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July 07, 2020, 12:29:39 pm

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3.7v Li-ion as a battery replacement for 4 cell NiHm pack?

Started by firefox, November 19, 2019, 13:45:28 pm

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firefox

What are peoples views on replacing a 4 cell battery pack with a single 3.7v Li-ion

Have you done it?
Nothing is foolproof to a sufficiently talented fool......

PDR

The servo power drops dramatically and digital servos may refuse to work at all, but the major issue is that it's likely to risk frequent brown-outs from any microprocessor-based Rx (eg any 2.4GHz Rx).

A better bet is to use a pair of something like LiFe cells and a UBEC.

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

Chippie

As PDR, but perhaps an alternative, use a boost converter rathervthan a buck to lift the 3.7 ( 4.2 charged.....) to whatever....6-6.5 v.....
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Steve J

Some DLG flyers use single cell LiPos to power their models.

I am moving to 2S LiFe for my bigger models.

itsme

Old school here. Sub C nmh five cell packs are bomb proof. If it aint broke, dont try to fix it.

British Victory

Use 2 cell LiFe batteries without any gubbins, apart from the switch, between it and the radio, the only servos I have had problems with are very early (80s/90s in he last century) JR servos.
All new futaba rx and servos work with the batteries which give you the same output voltage as 5 cell NiMh or Nicads, probably slightly less when all are freshly charged.
there's only one f in RCMF,
               John

firefox

Quote from: Chippie on November 19, 2019, 15:30:45 pmAs PDR, but perhaps an alternative, use a boost converter rathervthan a buck to lift the 3.7 ( 4.2 charged.....) to whatever....6-6.5 v.....

That was my thoughts John.

PDF using 35 MHz so much of a problem.

Thanks
Nothing is foolproof to a sufficiently talented fool......

Phil_G

For smaller or slower models we do this all the time, for example most of my small IC models and gliders have a single cell with no boost converter. IMHO brownout is very unlikely, these cells have a very low ESR and are designed to give huge currents without voltage sag. Fresh off charge they sit around 4.1v and tend to stay high since the load of an R/C receiver and a few servos is so light, it wont tax the cell at all, and regardless of how you waggle the sticks a LiFe wont be sagging below 3.5v during a days flying.   I would even suggest that under load, the combination of a single cell plus a boost converter could be more likely to dip into brownout territory than a bare cell as the cell can give far more current than the converter. Analogue servos are slightly slower, but we dont generally find that a problem as modern servos are so fast to start with, of course if it is a concern then dont do it, but many of us have been running one cell for years  ;)

Cheers
Phil