This is just a testbed for the Esp12-e/MCP3208/SolarPV QUAD Disconnect.
GPIO pins 4, 5, 12, 13, 14 and 16 go to .1" header pins
Add onboard TMP36 temperature sensor,
"Divide by 52" resistor voltage divider (220kΩ nominator, 4k3Ω denominator)
On-board +Vcc and +3v3 monitoring, plus .1" pin dedicated to EXT in monitoring.
The picture has the pinouts, -but it's really small (the board is pretty tight),
You'll have to download the high-res .png to see it.
Step 1: Download the PCB File
To download the CAD file, click HERE.
You can view the CAD file using expresspcb.com CAD software. you can order etched, drilled silkscreened and printed PC boards directly from Express PCB. "Miniboard Pro" minimum order (3) 2.5 X 3.8" boards $68.50 -you will yield (3) of each of the 4 circuit designs, 12 circuit boards in total. Cut the PC boards using a fine blade hacksaw.
Step 2: Get the Electronics!
You can see a parts list by clicking HERE.
-The Esp12-e can be currently found on eBay for abot $2 each. http://www.ebay.com/itm/381374534484 Parts can generally be bought much cheaper on eBay, but Digi-Key guarantees parts sourcing...
Step 3: Calculate Voltage Divider Resistors
Voltage Divider Calculations
Let's design +165Vdc to be our V(max).
165Vdc input should generate <3.3Vdc after the divider.
165Vdc / 3.3Vdc = 50 That is "divide by 50".
Power through divider
I've decided to limit maximum divider power at V(max) to 125 milliwatts because I don't want to fry my 1/8th watt (125 milliwatt) resistors. We need to calculate our total resistance to accomplish this.
V²/P= (the total resistance we need), so...
165Vdc² = 27225 / .125 (maximum wattage dissipated by divider at V (max)
= 217.8k ohms.
A non-standard value.
Let's go up to the next standard value, 220k ohms.
As we go up in value, our current decreases a bit.
The "denominator" resistor is 1/50th the value.
220k ohms / 50 = 4.4k ohms.
A non-standard value.
Let's drop to the next standard value- 4.3k ohms.
As we lower our numerator, our multiplier goes up.
Using 4k3 + 220k 1/8 watt resistors:
V²/R = power (Watts)
165Vdc² = 27225 / 224.3k ohms (220k + 4.3k)
= 121.37761925991975033437360677664 milliwatts dissipated at V (max).
3.8 milliwatts below my design P(max) of 125 milliwatts. Good.
Current through dividern 165Vdc IN
V/R = current (Amps) 165Vdc / 224300 ohms
= .73562193490860454748105216228266 milliamps
Voltage drop, 165Vdc IN (4k3 resistor)
V= I * R
I= .00073562193490860454748105216228266 amp
X 4300 ohms
= 3.163174320106999554168524297804 volts
Divisor / Multiplier
Our MULTIPLIER valuse is calculated byVolts In / Volts Out, so...
165 Vdc / 3.163174320106999554168524297804 Vdc
Okay, I was shooting for an EXACT /50, but it's difficult using "standard" resistor values. I'd rather be coservative. I want to be sure that at V(max) my divider network won't start smoking.
My "actual" V(max) is now 172.1372093023256 volts- 3.3 volts X 52.162790697674418604651162790886 but DO NOT do that!. The PC traces will probably start arcing @ 150v. Each ADC voltage increment is 0.1681027434593023 for the MCP3008.
Each ADC voltage increment is 0.0420256858648256 for the MCP3208.
I designed the PC board for a "nominal" voltage of 90Vdc. My SolarPV nominal voltage is 90Vdc so I should NEVER have a worry about voltage overloads! This calculated multiplier will be gnats-ass spot on.