Electric Bikes - Separate battery for accessories?

I ran out of juice on the way home tonight which means, besides pedaling a 100 pound bicycle 3 miles in a very low gear (excellent aerobics but not what I wanted to do) I had no lights.

For those of you who are into diy do any of you run your lights, horn, etc off a separate battery? I would appreciate any input you can provide on this.

Also, what is the most commonly available voltages for lights?

My lights run off a wheel generator. My horn is only a bell for pedestrians. If I wanted a LOUD horn capable of being heard over traffic I'd use one of those CO2 powered air horns.

Powering lights and stuff from your prime mover battery is tricky at best. Voltage will often be wrong and converting voltage up/down wastes power. Also, hard to tell how much power you're taking away from your motor battery for lights/accessories. Lights can drain your battery simply sitting going nowhere.

Seems like you could use a "reserve" battery for your motor until you figure out your worst range scenario.

I know folks ask all the time about pedaling eBikes without motor power. I've yet to find one that actually pedals like a normal bike when the motor doesn't work. Weight, friction all add up to make it something I don't care to do. Even my 45lbs Panasonic feels much heavier than it is when the battery runs out.

IMO - A practical reserve/economy system would be a controller with a mode that ONLY provided enough motor to overcome the total eBike system friction/weight. To be used when battery capacity drops below 50% or so. This would give true non-powered pedaling ability for quite some distance.

As BroadwayJoe says, running your lights off your battery requires you to convert the power, losing efficiency. Now, as far as lighting goes, what do you need for lighting, to see or to be seen?

Most people run a red light in the rear and a white one on the front. I just have what are classed as emergency lights on the mountain bike, little LED emitters that just bungee on. These are *no good* for seeing where you're going. What they do is let other people see you, so its a measure of safety. I don't typically ride the mountain bike around the city so this suits the need. They're just there in case I happen to be out in the night on that bike for some reason. These little lights are so tiny that they usually just have a flat cell in them.

However, if you want to be able to properly see where you're going at high speeds, you need a real lighting system. Building your own lighting system with LEDs and batteries is certainly possible and has been done, but the elliptical light patten is what you need, thats the hardest part to do. Without it, a lot of the light is simply lost to the air or focused somewhere you don't need to look. While there are much better lighting systems out there, you can get fairly low priced ones that will let you see where you're going in "average" conditions, and they'll take less work than DIY. I've seen a few of these and they work pretty well: http://ecom1.planetbike.com/3031.html

Not too pricey, but it won't compare to a Dinoette or some of the others. The Electronics, Lighting & Gadgets forum has the best information on lighting around here, I think.

As BroadwayJoe says, running your lights off your battery requires you to convert the power, losing efficiency.

I'm sure it's possible to rig up lights that run at a motor's voltage.

I bought a 24V motor and a 12V/1W xenon strobe, and I was thinking about trying to buya 12V/1W LED lamp (I know that 12V LED lamps exist)... that way I could have a solid light as well as a strobe, and run them off the 24V battery.

I don't think I will do that, because I suspect it wouldn't actually be more convenient than simply running the strobe off of a 9V cell and not using a solid light.

I'm sure it's possible to rig up lights that run at a motor's voltage.


Of course it's possible but in daily application it may not be too wise and that's all we're attempting to advise. eBikes already have so many variables affecting motor/battery-range/performance why clutter an already murky situation?

Sure, if you KNOW how much AH you need to ride your needed distances, own enough cell capacity and can tinker - use the motor battery. But, unless you BUY into genuine lighting instruments - lights on bikes are more for visibility by other traffic and to comply with local laws. My wheel powered Sanyo dyno-lamp does that and actually a good job in very dark alleys/roadways so I never have to worry about a battery for it to light the way.

Of course it's possible but in daily application it may not be too wise and that's all we're attempting to advise.

Yeah, like I said, I'm not trying to do it now because I think it'd be more trouble than it was worth.

In theory, I like the idea of having my bike run off of one battery so I don't need to fiddle with multiple batteries and chargers every day, but in practice I don't think it'd be very convenient. Now, if someone were selling good lights (and waterproofed wiring hookups) specifically to go with my 24V battery/motor setup, they would certainly have my interest.