Does anyone have a cheap method to check their Rx batteries?

I just need something that will tell me if I am 1/4, 1/2 or full. Just a piece of mind before taking off for a second or third time.

I use JRreciever and Tx with a 4 cell NMah pack 1500.

thanks!

A loaded volt meter will tell you if you have a full charge but you will need a battery cycler to tell you if your battery is is drawing down the mah. I just cycled my batteries and I had one that was a 4.8 volt 1450mah. It took a full charge but when I cycled it the battery would only draw 300mah. A good battery shouled draw at least 80% of it's rated mah. Mine wasn't good!! I tested it several times. Same thing every time. I'm having some new RX packs made up for me now. A good charger that will cycle is a must have item for good battery maintance.

These will check the battery under a load similar to that of servos in use, and give you a good idea of your battery power. http://www3.towerhobbies.com/cgi-bin...?&I=LXWDZ5&P=7 It is a must for any field box.


Another nifty device that is often recommended and they do work well is http://www3.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=ML.

The voltwatch is optional but for sure invest in the expanded scale voltmeter. These devices will save planes.

Or buy Hitec Aurora 9 2.4 Ghz Transmitter which on it's 5.1" screen shows you the flight pack/Receiver pack's voltage on real time on your screen as well[8D]

Just whatever you do use a loaded voltmeter......something like a fluke will only tell you the voltage of the pack...not how the pack will do with a load like your servos and receiver....there is of course a volt watch that will constantly tell you the voltage...and it will use the aircraft for the load

You can use a standard meter the same way you use a voltwatch. Just run an extension from an empty channel on your receiver that you can test with your meter. If you'll manually put a load on one of your control surfaces, that's enough to tell if your battery is good.

There is a inexpensive volt meter at Pepboys right now in the bin and bargin section. Its 7.00 dollars

Those $3 harbor freight ones work for the way I was describing too.

If you are having trouble with your NiCd or NiMH batteries, you should look at the LiFe batteries. I have a couple from Hobbico and their charger. These are awesome. I didnt charge it in a couple of months as this is currently my spare. When I put it on the charger, it was still full. Discharging insing a NiCd routine on another charger it gave 3200mah even after a couple of months of not being used. They are still safer than using LiPo batteries and can take a lot more abuse

Ameyam

This Expanded scale voltmeter is rated only for 4.8v batteries, does anybody knows if they also come for 6v 1600mAh 5 cells?

This Hobbico one does 4.8v, 6.0v and 9.6v batteries. I have used mine for 3 years now and it has worked flawlessly every time!

http://www3.towerhobbies.com/cgi-bin...?&I=LXWW16&P=0

It does them all you just change the positive lead to the right side for higher voltage

If people like myself are set up and using Nicad and Nim then they have to go to the added expense of a new charger plus the batteries. This isn't such a big deal right now, the chargers have come way down in price. I got lucky and someone gave me there old charger when they bought a couple of new ones. I also got lucky, the one I was given will go AC/DC so it can be used in the field. It charges all types of batteries we use in RC, more luck.
Chargers are good but unless you can cycle your batteries you don't know the condition of them. I just picked up two new packs I had made up for me, both 6 volt NIM. Before I set them on a charger I used an unloaded meter, they are both right at 6 volts, under load they took a drop to about 4.8. Being brand new they will be charged and cycled from three to four times to get them up to full capacity. Unless you can cycle all you know is the voltage. Volt watch and meters can tell you it's safe to take off but that fully charged battery can poop out on you within minutes of that take off. It only takes one bad cell to kill the pack.

The original question of a simple method to detemine "how much is left" requires a little homework on the part of the OP. There are two ways of approaching the question. First, if your setup is a 1500 mah 4 cell nicad or NIMH battery on a typical 40-90 size plane, 4-5 servos, it is probably drawing around a 400 mamp rate. At that rate, the battery should last for a total of over 3 hours total flying time (300 mamp x 3 hours = 1200 mah).

The typical flight lasts around 10 minutes, but your style may differ. With 10 minute flights, that's 18 flights. I don't think I've ever made 18 flights in one day on a single plane.

Now the question of voltage. The most accurate way to establish the "no fly voltage" on your set up is to create a battery discharge curve. You can do this from just about any charge state on the battery (as long as its not fully discharged). Fully discharged state for nickle based batteries is 1.1 volts per cell (4.4 volts in the OP's case). The curve is easy to create. Plug your loaded volt meter into the charging plug and leave it there. You can use the loaded volt meter to discharge the battery (it should be around 200 ma rate) or just turn the plane on with all servos connected. Either way, you want a constant discharge rate. Now record the voltage every 5 or 10 minutes. When the voltage drops to 4.75 volts, check it more frequently. You'll eventually see the point where the voltage drops off quickly. You can go down to 1 volt per cell without damaging the battery, but there is no point in going so low.

Now make a graph of time and voltage. Look for the "knee" of the graph, and then go back 15 minutes. That voltage is now you're "no fly" voltage. In otherwords, that point where you are no longer confident that you have at least 15 minutes left. That graph can be laminated and kept in your flight box for reference. If you're really worried, do this annually for each of your batteries.

In my experience, that drop typically occurs between 4.5 and 4.6 volts for Nickel batteries. I usually set my no fly voltage at 4.7 volts.

Brad