FSAE Electric - Battery Temperature Sensors

[jharmon]

Hey guys, we're a first year team, and we're having trouble designing our batteries. Specifically, I was hoping someone could clarify EV 3.6.3:


The AMS must continuously measure the temperatures of critical points of the accumulator to keep
the cells below the allowed maximum cell temperature limit stated in the cell data sheet or below
60°C, whichever is lower.
Cell temperature must be measured at the negative terminal of the respective cell and the sensor used
must be in direct contact with either the negative terminal or less than 10mm away from the terminal
on the respective busbar.

We were looking at using Elithion's BMS (http://elithion.com/1PR0xxxX.php) in our pack. The problem is, the temperature sensors are on the PCB's. Does this count as "in direct contact with... the negative terminal"? The PCB is attached directly to a ring terminal which is attached to the negative terminal, but we cannot determine if that is rule compliant. (picture (http://elithion.com/img/1PR0064M_sm.jpg)for reference)

If this wouldn't pass tech inspection, do you have any other suggestions of BMS products that work well with FSAE Electric?

Thanks,
Jake Harmon
Caltech Racing

[nat45928]

I'm Nathan, the electrical lead from Missouri S&T.

We used Elithion's system for our pouch cells last year and the judges were not a fan of the temperature sensing. It does not meet the rules explicitly so we switched to a in-house system. They were open to the idea of it being ok though so some arguing over a rules question will likely get it ok'd.

Hope this helps, feel free to ask me anything if you can't figure out something with the system.

[B757]

You could build a network using temperature sensors such as TMP37 (5V in, linear analog voltage out)or DS18B20 (one-wire digital protocol) and read their values with a microcontroller, which can then activates the shutdown circuit independently of your main BMS. That was our plan over here at Boston University, though we are no longer planning on going to FSAE-Electric this year and only to Formula Hybrid, which does not have the 10mm rule.

[AndrewMcCooey]

I am Andrew from Auburn University. We are a first year team as well.

I want to add a question to this forum about thermistors. Orion sells a thermistor expansion module which will help our small cylindrical design because we want to monitor all of the temps.
I am still not sure, however, that a thermistor only needs to touch the negative end of the battery. We were thinking soldering thermistors onto the busbar of the battery pack.

My question: How do thermistors hook up to the battery? Would it be rules compliant?