Motec PDM

[Anon]

Hello,
Are we allowed to use a Motec PDM-30 instead of using fuses and relays in the car? Though the rule book specifies where to use relays and fuses, can we us the PDM as an alternative?

[Menisk]

Plenty of teams run PDMs, mine included. They are an awesome option and definitely legal.

[Rex Chan]

Hello,
Are we allowed to use a Motec PDM-30 instead of using fuses and relays in the car? Though the rule book specifies where to use relays and fuses, can we us the PDM as an alternative?

The BOT switch still needs to run through a relay, I think. And I would use a relay for the starter motor (CBR600RR). Everything else can be PDM

[MCoach]

Yes, PDMs can be used for everything except safety critical items (the BOT switch, dash kill, any other kill switch).

The reasoning here is that solid state relays usually fail closed rather than open, so it becomes a hazard to permit their use for those items.

[Menisk]

Unless you're in Australia in which case your addendum deletes the clause and you can use them for kill switches too. Makes for a much neater system.

[MCoach]

Ah.

We had to go as the rules committee to double check and that was the response and reasoning I was given. Very interesting...

[apalrd]

Again, it bugs me that the FSAE/FS competitions are so far apart on some rules. FSAE US Rules Committee had this to say about solid-state relays

Andrew,

Use of an SSR on the cockpit mounted master switch or brake over travel switch is not acceptable, a mechanical relay should be used.

The loads that will be switched by this relay are generally all inductive. Protecting the SSR from the multiple inductive loads would be critical to having robust operation and this protection system may be somewhat complex and cannot be easily inspected at competition. Additionally the most common failure mode of an SSR is to fail closed or shorted meaning that the safety switches will be inoperable to shutdown the vehicle.

Dan B

As for fuses and relays, I don't think any fuses or relays are specified other than the brake over travel switch/cockpit master switch relay. That is the only relay we use.