Running dynamo lights off a battery.

[g1nko]

Trying to power a B&M Eyc from my battery:

I have a converter from Grin that steps down my 48v battery to 6vdc. I was using this to power a B&M Cyo and a tailight without any problems. Then I came out of the market the other day and saw that someone had decided to liberate my headlight.

I replaced the Cyo with an Eyc. The headlight won't power on from a dc source. If I attach it to a dynamo, the ac source will fire up the light and charge the capacitor, so I know the light is good. If I wire it to the Grin dc converter while there's still a charge in the capacitor, it'll light up just fine. From zero, however, it won't light up.

I had to use a front hub motor because I have an IGH and roller brakes, so a hub dynamo is out. I suppose the easiest solution is to get a B&M bottle Dymotec 6 and call it done, but I'd really like to find some way to fire up the Eyc w/o having to drop $50 on a bottle dynamo when I already have the Grin dc converter. Any ideas, or am I just outta luck?

 

[amberwolf]

Well, that's kinda odd that it will only light up the way you describe.

If it is just a capacitor then DC would charge it up just fine, and AC would only charge it up if there is a rectifier diode or bridge in front of it.

FWIW, the dynamos (tire friction type rather than hub) I've dealt with produce DC, not AC; it's just not a constant level voltage unless the wheel is spinning the same speed all the time.

If your dynamo is the same, then there's no reason a battery wouldn't also power the light, unless the light is taking so much startup current becuaes of the uncharged cap's inrush current that the DC-DC converter is shutting down.

Best bet is to open it up and see what electronics it has inside. Probably something easy to bypass to fix it. If it is just the cap, then you could disconnect that and fix the problem super easy.