[sabahtom]

Hi....if someone could enlighten me. I have a cateye bike light that cost a lot. it worked great until I changed the cells to 1.2v energiser rechargeables. now its dead.

I opened it up and its got a super-compact LED, and the circuit board around around the LED is peeling. The plastic reflector is turning brown around the edges. assuming cateye is a quality product and their stuff is rated for the expected heat, could it be that at 1.2 its drawing extra current and overheating?

Cheers
Thom

[Ziggythewiz]

It depends on your device. Some will work on lower voltage, some will not. How many AAAs does it take? I was pretty ticked when Rayovac switched from 1.5V rechargeables to the 1.2s. I have several devices that will run for just a few min on a fully charged 1.2, while they would run for hours on the 1.5s.

[dougingraham]

Originally Posted by sabahtom

Hi....if someone could enlighten me. I have a cateye bike light that cost a lot. it worked great until I changed the cells to 1.2v energiser rechargeables. now its dead.

I opened it up and its got a super-compact LED, and the circuit board around around the LED is peeling. The plastic reflector is turning brown around the edges. assuming cateye is a quality product and their stuff is rated for the expected heat, could it be that at 1.2 its drawing extra current and overheating?

Cheers
Thom

I don't know what product you have but it doesn't seem likely that they have a boost converter in the unit. White LED's need 3.2 volts to operate. This means at least 3 cells in series. Typically you would use three cells in series and a resistor to limit the current. The next level would be to use a transistor to control the current so the brightness doesn't change with the state of charge. If you really wanted to make a top of the line device that would maximize the battery life you would use a buck regulator to switch the power down to the voltage needed to activate the LED. This won't gain you a lot of extra life and would cost a lot more than just a current limiting resistor.

I dont know why it would fail. Those are good batteries. The fact that the rechargable cells are 1.2 volts instead of 1.5 shouldnt cause the unit to fail. Dry cells when they are depleted have low voltage too. They would exhibit the same behavior.

How many and what kind of batteries did it originally use? Cateye seems to sell mostly rechargeable headlights.

Send it in under warranty. Take it back to the place you got it.

[lithiumlogic]

The only devices I've encountered which warn you not to use 1.2V rechargables instead of 1.5V primaries are ones with no current regulation in the circuit at all.

For example, very cheap LED lights where the LED is directly connected across the battery, and the internal resistance of the battery itself provides current limiting.

Also, those micro radio controlled cars costing £15 or so that were all the rage a few years back. The car (about an inch long) had a minature rechargable battery in it. You charge it by plugging it into the control, which runs off three AA batteries. Presumably it just directly connects this little RC across the AA's, and the charge cycle (which takes only a minute or two) is current limited by the internal resistance of the AA cells.

The problem is NiMH batteries have much lower internal resistance even than Alkaline cells, and NiCads are capable of more current still.

I doubt the voltage is an issue, in fact rechargables and non-rechargables are a lot closer than you think.

Brand new, fresh Alkaline batteries read 1.55V per cell under no load.

Hook them up to a Halogen bulb (the sort that flattens them after 4 to 5 hours operation, typical on a bike light) and they immediately sag to not much over 1.4 for the first 30 minutes of runtime.

For the remainder of the lifespan it's more like 1.2V, and they are considered dead at 0.9V to 1.1V depending on the application.

NiMH rechargables are more consistent.

They start at 1.4 something when fully charged, and sag much less under load because of the lower internal resistance. They maintain a voltage over 1.2 for 80% of their life.

For this reason, most flashlight bulbs are designed for 1.2 V per cell. Eg. a 4 battery bike light typically runs a 4.8 Volt bulb, even though it was not supplied with rechargable batteries or a charger.


So anyway, i'm not convinced this Cateye light is quite as cool as the guy in the shop reckons it is. In fact, a bike light that cannot use rechargables does not sound fit for purpose. Like many i suppose - back in the 90s i ended up building a couple of my own custom lighting systems.