H22 and qusp,
Thank you for your replies!
OK, here's my application:
I want to power a DACmini CX using a hardcase, 4-cell, 5000mAh LiPo pack (16.8V when fully charged):
For H22's benefit, as I can tell from the post I quoted that you're probably already aware of this, qusp...
RC LiPo batteries are rated at their nominal voltage - assuming 3.7V per cell, but when fully charged, they deliver 4.2V per cell, thus a battery like this one, which has a "4S1P" designation (4 cells in series, with no parallel connections), can deliver 16.8V when fully charged (4.2V x 4 cells), despite being labeled as a 14.8V battery (3.7V x 4 cells.)
A "5S1P" battery has an 18.5V nominal rating, which sounds attractive, at first consideration, for use with the DACmini CX, given the fact that the DACmini CX can accept any voltage from 9V up to 19V, but a 5-cell LiPo (like the Energizer XP8000 and XP18000) can deliver 21V when fully charged (4.2v x 5 cells), and thus, would need voltage regulation in addition to current limiting.
As you know, these LiPo packs can deliver A LOT OF AMPS. The C rating of a LiPo battery can be used to calculate the number of Amps it's capable of delivering continuously. The 5000mAh battery pictured, above, has a 40C rating. To calculate the number of amps that can be delivered with a continuous load (peak current is typically 50% higher still), just multiply the C rating by the mAh rating and divide by 1000:
40 * 5000 / 1000 = 200 Amps!
The DACmini's switch-mode AC power adapter is rated at 2630 mA.
So... I already see that I'm going to have to teach myself how to solder - even IF I can get my hands on a schematic for a noise-free device that can be inserted, inline, between the LiPo pack and the DACmini CX. In an ideal world, this imaginary device would limit current to 2630 mA (3000 mA would be fine), without voltage regulation.
There's no need to regulate the voltage of a 4-cell pack. It can start out at 16.8V (4.2V per cell) and discharge down to 12.0V (3.0V per cell) - at which point, this audible alarm (that I currently use with a different LiPo pack application) would signal that it's time to recharge the pack:
The DACmini CX can handle anything from 9V to 19V, so an input that decays from 16.8V to 12V is ideal. David McKrell, of CEntrance, has assured me that the DACmini's internal power supply takes any voltage that's coming in and converts it to a constant supply voltage at the rails. Input voltage has no impact on sound quality, as long as there are enough amps and it fits the range 9V to 19V.
Thank you, again!