How to use Li-XX batteries with standard receivers?

That's a good point. ~20% of the overall poweroutput of the battery is wasted (dissipated as heat). I think this is acceptable. Please note, that a switching voltage converter also gives some power loss (albeit probably not as much as 20%). Given the very low weight of the diode-based solution, I guess you can afford to have a slightly larger battery to compensate for the loss of battery time compared to a switching device.

How many/how big are the servo's Dirk?
If tiny/not many take a look at the hobby king step up
Device which allows use of one of the 130mah 1s lipo's
Very very low weight solution.
Or poss a small 2s with a small ESC instead of an expensive and
Heavier Regulator.
Or if you're say .40 sized and above (IMHO) the Powerbox
Digiswitch is unbeatable/ not cheap though.

Oh oh just read the whole thread.....
As for cost I bet you spent an hour with the
Soldering iron. Even at minimum wage thats
10 bucks of your time.

A possibly dumb question from someone with admitted ignorance of this subject:

Is the voltage of a Lipo battery dictated by it's internal workings, or were they engineered to match some industry standard? If the second part is true, is it then possible we might see a company step up with "plug-and-play" voltages from these batteries?

Already done Kim, Futaba and Hitec already produce hi voltage
Servo's with JR in hot pursuit. However they are v v ah say v
Expensive.

There are pro's and cons with everything of course.....
Lipo's REALLY don't like the cold I haven't flown my biggie
For a few weeks cos it has lipo's in it.
To give an indication... Yesterday we had max temp of 3 celcius
And my little glow stuff with nimh batts flew like they always do..
My foamy 3s yak flew ok while I had the lipo's warming on
Heater vent of car but as soon as batts were out doors for more
Than 10 mins they didn't want to work.

Dirk in my Bacaruda (2 hs50's) I have a 120mah nmih batt
It weighs 8 grams.

John Goddard wrote:Oh oh just read the whole thread.....
As for cost I bet you spent an hour with the
Soldering iron. Even at minimum wage thats
10 bucks of your time.

I guess minimum wage over at London is a bit different than down here
Actually, the whole thing took me 10 mins, and that includes taking pictures while I was on it.

Kim wrote:Is the voltage of a Lipo battery dictated by it's internal workings, or were they engineered to match some industry standard? If the second part is true, is it then possible we might see a company step up with "plug-and-play" voltages from these batteries?

Keep in mind that this comes from someone who is admittedly ignorant on almost all subjects.

Battery voltages were generally set based on industry need rather than by the physics and chemistry associated with battery design. For example, my first R/C Tx required a 90v cell to drive the vacuum tube filaments.

I believe the original specifications for the nickle based cells, NiCd and NiMH, were set by industrial, military and aviation standards. The original voltage was 1.25, but most nominal voltages quoted today for these cells is 1.2v. When the lithium technology came on the scene, nominal cell voltage was set to 3.6v or an equivalent of three nickle based cells in a series. The 3.7v rating of LiPo's is really more related to advertising hype (i.e., higher watt-hours) and, to some extent, tied to looking at the average voltage from discharge curves of the different lithium types. The lithium cells are all rated at 4.2v fully charged and 3.0v at a safe discharge voltage. Depending on how flat the discharge curve remains when loaded at .5C from a full charge 4.2v down to 3.0v, average cell voltages may vary from 3.6v to 3.8v for differing lithium chemistries. LiPo averages 3.7v.

I doubt that the R/C communitity can generate sufficient buying power to move the manufacturers away from the industry standard.

Actually, the voltage of a single cell of any given type is dictated by how "far away" electrochemically speaking, are the materials of the two electrodes from each other. How many cells are put together might be an industry standard, for example, you can find the regular alkaline batteries with 1.5, 4.5 or 9V (corresponding to 1, 3 and 6 cells, respectively). But you can't make a LiPol that is 2.4 or 4.8V, it will always be 3.7.

What could happen, is manufacturers could come up with 3.7V receivers and servos (I guess it is actually happening, to some degree at least).

re. servo lead colors: something doesn't look right. Red is positive, black or brown is negative (ground) and yellow, orange or white is normally the servo signal lead. It looks like your loom would be feeding battery positive to a receiver signal pin. Or am I missing something?

ahrma_581 wrote:It looks like your loom would be feeding battery positive to a receiver signal pin. Or am I missing something?

You're correct. I'm not aware of any major manufacturer that splits Rx power with the signal wire in the middle. The colors used are for JR -- and as you noted, brown is negative, red is positive. If he is plugging into an additional loom, then it may be adjusted there; if it is plugged into a typical Rx, then it could be problematic.

You guys are right, I messed up the wiring. Corrected now.
Btw, I gave it a run and it seems to work without any problems.

When LiPo's hit the market with high power/weight ratios, flat discharge curves and high capacities, I started looking at means to use them in my smaller planes. I had already switched to NiMH from NiCd's, but most available smart chargers did not have low enough charge rates to form charge the smaller batteries, so I ended up building a constant current charger which worked pretty well. The other problem with NiMH's is the high self-discharge rate, so unless I topped off the night before, a spur of the moment trip to the field could be dicey. LiPo's have a low self-discharge rate, can be easily balanced with smart chargers and are not as finicky about initial charge cycles as NiMH.

I found out several things. Many of the smaller servos have higher stall currents and higher operating currents than the standard sized servos. Secondly, a lot of the sub-micro servos don't run on 6v --- however, with the advent of spread spectrum, this seems to be slowly changing.

There are 3 DIY options available for handling voltage regulation.

1) Use a series of diodes to drop voltage. Simple, but ...... A fully charged 2s LiPo will meter 8.4v. With two diodes, you've got 7 volts out and a 4.8v servo may end up being toast. Secondly, output voltage is directly related to battery voltage. If you use 3 diodes to force down voltage, a nearly discharged LiPo running at 6v will have an output of 3.9v which can cause a reset of some of the 2.4 GHz Rx.
Should you choose to use diodes, I would suggest something like a 1N5400 or 1N5401 rated at 3A continuous. All the 1N400x series are rated for 1A --- the only difference is peak reverse voltage rating.

2) Switching voltage regulators are efficient, but a little more expensive. Secondly, the component count for the circuitry is higher than for fixed linear regulators. If it weren't for the needed components (many require an inductor) and higher cost, I would use these.

3) LDO fixed linear regulators. This is my choice. They are not quite as efficient as switching regulators, but they are inexpensive and have a minimal component count to be used -- available with a 3A 5v rating. With an LDO, you can maintain 5v constant output at 3A down to about 6.3v input (5.5v for a Fairchild chip).

Dunno how many servo's you guys get thru
I tend to use quite a few.....
The only one's that (in my experience) are a
6v no no are Jr even their 200 buck ones
Don't ask how I know.....
As for Nimh self discharge get Sanyo eneloop
Cells cos they do NOT discharge, again little
More expensive but no problems in life
Only solutions

Ps
Perhaps this needs a thread of it's own but......
Even on my tiny stuff (ie the peewee'd
Bacaruda) are all ball linked.
Which helps not stall servo's. Bit surprised they
Don't seem to have caught on in the C/l world either
But I guess control slop isn't an issue for those Guys.
You'll notice 2 things,-
1 more accurate control.
2 your batteries need less charging cos
The servos aren't struggling and drawing more current.

Give them a try you'll never use a z bend ever again.

John, this plane is actually called "Bacaruda", not "Barracuda"? I can't find it on google, can you please show me how it looks like?

Hi Dirk
Sorry about confusion the story went a little like ........



It's an FMK Models Mini Rainbow which as you can see I first had an 010 in.
After beer one Evening I drew the P40 type teeth on...

A few days later there was a 'muscle car' thread on here where one of the guys mentioned Plymouth

which prompted me to,-



That's where the Bacaruda da da legend was born.