About Battery Management Systems

Question

Hi all,

for my robots I'm trying to find the best solution to manage power and batteries. For my robots I use 4S and 6S LiPo.

What I'm searching for is a good Smart BMS solution to charge/control batteries without removing them from the robot. If the Smart BMS is not supported by ROS I'm ready to write the driver.

Do you have any suggestion for me?

Thank you

Walter

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Originally posted by Myzhar on ROS Answers with karma: 541 on 2017-07-26

Post score: 1

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Original comments

Comment by psammut on 2017-07-26:
Why do you need a BMS on a 4S, 6S LiPo battery? These battery packs can operate without the need of a Battery Management System.

If you are talking about cell balancing, any good charger, such as the SKYRC iMAX B6AC has a balancer connection which monitors the voltage of each cell while charging

Comment by Myzhar on 2017-07-26:
I use the iMAX B6AC to charge/balance the battery, but I would like to charge/balance it without removing it from the robot. Furthermore LiPo must be monitored to be sure to not let one of the cells to go below 3V of charge.

Comment by Myzhar on 2017-07-26:
The idea is to connect a "recharge cable" to the robot when ros_diagnostic says that the battery has reached a warning level and to continue to use it without turning it off tp replace the battery with a charged one.

Answer 1

If all you're looking for is a way to charge your batteries without having to take them off your vehicle, all you need to do is to branch off the power and ground wires from your pack, along with the balancer cable to a connector. Then you can connect that your charger. You can monitor battery voltage using a analog to digital converter on an arduino which can be running rosserial-arduino that posts the pack voltage. With this information you can have your robot handle an undervoltage condition.

To keep your batteries operating normally, all you have to do is to make sure you do not discharge them past the cutoff and also use a balancer each time you charge them.

However you can buy lipo packs with a protection circuit monitor that handles balancing on their own and also watch out for other stuff such as shorts, undercharging and undercurrent. I HIGHLY recommend you buy a pack that has such a protection circuit already built in, such as this one: http://www.batteryspace.com/lipo-battery-pack-tattu-22-2v-16ah-355wh-15c-6s1p.aspx

You can buy a PCM on its own here: http://www.batteryspace.com/pcm-with-equilibrium-and-temperature-protection-function-for-14.8v-li-ion.aspx but this will take lots of effort and troubleshooting to debug.

Battery management systems that interface with your robotic system, where you are monitoring every pack voltage and temperature along with real time discharge rates and required for chemistries other than LiPo, such as LiFePo4. With LiPo, you are fine with a PCM and just using a balancer on the charging cycle.

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Originally posted by psammut with karma: 258 on 2017-07-26

This answer was ACCEPTED on the original site

Post score: 0

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Original comments

Comment by Myzhar on 2017-07-26:
Your solution is something that I just took in consideration, but I'm searching for something more robust and professional. What I want to do is the same as a laptop: to connect the recharge cable and to continue to use the robot. I'd also like to try LiFePo4. What about them?

Comment by psammut on 2017-07-26:
A LiPo pack with a PCM is as professional and robust as you need. I have worked on many commercial robotics systems with LiPo and most didn't even have a pcm, and just required balancing every x amount of charge cycles. A LiFePo4 is diff chemistry that is more suceptible to thermal and cell voltage~

Comment by psammut on 2017-07-26:
differences. Here is a vid of a LiFePo4 pack I built complete with a BMS. It was a really big effort! https://www.youtube.com/watch?v=rUl_iSmuZhQ