B&M Toplight Line Brake Plus electrical connections
 

So apparently the polarity is critical, but I don't know to determine the polarity of the current (coming from the headlight, B&M IQ-X). In between the connections (bottom right below) is a switch - does that toggle the polarity?

So if I hook it up and it doesn't work, flip that switch and see if it works? (can't find any instructions for this thing)

edit: ok Peter White's website says the "switch" between the connection spades locks the wires in if you don't use the connection spades and just stick the bare wires into those little holes instead. But now I have to figure out the polarity of the wires coming out of the headlight.

edit: On the headlight there are 2 short wires with spade connecters coming out to be connected to the taillight wire. One of those spade connectors has more plastic covering - I assumed that one is the positive so I hooked up the taillight with that assumption. Seems to work.
https://cimg6.ibsrv.net/gimg/bikefor...b94ecf23d4.jpg

I thought that the light did not have a polarity issue, but if it does just switch the wires if it does not work.

Do not do what a friend of mine did, he was riding in front of me and he said he wanted to know if his taillight got brighter and asked me to watch it, I said ok. He then slammed on the brakes and I almost hit him.

Slightly off topic, but I have that same light but without the brake light feature. The nuts rusted onto the bolts and I tried to remove it from my rack, and the bolts turned under that much torque and mangled the plastic. I had to cut open the plastic housing to remove the bolts and replace them with stainless and glue that thing together again. My life might have been simpler if I had used stainless nuts in the first place.

When we were installing mine we did swap wires once but I don't remember which was which but I might be able to take pictures that probably may not help. It works fine and have had zero issues since I set it up.

I placed my wired up rear light in the front basket and road around to test the brake light feature. It works.

And I remember your post about rusted bolts - I'll grease them up when I mount it.

It is my understanding that the way the light knows when you are slowing down is lower frequency in the AC, but I could be wrong on that. If you have AC, you have no polarity.

is the ground wire on the tail light connected to the ground wire on the headlight and/or dynamo?
Sometimes B&M (and other manufacturers) connect one of the mounting bolts to one of the electrical connections. The same might be true of the headlight and dynamo. The idea is to make it easy to use the frame as one of the electrical conductors, and there may be some sort of ground symbol next to the bolt or electrical connection.
If the same wire doesn't go to the grounded electrical contacts at each end, it is possible to have the effect of allowing the current to flow around the tail light instead of through it.

a quick, lousy illustration of this issue....


https://cimg1.ibsrv.net/gimg/bikefor...e2dbb231a6.jpg

Steve in Peoria

Thanks I got it sorted out. There were 2 short wires coming out of the headlight to be connected to longer wires to the taillight, and the polarity the wires at the headlight wasn't obvious. Took a guess as to polarity, connected it up, and it worked.

No obvious grounding points anywhere (these are modern lights).

Just in case someone reads this thread later so that they can figure out how to wire up their circuit:

DO NOT WIRE A TAILLIGHT DIRECTLY TO A DYNOHUB AS SHOWN IN THE DRAWINGS IN THE TWO PREVIOUS POSTS ! ! !

Most taillights do not have the overvoltage protection needed, but the headlights do. Thus, you wire the taillight to the headlight, that way the headlight protects the taillight from overvoltage as the taillight power comes through the headlight circuitry. The overvoltage occurs when you go down a hill at higher speed. The headlight instructions should tell you how to wire your taillight to the headlight.

Instead think of the above drawings as showing headlights, not taillights, then it would be correct.

yeah... I noticed that too, after I drew it out. :) I did specify that it was a lousy drawing!

I thought it still made the point about the frame ground connections, but I'd hate to see someone use it as a guide to just power a tail light.

Steve in Peoria

Yes, your intentions were good.

Photo below, I picked up a cheap ($10) dynohub wheel at a bike charity and put it on my errand bike, Shimano so it is grounded to the fork. I had a D Lumotec headlamp sitting on the shelf, the headlamp was made for bottle generators, thus no switch and grounded to the mounting bolt. Simplest wiring job I have ever done, hub grounded to the fork, light grounded to the fork, so only a single conductor wire was needed.

https://cimg2.ibsrv.net/gimg/bikefor...17daeff62c.jpg

Light is too low to light up the road very well, but it is my errand bike so it is only ridden on well light city streets. Mostly used as a to-be-seen light, not a light to see with.

There's a lot to be said for simplicity.
I still like the idea of block dynamos, such as this Jos that I bought in the 70's. Almost nothing to go wrong... other than the basic issues of incandescent bulbs and being driven by the tire.

https://live.staticflickr.com/2946/3...0954ed_z_d.jpg

The Schmidt hub dynamos with the connections at the end of the axle, and which mate to contacts at the fork dropout, are possibly as good as can be done with a hub dynamo.

Steve in Peoria

Bottle or hub dynamo, I found neither mystifying to hook up. The concept of polarity on an A/C circuit is a little confusing to me, but there are only so many combinations to try, and I eventually find a working one.

The little clip is to lock in loose wires to the openings, I believe. Confused me for some time as I use the connector lugs and I tossed the instructions.

"polarity" of an AC voltage source is, to some degree, a matter of semantics.
As an electrical engineer, we don't really think about polarity for AC. Instead, we worry about phase angle, which is how much the sine waves of two different AC voltages differ. This is similar to how the sine and cosine function have the same shape, but the values are different for a given angle. This is a useful concept for electrical power transmission, which typically uses three sine waves spaced 120 degrees apart. For house wiring in the USA, we usually split the incoming 240VAC into two 120VAC voltages, but one is 180 degrees from the other. You can also think of this as one being an inverted version of the other.

Anyway... the problem isn't so much "polarity", it's that some lights and dynamos have one terminal connected to the bike frame (i.e. "grounded"), and this may not be well marked or documented. The ungrounded terminals of the dynamo and lights need to be connected together. Similarly, if you do want to run wires to the terminals that are connected to the frame, these all need to be connected together.
Failure to do this will mean that something is being shorted out, usually meaning that the lights won't illuminate.

Steve in Peoria

Thanks for all this. I'm with you so far.

I'm under the impression that the new stuff doesn't ground to the frame intentionally but might accidentally so that would be one reason you have to keep track of polarity. Is that right?

FWIW, the front light has no polarity indicators and is clearly not grounded to anything (plastic mounting bracket). The rear light has polarity markings and has bolts coming out of the casing that could get grounded.

Yeah I found that info in Peter White's website.

I haven't opened up a commercially built light in a while.
Some B&M tail lights that I've worked on in the past had one mounting bolt attached internally to one electrical terminal. No idea if they've changed that practice or not. There was usually a small chassis ground symbol molded into the plastic to indicate which terminal was grounded, but it wasn't easy to see and could be overlooked by the average consumer.

In case I haven't mentioned it lately, I make my own dynamo headlights and tail lights, so don't get exposed to the commercially made stuff very much.
I wouldn't expect to see accidental connection of a terminal to the frame, though.

Steve in Peoria

It's covered in the instructions:Black lead: current (+) / black-white lead: earth (–).

http://en.bumm.de/fileadmin/user_upl...ng_IQ-X_RZ.pdf

Son of a gun, it is in the instructions.

In your picture, there is a "plus" and "minus" molded into the plastic housing of your tail lamp, one near each of the spade lugs you mentioned. I'm pretty sure those were not randomly chosen by the B+M electrical engineer.

Steve, I recall some of the linear taillights had some special features, like sequential firing ot the LEDs as a function of speed, and flashing as speed was shown to decrease, a cheap n dirty brake light function. The speed info could have been decoded from the AC power wavform just by counting zero crossings and the circuit for that could have been in the taillight or in the headlight, but do you think that would require enforcing a polarity between the head and tail lights, or perhaps polarity relative to the dyno? It might be some sort of data transfer is in play, which needs a signal reference in common. OTOH I doubt any signal levels are being measured, just zero crossings, which of course meter time.

Correct. The polarity of the tail light connections are clear.

in response to the question... I don't see any intrinsic need to ensure some specific polarity relative to the headlight or dynamo in order to implement this sort of functionality. There's no reason that the power couldn't be rectified to use one or both halves of the AC voltage waveform.

In my tail lights, I usually just use one half of the AC voltage waveform, and the flashing is noticeable at slow speeds. A friend once asked if this was intentionally used as a way to grab the attention of other road users, and I was a bit sad to admit that it wasn't a clever bit of engineering. :)

Steve in Peoria