Amp ?

[plasticjoe]

when someone says..... the draw is a 1 amp.... is that draw per second ? minute ? hour ? Just trying to clear the fog in the brain over here.... been working alot.... My gut thinks it's per hour.... but who knows... I've been eating too much lately and my gut is starting to store more current than it needs to LOL

[rick.benjamin]

Means when the thing is on, it is drawing one amp.
1 amp hour means
http://en.wikipedia.org/wiki/Ampere-hour

[plasticjoe]

yea I found the specs on the thing I am working on...it's 1 AMP per hour... so that's 1000 Mah / hr correct ? so if I wanted to run it 15 minutes it would draw 250 Mah correct ?

[rick.benjamin]

yea I found the specs on the thing I am working on...it's 1 AMP per hour... so that's 1000 Mah / hr correct ? so if I wanted to run it 15 minutes it would draw 250 Mah correct ?

Yep, 250 mAh should run the thing for 15 minutes

[Brandano]

Hem, if you have something rated at 1 A draw and run it on a 250 mAh battery in theory you'd get 15 minutes of use out of it. but it will draw 1 amp for the whole of those 15 minutes. mAh is a measure of capacity, while Ampere is a measure of current flow. Essentially, the mAh tell you how big the bucket is, the Amp draw tell you how large is the section of the hose. And wanting to stress the analogy further, the Voltage tells you how high up the bucket is

[vintage1]

When I say something wieghs a pound, is that a minute? an hour? No, It's a pound...;)

[Ricardo RW]

Your gut is wrong, the draw 1Amp means instant current, right now, like volts, pounds, etc.

[slipstick]

When I say something wieghs a pound, is that a minute? an hour? No, It's a pound...;)
Don't be silly of course there's no connection between pounds and hours....it's probably pounds per foot or perhaps per inch ;).

But seriously plasticjoe, the Ampere is measuring the flow of current. It's instantaneous and also continuous. All the time the thing is switched on it's taking 1A. It doesn't matter if it's on for a second, an hour or 200 years it will still be taking 1A for all that time.

Steve

[Ricardo RW]

If you want to translate Amp as something per second, as water you have litters or gallons per second.

In short, one ampere represents the rate of 1 coulomb of charge per second.

The Coulomb of charge is related with the electrons jumping from atom to atom.

[BushmanLA]

when someone says..... the draw is a 1 amp.... is that draw per second ? minute ? hour ? Just trying to clear the fog in the brain over here.... been working alot.... My gut thinks it's per hour.... but who knows... I've been eating too much lately and my gut is starting to store more current than it needs to LOL

The ampere unit is the amount of electron flow past a point per second.

So when I say "this device is drawing 1 amp", I'm also saying "This device has 6,241,509,480,000,000,000 electrons flowing through it per second."


It is mostly meaningless to babble off how many amps something is drawing if you don't know one of the other pieces of Mr. Ohm's love triangle like resistance or voltage.

10 amps going into your brand new brushless motor setup might seem wimpy, yet 10 amps coming out of your home wall outlet is enough to run a huge honking vacuum cleaner. The difference is 11.1 volts in one system and 120 volts in another.

We should probably get in the habit of talking about things in terms of Watts because it gives the whole picture. When you talk about performace in terms of amps, you are assuming that the voltage (or resistance) of the system is also known, and that just isn't always the case.


Using the example above, your 11.1 volt system drawing 10 amps is a 111 Watt system, and the vacuum cleaner drawing 10 amps from the wall outlet is a 1200 watt system, makes things a little more clear doesn't it?

[Ricardo RW]

Yep, right in the middle of the target.

It's incredible how this stuff confuse people, well I'm a bit biased as I'm EEng.

[BushmanLA]

water analogy works every time.


Amps is rate of flow of water through a pipe.

Volts is the pressure difference between one point of the pipe and another.

Resistance is the resistance to flow in a pipe.


While rate of flow is a valuable thing to know when you want to know how much water is coming out of a pipe, its mostly useless for electronics devices because we really don't care about how many electrons are flowing through the wire. Its not like I'm trying to fill a bathtub with electrons so I can have a wash. :)
Indeed, since we are talking about a closed circuit anyway, the amount of electrons in the system stays the same, at any point in a circuit flow in = flow out. (So says some dude named Kirchoff anyway)


Say for example we have installed a sort of screw inside the pipe at some point, this screw will spin as water passes it and it can be attached to some outside device to do work, (like generate electricity :D).

The rate of flow past the screw is meaningless unless we know either
Resistance: How much the screw is resisting that flow
Voltage: What pressure difference on either side of the screw does it take to achieve that flow.

According to Ohms law:
Volts = Current/Resistance
and
Watts = Volts*Amps:

So power absorbed by the screw in the pipe is either
(Flow*Pressure Difference)
or
((Flow*Flow)*Resistance)
or
((Pressure Difference * Pressure Difference) / Resistance)

[ejaf]

Don't know whether this is the right thread to ask this, but it is along the same lines, so I may as well ;)

I agree the water analogy is great...here is my dilemma which I am in need of understanding:

With some of the stuff I have been playing with (micro RTFs), there is talk about either changing an nimH battery application to Lipo, or increasing the Lipo for longer run times. In reading, some people mention that a specific receiver can handle a 150maH lipo, but that a 250maH Lipo may be "too much", and cause the receiver to fry (I am assuming they are speaking of the mosfet controlling current to the motor, but not sure).

Why? If maH is only the amount of energy stored, wouldn't the circuit just take what is needed (ie. use the specific amperage regardless of the battery in question), and therefore one has no worries as far as burning anything up?

TIA...Eric

[Ricardo RW]

Don't know whether this is the right thread to ask this, but it is along the same lines, so I may as well ;)

I agree the water analogy is great...here is my dilemma which I am in need of understanding:

With some of the stuff I have been playing with (micro RTFs), there is talk about either changing an nimH battery application to Lipo, or increasing the Lipo for longer run times. In reading, some people mention that a specific receiver can handle a 150maH lipo, but that a 250maH Lipo may be "too much", and cause the receiver to fry (I am assuming they are speaking of the mosfet controlling current to the motor, but not sure).

Why? If maH is only the amount of energy stored, wouldn't the circuit just take what is needed (ie. use the specific amperage regardless of the battery in question), and therefore one has no worries as far as burning anything up?

TIA...Eric


If you change batteries with different capacities (mAH = how much energy is stored) and keeping the SAME voltage, you're in no danger.

If you change the voltage battery maybe you'll need additional analysis, for example, the receiver operation range.

If the increase of voltage is beyond operations limits of the receiver, you'll need voltage regulator.

The guys recommending you ti switch chemistry (and capacity) must warn you about the voltage of the pack.

It's not the capacity (mAH) of the pack that will fry your receiver, but the voltage.

[Dan Baldwin]

Don't know whether this is the right thread to ask this, but it is along the same lines, so I may as well ;)

I agree the water analogy is great...here is my dilemma which I am in need of understanding:

With some of the stuff I have been playing with (micro RTFs), there is talk about either changing an nimH battery application to Lipo, or increasing the Lipo for longer run times. In reading, some people mention that a specific receiver can handle a 150maH lipo, but that a 250maH Lipo may be "too much", and cause the receiver to fry (I am assuming they are speaking of the mosfet controlling current to the motor, but not sure).

Why? If maH is only the amount of energy stored, wouldn't the circuit just take what is needed (ie. use the specific amperage regardless of the battery in question), and therefore one has no worries as far as burning anything up?

TIA...Eric

I suspect that someone changed out the original 150 mah lipo for a 250 mah lipo, and the FET blew some time after that for an unrelated problem, so they assumed that it was caused by the larger battery, but it is possible that it's related.

Generally speaking, you can use a battery of higher capacity without a problem, you'll just get a longer flight, but it is possible that in this case it might cause problems. A 250 mah Lipo would probably have a lower internal resistance than the 150 mah, and it's possible that that could cause a higher current flow. The battery would no doubt be heavier, also forcing you to use a higher than normal throttle setting which would increasing current. It's also possible that the FET doesn't have adequate cooling, and it continually gets hotter. The normal flight time using a 150 mah is okay, but the longer flight time of the 250 mah could push it over the edge.

Dan

[ejaf]

Thanks, Ricardo and Dan...

That was what I thought...sure, if you're changing the chemistry from a 3s nimh to a 1s Lipo, since the voltage is changing, then I can see the possiblility of frying...but not from a 150 mah to 250mah Lipo.

Thanks for clearing that up for me...

Eric

[AndyOne]

Back to the original discussion; There is a huge amount of confusion about how battery capacity is stated. I worked in the battery industry for 17 years and people there (mostly management and mechanical engineers) think one should say "Amp per Hour" when they heard "Ampere Hour". This is why I always say "Amp Hour" and Milliamp Hour, trying to cut down on the misunderstanding.

For clarity and in case anyone was in any doubt, Amp is just short for Ampere.

Andy.

[Ron van Sommeren]

'Amp during an hour' is even beter.

[satanicoo]

yea I found the specs on the thing I am working on...it's 1 AMP per hour... so that's 1000 Mah / hr correct ? so if I wanted to run it 15 minutes it would draw 250 Mah correct ?

If it is rated at 1000Mah / hr, if you run it at 250 Mah / hr shoudn't it run for 4 hours?

[Ron van Sommeren]

It's rated at 1000mAh=milliAmpèrehour=milliAmpère*hour: sustained current during an hour, not per our. Product of current and time is batterycapacity. If you run it at 250milliAmpère, it will indeed run for four hours. A 'Amp per hour' would mean a change over time in current.

www.ezonemag.com (http://www.ezonemag.com) -> FAQ (lots of useful e-flight info)
Ampere is electrons per second (try counting them ;)):
http://en.wikipedia.org/wiki/Ampere

Prettig weekend ;) Ron

[Ron van Sommeren]

E-flight FAQ's:
www.rcuniverse.com/forum/m_7100376/tm.htm
www.rcbatteryclinic.com

Now you pretty much have everything covered :)

PRettig weekend ;) Ron

[BushmanLA]

"Can provide one Amp for one hour" is the best :D

[shanghai_fool]

If it is rated at 1000Mah / hr, if you run it at 250 Mah / hr shoudn't it run for 4 hours?

Not really. Batteries are rated by total Ampere-hours over a period of usually 20 hours. (C/20). Some manufactures use different periods (8 or 10) but NEVER just 1 hour. Heavier usage will decrease actual power delivered.

[Ricardo RW]

Not really. Batteries are rated by total Ampere-hours over a period of usually 20 hours. (C/20). Some manufactures use different periods (8 or 10) but NEVER just 1 hour. Heavier usage will decrease actual power delivered.

Good to know that, thank you.


Saludos.

[satanicoo]

So Mah (mili-amperes per hour) doesn't translate the capacity of a battery, only the intended discharge rate it was built for. Am i right now?
The Battery capacity is only correlated to the A rating, like 3 Amps, right?

Just checking.

[jeffs555]

So Mah (mili-amperes per hour) doesn't translate the capacity of a battery, only the intended discharge rate it was built for. Am i right now?
The Battery capacity is only correlated to the A rating, like 3 Amps, right?

No, mah is still mili-ampere hours, not mili-amperes per hour. What shanghai was saying is that battery capacity is rated at certain conditions(ie amp draw). For example, if a manufacturer specifies a battery as 200 mah, and he is using the C/20 spec(ie 200mah/20hr=10ma), it means that if you pull a constant 10ma from the battery, it will last for 20 hours. You can't necessarily infer that if you pull 5ma from the battery it will last for 40 hours or that if you pull 20ma it will last for 10 hours. It will usually be close, but the farther you get from the test conditions the more the capacity will differ from the rated capacity.

PS To confuse things even more, batterys will also have a maxim discharge rate (perhaps 20C) which is unrelated to the C/20 condition. This means that if a battery is rated 200mah and 20C then the battery can supply 4000ma. However, it does not mean that it can supply 4000ma for 1/20 of an hour. At the maximum discharge rate, the capacity will usually be much less than the rated capacity.

[Ricardo RW]

entering to the blur borderline between engineering and marketing...

[shanghai_fool]

If you don't believe that then look at the current of C times whatever is specified and the current rating of the lead wires.
I have a 16C 2200mah (32.5 Amps max) battery with #14AWG leads which are rated at 15 Amps.

[satanicoo]

So a 2000mah battery will deliver 2A during a hour, and it will be completely discharged at the end of it.

Right?

So when a battery is rated at 20A, it means it can be discharged maximum at 20 A without being damaged right?

Hope i got it now :confused:

[Ricardo RW]

So a 2000mah battery will deliver 2A during a hour, and it will be completely discharged at the end of it.

Right?
When you draw 2A from a 2000mAH batt. these guys are saying that you will not get 60 minutes, but almost.


So when a battery is rated at 20A, it means it can be discharged maximum at 20 A without being damaged right?

Do you mean 20C instead 20A?

In short, you will not get the mathematically calculated time for a given discharge rate, but it will be close. How much? You'll need to test.