Problem with Light Cannon and NiMh batteries?

[ifukuda]

I've blown out the fuse on my Light Cannon on my last 2 dives. The light went out after 37 minutes into my dive on Friday, then 32 minutes into my dive on the following night.

An inspection of the light revealed a blown fuse each time. But, the Light Cannon was completely hosed after the second time it went out...it would not work even after replacing the fuse. My Light Cannon has been working fine on longer dives with alkaline batteries, and it's been working fine for about a month on shorter dives with the current NiMh batteries.

Has anyone else had a similar problems with NiMh cells? I've had no problems with the shop swapping my broken light with a new one, but I'm reluctant to put my rechargable cells back in.

I've been using eight OEM 1.2V 4.2Ah NiMh cells that have been working fine in other lights manufactured by UK.

 

[diver_paula]

I've been using rechargeable NiMH batteries in my UK Light Cannon since I got it. & have never had a problem. I've done lengthy shipwreck dives in both warm (Pacific near the equator) and cold (Great Lakes in May) with no problem.

Paula

 

[Bob3]

It sounds like there was a problem on the little PC board in your light, that's more likely what caused the over draw of juice.
Get the board (or whole light) replaced.

 

[ScubaAaron]

Sorry to jack your thread but i have just received my 4200 mah NiMh batteries for my LC100. The charger have a timed cycle of 8 hours. It shows that this is good for 2800 mah C batteries and that 5000 mah D batteries require two 8 hour cycles.

So my question is do you charge your batteries for 1 or 2 cycles? Or 1.5? Can you just charge for a portion of a cycle to "top up"?

Aaron.

 

[Clutchcargo]

ifukuda: Have you tried it with the alkaline batteries after you replaced the fuse?

 

[ifukuda]

Bob3,

You're probably right about the LC drawing too much power from the rechargable batteries. The shop has already replaced my light...no problem there. I just don't know if I should put the rechargable cells back in, and risk having my light go out a third time while I'm 70ft underwater in s****y viz.

I've spoken to a UK rep a little while ago about the LC. He'd mentioned that the symptoms of my light could be a result of a number of different factors. But, he advised that I "shouldn't" be having these problems, and to go ahead and try my new LC again with the NiMh cells.


Clutchcargo,

In response to your question, yes, I've tried putting alkaline batteries back in the light after replacing the fuse, but this was after light was already broken. After the LC got into a completely bad state, the fuse would go out on the light without it ever lighting up, regardless of using alkaline or rechargable cells.


diver_paula,

Nice to hear that your LC is working fine. I think I'll try my NiMh batteries again once I use up alkalines currently in the light. This way, I'm guaranteed at least a few good dives with the light.

 

[Genesis]

Here's the mechanism.

The LC uses an electronic ballast. The draw of the lamp is 10w, and is electronically regulated.

A fuse is a CURRENT (not wattage) limiting device.

With alkaline batteries in it, each cell produces about 1.5V. In reality the voltage can drop to close to 1.2V before the cell is totally dead and cannot support significant current output. I've found that at ~1.3-1.4V I start having problems with the LC striking - the HV strike circuitry apparently requires more current than the batteries can deliver when discharged to that level.

So 1.5 * 8 = 12V, roughly.

NiMH batteries (and NiCDs) work differently. They have a nearly constant voltage output of 1.2-1.3V from full to almost completely discharged, and will support very strong current drain all the way down to nearly zero remaining capacity without much "sag" in their output voltage.

So 1.2 * 8 = 9.6V (!)

If we have a 10w lamp, we require 0.833A from the 12V pack.

But at 9.6V, we require 1.04A - or 24% more AMPERAGE.

Now is the fuse set THAT close to the "line"? I hope not. But it could be, or some other component could be unable to tolerate a 24% increase in current flow though it, leading to a meltdown.

It is interesting to note that WA, the maker of the ballasts, has two separate versions of their 10w HID ballast. One is designed for a 12V nominal voltage and dry cells. The other is designed for a 9.6v nominal voltage - NiCDs or NiMH cells.

I have no idea what UK is using for a ballast, or its specs.....

 

[ifukuda]

Genesis,

Your V x A = W explanation makes sense. But...

Although a 24% increase in current flow is significant, the LC comes equipped with an AGA-2A fuse (a pretty big cushion). I have a total of 4 blown fuses that indicate that the current flow exceeded 2A, which is almost double the expected amperage.

Another thing I probably should mention is that my LC was a lot brighter than my dive buddy's LC. Unfortunately, at the time, I just assumed my buddy's light was getting low on batteries, rather than to assume my light was too bright.

These symptoms suggest that the current flow was unreasonably too high.

 

[wetman]

I got some Nimh batteries for mine and did a burn test on it. It lasted for under two hours and at some point some large "pop" sound came out of it. I opened it up and a burning smell was present. I put some alkalines in and it seemed to work ok after a while

 

[vicky]

ifukuda once bubbled...
Genesis,

Your V x A = W explanation makes sense. But...

Although a 24% increase in current flow is significant, the LC comes equipped with an AGA-2A fuse (a pretty big cushion). I have a total of 4 blown fuses that indicate that the current flow exceeded 2A, which is almost double the expected amperage.

Another thing I probably should mention is that my LC was a lot brighter than my dive buddy's LC. Unfortunately, at the time, I just assumed my buddy's light was getting low on batteries, rather than to assume my light was too bright.

These symptoms suggest that the current flow was unreasonably too high.

The HID bulbs do not operate like regular filament bulbs- There is a ballast that busts up the 12V (or 9.6) up to approx. 6000 Volts. So I don't think the reason you thought your lamp was brighter than your buddy's is because of amperage- most probably he wasn't using fresh batteries...