"Convert" Electrical Shaver To Charge Via USB [solved]

[Darkwing]

24.07.2015: UPDATE on #8!

31.08.2015: UPDATE on #19!

20.04.2020: UPDATE on #19: Added lost pictures in again!


Good day folks!

I want to do little hardware hacking; if you have any suggestions or tips, I'd be glad if you share them! Here is the idea:

I'm planning to buy a Philips Multigroomer 3000. It has a NiMH accumulator in it. The original power supply sais 4.2 V, 60 mA. (I can't show you, but I saw it in the store.)

As far as I've seen it, in all such devices (like phones, tablets and stuff) a charge regulator (if any) is always inside of the device and not inside of the power supply. So pracically the device doesn't care where the power comes from, as long as it is strong enough to do the job ( = meet at least the specs printed on the power supply).

Am I right so far?

Now here's the fun part: I want to "skip" the power supply and charge the shaver via USB using a solar power bank like the Powertraveller Powermonkey Extreme, when I'm on outdoor expedition. It can easily provide 5 V, 1 A via USB. So basically it is sufficent to make the charge regulator work and charge the accumulator.

The plan is to cut the original cable, get rid of the power supply and instead solder a USB plug on it. I want to use a small diode to drop 0.7 V to end at about 4.3 V to kind of meet the voltage specs again, to not overdo it.


What do you think of it? "Suicide" or "this could actually work", or anything in between? 

Thanks a lot for your thoughts! 

[katzohki]

Yep. Sounds like you're on the right track. Not sure how I feel about shaving on outdoor expeditions though 

[wraper]

Yep. Sounds like you're on the right track. Not sure how I feel about shaving on outdoor expeditions though 

Nope, seems that he is on the wrong track.
This device unlikely to have any charging circuit inside. Otherwise charger won't be limited to 60 mA. Therefore voltage source need current limiting to the original specification. I also think That voltage from original charger unlikely to be 4.2V without any load, likely it is higher.

[wraper]

35 minutes of cordless use after 10-hour charge.

That's exactly what you get with dumb 0.1-0.2 C chargers which do not have any charging cut off function at all.

[katzohki]

I meant in the sense that the USB port will supply enough power, not that he won't have to add some circuitry.

[Darkwing]

Thanks for your (ambivalent) replies! 

These tiny 60 mA made me suspicious too – but I'm not sure if one can say, the original power supply is limited to 60 mA by intention, like a constant current source. I'd say the original power supply just can't provide more than 60 mA. It's a slight difference. My wishful thinking is, that the charge regulator inside of the shaver is responsible for not drawing more than 60 mA from the power supply.

Asking shopkeepers in electronic stores about this, all say that a charge regulator (if any) always is inside of the device, not inside of the power supply. The power supply is dumb, so to say.

I feel that it's exactly that, what I do need to test when I have the device: charging it with a power supply that can provide more that 60 mA and measure, if it will draw more than 60 mA.

If not, then we know everything is fairly simple.
If it does, we know I need a current limiter, not just a diode.


Maybe I give Philips a call, hoping someone can tell me more.



Btw: The Multigroom 3000 is a smaller version of the Multigroom 5000, which has quite different charging specifications, even a quick charge feature via button on the device ...

[amyk]

4.2V? That sounds almost like the voltage of a fully-charged single-cell lion - are you sure it's NiMH? 60mA for 10 hours would be 600mAh, a battery of that size would last roughly 0.5h on a 1.2A discharge - seems about right. Nothing in the linked site/datasheet on the shaver mentions what type of battery either.

--
Offtopic, but seeing OP's name, country, and the word "Suicide" in his post just seems a little bit off...

[mariush]

You could just test the power supply, see if it's really limited to around 60 mA or not.  An easy way to do this would be with a bunch of resistors, or if you want it even cooler, basic leds and current limiting resistors.

For example, if that power supply is supposed to be 4.2v, get a basic led and 100-330 ohm resistor and measure the current used and the voltage.  Add another led+resistor to the load and measure again.  Each led+resistor should eat about 10-20 mA depending on what resistor you choose.
If the power supply is really designed for maximum 60mA, then when you go over 60mA the voltage should drop or make the power supply stop working.

There are small adjustable linear regulators (limited to 50mA for example) that you could set to output 4.2v from 5v.

Anyway, the thing should have a charging circuit inside which should protect the battery, I doubt you need to limit the current. It should probably also work directly with 5v but again, one or two diodes in series should drop 5v down to about 4.2v  (1n4xxx have 0.6-0.7v drop but at something like 60mA the voltage drop is smaller)

[Darkwing]

Hello again after a while!

Now I own the device and here's an update about my findings so far. As a reminder: I wanted to convert an electrical shaver to USB charging.


The Power Supply
Philips A00390; 4.3V, 70mA
I testest it and it is limited to around 95 mA output current. (I even shorted it and it supplied these 95mA "to itself".) When in use, the voltage breaks down to about 2.0-2.1V. The power supply has no clever charging shutdown, not even time based; you could leave it on for days it would "charge" further on at 95mA.

The Shaver
Philips QC3340, Multigroom 3000; 4.3V, 0.5W
It has NiMH accumulator inside. I provided a voltage of 4.3V and it drew amps "out of limits" on my multimeter, so we can savely assume that there is no way a charging regulator inside of the device; the power supply is "in charge" of providing a pleasing current of 95mA for the accumulator. I assume the accu is built for standard charging at lower rates. While so, as far as my understanding of charging accus goes, it is not a big problem when the power supply has no charging shutdown, since it is not that incredibly unhealty when providing ongoing lower-rate currents. So Philips built this really down to a price; but hey, it's ok and it works (appears to do).

The Conclusion And The Ideas
–A–
In order to get rid of the power supply and convert to USB-charging, it seems, that I just need to current limit at about 90mA. Is there an IC or a small module that you could recommended for that kind of job? I already stumbled upon this kind of thing, the Infineon BCR 420. Are there alternatives to consider?

–B–
By measurement I obtained a value of 2.2-2.3V to provide to the accu in order to get a charging rate of about 80-90mA. I wonder if it will be ok, when I just set the right voltage and charge the accu with that simple method. I know I have to monitor the current rate over time to be absolutely sure that there is no mess going on at some point. Also temperature variation might be an issue.

–C–
I have a LiPo charging module with the TP4056 on it. I wondered, whether I could use such a thing to charge NiMH also. LiPo chargers do have a constant current charging phase before the constant voltage charging phase is triggered. And again, as far as my understanding of charging accus goes, this triggering will never happen with NiMH and it will charge ongoing at the preset constant current. This current (80-90mA) I can set by soldering a different resistor on the board, so the datasheet states. So maybe thats also a solution for me?


Thanks for bearing with me,
any suggestions and thoughts to this little hacking project are most welcome! 

Darkwing

[Zero999]

I doubt there's any need for anything complicated. A diode followed by a 33R resistor with a suitable power rating should do the job.

[Darkwing]

It really seams so; this would be idean B then.
I tried it out with 3x 10 Ohm (0,25W) resistors and I have my current at 86 mA. Hmm ...

(Can you explain why your suggestion included a diode?)

[Zero999]

The diode will stop the batteries from discharging back into the device if the power is disconnected.

[Darkwing]

Ok, thanks!

I figure that some kind of protection is already built into the shaver: I get (practically) no voltage reading on the contacts (11mV); and they also say the device is waterproof. By knowing that, I assume that a diode for that purpose is not necessary, would you agree?

[amyk]

There's probably an internal diode.

NiMH charging requires constant-current, the original charger is just trickle-charging at 0.1C because detecting charge termination requires complex circuitry for NiMH.

[SeanB]

I did the same with my Phillips shaver when the internal SMPS went kerfoof, from the 2 cells dying. Replaced them with 2 AA cells with tags, and, as I was not going to try to get a replacement controller (interesting one, it has an input voltage range of 10V to 350VDC, and will actually charge the shaver off a 12V car battery, though this is not really noted in the shaver specs, though Phillips does make a special car charger available in certain models as an add on) I simply disconnected it via a convenient link, and added some current limiting resistors to allow it to charge via the power input from a 12V supply. Now it is charged from a solar panel, using the nominal 12V from the panel.

Just added some external resistors as the internal ones allow too high a charge rate, so dropped it to something that will charge it in a day. Only issue is the charge level display no longer works, as this relies on the charger giving it a full battery signal for it to calculate runtime based on nominal battery capacity. As the new cells are 800mAH as opposed to the 300mAH of the originals the display was moot in any case.

Edit, added a phillips manual describing the charge circuitry, along with the newer model learning ability. My one is older, and does not have the fancy display, just 5 led's that show battery status, but uses the same charger board. Seems they do reuse a lot of parts, as the shaving foils and covers are almost identical across all units, and still are nearly identical to the original Phillishave design, which I do have an example of.

[G7PSK]

I have 2 Phillips shavers one charges straight from the mains the other has a switch mode power plug unit that outputs 12 volts. Both of the shavers have charge controllers inside the shavers.

[Darkwing]

@SeanB:
Interesting, from where did you get this "Circuit Description" document of that Philips shaver? A googling-around showed nothing similar available for the Philips QG3340 Multigroomer. What was you source?

@G7PSK:
Could you post the exact models of your Philishavers? (I still doubt that a charge controller is inside of my model QG3340. But I can't crack it open, it's waterproof sealed and stuff ... so I have to rely on logic reasoning to make a good guess.  )


Thanks!

[SeanB]

Waterproof and sealed, they are still easy to open, you just have to find the 3 pressed in covers for the 3 screws that hold it together, pop off the top, unclip the beard trimmer somewhat, and then use a spudger to undo the case clips. Done right it will go back together, and with some solicone grease as lubricant on the sealind rubbers it will be water resistant like before.

Phillips does service them, and the batteries are replaceable, though often the price is just barely below the cost of a new unit. I have been doing Panasonic ones for the boss, so know how to take them apart after destroying the first one seeing how it was clipped together.

[Darkwing]

That's exactly the problem: you always destroy stuff while figuring out how to open it.

I now tried it, but didn't come very far. Now the casing looks like sh!t with marks and cracks. I think I better let it be. ^^

[Darkwing]

Weeks later … *imaginejeopardymelody* 

Let me report quite a success on this!
I finally managed to make that cable and – surprise – it really does work just with a single resistor. Here it is:




I added some kind of status LED in parallel, whose current limiting resitor is measured in a way, that it is slightly over the verge of being 'on' at 5V. Below 4.8V its off and a bit higher as 5V it begins to shine very very brightly. It's like a little visual control for the USB power being 'ok' or 'not so ok'.



The connector to the Phillips I filed from an oldschool Molex harddrive plug. ^^



Here it is in action.



The 27 Ohms produce a very accurate current at 5V. The original power supply delivered 92 mA, we now have 94 mA – I'd say that's spot on. Ohm's law works quite well sometimes. 



Thanks to y'all for your suggestions on this little hardware-hacking project! 

[SeanB]

Glad you got it all working again.

[yonygg]

Hey,

Google just fished your post for me. I'm glad you had success with it.
Why didn't you just used a unit like the one in the link that let's you set the voltage and amperage?
Would that do the job?
http://www.aliexpress.com/item/Wholesale-1pcs-DC-Step-Down-Converter-DC-4-0-38V-to-1-25V-36V-5A-75W/32285636716.html

The reason I'm asking is that I'm traveling a lot and I'm tired of taking a separate (and heavy) block charger for every one of my devices (shaver, trimmer, water-pick and god knows what else in the future), and I thought it should be possible to charge them all off my ipad usb charger with the right controller.

Are there different requirements in order to charge NiMH, LiPo, Li-Ion and Li-Metal batteries? which one could I charge using the module in the link?

Thank you

[Darkwing]

Ou, that's a tough one.

I also equipped myself for traveling; but for minimalist style. I picked my electronics stuff very carefully for this. My setup is as following:
Travel Adapter with 2x USB output, 2.1 A. To charge iPad, camera, phone and converted shaver; and its normal outlet for laptop power supply in most compact travel size and weight. So I carry only one unavoidable power supply (laptop), the rest is suitable for the one and only worldwide universal power socket: USB. And to answer the question: I didn't pick a step-down converter, because I wanted a dedicated most hassle-free solution for just one device, namely the Philips trimmer.

At the moment, you do this the other way around: you already picked your stuff and now try to "convert" it for traveling. I would recommend you overthink at first, if you really need three devices (mouth-wash?!). Then do research and (maybe) pick new ones, that are "hacker friendly" (but maybe your devices are? -> research). I recommend devices with NiMH accus or NiCd, because they are very forgiving and you can slow charge them unattended over night; not like LiPo, they require a bit more effort to be happy. I tried such a LiPo charge module (similar to that) and it quite worked, but I had the feeling, that it ruined the accu. So I would consider this not really usable. And don't have devices with inductive charging, like electrical toothbrushes have.

One more thing: you say your power source should be the USB output from your iPad charger. If you feed that into the step-down converter, you will have a voltage drop; expect at least 1V, so you have about 4V for using. This should be sufficent to load an accu directly in a device, this means IF there is no charging device / power regulator built into the device prior to the accu. Your task is to find that out (->research) if you can connect directly to the accu, overriding any electronics. And the biggest thing: it must be easy for you to handle this stuff on the road. You probalby don't want to unscrew, fiddle around with little cables and reassemble devices just for charging them. That's why you need to pick the right stuff first.


So I suppose this message is maybe not very satisfying to you, but I hope it helps, to understand the challange of making equipment ready for minialistic travelling - or swapping to a custom "universal" power supply. The first challenge is picking the right equipment, by knowing what is right.


Please post your thoughts and ideas!

[denisab85]

Hey,

I have just one question if you don't mind: what is the correct polarity for the plug?
I want to make the same thing for my multigroom, since I've lost the original charger.
And I don't want to spoil the device.

Thx in advance!

[Darkwing]

Hi!

Look at your Multigroom like this:



Left is minus, right is plus. So you can model a plug accordingly. (I used an old HDD Molex plug.)


Please post your results!