homebrew rev limiter bench tested today

Dimbit · Post by **Dimbit** » Thu Feb 14, 2008 6:30 pm

I just tested my rev limiter on the bench and it seems to work. Grounding the input causes the resistance in line with the coil supply to jump to 22 Ohms. 'On' resistance is about 0.1 Ohms. It's based on Brent's schematic, but uses 2 SUB75P05-08 mosfets in parallel (to spread the load over 4 stripboard tracks, hope that's enough) and a single power resistor and was thrown together in a lunch break today so doesn't look nearly as professional.
I cut the board to fit in the mjlj case and will wire it in internally tomorrow. Crappy camera phone photos attached, and full write up to follow when it's in the car (if that's not stepping on anyone's toes).

Post by **brentp** » Thu Feb 14, 2008 8:01 pm

Looks interesting. Be sure to monitor the devices while running, especially since you don't have heat sinks on them.

Thanks for testing the design,

Dimbit · Post by **Dimbit** » Thu Feb 14, 2008 11:11 pm

When finally buttoned up I intend to put a dab of heatsink compound on the transistors which will be touching the aluminium case (one of them might need a copper shim but I'll figure something out). I assume the resistor won't get hot because the limiter should have a very small duty cycle and shouldn't be triggered very often. I will be sure to test all this once installed though.
Thanks for designing!

Salamander · Post by **Salamander** » Mon Feb 18, 2008 2:47 pm

Recorded a video and upload it to http://tinypic.com to see the functioning of the rev-limit

britlude · Post by **britlude** » Mon Feb 18, 2008 9:29 pm

.... maybe a hint to what we are looking for....????

Post by **brentp** » Mon Feb 18, 2008 9:38 pm

If you'd like to see a video of the rev-limiting in action, our friend Chris generously put up some clips on YouTube. See his testing here: http://www.autosportlabs.org/viewtopic.php?t=1498

Dimbit · Post by **Dimbit** » Thu Apr 24, 2008 6:39 pm

This is now fully functioning. I just tested it by setting the limit to 2k and it was incredibly effective. It stopped the revs bang on 2k and fired again as soon as the rpm dropped back. Veyr impressed with the design, but I kind of wish I'd held out for Brent's model as mine ended up costing around £8 in parts!

Dimbit · Post by **Dimbit** » Mon Apr 28, 2008 6:58 pm

I checked for overheating today. As soon as I got home I whipped the lid off and felt all the components and found the mosfets weren't even warm. In fact they were cooler than the case which is gently warmed by the temperate breeze drifting by my feet from the engine bay! The 150 Amp rating may have been overkill after all. Oh well, better to be safe...

I also learned today that hitting the limiter at 6k with wide open throttle results in BIG flames so I should probably put the shift lights somewhere more unmissable...

Post by **brentp** » Mon Apr 28, 2008 8:13 pm

Thanks for the update. You have some extra insurance with doubling up the mosfets- The unit offered in the kit has a ridiculously-low on resistance- on the order or even better than a mechanical switch (and far more reliable!)

Gremlin · Post by **Gremlin** » Sun Nov 09, 2014 6:03 pm

Is it agreed that when wishing to enable a hard limiter, supply the coil with a 22 ohm feed at the set rpm