Running Lights

drakep · #1 01-06-2010, 01:15 PM

Hi. I am beginning my journey to mod/build a motorized Micargi MTB Mustang. I recently found a great deal on retro headlamp and tail lamp, both wired to run off of a 12v circuit. Since I don't have a motor setup yet, can I simply wire the lamps and a switch directly to the 12V source, or will I need fuse/relay to avoid problems? Thanks. Great forum.

HoughMade · #2 01-06-2010, 03:46 PM

If they are 12v, you will need a 12v battery. I would most definitely fuse the positive side. No need for a relay. The engine puts out closer to 6v and 3 watts, so it will not run the 12v lights. See what the wattage draw is, they you will know what size battery you need. I have full turn signals, turn, brake and headlight. I use a 7ah 12 volt rechargeable and it will run the lights for hours, but I only have a 7 watt headlight that I use for a daytime running light, I do not ride at night. If I did, I would want at least a 20watt headlight (35 is better), and the battery would still run the lights for over a 2 hours.

Good luck!

drakep · #3 01-06-2010, 04:26 PM

Thanks Hough. What's easiest way to install a fuse inline, and how do you size capacity? Lights will be used sparingly. Mostly for show at the present time.

TheE · #4 01-06-2010, 09:49 PM

If you know the wattage of your lights, you can divide that wattage by 12V to get the current draw. In your case 20W/12V=1.67A, so a 3A or 5A fuse should do just fine. As for mounting it, they sell screw-cap fuse holders at Radio Shack, just wire that in series using either solder or wire-nuts if you don't have an iron (just watch out for vibration).

OKflyboy · #5 01-06-2010, 11:05 PM

Just wondering out loud here, but I wonder how long a 12v lawnmower battery would run a 20w headlight. At $20 (Walmart) they're cheap enough to replace if needed, large for a bike but small enough to make it work. Add a float charger and just remember to plug it in when you get home... Hmmmmm

HoughMade · #6 01-07-2010, 10:49 AM

Quote:

Originally Posted by OKflyboy

Just wondering out loud here, but I wonder how long a 12v lawnmower battery would run a 20w headlight. At $20 (Walmart) they're cheap enough to replace if needed, large for a bike but small enough to make it work. Add a float charger and just remember to plug it in when you get home... Hmmmmm

That's close to what I have. I have a 7ah battery and I had figured that with a 20w headlight (my brake, tail and turn signals are LED- therefore very little draw), I would get a very conservative 2 hours+, probably over 2.5 hours. With a larger battery- longer run time.

One thing about a float charger- that is fine if the battery is not too discharged, but once the battery falls much below 12 volts (fully charged, should be close to 13 or a bit over), the float charger will not like charging it. Most float chargers are made to maintain a charge. When my battery is discharged to any great extent, I have a "fast charger" which is just a 14 volt DC converter i found at a thrift store. It supplies only 1500 ma, which is below the max rec. charge rate of the battery of 2100 ma, and I use that until the battery is at 12 volts. Then I disconnect that, and leave it plugged into the float charger until the next ride. A Multimeter is essential....and I may be a bit obsessive.

[edit]

BTW- that amperage for the fuse is correct. I used an automotive blade fuse. The fuse holders are available in auto parts stores.

OKflyboy · #7 01-07-2010, 01:21 PM

Well, there's only about 4 miles of suburban streets between my home and work, so I'm not too concerned with a long run time, but I do work nights and early mornings quite often, so I am concerned with maintaining good visibility during that short commute (IOW, I want a bright light for my 8 mile total commute). Since I'm a DIY kind of guy, I plan to make my own 20w headlamp inspired by what they did over at KLORG (klorgdotcomslashbike) . (I would post a real link, but since I'm new, I guess I can't). He used different batteries, but I can get lawnmower batteries cheap, so I figure they're worth a shot...

Edit: Your "fast charger" is a really neat idea. I think I may steal it (the idea, that is, not your charger.

)

HoughMade · #8 01-07-2010, 02:28 PM

I made a battery case out of an old Polaroid camera case. I put a plug on the back of the case so all I have to do is plug in the charger. The case has a battery curoff switch on the front. I ran the charger wires directly to the battery, not through the switch so I can have the battery off and still charge. However, I originally did not fuse the charger circuit...then I went to check the voltage throigh the charger jack...and promptly caused a short (jack is kind of small) and had to replace all of the charger circuit wires as I burned all the insulation off. Now I have it fused with a 3A fuse- I have a 5A on the light supply circuit. Lessons learned.

BTW- I have seen the light you referred to- it's a good project.