I'm working on a robotics project with two Arduinos, two motors, a servo and several IR sensors. I want to provide a long running time before the batteries need to be recharged but I'm not sure what type of battery to use.
So far I've used Venom alkaline 9V, but it runs out pretty fast. Trying a 7.2V 1800mAh RC battery connected to a 5V regulator was my next move, but I'm worried about the regulator because it gets quite hot. I read about battery discharge C rates but do not know the C rate of the RC battery.
I was thinking of connecting the RC battery straight into the Arduino VIN and then connecting the power bus to the 5V out on the Arduino... is that a good idea? Can the high discharge rate hurt the Arduino?
If anyone has info/advice on batteries for use in an Arduino robotics project like this please let me know.
@Richard:
I have no way of measuring the current the entire robot draws. I also don't know how to draw up schematics, so this explanation is the best I can do:
Two Arduinos, one Sharp IR sensor, two Pololu IR sensors, a servo and three LEDs are what's needed to be powered. The two motors are connected to a ladyada motor shield with it's own 7.2V 1800mAh RC battery that works fine, but it's for the motors only. I went with a simple breadboard power rail so I can add more sensors and servos as needed, therefore I'm looking into a battery that will run all these things and more. Size and weight are not much of an issue, the platform is about 8x5.
@Mike:
The on board regulator is sufficient to get by, but as stated earlier I want to have the ability to add more sensors/servos later so I will need to use a power bus for sure. Thanks for the link to that switching regulator, I have one on order and I'm reading up on how they work.
I have a multimeter but do not know how to use it for current. I've read up on it and watched youtube videos of getting in line with the circuit and reading amperage but it just doesn't work for me. I have a cheap pocket RadioShack 22-810 meter as well as a Fluke 110 (I am in the USA).
I'm going to lookup all the datasheets and add up the current requirements. I'm using two of these devices:
I think the switching regulator is the way to go. I placed an order for one of the regulators Mike posted.
What would happen if I plugged the 7.2V 1800mAh RC battery directly into a Duemilnove that was running a sketch to blink the pin 13 LED every second. Would the high discharge rate of the RC battery burn up the on board power management circuit on the Duemilnove?? Will it work perfectly fine and run for like 3 days since it's a high capacity RC battery? I'd try it but can't risk burning up an Arduino.
Isn't the reason for losing energy through heat when connecting a 7.2V 1800mAh RC battery to a cheap 5V regulator is due to the high C rate of the battery? It's discharging much more current than the circuit needs per interval of time, hence the heat? When I connect a 9V 750mAh alkaline battery to a cheap 5V regulator the discharge C rate is low, hence no heat because the battery is discharging just enough current to power the circuit?
As I understand it, the higher the C rate, the higher current for shorter period of time. If that's correct that would mean the battery delivers 1800mAh for 60 minutes at 1C. Assuming this RC battery is 10C (others I've seen are between 10C-20C) then 1800mAh * 10C = 18000mA for 6 minutes.
If the battery is delivering 18000mA but the entire circuit requires much less, won't the extra amperage dissipate in the form of heat?
Although I have not measured the current requirements for all the devices and added them, I do know it's way below 1800mA. The goal is not only to power the entire circuit, but to power it for a long duration. The problem is finding a battery that combines the amperage, C-rate and voltage.
I don't see the point in using a battery that delivers the exact amount of current needed for a circuit at a discharge rate of 1C because that means the circuit will be powered for 60 minutes until the battery is depleted. I also don't see the point in wasting a bunch of unused amps every minute because the discharge rate is 10C. And finally I don't know where to find a rechargeable battery that provides a bit of extra current (to allow more devices in the circuit in the future) and a discharge rate 1C or less so I can power the circuit for several hours. I don't know what type of rechargeable to look for either due to several factors: 1 - NiCD, NiMH, LiPo, etc.... good god that's a huge topic. 2 - Connectors. All I need is a + and -, but most batteries have connectors with many wires for power management, etc. 3 - Chargers. I've found some batteries online that look pretty good spec wise but no chargers to be found. What about the type of charger? Is it going to cost twice as much for a charger than then entire electronics for the robot?
If I am way off on this please let me know, this is what I'm trying to understand overall.
Isn't the reason for losing energy through heat when connecting a 7.2V 1800mAh RC battery to a cheap 5V regulator is due to the high C rate of the battery?
No. Nothing to do with it. You are not understanding what it says, please read it again.
You are totally failing to understand ohms law. Please read it up.
If the battery is delivering 18000mA but the entire circuit requires much less
No the battery is only capable of delevering that current it won't actually deliver that unless the load is low enough.
Ok, I'm getting it now. The rate at which current is available from the battery is just a maximum, only used if needed by the circuit.
I think my next question is due to my lack of understanding Ohm's law: Why does the voltage regulator heat up more when using the 7.2V NiCd battery than the 9V Alkaline?
Why does the voltage regulator heat up more when using the 7.2V NiCd battery than the 9V Alkaline?
It is probbly due to the fact that the 9V battery can't supply enough current for the circuit and so the voltage drops. In fact it is droping below 7.2V and probbly not working at all.
Placing a NEW 9V alkaline battery into the circuit with the voltage regulator does make it get hotter than the 7.2V NiCd, and yes it only runs for ~3 minutes.
Going back to basics to learn to read current, I setup a 470 ohm resister and LED only circuit. As the multimeter manual suggested I broke into the circuit and connected my leads between the resistor and the LED - no reading at all. Continuing on in the manual it says to check the fuse, which indeed reads open, no continuity so it's bad.... No wonder I couldn't read current!
As I wait for the switching regulator to come in the mail, I bolted on a make-shift heatsink to the 7805 cheap 5V regulator so now running from the 7.2V RC battery the heat is lower.
Thank you guys so much for setting me strait! As soon as I replace this fuse I'll learn to read current and when problems arise (sure they wil) I'll post for more info. Thanks again!