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Old 06-07-2011, 10:57 AM   #63
Dr_Bean OP
Dr_Bean
 
Joined: Jul 2004
Location: The Netherlands
Oddometer: 101
Quote:
Originally Posted by gefr View Post
I believe the "optical" sensor is using ultrared signal and so is not blocked from dust (mud). I think the normal death of these pumps (excluding flooding with salt water or mud) would come either from rupture of the membrane or from Mosfet death that is probably operating the switching. I wonder how long is the life of these two components.
Well.. you are correct, but mud is mud.. when there is enough mud, it will be blocked :-) (but then you just rinse it... np)

I haven't seen any membrane rupture. Old pumps (>50tkm) do sometimes pump a little less volume (membrane/valves do not close perfectly), but since the pump is about 3x oversized, that will not be a problem.
pomp-bearings wear! (the rod gets clearance)
I have seen the pump rod getting stuck from corrosion.

Mosfet has a 10 years lifespan in normal use... and that is how it is designed.

ps.: The mechanical switch (contact breakers) does actually do a great job: MTBF is around 3'000'000 switches (which is quite good for a mechanical switch switching a 8 Amp inductive load)... But: If the pump switches around 1x per second that still means after 1000h it is done... 1000 h is 50tkm / 30t miles and that is just not enough! (so failure by design)

Losses in the mosfet are negligible, so it doesn't heat (proper switching, the correct fet).
The only heat comes from the pump itself and the engine. basically the whole pump should not get over 90 C (~200F): then there are no problems for sure.

I also use the pump for Honda Africa-Twin, Transalp and Varadero: There the pump is mounted behind the cylinder... hence running a lot hotter: No problems there.

From my design I think the LED from the optical detection is the most critical part.
But hey.. what is the real 'operating time' on a bike: 100'000 kms is about 2000 hours : thats peanuts for electronics.
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