Not as advanced in many ways to Louis’ battery mod but hey it works and I didn’t think “out of the box” enough to use a Phono jack as a power socket. Maybe the i-Light wasn’t that cheap to me that I didn’t want to take a knife/cutter to it so early on in the warranty stage!
Anyways, back to the mod. I don’t do video (but maybe with my 5D Mark II…) so I don’t need serious run time. Weight is an issue since the light and the battery will probably be hanging off one long end of a mono-pod most of the time. The Lowel i-Light runs with a standard automotive H1 headlight bulb. The stock Osram bulb is quite warm at 4800K. Osram automotive bulbs are probably not color balanced and my i-Light bulb temperature would probably differ from one to another. I replaced them with Philips Vision Plus which is slightly cooler (5200K) but most importantly, 2/3 stops brighter at 3 meters (measured with my Sekonic lightmeter). I’m not sure about power consumption but I use them on my 4×4 truck and visibility is improved.
What battery would I need. Nickel Metal Hydride (NiMH) is a proven technology, and simple to obtain locally. Lithion-Ion is a bit more fragile but packs a higher energy density so the battery pack can be lighter. So, back to high-school physics.
W = VA
Power (watts) equals to Volts multipled by Amps.
The standard H1 bulb is 55 watts. Most cars run 12 volts so that amounts to about 4.6 amps. In reality, automobiles run at high voltages because with the engine turning, the alternator usually outputs about 14 volts. For my first attempt, I made a NiMH battery pack with 12 Maha PowerEx 2700 cells. Why twelve? These batteries are sold in packs of four so no point wasting two but the idea is detailed in the calculations below.
12 AA sized NiMH batteries in series output a total of 14.4 volts (1.2V x 12).
With 14.4 volts, I only needed about 3.8 amps to drive the i-Light at full power. I didn’t build a current limiter into the battery so at full power it probably used a bit more. The other important bit was that to calculate runtime, you need to know battery capacity and the current the light is pulling. Quite easily done.
2700 mili-amp/hour equals 2.7 amps for one hour. 2.7 amps divided by 3.8 amps is roughly 0.71.
Multiply that by 60 minutes and you get 42 minutes.
Of course that’s in a perfect world so I decided to use 50 minutes per hour for my base so 0.71 multiplied by 50 is just about 35 minutes. More than enough for my needs. However, charging a pack of 12 batteries is a hassle and they were unwieldy and heavier than what I wanted. Lithium-ion is definitely the answer but where do I get the cells? I decided to go for 18650 Li-Ion cells. They look like oversized AA batteries at first glance. Since Li-ion batteries are more sensitive, I decided to order a pre-made battery from Battery Space. My choice was a 4x 18650 cell pack. Li-Ion cells output 3.7 volts so four cells result in 14.8 volts. This is also how your digital camera battery is made. Look carefully and you’ll see voltages like 7.4 volts (2 cell) or 11.1 volts (3 cell).
So, I bought this 4-cell pack from Battery space. Excellent service and super fast shipping — I got it within a week. So I wouldn’t hesitate to recommend them if you have specific battery needs. At about half the weight of my NiMH AA cells, I also got the Li-Ion smart charger which makes charging the battery pack a snap. The cool thing about this battery pack is that it comes with a status indicator. Kind of like the type built into your noteboook PC battery. Well made and put together, it saved me the hassle of wiring up individual cells. They also do custom packs if you have more esoteric needs. I modified it to take the standard cigarette lighter socket since that was what my i-Light came with. Interestingly, at full power, it’s another 2/3 stops brighter compared to the NiMH pack but ran the battery pack slightly warm so I made a mark at about three-quarter turn on the i-Light’s rotary switch. With the cables coiled and the battery pack snug in a neoprene pouch, it became a flexible light and with the built-in current limiter circuit on the battery pack, I know that I won’t be over-discharging the circuit plus there’s a low-voltage safety guard to prevent running the battery flat. A no-no for Lithium-Ion batteries and it also jacks the safety factor up so that’s always a good thing.
Still plenty of juice after two weddings
How long of a run-time do I get with this Li-Ion battery pack? The cells are rated at 2400 mili-amp hours but at 14.8 volts.
55 watts divided by 14.8 volts (voltage) gives me 3.7 amps
2400 mili-amp/hour equals 2.4 amps for one hour. 2.4 amps divided by 3.7 amps is roughly 0.65.
Multiply that by my conservative 50 minutes and you get 32 minutes, just a bit less than the 35 minutes of my NiMH pack.
So far, I’m happy to report that the on-off-on-off kind of use actually results in fairly long runtime. I’ve used it for two shoots without charging and the battery still is at three dots. It also takes about 45 minutes for a full charge (from 2 dots) and it a small handy package. My next mod will be to replace the cigarette lighter plugs with Phono jacks and to pack the whole unit, phono jack, battery status monitor all with a neat heat shrink pack. That will reduce the messy wire arrangement I have now. That said, Battery space already saved me a ton of work and I could have a working battery pack for my i-Light within thirty minutes of opening the box (time needed for adding the cigarette socket). After this, probably I’ll get a second battery pack but for a more compact arrangement, I might get the square pack or make a more compact unit with Lithium Polymer flat cells. I’ll put up an update when I mod the pack with a Phono jack.
Portable and flexible lighting!
