tomgreen

I am using a 4.8 1100 Rx pack in my plane. Can someone tell me how low can the voltage drop and still be able to fly safe, before calling it a day at the field ?

MajorTomski

NiCads have an unique power curve, they drop rather rapidly from their full charge to nearly a flat line just above their rated voltage. They hold that for a long time then suddenly drop off from there.

I stop and recharge at 4.9 volts

MajorTomski

Sorry don't know why it double posted

But the Hobico/Tower voltmeter has a built in load, it works quite well at the field

http://www3.towerhobbies.com/cgi-bin...?&I=LXWDZ5&P=7


Tom

P-40 DRIVER

Using a loaded volt meter, I stop flying if I see anything below 4.8 volts. you must use a loaded volt meter of at least 300 mil amp load. No load readings are useless.

tomgreen

So last night a gave them a full charge, when I get to the field it's reading 3.8 volts. So I put the pack on a quick charge. this took about 7 minuites to go to trickle. Still reading 3.8 volts. Do you think i have a bad cell?

guver

My Feedback: (325)

Yes, 1 or 2 bad ones.

P-40 DRIVER

time for a new pack

tomgreen

Thanks, to the hobby shop I go.

KW_Counter

I agree with P-40 Driver.
A battery will hold at its nominal voltage of 1.2 volts per cell for a long time.
Once it gets below that it can fall off rapidly.
And yes, it must be checked with a loaded meter.
I make my own loads for my $18 Wal Mart multimeter.
I use about 24 ohms so I get about 200 mAh.
Using 300 mAh load would be better.

Good Luck,
KW_Counter

YellowBlueBird

It took me two months to isolate a problem that looked like a bad pack. The pack which had some age on it only charged to about 5.1 volts. after one flight it was down to 4.9 and then another flight down to 4.8 even below by third flight of ten minutes. A new high quality 1100 nicad pack was installed in the plane which gave good results on a cycler. after a few flights this pack also looked liked it had gone to pot. It looked like three old packs had all died in the same week and the new one did not look so good. Time to look somewhere else. It turned out to be the cable that attached the Futaba tester to the battery. I have checked that cable with a high quality ohm meter good down to .01 ohms. It checks the same as the good cable. Put the cable back in the tester and the battery reads about .5 volts lower than with the good cable. What would have happened if that cable had been used as an extension cable between the battery and receiver? I am still puzzled as to what is going on there. It has got to be resistance in that cable somewhere. any thoughts on how to analyze the cable further.

guver

My Feedback: (325)

I take it this is some kind of extension cable? and hopefully only has 2 wires to it. It sounds like you already know it's trash , but if you want to further pinpoint the trouble perhaps you can actually run some current thru it (maybe even 1 at a time to isolate the bad one) and using a temp gun find the hot spot? I'm no electrical guru , and I just made that test up. Perhaps the actual connections would be the first place to look? Clean them, wiggle them during the battery test?

P-40 DRIVER

More then likely, the problem is in the connector. When your ohming the wire out, its not under load, so you may not see breakdown. you are also not checking at the pins most likely so your bypassing the problem. Toss it and move on. At least you know you have an issue unlike so many people who have not a clue untill they crash.

YellowBlueBird

Thanks Guver,

I some times used an oversized power supply to find shorts on mother boards. Thanks for the reminder. These new fangled temp measuring things are probably better than my fingers at finding differences. So its off to HD to buy a new toy.

The cable is identical to a servo extension cable. The thing that has made this interesting is that each of three servo extension cables gave me a slightly different voltage. As much as two tenths. What would have happened if this cable had been used as an elevator extension cable? The reading with this cable is about four tenths low. After it has been pummeled and beaten on in every way that we can think of I am going to cut the ends off and put new pins on. Each end can then be tested in someway and so can the middle.

After a lot of testing it turns out that one of my three old batteries is bad. It will charge up to a good operating voltage and appears to work ok but by next morning it is down to 3.4 volts.

P40 Driver,

Rest assured that this is not going back in an airplane. The thing that bothers me is that there is not a good way to test extension cables and there are some that have been in my planes for five years and could be developing the same problem that this one has.

Mo Lata

Jerry

richrd

Rest assured that this is not going back in an airplane. The thing that bothers me is that there is not a good way to test extension cables and there are some that have been in my planes for five years and could be developing the same problem that this one has.

Mo Lata

Jerry


As said above all cables are placed under max load (1 to 2Amps)an voltage loss in cables measured, also pulling on all connection under load is monitored.
You could test all cables in minutes once the jig is setup. Would will find the bad crimp or loose connecter the second it was plugged in.
Rich

YellowBlueBird

The problem was on the battery end of the cable. A solid push on an individule pin and the problem went away. The voltage jumped from 4.4 to 4.8 and the problem could not be made to come back. The pins have been released from the connector. They look OK and so does the crimp. It looks like this horse has been beat enough.

Thanks for the help guys.

Jerry