I have a 6V lantern that works with a 6V H3 55 Watt halogen bulb. Its on its third Lead-Acid battery now. The two previous ones just gave up with some use. Then I thought why not use a more reliable Lipo pack. It also meant I would have a brighter beam because it will overvolt it a little bit!
Well I tried it with a 7.4V Lipo RC pack. It was basically an insta-flash...
What 6V halogen bulb with the same dimentions, that will fit in this light, will work with a 7.4V Lipo pack?
I don't know if I'll find one that will fit in the light. And I would prefer to use the extra 2S lipo packs I allready have than to buy additional lead-acid batteries.
I'm sure there must be a 6V bulb like this that can take 7.4V of lithium power. It does not matter the watts. Can be from 25W to 150 Watt. Anyone that will fit without mods needed in the place of the old bulb.
As Ictorana said, the H3 is probably rated for higher than 6 volts, just like standard 12 volt car headlamps which constantly cope with 13.8 volts and even higher. Have you considered that maybe the bulb in your lantern was already well used and right on the verge of giving out anyway? The extra voltage of the LiPo was enough to send it to an earlier death than it might have had with continued use of the lead-acid battery. A brand new H3 bulb may very well handle the LiPo without issue, although I imagine that the overall lifespan of the bulb might be slightly reduced.
No, Now I sit with two blown H3's..
But before I tried it with the lipo I tried it with a GP Racing car pack. 7.2V 3300mah. This battery was fresly charged 5 days ago. Testing was done with a hobby watt meter. The H3 draw 10.3 Amps and put out 71 watts according to the watt meter.
Then it was the Lipo's turn. It is not even fully charged. It instantly blew the H3.
But here is the strange part.... The resting voltage of the cells after the test is 7.96V for the NIMH pack but only 7.69V for the Lipo pack.
Why then did the lipo pack poofed the H3 and not rather the Nimh pack? It does not really makes sense to me. I'm using the Nimh pack in a RC Truck and it really delivers a good punch.
Due to the design properties of LiPo batteries in general, I'd say that the "voltage while under load" of your LiPo pack was much higher than that of the NiMH pack "while under load". From my limited knowledge of LiPo cells, I believe that they suffer less voltage sag than any other type of battery chemistry.
If you're open to the idea of possibly wasting yet another bulb, and assuming that the bulbs you have are not name brand, then you might try a more premium brand of H3 (GE, Sylvania, or Osram). They may have slightly wider voltage parameters.
Failing that, I'd try to get some more specific information about that NTC from Ictorana. He seems to have lots of hands-on experience with these types of "old school" mods.