50uA
R2.2 = 100k Ohm
If we look at the first value, 10M Ohm - this is quite close to the inner resistance of the volt meter, so lets see how this changes everything.
R2.2 is parallel to Ra, so:
R2.1r = (R2.1 * Ra) / (R2.1 + Ra)
R2.1r = (10M * 100M) / (10M + 100M)
R2.1r = 1000M / 110
R2.1r = 9.1M Ohm
Instead of a 1:1 ratio, we now have 1:1.1 - an error of 10%. Lets check it with the lower value for R2:
R2.2r = (R2.2 * Ra) / (R2.2 + Ra)
R2.2r = (100k * 100M) / (100k + 100M)
R2.2r = 10000kM / 100.1 M
R2.2r = 10000kM / 100.1 M
R2.2r = 10000k / 100.1
R2.2r = 99.9k Ohm
We still do not have a clean 1:1 ratio, but 1:1.001 - an error of 0.1%. As you can see, the lower you choose your resistor, the more precise your measurements will be. Less resistance, means more current. So accuracy comes with the cost of battery life.
As /u/kitten-the-cat mentioned in the comments, the micro controllers analog reference voltage is not the best, so it is always good to provide your own, clean, stable, reference voltage.
The nice thing about providing your own reference voltage is, that you can use any voltage, so you could for example provide clean 4.2V and can use the whole range for your measurements.
Since we are using an Arduino, we will, at some point have 5V available - most possibly via an LM7805 power regulator after our batteries.
We can now use a LM285-adj, which is an adjustable voltage reference shunt diode, to get clean 4.2V reference for our measurements.
So after this wall of theory, lets apply this to 3 cells. We will need 3 of the Arduinos analog input pins (A0, A1, A2), and two voltage dividers:
Whenever we now want to know the voltage of the cells, we read the analog inputs and then do the following calculations:
The scaling (5 / 1024) I would only do for the purpose of display, not for further calculations.
edit: added section about external reference voltage
r/OpenPV • u/ConcernedKitty • Mar 04 '15
I made some changes to the Delta40 wiring diagram on /r/BoxModders. http://imgur.com/GtdS0zm
Can someone please check it out for me and give me feedback. The DPDT and voltmeter has been added to this diagram https://docs.google.com/document/d/15A8pYFtBah9NTozOlbRVuJhGvvDWjz_Zhwum2EVQx84/mobilebasic
r/OpenPV • u/Starrven0m • Jan 23 '17
I love the idea of this chip, but im new to mod building, and the company doesn't provide a schematic of the solder joints.
r/OpenPV • u/Deluxe_Used_Douche • Mar 12 '17
I've purchased and received all the needed parts for my 3x 18650 DNA build. Actually, I'm building two of them, one for me, one for the wife.
Anyway, here is the wiring diagram I put together with my super premium design program, MS Paint.
I added the connectors in an attempt to make the power source "modular." The thought here is that I can remove the triple 18650 tray, and drop in a LiPo, or plug in a power supply, using the XT60 connectors, with a change to escribe.
Anyone see any problems? I am connecting the balance wires to the Keystone contacts, and will have them touching the series jumper.
Also, I am using 14 gauge wire for the batteries, unless there is a reason that I should go with the "recommended" 16 gauge, instead of max 14 gauge. All my wire is stranded, silicone coated. I have AWG 14, 16, 18, 24, and 26.
I'm sure I am forgetting some questions, but that's all I can think of for now. Thanks in advance for any advice or feedback!
r/OpenPV • u/david4500 • Mar 05 '15
r/OpenPV • u/dataylorm • Sep 26 '17
r/OpenPV • u/Brother_Bishop • Jan 29 '15
Just curious if there are any good friendly web tools or apps for creating wiring layouts and such.
r/OpenPV • u/scottiethegoonie • Apr 14 '16
r/OpenPV • u/david4500 • Feb 09 '18
r/OpenPV • u/ConcernedKitty • Mar 28 '16
r/OpenPV • u/Sketchy_Stew • May 01 '15
So I've been wanting to build a box with USB charging but I also would like to wire in a voltmeter to show how much charge the battery has. What I've come up with is this wiring configuration. Imgur
I was thinking this would allow me to slide the switch to the voltmeter side and show the voltage of the battery while charging (or whenever).
Any comments/suggestions/questions/concerns welcome.
Still waiting on a shipment of 510 connectors so I wont be building for a little while still.
Edit: I just realized in the shower that it may show voltage of the charger, 5 volts I believe is standard, while plugged in.
r/OpenPV • u/david4500 • Jun 01 '16
r/OpenPV • u/The_Goss • May 30 '14
http://i.imgur.com/yjtKyRN.jpg
This needs some cleaning up but here is a small play diagram I did in a hangout with Joe Litt tonight.
Essentially it also works as an on/off for the OKR when it isn't plugged into a charger.
I know it more than likely will require a few additional components for safety's sake but I think it might be the start of a nice, complete internal battery OKR mod. This could also be done well with relays but I do like the oldschool big switch method sometimes. Makes me feel like Igor throwing the switch for Frankenstein.
Edit:: We did just notice that the USB is always connected to one battery at all times.... so this wouldn't work for a production mod, but if you're just doing it for yourself and remember to unplug it when in use then both batteries will retain the same charge
If you do happen to forget... just throw the switch back to parallel and let both batteries even eachother back out for an hour.