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May 25, 2007, 03:31 AM
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Discussion

The ultimate battery charger.


The LiPo's have gotten unbalanced enough that the Astro Blinky isn't doing the job anymore. Anything faster than a 10 hour charge causes them to exceed 4.2V while the Blinker blinks away. There is value in a custom charger. The problem is how to test it.

Requirements:
- 1-6 cell support with automatic detection of the number of cells.
- Momentary pushbutton to start and stop charging.
- Charges through the balancing receptacle.
- Disabled if reverse polarity detected.
- Independant voltage readings for each cell.
- Provides minimum current until all cells are over 3.7.
- Provides user selected current if all cells are over 3.7.
- If cells are unbalanced, only the weakest cell is charged until all
cells are within limits.
- If cells are balanced, all cells are charged until all cells are 4.2.
- Once charging finishes, cells that drop below 4.2 are topped off using minimum current.
- LED's for each cell show status: flashing if charging, solid if done.
- Total cost < $50

Implementation notes:
- 1 * LM317 current regulator for each cell
- H bridges to allow individual cells to be charged
- PWM to switch current
- Apply current for 29s to charge batteries, stop charging for 1s to measure battery voltage
- Ground lowest cell when not charging.



Meanwhile, stepped up the IMU rate again and enabled compiler optimization. Using 33% CPU, she now does 5 IMU updates for every compass update. The IMU sample rate is 172Hz and the Kalman rate is still 31Hz because this is locked to the compass rate and the servos only respond at 20Hz.

Well, we've tried many different techniques but nothing seems to be holding attitude enough. A derivative 4x bigger than the proportional term actually kept her within 10ft of the target position, but she was pitching 45' each way.

It's a good time to focus on astrophotography now.
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May 25, 2007, 07:05 PM
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Discharger function would also be nice ... to drop lipo voltage to 3.7 - 3.8 Volt before storing.

Kos
May 26, 2007, 12:42 AM
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Probedude's Avatar
How about just building multiple single lipo cell chargers? Like the DN charger. Add as many of these modules as cells you want to charge. Put some smarts on it to do the functions you want.

BTW, I don't get the part where you are using a LM317 but then are doing PWM to switch current.

Dave
May 26, 2007, 03:43 AM
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Since the balancing header on a battery doesn't allow charging each cell on an independant circuit, it's more likely to be switching current between cells very rapidly. This simulates simultaneous charging on independant circuits but is really charging 1 cell at a time on the millisecond scale.
May 26, 2007, 02:08 PM
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Probedude's Avatar
Quote:
Originally Posted by Jack Crossfire
Since the balancing header on a battery doesn't allow charging each cell on an independant circuit, it's more likely to be switching current between cells very rapidly. This simulates simultaneous charging on independant circuits but is really charging 1 cell at a time on the millisecond scale.
Okay, gotcha.
However if your individual charge circuits were electrically isolated from each other BEFORE attaching to the balance tap, you can in fact charge the cells individually through the balance tap.

Again, this is how the DN charger works. It is really 4 individual 1 cell lipo chargers, electrically isolated using transformers.

Dave
May 26, 2007, 02:28 PM
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Draw a schematic and I'll implement it. I'm not paying $90 for a battery charger.
May 26, 2007, 02:46 PM
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Probedude's Avatar
Take a look at this dwg. 4 individual charging ckts, all charging individual cells but through the balance tap connector.
https://www.rcgroups.com/forums/show...48#post7457148
May 26, 2007, 06:44 PM
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Jack Crossfire's Avatar
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Now if you can get the cost of 6 transformers below $20.
May 26, 2007, 06:50 PM
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Probedude's Avatar
Post an update when you have your setup working. I'm interested in seeing how it performs and what your end costs are.

My information was just a rebuttal to your statement here:
Quote:
Since the balancing header on a battery doesn't allow charging each cell on an independant circuit,
It can be done, and has.
Last edited by Probedude; May 26, 2007 at 06:59 PM.
May 26, 2007, 09:44 PM
kit
kit
Registered User
This is what the inside of the DN charger looks like. Go for it. Keep the cost down! Lol
Wind your own isolation transformers. 12v in -> 5 or 6v out @ 2 or 3 amps.
Here's the thread about it.

https://www.rcgroups.com/forums/showthread.php?t=535274
Last edited by kit; May 27, 2007 at 04:27 PM.
May 26, 2007, 09:52 PM
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Quote:
Originally Posted by Jack Crossfire
Draw a schematic and I'll implement it. I'm not paying $90 for a battery charger.
What about 39$ ?

https://www.unitedhobbies.com/UNITED...idProduct=3824

Sometime it if far less expensive in time and money to buy something the then actually make it !

Kos
Jun 19, 2007, 10:06 PM
kit
kit
Registered User
You have the lipo charger done yet? Something that Others could actually Use?
Jun 28, 2007, 11:03 PM
kit
kit
Registered User
Still waiting for your lipo charger design.
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tap
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tap
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tap
Jun 29, 2007, 12:13 PM
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Jack Crossfire's Avatar
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TODO list:
1) 2 way RS232 communication
2) complete autopilot
3) software releases
4) battery charger

Can U offer something to speed this up?


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