Originally Posted by
fietsbob
USB is 5v, so even 230v would be stepped down to 5v, if the output is to not fry the gear attached to it.
I suppose you could bring a 12v battery and charger for it, then go from 12v to 5v while on the move..
another transformer & voltage regulator.
There often seems to be a fairly liberal amount of latitude when it comes to voltage.
Lithium-ion rechargeables say 3.7 volts on the label -- I just double checked this and it is there on the label -- but if you measure the actual voltage, it's about 4.2 at full charge. And it is down around 2.9 toward the end of its run when it is nearing time to recharge.
So it's actually providing a range of voltages, most of which are higher or lower than the 3.7 volts on the label.
Same sorts of things apply with alkaline, NiMH, lead acid, and other types of batteries. They all vary over a range during their cycles.
I don't know what the acceptable voltage range is for USB, maybe someone call fill this in?
It would be great to be able to charge or run devices directly from a battery without losing efficiency by having to boost or buck the voltage. It would also keep things simpler. Then again, the losses might not be to bad.... (I've heard that bucking is more efficient than boosting.)
Anyway, the twelve volts coming out of a cigarette lighter in a car will vary quite a bit (both up and down) from exactly twelve volts, so there is probably some latitude there when it comes to choosing battery pack voltage. (Seeing a discharge curve for a lead acid car battery might help here. If anyone finds one, or knows more, please post.)
The HK (lithium) battery packs come in 7.4 (2 X 3.7) volts, 11.1 (3 X 3.7) volts, 14.8 (4 X 3.7) volts, 18.5 (5 X 3.7) volts, etc.
I'm thinking that both the 11.1 volt and the 14.8 volt would work for a 12-volt system. The 11.1 volt would give exactly 12 volts at a certain stage in its cyle; the 14.8 volt would do the same at a later stage in its cycle. The 11.1 would fall off toward the end, and might get too low at a certain point to be effective. At full charge, the 14.8-volt battery pack would start out at about 16.8 (4 X 4.2) volts, which might be too high for some 12-volt devices or systems. But the chargers let you control the high end voltage, so you wouldn't have to charge it that high.
It might be worth checking to find out the usual range of voltages found in automobile cigarette lighters. I'm thinking it might be pretty wide, depending on the state of charge of the (often lead acid) car battery, the alternator, and other conditions. If anyone has more on any of this, or related issues, please post.