BMW K bikes (Bricks)

You are not connected. Please login or register

View previous topic View next topic Go down  Message [Page 1 of 1]


robmack

robmack
Life time member
Life time member
It's a common complaint - a low battery voltage can cause the starter relay to fail resulting in the starter motor failing to shut off even after turning off the ignition.

So, some people fix the problem by buying an aftermarket starter relay and replacing the OEM one.  It's a cheaper option however  BE CAREFUL TO SELECT A RELAY THAT HAS PROTECTION DIODE ACROSS THE RELAY COIL.  Yes, all caps.  If you fail to observe this caution, you risk very quickly taking out your Ignition Control UNIT (ICU) which is a very expensive mistake.

There was a discussion about this topic on EEVBlog, but I'll include the two oscilloscope traces from that thread to illustrate the threat.  When the engine catches, the ICU cuts the connection to the relay.  The electricity does not stop flowing through the relay coil immediately and a very large voltage spike can result.

Observe caution when replacing the Starter Relay with an aftermarket one ?action=dlattach;attach=326880;image

The oscillation apparent on this scope trace shows the voltage spike when power is removed from an automotive starter relay.  Take note of the annotation at the bottom.  The minimum observed +ve voltage is 300V, the minimum observed -ve voltage is 388V, the peak-to-peak voltage is 688 Volts.  This same voltage will appear across the transistor driver in the ICU, which will immediately kill the device.

This whole threat can be eliminated by including a simple 1N4007 diode across the starter relay coil in the reverse direction, as shown below

Observe caution when replacing the Starter Relay with an aftermarket one 002

The trace below shows the same relay with a snubber diode installed as above.
 
Observe caution when replacing the Starter Relay with an aftermarket one ?action=dlattach;attach=326882;image

Now note that the oscillations are completely damped and the peak-to-peak observed voltage is 16.8 Volts.

If you purchase an aftermarket starter relay, just make sure to add the required diode.  It will cost you $0.50 more but you potentially save having to replace a $200.00+ ICU.


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

Dai

Dai
Life time member
Life time member
Rob - you're showing a zener there too; what is it?


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

robmack

robmack
Life time member
Life time member
I'll see if I can find a simpler schematic.

There's no harm using the Zener and adding the Zener will assist the relay in releasing faster. The zener voltage should be low enough to avoid damaging the ICU's driver, but high enough to prevent the relay holding on too long -- probably 10-15V.


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

duck

duck
Life time member
Life time member
The diagram on this relay looks like it has what you're referring to:

Observe caution when replacing the Starter Relay with an aftermarket one 75552fl


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

InkandBrush

InkandBrush
active member
active member
@duck wrote:The diagram on this relay looks like it has what you're referring to:

Observe caution when replacing the Starter Relay with an aftermarket one 75552fl

So will that^ relay work with no issues?
Apologies to revive a dead thread, but I may need one of these.

    

robmack

robmack
Life time member
Life time member
YEs, that relay will work with no problems.


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

yamaguzzi

yamaguzzi
Silver member
Silver member
@robmack wrote:YEs, that relay will work with no problems.
using this relay do you still need to add the diode ?


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://motoguzzi850t.blogspot.com/
    

InkandBrush

InkandBrush
active member
active member
@yamaguzzi wrote:
@robmack wrote:YEs, that relay will work with no problems.
using this relay do you still need to add the diode ?
That is my question as well, does this relay have the built in diode, or do we need to add it?

    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
Euro Moto Electrics are a reputable Beemer spare parts supplier. Their offering will work as advertised. It is a Tyco/Bosch relay with the correct cross referenced part number. The less expensive version YamaGuzzi linked to is the same thing.


__________________________________________________

1987 K100RS, '89 K100 w/K1100RS engine, '93 Framed K11/K12 engine 'Big Block', '96 K1100RS, '09 K1300GT, '07 K1200R, '95 R100 Mystic & '77 R75/7.

    

InkandBrush

InkandBrush
active member
active member
@Two Wheels Better wrote:Euro Moto Electrics are a reputable Beemer spare parts supplier. Their offering will work as advertised. It is a Tyco/Bosch relay with the correct cross referenced part number. The less expensive version YamaGuzzi linked to is the same thing.
OK... and I'm not trying to be funny, but that doesn't answer my question.  I've seen no advertising.  I don't know if they have the necessary diode in there.  I'm totally going off the information in this thread, and apologies, but it's not clear if this relay has the diode everyone is talking about.
So, again, is this relay all I need, or do I need to add the diode?

    

InkandBrush

InkandBrush
active member
active member
@Two Wheels Better wrote:Euro Moto Electrics are a reputable Beemer spare parts supplier. Their offering will work as advertised. It is a Tyco/Bosch relay with the correct cross referenced part number. The less expensive version YamaGuzzi linked to is the same thing.
I mean no disrespect.   Just trying to be precise.

    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
It's no joke. Go up to post number 6 above, read it, and if you get a warm and fuzzy feeling you might have hit the jackpot.

I have been using this relay for several years now, like a whole heap of folk, I suppose.


__________________________________________________

1987 K100RS, '89 K100 w/K1100RS engine, '93 Framed K11/K12 engine 'Big Block', '96 K1100RS, '09 K1300GT, '07 K1200R, '95 R100 Mystic & '77 R75/7.

    

InkandBrush

InkandBrush
active member
active member
@Two Wheels Better wrote:It's no joke. Go up to post number 6 above, read it, and if you get a warm and fuzzy feeling you might have hit the jackpot.

I have been using this relay for several years now, like a whole heap of folk, I suppose.
Noted. 
Tyco V23232-A0001-X003 is a direct replacement for the stock/standard starter relay.
Good thing.  These are less than half what the stock replacement is going for, if you can even find one.

    

robmack

robmack
Life time member
Life time member
If you note, the schematic depicted on the top of the relay case in that picture shows a capacitor across the coil terminals and a diode in series with one of them. The capacitor can also act as a snubber in this application as much as a paralleled diode or resistor.  I would assume that the manufacturer builds this device in accordance with this schematic.  Since they depict a capacitor snubber, then I'd conclude it is safe to use on the Kbike.  The specs printed on the relay also align with BMW's specs.  You're good to go.


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

InkandBrush

InkandBrush
active member
active member
@robmack wrote:If you note, the schematic depicted on the top of the relay case in that picture shows a capacitor across the coil terminals and a diode in series with one of them.  The capacitor can also act as a snubber in this application as much as a paralleled diode or resistor.  I would assume that the manufacturer builds this device in accordance with this schematic.  Since they depict a capacitor snubber, then I'd conclude it is safe to use on the Kbike.  The specs printed on the relay also align with BMW's specs.  You're good to go.

Thanks.  I've just never, ever, ever, ever, EVER done any kind of electronics or wiring (besides some VERY basic household stuff).  Ever.  At all.

    

InkandBrush

InkandBrush
active member
active member
I just ordered this relay from The Electrical Depot.  Great service and communication.   I was going to order from Wayteck Wire, but they were asking a bit more per unit and almost double the shipping cost of TED.
Oh, and they also didn't have any.  Claimed there was a huge backorder on them.

    

chris846

chris846
Life time member
Life time member
Much appreciated guys, Robmack et al, I'm about to start the electrics for the K75k project and I was considering ordering a cheaper alternative to the very expensive OE starter relays. Good info, thanks.


__________________________________________________
The Longest Lunch
    

View previous topic View next topic Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum