about modded hid hosts and ebay ballast/ light bulbs

[R10500]

hi, so i know that this is an oft repeated topic but one cannot expect to remember everything being discussed about all these things so i hoped that experienced folks could chime in on this.

i've been reading a lot about those 100W ebay ballasts. some are labelled AC but i don't recall seeing any being marked DC and in many pictures of modded host lights, the ballasts in those pictures look exactly the same as those on ebay, AC or not. can we really use the AC ballasts for handheld spotlights? also, there are some that are too cheap when compared to other similar specimens, like this one selling for around 32$ w/o shipping and those at 80$ also w/o shipping. is that something to be wary of?
about the ballasts' material, i've seen some sources describing their shell as being made of metal but i am apt to believe that it's really plastic instead. am i right?
then i've seen how some people either mount the ballast inside or outside of the host shell, are there any concerns with where we put it and has any of these units every failed in some disastrous way?
so far i've only heard of people using stock SLA 5.5 or 7.2A batteries or buying Li-ions for them. are there any other known specific alternatives?
lastly, are all the bulbs used in these mods automotive types found on ebay? any reviews on them?

thanks

 

[BVH]

The vast majority of automotive-type HID ballasts produce AC output from DC input. I've seen only a few DC output ballasts and they are usually the round type with the bulb mounted on the then. Flickering is common with small DC output ballasts. All automotive-type ballasts I've had utilized all metal cases. Mounting inside certainly makes for a much cleaner and stock looking installation. If running a 70+ Watt ballast inside, you need to consider the heat build up in the ballast due to its' produced heat and heat given off by the reflector from the bulb. The easiest way to manage the heat is to limit run time. There are as many battery options as your brain can think of. I haven't seen any specific reviews on bulbs.

 

[R10500]

the round ones would be the ebay hid flashlight ballast/bulb unit then? ok, do they stand up well to those internal resistors mods as well? can't disagree lol i'm thinking of adding a small cpu fan for ventilation and maybe like some others replace part of the shell with aluminum panels with vents. how quickly does it heat up to 50 degrees? has anybody been able to get an hour's runtime out of their modded hosts?

 

[R10500]

would fast start-ups also shorten the life of the bulb or some other components? and has overdriving HID bulbs ever resulted in explosive failures? i read how 2100 overdrove his 55W bulb with the 100W ballast but it seemed to fare just fine. also, i just found out about ddm tuning and found this 35w/55w kit attractively cheap. why would a 100W ballast alone on ebay cost from 30 to 80$? which is the actual reasonable price?