Does anyone see any red flags in using the following cheap bulk charger setup for a 12s3p Lipo 15ah (Using six Turnigy 6s1P 5000mah 20C packs)?
- 48V 20A server power supply with 20' of 17ga lamp cord to limit current
- CellLog8s to trigger a HVC device ("Improved simple auto disconnector for battery charging/testing" -- a DIY circuit in RC Groups: http://www.rcgroups.com/forums/showthread.php?t=1131817
Thanks for any fire alarms you can pull in advance,
(My wife made me write this after seeing lipo fires on youtube)
Honestly my friend if your using the Turnigy packs... yes I could see an issue.
At empty those packs will attempt to sink/source (damn I wish i could remember the right word, but you understand) as much current as they can. If your planning to attempt to charge less than 4 6S packs (connected via seperate cords) you will be pulling 20A through these lines - DC current (I recall you have to cut the rating by 1/2 when going from AC to DC conversion the scale for voltage - could be wrong).
Biggest issue I see is if your planning to actually use the little guage for current limiting, sure they will block a huge portion of current but that results in HEAT and will melt them if you just ran 20' of lamp cord to teh eBike. Good news it's only the lamp cord which will heat up and melt.
Given this knowledge - we need to look at the C rate:
5AH @ 20C (I think you mean the 20C/30C packs - slightly different, lower internal resistance)
That means in continuous discharge they can provide 100A (they will get warm at this level, hot even) and peaks for a few seconds of 30X5A 150A.
These packs recommend a charge rate of 1C so.. that is 1 x Capacity or 5AH however you seem to be wanting to charge all 6 6S packs so - the question is...
Will you be charging them all at once?
Here's the break down -
6P6S (what your charging in parallel mode) is actually 5Ax6 = 30AH Capacity so first there is no need to limit current for the safety of the LiPo.. that's 10A under 1C (which also means you could charge 4x6S in parallel for 1C charging.
If you planning on using a seperate lamp cord to each pack positive and negative, sure that would mean 6 lamp cords and each would only carry a portion of the current total. So if charging in 6P it would be 1/6th total current or 20 / 6 = 3.33 A per cord over 20' - should be okay (should I still wouldn't do it - too many individual wires, too small a guage and too long a run) - 18G cable gets warm after a while at 36vdc and 22A continuous and for the first 70% of the charge cycle your current will be similar but the voltage higher.
Consider lamp cord is rated for use with 100-150w lamps at 110v so (110 / 100) = 1.1A , this is not the limit but really I wouldn't use lamp cord... id use at a minimum 10 guage harness of less than 20'... if you need to run a charge cable from an outlet to the eBike or charging station - please use a 20A rated outdoor extension cord of 20' - the drop will be less and the wires are insulated better to prevent shorting or overheating.
If you can be more specific about how many of these packs you plan to charge at once... if you plan to parallel the balance taps durring the charge or just the discharge wires, etc... I can provide you with a much more accurate electrical requirement - be a bit more specific on the power supply type too... it may have adjustable current limiting internally (variable resistor pot) or ... you could limit/reduce the current by increasing the internal shunt resistance - there are many more ways you could do this which would be safer and more efficient (heat is always wasted energy).
Hope this helps,