Author Topic: Wiring a Rear Dynamo Light to a Cycle Trailer  (Read 609 times)

Bernster

  • ACME (Herts Branch)
Wiring a Rear Dynamo Light to a Cycle Trailer
« on: September 25, 2019, 04:26:46 pm »
First of all, apologies if this has already been asked, I did have a quick search through, but couldn't find anything directly relevant.

I need a way to wire a rear B&M Toplight (Line Plus) dynamo light to my daughter's cycle trailer. At the moment, the Toplight is attached to the rear rack of the bike, so I have a standard cable running from the front B&M light which connects using female connectors to the male connectors on the underside of the Toplight.

I have another length of the same cable which I can use for the trailer, which has a female connector to attach to the Toplight, but no connector at the other end (which needs to attach to the wire coming from the front light). I've had a look on SJS cycles (my usual go-to place for small, specialist parts) for the right male connector, but it's not clear to me size/type I need.

Also, am I approaching this the right way, or is there a better way to do it, e.g. is there anything I can do to make the connection more weatherproof, whilst still being able to detach it to remove the trailer from the bike? Worth saying that I'm not that mechanically / electrically competent, so any solution has to be relatively easy to achieve  ;)

Thanks in advance for any help.

Kim

  • Timelord
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #1 on: September 25, 2019, 06:34:40 pm »
I've used Tamiya connectors to good effect for disconnectable dynamo wiring.  They're not waterproof, but there's enough physical separation that they don't short when wet, and the relatively open design dries out quickly.  This seems a better choice than a truly waterproof connector, if it's going to spend some (or most) of the time exposed to weather without anything plugged into it.

The female Tamiya can be solidly cable-tied to a convenient bit of bike in such a way that it doesn't interfere with the male part connecting, which strain-relieves the cable:




Alternative solution:  Reelights on the trailer.  I fitted a bargain-bin Reelight to my Carry Freedom trailer.  When its wheel turns, it flashes - completely fit and forget.
To ride the Windcheetah, first, you must embrace the cantilever...

FifeingEejit

  • Not Small just Far Away at the back
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #2 on: September 25, 2019, 07:12:51 pm »
SON Co-Ax connectors but you need to be good at both soldering and heat shrinking...

Karla

  • car(e) free
    • Lost Byway - around the world by bike
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #3 on: September 25, 2019, 07:24:45 pm »
Given how long battery lights last, surely you're overcomplicating things here?

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #4 on: September 25, 2019, 08:47:05 pm »
some B&M lights have both bare wire terminals and male blade terminals.  This means that you can very easily wire a second rear light in parallel with the first, by using the otherwise unused terminals on the rear light.  Whether you run the wires direct to the trailer or via an intermediate plug is up to you.



the lamp above (B&M toplight line plus brake) is a case in point; blade terminals as well as bare wire terminals ( the holes between the blades).

NB If any two (or more) from  the three lights and one generator in use has an earth return connection, you need to be careful about polarity. Otherwise you don't.

cheers


Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #5 on: September 25, 2019, 11:13:30 pm »
At the moment, the Toplight is attached to the rear rack of the bike, so I have a standard cable running from the front B&M light which connects using female connectors to the male connectors on the underside of the Toplight.

I have another length of the same cable which I can use for the trailer, which has a female connector to attach to the Toplight, but no connector at the other end (which needs to attach to the wire coming from the front light). I've had a look on SJS cycles (my usual go-to place for small, specialist parts) for the right male connector, but it's not clear to me size/type I need.

You want 2 of these (plus some heat shrink, probably)
https://www.sjscycles.co.uk/lighting-spares/wurth-cable-connector-noninsulated-28mm-x-08mm-male-x-1/


Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #6 on: September 25, 2019, 11:13:49 pm »
Given how long battery lights last, surely you're overcomplicating things here?
I'm inclined to agree. I've always just stuck a battery light on the trailer. Strictly I think the main vehicle still needs lighting, and I'm not even sure if a dynamo would power the extra light without, at minimum, loss of brightness?

Kim

  • Timelord
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #7 on: September 25, 2019, 11:41:33 pm »
I'm not even sure if a dynamo would power the extra light without, at minimum, loss of brightness?

Two rear lights works fine, barakta has such a setup on her trike.
To ride the Windcheetah, first, you must embrace the cantilever...

Bernster

  • ACME (Herts Branch)
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #8 on: September 26, 2019, 09:28:54 am »
Really appreciate the replies from everyone - some very useful info there  :thumbsup:

Probably didn't make it clear, but I'm planning to move the rear light from the bike's rack to the trailer, rather than have an additional rear light - this bike is solely used to pull the trailer, and in the event that I need to ride it without the trailer, I have a cheapo battery light that I can attach to the seatpost.

Regarding dynamo vs battery, I do agree and if I was starting from scratch, I would probably buy a decent battery light (e.g. a battery equivalent of the Line Plus), but I already own the dynamo light, have a hub dynamo on the bike and own the cabling needed to connect it all up (just missing the connectors).

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #9 on: September 26, 2019, 10:33:40 am »
Probably didn't make it clear, but I'm planning to move the rear light from the bike's rack to the trailer, rather than have an additional rear light - this bike is solely used to pull the trailer, and in the event that I need to ride it without the trailer, I have a cheapo battery light that I can attach to the seatpost.
Again, I don't think that you can do that. Towing a trailer does not, as I understand it, remove the requirement for a vehicle to be properly lit; it simply adds requirements for the trailer to be lit as well. This applies to bikes just as much as to motor vehicles.

There's an exception for vehicles manufactured before the mid-80s, but I assume that your bike is not that old? I think there are also exceptions for older trailers, but ditto. Let's not restart the Trigger's Broom debate ;D

Regulation 18 referred to in the above link is just the one that says that you need the lights in the first place. I'm not quite sure whether the linked regulations are the latest version, but any change that would affect what I've said is unlikely anyway.

Bernster

  • ACME (Herts Branch)
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #10 on: September 26, 2019, 10:54:14 am »
Thanks drossall - useful info... with that in mind, I will mount the cheapo battery light on the bike rack or seatpost to stay road legal (in effect, it will be near useless as the trailer will obscure it from everything other than side on), and move the dynamo light to the trailer, as it's a much better light, and will be fully visible on the trailer.

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #11 on: September 26, 2019, 11:11:39 am »
Yes. But then the point of the requirement for lighting trailers (and rear racks) is that the vehicle lights are obscured, otherwise why bother? So the regulations clearly intend that vehicles be lit anyway. One consideration is probably something approaching from the side (e.g. at a junction), when two sets of lights make it easier to understand what is happening on the main road.

Regardless, it's the law, so... :thumbsup:


Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #13 on: September 26, 2019, 01:59:36 pm »
Regarding dynamo vs battery, I do agree and if I was starting from scratch, I would probably buy a decent battery light (e.g. a battery equivalent of the Line Plus), but I already own the dynamo light, have a hub dynamo on the bike and own the cabling needed to connect it all up (just missing the connectors).
If you make a decent job of the wiring, dynamo lighting just works.

With battery lights, you are into the whole rigmarole of charging, deciding when new batteries are needed, taking quick release lights off the bike when you park it in public, and finding the lights before you leave home. If you are using the light on a daily basis, that can become a matter of habit, but if the bike concerned is only in occasional use (as implied by "used only for towing the trailer"), you are very likely to get it wrong sometimes. For example, discovering when about to leave that the batteries that have self-discharged in the several months since you last used the trailer, and which would take a couple of hours to recharge.

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #14 on: September 26, 2019, 02:33:18 pm »
one battery light and one dynamo light seems almost like the worst of both worlds to me.  If you are keen on a dynamo light on the trailer, as a 'main light' I'd certainly have a second dynamo light on the bike too.

cheers

Bernster

  • ACME (Herts Branch)
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #15 on: September 26, 2019, 02:52:53 pm »
To give a bit more background to my situation - I'm basically looking for a fairly cheap solution to get a decent light on the back of the trailer, which is why I'm trying to work with the existing lights I have. I use the trailer 3 days a week for the nursery drop off (in reality this is always during daylight hours, although it can get pretty dingy in the middle of winter, hence why I'm keen to have decent rear lights).

The trailer has been permanently attached to this bike since I bought it 6 months ago, so good rear lighting on the bike itself isn't a high priority. Whilst I'm keen to be road legal in the unlikely case I have to tow the trailer at night, I don't think it's worth buying another dynamo light, when I can achieve this with an existing cheapo battery light (I can always pilfer a battery light from another one of my bikes in the event of flat batteries).


Bernster

  • ACME (Herts Branch)
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #17 on: September 26, 2019, 03:08:29 pm »
OK, fair shout - it's hard to argue with that price... although thinking aloud, wouldn't that need the light with the two sets of terminals to be on the bike, rather than the trailer?

Kim

  • Timelord
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #18 on: September 26, 2019, 03:37:39 pm »
Meh, twist the wires together and one set of terminals will suffice.
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #19 on: September 26, 2019, 05:16:38 pm »
I have a few B&M rear lights now surplus to requirement.  PM me if you like as to what you are looking for and I'll see if I have something suitable.  You can then simply wire in parallel to the existing rear on your bike and hopefully sorted.


Bernster

  • ACME (Herts Branch)
Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #20 on: September 27, 2019, 10:29:33 am »
Thanks Polar Bear - will PM you now  :thumbsup:

Re: Wiring a Rear Dynamo Light to a Cycle Trailer
« Reply #21 on: September 27, 2019, 03:23:10 pm »
Will pm you over the weekend.