BMW K bikes (Bricks)

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robmack

robmack
Life time member
Life time member
Dave of EEVBlog posted a blog video recently where he talks at great length about relays and the need for snubber / freewheeling diodes to protect the switching transistor.  We all will be familiar with the problem he describes. There are numerous posts from guys whose starter relay suddenly ceases to work and they eventually find out the ICU has been toasted.  The reason for the toasted ICU is the super high voltage caused by backEMF. across the starter relay.

https://www.eevblog.com/2021/07/31/eevblog-1409-the-dangers-of-inductor-back-emf/

It's a very technical discourse about the electronics of relay switching circuits so be warned.  This is for entertainment purposes.  Dave goes to great lengths to talk about the theory and then spends a great deal of time simulating the problem.

The take away is to be sure to use snubber circuits on the starter relay especially if you're replacing the OEM relay with a different aftermarket one.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

brickrider2

brickrider2
Life time member
Life time member
Snubber circuits?  Never heard of those before today.


__________________________________________________
1996 K1100LT
    

92KK 84WW Olaf

avatar
Life time member
Life time member
@brickrider2 wrote:Snubber circuits?  Never heard of those before today.
Ignore at your peril. Just be careful if you ever need a replacement relay.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Dan Pete

Dan Pete
Silver member
Silver member
I vaguely remember snubber circuits from electrical theory classes bac in the late '70s. But can we get a "you need to add this" type tutorial post, for us that the theory of why hurts our brains?

    

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