Hub Dynamo efficiency comparisons?

[SA_SA_SA]

Electronics world magazine published a dynamo battery backup which worked by having a voltage doubling rectifier
followed by a step down switching regulator which powered all lamps and the backup charge: it let the dynamo voltage rise to 27V so it got less resistive losses and used the extra 0.5Watt to charge the battery. The output was 6V dc with the battery simply connected via a diode (and parallel charging resistor).

Any idea how efficient this lot was?

Well, he seemed to claim to never to have needed to charge his water bottle backup cells from the mains..but see about bypass switch....

BTW the maximum RMS open circuit voltage I can measure on a (health) SA GH6 dynohub is about 9V (IIRC),

Interesting.

A further consideration is that at lower speeds, one may be paying the penalty (in terms of losses in the circuitry) without having any of the benefit.

He had a bypass switch to use in slow traffic llights connected to dynamo as normal:

this is what made me like the circuit idea: no bridge rectifier, so only a single pole switch needed.

[Tony1951]

Have I got a chance of pulling this off?

NB From their website blurb I wonder if reflectalite dynamo led bulbs have a polarity (light for one AC half cycle only) : I prefer their ordinary led bulbs and a separate heavy duty regulator(s) for AC cycle generators.

The reflectalite for the old type 1.8w dynohubs is optimised for AC so it is surely using both halfs of the AC cycle.

Noted other points about the use of modern lights, but I want to keep the bike in its original condition which is why if my drop in car led is useless I will make minimal modifications by changing bulb holders inside to accept the reflectalite bulbs. Besides being the cheaper option, they make front and rear bulbs optimised for six volts.

[SA_SA_SA]

The reflectalite for the old type 1.8w dynohubs is optimised for AC so it is surely using both halfs of the AC cycle.

Well their ordinary led bulbs are described as no polarity (and do indeed work from bicycle AC when protected by a standard dynamo regulator) but the dynamo ones (NL4xx) say battery backup should be arranged to have the tip +ve: that sounds polarity sensitive to me: the proprietor didn't have the actual circuit available to satisfy my curiosity.
Perhaps someone could see if the NL4xx bulbs light when tip -ve?

Noted other points about the use of modern lights, but I want to keep the bike in its original condition which is why if my drop in car led is useless I will make minimal modifications by changing bulb holders inside to accept the reflectalite bulbs. Besides being the cheaper option, they make front and rear bulbs optimised for six volts.

I thought of approved led rear lamp for legal peace of mind: note the Axa Blueline is very cheap for a linetec style rear lamp.

[edocaster]

IIRC these cheap LED sidelight bulbs just have a series resistor and (not always) a blocking diode.

Most of the LED makers don't recommend that you use the LED itself as a blocking diode (they are not reliable and tend to break down I think) but bulb makers will gamble on them at least not breaking down when the bulb is being fitted; the push in type can be installed either way round so if it doesn't light up, you just stick it in the other way round until it does....

cheers

You're probably right it's just a resistor. In that case it really is quite wasteful, for a hub which is already somewhat low on output.

[Tony1951]

I thought of approved led rear lamp for legal peace of mind: note the Axa Blueline is very cheap for a linetec style rear lamp.

Thanks for the info.

The bike is UK legal anyway - even with glow worm incandescent bulbs because it pre-dates the 1990 cut off date by twelve years.

Those lights do look pretty good. The front one I could live with easily, and it would straightforwardly mount to the original headlight bracket. They seem to be available for about £28 delivered. The rear light has lots of advantages. It would not so easily mount to the bike I think and would not look authentic. The stand light would be a great advantage though. Like you say - it is also very cheap at under £10.

[Brucey]

IIRC these cheap LED sidelight bulbs just have a series resistor and (not always) a blocking diode.

Most of the LED makers don't recommend that you use the LED itself as a blocking diode (they are not reliable and tend to break down I think) but bulb makers will gamble on them at least not breaking down when the bulb is being fitted; the push in type can be installed either way round so if it doesn't light up, you just stick it in the other way round until it does....

cheers

You're probably right it's just a resistor. In that case it really is quite wasteful, for a hub which is already somewhat low on output.

I have a feeling that they put the LEDs in series and thus use a smaller resistor than you would otherwise. Whilst this leads to different brightnesses on battery (12V) vs charging/engine running (14.2V) voltages it does increase efficiency.

cheers

[SA_SA_SA]

.....The bike is UK legal anyway - even with glow worm incandescent bulbs because it pre-dates the 1990 cut off date by twelve years...

That exemption only applies to front lamps, one rear lamp still needs to be approved.
And now for something completely different :

did the efficiency tests on a donor SA GH6 get done?
where there any results?

[Brucey]

re the SA hub tests; its a while ago now but IIRC I had a pair of hubs all boxed up and ready to ship but CJ called it off for some reason. So no test data, sorry...

Thinking about it I wonder if the tests would have been that great anyway, since they would have been carried out using a DIN standard load of 12 ohms. This would perhaps have had questionable validity since one would never use such a load connected to a standard GH6 hub.

cheers

[[XAP]Bob]

.....The bike is UK legal anyway - even with glow worm incandescent bulbs because it pre-dates the 1990 cut off date by twelve years...

That exemption only applies to front lamps, one rear lamp still needs to be approved.
And now for something completely different :

did the efficiency tests on a donor SA GH6 get done?
where there any results?

Or flashing (only)

The front light does need to be "visible from a reasonable distance"

[SA_SA_SA]

.....exemption.....approved....

Or flashing (only)[/quote]
I was following CJ and using 'approved' to include suitable flashing only lamps (1-4hz, >=4cd, fixed markspace ratio etc).

[[XAP]Bob]

It's a non obvious approval though, because you can only tell if you cycle through all modes - which is a bit of a wierd one.

[Tony1951]

I don't think you will need a 6v regulator, because (as per my DIY system) the 'LED bulbs' will always draw enough current that the voltage will never rise to a high enough level to be dangerous.

cheers

An update:

The 12v LEDs I ordered turn out to be coming from China even though the Ebay auction clearly said they were in the UK... That doesn't bode well for any other claims made by the seller. They have not arrived yet of course.

Meanwhile while browsing about on the auction site, I spotted some 6v led side light bulbs for 'classic cars'. Personally, having lived during the 'classic car' period I am not aware of cars with 6v systems, though I did have a few 1950s British motorcycles in the early 1970s that had classic 6v systems. Anyhow - I fitted these LEDs and they seem to work great (only tested in daylight so far as it is only now mid day).

The bulbs have 5 leds on them and they are MUCH MUCH brighter than the pathetic bulbs which came in the lighting set, but I foresee the possibility of rather diffused headlight beam for the well known reason of the different optical need of LED bulbs.

I tried a few rough tests with a multi meter and pushing the pedal in high gear and the voltage across the parallel connected front and rear LEDs rises to 7.7v at maximum with a single, hard pedal thrust while holding the rear wheel off the ground and letting it freewheel. It rises on an instant to 7.7v and rapidly decays back to 6v. The light is well bright enough for my urban riding AND the old fashioned Filter Switch unit also works as a standlight when stopped or slow running.

One thought I had was to insert the tail LED one way around and the headlight the other so that they would each use a different side of the AC cycle, but the bulbs won't light when inserted the 'wrong way around'. The bulbs either have their own rectifier circuitry inside them -or the standlight circuit in the Filter Switch unit is already rectifying the AC output from the dynohub. Alternatively, maybe the constant flow of about 4v from the Filter Switch unit in one direction, overcomes the unused side of the AC cycle.

I could test this by removing the alkaline cells that are inside the FSU and trying the reversed LED test again. However, given that the voltage is rising to 7.7v at speed, extra current availability is not required as the LEDs are already receiving everything they can handle.

If they will stand 7.7v...... I will count this as a success. There is low speed strobing, but I'm not that bothered about that.

It will be interesting to substitute the 12v Bulbs and see how much light they give when they eventually arrive.

Any advice or comment very welcome. Thanks in advance.

[SA_SA_SA]

.....Either that, or the standlight circuit in the Filter Switch unit is already rectifying the AC output from the dynohub. ...

Yes, it does:
http://hubgear.tripod.com/fsu.html

[[XAP]Bob]

Well their ordinary led bulbs are described as no polarity (and do indeed work from bicycle AC when protected by a standard dynamo regulator) but the dynamo ones (NL4xx) say battery backup should be arranged to have the tip +ve: that sounds polarity sensitive to me: the proprietor didn't have the actual circuit available to satisfy my curiosity.

My B&M Lyt is polarity sensitive - you get more light with one polarity than the other when pushing a 9V battery across the contacts...
But it does work both ways round

[Tony1951]

.....Either that, or the standlight circuit in the Filter Switch unit is already rectifying the AC output from the dynohub. ...

Yes, it does:
http://hubgear.tripod.com/fsu.html

Yup - Just found this:

https://hadland.files.wordpress.com/2012/07/fsu.pdf

Thanks. You must have posted that just as I found that circuit, though it should be noted that I think the bleed resistor is not standard. Also, my FSU uses an actual separate wire as the earth return and not the bike frame.

I might be inclined to try that bleed resistor to trickle charge some NIMH rechargeable cells inside the FSU. It might destroy them though. I suppose the diode between the cell pack and the main rectifier and load prevents cell charging during fast running.