MTB head light project

[bike_light_project]

Hi boys and girls,

Need some help here! I have very little knowledge about electronics. I'm making a pair for head lights for my bike. Powered with a 10 x 1.25V 2500mAh rechargeable batteries placed in series (10 AA battery box). I guess i can get 12.5V out of it. Correct me if i'm wrong. I've got 2-off these battery box and i'm planning to put them together in parallel which i believe i can get 12.5V but 5000mAh. Rite?

2nd road block is, I'm planning to use a MR16 12V 20W Halogen bulb (flood light) on the left, and a 12V 4W LED bulb (spot light) on the right. I've wired them in parallel. My road block is, when I turn on just the LED on only, it works. When I turn on the Halogen bulb on together with the LED, the LED switches off automatically. I'm guessing LED only allow current to flow in one direction and Halogen light will change the current flow??? or since halogen bulb has no +/- poles, when they were switched on, it kinda created a short circuit and the LED turns off automatically??? In my mind, I was thinking of adding a Diod just before the Halogen to make sure the current only flow in one direction?? If so, which diod should I use? is there going to be V drop across the diod which will make my light less bright?? The circuit works fine with two LED on, so I'm guessing the Halogen is causing the problem in this circuit??

Many thanks,
BLP

 

[dougy83]

the 20W halogen draws a lot of current and may be pulling the battery voltage too low for the LED to work. If you have a multimeter, you can measure the battery voltage when the halogen is connected and also when it is not.

 

[bike_light_project]

Thanks dougy83, will give it a try later.

 

[audioguru]

I think your battery is not fully charged, or your wiring has a high resistance because the wires are too thin.
The 12.5V/5000mAh battery should be able to power both the 20W bulb and the LEDs together for at least 3 hours.

Maybe the contacts in your battery cases are loose or are corroded.

 

[bike_light_project]

Thanks Audioguru

I'm only concentrating on Voltage and Wattage, forgotten about amps! I just realised that my power supply to test this setup is 12V, 400mA. Its battery charger for my hand drill and its the only thing I can find in my house that gives me 12V to test the wiring and bulbs. I brought 2 dozen of rechargeable batteries from Ebay and they are still in delivery. I guess my wires are 'OK', they were rated 3A. correct me if i'm wrong.

 

[bike_light_project]

is there any way to make these LEDs brighter?? Adding a capasitor maybe?

 

[mneary]

The LED modules are probably designed to give the greatest brightness while providing an acceptable lifetime. If you measure 12V, it's probably operating at this optimum point.

 

[bike_light_project]

Many thanks to all. Much appreciated.

 

[bike_light_project]

Additional question, I got 10 off 1.25v rechargeable batteries placed in a battery holder. They were rated 2500mAh. I'm not too sure how much Amp they product. I've got a 12v, 500mA charger. What is the calculation to determain how long do I need to put them on charge? If I got 2 off battery holder, put them on charge at the same time, should I expect to double the charging time? Assume my charger can produce 1A, I suppose this will speed up the charging process but will reduce the life of my batteries, rite?

 

[audioguru]

Ni-Cad and Ni-MH rechargeable AA cells can discharge at 2.5A without a problem and the capacity is still 2500mAh. They can discharge 5A for a little less than half an hour but the voltage is low and the cells get hot.

Ni-Cad cells can be continuously over-charged at a current that is 10% of their capacity for years. ni-MH cells are recommended to have the charger turn itself off when they are fully charged or switch to a trickle-charge current that is only 2.5% of their capacity.

Put the cells in series then the same charging current flows in them all and the charging time is the same as a single cell.

If you charge at 1A then you should use a charger IC to detect when the cells are fully charged which might be in 2.5 hrs to 3.3 hrs.

 

[bike_light_project]

Mine are Ni-MH cells......Thanks uncle scrooge! Its really useful.

 

[bike_light_project]

Will I damage my batteries if I charge them up in reverse, ie connecting negative to positive and positive to negative?

 

[audioguru]

We don't charge batteries backwards so we don't know what happens to them.
They are probably destroyed.

 

[bike_light_project]

LOL, I think I might accidentally clipped them in the opposite direction when I charge up the 1st set of batteries with crocodile clips.....RIP..... thanks Uncle Scrooge

 

[mneary]

If they don't work, they were destroyed. If they work, extent of damage, if any, will be known after usage.

 

[bike_light_project]

Rite, thanks....Other than that, i think they are dodgy anyway....written 2500mAh but they dont last very long. Got them cheap from ebay. I've brought myself a motorcycle battery, 12V and weights around 2kg....i get 7000mAh with it, and i'm happy carrying the extra weight around.

Having said that, can anyone suggest a quick and cheap way to get my LEDs to blink. I thought it would be a great idea to have flashing like while i'm on the road and when i'm off road, i will be just on. I'm thinking of a 3 way toggle switch, On-Off-On...but one of the On will be flashing. Any circuit diagram and components that i need to get?