Using Lithium Batteries on FRC robots

I feel that there needs to be a new thread for the discussion of using/testing lithium-type batteries on FRC Robots. Also, the practical implications and information you need to understand if you are using lithium-type batteries on an FRC robot.

DISCLAIMER
USING LITHIUM BATTERIES ON AN FRC ROBOT IS NOT LEGAL. THIS IS JUST FOR THE SAKE OF EXPERIMENTATION. ONLY DUE THIS IF YOU HAVE SOME EXPERIENCE WITH LITHIUM BATTERIES. TRY AT YOUR OWN RISK

This topic will also discuss what an FRC viable battery needs to look like and what kind of impact and consideration there will be on the robot.

This battery would work to run the robot for quite a while but @Mark_Wasserman is right. The discharge rate is cutting it close and you may be destroying the battery if you were to run a robot at full tilt. Real and “advertised” performance is a big problem among battery vendors in the RC space. You may not want to use it due to the battery’s fully charged voltage being above 16V.

You have the right idea with this battery but I would increase the capacity a bit to give you more headroom. It should work great for a normal match duration though. I would increase the capacity so you have more headroom for discharge current and charge current. This would also allow you to maximize the cycle life. Make sure you monitor your voltage if the battery drops below ~2.8V per cell the battery will begin to be damaged (Resistance goes up and gets puffy, loss of capacity) I would try and make sure you never push the battery below 3.0V per cell. You will want to be extra careful with the fact that you are running just over the voltage limit of many CTRE components.

I would make sure you check each component (product) to make sure it would be safe. I can tell you now a =+16V battery would be out of spec for the CTRE control system. A 4S battery (14.8V nominal,16.8V fully charged) is too high for the CTRE control system. That also applies to @JohnFogarty and @Mark_Wasserman. I am all for experimenting but you will want to be careful and willing to lose some components if you are going to use a 4s battery. What would be safer is a 3S battery (11.1V nominal,12.6V fully charged). I also think that using a 3S battery would be better due to the fact that it would more closely resemble a good-performing lead-acid battery. Using a 4s battery will make your robot performance, I think, significantly different from the lead-acid battery. This would not be helpful for teams who want to practice for longer and have more consistent aoton runs.

While I like Li-Po batteries for my RC stuff I don’t think they are great for the general use of FRC robots. They have great energy density and okay cycle life but they can not be stored at full charge and will degrade within days if kept fully charged. Not to mention they are the most prone to causing fires. A thermal runaway situation can be very problematic (due to over-discharge and heat build-up). It normally does not happen to smaller capacity battery packs but it definitely is a concern. (That is why any real application of LI-po uses a BMS) The larger concern with smaller batteries tends to punctures, over-discharge damage the life of the battery, and over-charging leading to a fire. Here is a great example of a thermal runway Light Speed: Racing A Solar Car. Also Light Speed: Catastrophe It was not clear what battery tech they were using but heat is a big problem when your battery gets big.

If you have any good resources for Lithium batteries send them to me and I will add them to the bottom. (i will add some once I get more time)

Well, a lithium battery on fire might kill some ants :laughing:

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On a more serious note, I think testing the ETX680 would be well worth it if someone wants to invest the $ in doing so, as it’s a 12V battery with user-friendly specs (e.g., can be charged with a lead-acid 12V charger), and is similar in physical size to the current lead acid batteries so would be easier to mount.

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My team was already responsible for a battery fire at Championship on Einstein in 2011 during the semi-finals (I don’t recall the exact match but Aidan had throw it in a bucket and extinguish it). Our mini-bot went flying off the pole at the end of the match and started smoking, shockingly almost no one noticed this and people seem shocked every time I mention it.

I leave this here as an example to be clear, Lithium Ion batteries are not safe for FRC use, there is too much possibility to damage them. Then add in the shipping issues with robot transportation things get problematic quickly.

As you’ve seen, a non-lifepo4 lithium battery with no protections on overdischarge or temperature can be pretty dangerous if mishandled.

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Pretty sure the batteries from that era of FTC were still Ni-Cd batteries, so not lithium, to clarify. Though this does bring us around to that drill-style lithium batteries would probably work quite well for FTC…

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