HID w/Nmh Burn Test

[Corndogg]

I just bought a slightly used Dive Rite HID canister light. It is an HID MR11 I believe. It had a small Nmh battery pack that is taped together, they almost look like AAs. I don't know the exact model of the light but I am told it is only a year or so old.
Anyway, I've used it three or four times now. It always charges up in just a few hours. This last weekend at Wazee I used it on the first dive for an hour, then maybe half an hour into the second dive it shut off. I turned the switch off then in five or ten minutes turned it back on. It lit up but next time I looked it had turned off again. I charged it again in just a few hours and it is now holding at 13.12 V.

I want to burn test it, but want to get more info. The Dive Rite site has some info butt doesn't go into detail about the differences between the three battery types, Nmh, gel cell, lead-acid.

I also don't have a halogen head to test with so I wanted to use any halogen 12 volt bulb or just use the hid and be carefull. Any one got any experience with this?

[DanL]

Corndog-
You probably have a 10 watt (W) HID light with a 4.5 amp-hour (Ah) NiMH battery pack.
It should burn, with a full charge, for up to 4+ hours.

You can burn test the HID bulb, but put it in a sink full of water to keep the lighthead cool.

A number of things could be happening that shorten your burn time - cold water and resulting cold battery; a bad charger (although your 13V sounds about right); a weak cell in the battery pack; a bad cord, switch or voltage regulator causing low burn voltage to reach the bulb (and therefore higher current flow and lower burn time), etc.

A simple equation to estimate burn time:

P= E x I, where P is power (10W for your bulb), E is the voltage at the bulb (probably about 12V for your light) and I is the current flow in Amps (A).

To get current flow, use I = P/E, or for the above values,
I = 10W/12V = 0.83A.

Your 4.5 Amp-hour battery should theoretically burn for
4.5 Ah/0.83A, or over 5 hours. That won't happen, but if all is working well, you should get 4 plus hours easy. My guess is that you ahve a weak cell or two in the battery pack, perhaps from moisture or corrosion. Do a full charge overnight, then a burn test in a bucket of water and see how long before the light dims.

Good luck.

[Inspirationdiver]

I have the same light you are using. I've used it over weekends on repetive dives for up to 4 hours without it ever shutting off on me. I think DanL is probably right, there must be a bad cell or two in that battery pack.

[Corndogg]

So when I burn test, what is my cut off voltage? 10V or what? Do NiMH batteries suffer damage if they are run down too far?

[Inspirationdiver]

Yes, actually they do. That's one of the disadvantages of a HID light. With a halogen lamp, you will notice a change in color of the beam indicating that the voltage is getting low. This gives you a chance to turn the light off before doing damage to the battery. With the HID, it will continue to burn the same color until the battery has been drained. :'(