Newbie Lipo questions

[croninkyle124]

Can anyone answer any of my basic questions about Lipo battery's, or give me a link to where I can find a beginners tutorial or forum on Lipo's. I am trying to decide which battery to buy for my trex but have no idea what most of the terminology means...so,

1)What is the effect of using higher or lower voltage packs for example a 7.4V, 11.1V, 14.8V 18.5V
pack, and can too high a voltage damage my electronics?

2)What is meant by the "mAH" and again could it possibly damage my electronics if I have to much mAh?

3)What do terms suvh as 2S2P, 3S1P, 5S2P ect refer to?

4)What does the "c rating" describe and what is meant by 15C to 20C bursts?

5)What difference performance difference does the does the apm make, for examplewhen comparing a 30amp 2500mah 7.4 volt pack with a 26.4 amp 2220mah 7.4 volt pack?

6)How does the amount of cells connected in series and the amount of packs connected in parallel effect aspects like voltage, c rating, mAH and flight time?

7)What is the correlation between the ESC Amp (10A,25A,30A ect) and the amount of cells in the pack, voltage, c rating ect?

8)What is the correlation between the motor Kv rating (2500Kv,2800Kv,3200Kv ect) and the amount of cells in the pack, voltage, c rating ect?

9)Finally what would be a recommend battery configuration for a tex with an Align 35A and AON Power House 3500 Brushless Motor? I am more focused on having longer flight times than power or lightness for 3d flying.

[Coolice]

Hey,

I'll have a good go answering all of them for you.

1. Higher voltage, like higher nitro in IC means you will have a higher head speed. Most electric motors power figures are rated by a Kv figure, this equates to how many RPM's the motor will produce for a given amount of voltage put into it. The higher the voltage then going to the motor the more RPM it will give out.

If you try to push to much voltage through an electronic speed controller or motor that isn't capable of that voltage rating then yes, you can and will damage something or it will go bang.
Normally in this situation the motor & ESC will get very hot, left in this state they will then give up. This is where good information about the various components come in and checking first that all your parts will work with one another ok.

2. Mah is different to above, liken this to the size of a fuel tank in an IC machine or in your car. The greater the Mah the longer you can fly for between charges.

This figure will not kill electronics like the above over voltage scenario, but with the increased flight time comes the need to monitor components in case they get to hot with little air flow around them.
Take for instance the small electric indoor models with LiPo batterys, if they are flying for to long the small motors get quite hot as they are worked hard. In this case in a 20 minute flight you are advised to land after 10 minutes, allow things to cool off and then fly the last 10.

3. These figures refer to the layout/configuration of the LiPo.
2s2p = 2 cells / 2 parallel. The two cells tells us this pack will be a 7.4 volt pack, the 2 parallel means there are another 2 cells wired in parallel effectively doubling their capacity for the same output voltage.
In effect there will be four cells, but there will be two pairs.

3s1p = 3 cells / 1 parallel. 3 cells means a pack of 11.1 volts, with one in parallel so if each cell was 1000mah thats all the pack would be.
Now if it was 2p then that would be 1000 x 2 = 2000mah.

4. The C rating refers to the amount of power that can be drawn out of the pack while flying or put back into the battery through charging.

A 1000mah pack capable of 20c continous discharge = 1000 x 20 = 50. Hence 50 amps can be drawn out of this pack continously during flight without effecting it to much. The lower the current draw during flight the longer life span the pack will have and give many more flights before it's performance drops away.

Current "Burst" is figure given to a batterys performance for a short while, eg. during a high pitch climb, again without effecting it's life span to much. If you kept drawing this burst figure from the pack during a flight though you will greatly reduce the batterys life span in doing so, hence why it is important to buy a battery up to flying the machine you have so you are not wasting money.

5. This figure doesn't really make much difference, unless you were going to use the battery in a high load environment like a 3D heli. In this case the higher C rating would be better as the pack would be more up to supplying the loads.
Having said that it all depends on the heli's setup as to if you'd even pull the kind of currents that would overload it.

Remember it's the packs Mah that dictates duration and voltage that effects performance.

6. Series & parallel change the configuration of the pack somewhat. I learnt a lot about series & parallel from install car stereos, amplifiers & speakers as these terms were used to extract the best out of the system for a given power.

Series :

2 volt cell ~ 2 volt cell = 4 volts output
2 volt cell (1000mah) ~ 2 volt cell (1000mah) ~ 2 volt cell (1000mah) = 8 volts (1000 mah)

Parallel :

|2 volt cell | (1000mah)
|2 volt cell | (1000mah) } = 2 volts

The Mah will be doubled as they are wired in parallel (2000mah)

7. This figure on an ESC refers to the amount of constant current draw the ESC can handle without problems. To low a rating fitted to a model capable of drawing more amps than the ESC is rated at will generate a lot of excess heat and the controller will not last long of shut down due to it's own internal current protection circuitry.

8. See answer 1 above as that explains the relationship between motor Kv and battery voltage. The batterys MAH has no bearing on a motors output RPM just for how long it will run for.

9. For the Trex battery wise it's got to be 3s1p 11.1 volts. I have two in my club one use's an 1800mah pack which is a little lighter for 3D flying but lasts less than the others guys running a 2500mah pack which is obviously heavier.

For yourself I'd go with the 2500mah for hovering as you will get 10+ minutes with this easily I am sure.

http://www.flightpower.co.uk/core/datasheets/EVO20_Data_3s1p2500.htm

Hope this helps?
.

[WayneBrown]

Well, there's a lot of questions, so theres gonna be a lot of answers:
1)What is the effect of using higher or lower voltage packs for example a 7.4V, 11.1V, 14.8V 18.5V
pack, and can too high a voltage damage my electronics?

Higher voltage generally means less amperage required for the same amount of power. For instance, your 100W lightbulb is rated at 100W @115 volts. If it could operate at 220v, it would only require 50W for the same brightness.
You absolutely have to stay within the voltage range specified by the manufacturer of both the ESC and motor or fry your gear.
2)What is meant by the "mAH" and again could it possibly damage my electronics if I have to much mAh?
milliAmp-hours(ampere) (mAh) is basically how much energy can be stored in a battery and is rated at a specific amount of drain over an hour to set a standard. This has zero affect on voltage.
3)What do terms suvh as 2S2P, 3S1P, 5S2P ect refer to?
example: 2s2p; 2 cells SERIES 2 cells PARALLEL. Each Li-Poly cell is 3.6v x rated mAh, to increase capacity more cells in parallel, to increase voltage more cells in series.
4)What does the "c rating" describe and what is meant by 15C to 20C bursts? C is a standard used to determine the rate of charge, or discharge of a battery at a safe level without damaging the cell.
Suffice it to say the higher C rating, the more useful the battery will be.
5)What difference performance difference does the does the apm make, for examplewhen comparing a 30amp 2500mah 7.4 volt pack with a 26.4 amp 2220mah 7.4 volt pack? This one is a bit harder, we aren't comparing apples to apples. the 'AMP' rating is actually the 'C' rating, and there is a difference in that the higher 'C' pack will discharge more aggressily without damage to the pack. The mAh rating means the larger number will also have more duration.
6)How does the amount of cells connected in series and the amount of packs connected in parallel effect aspects like voltage, c rating, mAH and flight time? mAh and C rating are a fixed value. Adding packs in parallel will increase your total capacity multiplied by the given mAh of the packs used, ie; 3 cells rated at 1000 mAh in parallel nets 3000mAh. In this instance the voltage remains that of the cells (3.6v) ((1S3P))
7)What is the correlation between the ESC Amp (10A,25A,30A ect) and the amount of cells in the pack, voltage, c rating ect?
None. The manufacturer of the ESC states the unit will work within a given voltage range.
8)What is the correlation between the motor Kv rating (2500Kv,2800Kv,3200Kv ect) and the amount of cells in the pack, voltage, c rating ect? Again the manufacturer will state a range of acceptable voltages and maximum amperage the unit can handle reliably. Rule of thumb= more voltage, less amperage for the same power.
9)Finally what would be a recommend battery configuration for a tex with an Align 35A and AON Power House 3500 Brushless Motor? I am more focused on having longer flight times than power or lightness for 3d flying. The trex was designed around a 3S2P 2100 mAh pack.
You are pretty limited to the physical dimensions of the frames also. A quality pack of 10C will fly the chopper. this is a case of more os better, get the highest C rating you can and still maintain the physical dimensions or the battery wont fit the frames.
To make it easier, go for the Align 3s1p 2100's for budget, or TP 3s1p 2100's for more grunt.

All this before coffee.. whoa! :shock:

[croninkyle124]

Wow! thanks alot for the help guys this is some good stuff :drool:
I have been googling my ass of for hours trying to get some simple answers but all the lingo just went over my head. This pretty much answers everything i was confused about

So just to clarify if i have this configuration:

My motor supports:
Input voltage: 7.4~14.8v
Max Continuous current: 25A
KV Value: 3200KV

My ESC Supports:
Input voltage: 5.5V~16.8V
Continuous current: 25Amps
Surge current: 35Amps

This is telling me that that to avoid damaging my components i can have no more than 4 cells in my battery pack (since 3.6v*4=14.2v, just bellow the motor maximum) and can have no less than 2 (since 3.6v*1 does not meet the minnimum requirement).
Say i went with the 4s1p, if i wanted more oopmh for 3d flying my only option would be to go for higher discharge cells 'c rating' since my voltage is already maxed out...But i can compensate for the flight time by having as many 4cell packs in series as i want..Is this correct?

Also you say that "Too low a rating fitted to a model capable of drawing more amps than the ESC is rated at will generate a lot of excess heat and the controller will not last long of shut down due to it's own internal current protection circuitry".
So would it make sense that if my motor can draw a max continuous current of 25A, instead of matching it with a 25A ESC i could use a 30A or 35A ESC, to reduce the amount of heat generated? (Because the ESC is not working close to max current draw when the motor is running at max 25A)

[WayneBrown]

In theory, going with a 35A ESC will work, but the real deal on how many amps a given product will use is the setup you choose. You can force a 35 AMP ESC to overcurrent even with a 3200kv motor by having too much pitch..

[WillJames]

In theory, going with a 35A ESC will work, but the real deal on how many amps a given product will use is the setup you choose. You can force a 35 AMP ESC to overcurrent even with a 3200kv motor by having too much pitch..



Same with pinion selection. You can take the same setup and dramatically change how hard it is on teh motor and packs by your chioce of pinion.

[WayneBrown]

In theory, going with a 35A ESC will work, but the real deal on how many amps a given product will use is the setup you choose. You can force a 35 AMP ESC to overcurrent even with a 3200kv motor by having too much pitch..



Same with pinion selection. You can take the same setup and dramatically change how hard it is on teh motor and packs by your chioce of pinion.
uh...yeah, forgot about that.. the pinion thingy too!
;)

[croninkyle124]

so is it higher pinion (15T) or lower pinion (8T) is harder onthe motor?

[PaulH]

It depends on what you're trying to accomplish. A taller pinion will allow the motor to spin slower and acheive a higher head speed, but at the expense of a higher current draw. A shorter pinion will allow the motor to rev higher for a lower head speed, a lower current draw, and possibly longer flight times, but you won't be able to 3D it as much because of the low head speed.

The answer to this depends on the type of flying you do, the kV rating of the motor, how many cells (3S or 4S) you intend to use, and the headspeed that you would like to maintain.

So to answer your question, either the 8T or the 15T pinion could be hard on your motor, but it depends on other factors too, not just the pinion or the motor.

[theturd]

First few things that are important to any Heli are;
(1) Headspeed
(2) Torq at the above headspeed
(3) Pinion/Spur combination that will provide max use of (1) & (2), opinions will differ on which is important
(4) Make certain that the current draw of (1), (2) & (3) is within the ability of the ESC and Battery pack.

Since you mentioned AON 2815-3500 motor, then I would recommend using 11T pinion of max efficiency in time and performance. If you wish to increase the performance, then increase the headspeed from 2800 to 3000 by going to 13T pinion. However you will now loose flying time, because you will draw more current.

So start with 11T, and see how you like it.


Peace,
Steven Chao,
AON Electric