Peak circuit question

[archimedes]

Had an interesting discovery recently, when I found that a rechargeable NiMH N-cell (presumably 1.2v) would not power an older-style 3-LED UV Baltic, which runs just fine on a 1.5v alkaline.

This surprised me, since the lower voltage NiMH cell works just fine with all of my other Baltic/Shasta/ShastaX Peaks (including both power LED and 5mm LED versions in white).

Is there something different in the circuit for the ultraviolet version? Perhaps the boost driver requires higher input voltage, though the difference between the 1.2v and 1.5v seems relatively small. The output is not simply reduced, it completely will not light on the other cell, BTW.

Just wondering if this is a quirk, expected behavior, or some problem with the circuit ???

 

[cave dave]

Maybe its not making electrical contact?

 

[jabe1]

My guess is also that it's not making contact. I had an old Shasta that needed a shim in it to work well.

 

[archimedes]

Maybe its not making electrical contact?

Well, certainly possible I guess, but both types of cells appear to be identical in size. Also, it is not intermittent, and completely reproducible. In other words, each alkaline that I test works perfectly and none of the NiMH cells work at all ... ?

 

[cave dave]

Try using wire instead of the body to make electrical contact. Some of the Nimh N cells are shaped differently than the Alkaline versions.

 

[Curt R]

I have run into that same problem with a couple of lights. A very few
electronic circuits will not fire on a low voltage input but once lit off
they will run to about 0.8 volts. The cause is most likely the 22 uF
input tantalum capacitor. Also all of the older lights used a 5.0 volt
boost circuit, when we went to the Cree XPG we were able to use a 3.3
volt boost circuit that uses less start up power and is more efficient.

The difference between 1.2 and 1.5 volts when boosted to 5 volts is
really quite a bit on start up. N cell batteries have very small current
collectors internally as compared to the longer AAA batteries.

Curt

 

[archimedes]

I have run into that same problem with a couple of lights. A very few
electronic circuits will not fire on a low voltage input but once lit off
they will run to about 0.8 volts. The cause is most likely the 22 uF
input tantalum capacitor. Also all of the older lights used a 5.0 volt
boost circuit, when we went to the Cree XPG we were able to use a 3.3
volt boost circuit that uses less start up power and is more efficient.

The difference between 1.2 and 1.5 volts when boosted to 5 volts is
really quite a bit on start up. N cell batteries have very small current
collectors internally as compared to the longer AAA batteries.

Curt

Thanks for the quick response, makes sense to me (I had guessed it might be a boost driver issue).

Not really a huge problem, since I don't use that light too often, but I just hate risking leaks with alkalines. I can't remember if the Baltic heads can fit any other size battery tubes, though. I have tubes for those heads in HA, SS, and brass, but they are all N-cell sized. If I could get an AA or AAA (or CR2 or CR123) tube that would fit, I could just run it on lithium instead ....

 

[jabe1]

Thanks for the quick response, makes sense to me (I had guessed it might be a boost driver issue).

Not really a huge problem, since I don't use that light too often, but I just hate risking leaks with alkalines. I can't remember if the Baltic heads can fit any other size battery tubes, though. I have tubes for those heads in HA, SS, and brass, but they are all N-cell sized. If I could get an AA or AAA (or CR2 or CR123) tube that would fit, I could just run it on lithium instead ....

The Baltic Sea bodies are available in AAA and 2xAAA. You could post a WTB in the MP. Or Email Robyn at Peak. Both options require patience.