Power Distribution

[Tickers]

In professional motorsport, most teams use solid-state power distribution boxes to control high-current devices (fans, motors, pumps etc).

Making the loom for the FSAE car last year and using relays/fuses was a PITA after having used a proper PDU before.

Do any of you guys use a power box in your SAE cars? If you have, which did you go for? If you looked into it and chose not to, why?

[Tickers]

In professional motorsport, most teams use solid-state power distribution boxes to control high-current devices (fans, motors, pumps etc).

Making the loom for the FSAE car last year and using relays/fuses was a PITA after having used a proper PDU before.

Do any of you guys use a power box in your SAE cars? If you have, which did you go for? If you looked into it and chose not to, why?

[NickFavazzo]

Not being the electrics guy, we create our own power boards using plenty of solder and mosfets, we have looked at buying a MoTec system though due to the simplicity and fact that you know it will work. That being said, our own power boards do work quite well and have done since at least 2005.

[Tickers]

That's pretty interesting. What made you go with that solution? Is there any sort of customisation built into it?

[wweissin]

Tickers,
If I had to venture a guess it would be cost. While I whole heartily agree with you on it being simpler to use a PDM it just seems as though it is out of the budget of most FSAE teams. It seems also to be out of budget for most club level races too. I believe we have sold two this year and built full nose to tale harness for dozens of cars in the same time frame. Though it's not as slick as a PDM, relay and circuit breakers are very robust and effective and when a panel is done correctly it can look quite amazing.

[NickFavazzo]

I believe it is cost and we can make it to suit exactly what we want. The entire unit we create is custom, but I do believe we have a few tricks and things in it, again I am not electrical.

Relays and such are great as anyone can understand them and they work just as well as fancy PDM, just without the tricks.

[TMichaels]

The number of teams at FSG using a PDU instead of fuses and relays increased in the last years. Most of them use their own designs (for cost reasons I suppose).
Usually they also include current readings etc. in their DAQ systems which may give a hint, if a fuel pump for example is about to fail.
Additionally you could do things like switching off the radiator fan while accelerating to take load of the generator. Seems to be more a fancy thing though as I doubt that it really makes a difference.

Regards,

Tobias

[Tickers]

Tobias, what would you say the percentage of people using PDUs instead of relays/fuses/circuit breakers was, and of those how many are designing their own systems?

I always wondered how many electronics guys some of the teams must have to be designing their own PDU/DAQ/ECU. There were two dedicated electronic guys on our team last year (both of us were MEs), and that's probably two more than most years.

[coastertrav]

I've looked into it a bit, but didn't really see the need. I think we only have 5 standard relays on the car and one solid state for the waterpump. Any trick things I could think of doing through a PDU can be done through the Haltech Sport 1000/2000, minus the current load readouts, which if anything are just neat features, although not really necessary.

A PDU/DAQ for a senior project is something I have thought of doing though.

[Rex Chan]

Re: Tickers - Yes, we (Melbourne Uni) have just started using solid state power distribution this year (2011). Previously, we just ran relays controlled off the MoTeC M48 ECU. We bought a MoTeC PDM15 (and M400). I don;t think there was one big, main reason why we went to PDM's over relays, but MoTeC is the cheapest for these kind of units.

I could only find one brand that was cheaper, called ISIS, but they're geared towards rewiring passenger cars/hothods, restorations, etc. Too fiddly and not enough control for FSAE. Other brands I found were OBR, a specialist motorsport UK-based firm doing custom boxes (can't remember the name), and another US based aftermarket "racing" company that was about to release one. The two real motorsport ones seemed to be very pricey, and the other one hadn't launched yet, but was not as CAN aware as MoTeC.

So, onto the reasons why we went with MoTeC: more reliable than mechanical relays, smaller space. One of the reasons the Integration team went with PDM and M400 was to put our team down the CANbus route, and the PDM sends all of its monitored data (voltages, current, warning states) over CAN, which means you can do stuff with it if you run a SDL/ADL or other CAN device.

Having used teh PDM on the dyno and now having wired it up in the car, it doesn't save you that many relays (still have ones for starter, kill switch circuit, and SSR for electric water pump). What it DOES let you do (and this to me is the biggest selling point of any programmable power module) is have CONTROL over how and when you power your devices. On the most basic level, it lets us remove the Davies, Craig EWP controller, which has an annoying mode where if the ET was cold for too long, it would run the pump at full bore. This might be a great safety feature in a road car, but got really annoying when you wanted to sit around and adjust things in the ECU.

The more exciting control things are warmup RPM limits, engine self protection logic, smart engine cool down procedures, cranking power management. And of course, the continously ressettable circuit breakers (we're not using this feature now, as we'd like to know what's wrong if something bad happens, but for comp, we can just make everything keep on getting power, even if it keeps on tripping the "fuse").

The PDM doesn't make us go faster, but does let me worry less about managing the cars batteries, and I don't have to worry as much about ET/OilT/OilPressure, as the PDM should turn the engine off if any danger conditions are reached.

Re: wweissin - the cost of a PDM15 (cheapest model) is about $1500AUD, so while its an expensive relay box, isn't too expensive if you consinder how much FSAE teams spend on some things. I'm also hoping our engines will last longer with the PDM to keep an eye on things. I'm not saying its for all FSAE teams, but $1500 is not a huge sum for many teams, and compared to what it can do.

Re: NickFavazzo - I def agree with a PDM being more complicated to program. The person in charge of initially making the setup and then making changes HAS no know what they're doing, overwise bad things can happen very fast. MoTeC actually make it very easy to program the logic, but it is by definition more complex than plain relays.

Re: TMichaels - I'd say its much more than a fancy toy, and it won't make you go faster, but it does make life a lot simler/easier/less stressful. Which means you can concentrate on other things, rather than checking data logs for engine health.

Re; Tickers - for the 2011 FSAE-A comp, Melbourne and Monash will be running PDMs, as well as UQ, who ran one last year too.

[TMichaels]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Re: TMichaels - I'd say its much more than a fancy toy, and it won't make you go faster, but it does make life a lot simler/easier/less stressful. Which means you can concentrate on other things, rather than checking data logs for engine health. </div></BLOCKQUOTE>
Don't get me wrong. The "fancy thing" was related to doing things like taking load of the generator while accelerating, not the use of PDMs in general!
I second all of your arguments although we never had reliability issues with relays.
If I would still be in a team I would definitely build a PDM.
I sometimes think about doing open hardware development for FSAE...hopefully I find the time some day...

Have you compared the weight of both solutions?

Regards,

Tobias

[Rex Chan]

On a car, I've only had one relay break, and that was due to the relay being inside a non-water proof box that got filled with water, and so shorted out.

Off the car, I've had relays behave funny, so I've thrown them out so that no one else can use them. Not really sure if they're always "broken", but better be safe, as we have lost of those 30A Bosch relays.

Thw weight I have not compared, but with PDM would not be much lighter, if at all. However, the space taken up is a lot less, as the PDM is quite compact/small, and we've put the relays on the firewall, so there's no big relay box.

I wonder how much gain taking load off during accel is worth? That's the time the alternator can make the most electricity I would have thought, and its not like the 4-cylinders are short power. If anything, the only benefit to teams being forced to make their own alternator (such as Auckland with their custom single) is that you get to choose a very big one, for all those power hungry electrics on an FSAE car. If I could easily put in a bigger stator/coils on teh CBR600RR to make more current, its something I would seriouly consider.

[murpia]

Are there any open-source or otherwise public domain designs around for PDM circuitry?

Although not FSAE related we control a number or automotive type loads using relays. It would be good to replace those with MOSFETs but the reliability / robustness issue is a concern.

I suppose there must be application notes around for the types of MOSFETs in use?

Would be good to see this technology more in use.

Regards, Ian

[TMichaels]

It is standard in the body control units of production cars to use FETs. If you are interested, just have a look at the PROFET series by Infineon: Infineon PROFET (http://www.infineon.com/cms/de/product/automotive-ics/smart-high-and-low-side-switches/profet%E2%84%A2-smart-high-side-switches/channel.html?channel=ff80808112ab681d0112ab69e2d40 357)
They offer high-side switching, over-current detection and protection and current sensing. I have seen teams successfully using the BTS555-series for switching the starter motor current.
They are not the cheapest available option though.

Regards,

Tobias