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lipo usage time

Old 01-07-2012, 06:47 PM
  #1  
mrbicknell
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Default lipo usage time

Hey guy's, I am trying to work out a good usage time for my lipos. I know how to work it out if I know what amps the motor is pulling, but I have a few models with old brushed motors which i don not know the amps. How can I work out a flight time?

Thanks
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Old 01-07-2012, 07:08 PM
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quorneng
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You really must invest in a meter to actually measure the current draw.
If you consider the cost of replacing a LiPo damaged by over discharging (or for that matter the ESC and motor by over loading) it is a sound investment.
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Old 01-07-2012, 07:16 PM
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mrbicknell
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yeah, I am new to all this and my dad only ever flew nitro stuff. I shall look for a meter. Silly question, how do I use one, like a volt meter I guess, but how do I use it to measure the amps being drawn?

Thanks
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Old 01-07-2012, 07:44 PM
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dumo01
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The watt meters go in line between your battery and ESC. They measure voltage applied from the battery and current draw, display volts amps and calculated watts.
You can also get different type of meter that is a clamp around one of the wires between the battery and ESC that will measure current. Little different set up to do the same thing, but not as dedicated

http://www.sears.com/craftsman-digit...p-03482369000P
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Old 01-07-2012, 08:02 PM
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mrbicknell
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ok cheers, I will try and find one
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Old 01-13-2012, 08:58 AM
  #6  
solentlife
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Ebay .... Hobby King .... Local Hobby Shop ?

It's a common item and called by the generic term : Wattmeter

I use mine every day to check LiPo's charge and usage ... balance etc.

With new set-up out of interest - I run up to check amps and watts ...

For about $30 ... it's a good tool.
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Old 01-13-2012, 02:18 PM
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whitecrest
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Originally Posted by mrbicknell View Post
. . . how do I use one, like a volt meter I guess, but how do I use it to measure the amps being drawn?

Thanks
Here's an illustration using an inexpensive DVM that are widely available:
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Old 01-13-2012, 07:48 PM
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mrbicknell
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yeah, I'm sure I have one of those, I will check it out, Thanks
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Old 01-13-2012, 10:25 PM
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kyleservicetech
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Originally Posted by mrbicknell View Post
yeah, I am new to all this and my dad only ever flew nitro stuff. I shall look for a meter. Silly question, how do I use one, like a volt meter I guess, but how do I use it to measure the amps being drawn?

Thanks
One of those generic "wattmeters" will serve your purpose well. As for the common digital multimeters, their maximum current range is generally on the order of 10 Amps, far to low for most electric motors used in our models. (My kilowatt sized motors typically pull some 60 amperes.)

Take a look, this explains some of this stuff.
http://www.wattflyer.com/forums/showthread.php?t=52821

If you want to spend the $$$$, (About $60) the Sears Craftsman #82369 meter can measure the current pulled by just about any electric motor you have access to. Including the starter and alternator in your car/truck. Its current ranges are 0-40 and 0-400 Amps, AC and DC. It doesn't require special connectors, just clamp it's jaws around one battery cable. Note that most clamp on ammeters are AC only, not suitable for our stuff.

This meter can also measure current pulled by your AC appliances and so on, but it needs to clamp its jaws around ONE wire of the power cord. Clamping around the usual two wire extension cord will result in zero current measured.

But, this Sears meter can't measure things like ampere hours and such, only the usual volts, amps, resistance, temperature and so on.
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Old 01-14-2012, 11:28 AM
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AEAJR
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See chapter/post 71 in this e-book
http://www.wattflyer.com/forums/showthread.php?t=31368
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Old 01-14-2012, 01:51 PM
  #11  
mrbicknell
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cool thanks
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Old 01-18-2012, 06:20 AM
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betomxl
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nice info
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Old 02-21-2017, 04:29 AM
  #13  
Barry ALgrim
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Originally Posted by solentlife View Post
Ebay .... Hobby King .... Local Hobby Shop ?

It's a common item and called by the generic term : Wattmeter

I use mine every day to check LiPo's charge and usage ... balance etc.

With new set-up out of interest - I run up to check amps and watts ...

For about $30 ... it's a good tool.
Good! I got a free one from HarbofFreight. Wondered what to do with it.
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Old 02-21-2017, 11:56 PM
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AEAJR
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I would be surprised if Harbor Freight sold a wattmeter suitable to our models.

I have this one but it is for the house current, not my model airplanes
http://www.harborfreight.com/kill-a-...tor-93519.html

I have this one
http://www3.towerhobbies.com/cgi-bin...?&I=LXLMV0&P=7

I also have one from HobbyKing that measures motor watts and servo power draw, but it seems they no longer carry it.
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Old 02-22-2017, 12:32 AM
  #15  
dereckbc
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Watt Meters work great on the ground. Not worth a flip when flying to get real numbers. You can do static test, and that will give you very liberal numbers. Static test amps will be higher than flying at a given throttle position.

Having said all that, none of the above tells you much. Best method is to take a fully charged battery, fly a few minutes, then charge it back up and see how many AH you used. Voltage does not tell you squat.
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Old 02-22-2017, 12:37 AM
  #16  
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Set your timer and fly the plane. Check your voltage afterwards. Adjust timer to suit, rinse, repeat.

Your flying style for any particular model as well as it's flight characteristics play the largest part, unless your entire flight is performed at full throttle.
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Old 02-22-2017, 07:28 AM
  #17  
solentlife
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OK Derek has a point - but static ground test is a good starting point to set a safe time of flight/ setup a combo motor / ESC / battery.

The figures obtained on ground are used by millions around the world to good effect.

Once a setting is arrived at - then as others say - fly, test voltage remaining, adjust timer setting, charge fly again etc. till you arrive at ideal for you.

Personally I stay with max power, min timer setting - that way when beeper goes of - I know I have more than enough power to do a couple of circuits to land.

Example : my electric big zlin static test says with my usual battery I should get just 4 mins at full power to safe low voltage on pack.
In the air because I throttle - I get easily over 5 mins. But my timer goes of at 4 .... I then sort out to land.

Nigel
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Old 02-23-2017, 03:33 PM
  #18  
ron_van_sommeren
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Originally Posted by quorneng View Post
You really must invest in a meter to actually measure the current draw. ...
To trust is good, to calculate is better, to measure is a must. Without a watt-meter you are in the dark, until something starts to glow
A watt-meter will more than pay for itself, several times over, your battery, ESC and motor will love you for it. After calculating, always check current when you have a new/changed setup. Will also help you find optimal setup.

close out sale: Hyperion watt-meter II (optical tach, servo tester, local&remote logging) - RCG

Originally Posted by mrbicknell View Post
... I am new to all this ...
Some well-structured reading and handy e-tools for rainy/windy days. Will save you, and us , a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools
.
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Old 02-23-2017, 05:25 PM
  #19  
Wildflyer
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I check every new plane before the maiden flight, with a known good wattmeter. Mine is an Astro Flight.

I bought an expensive powered glider that was set up by the previous owner but not tested.
The motor hit maximum current and wattage at about half throttle.
I could have burned up a very expensive motor and possibly the whole glider if I had ran it even for the 30 seconds at full throttle.

I had to change from a 3s to 2s battery and drop from an 11x8 carbon folding prop to a 10x6. to keep the power in line.
Plane still climbs like a skyrocket.

Another time a wattmeter surprised me.
I had a 36" 3D flat foamie, with a geared Himax motor. played around until I had the perfect 11x7 prop to put out 170 watts with the cheap Lipo batteries I had at the time.
Then one day I bought a Hyperion battery of the same size but a higher C-rating.
I almost ripped the wings off! The Hyperion was such a better battery, with much lower internal resistance, that it was putting out 275 watts on the same prop.
Ok get out the wattmeter and find a new prop to tame the thing down.

In electric powered modeling, GOOD instruments, and understanding how to use, and what they are telling you are a must to understand what is happening inside the system. (battery, ESC, motor)

If the "Magic Smoke" comes out you can't fix it.


For a clamp on type DC meter, I bought the Vici meter that Hobbyking carries, but they do not make it. I am very happy with it. It will measure the current of a single small light bulb, up to and beyond, the starting current of my diesel truck. It was less than $40.00 shipped price form the US hobbyking warehouse.
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Old 02-24-2017, 04:48 AM
  #20  
dereckbc
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Originally Posted by solentlife View Post
OK Derek has a point - but static ground test is a good starting point to set a safe time of flight/ setup a combo motor / ESC / battery.

The figures obtained on ground are used by millions around the world to good effect.
Nigel I never said it was not a good starting point, because it is a good starting point. It will be a very liberal starting point because static test currents wil be higher than in flight.

If you have a 40 amp ESC, and at full power you note 35 amps, then you know your power plant is within safe limits. Back off the throttle to say 2/3 power and you see 30 amps. om a 2200 MAH battery you know you have roughly [2.2 AH / 30 amps] x 60 = 4.4 minutes. So you start at 4 minutes, recharge, and note you only replaced 1.5 AH. Keep bumping it up until you have only 20% left in th epack or whatever you are comfortable with.

Now there is some gotchas. To start LiPo batteries capacities are rated at 1C. There is a little thief in physics called Peukerts Law which states the faster you discharge a battery, the less capacity it has. Pb batteries are significantly affected by Peukerts Law, Lithium not as severe but still has it, If you discharge at say 10C, you lose 20% of the capacity.

Of course the second gotcha is very few new LiPo's have the rated capacity. Even if they do lose capacity with each cycle.

So using a watt meter is a good starting point. It will be so liberal, your first few flights will get back on cloud terra firma with more fuel left in the tank than you expected. And that is a good thing.

I may not be a good pilot and inexperienced builder, but I am a top notch electrical engineer (PE Licensure) with 40 years professional experience working with batteries and control circuits.
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Old 02-24-2017, 06:39 AM
  #21  
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Default LiPo Battery Alarm

I have one of these on every helicopter I have. I set the Alarm at 3.80 volts, by the time I land, it's right above 3.70, just where it needs to be. If you use the timer on your radio or a separate timer, you have your answer. The little button in the center is where you set the voltage alarm.

This solve my LiPo problems on ALL of my batteries. Since using these, my batteries last a lot longer. And at about $2.00 each, it's well worth the investment. I mount it where I can see it from the ground, when it starts blinking, it's time to land.

Here is the one I use, but there are several more out there more expensive. It's your choice.

Put this part number in the Amazon search bar, 150117-F2, the buzzer should be in the top 5 and easy to see. The system won't let me put the link in.

The post following let me put the image link in. Most don't realize you can leave this on your balance connector while flying.
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Old 02-24-2017, 06:39 AM
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It let me put the link in this time.

This one is the lowest price alarm I have seen. http://www.ebay.com/itm/162143334076...%3AMEBIDX%3AIT
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Old 02-24-2017, 07:51 AM
  #23  
solentlife
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Hi Derek .... please was not poking a stick at you at all. I agree with you.

Trouble is we don't have anything else to use being modellers.

I personally stick with the max rate draw and short timer setting - then I know I will always get home when buzzer sounds ....

Nigel




Originally Posted by dereckbc View Post
Nigel I never said it was not a good starting point, because it is a good starting point. It will be a very liberal starting point because static test currents wil be higher than in flight.

If you have a 40 amp ESC, and at full power you note 35 amps, then you know your power plant is within safe limits. Back off the throttle to say 2/3 power and you see 30 amps. om a 2200 MAH battery you know you have roughly [2.2 AH / 30 amps] x 60 = 4.4 minutes. So you start at 4 minutes, recharge, and note you only replaced 1.5 AH. Keep bumping it up until you have only 20% left in th epack or whatever you are comfortable with.

Now there is some gotchas. To start LiPo batteries capacities are rated at 1C. There is a little thief in physics called Peukerts Law which states the faster you discharge a battery, the less capacity it has. Pb batteries are significantly affected by Peukerts Law, Lithium not as severe but still has it, If you discharge at say 10C, you lose 20% of the capacity.

Of course the second gotcha is very few new LiPo's have the rated capacity. Even if they do lose capacity with each cycle.

So using a watt meter is a good starting point. It will be so liberal, your first few flights will get back on cloud terra firma with more fuel left in the tank than you expected. And that is a good thing.

I may not be a good pilot and inexperienced builder, but I am a top notch electrical engineer (PE Licensure) with 40 years professional experience working with batteries and control circuits.
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Old 02-25-2017, 04:21 PM
  #24  
dereckbc
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Originally Posted by solentlife View Post
Trouble is we don't have anything else to use being modellers.
Watt Meters are good and chances are you have another great tool to use, your battery charger.

Having said that I realize not everyone's charger can be used. but many do have the features you can use. If your charger meters how many Amp Hours you put into a battery is about as accurate as you can get. Even better if you can perform Discharge Capacity Test so you actually know what your battery capacity actually is.

It is called Coulomb Counting and is what many Electric Vehicles use as a gas gauge so to speak. So if you know you have a 2000 mah battery, and after a flight you only pump in 1000 mah, then you know you have 1000 mah left in the tank.

So start with a Watt Meter, and fine tune with a charger.
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Old 02-25-2017, 04:35 PM
  #25  
solentlife
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Hi Derek ... even the common old B6 gives mA in to a battery when charging. The later Mini and so on also have the Battery Meter / iR functions as well.

You don't have to convince me !!

Cheers
Nigel
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