Battery / relay /PUZZLED

StuartOstroff · 09-03-2006, 07:16 PM

I think I found the cause of my 3-week old battery dying. I replaced my original (yr 2000) battery a few weeks ago with a new BMW AGM. I installed it myself, and I thought I heard a click (like a relay clicking) when I made the final connections. Took a few rides within the next week, everything seemed OK.

I then went off to China for a 10-day business trip. This morning I went to check on my bikes and the battery was totally dead, even the clock was out. I plugged in the charger and it never started to charge.

Pulled off the plastic this afternoon. Battery measured 0.4 volts. Disconnected the + leads to the battery - the main lead from the bike harness and my additional leads to aux fuses. With no connection the battery measured 0.8V. The resistance from the main harness + lead to ground was measured at 137K ohm, which would calculate to a draw of about 0.0008 amps.

When I reconnected my old battery (to the main + lead AND my aux feeds) I immediately heard a relay click. I found that my new horn relay was clicking on, but the horns were not sounding. When I toggled the aux horn fuse the relay clicked on and off, but no horns. Pulled all the leads off the relay. The #30 terminal is fed directly from the aux 15A fuse, tied to the battery +. The two leads from the harness just power the relay from the origanal system wiring and horn button. The two new horns are both connected to the NO contact on the relay. I noticed that one of the leads from the harness was loose within its crimped female terminal. I replaced this and recrimped (better!). BTW this relay and new horns have been on board for a full year.

Why would the relay be clicking on when I just connected the battery, and the horns not sounding? After correcting the loose terminal (which goes to one side of the relay coil) the relay seems to work fine. When triggered by the horn button the relay clicks; only if the aux fuse is in do the horns sound. Just like it is should work!

This electrical engineer is puzzled !! Do I replace this relay, get a new battery, and move on? I cannot understand how the relay could be "mis-firing" due to a loose coil wire, with the horns NOT sounding? A relay is a simple device - this one seems possessed, and I've had waaaay too much practice opening up and replacing the tupperware on this bike!

Thanks for all comments. Stuart

Flatbutt1 · 09-03-2006, 08:39 PM

OK no EE here but, does the relay work with a solenoid? If so could the solenoid be tripped but NOT close the ciircuit?

R111S · R111S's Garage

Check the Relay for a leak path to one of the other terminals. There should not be any connection between the Coil Circuit Terminals and the Contact Terminals.

GS ADDICT · 09-04-2006, 04:07 PM

I do a lot of m/c electrical work in the evenings and see battery discharge problems a lot. There are a few causes including a shorted diode in the alternator but before we go there, who wired up the relay coil circuit? I suspect that is the problem.
First things first. Ignition off as well as any added accesories off also. Connect a fully charged battery up with an ammeter in series with either +or -. Start off on the high current scale and work down to where you can measure milliamps.
Please advise what that figure is. (hopefully less than 1 or less mA.) If the current is higher, pull 1 wire off of the relay coil (or pull the aux horn fuse) and see if the current drops. Let me know what you find so far.
Regards
Reto

StuartOstroff · 09-04-2006, 04:50 PM

Thanks for comments. I pulled out the relay and popped it open - no apparant leak paths between coil terms and contact terms. Checked with Fluke on hi-ohms. Anyway, I'm replacing this relay with a better quality (Made in USA) relay.

I did reconnect my old battery to the bike harness, and I also checked for any flow on the ma scale. None to be found, no leakage whatever. On the ohms scale I measure about 137K which would indicate a current draw of 0.0008 amps. This I assume is for the clock?

I've gone a step further and installed a heavy duty toggle switch hidden under the seat to disconnect all 3 of the aux circuits which connect directly to the battery. So I can shut down these feeds and eliminate any future surprises.

Stuart

GS ADDICT · 09-04-2006, 05:35 PM

Hmmmm..... very weird. I agree the clock would be a high resistance. Until you are sure that the problem is not going to come back, disconnect the battery when you are gone for any extended period of time. If a battery is discharged below 9 volts it permanently affects it's life. If it is discharged to 1 volt or less the damage is even worse and sometimes cannot be salvaged. You can try to revive the AGM by hitting it with an old style 10A "battery boiler" while constantly monitoring for overheating - you may get lucky.
After all what is there to lose?
R