HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Aug 31, 2003, 10:13 AM
Registered User
slammin's Avatar
Everett Snohomish, Washington, United States
Joined Jun 2002
238 Posts
Can you charge lipoly batts through a wattmeter?

I need a charger for my lipoly batteries, and would rather not spend the money for something like the trition with a built in display, so I'm wondering if you can charge lipoly batts on a cheap charger, through a wattmeter, to see how many mah has been put into them. I have heard of people doing this with nickel batteries, but those have a peak detection, not a constant current/constant voltage charge like lithiums do. Anyone done this or have any thoughts?

Chris
slammin is offline Find More Posts by slammin
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 31, 2003, 11:04 AM
Crash Site Instigator
sheerLuck's Avatar
Novato, CA USA
Joined Jan 2002
917 Posts
Yes, I do it. I don't think the WhattMeter knows or cares what chemistry the batteries use...

Larry
sheerLuck is offline Find More Posts by sheerLuck
Reply With Quote
Old Aug 31, 2003, 12:31 PM
Registered User
Winnipeg Intl, Canada
Joined Mar 2002
657 Posts
Chris:

How many cells are you running in your battery pack? If it is the typical 2 cell, then look into using a cell phone charger specifically made for Lithium batteries.

All you need to do is put an appropriate connector on it to charge your expensive cells with safety and next to zero risk....after all, they are made with the lowest common denominator intelligence level end user in mind that will accidently leave the battery on charge for 2 weeks while they go on summer vacation!

I have had great results using them on LiPoly cells, and if you know one end of a soldering iron from the other and have a voltmeter, just find the positive and negative feeds and connect it up.

The cell phone industry is changing from using 2 cells to a single cell, so make sure the charger is for an older, 2 cell phone. Mine cost $1.99 on sale, so price is sure not a factor. There are many after market manufacturers of cell phone chargers that will work nicely.

The one I use was originally made to charge a Motorola model SC-3100 phone.

Lee Smith
Radioguy is offline Find More Posts by Radioguy
Last edited by Lee Smith; Aug 31, 2003 at 12:33 PM.
Reply With Quote
Old Aug 31, 2003, 01:59 PM
Registered User
slammin's Avatar
Everett Snohomish, Washington, United States
Joined Jun 2002
238 Posts
I do use a couple of cell phone chargers currently, but it would still be nice to know how much energy it is putting into the packs. I would also like a charger that does the proper constant current/constant voltage charge, as opposed to the constant voltage charge of cell phone chargers. It would also give me some more performance, since the cell phone chargers have to cut out at a lower voltage.
My conern is what the voltage loss through the wattmeter might do to the charge cycle. Correct me if I'm wrong, but for nickel chemistry batteries, the charger is looking for a peak. Even with the voltage loss through the wattmeter, it can still see a peak, and it would then stop charging. For a lithium cell, the charger is looking for a certain voltage, correct? So would the voltage loss through the wattmeter cause the charge to stop early? Or is the voltage loss through a wattmeter so small that it really doesn't matter?

Chris
slammin is offline Find More Posts by slammin
Reply With Quote
Old Aug 31, 2003, 02:42 PM
Registered User
WJ Birmingham's Avatar
St. Louis Metro
Joined Apr 2003
2,440 Posts
Yes, you can use a Whattmeter to monitor battery charge. I do so on every pack I charge.

The Whattmeter consumes 17milliamps for power, so it's really a non-issue for power consumption during charge or discharge.
WJ Birmingham is offline Find More Posts by WJ Birmingham
Reply With Quote
Old Aug 31, 2003, 05:29 PM
Radix malorum est cupiditas
radix2's Avatar
Joined Jul 2000
460 Posts
As the batteries become fully charged, the charge current drops to nothing - therefore, there will be virtually no drop across the wattmeter as the charge is completed - and no error to be concerned with.
radix2 is offline Find More Posts by radix2
Reply With Quote
Old Sep 01, 2003, 12:30 AM
Flys with Thumbs
Danal Estes's Avatar
Frisco, TX, USA
Joined Sep 2001
1,858 Posts
See this thread, scroll down to photo:

http://www.rcgroups.com/forums/showt...hreadid=144198

The black square on the edge of the fire safe, in line in the wiring from the constant current / constant voltage power supply to the battery, is a whattmeter.

Didn't realize it was face down when I took the picture...

So, the answer is: I use a CC/CV power supply + a whattmeter to charge LiPos. More description on the Power Supply technique here:

http://www.rcgroups.com/forums/showt...hreadid=144348


Danal
Danal Estes is offline Find More Posts by Danal Estes
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Can you charge Li-ions with a Li-poly charger? VFR750F Batteries and Chargers 7 Oct 01, 2004 09:02 PM
How often can you charge Li-polys? scottym Batteries and Chargers 5 Aug 25, 2004 03:27 AM
How cold can you charge? mtbrider Batteries and Chargers 2 Mar 01, 2004 03:34 PM
Can you charge Li-poly with Shulze? SWE-flight Batteries and Chargers 3 Apr 10, 2003 07:19 AM