Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Sep 07, 2012, 08:33 AM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
haha! thanks porcia.
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 10, 2012, 05:21 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
Just a follow-up:

I received a refund of the battery cost but no shipping adjustment. They said the shipping cost for 3 is the same as if I bought only one. Well yes but naturally I bought 3 to rduce the impoact of shipping. To buy a new single battery from HP will now cost half again as much as the battery just to get it shipped. If they'd sent a replacement, I wouldn't have had to pay additional shipping. Oh well.

Anyway, out of curiosity, before throwing the defective battery away, I thought I'd take the shrink wrap off to see if there was anything amiss. As I said the battery showed no outward signs of problems. It was tight, with no evidence of puffing. And my charger said there were only 2 cells. The balance plug showed no voltage difference between the 3rd and 4th wires (last cell)

What I found was a cold solder joint on the last balance wire. There was no connection there -- it was just held in place by a piece of melted insulation.
vtdiy is offline Find More Posts by vtdiy
Last edited by vtdiy; Sep 10, 2012 at 06:10 PM.
Reply With Quote
Old Sep 10, 2012, 05:59 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
Here's a close-up of the bad joint.

I decided to try re-soldering it. I used a weller gun and made the joint good. Then tried it on the charger (outside). My charger charges each cell up individually through the balance plug. There are LED lights for each cell. When charged they turn from red to green.

Originally the bad cell didn't light the LED at all. After re-soldering it turned green. However a check of the main battery leads showed only the voltage you'd expect on 2 cell, not 3.

I then checked the voltage across the single bad cell. It was only 0.1 volts -- almost nothing. This was confusing, since the cell was nice and tight, not puffed. My understanding was that if cell voltage dropped below about 3, you could expect puffing. This cell was only a tenth of a volt!
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Old Sep 10, 2012, 06:04 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
I considered taking the bad cell off and making the pack into a 2 cell pack. Maybe recoup some of the lost postage money that way.

But I thought I'd try slow charging the bad cell to see if I could rejuvenate it. I have an old nicad flat charger that lets me set the charging current. I set it at 30 milliamps -- very conservative, but I'd read not to charge at regular rates until a Lipo reached about 3.2 volts. Charge rate should be very low before that point.

I should say that in all of the reading I've done, nobody says you can rejeuvenate a lipo at 0.1 volts. In fact most say they are dead below 2 volts. But in the interest of experimenting before discarding, I decided to try trickle charging that cell. Again, I did this outside for safety reasons.
vtdiy is offline Find More Posts by vtdiy
Last edited by vtdiy; Sep 10, 2012 at 07:27 PM.
Reply With Quote
Old Sep 10, 2012, 06:34 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
I watched both voltage and charge current for about 15 minutes, and checked the cell temperature, which was cold the whole time. When the cell reached 3.4 volts I switched to my normal Lipo charger and set the charge current to 0.5 amps. This was its lowest setting.

The LED lit red for that cell, which is normal for charging. That is the first time I've seen this cell charge. The charge rate was less the 0.4C, still conservative.

It's been charging now for about 3 hours and the cell voltage is up to 4.0 V. I have no idea if it will reach 4.15 V which would be fully charged, or whether it will hold a charge. Or what the capacity will be, if anything. But so far, the cell is cold and there has been no puffing.

Guess we'll find out.
vtdiy is offline Find More Posts by vtdiy
Last edited by vtdiy; Sep 10, 2012 at 07:29 PM.
Reply With Quote
Old Sep 10, 2012, 07:18 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
The cell reached the charger cutoff point so I disconnected it. My voltmeter shows 4.1 volts after an hour off the charger. We'll see how it holds the charge overnight.
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Old Sep 10, 2012, 10:42 PM
Well, now that you know ...
Bigster's Avatar
Grafton, Massachusetts, United States
Joined Sep 2004
5,604 Posts
From what I understand the longer the cell is below 3v or so, the more damage is done. You'll probably get some service out of it but I expect it won't perform like the other two. Keep an eye on it. Having one cell dump out on you at a bad time might not be fun.
Bigster is offline Find More Posts by Bigster
Reply With Quote
Old Sep 11, 2012, 08:06 AM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
This is all just out of curiosity bigster.

I've read the same things you have. But also that going down to 0.1 volts means a completely shot cell, and results in serious puffing.

This one isn't either of those things, at least so far. Sometimes I like to see things for myself.

I have a wattmeter and test stand and a newly rewound motor, so I will be looking at what that cell does under test compared to the others in the pack. Should be interesting.
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Old Sep 11, 2012, 09:43 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
I ran the battery in my foam Mambo drawing about 10 amps WOT, and held it static for about a minute. Then let the battery rest (it was warm, as was the motor) for 5 minutes and measured all of the cells. All measured 3.9-40V. I re-measured 3 hours later and they were all at 4.0 V.

This certainly isn't an exhaustive test, but it is looking good so far. I'll probably exercise it a little deeper tomorrow.

If the bad cell maintains its voltage equal to the other cells all the way down to 3.7 V, and then goes through a few cycles like that, I'm going to call it cured, and put the pack back together again.
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Old Sep 12, 2012, 08:55 AM
Well, now that you know ...
Bigster's Avatar
Grafton, Massachusetts, United States
Joined Sep 2004
5,604 Posts
It would be interesting to get a voltmeter (or a cheapie cell voltage meter) onto that cell when you're running it. The reason I say that - I have a HobbyPartz 1800mah 3 cell battery, and one cell is shot. Very few cycles. But, I can measure the voltage before and after flying and it appears fine. When I watch it under load, it completely craps out.
Bigster is offline Find More Posts by Bigster
Reply With Quote
Old Sep 12, 2012, 06:52 PM
low tech high tech
vtdiy's Avatar
Southern Vermont
Joined Feb 2007
3,028 Posts
Well, I'll try it Bigster. Should be possible to do through the balancing plug. And I should probably get the voltage of a good cell at the same time to compare.
vtdiy is offline Find More Posts by vtdiy
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion HobbyPartz.com - The second worst Customer Service on the Planet YouMadeMeDoIt Vendor Talk 4 Feb 03, 2012 02:41 PM
Discussion HobbyPartz Customer service Shuedog HobbyPartz.com 19 Apr 22, 2011 07:37 PM
Discussion HobbyPartz "Customer service" TexasFlyr HobbyPartz.com 0 Feb 25, 2011 12:42 PM
Rant Disappointed with Hobbypartz Customer Service typhoonmaster HobbyPartz.com 10 Jan 28, 2011 11:34 AM
Discussion hobbypartz crappy customer service b-29er Vendor Talk 20 Dec 23, 2010 03:35 PM