@Yash Gupta You might want to start with the battery physically outside from the robot (so the robot does not need to lift the weight of the battery), meaning you can use any normal 6V pack (NiMh for example). If you need the robot to support the battery, it would need to be lightweight, and you should really consider 7.4V servos and a 7.4V LiPo pack which saves considerable weight. The pack needs to be able to discharge continuously at roughly 50% of 1.2 amps multiplied by the number of servos in operation. Hard to provide details without knowing more about the project details - consider creating a new post on the RobotShop Forum.
Hi sir,
Can we find how long a battery can run a load(LED/motor etc) by knowing just Voltage in a battery(V),Current drawn by load(I) and WATT of l load(w), For example: A 9V battery(Non Rechargable and mAh is unknown) is connected connected to a LED which in series with 100 ohm Resister, where current drawn by LED is 25mA, WATTS of LED is 50.4mW, Resistance of LED is 140 ohm, so can we find how long battery can lights up that LED. I have tried lot of methods, pls give some idea that how can i achieve this!
Regards,
Akshay Theertha
IoT Developer and Solution Architect
@Akshay Theertha If the capacity and discharge curve are unknown for that battery, you’ll need to do experimentation; measure the current draw and the voltage and time how long it takes. The current draw should be steady with a fixed load.
@Coleman Benson , Sir if i know just mAh (say 500mAh), then will it be easy to calculate the time right?
like current drawn by led is 25mA, soo (500mAh/25mA)= 20 hours?
@Akshay Theertha That would be the correct “napkin math” assuming the discharge rate and voltage were linear. In reality, you’ll get a percentage of that. Therefore you might make that calculation, assume you might get around 75% of that (so 15 hours), and then test how long it actually works (might be somewhere between 15 and 18 hours). Note that you will need to monitor the voltage and stop it when it reaches its “discharged” state without damage (depends on the battery chemistry).
@Coleman Benson,
Yeah Thank you sir!
Hi sir,
my small dc motor is running by a Li-Cd battery of 1.2V, 600mAh, current drawn by motor is 40mA.
soo 600mAh/40mA=15 hours, soo it can run upto 9-10 hours.
And what i understood is if i connect that battery with another battery of 1.2v, 600mAh in paralell,
then the Amp-Hours will be added ie. 1200mAh,
soo now 1200mAh/40mA=30 hours, so motor can run upto 24-26 hours.,
Now What happens if i connect that both Batteries in Series,
then 1.2+1.2=2.4v and Capacity will be same 600mAh,
soo now 600mAh/40mA=15 hours,
which means the motor will run upto only 15 hours but with increase in Speed???
Thank you!
@Akshay Theertha The effect of series / parallel is to either increase the capacity or the voltage. This is how battery packs are made. Remember, the theory is different than reality since discharge is not always linear as the battery voltage drops.
I am deigning a tracking device using arduino uno and sim900 gprs shield. using two 3.7v 2200mah batteries in parallel … my device runs for 7hr . I am sending sms and to thingspeak 2 times i an hour. I want to minimize the current consuption so that my device will run for at least 24 hrs. What should I do… please hepl.
@ALEKOS DIGITAL Using GPS constantly consumes quite a bit of current - can you see if connecting to the GPS only when needed (twice per hour) helps? If not, you might just need a larger battery pack, or add three such packs in series.
I have a RC car with 4.8v NICd battery, can i use LiPo battery to increase power ?
@Mrityunjay This is hard to tell because the 4.8V may power electronics which are not 7.4V tolerant and would burn. The main motor may also not be 7.4V tolerant. You’d run quite a risk of damaging the system.
Hello, I have an arduino uno with five flexiforce sensors, five flex sensors, and five High Torque - Metal Gear Servo. Is it possible to operate them on one or two Lithium Ion Polymer Battery - 3.7v 2500mAh? if yes, how long will it last? Thank you
The Flexiforce sensors likely need to be connected to a voltage divider circuit operating at 5V, and the servos likely operate at between 4.8V to 6V. A 3.7V LiPo would need a 5V step-up regulator and then you should be fine. It’s really hard to determine how long a system will last (how long and how often will the servo be used for example?).
Hi sir,
I am making a humanoid robot .I plan on using 15 servos(60 kg servos) that have nominal voltage 7.4 V and consume 5 A at maximum load that would add up to 75 A totally.I want to use it for 30 minutes(Let’s assume all servos work at all times-Worst case scenario). Could you suggest a suitable Li ion battery/batteries that I can buy online?
Thanks in advance.
Also,I was thinking of using 3 2S 6000mah 25C Lipo Batteries connected in parallel so it would run
for about 20 minutes.Would this suffice?
You’re certain that you’ll be operating each and every motor at its maximum load, such that ALL 15 servos draw 5A each? Normally in a humanoid, the current draw is very different for different joints. If you use 3x 6Ah = 18Ah batteries, and you determine that you’re actually drawing 75A, it’ll last 18/75 = 0.24hs = ~14 minutes. This does not factor in inefficiencies of the battery, controller, motor etc. which can easily reduce it by 50%. You should take a look at each motor and see if you’ll actually be drawing a full 5A. You might need to calculate or estimate the torque at each joint under normal operation
Thank you for this excellent primer - very useful for this total novice!
I have a project that requires 16 digital micro servos (I’ve opted for the HiTec HS-503HD). This servo’s stall current draw is 360 mA and 8 mA at idle, operating at 4.8-6V. The servos would only be needed to operate for very short periods of time (~< 1 sec) only periodically (e.g. twice daily), either all together, independently, or in groups.
I also plan to add an Arduino to the mix (not sure which one yet), possibly attached to a lux meter, to automate the operations of the servos on a schedule or on input of variable data (e.g. open/close at dawn/dusk).
What battery would you recommend for this?
If you plan to operate them all at peak torque (which, according to you would require a current draw of 360mA?), you’d need a power supply of between 4.8V to 6V capable of providing 16 x 0.36A = 5.76A. A 4x AA pack will likely struggle with that current, so you might need something “beefier” like a 6V lead acid battery. Check the Arduino’s specs to see if the Vin pin can operate at ~6V and if so, you won’t need a second battery.
Suggest double-checking the 503HD specs to confirm the current draw is UNDER LOAD, since most small servos can consume pretty high current.
I have one stepper motor with 5V nominal voltage and i use 3xAAA 1.5 V battery to run it and it works
But my problem now is that i have to use 2 stepper motors
The motor requires 200mA and the battery capacity is 900mAh
Can I run both of them with the battery that i have? Should I use 2 separate power supply for the motors, each supply at 4.5V?
@Bianca It becomes less about the capacity and more about the battery’s maximum discharge current. Can you find that information about the battery you’re using? If not, do some research online and it’s a brand name battery, you might try to draw up to 2x 200mA = 400mA (napkin math) from those batteries. Ideally you’d use a higher capacity battery which tends to also provide a higher discharge rating. Using two battery packs is another option, but less “clean”.