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Topic: how to run entire project from one set of batteries (Read 1 time) previous topic - next topic

3z33

I am a total arduino/electronics n00b.

The image below (.fzz attached) is for a circuit that will sense the temperature with the TMP36 sensor, and then turn a 5V heating element on or off depending on that temp reading.  I'm using the MOSFET instead of wiring directly to a 5V pin on the arduino simply because I'm afraid the .6 AMPS the heating element draws will fry the arduino chip.  The entire system needs to be portable (battery powered)

Two questions.

1.  I've only had one other forum look at this circuit.  So, please review it and let me know if I should change it or improve it in any way.
2.  I'd like to eliminate the 9V battery and run the arduino AND the heater off the bank of nimh AAs.  How would I modify the circuit to accomplish this?

thanks.


MikMo

How long are you hoping to have the thing running from a set of batteries ?
Is space / weight an issue ?

The 9V battery is a poor choise for powering the Arduino. It will not last long.

Depending on how often the heater is on it too will drain the 4 AA batteries pretty fast i think.

3z33

#2
Oct 11, 2012, 10:13 pm Last Edit: Oct 11, 2012, 10:21 pm by 3z33 Reason: 1

How long are you hoping to have the thing running from a set of batteries ?
Is space / weight an issue ?

The 9V battery is a poor choise for powering the Arduino. It will not last long.

Depending on how often the heater is on it too will drain the 4 AA batteries pretty fast i think.


space/weight is def an issue.
it will be on intermittently for 60-90 minutes.  The "intermittently" depends on the temperature....it will be "on" when at or below a setpoint and "off" when at or above another setpoint.  The whole contraption is in a very thermodynamic insulated foam enclosure with reflective mylar interior...so it will be insulated as well as anything on earth, and have a very small space of just a few cubic inches to heat.

The temp outside however will be as low as -40C.

I think the 4 AAs will have sufficient capacity, but if testing turns out that it is not, then I'll up to a 6 pack.

any advice on how to get rid of the 9V and run the arduino on just the AAs?

MikMo

Maybe the 9V will have enough mAh to run your Arduino for up to 90 minutes. You need to do the math :-)

First you need to measure current use for both the Arduino and the heater and then figure out how many mAh each of the two battery "packs" can hold.
Then hit your calculator.

The absolutely best 9V batteries have around 500mAh of juice, if memory does not fail me.



3z33

thank you for the reply, but I'm looking to remove the 9V and run off just the 4xAAs.

I'm new to electronics and arduino, so the answer I'm looking for will explain how to wire this to remove the 9V and use just the 4AAs.

MichaelMeissner

#5
Oct 12, 2012, 12:06 am Last Edit: Oct 12, 2012, 12:29 am by MichaelMeissner Reason: 1
I tried to reply before, but it got lost.

Rather than mess with AA battery packs (or worse those 9v batteries which don't have much capacity), I got a cell phone charger that has two USB ports, each of which can deliver 5 volts of 1 amp power with a total battery capacity of 5000 mAh (or 5 hours of 1 amp discharge).  The particular model I got was the EZOPower 2 USB Port 5000mAh Universal External Rechargeable Backup Battery Power Bank (http://www.amazon.com/EZOPower-Universal-External-Rechargeable-Smartphone/dp/B004I0J4E6/ref=sr_1_3?ie=UTF8&qid=1349992758&sr=8-3&keywords=ezopower+5000mah+2-port+usb+universal+external+rechargeable+backup+battery+for+cellphone).

This charger has two outputs, so you could plug the Arduino in through one (using the USB port) and the heater on the other.  You recharge it via a USB wall wart with 5v of power.

I ran my Arduino running blink continuously for around 4 days on the battery.  Since your heater draws more power, my WAG (wild a%% guess) is perhaps 6-7 hours if you run the heater continuously.

You can get units with even more capacity.  I've seen units with 12,000 mAh capacity, which might get you 16-17 hours.

dc42


The absolutely best 9V batteries have around 500mAh of juice, if memory does not fail me.


Standard 9V batteries are around 350mAh. Lithium ones are up to 1200mAh depending on manufacturer, but they are expensive.


thank you for the reply, but I'm looking to remove the 9V and run off just the 4xAAs.


As the AA cells are NiMh, four of them in series won't produce significantly more than 5V, so you can connect the +4.8V directly to the Arduino 5V pin to power it.

It's recommended to insert a series resistor with a value in the range 100 to 200 ohms between the Arduino digital output and the mosfet gate, because of the high input capacitance of power mosfets.
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