cruzomatic

My Feedback: (17)

This past weekend after charging my GP J3 Cub all night on the wall wart I get to the field and fire it up. Went though my preflight checklist and noticed my voltwatch was reading a bright red LED. I figured it just didn't charge up all the way so I put it on my field peak charger. After it tells me it's done, I fire it all up again and again bright red LED. I check the battery with my loaded voltmeter and it tell me a "no go" 3.9volts. I tell myself bad pack or bad cell.

For giggles and grins and put it on my cycler here at home. Cycle it numerous times (5) and it takes in 940+mah each time. Battery is a 4.8v 1400mah Nicad (JR pack) I put it on my loaded voltmeter and it tell me 5.4volts+ each time (did this about 5 times). Oh, also put it back on the planes voltwatch and it tells me green fully loaded battery.

Thoughts,,,,?????

bassmanh

My Feedback: (5)

cruz,

sounds like your switch might have a bad/loose wire in thats not letting you charge through it. first thing i would check is the switch.



bassman

Missileman

I would replace the battery myself and not risk my plane to a suspicious battery. It failed once so even if it reads ok now it can very well fail in flight.

draftman1

I would replace it also. I always plug the battery charger directly to the battery, I bypass the switch

n19htmare

My Feedback: (1)

Replace it. RMA it with JR if it's new bad pack. But really, I've heard some mixed reviews on the packs that come with the JR radios, including the DX7. Really not worth the hassle. I cycled my 1650nimh pack after about 100 flights and it took 1630mah. This is a Sanyo pack from Radical RC.

RCKen

My Feedback: (9)

It sounds like the pack has a dead cell in it. When they have a dead cell it will do exactly what you described. The battery will appear to charge normally, but as soon as a load is placed on it the voltage will drop drastically. Don't risk your plane on a pack like this. Replace the pack.

Ken

Allfat

My Feedback: (1)

Well, the battery is only taking about 67% of its capacity when you were cycling it. I would toss it and get a new one. They are cheap compared to a new plane.

Campgems

Your volt watch story sure sounds familiar. I had exactly the same thing happen, although I lost control on take off. I could not find a single thing wrong with the battery, switch, or the receiver. After two times with a red light, followed by a full green before charging, I came to the conslusion that I had a bad switch and replaced it. I am currently flying that same battery after skinning it and checking each individual cell under a 10 Ohm load. All cells read withing 0.001 volts of each other, all welded tabs were tight. I wrapped it back up, replaced the lead, and put on new shrink tubing. Don't know what the issue was.

At a minimum, I would replace the switch harness. I would also skin the battery and have a look. The 3.9 is a bit suspissious as that would be 1.3V per cell in a three cell pack. Add one more 1.3 and you're up to 5.2V Close to the reading you were getting right after a fresh charge when things seemed to go well. It sure points to a battery on your porblem. One with an interment short in one cell.
Don

cruzomatic

My Feedback: (17)

All good thoughts. Thanks for your input. I'll replace the battery.

cruzomatic

My Feedback: (17)

UPDATE:

I was in the shop today and figured I'd check each cell individually. The first three I checked had 1.2v respectively and the fourth,,,,,,,,sure enough had 0.0v. Dead cell, bad pack, no bueno.

Thanks for the help guys. That was a close one,,,,could have lost my Cub.