787
RR_NDB
Thank you for taking the time to give your explanation, great stuff.
So far as I know model LiPos and LiIons are both charged serially, but the balancer takes a reading from each cell to ensure that cell voltage does not exceed the max value of 4.2. Individual cell voltage can be checked on the charger LED display and in a healthy pack the voltages stay VERY close together, suggesting that the balancer is working well.
Interestingly the LiFe charger that I have actually charges through the balance cable so I presume this is using parallel charging in the form you suggest. Battery reliability of my LiFes has been excellent even though it takes quite a load on engine start, certainly better than LiPos.
Of course we don't charge packs in flight in a model but obviously the 787 does, so is there any way the crew could be advised of a developing internal battery problem such as a defective cell, say through the EICAS, and could a defective cell be automatically isolated from the rest of the battery ?
I certainly like the positive (no pun intended) attributes of lithium for model use and with careful charging, and with a professional radio system which samples and records (both on downlink and internally on an SD card) battery voltage and currents every .1 second, they certainly show good performance, albeit with higher failure rate than NiCds or NiMhs.
I think parallel batteries have been mentioned earlier In some receivers I connect two LiIons to the receiver, (To create redundancy and a very secure power supply to a critical system, although I have never had a LiIon or LiPo failure in flight) one at each end of the receiver bus. One battery always seem to discharge considerably more than the other even though connected to the same bus without isolation.
Other receivers have a main and standby (with automatic switchover at a predefined voltage) for the redundancy but are never paralleled so the standby battery always stays fully charged.
Finally, someone queried whether the main battery could/should be used to start the APU on the 787. Isn't that one of its main functions ? I seem to remember frequently staring the APU on the ground on the 75 and 76 and in the event of double flameout and loss of both gens. in flight starting the APU from the battery would be a very high priority ! One might think that a main battery or separate APU batt should be able to do two or three APU starts with ease.
Anyway, I digress, back to the 787 !
P. S. I may have missed it but no one seems to have mentioned the electrical fire and emergency landing on a 787 during test work. Anyone know the cause of that fire?
Last edited by RetiredBA/BY; 13th Feb 2013 at 20:03.