*Checking Batteries Between Flights*

*Checking Batteries Between Flights*
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> *Checking Batteries Between Flights*

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*Checking Batteries Between Flights* - 7/2/2007 3:02:02 PM

Zippi

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Joined: 6/29/2004
From: Evansville, IN, USA
Status: online

I'm running two 4.8 1800 mAh packs, one for ignition and the other for the onboard gear. When the batteries have been charged and I check them before I fly they check around 4.75 - 4.8. In between flights when I check the batteries, what reading am I looking for to say, the battery level is to low to fly anymore?

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RE: *Checking Batteries Between Flights* - 7/2/2007 5:09:40 PM

Rodney

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IMHO the best way to check your batteries is to use a Voltwatch on each battery. When flying, check it at the end of each flight before you turn off the transmitter and receiver switches. This will give you a very accurate state of charge with the actual loads you are using in flight and let you know if another flight is safe.

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RE: *Checking Batteries Between Flights* - 7/3/2007 10:56:14 AM

mrasmm

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I agree with rodney. I think that is also the best way. Another way that can work is to get a loaded voltmeter with about a 300mA load and go off of that voltage. Depending on who you ask and how conservative they are, you'll get answers anywhere from 4.4v to 4.8v under load.

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RE: *Checking Batteries Between Flights* - 7/4/2007 10:36:34 AM

bob_nj

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The discharge curve for nicads anyway is fairly flat until they reach the end of their capacity.
They usually hang around the nominal voltage for awhile, then fall off like a lawn dart.
I keep cycle sheets on my packs to see how they're doing so I get an idea of what kind of shape they're in.

Take readings at the field often and get a feel for how they hold up.
Don't be afraid to charge at the field when needed.

I'm not one of those guys that needs mega capacity packs so I can fly all day without a charge.
I use several Sirius chargers and charge them for awhile when needed.

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RE: *Checking Batteries Between Flights* - 7/4/2007 7:50:52 PM

Jazzy

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From: Erie, PA, USA
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When fully charged, a cell will have a voltage in the range of 1.2 to 1.35V. A charged 4.8V (nominal) pack will have a voltage above 4.8V and likely above 5V.
I built a loaded digital voltmeter a few years ago out of a pocket type meter, a 1Watt 10 ohm resistor, and a DPST micro switch. With the switch in the down position the meter reads the floating voltage. With the switch in the up position the meter reads the voltage across the load. The resistor puts around a 500 mA load on the pack. In the time it took me to flip the switch and take the pic (~4-5 sec.) the resistor was already quite hot! This meter is for momentary readings only.
The pics below show the loaded and unloaded conditions.
The whole point of having a loaded meter is to identify a pack whose voltage drops below 4.8V under load. If, when testing a pack, the voltage drops below 4.8V - DO NOT FLY!.
As previously mentioned, the discharge curves for rechargeable batts drop fairly sharply below 4.8V (different cell types have different slopes). The type of cell really does not matter. When the operating (loaded) voltage is below the nominal voltage it is time to recharge.

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< Message edited by Jazzy -- 7/9/2007 10:30:26 PM >

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RE: *Checking Batteries Between Flights* - 7/4/2007 8:21:34 PM

Zippi

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From: Evansville, IN, USA
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Thanks guys. I was looking for a number to watch for on my volt meter but I guess there isn't any one number for all batteries. I guess I'll just fly my normal flights next time out and then check the batteries and see where they are at and use that as a stopping point.

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RE: *Checking Batteries Between Flights* - 7/4/2007 9:44:49 PM

Don J

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From: Le Mars, IA, USA
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Zippi,
Anything under 4.8v with a load, I usually charge or just don't fly.
I think some people will go to 4.4v.
I just purchased a field charger, so charging at the field is not a problem for me.

Jazzy,
I have the same volt meter setup. Try using multiple resistors in parallel ie; 5-50 Ohm.
This will dissipate the heat better or another option, Radio Shack has 20 watt power resistors.

Don J

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RE: *Checking Batteries Between Flights* - 7/4/2007 10:33:05 PM

Zippi

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From: Evansville, IN, USA
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Don J,

Thanks for the input. My numbers were off on my first post. It should have read 5.75 - 5.8. I just recheck both packs on my plane after it has sat for 4 days and both packs are still reading 5.8. looks like no flying below 4.8.

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RE: *Checking Batteries Between Flights* - 7/5/2007 2:13:21 AM

warhwk

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From: San Marcos, CA, USA
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A battery cannot be accurately tested without a load. Static Voltage is not a reliable gauge of battery capacity. I use this inexpensive loaded voltmeter from Horizon on my smaller planes (40-90 size)

http://www.horizonhobby.com/Products/Default.aspx?ProdID=EXRA502

If you are flying large or gas planes with multiple, hi-torque servo's, I think the VoltWatch will give you a more accurate reading on the state of your battery.

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RE: *Checking Batteries Between Flights* - 7/5/2007 3:47:57 PM

Don J

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From: Le Mars, IA, USA
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As warhwk stated, make sure you have a "LOAD" on your volt meter when testing.
My new 1100 mah RX packs, when fully charged, show around 5.40 with .260 amp load.
Your can go to Radio Shack and purchase a "10 ohm power resistor". If they don't stock a
10 ohm, they will have an 8 ohm. This will work, but current draw will be around .500 amp.
Just attach the resistor across the leads of the volt meter, one side of the resistor on + and the other on -,
check the battery and this will give you a good voltage capacity.
My rule of thumb is: When using the 10 ohm resistor, I never fly below 4.8 volts. When using
an 8 ohm resistor, I never fly below 4.7 volts. Even at these values, I will have gotten the
field charger out already. Not worth the loss of a plane.

Just got back into flying this last spring. My planes have sat on the shelf for 3-4 years with the same batteries.
I never paid much attention to batteries until this year.
I was quite surprised when I decided to start monitoring batteries when I'm at the flying field.
I have never lost a plane due to battery failure, but I believe this would have been the year.

Good Luck,
Don J

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RE: *Checking Batteries Between Flights* - 7/8/2007 3:39:01 PM

Jazzy

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From: Erie, PA, USA
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Don,
I built my loaded meter before I had much electronics experience (6-7 years ago). I think when I built it I based the resistor on the power rating. I didn't take into account the distributive effects of parallel paths.
Five 1/2 Watt 50 ohm resistors would work great. I don't know if they exist though... Five 1/4 Watt 50 ohm resistors might work a little better. It was quite some time ago. I'm not really sure what I tried or didn't try.
Thanks for the input though!

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RE: *Checking Batteries Between Flights* - 7/8/2007 8:17:13 PM

warhwk

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From: San Marcos, CA, USA
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Ohms Law for Current is V/R (I=E/R) so at 10 Ohms, you are pulling .48 Amps. I'm sure this is excessive for ignition, and may be about right for the Onboard gear of a Large Plane. With a 4.8v rx pack for standard plane, 12-15 Ohms will work better. If you are going to use a resistor, buy one of the large 5 watt cement resistor, or you could burn your fingers.

< Message edited by warhwk -- 7/8/2007 8:32:56 PM >

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RE: *Checking Batteries Between Flights* - 7/9/2007 5:00:25 PM

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Please dn't take offense to this Zippi. I'm just trying to help/understand the issue:

At first you said you were getting 4.75--4.8V readings after flying.

If that were me, I'd be freaking out and happy that I didn't just wreck my plane. I wouldn'y fly a 4.8V battery below 4.9 under a load--just to be sure. At 4.9V, I might fly one more quick (5-8 minutes) flight and then take it home to cycle it.

Then you said you'd made a mistake and those numbers were actually 5.75--5.8V Thats rediculously HIGH voltage for a 4.8V pack. Even right off the charger, thats enough to just about pop a 4.8V pack wide open. Thats about 1.45V per cell.

And you said that was your voltage after flying. To me, thats darn near impossible. Even with 1800mah batteries. If they charged up hot off the charger and you went and flew them 3 times (30 mnutes total flight time) I can't see them at 5.75V--5.8V.

If your flying 6V packs--then your going to loose a plane if your flying them down to anything under 6.0V or 5.9V-- and thats the danger zone to me. I won't fly a 6V pack under 6.1V under a 500mah load. At 6.1V, I'll go home, charge or MAYBE do one more quick flight and then call it a day.

Most of my 6V packs will charge up to about 7.3--7.4V hot off a quick charge. They will drop to 7.2--7.3V after an hour or two of sitting. They hold steady between 6.4V and 6.8V almost all day and then start to drop.

I guess what I'm saying is 5.8V on a 4.8V pack is ready to explode. Can't see them showing that much voltage after flying.
5.8V on a 6V pack is ready to crash.

Could you clarify for me? Are you flying 6V packs or 4.8V packs? I don't want you to crash a plane. The last thing I want to see is a thread from you in the Crash forum.

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RE: *Checking Batteries Between Flights* - 7/9/2007 10:25:19 PM

Jazzy

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From: Erie, PA, USA
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Warhawk,
I am very familiar with Ohms Law. The meter I used at the time did not agree with the calculations and gave me a value around 320mA. I guess I forgot about it and figured it was just extra insurance. It hasn't let me down yet.
Fingers do not go near the resistor. A one or two second check does not heat up the resistor very much.
The nice thing about the meter is that one can check the voltage level BOTH loaded and unloaded.

Good catch. I'll fix my previous post.

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RE: *Checking Batteries Between Flights* - 12/12/2007 9:23:44 AM

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From: Tehachapi, CA, USA
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quote:

ORIGINAL: Don J

As warhwk stated, make sure you have a "LOAD" on your volt meter when testing.
My new 1100 mah RX packs, when fully charged, show around 5.40 with .260 amp load.
Your can go to Radio Shack and purchase a "10 ohm power resistor". If they don't stock a
10 ohm, they will have an 8 ohm. This will work, but current draw will be around .500 amp.
Just attach the resistor across the leads of the volt meter, one side of the resistor on + and the other on -,
check the battery and this will give you a good voltage capacity.
My rule of thumb is: When using the 10 ohm resistor, I never fly below 4.8 volts. When using
an 8 ohm resistor, I never fly below 4.7 volts. Even at these values, I will have gotten the
field charger out already. Not worth the loss of a plane.

Just got back into flying this last spring. My planes have sat on the shelf for 3-4 years with the same