NoGuts_NoGlory

My Feedback: (41)

Are there any issues when using a dual battery setup ( 2 packs, two switches) but using different capacity packs (same voltage)?
Thanks,
Howard

Red Baron Gary

My Feedback: (59)

Yes. You will discharge the lower capacity battery first leaving you with a much lower working voltage.
Capacities must match, but C ratings do not need to as long as the lowest C rating is not exceeded.
Gary

JustPlaneSweet

Not a problem - [link=http://www.hangtimes.com/id33.html]Red's RC Battery Clinic[/link]

Stan

rcairflr

My Feedback: (44)

This information is just plain wrong. I used 2 different capacity Nimh batteries for 2 years until I switched to A123. My experience is that the higher capicity battery discharges at
a faster rate than the lower capacity battery (this makes sense, since the receriver is going to pull the most current from the battery with the highest voltage). A good rule of thumb when doing this is, use the same chemistry battery, same voltage and the internal resistance of the twe batteries should be close.
For example, you will not see as good of results if one battery is 25m Ohm internal resistance and the other is 5m Ohm.

As a percentage of capacity of the battery packs I used, both batteries recharged the same. For example, the larger battery was 2000mA and the smaller battery was 1500mA. After a day of flying I would
have to recharge the larger pack about 500mA and the smaller pack about 350mA.

NoGuts_NoGlory

My Feedback: (41)

Thanks for everyone's input!
Howard

Red Baron Gary

My Feedback: (59)

My gaff !! I was thinking about Lipo's
Gary

ScottMcM

My Feedback: (66)

http://www.smart-fly.com/Products/BatShare/batshare.htm

Rodney

Also wrong for LiPo's. As long as the number of cells in each battery is the same and they are of the same chemical makeup, you can mix any size and all will discharge to equal voltages.

Red Baron Gary

My Feedback: (59)

Took a look at page 33 of my Great Planes Zlin manual. Quoting: "Never connect battery packs with different capacities in series or parallel." Pic shows each batt having same voltage. (cell count)

Also shown is two packs (one 3s one 2s) in series, same capacity for use as a 5s equivlent battery. Quoting: "Its oaky to connect batteries with diffente votlages in series to achieve the new, desired voltage."

This wasin reference to matching/mating LiPo's.


Gary

rcairflr

My Feedback: (44)

Gary, you need to get your facts straight and quote proper sources. Page 33 of your Zlin manual is talking about hooking up electric motors not receiver batteries and the picture looks like it is through a Y connection. Doing that would be an issue during charging. As I said above, I did this for 2 years on my giant scale Extra 260 with absolutely no issues. I have also read on FG website of other people doing this with the same results as me. Also, below is from the Hangtime hobbies website, batteries are his business.


: Can I run packs of different size in parallel?



A: Yes.. if by size you mean ‘capacity’. Remember; battery packs are rated in three ways.. capacity, impedance and voltage. In a parallel system the number of cells in the 2 packs should be the same, and we recommend you use packs with similar impedance ratings but the capacity (milliamps) rating can be different.

Rodney

The batteries can even have very different impedance characteristics with no problems being caused by the impedance differences.

Mikecam

Not required, something else to fail.

http://www.hangtimes.com/id33.html

Red Baron Gary

My Feedback: (59)

Again I have overlooked the obvious. The discusison was about RECEIVER batteries. Ther's nothing else I can say but thanks for setting me (and the hints) straight.
Very much embarrassed I am, Gary [][X(]