Quote:
Originally Posted by ainarssems
Goran what voltage is your lithium battery and did you change or modify voltage regulator in alternator to provide higher voltage and allow batteries to fully charge. 12.8V(4x3.2V) lithium battery require 15V charge voltage, and if it 's higher voltage battery using 3.6V or 3.7V cells then would need even more charge voltage.
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Its LiFePo4 so nominal voltage I guess 3.2Vx4=12.8V. It usually sits at around 13.2V and that's probably 50% to 60% charge. I dont know what cells they used, big prismatic or lots of little Panasonic cells. If Panasonic cells they kind of limit my low cost replacement option if/when they need replacing.
Its a good question about the alternator and it worried me slightly. Voltphreaks website says it should put out a minimum of 14V which would theoretically charge each cell to 3.5V per cell, which should be fine.
http://www.voltphreaks.com/technologydir.php
In the video my alternator is outputting only 13.6V which would be too low.
However I kept an eye on the alternator, after a short drive it seems to build up the output to 14V or 14.1V so its just about ok. At some point I would like to clean up all the connectors between battery and alternator. At some point when I get round to it I would like to change or modify the voltage regulator in the alternator.
So far the system seems to be working ok, sometimes after a longer drive the battery holds as much as 13.4V so its getting a fairly good charge, and seems to be able to last 7 days without driving and hasn't triggered the Low Voltage cutoff yet.
You have a great idea for putting together your own battery much cheaper than the ready made ones. I'm not as confident with electronics
but I would like to give it a go in the future.
Quote:
Originally Posted by daviesbike
Could you use a lipo or is the balance charging an issue.. ? I'm sure you use lipo in your RC jet ?
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You can use lipos, as Ainars says they have a different chemistry and higher voltage so alternator may supply too low a charging voltage? You still need a balance/maintenance circuit similar to the one that comes with the LiFePo4 starter batteries currently available.
The advantage of lipo is power density, they can output much more current for the same capacity as LiFePo4. One of the downsides seems to be volatility (some people say), they seem to go into thermal runaway more easily. But this may be mostly due to the fact that they are used in more demanding conditions drawing high current on the very limit of the battery (like in RC jets).
Also I don't know how lipo compare in longevity, can LiFePo4 last for more cycles? I dont know.
I don't think they are cheaper either, if you look at Hobbyking for some of the cheapest ones, I think a 10Ah 3 cell is close to £100, the option Ainars posted for 20Ah LiFePo4 cells is a much better price and double the capacity.