[Gump]

Looking for information on lipo discharge rates as rated in 'C' of discharge.
I want to find out whats suitable for 10th scale 4wd specifically - is 20C for example, too low for a 10th 4wd? Any other information as it applies to other scales would also be great (18th, 16th, 10th, 8th, etc.).

Thanks.

[Gump]

Forgot to add that its for a mamba 5700, but I'm also interested in finding out whats suitable for everything from a 27turn brushed all the way to an 8000kv brushless and beyond.
Thanks again!

[Abiye]

thats a loaded question because it all depends on the capacity of the battery... for example a 15C 8000mah battery can supply 15x8 amps (120 amps)... a 20C 4800 can only supply 96amps... so its not just the "C" rating of the cells you need to look at... that being said the to determine what capacity and "C" rating lipo you should get, you only need to look at the maximum capacity of your esc... for example the mamba max has a 100amp continuous rating... it doesn't matter what motor you have hooked up to it the limiting factor is always the esc... its not to say that some motors won't draw more current than others but when choosing a battery you should always look at the esc...

[johnnyboy]

I run the Orion 4800's that are only 15C and have never had a problem in my 4wd running a 5.5.

[Narly1]

OK would you guys then agree that you could also take the wattage rating of the motor and then divide that figure by the pack voltage to get the average motor current drawn?

For instance a Novak Velociti 3.5R is spec'd at 620 watts, divided by 8.4 volts = 73.8 A

Thus a 20C/3800 (76A) pack would be right on the ragged edge which sounds about right to me......right?

Narly1

[imported_Aqwut]

Honestly, the best thing for lipos is to get the high Continuous discharge rating as possible(whatever you can afford)...

But SS_maradona is right.... An IB 4200 Pack is about 15 or 18C continuous... so that's around 74 Amps discharge rate Continuously... When/If you're running a brushless motor....
let's say for example.. the MM 5700 motor on 2S, it would draw about..60Amps... if using the same motor with 3S would draw more amps.. about 80-90 Amps...

So get the best you can afford when buying Lipos because the lipo will last longer, and would almost never get warm...

And the MambaMax setup is able to draw more than 130Amps @ peak.... especially when using the higher KV (hot motors)...

best thing to get is a power analyzer.... or an A/C Amp meter...

but look at the total power of the setup.. in wattage.. and divide by voltage... that is just a simple way to see what Kinda of Amperage the motor/ESC can pull.... but also depends on your gearing...

Am I making any sense.. I'm gettin' confused myself.. there are so many answers for your question bro...

first step is to see how many amps your setup draws... then you can go from there..

High powered brushless setups, let's say over 1500 watts...
requires good quality batteries, or you could get a lot of cogging and major voltage drops/spikes....

usually the higher the C rating... let's say 20, 25, 30C.. the less the voltage drops at load...

[Narly1]

Originally Posted by Aqwut

best thing to get is a power analyzer.... or an A/C Amp meter...

first step is to see how many amps your setup draws... then you can go from there..

I found this gem of an article a while back:

http://www.rcgroups.com/forums/showthread.php?t=393591

If you had a meter with a "peak hold" function, I think it would be possible to blip the throttle and take a peak reading without overheating the shunt excessively and degrading its accuracy.

Originally Posted by Aqwut

but look at the total power of the setup.. in wattage.. and divide by voltage... that is just a simple way to see what Kinda of Amperage the motor/ESC can pull.... but also depends on your gearing...

So you agree with what I posted earlier in this thread re calculating amp draw, right?

Narly1

[imported_offroader]

I picked up one of these great meters tells you everything you need to know. You can install it and run your BL it will show your max peaks. Nice little meter easy to use for testing.

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=014

Product Key Features


Measures energy (Wh), charge (Ah), power (W), current (A) and voltage (V) for any rechargeable battery pack from 4 - 60V, including NiCd, NiMH , and SLA, and Li-Ion battery packs
Connector to use a receiver battery for measurement down to 0 V
Captures current peaks and voltage minimums(droops)
Accurate & precise - 0.01 A current and 0.01 V voltage resolutions
Rugged - handles 50 A continuous and 100 A peak at 60 V 14 ga., 7 x 37 stranded, high temp silicone rubber insulated wire without connectors
Small & Light: 2.8" long x 1.7" wide x 0.83" thick (70 mm x 44 mm x 21 mm), 2.5 oz.
Acts like a wire so doesn't affect model's performance. Precision current sensing resistor, with only 0.001 Ohm resistance and circuitry only draws 0.007 Amps
Uses DSP to increase ADC resolution and differential measurement amplifiers to increase noise immunity Factory calibration stores constants in EEPROM to compensate for component tolerances
One Year Warranty
Complete User Manual

Specifications:

Voltage 0-60 V, resolution 0.01 V. That's a 14 cell series li-poly pack!
Current 0-100 A peak, 50 A continuous, resolution 0.01 A
Charge 0-65 Ah, resolution 0.001 Ah. That's ~32 Amps for two hours!
Power 0-6500 W, resolution 0.1 W. That's ~8.7 Horsepower!
Energy 0-6500 Wh, resolution 0.1 Wh. That's lifting a 50 pound model into outer space (65 mi.)!
Operates from 4.0-60 V, 0 V with optional receiver battery pack
16 x 2 STN LCD display
Powerful, 8 MIPS micro-controlle
Color: Electric blue
Version 2

Applications:

Specially designed for RC Battery Packs to help you:

Set speed control cutoff voltages and currents
Tune performance by comparing different setups of propeller, motor, gearing, speed control and battery
Measure a full battery charge and compare to spec when charger claims done
Check peak currents are safe for battery, speed control, motor, wiring and connectors
Predict airplane flight time based on ACTUAL conditions in your model
Check battery capacity and health and whether battery should be retired
Verify that the minimum voltage under load is within specifications
Check for wiring and connector power losses.
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Combine the power analyzer together with our 2.4V - 7.2V, 7.2V - 12V, 24V NiMH universal smart chargers , and with 3.6V - 14.8V Li-Ion battery charger It is perfect tool to monitor battery pack's performance

[imported_Aqwut]

Originally Posted by Narly1

OK would you guys then agree that you could also take the wattage rating of the motor and then divide that figure by the pack voltage to get the average motor current drawn?

For instance a Novak Velociti 3.5R is spec'd at 620 watts, divided by 8.4 volts = 73.8 A

Thus a 20C/3800 (76A) pack would be right on the ragged edge which sounds about right to me......right?

Narly1

Absolutely, the concept is right... the motor is able to handle that load for 6 minutes, according to novak.... but it's kind of confusing...

* 8.4 Volts, it would draw more Amps than it would @ 7.2 Volts...

you can't always do watts/voltage... there are more to factor into this calculation but I'm not really sure...

.. That watt meter is good to use... just hold ur car, in a still position, and give it throttle from 0 - 100.. and keep an eye on the meter...

something like this, back in the summer... I just used an A/C Amp Meter, and put it around one of the 3 wires from the esc to motor...

http://us.share.geocities.com/aqwut/...EST2NDGEAR.WMV

I think the highest amp draw I read was almost 83 Amps... with 24 Cells NiMH IB4200... that's the most that battery would pump out... And that's using a Pop Can sized motor that is able to draw more than 300 Amps... I know, I know.. the answer is confusing.... but it's hard to explain without a WattMeter... Feigao makes one as well...

You'd also have to factor in the efficiency of the motor..... (for example, efficiency is not the greatest with that hot 3.5R motor)...
And you'd also have to factor in the rpms... it's hard to find what rpms brushless motors run best at.. "most run best around 35-45K"....

Lehner motoren has a nice Excel sheet for their motors.. they have test results of their motors @ different voltages/amps and when they are most efficient... if you guys take a lot, you will see why high voltage setups are the most efficient...

1950/11T @ 27 Volts.. http://www.lehner-motoren.com/motord...950-11.27V.xls
versus.
1950/11T @ 34 Volts.. http://www.lehner-motoren.com/motord...950-11.34V.xls

if you look @ the Excel sheets you will notice that the efficiency are best when the batteries are @ their peak voltage.. that is why it is a good idea to get the best battery that you can afford..

when buying Lipos.. you need good quality... lets for .. if we compared my PolyQuest 11.1V 3S 3700 mah 25C lipos vs MaxAmps 11.1V 3S 5000 mAh 20C.

just an example...

PQ pack is able to output 92.5 Amps continuous..
MaxAmps pack is able to output 100 Amps continuous..


but at 92.5 Amp load...the Polyquest may hold a voltage of 3.5 Volts per cell...
where as the MaxAmps would probably drop down to 3.0 Volts per cell....

so PQ would output (10.5 Volts * 92.5 Amps) = 944 Watts
and MA would output (9.0 Volts * 100 Amps) = 900 Watts

big difference from quality... Does make any sense..

Oh yes, and buy the way if you guys are running MaxAmps packs.. disregard their continuous "C" rating... they don't perform as well as their specs .... where as Hyperion, Flightpower, PolyQuest, Neu.. these manufacters performance exceeds their posted specs...

[Narly1]

Originally Posted by Aqwut

* 8.4 Volts, it would draw more Amps than it would @ 7.2 Volts...

you can't always do watts/voltage... there are more to factor into this calculation but I'm not really sure...

Sounds to me like Novak's wattage spec is only a "guideline". Maybe it's the max you can expect one of their motors to draw? Who knows. At any rate it's good enough for me to make a rough calculation as to whether I have enough battery or not. Call me conservative but I think I would add 20% to be on the safe side.

Intuitively the difference in amp draw at various battery voltages makes sense as P= V*2/R and if R stays the same well then P just has to go up.

Now I realize that "R" is not going to be a fixed value in a brushless motor application, but I think that it's safe to say that it doesn't change a lot.

I suspect that the main factors affecting the value of "R" are RPM (and thus efficiency) and motor temperature.

Originally Posted by Aqwut

I just used an A/C Amp Meter, and put it around one of the 3 wires from the esc to motor...

I also read somewhere that using an Clamp-on AC Ammeter isn't very accurate for a whole bunch of reasons, mainly that the current going to the brushless motor is not sineusoidal......

Also thanks for the heads-up on the various battery manufacturers claimed "C" ratings. Might save some costly mistakes!

narly1