View Single Post
Old 04-03-2012, 12:47 AM   #734
Box'a'bits OP
In need of repair
Box'a'bits's Avatar
Joined: Sep 2008
Location: Wellington, New Zealand
Oddometer: 2,361
Wiring in resistors to slow indicator hyper flashing.

Let me start with a disclaimer & assertion. While I love figuring stuff out, I generally hate playing with wiring & playing with electrics, mostly because I have trouble finding out where the magic smoke leaks out. I can do it Ė but I prefer not to.

Why Did I Do This:
Some time ago I replaced the stock 21w indicators with KTM 10w ones. This was primarily for aesthetic reasons, but also because I thought the smaller & more flexible KTM units would be more durable (& because I got them at the right price).

The replacement has caused an issue, because the flasher unit has detects lower current draw, & thinks that indicates a bulb is out, resulting in hyper flashes (the indicator flashing much more rapidly than it should).

Until now I have put up with this, & have actually gone thruí a couple of WoFs without this being presented as an issue. However this WoF check I was pulled on it. As a result I need to do something to remedy it.

Resolving The Issue:
There are generally a couple of ways to resolve this issue: 1. Get a new flasher unit that can accommodate the difference indicator draw; 2. Get an electronic flasher that isnít sensitive to current draw; 3. Wire in resistors to increase current draw to approximate the current draw of the 21 w units. Hereís a link across to some elseís site, where theyíve looked at solutions to the problem.

It was always going to be problematic & somewhat expensive to replace the stock BMW flasher unit because of the manner in which the switches work (left switch, right switch & cancel switch). The stock unit has about 8 wires running into it. Not an easy replacement, & expensive if possible.

So Iíve chosen to go the Ďcheaperí resistor pathway. The appropriate resistors are $2 ea at Jaycar. Rather than have a resistor per indicator, Iíve chosen to have one per side. The resistor Ďburnsí current as heat. Iíve chosen to hide the resistor in the headlight bucket. Realistically the indicators arenít on for too long, & so Iím not too worried about airflow to dissipate that heat. You just wouldn't want to hold the resistors if you have run the indicators for more than a couple of minutes. I figure no worse that the H4 bulb though...

The Theory:
To figure the load difference, Google told me that Ohms law states V=IxR, or R=V/I
V= voltage, I = current (measured on amps), R = resistance (measured on ohms).

On Gus the voltage varies between 12.6v min to 14.2v max. (using an Enduralast alternator & regulator).

The difference between the indicator load is (stock 21w x 2) Ė (KTM 10w x 2) = 22w.

22w / 12.6v = 1.788618 amps (min). 22w / 14.2v = 1.549296 amps (max).

12.6v / 1.789 a = 7.04 ohms resistance (min). 14.2v / 1.55 a = 9.16 ohms resistance (max).

Given the flasher is off Ĺ the time, then a 10w resistor is said to be acceptable. This comes is a variety of resistance values, but I choose 2x 8.2 ohm resistor - one per side (the resistors available were 10 ohms, 8.2 ohms, or 6.7 ohms). Iíve made up a little sub loom to accommodate the resistors, running in parallel with the normal indicator circuit. I also took the opportunity to tidy up one connector block, by taking this into the headlight shell.

Tested & works well. Success!

The Bloopers Reel
The link for the Gixxers above shows 10 ohm resistors. Didnít work. But running both resistors thru both indicators did. But interesting factoid. 2x 10 ohm resistors doesnít double resistance. Does your head in. The difference was the resistance in the additional 10w bulb.

Postscript 07/04/2012:
Took Gus for a resit for the WoF. Passed. The initial test was at 210,495. The re-sit 2 weeks later was at 211,454. Must have been all that time on private land & road, Sir.

Postscript 22/05/13:
Had an accident 25/11/12, which turned Gus upside down & tore out the wiring on the left front indicator. Because I couldn't see that the left indicator was flashing, I rode home without that corrected. This overheated the resistor for the left side, melting the heatshrink, then because the resistor was close to the H4 bulb holder, melted that too. End result was nearly a fire. Fortunately the headlight relay fuse popped (it's also in the bucket) & the resistor burnt out before too much further damage occurred.

I have since relocated the resistors at the rear of the bike, with the resistors epoxied inside a steel tube, clamped to the frame. That gives a better heatsink, & no opportunity to overheat any other component. It also protects the ceramic exterior of the resistors. Much cheaper than the set up you can buy from Trademe or Ebay.

Interestingly I needed a 6.8 ohm resister to replace the burnt out 8.2ohm one. Obviously here is some variance within the ratings.

I have also mounted LED indicator warning lights just under the speedo, so a burnt out bulb shouldn't allow the same thing to happen in the future.

My '91 R100GS thread is here
My Ride photos are here

It's just better when there's twins involved....

Box'a'bits screwed with this post 06-02-2013 at 07:08 PM Reason: Add Postcript
Box'a'bits is offline   Reply With Quote