I've been working on a portable winch based off an Arduino Nano.
The main components involved are as follows:
Arduino Nano
12v dc motor
TB6612 Motor Driver
U3V12F12 Boost converter
3.7v 1800mAh battery OR 7.4v 460mAh battery
The idea is that I feed the 3.7v OR 7.4v battery into the U3V12F12 boost converter, thereby feeding the Arduino and the TB6612 Motor Driver with 12v of power. This entire setup works fantastic with the smaller capacity 7.4v battery. The motor moves when it should and performs exactly as expected.
However, with the 3.7v battery, I'm noticing that while the arduino powers on, the motor is not able to move when commanded.
Both batteries have been charged overnight, and should be in great working condition.
Any ideas as to why the 3.7v battery is not working would be much appreciated.
I assume it is due to a high current draw. The batteries have to provide the same Watts (Energy per second) in order to operate the motor.
W = U * I
So W has to be constant.
U as 3.7 V is half of 7.4 V
Calculating the required current (rearranging the formula)
I = W / U
Hereby, we can see that I has to be twice as large, if U is halfed. (anti-proportionality)
So either your boost converter can not handle the high current or your battery is not capable to provide the current fast enough.
You can check it by measuring the cell's voltage using a Voltmeter. (you put the 2 rods onto one of the connections with the battery)
If the voltage drops very much, it means that your battery cell colapsed.
Solution: connect 2 3.71800mAh batteries in series in order to get a higher voltage and the 1800mAh of the battery.
It's also worth checking the C-rating of the single cell. Not all lipos are equal. There are some around that are only rated for 1C and have a BMS fitted which limit their output current.
Thanks for your replies! I really appreciate you guys taking the time to help me out!
@sLucas & @Steve -> This is the battery I'm using -> Lithium Ion Battery - 1Ah - PRT-13813 - SparkFun Electronics. They don't excplicitly mention the current draw so I can't quite figure out if I'm exceeding it, but it should be fine for just a standalone Nano (which I've been primarily testing on).
Additionally, the efficiency-current plots of the voltage regulator seem to suggest that at up between 20mA to 100mA output current @ 12v I should be about 80% efficient, which probably indicates that architecturally, the boost converter is a decent choice.
I've worked on this for a little while more and have a couple more observations that might be helpful in diagnosing what's going on.
When I connected the battery to the boost converter and the circuit has a minimal load (only the Nano, motor is disconnected), I notice that the Vin into the boost converter was approx 4.1V and the Vout of the boost converter was also 4.1V. To me this indicates that the battery is working fine, but the boost converter is not able to boost the voltage to 12v.
Based off this, I replaced the 12v Boost converter. At this juncture, I got the 12V I was expecting.
However, during my subsequent testing, I disconnected the battery from the boost converter and connected the mini USB cable to my Nano to program it. As part of my circuit, the Vin of the Nano is connected to the Vout of the Boost converter. By connecting the USB cable to the Nano, did I inadvertently destroy another of the Boost Converters?
Once again thank you for all your help and advise!
One possibility is that most lithium ion batteries like the one you are using have protection circuitry. If you set off the overcurrent alarm, it will shut down. In this case, you normally have to disconnect and reconnect the batter since it will shut down power to the system.