i finally purchased a volt meter to keep tabs on the rx and tx batteries. i bought the hobbico expanded scale voltmeter mk II. i have never had any problems with my tx battery. put the tx battery on the charger last night and got up this am to fly. so i use the new volt meter. first of all i plug it in and nothing happens. so i turn the tx on and the needle go up but its just over the red marks and showing almost no charge. so i think that odd i look at my tx and the red low battery light is on. my tx is a futaba t4ybf. and to add to the oddness when i touched the antennea then needle would jump up from 5 volts to 8 volts. and when i pulled the antennea out the needle pegged at 11 volts. i removed the battery from the tx and tested it seperatly. and it reads 5 volts. first of all are you suppose to turn the tx on to get the voltmeter to work? why does the needle go up when i touch the antennea and extend the antennea? why would the battery go bad all of a sudden? do i have a bad voltmeter and did it damage my battery? or could i have crossed the leads and damaged the battery? please i need some help!

Hey mrbass111... A expanded scale voltmeter is a great tool to assist
in keeping you out of battery problems with the onboard system..
It's a quick check of the receiver battery while at the field... I would
get in a habit of checking after 3 flights to keep tabs on the battery
then give it a quick charge if you fly more... On the Transmitter IMO
it's pretty much useless.. I just use the radio's battery monitoring
system built in the radio... I think it's on all radio systems, but may
be not.. They have a diode(think that's what it is) which will not let
the battery lose voltage in that direction, which also prevents a
reading on the voltmeter and or allow you yo cycle the battery while
it's in the transmitter... You need to remove the battery to read the
voltage and or cycle it..... Not sure about the rest of your questions
you could have a battery going bad... I do not believe you can hurt
the batteries by just flipping the correct plug over.. But if you use
the wrong plug it could cause a problem. Only thing I would do on the
trans battery is to pull it from the tranny and cycle it if you have a
cycler, than see what condition it's in Hope this helps..

ya know i may have had a brain malfunction. does anyone know on the futaba t4ybf. when its turned on does the red and green light alway shine? and the green goes out when it get low?

http://www.futaba-rc.com/faq/faq-4yf-q738.html

From futaba,

"Radio System FAQ
I don't understand the red and green battery LED's on my 4YF, how do I know when my batteries are charged and when they are getting low?"

"Your batteries are sufficiently charged when the green LED comes on, on your transmitter. As you are using the transmitter BOTH LED's should be on steady. As your voltage gets low the red LED will start to blink as an indication that you need to charge."

boy do i feel stupid. ill never use that voltmeter on a tx again!

Well if you are using an esv they usually have two scales. One for tx's and one for rx's. 5v on the rx scale is around 10volts on the tx scale. I'd recheck it with the esv and note the reading on the tx scale. Better yet make yourself a loaded digital voltmeter. Probably cost 15$ at walmart.


There are instructions for a loaded digital voltmeter here.

http://www.rcbatteryclinic.com/

An expanded scale voltmeter is useless for anything except as a confidence booster. All it can tell you, with accuracy, is if the pack is already discharged and unsafe to use.

It's use is as effective as determining the VOLUME of air in a wheel by reading the tire pressure. Logic will tell you that this can't be done. Consider a small trailer wheel and a semi wheel. Inflate both to 40psi - which one contains the most air? The ESV's don't allow for diferent capacity packs, only cell count - go figure. NiCads and NiMH voltage curves are so flat when not in a discharged state that voltage reading indicates NOTHING of the remaining capacity.

The safest way is to discharge the remaining capacity after use and deducting it from the actual capacity. Divide the used capacity by the number of flights and you will know how much capacity is used, on average, during each flight. This way you can determine how many safe flights can be made with a pack. A good cut-off point is at least 30% before the capacity will be used up. (Ie, only use 70% of the capacity.) Remember that averages during flights will vary.

The fire and forget method of wall-wart chargers and guesswork, will eventually cause free-flight - not fun at all.

Safe Flying!

The flat discharge curve of nicads is the reason for the loaded digital voltmeter. The loaded digital meter reads in tenths and hundredths of a volt to be able to better estimate the portion of the discharge curve you are on. The discharge curve steepens quickly at both ends of the curve. This means the pack loses voltage quickly when fully charged then maintains a pretty steady voltage until it is almost discharged then loses voltage quickly again until it is dead. The point at the end of the curve where the voltage drops quickly is what you are looking for.

Coqburn

You are correct that digital meters will give you a more accurate reading. The problem still remains that you can only really do a proper determination of the nearness of the drop-off at the end of the discharge curve. You still cannot reliably determine if there is still sufficient capacity remaining for safe flight.

As no 2 packs are identical, absolute voltage values cannot be used either. Unless you have an accurate discharge curve for each pack to refer to in reference, you cannot determine where you are on the curve.

An ESV cannot be used as a Go, No-Go tester. It can be used for No-Go determination only.

We RC pilots can expand on the 3 most useless things to a pilot - runway behind you, altitude above you, fuel back home and charge still in the charger.

Safe Flying!

BTW- raideron- The diode is to prevent you from putting a charger on with reversed polarity which would be very baaaaad. [:'(]