Hub dynamo with capacitor in light

For discussions about bikes and equipment.
User avatar
simonineaston
Posts: 8003
Joined: 9 May 2007, 1:06pm
Location: ...at a cricket ground

Re: Hub dynamo with capacitor in light

Post by simonineaston »

Is that how it works? I thought it used an accelerometer...
Yes - me too. I'll see if I can find the original description.
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
User avatar
simonineaston
Posts: 8003
Joined: 9 May 2007, 1:06pm
Location: ...at a cricket ground

Re: Hub dynamo with capacitor in light

Post by simonineaston »

See here link to page on B&M's website...
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
robc02
Posts: 1824
Joined: 23 Apr 2009, 7:12pm
Location: Stafford

Re: Hub dynamo with capacitor in light

Post by robc02 »

Very clever! I wonder what rate of deceleration is needed to trigger it. Would it, for instance be triggered when being slowed down at the foot of a steep hill? I suppose that might not be a bad thing though.

I don't suppose most other road users would recognise it as a brake light but it might serve to draw a bit of extra attention which could be beneficial.
Jdsk
Posts: 24640
Joined: 5 Mar 2019, 5:42pm

Re: Hub dynamo with capacitor in light

Post by Jdsk »

Stroud Active wrote: 10 Jun 2021, 10:58pm I've taken the back light apart. Inside are 4 diodes and an LED. i.e: a rectifier. There's no capacitor so it has no ability to hold charge. I believe the old front light was running as the master and feeding AC when the wheel was spinning and DC from capacitor when stopped. I'll read the specs of the old and new front light.

The old front light was a Spanninga Kendo+ with an XDA label on it https://spanninga.com/product/kendo/
The rear light looks like one of these which is also a Spanninga unit, a Pixeo: https://spanninga.com/product/pixeo/

The description doesn't eliminate all doubt but it does suggest that the safe-stop function is relying on the front light.
"The dynamo version of the PIXEO features the innovative Safe-Stop function. This function makes the light burn for 4 extra minutes after the bike stops and increases the safety for you as a cyclist tremendously."

"* The dynamo version of the PIXEO is connected to the dynamo (3W) via the headlamp."

The new front light is one of these https://www.bikester.co.uk/busch-muelle ... 23459.html

I've seen this Pixeo XS on Amazon and I think you can see a capacitor through the lens: https://www.amazon.co.uk/dp/B007MJTKIA? ... yp_imgToDp
Yes, I suspect the new B+M front light doesn't internally provide a rear standlight function.

Have you got B+M's own guide? And they're good at answering email.

Jonathan

PS: Yes, everyone assumes that my brake light works off an accelerometer. : - )
wjhall
Posts: 265
Joined: 1 Sep 2014, 8:46am

Re: Hub dynamo with capacitor in light

Post by wjhall »

i have two bicycles fitted with Axa Ray Steady rear lamps connected in parallel to front lamps directly across bottle dynamos. The front lamps are different generations of B&M units. One dynamo is an Axa-HR with clipper diodes, the other is a Miller, without clippers.

The rear standlight function works perfectly, which is what I would expect from a lamp with STANDLICHT printed across the plastic.

From my recollection when fitting them the two terminals on the front lamp are connected directly to each other, the resistance between them measuring zero ohms on a multimeter. They are there for mechanical convenience in attaching the rear wiring, not to provide an electrical function. As it happens both my bottle dynamos are at the rear and the parallel connections go separately from them to front and rear lamps.

As pointed out in some earlier posts in this thread the answer to what the connections do and what you can connect to them should be in the manufacturer's documention, preferably as a simple circuit diagram. If it is not, then the manufacturer deserves to be asked for the information.
User avatar
freiston
Posts: 1504
Joined: 6 Oct 2013, 10:20am
Location: Coventry

Re: Hub dynamo with capacitor in light

Post by freiston »

robc02 wrote: 11 Jun 2021, 10:15am Very clever! I wonder what rate of deceleration is needed to trigger it. Would it, for instance be triggered when being slowed down at the foot of a steep hill? I suppose that might not be a bad thing though.

I don't suppose most other road users would recognise it as a brake light but it might serve to draw a bit of extra attention which could be beneficial.
I have such a rear light (this one) but I cannot report on its effectiveness because, try as I might, I find it impossible to watch the light whilst braking.
Disclaimer: Treat what I say with caution and if possible, wait for someone with more knowledge and experience to contribute. ;)
2_i
Posts: 216
Joined: 25 Feb 2020, 3:12am

Re: Hub dynamo with capacitor in light

Post by 2_i »

Historically, there has been only one bike dynamo (Jenymo) in the market with a built-in backup, but it was a bottle, not a hub dynamo. The backup relied on rechargeable cells, rather than a capacitor - there were no supercaps yet at the time. Rear lights with backups are not that expensive. For safety it is worth recovering the functionality.
User avatar
Sum
Posts: 331
Joined: 17 Jul 2010, 9:13am

Re: Hub dynamo with capacitor in light

Post by Sum »

Stroud Active wrote: 10 Jun 2021, 10:58pm I've taken the back light apart. Inside are 4 diodes and an LED. i.e: a rectifier. There's no capacitor so it has no ability to hold charge. I believe the old front light was running as the master and feeding AC when the wheel was spinning and DC from capacitor when stopped. I'll read the specs of the old and new front light...(snip)
I would be interested to see the internals of the rear light you've taken apart. Can you post up some pictures please?
Bmblbzzz
Posts: 6261
Joined: 18 May 2012, 7:56pm
Location: From here to there.

Re: Hub dynamo with capacitor in light

Post by Bmblbzzz »

freiston wrote: 11 Jun 2021, 11:58pm
robc02 wrote: 11 Jun 2021, 10:15am Very clever! I wonder what rate of deceleration is needed to trigger it. Would it, for instance be triggered when being slowed down at the foot of a steep hill? I suppose that might not be a bad thing though.

I don't suppose most other road users would recognise it as a brake light but it might serve to draw a bit of extra attention which could be beneficial.
I have such a rear light (this one) but I cannot report on its effectiveness because, try as I might, I find it impossible to watch the light whilst braking.
I'm not sure I've ever seen one in action but I'm told by people who have that it looks like a fault in the light making it flicker.
Stroud Active
Posts: 24
Joined: 11 Jul 2020, 3:53pm

Re: Hub dynamo with capacitor in light

Post by Stroud Active »

It's fixed. I ordered a replacement rear light from the same brand and design with the stop light feature. The circuit board has a capacitor on it.

Looks like my original hypothesis was correct - the lights were sold as a pair with the front light containing the capacitor. Possibly an OEM only version to save cost.
Jdsk
Posts: 24640
Joined: 5 Mar 2019, 5:42pm

Re: Hub dynamo with capacitor in light

Post by Jdsk »

Thanks for posting the solution.

Jonathan
Post Reply