Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Electronics, Lighting, & Gadgets HRM, GPS, MP3, HID. Whether it's got an acronym or not, here's where you'll find discussions on all sorts of tools, toys and gadgets.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-27-08, 01:34 PM   #1
bcubed
Senior Member
Thread Starter
 
Join Date: May 2008
Bikes:
Posts: 78
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Battery backup to 6V gen?

Hi, I'm running a 6V, 3W light setup (Union brand). What I'm interested in is adding battery backup for illumination at slow/no speed, as well as a redundant system in case of gen. failure, plus if I just want to be lazy and let Duquesne light do all the illumination work, lol.

I happen to have 10, Ni-mh batteries that output ~1.35V each. I was thinking that I'd wire 4 of them in parallel with the gen, and at lower speeds, the batteries would "win" the voltage war and drive the lights. At higher volts, the gen would win.

Three Q's:
1. Do I need to put a diode coming off the batteries? (At high speeds, the gen would otherwise attempt to "charge" the batteries, and I'm not aware if there'd be an overcharge concern.)
2. Do I need to put a diode coming off the gen?
3. Does this sound otherwise workable?
bcubed is offline   Reply With Quote
Old 10-27-08, 04:13 PM   #2
wmodavis
Bill
 
Join Date: May 2007
Location: HIGHLANDS RANCH, CO
Bikes: Specialized Globe Sport, Specialized Stumpjumper FSR Pro
Posts: 630
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Just hooking the batteries directly might work but in a very limited way.
1. Batteries may overcharge depending on the generator characteristics and lead to premature battery failure.
2. When stopped the batteries would discharge into the generator as well as the light so not good.

You do need some sort of isolation between battery and generator to properly control charging and discharging. A diode is a simple solution to discharging into the generator.

Another important question to answer is: Does the generator put out AC or DC? AC is OK for the light but not so for the battery.
wmodavis is offline   Reply With Quote
Old 10-27-08, 04:26 PM   #3
bobn
Senior Member
 
Join Date: Mar 2005
Location: South Florida
Bikes:
Posts: 726
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Why not just isolate one from the other with a couple of cheap switches from Radio Shack?
bobn is offline   Reply With Quote
Old 10-27-08, 07:01 PM   #4
bcubed
Senior Member
Thread Starter
 
Join Date: May 2008
Bikes:
Posts: 78
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks for the responses.

Didi a bit of looking on the 'net and Sheldon Brown covered this already here: http://www.sheldonbrown.com/dynohubs.html

Sounds like he just hooked them up in parallel and let the gen charge the batteries. The only thing I wondered was if an unregulated charge of the batteries might harm them (recall from my flying days that Ni-Cds are subject to a peculiar little phenomenon known as "thermal runaway.")

Pretty sure it's DC because I already tested output w/ a voltmeter and got good results...imagine it'd have a hard time making heads or tails out of AC current in DC setting.
bcubed is offline   Reply With Quote
Old 10-27-08, 07:01 PM   #5
jbabic
ol' Icebeard
 
jbabic's Avatar
 
Join Date: Jul 2008
Location: Cleveland, OH
Bikes: Dynamic Crossroad 8
Posts: 148
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
You could try these:

Altronix AL624 6v/1.2a power supply
Altronix SMP3 6v/2.5a power supply
Altronix SMP5 6v/4a power supply

Just keep in mind that they are designed for charging SLA batteries, not nicd or nimh. I think a hub dynamo could replace the transformer input to these units and charge the batteries during riding time with lights off.
jbabic is offline   Reply With Quote
Old 10-28-08, 09:00 AM   #6
n4zou
Scott
 
n4zou's Avatar
 
Join Date: Jun 2006
Bikes: Too Many
Posts: 2,393
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Here's how you do it.

4 diodes form a bridge rectifier converting AC to DC current.
S2 disconnects the batteries from the bridge rectifier and dynamo.
S1 turns the LEDs on and off.
The 4 Ni-MH batteries must be solder tab type with no possibility of poor or open connection.
Paralleled resistors are used to obtain the required values.
350mA LED is used in the headlight and the 36mA LED is used in the taillight.
The LEDs must not use more current than the dynamo can produce. The small excess current recharges the batteries as you ride compensating for stops when the dynamo is not producing power. Closing S2 and opening S1 allows rapid recharging of the batteries at 500mA while riding.

Last edited by n4zou; 10-28-08 at 09:07 AM.
n4zou is offline   Reply With Quote
Old 10-28-08, 09:05 AM   #7
n4zou
Scott
 
n4zou's Avatar
 
Join Date: Jun 2006
Bikes: Too Many
Posts: 2,393
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by bcubed View Post
Thanks for the responses.

Didi a bit of looking on the 'net and Sheldon Brown covered this already here: http://www.sheldonbrown.com/dynohubs.html

Sounds like he just hooked them up in parallel and let the gen charge the batteries. The only thing I wondered was if an unregulated charge of the batteries might harm them (recall from my flying days that Ni-Cds are subject to a peculiar little phenomenon known as "thermal runaway.")

Pretty sure it's DC because I already tested output w/ a voltmeter and got good results...imagine it'd have a hard time making heads or tails out of AC current in DC setting.
The batteries act as there own voltage regulators. As output voltage from the dynamo increases there internal resistance also increases. The resistance reaches a point where the dynamo is so loaded down that it can't produce more voltage. 4 series connected rechargeable Ni-MH batteries will limit voltage to 5.2 volts.
n4zou is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 08:21 AM.