DIR ? : Re-chargeable batteries in a backup

[King Kong Matt]

Cave Diver once bubbled...


Actually, most of the info I stated came from my cave instructor, who was definetly not a DIR tenet. Still made good sense to me tho, and so do most of the DIR things.

And that's why I'd like to see this thread continue.

It's quite possible that the reasons you guys have thrown out are consistent with DIR on this one. I'd be interested in getting the skinny from someone who can speak definitively from the DIR side of the house.

Anyone? Bueller?

 

[JamieZ]

Correct me if I wrong but the lights out caused by rechargables running low is not accurate. The lights out instead of the dimming effect is caused by not enough voltage being supplied to the ballast of an HID which in turn shuts the ballast down. I could be wrong. If you use NiMH batteries in a regular flashlight it will go dim before it shuts off, wouldnt you think. If someone has some NiMH "c" cells It would be neat if you would try this and let us know, because I'm not sure if I'm right.

 

[wetman]

I've got a multitude of AA batteries here and a mini - Q40 - we'll see just how long they last and i'll get back to you

steve

 

[JamieZ]

Sounds good. You have AA NiMH?

 

[wetman]

Ok, so heres what i saw - started it at 11 am and put in 2 sets of brand new nimh AAs in my 2 Q40s.

Both sets freshly charged. Left one on till it died and used the other to compare ever hour or so for brightness against a fully charged set - one set was 1800 the other was 1850.

1st hour seemed to be at about 100% the whole time, second only slightly dimmer (maybe 98%), 3 hour was about 90% brightness and somewhere in the 4th hour complete darkness - unfortunately i wasnt watching at the time it went out, but seemed like it went out pretty quick.

This pretty much coincides with what i'd expect for performance from nimh cells.

steve

 

[Rev. Blade]

scubanarc once bubbled...
Correct me if I wrong but the lights out caused by rechargables running low is not accurate. The lights out instead of the dimming effect is caused by not enough voltage being supplied to the ballast of an HID which in turn shuts the ballast down. I could be wrong. If you use NiMH batteries in a regular flashlight it will go dim before it shuts off, wouldnt you think. If someone has some NiMH "c" cells It would be neat if you would try this and let us know, because I'm not sure if I'm right.

I think the NiCad batteries and NiMH batteries tend to have the sudden shut down even with a standard incandecent (including halogen or xenon) bulb. I have heard that HID lights will suddenly shut down when the voltage drops below their threshold, but lose very little light output until they reach that trigger threshold.

If that is the case, does DIR have anything to say about HID lights in general? The bulbs tend to be more delicate too, I have heard.

 

[Caffiend]

HID lights don't dim regardless of battery type.

The overwhelming problem with rechargeables is as stated, they don't hold a static charge (rechargeable alkalines aside). NiMH batteries lose their charge at ~5% per day if I recall correctly. A backup light isn't a charge-and-use type device. When you need it, you want it to work.

-will

 

[RichLockyer]

King Kong Matt once bubbled...
It's quite possible that the reasons you guys have thrown out are consistent with DIR on this one. I'd be interested in getting the skinny from someone who can speak definitively from the DIR side of the house.

From http://www.gue.com/equipment/lights.shtml#reserve

"Reserve lights should not use rechargeable batteries as they tend to have a more unreliable burn time when not frequently used."

If we're talking about a BACKUP light, it needs to have conventional batteries, and if they are actually used during a dive, I would replace them. They're cheap enough so that it's worth it for the reliability and safety.

All batteries self-discharge over time... some in as little as 30 days. If you forgot to put your backup lights on charge, are you going to call the trip? NiMH have advantages over NiCd in that they don't have the memory issues, but there are still potentially capacity issues over long-term intermittent use (or DISuse).

For travel, I see no advantage to rechargeables, and do see disadvantages.

 

[RichLockyer]

Rev. Blade once bubbled...
If that is the case, does DIR have anything to say about HID lights in general? The bulbs tend to be more delicate too, I have heard.

HID is fine. Like your scooter, the batteries are burn-tested so you KNOW how much run time or burn time you have, then you pad to provide a reserve.
Light capacity planning is no different than gas planning. I'm sure George and JJ "staged" canisters on their 3-mile penetrations just as they did with tanks.