Lithium Manganese battery temp question

[robert.schwartz]

Must Lithium Manganese batteries be kept cool while in use?  The electrathon car that I am working on uses a 48V  26AHr battery that is breaker protected at 100 amps.  We are running a 10KW brushed 48V motor.  We are geared to run the motor at 3600rpm under load.  The teacher running the club is convinced that the battery is over heating and wants to cut vents in the body to cool the battery.

Any thoughts?

Thanks,

Rob Schwartz
aka the bike guy 

[rich.carroll]

I'm not so sure that Lithiums need to be "kept cool," although they certainly need to be protected from overheating.  I am somewhat aware of the dismal airflow inside some ot the electrathon cars, judged by seeing drivers emerge from a session on a hot day, and a couple of conversations with drivers about the heat inside. It should not be difficult to use a small, cheap,  IR non contact  temp sensor.  I have two and would be glad to lend you one.  Taking battery temps after a session will tell you if the batteries are much hotter than ambient temp.

Air cooling is one choice, but using ambient air on a hot day will mean you need to move LOTS of air.  Vents in the body need to be intelligently positioned by looking at airflow (dpeending on the top speed of your vehicle) and are not always a good solution.  Remember, back to the simple science, you have several means of cooling, contact, radiant, etc.   Radiant cooling is the cheapest, but lesser in effectiveness.

[tim.moore]

Computer / server fans are 12 volts will not take up much energy.  I definitely would cool batteries to be safe rather than sorry.

[ted.lowe]

i will mostly defer to Rich Carroll's excellent reply, but i thought instantly that with that setup, passive cooling (vents in car body), will not be enough to dissipate the thermal energy in those batteries.  So, as Tim Moore mentioned, i'd suggest active cooling with fans. 

i don't know how fancy you wanna get, but the Arduino-based Battery Box Temperature Controller i recently completed could be adapted rather simply to be a battery-cooling controller.  It can separately measure 4 temperatures and control 4 loads (heaters or fans).  On/off temperature thresholds can be set.  There is an LCD readout that shows you the temperatures being measured in real-time.

[rich.carroll]

Ted, I think your feeling that the vents would not be enough is on target.  Vents work well for higher speed verhicles (like race cars) and for vehicles run with a big hear source and a significent temperature differential.  I'm betting that the electrathon cars have their greatest need for cooling on hot days, and the temp. differential is the least on hot days. Radiant cooling is ideal, basically installing "heat sinks" (finned aluminum cooling plates) on the batteries, but you also need to look at where you are radiating the heat to.  If you are radiating it to a limited air flow cabinet, the radiant cooling effect will be less.  Vent the compartment, and the radiant cooling is more.  Vent the air across the top of the batteries, and you add conductive cooling.  I agree with the 12V case fans.  They are available in several sizes, and upgrading to a ball bearing mount still keeps fan costs very minimal.  Consider your desktop computer.  A fan on a heat sink has been the norm for the processor cooling for years.  Get into gaming, and multiple fans, cases designed for good airflow, and liquid cooling of the hottest areas, redistributing the heat (still within the case) to where it can be managed by case cooling and exhaust fans is common.   Power supplies for computers have had internal fans for years also, and the fan takes very little energy as Tim pointed out. There is no cost to running heat sinks, only the initial build. And, unless you thoughtlessly mount the fans in a 'dirty' area, there is almost no cost to running good case fans, only the initial design.  Both would be expected to be trouble free between maintenance sessions.

There will come a day when electrathon cars have a high enough speed to consider aerodynamics, but we're not there yet.  Aerodynamics and cooling air flow for batteries is a really interesting science, and takes significant resources to develop.

[robert.schwartz]

Thank you Rich, Ted, and Tim. 

Rich, if you could direct me to where I could buy one of the temperature sensors that would be great. 

Ted, I will talk to the kids, I am sure that one of them is familiar with the arduino as it is all magic to a mechanical guy like me.

Maybe at the next meeting you guys can show me how to mount fans on the battery box without admitting rain water?  Two of the last four years the race at Road America has been in the rain.

Thank you so much,

Rob

[rich.carroll]

I see non-contact IR temp sensors many places.  Try your local tool store, or Auto Parts store.  If you want to wait a week and have it land in your mailbox, there are several on EBay: https://goo.gl/vG37rv  and on Amazon https://goo.gl/5PJhdq
These are so easy to use: point, press the button and measure.  Pick a consistent spot on the battery (maybe the anode or cathode) and scan each battery in the pack. 

[rich.carroll]

Add one more, in my mailbox today.  This one is from the far east, so it make some time to arrive.    http://www.gearbest.com/measurement-analysis/pp_164704.html?wid=21  $12.63 includes shipping.