Skip to main content

2026-09-12 Braun F900 Battery Pack Possible Rebuild Details

I was recently given a Braun F900 battery pack and two heads. 


This is a side view of the battery pack with the battery removed.


This is the battery pack to power pack connection

Opposite the slide-in battery the power pack has the connection for the head plug.
    The battery pack had a lead acid battery holder installed, but the holder didn’t have any contents. I downloaded the Braun F900 manual, which mentions there was a NiCad pack available. What the manual doesn’t mention is the working voltage of the battery supply.












Lead BatteryPack—(from top) end view, inside shell view, outside shell view

    Lead acid cells are 2VDC each. The F900 lead acid battery pack shows four separate cells which would indicate the pack produces 8VDC. Since the Ni-Cad cells are 1.2VDC each, you would need 7 cells to make slightly over that voltage. To add to the confusion, on the internet one person is using his motorcycle’s battery—which I assume is 12 VDC—to power a F900.
    Batteries also have characteristics beyond straight voltage. Load is another characteristic. Some batteries can only handle small loads and keep a relatively constant voltage. Think light meters. On the other end of the scale electronic flash are huge loads and so their batteries have to face huge demands. Lead acid batteries can face huge loads as witnessed by starting a car with a 12-VDC battery that can briefly put out 200 amps. NiCad batteries can also put out huge amperage while maintaining close to their rated voltage.
    There are people out there that rebuild battery packs. I just assume I can’t afford that. So I started to look for battery packs for rechargeable power tools at thrift stores. I found a Craftsman™ 12V/20V lithium battery charger for $2 at one thrift store. Weeks later I found a Yardworks™ 24VDC NiCad battery for $4 at another thrift store. 

    Now I have several questions I have to answer—
    




    Should I use the NiCad batteries to fill the F900 battery pack I have? The advantage would be a compact battery supply unit (as opposed to the next possibility) with the disadvantage of a smaller number of flashes. The manual say the lead acid pack provides twice the flashes of the NiCad pack. I suspect that is because the electrolyte area is smaller in sealed NiCad batteries than the relatively huge lead acid cells. The original F900 NiCad battery will supply 70 full power flashes.
    


   These are end and side views of the Craftsman battery pack (left) and the Braun F900 Lead Acid battery pack shell.
     I could simply rewire the 24 VDC Yardworks™ NiCad to be two 12 VDC in parallel. This would give me 12 VDC at 3.4 amps. Not quite car-starting range, but sizable compared to the 1.7 amps an individual 12 VDC string of ten 1.2 VDC 1700 mAh cells. If I make the wiring changes and simply close the Yardworks™ battery up again I just have to find a way to attach the much bulkier Yardworks™ battery to the F900’s power supply. This would also make it easier to charge the Yardworks™ battery pack with my Craftsman™ battery charger.
    After further research it seems 12 VDC at 8.3 amps doesn’t blow the F900 up, and all the modified 20 cells rigged as mentioned can produce steadily is 3.4 Amps. at 12 VDC. 

Next I opened up the Craftsman 12V/20V charger to see how it is wired.

There isn’t much to learn inside the case. The case is held together with four star-point self-tapping screws (luckily I had the correct bit—they were really tight!).


    From what I can see from the AC cord in—black cord lower left—the blade terminals  (right) are marked from bottom up B-, ID, NTC and finally B+ at the top. Now all I have to do is transfer those markings to the blades once the case is buttoned up again. 
    Did a mention a real fear of dyslexia could crop up here?


    Now the board has been flipped over with AC cord lower right and the blades just poking out lower left. The blades are still B-, ID, NTC and B+ running towards the center of the board.

From a YouTube video on the Craftsman 20-VDC battery—


    I have measured the voltage and made the basic wiring diagram for Craftsman 20V battery.
In summary, the Craftsman 20V battery consists of 4 pins, namely
  • Positive B+
  • NTC (Mostly for Thermistor Data)*- For temperature monitoring
  • ID - ID stands for Identification of the type of battery the charger has to charge as it is rated as a 12/20 VDC charger
  • Negative B-
There are 5 pieces of 4V-18650 battery for my Craftsman battery pack. Inside the battery the voltage between (NOTE: there are four pads on the battery pack’s electronics board marked C1 to C4)—
  • Negative and C1 - Around 4V
  • Negative and C2 - Around 8V
  • Negative and C3 - Around 12V
  • Negative and C4 - Around 16V
The voltage measured between the terminals are as follow
  • Positive and negative - Around 20V
  • B+ and NTC = 0V
  • B- and NTC = Around 20V
  • B+ and ID = Around 20V
  • B- and NTC = 0V
One surface-mount resistor--1002--ties the positive terminal to the NTC pin.
We determine that the resistor value is 10000 ohms, or 10 kilo-ohms.

*NTC=Thermistor used for temperature measurement

    It appears the Craftsman™ battery charger is too complicated for my purposes. I have several straight 12-VDC computer battery supplies lying around here I could rig up easier than trying to rework the Craftsman™ to my purposes.
    Now I just have to round up some reasonably heavy wire. 
    And there is still a way to go until I actually cut the Yardworks™ battery up. 

Comments

Post a Comment

Popular posts from this blog

2026-03-14 - History and Evolution of the Kodak Logo

  While working as a junior clerk at the Rochester Savings Bank, George Eastman first began commercial production of dry photographic plates in a rented loft of a building in Rochester, New York in April 1880. In the next few years, Eastman became very successful and expanded the company several times. His company started as the Eastman Dry Plate Company in 1881, later became the Eastman Dry Plate and Film Company in 1884, and soon after the Eastman Company in 1889. The last name change occurred in 1892, when the Eastman Kodak Company of New York was organized. The company has been called Eastman Kodak Company ever since.  The word "Kodak" was first registered as a trademark in 1888. The letter “K” had been a favorite of Eastman’s, he is quoted as saying, "I devised the name myself. The letter 'K' had been a favorite with me; it seems a strong, incisive sort of letter. It became a question of trying out a great number of combinations of letters that made word...
Post a Comment
Read more

2026-03-20-Manfrotto monopods

  Sometimes collecting is a matter of persistence.       The Manfrotto “GRUPPO” 434SSB monopod (shown top) showed up one day at my local thrift store. They had a price tag of $25 on it. I had bought the lower Manfrotto Compact MMC3-01 monopod at the same thrift store for $3. So I asked, “Why so much?” They answered their “expert” had found it sold for $200 on the internet. I find experts—who almost never clerk in the thrift store, so are unreachable—hard to deal with. There is also the matter someone might actually pay them $25 for a 2.27 kg (5 pound) aluminum pole, so I decided to let the Gods-of-Collecting decide if I was going to ever own it. For weeks I would pick it up, check the price tag to see if they had come to their senses, and return it to the shelf. I did try various clerks to see if they would lower the price, but they said they were not authorized to change prices. I plodded on, week after week without much hope.         ...
Post a Comment
Read more

2026-06-23 Olympus Camedia D-535 Digital Camera

The Olympus Camedia D-535 digital camera is a cute little camera, introduced September 16, 2004. It was modestly priced at about $175 list.   It had the motto, “one button/one function.” There were four scene modes available, as well as movies (QuickTime / 320x240 at 15 fps for as long as the memory held out) and “Program-Auto” on the rotary dial. A four direction with a center “OK” allowed rapid access to (starting at 12 and going clockwise)— EV adjustments plus and minus 2EV in ½ EV steps Macro (including Super-Macro allowing shooting down to 2 cm (0.79”) Reset Self-timer (12 seconds)      The three buttons under the 1.5 inch (130,000 dot) screen (from left) are delete, menu access and flash modes. The two buttons to the right of the screen are camera (top) and playback. There is a rocker switch for zooming that doubles as a magnification /file views switch on playback. The power-on button is inset into the top at the middle of the camera, with the shutter button ...
Post a Comment
Read more