All Gurus of Electric,

LiPo seem to come in 3.7 volt/cell ratings.

Now the question is that if we use multiple cell packs, does it not increase the weight? What is the advantage of going with multiple packs rather than increaing the cell per pack (i.e why 2x 2S and not 1x 4S)?


Pankaj

2x2s connected in series = 1x4s  (double the voltage with same mah/duration)
2x2s connected in parallel = 2x2s (same voltage double the mah/duration)

Which one did you mean ?

I was more concerned with the weight and cost.

Is the weight distribution linear ( 1x 4S = 2x 2S) and is it same for the cost?

Secondly, what about operating voltage? I mean most of the motors that look at say something like xxxx rpm /V, so does it have a cut off volt? I am sure at the battery discharges, there would be a drop in potential difference across the terminal.

Pankaj

The advantages of  using 2 packs in series  as against a single pack  is as follows :
1) In the event of a crash the chances of both packs getting damaged is less where as in the case of a single pack you would have to write off the whole pack so the replacement cost will be half
2) The flexibility of using the same packs for a lower voltage requirement eg 2 nos 3 S Lipos can be used  for the 6 S application as well as for 3 S application

These are the basic reasons for me using 2 packs in the case of any application beyond 3 S . In terms of  both cost and weight the difference is very very marginal as in case of a 6 S application whether it be 3S X 2 or 6 S the number of batteries in the  pack is the same 6 nos , hence it is only the weight of the wrapping and connectors that is extra.

Sai

Quote from: PankajC on August 04, 2009, 03:32:59 PM

I mean most of the motors that look at say something like xxxx rpm /V, so does it have a cut off volt? I am sure at the battery discharges, there would be a drop in potential difference across the terminal.

Pankaj

You will find either cell count or voltage mentioned against a motor , this is the nominal voltage .

Eg 11.1 V 3 S means the battery voltage at full charge will be around 12.6 V  and minimum discharge is 9 V .  hence  for 1000 rpm/v motor the  RPM will drop from around 11,500 rpm at peak charge  as the voltage of the pack drops .

Sai

Thanks Sai.... You are a truck load of information.