Microcontrollers > Microcontrollers/General

Control for heating with solar off grid no batteries

(1/35) > >>

ontfarmer:
Put up solar panels with heating water planned. I have had a lot of help from the members
of the forum.
Planning on putting the controller together have capacitors, mosfets, opto isolater,resistors,
diodes, arduino.  to use for PWM control.
Will let you know how it goes.

OperaHouse:
Where to start......
The voltage of the solar array will have to be monitored.  Here is a way to easily calculate
the values for the voltage divider.  Determine the maximum voltage the divider will see using
the total open circuit voltage of the panels.  Lets say that is 140V.  Choose a common resistor
value for the lower resistor R2 of 22K.  The A/D value can be easily multiplied in the micro
by a whole number, avoid floating point math in a micro.  That calculation can get you close.
Adding a pot between R1 & R2 will allow you to adjust the A/D value slightly to get the calculated
voltage spot on. If you only have a 25,50 or 100K pot, a 5K or higher resistor in parallel can
reduce the effective resistance to 5K.  With the pot set to mid position, that adds 2.5K to the
value of R2 for a total of 24.5K ohms.  We are setting the max value the A/D will see at 4V to
give some safety margin.  There are 35 four volts in 140V.  One of those 4V is across R2.  That
leaves 34 four volts on R1.  24.5K times 34 gives 833K for R1.  A standard value for R1 is 820K.
I suggest a couple resistors in series to prevent flash over or a single 1W resistor. A capacitor
of .1uF at the A/D input provides noise protection and a stable low impedance for the A/D converter.


If you have at least a 36V array, the best way to power the micro is with electronic wall warts.
The most common is the 5V used for cell phones. I have a local thrift store that sells them for
29 cents each.  I use them all over my system to power meters.  They are electrically isolated
and if they fail they won't destroy your electronics like non isolated step down converters.  I
love those $2 ebay 2596 converters but won't use them anywhere near their voltage or current
ratings. Two 5V wall warts can be used in series to make 10V to supply the UNO board. An additional
5V unit in series will supply 15V for the FET driver electronics.

ontfarmer:
   The wheat harvest is now done. Hope to get back to this project.

Very impressed with the detailed  instructions and diagram that you done in terms
l can understand.
 
  Will make it possible for me to put this together.

Thanks

OperaHouse:
The schematic shows how to connect three 5V electronic wall warts.  It is a good idea to add an
extra capacitor for surge capacity and maintain voltage during momentary dropouts. It is suggested
tat a diode be used ot isolate the solar panels from the capacitor bank to prevent current back
flow. Use a diode for each series string prevents back feed form other panel strings and allows
you to use smaller cheaper diodes.  Remember that once the capacitor bank voltage drops below
the set point of the micro, the current draw stops except for the bleed resistor on the capacitor
bank.  Even new capacitors will need some forming before rated currents are drawn.  VFD motor drive
instructions suggest that the unit be powered up for 24 hours before the motor is operated.  This
would be a good idea for this capacitor bank too.  Use the array to power it for a day or power up
with line voltage.

A convenient way to get signals in and out of the board is with these Dupont leads. 
http://www.ebay.com/itm/40PCS-Dupont-Wire-Color-Jumper-Cable-2-54mm-1P-1P-Male-to-Female-20cm-WC-/172024782427?hash=item280d79de5b

Buying the male and female leads allows me to cut them in half and also use them with pin headers.  Following resistor number color codes for the wires makes it easy to identify input and outputs, input1 would be a brown wire.

ontfarmer:
Picked up resistors, pot, capacitors, diodes, soldered them together I have  male and female leads.

Was  able to get old TV, PC from a drop off have to get the 5 volt wall warts.

Look forward to your reply.

Navigation

[0] Message Index

[#] Next page