Light and power from a Shimano dynohub?

[interestedcp]

I think that devices themselves switches off for various reasons

But if the Kemo device is regulating effectively, the device connected to it should have no knowledge of the bicycle's speed, so would have no reason to switch off.

Could it be that the regulator overheats at higher speeds and goes thermal shutdown? Say a USB device usually draws 500mA@5V, and it is connected to a regulator set up to provide a constant 5V via a dynamo producing 6V. In this case, the regulator dissipates 0.5W. If the USB device only draws 400mA, a hub dynamo's output voltage could rise to 10V, say. In this case the regulator is dissipating 2W. This is all at a fairly average speed. If the bike is travelling fast, the the power the regulator is having to dissipate could be two or three watts higher. It would be interesting to see whether the regulator has a heatsink.

First of all, the Kemo may not be well regulated by design or by manufacturing faults. I am not defending the Kemo as such, but I suspect that the troubles some people experience with devices drawing a lot of power, isn't caused so much by the design of the charger, but more by the many quirks and pit falls that exist in both the USB specification and how naughty device manufacturers abuse the USB port, and of top of that, few if any, manufacturers design or test their devices to charging from a hub dynamo.

I won't go into detail, but the USB 2.0 specification had major revision when it came to charging, years after (2007) the original specification from 2000, and it keeps getting revised (latest oct. 2011), so USB device charging is a moving target with incompatible devices depending of manufacturing year. Usually, the end users doesn't feel too many problems, because most USB devices are either plugged into a dedicated charger from the manufacturer, or a PC, but when you stray from that path, you may experience problems.

The major reason for the patched USB standard was that smartphone and GPS manufacturers needed much higher power than the 500mA as the original spec stipulated. So they started doing naughty things with the USB port, like shortening D+D- to signify a dedicated charger. Some of these tricks was later incorporated in the USB spec where they may live a spectral half-life of not being directly prohibited by the standard while not being sanctioned by the official USB 2.0 standard either. See fx http://compliance.usb.org/index.asp?Upd ... t=Standard

So eg. smartphone manufacturers have several different proprietary standards for recognizing a "dumb"/dedicated charger; Some use a shortened pin 4&5 to signify a charger, others, like BlackBerry tie pin 4 to 5 (ground) using a 220k ohm resistor to indicate a "dumb charger", other like Garmin, tie pin 4 to 5 (ground) with a 17k ohm resistor to indicate a 1A charger, and tie it directly to ground (exactly like HTC devices) to indicate a 500 mA charger. (see http://garminoregon.wikispaces.com/Power )

So here is my take on what happened to the BlackBerry; At first it was just connected to the Kemo with a normal USB cable, (pin 4&5 not shortened). At 6 MPH the hub generated enough power through the Kemo that the BlackBerry discovered activity on the USB port; it then tried to digitally negotiate with the Kemo charger since it couldn't know it was a dumb charger. The phone may have charged a little (the free 100mA "no dead battery proviso"), but the negotiation failed of course, so the BlackBerry closed the connection with an error. The Brando adaptor solved the problem (making it less likely that problems was caused by the charger shutting up because of heat), since it can switch between normal (data) and charge mode, and could therefore tell the BlackBerry, the the Kemo was a "dumb" charger. Unfortunately I haven't seen any specs on the Brando, so whether it shorten pin 4&5 directly, with an resistor, or D+D- instead, is unknown. I guess one of the two latter options, since folks have reported the Kemo to work with Garmin devices when pin 4&5 was shorted. I guess the Garmin cut off at 16MPH for similar reasons; at a certain speed the Kemo generated enough power to trigger a threshold event at the Garmin device. It is possible that the Kemo was 100% within the USB power spec, while still being incompatible with some proprietary Garmin charging standard. The problems with the Garmin may be solved with a correctly shortened cable, or with a change in its setup (spanning mode, or "stay on when charging" or "don't attempt data transfer mode" or similar) or both.

The problem with dynamo hub chargers are that they are "dumb" chargers with highly varying output. That is quite an unusual device, and most manufacturers doesn't test for such marginal cases. So pioneering users are likely to hit all kinds of quirks and snags. OTHO, using the hub dynamo to charge those ubiquitous power hungry smartphones and GPS devices, is such a logical and tempting idea, that many more people will try it the next couple of years.

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Regards

[stewartpratt]

An update. I've connected the hub/frame connections of the charger to the outward terminals of the Cyo (normally used for the rear light). As I understand it, this places the charger in parallel with the lamp.

From a quick spin up and down the road, it seems to happily supply power to the eTrex at anything above walking/jogging pace. I've yet to test it at high speed. Long ride coming up on Friday, so we shall see, but it's looking good so far.

[stewartpratt]

Update following a proper ride on Friday to test it out.

Things are, in practice, not good - but on the face of it the issues seem to be attributable to the eTrex (mine is a Vista C) rather than to the Kemo.

Clearly, there is no "standlight equivalent" output from the Kemo. Not a problem in itself - and you know what you're getting - but of course you do need to have batteries in the eTrex to keep it alive any time it's stopped. However, this does trigger some quirks of the eTrex:

- When the eTrex detects loss of USB power, it doesn't simply revert to battery power. It reverts to battery power and pops up a dialog on the screen saying "Press any key to use battery power, or shutdown in 30 seconds", and down it counts. So for any stop of 30 seconds or more, you need to interact with the unit to preventing it turning itself off. It's not the end of the world (especially as it beeps to notify you) but it's a usability annoyance.

- The real problem is that, as far as I can see, the eTrex will crash under certain set of conditions; namely, when there has been a switch of power source (USB to battery or vice versa - possibly just the former, I'd need to conclusively test it) and it subsequently shows the "junction navigation" screen. This is the screen which, when navigating a route (and I use those words in the strict Garmin senses of them) it shows a static map of the junction in advance of your arrival at it and during your passage through it. At this point, the screen freezes and the only way to fix it is to take the eTrex off the bars, take the back off, remove the batteries, replace them and turn it back on again.

The latter is a showstopper, making it unusable in practice. After several stops to reboot the device, and after a number of tests of trying to plug the cable in whilst riding, and this, that and the other, I resorted to just using the batteries.

I've got an external USB battery pack which may fix this issue when placed between the charger and the eTrex, or it may not - it's worth a punt anyway.

As it is, no dice with the Vista C (maybe the crashing is fixed in other/later models) - but the Kemo does seem to provide power just fine in principle. I'd probably want to test the output at speed with a multimeter before trying it on more expensive items like my phone, but for £25 it does seem - so far - to do the job.

I'll report back once I've managed to test it with the battery...

[interestedcp]

- When the eTrex detects loss of USB power, it doesn't simply revert to battery power. It reverts to battery power and pops up a dialog on the screen saying "Press any key to use battery power, or shutdown in 30 seconds", and down it counts. So for any stop of 30 seconds or more, you need to interact with the unit to preventing it turning itself off. It's not the end of the world (especially as it beeps to notify you) but it's a usability annoyance.

Accoding to the manual (page 56) the solution to that problem is to go into "Setup" -> "System" and change "External Power Lost" from "Turn Off" to "Stay on"

- The real problem is that, as far as I can see, the eTrex will crash under certain set of conditions; namely, when there has been a switch of power source (USB to battery or vice versa - possibly just the former, I'd need to conclusively test it) and it subsequently shows the "junction navigation" screen. This is the screen which, when navigating a route (and I use those words in the strict Garmin senses of them) it shows a static map of the junction in advance of your arrival at it and during your passage through it. At this point, the screen freezes and the only way to fix it is to take the eTrex off the bars, take the back off, remove the batteries, replace them and turn it back on again.

Nasty bug.
It is worth checking if you have the latest firmware:
https://buy.garmin.com/shop/store/downl ... 67&pID=263

Perhaps worth using the diagnostic menu to check for bad ROM/RAM or other problems. It will also show you software version and a hidden thermometer:
http://www.weethet.nl/english/gps_garmi ... ostics.php

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Regards

[stewartpratt]

Ah, useful stuff, cheers. "Power lost" setting now changed; firmware is latest; diagnostics says no errors.

[Meshuga]

Hm. Thanks for the reply.

AFAIK the light is 2.4W (leaving 0.6W for a tail light) so that would in theory give a bit of capacity for USB power when the hub is putting out 3W.

Ideally what I'd like to do is be able to draw a full USB charge (5V/800mA, I believe) when the light is off and take advantage of whatever I can get when the light's on, even if it's just a trickle, and to be able to do so automatically (ie without having to get off and rearrange any plugs).

I am rather a novice when it comes to electronics, however.

I did find this post mentioning a Kemo USB charger being used in parallel with the same light as mine, on a Shimano hub, and thought that would be the answer - but then found this thread which suggests otherwise.

Hi, I wrote the first post that you quoted on running the Kemo in parallel with the light. I have used this system for almost a year without problems. When wired up in this way, flicking the switch on the Kemo effectively just turns off the charger, and sends all the power to the lamp. At night this results in a slight but noticeable increase in lamp brightness so I use it on un lit roads. Otherwise I can run front and rear lights plus the charger without problems. The battery being fed by the charger obviously takes 3-4x as long to fully charge when I have the lights on too.

When just running the charger I can charge a 1000mA battery in 2 hours of riding. If you are continuing to have problems charging your eTrex directly I would suggest having two 1000mA batteries, charging one whilst discharging the other. Provided your eTrex draws power at 0.5A (i.e. the same as the dynamo/charger delivers power to the spare battery) you should be ok!!

And to answer a question in your other thread - the freeloaders that I have will not turn off when the device is full, i.e. they will trickle charge

[stewartpratt]

Ah, now I've done a data reset and reinstalled the firmware, I've gone into the menus to set it all up again and found there's an option to disable the turn pop-up screen. So hopefully that'll fix it if nothing else does. And since I didn't even like that screen anyway...

[stewartpratt]

An update... Having disabled the "upcoming turn" screen, the Garmin no longer crashes. It does have a tendency to dim the backlight when external power is lost, and not restore it once it returns, but this is only a minor annoyance. Setting the unit to stay on when power is lost does its job, although sometimes leaves a message dialog on the screen which must then be cancelled. Again, a minor annoyance.

The Kemo seems to work well. In parallel with the Cyo, it drops the USB power only on the chewiest of hills, ie a little above walking pace. I've not noticed any problems at high speed.