FS Rules Implementation

[Rootthecause]

This thread is for discussion of Formula Student Rules applied to the DC/DC converter.

[Hazelnutter03]

Hi, FSUK team here - just a few quick questions if you don't mind.

As far as I can see, the rules are practically identical to FSG re DC/DC converters. We run a much lower draw system, about 80W continuous at 12V (Accy is 250-430V), if you could point us in the right direction on how we can adapt the design to our use case.

Does the DC/DC connect to the accumulator before or after the AIRs - I would be concered with an insulation fault in the DC/DC and not being able to isolate it.

[Hazelnutter03]

Perfect thank you. What would the efficiency be at the lower power draw? Is there a way to improve the efficiency at lower power, potentially at the cost of peak power?

Yes thats true, I hadn't considered the BMS connecting to TS before the AIRs, that does give me a bit more confidence!

[Rootthecause]

What would the efficiency be at the lower power draw?

Very hard to say. There are a lot of factors affecting the efficiency. If you just decrease the the secondary winding to just one turn, then you might reach 87% at 80W. Here's the Plot from the Datasheet, but for lower efficiency ranges:

Is there a way to improve the efficiency at lower power, potentially at the cost of peak power?

Jupp, definetely! If you decrease the Airgap between the cores, your magnetizing inductance will increase (decreasing switching frequency and resonant current). The resonant current cycling around in the resonant circuit actually is the main cause of power loss in idle. In order to increase the frequency in order to not saturate the transfomer, the resonant capacitors need to have smaller capacity. If you do the resonant circuit just right, I belive you could hit 95% (4W loss at 80W output).
But let me tell you this: Designing your own resonant circuit is a massive rabbit hole with many hurdles.
If you value your time, just build the original design with one secondary turn. At the end of the day, the efficiency will not matter, unless your converter overheats due to the power loss. In your case, you will look at around 10W of power loss, which is far away from any thermal issues, even in a enclosure. Also driving for 1 Hour will leave 10 Wh on the table - your battery is probably in the order of kWh ;)

Yes thats true, I hadn't considered the BMS connecting to TS before the AIRs, that does give me a bit more confidence!

It also gives you a way of closing the loop 😄 It is as always: "Caution! Life can lead to death."

[Hazelnutter03]

Thanks for the help! We will keep you posted

[sebgothard]

Thanks for the help! We will keep you posted

Hi, I'm also thinking of implementing this for FSUK, just wondering how far you've got, I've also been wondering how to interpret the rules that define if this kind of thing can be pre-AIRs. If you have a definitive answer that would be appreciated.

[Hazelnutter03]

Thanks for the help! We will keep you posted

Hi, I'm also thinking of implementing this for FSUK, just wondering how far you've got, I've also been wondering how to interpret the rules that define if this kind of thing can be pre-AIRs. If you have a definitive answer that would be appreciated.

Not anything definitive, but based on UK normally following the same idea as FSG i think pre-airs should be fine, but i dont know of any uk teams that run a dcdc, I think warwick were looking into it

Havent got very far at all yet tbh, have been a little preoccupied with other things