SP-PD8, Sinewave, Exposure, Garmin, "External power lost"

[VeganGraham]

I'm sure every possible question about dynamos etc. has already been asked several times, but I can't find the answer to this one.
If I connect my SP-PD8 to my Exposure 6 pack via a Sinewave Revolution, it appears to be keeping it charged indefinitely.
However, if I connect the Sinewave to my Garmin 800, I keep getting the "External power lost" screen. 12km/h seems to be the threshold speed on 29+.

So,the obvious thing to do is buy this splitter cable so that at over 12km/h I am charging both and at below 12km/h, the Garmin will draw power from the exposure via the Smart Port.
I suspect it may not be that simple though as http://www.ultimatesportsengineering.co ... e/fid/1670 says "WARNING - Ensure that the Smart Port is switched off before charging".

Is it possible to connect a dynamo, battery and load together so that the load will automatically switch between dynamo and battery as the dynamo voltage varies, just like it does on a car?

[Bearbonesnorm]

I might be missing something ... can't you just run a buffer battery and feed your Garmin off that? It appears to be the usual way to do it.

Is it possible to connect a dynamo, battery and load together so that the load will automatically switch between dynamo and battery as the dynamo voltage varies, just like it does on a car?

It doesn't. The load is always fed by the battery but the alternator (via the regulator) will provide more or less output as load increases / decreases and aim to maintain a battery voltage of 13.5v to 14.5v.

[VeganGraham]

Perhaps "switch" was the wrong word as I didn't mean a physical switch, although old fashioned car dynamos did have contacts in the regulator box that would switch in the dynamo once it reached charge speed. I meant that I want the Garmin and Exposure to draw their current from the Exposure's battery or dynamo as available.
Yes, a buffer battery is what I need, I was just hoping to use the Exposure's internal battery as that buffer battery.
I've got an Exposure Triple Piggyback. Would that work as the buffer battery using that same splitter cable?
I've been searching the forum for advice and found several mentions of people doing similar to what I want to do, but no specifics on what cables to buy.
Would that one I linked to above do the job?

[Taylor]

http://www.amazon.co.uk/gp/product/B00M ... 26&sr=8-26
This should do the trick. No extra cables required.
The only thing you'll have to do is shave a bit off the side of the usb plastic as the ports are too close together. I done this by a quick press on the side of a bench grinder.

[VeganGraham]

Thanks Taylor, that should sort out the External Power Lost problem. It would have been nice to have been able to use what I have already got, but £8 and 82g is OK.
The Garmin 800 lasts 12+ hours on a simple speed and distance display, but using the live scrolling map with the brightness turned up knocks that down a lot. That's why I want to be able to charge it while riding, even on one day trips.
It would be handy to charge the Exposure as well at the same time, so would this work?



I can't be the only one who wants to charge two items at once. How do other people do it? Can you connect multiple loads to a bicycle dynamo, or do you have to swap the cable and charge one at a time?

[mountainbaker]

You're better off charging one thing, faster, then another, than trying to charge both at once. I say this from experience.

[Bearbonesnorm]

The dynamo won't produce enough output to fully perform 2 tasks at once. I use a Cycle2charge, the dynamo is wired in parallel to it and a Revo and although the Revo will light and something connected to the Cycle2charge will show life ... neither is recieving full power / charge. If I want the light on I unplug the usb cable and if I want to charge something I unplug the light - not really a problem.

However, I see you're running a buffer, if the capacity of the buffer is big enough then it should charge 2 items and the dynamo should keep it topped up ... although it might not be able to keep up depending on what's been charged.

[VeganGraham]

Thanks both. Thinking about this a bit more and looking up the numbers, what you're saying sounds right.
If the dynamo puts out 6v 3w, that's only about 0.5A. Whatever the Sinewave does, it can't create power, so it's not going be much more than 500mA at 5v.
An Exposure charger is 1.5A output, a Garmin charger is 1A, although both devices can be charged from a standard 500mA USB supply.
I need to do some experimenting once I get the buffer battery. If I start with everything at 100%, I'll see if I can keep the buffer battery topped up above 12km/h so that it will keep the Garmin at close to 100% while riding slower indefinitely.

[composite]

My article might be of interest.
http://www.composite-projects.co.uk/201 ... the-trail/

[Richard G]

Vaguely related, I'm going to be trying to make a more water resistant USB cable for my Garmin 1000 with sugru. There's no way in hell that thing is going to do more than 12hrs without an external battery, and because of the placement of the port I can pretty much guarantee water would get in there at some point during a ride.