Advice shopping for DC motor, driver, batteries, solar

Other Hardware Motors, Mechanics, Power and CNC
1

Success! I have a working program. Now I need to upgrade from the prototype to the real toys.

I'm still new to electric circuits etc. So, If you see something wrong in my thinking or could offer advice, you are my hero.

Here is my project, and what I'm thinking to use as components:

My program is a thermostat which tells two DC motors to run forwards @ set temperature and backwards @ set temperature. The program has been set so that when in use, each motor should run twice a day for about 30 - 40 seconds each run. It would be ideal to run these motors in unison however, it is not necessary. If run in unison, then the power supply set up would look different (this is mostly what I need help with).

Currently I am using the L293d motor driver for a 5v motor. The final project will run off a 12vDC battery, and include two 12v DC motors which will draw more power. The battery will be charged by a solar panel and charge controller. I am also planning on using some type of voltage regulator (linear/switching/zener) so that I can use this same power source to safely supply the arduino.

The motor: In testing, I discovered that a common 18v lipo powered drill had enough power to easily handle the load of my project. I just chucked up the load directly onto the drill and watched the drill lift the load. The drill has a max torque rating of 340 inch-pounds. So, I will need two motors that are capable of at least that much torque. Speed is not as important. I will use PWM to control speed. A lower speed is better. The drill uses a 24WH battery and 18v. This is also equal to 1333mAH.

Motor driver: I am thinking to use the DRV8844 Quad 1/2 H bridge driver IC. The DRV8844 can supply up to 2.5-A peak or 1.75-A
RMS output current per channel (with proper PCB
heatsinking at 24 V and 25°C) per H-bridge.

The battery: I'm thinking to make or buy a battery pack. This will be an outdoor (although dry) application. Temperatures will be between 30 and 110F. I know that the program will run the motors twice a day.... for a max run time of 1 minute per day per motor. Since I know my drill works fine for this, and it can carry the load for over 1 minute per day per charge, I plan to just re-create the drill's battery pack - only with double the available power; that would be twelve C NIMH batteries. Second option would be to make 2 or 3 separate battery packs, one for each motor and one for the micro-controller. The tricky thing (for me) using multiple battery packs would be ...how to hook all of those packs up to a charge controller (from a solar panel).

Solar panel: What size do I need? Again, both motors operate twice a day. Since I do not know the exact amount of amps that the drill uses,..it is hard for me to figure the exact power requirements. In the worst case senario, I am consuming 24wh per day. I'm sure, in actuality, it is closer to about half that. I'm thinking I could use a 25W solar panel, which by my calculations would supply 70 or more Wh. Calculated by 25W x 5hrs sunlight x 70% direct sun x 85% efficiency of charge controller.

That's it! Thanks for taking a look.

2

Are you planning to use the whole drill in your project (or is it two drills). If so why not just use the motor driver that is already in the drill?

My guess is that a drill motor would draw a great deal more that 2.5 amps - maybe 10, 20 or 30 amps.

...R

3

Byrner00:
Success! I have a working program. Now I need to upgrade from the prototype to the real toys.

I'm still new to electric circuits etc. So, If you see something wrong in my thinking or could offer advice, you are my hero.

Here is my project, and what I'm thinking to use as components:

The battery: I'm thinking to make or buy a battery pack. This will be an outdoor (although dry) application. Temperatures will be between 30 and 110F. I know that the program will run the motors twice a day.... for a max run time of 1 minute per day per motor. Since I know my drill works fine for this, and it can carry the load for over 1 minute per day per charge, I plan to just re-create the drill's battery pack - only with double the available power; that would be twelve C NIMH batteries. Second option would be to make 2 or 3 separate battery packs, one for each motor and one for the micro-controller. The tricky thing (for me) using multiple battery packs would be ...how to hook all of those packs up to a charge controller (from a solar panel).

That's it! Thanks for taking a look.

Cold Batteries will have reduced voltage and cold-cranking-amps.

Using a solar panel to charge multiple batteries is not difficult.
If the batteries are the same voltage they can be charged in parallel.
If the batteries are the same voltage but different amperage ratings, care needs to be taken so that the batteries are not overcharged. This will cause excess heat to build up in the batteries. LiPo batteries will "balloon" and the small one will burst and catch fire.

A slow trickle charge is better than a fast charge.

!2 "C" batteries are going to weigh a good deal.
NIMH batteries are easier to charge separately. I have never tried to charge 12 "C" batteries in series at one time.
1.5 volts * 12 batteries == 18 volts.

The weakest battery will dictate that performance of the batteries.

I have several wildlife cameras around my property. They normally use 8 "AA" battery for 12 volts. These generally last about one week. Depends on the number of videos captured and the nighttime activity.
If the IR LEDS are being activated by movement the batteries discharge faster.

I have been using 12 volt sealed lead-acid motorcycle battery and a simple solar panel charger to keep it charged. The Lead-acid batteries are more forgiving than the NIMH or LIPO.

With outdoor projects you need to use armored cables. The rodents and squirrels will eat the wires.
Even using armored cables is no guarantee against squirrels. Aluminum armored wire squirrels get right through.

4

Don't forget, your drill motor is turning the chuck through a gear reducer, multiplying the torque. Do you have an idea how much current and voltage your motor will require at full load?

5

Robin2 : I was planning on NOT using the drill; at least, not my drill.
You are right! Thanks for catching that. The motor driver needs to be able
to handle more like what you said. I did some googling and found typical
current draws for drills like this are around 30 - 40 amps at higher loads.
It is probably then, a great idea to cannabalize drills for this project;
as I could really make use of the motor, driver, chuck, and gear train.

Forge: Good tips, thanks. I was originally thinking car battery. I know that
charging a single 12v battery with a solar panel and charge controller is the
least difficult of my options. I am wondering if I go that route though, I might
need to get a deep cell battery. Based on new information, total power used
by both motors (if run in unison) is 1260W. So if total run time in a day is
equal to 60 seconds, then 1260 x .016666 = 21Wh. Now, twelve AA NIMH
batteries contain apx 30.25 Wh, twelve NIMH C batteries contain 64.8Wh, twelve
NIMH D batteries contain 136.8wh.
In contract, a typical motorcycle battery contains 12 to 18AH. So, at 12V that
means 12v x 18AH = 216WH.
Power-wise, it seems either battery would work. I'm chiefly concerned about the
re-charging part. Something like NIMH is designed to be re-chargeable, where I
know that lead-acid batteries are not designed to be drained beyond a certain
point unless they are deep cell batteries (and very expensive). Perhaps, due
to my low energy demand, I could use the lead acid battery in this application
without any problems. Whichever battery I choose, it should perform well in
heat and cold. Temperatures could get somewhat below freezing and possibly
up to 120F....I have no idea as to the CCA's of NIMH, lipo, or NICAD, although,
I was pretty sure that one of the big bonuses of lipo is the ability to provide
power @ colder temperatures.

Outsider: This is key. Yeah, so it should be around 40 -45A max per motor. More
realistically in my project, it should be drawing between 15 and 35A.

6

Did you say you were using a 5V motor with an L293? An L293 can only handle about 1 Amp so that's only 5 Watts with a 5V motor. You said your 340 oz-inch drill could easily drive the load, why do you think you need a 340 oz-inch motor?
You may only need 50 (or less). Can you measure the torque required and speed (RPM)?