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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> A123Racing Support >> Homemade charger
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Homemade charger - 2/1/2008 4:41:05 PM   
dirtybird


 

Posts: 2818
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline 		I plan to make my own A123 charger. I am planning an airplane that needs a 10s2p pack.
I have obtained a 400w inverter. I happened to have a Variac I used with my foam cutter. I plan to plug that into the inverter and connect a 25A FW rectifier to the output and use the output directly. I will be able to adjust the voltage with the Variac.
Of course I will have to keep an eye on the voltage and current while charging, but after awhile I should be able to just set the Variac and forget it.
Anyone care to comment?
       Post #: 1

RE: Homemade charger - 2/4/2008 11:09:30 PM   
ScaleFreak



Posts: 158
Joined: 5/29/2004
From: Zebulon, NC, USA
Status: offline 		Sounds like a cool project. I am interested to see the results!

Chris

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Chris
KF4DBX, AMA 498981

(in reply to dirtybird)
       Post #: 2

RE: Homemade charger - 2/7/2008 3:15:40 PM   
dirtybird


 

Posts: 2818
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline 		I made up the charger and checked it using line voltage and charging two lead acid cells in series. The voltage measured at the battery was 37 volts while charging at 10 amps. Since the DC voltmeter is recording the peak voltage this is what you would expect to see. 37x.707=26.9V.
I am wondering if the peak voltage will have an adverse affect on the A123 cells. Is a filter required?

(in reply to ScaleFreak)
       Post #: 3

RE: Homemade charger - 2/19/2008 2:24:19 PM   
dirtybird


 

Posts: 2818
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline 		I checked out the charger on a stack of 6 cells. They charged just fine at 15 amps. The peak voltage does not seem to bother them.

(in reply to dirtybird)
       Post #: 4

RE: Homemade charger - 3/9/2008 2:04:00 AM   
dirtybird


 

Posts: 2818
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline 		I have made two full wave rectifiers in one box. Each output is 10 A capability. With the variac connected to a 1K motor generator I got from Pep Boys for $100, I can charge two 10s A123 packs in 15 minutes. I checked the ripple voltage with an oscilloscope. Its less than 5 V. It does not bother the batteries.
I do have to watch it and make sure the voltage does not get over 40 volts/pack

(in reply to dirtybird)
       Post #: 5

RE: Homemade charger - 3/17/2008 1:33:01 PM   
FenceMagnet


 

Posts: 344
Joined: 3/15/2005
From: Treasure Island, FL, USA
Status: offline 		Unless you have a really strange meter, it shouldn't be reading peak voltage.... typical DVM's are average-reading meters and are calibrated to read rms on a pure sinewave. Better meters are true-rms. I believe the issue here is the non-sinusoidal output of the inverter. Nevertheless, results are what counts.... Great Idea


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Jim White

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RE: Homemade charger - 3/18/2008 7:27:21 PM   
dirtybird


 

Posts: 2818
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline
quote:

ORIGINAL: FenceMagnet

Unless you have a really strange meter, it shouldn't be reading peak voltage.... typical DVM's are average-reading meters and are calibrated to read rms on a pure sinewave. Better meters are true-rms. I believe the issue here is the non-sinusoidal output of the inverter. Nevertheless, results are what counts.... Great Idea


I have to agree the meter is strange. I think something is wrong with it.
I checked with Radio Shack-they have a True RMS meter but they want $60 for it. I know, thats cheap for such a meter but then I am even cheaper.
The ripple voltage is less when using the inverter than when inputing from household power.
I got my packs from a disassembled Dewalt 36V battery. It comes with plastic holders that have a connection to each cell. I preserved the holders in my airplane so I can check the voltage of each cell. So far I have not needed to do any balance charging

(in reply to FenceMagnet)
       Post #: 7

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