I have read in various threads some things about LIPO batteries that confuses me.

E.g.
that if you use a battery with too little C-rating you can actually damage the ESC (and/or motor).

- Is this true?
- And if so, why is that?

I would have thought (as with NIMH) that if you use to small batteries, the truck just drives slower. But with no harm to any parts. But I have seen some manufactures writes xx C-rating is minimum for the given truck.

Also I have read, that a lower C-rated battery pack won't last for as long run time as a higher C-rated pack.

- I thought that C-rate told to what rate the battery pack could discharge its power. I.e. the "punch" of the battery pack?

Whereas mah rating (solely) would tell about run time. And if anything a lower C-rating will give longer run time, as the battery cannot give out its power so fast.

- Are there any good "understanding LIPO batteries, ESC and motors for dummies" links?

Kind regards
Jens
Denmark

http://www.hangtimes.com/redsbatteryclinic.html
http://www.batteryuniversity.com/
http://www.buchmann.ca/faq.asp

Rich

Hi

Thanks for the links.

I have gone through them, and I have read tons os other posts. But I haven't yet found an answer to the simple question.
If I in an ordinary setup (e.g. NIHM) uses a battery with too low volt or too low discharge capacity, the truck just runs slower. But nothing explodes.

From one of the threads I have read (http://www.ultimaterc.com/forums/sho...d.php?t=115264) it says:

"...[using] lipos rated for slower discharge rate will cause your system to overheat and cog. "

"...100Amps is not enough for out 130Amp motor! It will create heat, cogging, resistance, some more heat and so forth in a vicious circle. "

- Why is it, that a Lipo battery with too little discharge capacity will explode a system, rather than just run slow? What is the chemical explanation?

- What is that heat/coq. Typically the engine? The ESC? The battery?

And the last question is for the other way around.
- Is it always safe to use lipo battery packs with higher than needed discharge levels?

I would guess it is, and bying these makes it more possible it will suit future systems, have better charge rate, and have an extra spare for the diminishing punch of the pack over time.

But I have read of people who have made a discharge setup of their own with e.g. car lamps, telling that the systems gets too hot and is close to melts down socket and lamp.
It makes it sounds that, rather than the source (the lamp) "pulls" the power needed, LIPO packs "pushes" power to whatever source connected and can explode/melt/flame these down if they are not strong enough. This sounds weird to me - but is it the case?

Thanx

Technically yes. In your question there is a lot missing. First Battery is a power source like any other source unless you place a load no current flows. So it’s only the load that determines the current draw. Now batteries are rated in “C” in time to discharge at some current load. So they use this to rate current max. and current max may be destruction or over heating or made up “LOL”. BUT it is caused by the "ri" internal resistance of the battery.
Bottom line to low “C” overheat to high ”C” only weight an size.

Rich

Lipos are no different than other batteries when it comes to HOW it supplies power.

Batteries, including lipos, do not push, shove, or force power to your system. They are only a source of power that your system can draw from.

Think of your Lipo like a gas tank in your car.
MAHs are the size of the tank.
Discharge c rating is the size of the fuel line to the carburetor.

Your system only draws what it needs from the battery. The battery does not push power into your system. In the car analogy, it doesn't matter how much fuel the tank is holding, the engine will only draw what needs to run. As you press the accelerator the engine will draw more fuel. If the fuel line ( c rating ) is larger than it needs to be it makes no difference to the engine as long as it can supply what the engine wants.

If the fuel line ( c rating ) is to small the engine cannot get enough fuel to run properly.

As to your question weather too small a discharge c rating will damage your system?. I have never heard of that happening. If anything it can damage the battery, because it can't keep up with the demand.

Yes, things could be missing. I'm trying to understand :-)

Could you elaborate on "...too low “C” overheat..."

- What is it that overheat? (i guess the battery, but just to be sure).

- And then my specific question again -> Why does a low C cause overheat and not just slow running?

Thanx for a fine description.
It's just as you describe it, I would expect it to Work.

But I have seen more threads describing the problem of: " too small a discharge c rating will damage your system"
and it is the very technical reason for this to happen (on LIPO systems) that puzzles me and I would like to understand. As I otherwise understand it just as you describe it.

It seems richrd knows of the overheating/damaging issues. Perhaps he can elaborate.

Also see the "...100Amps is not enough for out 130Amp motor! It will create heat, cogging, resistance, some more heat and so forth in a vicious circle. "
above.

If others can - please add in.

(I have read tons of "understand lipo" threads to find the reason with no luck)

Iam beginning to see your question.
Batteries cannot damage your system. Only you can by incorrect gears, incorrect motor voltage, incorrect propping etc. These cause system to draw more current than system can tolerate. But if you draw more than "C" rating then the battery can not tolerate an it's going to fail.
So what we use is a wattmeter placed between battery and the system "esc" an measure this current an it tells the whole story then we can decide if battery is to weak or if excessive current to systems parts.
Rich

Thanx for your answer.

- What is the explanation as to why the battery will fail, as compared to NiHM system where it just runs slower ?

Starting the thread I have thought it would be due to some chemical/technical reasons for the LIPO batteries (if it is the case).

As said ri times current is watts ,,watts is heat and heat distroys battery. Larger "C" lower ri an less heat so higer current aka Faster

Current is heat, voltage isn't which leaves watts not really the heat answer as the voltage could be high making for higher watts but still having low current.
1V 100A will be very much hotter hotter than 100V 1A. but both have same Watts.
Low C ratings cause voltage ripples that causes the components in the esc to fail. Some esc's you can buy capacitor banks to fix this.

low current flow can damage electric motors,as they will overheat trying to work just as hard with less amps and or volts.too small of a battery or a weak battery cannot supply what is needed to keep up with load.especially with other accessories in the circuit causing amperage draw.

Hi,

this is the part that I do not understand.
" they will overheat trying to work just as hard with less amps and or volts". Well, I would think, the motor can only get as much power as the battery actually can supply. The battery has too less power, including insufficient power to overheat (the motor is capable for much more than the too small battery supplies).

If I put your argument a little on the edge, and you say "...will overheat with less amps and/or volts..." then it could also be said that the motor will overheat if you put on a AA 1,5v battery (less volt and amps). You will reply "no, no, of course not with such small battery", but basically that is the relation in your answer.

It is this answer that is often seen, but my mind simply doesn't accept it. (no offence, but I'm the type who would like to dig to the full answer when I put an interest to something...)
It could very well be, that the real reason ends up in the same correlation (too less powerpull a battery causes problems) but it must be for other reasons.

The real reason could very well be the voltage ripple as described in another thread.

Thanks man,

see, this is an explanation that makes sence. Now I'm at rest :-) I'll Google voltage ripple a bit.

One quick question:
- Is there any risk/problems, in too high c-ratings? For a given car.

For me I would think, buying an even higher (better) c-rated battery for my car, is good as
- it gives a reserve if it over time looses some punch
- can be charged quicker
- can keep up, if I later on upgrade motor and ESC

Downside would be higher price, but there will be a "sweat spot" where a bit better battery isn't more expensive than I would pay.

The lipo specs should exceed that of the esc. The esc specs should exceed that of the motor. But you have to stick with the acceptable voltage.
- eg. A pack capable of delivering 180A constant would suit an esc that can handle 150A and the motor 120A. Put it the other way around with the motor at 180A and the lipo at 120A and you'll have nothing but very bad things happening.

Don't be tricked by high price lipo's being quality, some have good warranties that are added in this price.
Get packs that are tried and tested by many users and happy with them,

C ratings are questionable, one companies 40C might be weaker than another companies 25C.
Personally if i was upgrading motor and esc later on i'd get new lipos and if the old ones are still good, sell them on.

Thanx, trax de max. Fine answer. And as expected.

My kids would say "I want to try also, dad", when I buy a car. I expect to buy something 4-6S that I run 4S. And the kids aren't ready yet for 4S speed/power. (E.g. Thunder Tiger MT4 G3, or the like - not sure which car yet)

So I thought i put in a 6 cell NIHM when they should try it out and learn. For slower speed.

- Would a 6 cell NIHM in a 4S-6S system give Voltage Ripple also?

- Does some ESC have training modes, where you can reduce the speed by direct programming (on the ESC, without PC and other deviced)?

I'm not to sure which have specific training modes. There is other settings that could help though.
6cell nimh is similar peak voltage as a 2s lipo. I'd stay with lipo than nimh, just becarefull of dropping the packs or knocking them about.
Pick an open field with no tree's or posts for the kids to try.

Actually, that's not directly so.
Available power is more to the point.
Consider this. An A/C or DC motor has a specification and rated referred to as "locked rotor".
This is the maximum power that the motor can consume, If maintained for longer than a very short time, the motor goes up in a cloud.
As the load decreases, and the applied voltage stays the same, generally, the current drops.
When a load increases, the current draw goes up. If the source of power cannot supply the need, then the voltage will drop.
The resulting current will be as much as the motor can draw from the source.
(There are motors that can "run away" under some of these conditions, but they aren't in common use, or are defective in a particular way.)
With the usual R/C motors and ESC's, it's more a case of having a motor sized properly for the load, supplied by an ESC that's correct for the motor,
and a battery capable of supplying the needed power. If the motor is undersized for the load, everything else being OK, it's the weak link.
More often, you might see an ESC fail. because it was over rated and undersized.
When Lipos fail catastrophically, and were not previously physically or electrically damaged, it's likely that they were exposed to an external condition, such as a shorted ESC, that caused
the failure. (Remember the 'Burst Rating")

How I tend to do things - -
The model requires a certain amount of power (Watts per pound)
The model has a limitation on propeller length due to clearances
Motors and propellers have RPM limits.
I start out with 10,000 RPM as the rule of thumb for the general type of models I have an interest in.
Cost and availability factors make 3 to 6 cell lipos the preferred range.
The KV rating of the motor and 10,000RPM can be used to determine the desired cell count.
Or the projected cell count and RPM can be used to determine the needed KV rating.
Finally, the propeller can be fine tuned in length and pitch to obtain the desired end result.

I usually use E-Calc (propeller calc) to get a reasonable approximation of the resutls, without the usual expensive trial an error
that might otherwise be needed.

It's worthy of note that some ESC's, such as many of the Castles, are actually under rated to some extent. Others, usually the "cheapies",
may be over rated. Motors can also follow a similar pattern. Batteries are in another similar situation, with a few added complications.
(A battery with a maximum "C" rating of 50C and leads/connectors that cannot carry the 50C current as an example.)
I had a 6C 5000mah battery that had the attached ESC catastrophically fail. The ESC had shorted out, and went up in a cloud.
The actual end of event failure was that the ESC to power lead solder joint melted on the ESC circuit board.
Normal peak current draw had previously been measured as 78A at full throttle in a static test.
The actual peak current at failure was unknown, but had to be, based upon the smoke and melted solder joints,
in excess of 150A. The ESC was rated at 80A continuous.