cubkadet

i am trying to determine if a battery is any good.can anyone tell me how much amp draw is on a nitro airplane reciever battery?i know you can;t tell exactly but is there a number that would be real close?i want to discharge the battery at that voltage to determine what my flight time would be.

chuckk2

Not easily. There are a bunch of variables.
Battery voltage
Number of servos, type, and current draw of each servo
Flying style
(To name a few!)

An analog servo usually draws less peak current than a digital one.
A digital receiver generally does not like voltage dropouts due to servo current draw.
(They go into some sort of re initialization, signal re acquisition, etc.)

The "old" analog standard was to use a 4.8v 600ma NiCad battery. This is inadequate for
the usual system today.

My preference is to use a LiPo battery with a switching BEC, and supply 6vdc to the receiver and servos.
With 6 digital servos, a BEC that provides 2A current is, based on experience, marginal.
5A capability is much better.

A digital servo can draw quite a bit of current, such as an amp and a half for a short period.
Electric retracts are another high peak current user.
  

BillS

I usually fly once or twice on a good battery and use the charger to tell me the mah were put back in the battery. If your charger doesn't report the amount of charge put back you might get a friend to charge the batteries for you.

Bill

flyinwalenda

My Feedback: (5)

First you need to make sure your battery is fully charged and in good shape. As stated , do you have a charger that displays voltage and amps put into the pack? Does your charger have a "cycling" function? If not then you should get a better charger that can perform this function. A typical"4-button" multicharger can be had for around $30.00 and up.
Otherwise as stated , get someone to cycle the pack several times and they can tell you the health of the batteries.
Do you have a load meter? if not you should get one. Install the fully charged pack in the plane and fly it two or three times and then check the pack with the load meter and it will show you if the plane is safe to fly.
You don't state the voltage or mah rating of the pack or the size of the plane and type and number of servos. All of this information is important .

jrlingrel

Get a charger that also cycles. They will usually tell you battery voltage and how much was put into the battery. WHen the discharge cycle runs, a 4.8V battery should drop down to about 4.2. The discharger should also tell you how much came out. I generally see about 450 mah out of a 600mah pack.

John

mehrshad

Discharge the battery with 0.5A and see the time.
The average current for your application is around 300mA and even less.
if you have a healthy pack with more than 1100mAh capacity, nothing to worry about.

chuckk2

There is an obvious difference between ampere "draw" and the battery capacity.
a 600mah NiCad battery might have 400mah or so available.
Current "draw" vs output voltage curve is more to the point.
As the current draw increases, the battery output voltage decreases.
Obviously, if it decreases enough, servos slow down, and receivers may stop working.
Some testing using 2000mah "quality" NMIH batteries showed that they had significant voltage drop
above 1 to 2 ampere draw. There are battery voltage/current charts floating around the web.
It is possible for a failing digital servo to draw 1 1/2 ampere, and still function (but poorly)
(Had it happen!)

mehrshad

Quality NIMH doesn't mean lower voltage drop.
A 1100mAh NiCd has an internal resistance around 15mOhm and a 2200mAh NIMH around 25mohm.
A normal NiCd can handle 2C easily that a standard NIMH couldn't.

opjose

Right and even properly functioning higher torque analog servos can draw 1500mA @ 6v or more when they approach stall.

It is best to assume that EACH SERVO on your plane can draw close to or over 1000mA in flight and size your capacity accordingly.

Average draw is less, on the order of 200-300mA per servo, but it's those momentary peaks that cause brown outs and voltage drops...

Better to overdo it than not in this case.

IMHO it is silly to try to fly a plane with an 800mAh to 1200mAh 6V pack now-a-days.

I see many people show up with giant scale planes and 8 digital servos, using measly 2000mAh packs or dual 1200mAh packs... very foolish.

chuckk2

"Quality" was used to say that the batteries were not from no name or unknown sources, not that they might have more or less capability than another brand.
You cannot expect a no name battery to behave the same as say a Sayno Enloop?, so using the charge discharge curves for the Sayno to predict another mfrs battery behavior is like throwing dice.