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January 17, 2008 07:03 PM

Categories: Dragonfly

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Outpatient

Member
Joined: 12/30/2007

My blue DF's flight time is down to about 2 minutes on a full charge. I suppose there is no other option than buying a new lipo battery and performing surgery on the little bugger?

Where can I get a similar or slightly larger replacement battery? About how much do you think it'll cost? 

---
http://0utpatient.com
http://oeyec.com

Discussion:    Add a Comment | Comments 1-9 of 9 | Latest Comment

GWJax Avatar
  Member
January 17, 2008 8:41 PM

Just a question and possible solution. When you recharge the dragonfly are you letting all the power out or recharging it before it is complety discharged? What type of battery is it? incase you have what is called a memory effect. try discharging it completly with a 100 ohm 1 watt resistor across the battery and let it stay there over night and recharge it back up to see if that works. GWJax

GWJax, To Hack and make mods on robots is a life style and comes natural and not by choice. If a robot has a screw to open it then it must be opened!

MrScott Avatar
  Moderator
January 17, 2008 8:50 PM

This from the official WowWee Dragonfly details page

Power: Rechargeable lithium polymer battery
Flight time: Up to 10 minutes on a single charge

If those are Lithium Ion batteries, you should not dead flat discharge them.

http://batteryuniversity.com/partone-12.htm 

A quote from that page

" Extreme low voltage must also be prevented. The safety circuit is designed to cut off the current path if the battery is inadvertently discharged below 2.50V/cell. At this voltage, most circuits render the battery unserviceable and a recharge on a regular charger is not possible.
There are several safeguards to prevent excessive discharge. The equipment protects the battery by cutting off when the cell reaches 2.7 to 3.0V/cell. Battery manufacturers ship the batteries with a 40% charge to allow some self-discharge during storage. Advanced batteries contain a wake-up feature in which the protection circuit only starts to draw current after the battery has been activated with a brief charge. This allows prolonged storage.

In spite of these preventive measures, over-discharge does occur. Advanced battery analyzers (Cadex C7000 series) feature a 'boost' function that provides a gentle charge current to activate the safety circuit and re-energize the cells if discharged too deeply. A full charge and analysis follows.

If the cells have dwelled at 1.5V/cell and lower for a few days, however, a recharge should be avoided. Copper shunts may have formed inside the cells, leading a partial or total electrical short. The cell becomes unstable. Charging such a battery would cause excessive heat and safety could not be assured.  "

ScottE -- Member (always) & Moderator (when needed)

GWJax Avatar
  Member
January 17, 2008 9:01 PM

got ya I did not know what type of battery it had. Thanks for the update.  When I get my Dragon Fly, I will not misinform anyone or atempt to do anything that would harm their bot.

I love this forum everyone learns something everyday,GWJax

GWJax, To Hack and make mods on robots is a life style and comes natural and not by choice. If a robot has a screw to open it then it must be opened!

milw Avatar
  Moderator
January 17, 2008 9:23 PM

Yours truly did a blog post on the Dragonfly battery, you should be able to find a LiPo match at one of the online R/C hobby sites...

Rovio rules!
Wisconsin Iron :: Cellular Atomics

GWJax Avatar
  Member
January 17, 2008 9:35 PM

Who is yours truly? is that santa? LOL just kidding. I'll check it out thanks,

 GWJax

GWJax, To Hack and make mods on robots is a life style and comes natural and not by choice. If a robot has a screw to open it then it must be opened!

Outpatient Avatar
Member
January 17, 2008 9:55 PM

milw said: Yours truly did a blog post on the Dragonfly battery, you should be able to find a LiPo match at one of the online R/C hobby sites...

At the end of your article you say:

he Dragonfly remote is built to charge the 50 mAh battery safely, and the Lithium Polymer batteries do need careful control of the charging current and duration. This will be the subject of future investigations- opening the remote and examining the charging ciruitry- 

 Has there been any future investigations?

---
http://0utpatient.com
http://oeyec.com

milw Avatar
  Moderator
January 18, 2008 8:51 AM

Ah, oops. Well, 'what is today but yesterdays future?'

Rovio rules!
Wisconsin Iron :: Cellular Atomics

Nocturnal Avatar
  Member
January 18, 2008 10:42 AM

While I never looked in to the charging circuit, I did crack open the remote and take some photos. You can see them on my site here.

RoboGuide - Your guide to hacking all things WowWee

milw Avatar
  Moderator
January 18, 2008 12:00 PM

I opened up my DF controller, it appears that the charger is based on an AMS1117 1A adjustable voltage regulator, whose output is controlled by another transistor. The battery company has a new URL for the battery page as well, look for the 501417 50 mAh battery. Since the recommended charge rate is 4-6C, that means 200 mA to 300 mA for 10-15 minutes; but also the pulse charge rate (for <5 sec durations) is 20C = 1 A. So I'd say it looks like the charging is being done in pulses at currents between 300 - 1000 mA, given the way the LEDs pulse on and off while charging.

I'd also suspect the brains that are controlling the pulsing are located in the epoxy-potted mystery IC that can be seen on Nocturnal's photos (a soldered-in daughterboard at right angles to the main board, next to the throttle controller. There are no other ICs on the board, just some transistors and discrete components.

ps I followed Nocturnal's advice and drilled small holes in the centers of the controller knobs, to get at the screws that hold the knobs on. Worked like a charm, thanks Nocturnal! 

Rovio rules!
Wisconsin Iron :: Cellular Atomics

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