Help troubleshooting a non-functioning dynamo lighting system

[hoj]

After reading all the rave reviews about dynamo lighting, I decided to give it a try on my commuter this past winter. Purchased brand new Shutter Precision SV-9 dynamo hub and Busch & Muller IQ-X wired front light at the end of November from StarBike. Once I got it set up, it was awesome — I was seriously impressed by the set up and loved it from the moment I started riding with it.

Fast forward to this past week (only five months since original purchase, less than 4 months of actual use) and I notice that the light is completely dead — toggling the light on/off while riding does nothing. I’ve never crashed the bike, it’s always stored indoors and I clean it regularly (ie, no signs of corrosion whatsoever).

I am by no means an expert on diagnosing electrical problems, but I purchased a multimeter to see if I could identify whether or not it was the hub itself or a short circuit in the light that was causing it to not work. I can’t get any reading on the multimeter when spinning the wheel, and when I try to test the circuit on the light using the diode setting on the multimeter nothing happens.

Any experts here that could recommend what I should do? I’m not even sure if the multimeter is the correct way to diagnose the problem, but are there any other ways to test what is wrong with the system? Both parts are under warranty but I would rather not have to deal with disassembling the wheel and shipping everything overseas if it is something I can fix on my own.

Thanks in advance for the help!

[unterhausen]

on the light, the multimeter is not going to tell you anything. I have never tested the voltage of the hub with a voltmeter, so I'm not sure what you will read. I would check the resistance across the hub terminals.

Are you sure the wires are making good connection at the hub? I have had that problem before.

[weisan]

So it was functional for a while and then it stopped functioning, is that correct?

Yeah, check the connections.

[Peter P.]

Place the multimeter in the AC Volts mode.

Have a friend spin the wheel while you hold the meter leads on the two connections to the dynamo. Your other option is to get a pair of alligator clip leads and connect one end of the lead to the tip of the multimeter lead, and the other end to the terminals of the dynamo. That will leave your hands free to spin the wheel yourself.

Spin the wheel fast enough, usually 5mph or higher, and the meter should read about 4VAC with the dynamo output reaching a max of 9VAC if I understand the [URL="http://www.sp-dynamo.com/9seriesdynamo%20hub.html"]Shutter Precision chart.

As far as I know, most dynamos output AC voltage. If you don't get a reading on the AC volts setting, try DC volts. If you still don't get a reading, the dynamo is dead.

If you do get a correct voltage, post your results and we'll troubleshoot the light and wiring.

[hoj]

Originally Posted by unterhausen

on the light, the multimeter is not going to tell you anything. I have never tested the voltage of the hub with a voltmeter, so I'm not sure what you will read. I would check the resistance across the hub terminals.

Are you sure the wires are making good connection at the hub? I have had that problem before.

Yeah the connections look to be just fine and are definitely making contact with the hub terminals, but I can always double check again. Didn’t think to check the resistance across the hub terminals, so I’ll check that tomorrow after work (already late where I’m at).

[hoj]

Originally Posted by Peter P.

Place the multimeter in the AC Volts mode.

Have a friend spin the wheel while you hold the meter leads on the two connections to the dynamo. Your other option is to get a pair of alligator clip leads and connect one end of the lead to the tip of the multimeter lead, and the other end to the terminals of the dynamo. That will leave your hands free to spin the wheel yourself.

Spin the wheel fast enough, usually 5mph or higher, and the meter should read about 4VAC with the dynamo output reaching a max of 9VAC if I understand the [URL="http://www.sp-dynamo.com/9seriesdynamo%20hub.html"]Shutter Precision chart.

As far as I know, most dynamos output AC voltage. If you don't get a reading on the AC volts setting, try DC volts. If you still don't get a reading, the dynamo is dead.

If you do get a correct voltage, post your results and we'll troubleshoot the light and wiring.

Thanks for the response. I did pretty much exactly what you outlined with my wife holding the leads on the hub terminals while I spun the wheel as fast as I could get it to go. Didn’t get any consistent reading other than the occasional signal noise.

Assuming the hub is dead, what would be my options to test the light? I thought running a diode continuity test with the multimeter might work since the light is LED, but sounds like from the previous poster that may not be possible? (Again, my expertise with wiring/electricity troubleshooting is very limited).

[Peter P.]

How to measure a typical diode:

Set the multimeter to resistance (ohms). Use the lowest scale unless the meter is autoranging. If you're lucky, your meter may have a diode test function, as my Fluke 179 does. The only problem is, I don't know where the rectification (conversion from AC to DC volts, which is required for LEDs and diodes to work) occurs. That's why I had you measure the voltage output of the dynamo in AC and DC mode. If you don't see an output in the 5-9V range, AC or DC, then the dynamo is kaput.

Place the meter leads across the terminals of the diode.

Write down the value. Reverse the leads. In one orientation you should get a low value, in the other orientation you should read a much higher value. Don't forget to change the range reading on your meter if necessary.

Those instructions hold for a typical diode; I don't know how an LED assembly would test. But since the dynamo puts out 9VAC which is rectified somewhere inside the light I'd say there's no harm in trying this test:

Using some clip leads, connect a 9V battery directly to the LED light terminals. If it doesn't light, reverse the leads. If it lights, even briefly, the LED is likely fine.

Update: I grabbed an LED at work and put a 9V battery across the terminals. Lights up one way; doesn't when the leads are reversed, so this is a valid test. I tried it with a 1.5V AA battery; not enough voltage, which is similar to what I'd expect from the dynamo-no light until a minimum voltage of 4 or 5 before the LED lights.