Cycling UK Forum

Hi. I want to pull my long cargo trailer at night so feel I aught to have some rear lights for it. I would much

I can fit a bottle cage dynamo to the trailer but is it possible to run only rear lights? If so how many would that be?

Hopefully it's possible.

The bottle dynamo I have produces AC into a halogen bulb. To run LED I will need to insert a rectifier into the circuit. So that will probably be the first thing to check.

A 2.4W or 3.0W dynamo would have plenty of power for a few rear lights. Some dynamos have limiters to protect from blowing lights. If you find you have too much juice you'll need to include extra resistance to protect the LEDs. If you know a radio tech or an auto electrician they should be able to do the calculations for you.

OB

Don't rear dynamo lights pull around 0.1A or 0.6W.
So 3W/0.6W = 5 +/-1 depending on how bright vs overhead you want.
But front lights tend to have voltage regulators in them but rear light dont, so you may need to make/aquier one.

While you're at it add a capacitor to give you a standby light function.

With any reasonably modern rear lights they’ll do the voltage regulation etc themselves...

And have a stand light built in.

Conventionally you’re looking at 2.4Wbfor the front and 0.6 for the rear, so 5 lights should be trivial. Dynamos will over produce if needed though ...

I’d caution you to use the same type of light so that the voltage regulators don’t fight too much... my ‘always on’ rear light goes off (or dim) for a couple of minutes when my front (and secondary rear) light turn on as they drink all the juice available...

eddiewalkling wrote:Hi. I want to pull my long cargo trailer at night so feel I aught to have some rear lights for it. I would much

I can fit a bottle cage dynamo to the trailer but is it possible to run only rear lights? If so how many would that be?

Hopefully it's possible.

Do you have dynamo lighting on your bike?

If so then disconnect the rear light on the bike and connect the trailer light to the rear light wires using a waterproof connector.

When you unhitch the trailer you can reconnect the bikes rear light.

HTH

Technically the bike still needs it’s light, even if it entirely obscured by the trailer...

I’ve done the above though, when towing kids it’s just not sane to have a rear light 2 feet from their faces.

In that case just splice it in with the bikes rear light and run both.

Still use a waterproof connector for ease of hitching up/ unhitching.

The extra 0.6W won't make any perceivable difference to the light output.

[XAP]Bob wrote:Technically the bike still needs it’s light, even if it entirely obscured by the trailer...

When towing kids it’s just not sane to have a rear light 2 feet from their faces.

+1 on that ^^^^ especially as I have my lights on all the time.

I tow a dog trailer.

Thank you for the replies.

Sorry for not getting back sooner.

So in theory I could run maybe two orange side lights and 3 rear red? That's great, 2 rear red would be fine also.

My dynamo system (planned) is complicated, but I believe I will not fix the trailer with its own power source but instead have a PTO from a bottle cage dynamo on my tractor unit. Via a connection, I don't know yet, but maybe similar to my SON hub connectors.

I studied building systems but never got my head around electricity, volts, amps etc.

Is there anyone on here who may be able to advice/consult on a suitable wiring loom light combination?

For example, a cable like phones used to be (for want of a better word, curly) that connects to the tractor unit. It then runs one orange light, two red, one orange then grounds? Is that how it works?

Thanks for your time.

3.5mm headphone jack

There's a lot of good info on this page here -> http://www.reflectalite.com/LEDpage.html

Luck .........

Tigerbiten wrote:There's a lot of good info on this page here -> http://www.reflectalite.com/LEDpage.html

Luck .........

I used this to convert an old halogen dynamo lighting system on a LINEAR recumbent.
I'm running one head and two rear's off an old FER spoke drive dynamo.
They're absolutely brilliant and work as described on their site.

It certainly is a very informative site. Thank you for the link Tiger.

Modern LED lights, especially rear ones, use much less power than the original incandescent bulb versions.