Mountain Bike Reviews Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
45 Posts
Discussion Starter · #1 ·
Hi!

I built myself a DIY light system using the Sigma Mirage Evo X 10W, 6V MR11 halogen light with a 4.5Ah battery made with 6 D size NiCd cells working at 7.2 volts - so I am overvolting the light by 20%.

Sigma light housing has some electronics in it so that you can switch it to 50% power and it really draws 50% less current.

What I need though is a voltage regulator that does not have to have any indicators, any switches (I have one on the light), and no power level capabilities as PWM reduced power really makes the light yellow and useless.

All it needs to do is to cut the voltage of the freshly charged battery pack from 8.5V volts or so (freshly charged NiCd cell is 1.47V, times 6 cells) to 7.2V and I need the regulator to disconnect the battery when it reaches 6 volts to prevent overdischarge.

So it needs to limit the voltage to 7.2V if batt voltage is higher, when it reaches 7.2V just let it through (no pwm) and shut off at 6V. I have looked at the LVR, but it does not have the specs that suit me (I use 6v bulb @ 7.2v and a 7.2V battery).

I know of the LVR1,2,3 regulators, Lightbrain DIY ones and the od LBrain ones from http://www.geocities.com/sunsetstrip/concert/2301/basic.html. I like the old LB ones because it uses the PIC16F84 I can get in Croatia, but it is made for 20W, and 12V systems only. LVR does not offer my specs, and Lightbrain DIY could be sized for me - but I cannot find a hexfet nor the microprocessor in Croatia, plus I don't need the soft start option and power levels nor the on off switch on the regulator!

I am not huge into electronics, and I would like to order something reasonably priced from the USA (friends can bring it for me), but if not available, I would really appreciate the help with how to build one and where to order the electronics from the USA. Sorry for the longer explanation and I hope some of you wizzards might be able to help me :)

Greetings from Croatia

Domi

P.S. a bonus question - I recently tried to discharge my brand new battery pack mentioned above with a halogen bulb, and forgot about it until the bulb stopped shining and the voltage of the pack fell to 4V :(((((((((((( I recharged it but it would only go to 8.3V. Have I permanently damaged the battery pack by this overdischarge? It was connected to a 12V 20W MR16 halogen for maybe one hour, not more? Please tell me it is OK as my system is brand new :(
 

·
R.I.P. DogFriend
Joined
·
6,891 Posts
Six healthy D sized are only giving you 7.2v under load. They are 1.2v cells. They will show more than that when freshly charged, but like I said, don't worry about that.

But you may have reversed the polarity of one or more cells by leaving the discharge device on for so long. A lo-tech way to check it out: Charge the pack again and put it on the discharge device and feel the cells for warmth while discharging (if possible). If one or more remains cool, there is a problem with those cells.

In the future, watch it closely and take it off the discharge device as soon as the bulbs dim noticeably. This is close enough. If you use the lights regularly, you can store the cells in this condition.

Also, you are using a 7.2v pack with a 6v system. This could be of some concern, but you knew that already. Why not just use a five cell pack?

Regards,
 

·
Registered
Joined
·
45 Posts
Discussion Starter · #3 ·
jeffj said:
Also, you are using a 7.2v pack with a 6v system. This could be of some concern, but you knew that already. Why not just use a five cell pack?

Regards,
I know what voltage I get. I am overvolting a 6V bulb by 20%, increasing the light output by a whooping 85%. I know I kill the life of the bulb and increase the power consumption but that is OK.

I want to limit the voltage to a max of 7.2V because if I hook up a freshly charged 8.5V pack to a 6V bulb - it might cost me a new 20 USD bulb :) The shut off should help with not killing another battery if I accidentally leave the light on. That is all I want :) Hope it makes sense.

Greetings, Domi
 

·
Registered
Joined
·
1,902 Posts
Sorry, I've been out of the Halogen technology side of things, all my lights are LED based these days - which means current buck and/or boost regulation. A few years ago, I did play with voltage regulation on incandesants, and the LVR circuit was the only one I looked at. But I concluded that putting the correct voltage battery pack to the bulb directly, with nothing fancier than a mechanical switch, was the best, most reliable and efficient way to drive a halogen.
 

·
the wrench
Joined
·
469 Posts
a soft start cct will be of more use to prevent the bulb from blowing prematurly. this is because when the bulb is turned down the cold filament has a low resistance and causes a current spike for the furst few miliseconds untill the filament reaches full temp.
 

·
Registered
Joined
·
1 Posts
beanbag said:
If you want to DIY, you can look at various semiconductor companies like national.com to find a chip. Externally, you add a capacitor, inductor, and diode.
...and most of these chips are designed to be surface mounted and have absolutely miniscule solder pads. I don't have confidence that I can solder something that has pins 0.6 mm wide, and 0.4 mm between pins.

To the OP, you should consider this adjustable voltage regulator. It's limited to 10 Watts, but you might be able to push it by that extra 20%, especially if you add some extra heat sinking. Dunno. Except for the 10W thing it looks perfect. The web site says you can use two in parallel, but that'd cost US$30...
 

·
Save Jesus
Joined
·
2,947 Posts
likeguymontag said:
...and most of these chips are designed to be surface mounted and have absolutely miniscule solder pads. I don't have confidence that I can solder something that has pins 0.6 mm wide, and 0.4 mm between pins.

To the OP, you should consider this adjustable voltage regulator. It's limited to 10 Watts, but you might be able to push it by that extra 20%, especially if you add some extra heat sinking. Dunno. Except for the 10W thing it looks perfect. The web site says you can use two in parallel, but that'd cost US$30...
There exists regulators with other packages than surface mount, such as T0220. The regulator you mentioned won't work because it will drop a minimum of 1.3V. The really nice thing about the one you mentioned, though, is the small size and lack of external components. There probably exists one out there that will do the right thing, but that requires searching. Otherwise, you will just have to look at datasheets and build one yourself. National Semiconductor has tools on their website to help you do this.
 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top