Rattling Nikon MH-18a charger: how to fix/prevent

During my holiday in Thailand, I was silly enough to drop my Nikon MH-18a battery charger on the floor from a height of a metre or so. As soon as I picked it up, I heard a rattle. When I looked inside, this is what I found:

Nikon MH-18a shattered inductor

The core of the inductor had broken into several pieces. The pieces are shown here, below the copper coils of the inductor. Even though inductor cores are made from ferrite, a notoriously brittle ceramic, I was pretty disappointed to see that the charger was so fragile. After failing to find any suitable replacement parts, I decided to figure out what it was for.

What is the inductor’s job? (Don’t care? Skip to ‘How to fix to fix the problem.’)

A reverse-engineered schematic of the mains electricity conditioning part of the circuit is shown below, with the broken inductor core depicted in red:

The flyback converter draws pulses of current at a frequency much higher than the 50 or 60 Hz of mains electricity. The two capacitors and inductor combine to form an LC filter, which prevents this high-frequency energy from leaking back into the electricity supply and interfering with other devices.

What effect does the broken core have?

If you plug in the charger while ferrite fragments are still sitting in the box, all sorts of nasty short-circuits could happen.

Even with the inductor effectively absent, the voltage in the two capacitors is still topped up 100 times per second by the mains electricity supply. The flyback converter should therefore have plenty of energy to run the rest of the circuit with, and the battery charger should still function normally. As mentioned in the previous section, the only issue I can identify is that the current waveform being drawn from the electricity supply will be different and noisier, which may cause interference to other devices nearby, or a slight reduction in efficiency.

How to fix the problem

High Voltage

Do not open the charger while it is plugged in, or if it has been plugged in for the past few hours. Capacitors inside the device are charged to potentially lethal voltages during operation, and may maintain this charge after being unplugged. Do not plug the device in unless it has been completely re-assembled, and test it under close observation at first as overheating/fire are possible with any mains electricity device. Do not open the charger if you don’t completely understand all the points mentioned in this box.

Opening up the charger and removing the shattered pieces should remove loose bits of shrapnel that might have caused short circuits, and leave your charger completely functional — the inductor core is completely unnecessary.

To disassemble the charger, simply remove the sticker on the bottom (which is hiding one of the screws) and undo the two screws. The screws are designed to take a funny 6-point star driver, but fortunately a plain small flathead screwdriver did the trick for me.

How to prevent the core from breaking

If you’re very clumsy, or want to cover all your bases, you may wish to open up your charger and preemptively pot (surround) the inductor with epoxy (e.g. Araldite) or similar. Make sure you pay attention to all the notes in the yellow box above, though.

Share
Leave a comment

21 Comments

  1. Thank you for this posting of repairing the failed MH-18 nikon charger. I did have the same problem as you, and carefully followed your directions as provided… I crossed my fingers in my head and tried it…still broken…I opened it back up and blew out the “shrapnel”, sadly still broken. I had to buy a new one, $60 is way to expensive for this charger! I did get a discount of 13 dollars and feel just a little better about it. I would have felt so good if I could have repaired it like you did. I could have added it to my list of minor home repairs, my oven and my cloths drier. I love the internet for these things, and am very happy for people like you that make easy to follow repairs.

    Reply
  2. Emma

     /  January 18, 2012

    Hi,

    I have the same problem. A new charger is very expensive.
    I am french, i’m not sure that i have really understood. I said that i can use the MH-18a without the “core of the inductor” ?
    There is no problem : fire, short circuits or battery explosion ?
    Thanks a lot
    Sory for my bad english

    Reply
    • Robert

       /  January 18, 2012

      Bonjour Emma,

      Fr: Vous avez compris correctement. Si vous ouvrez le chargeur de batterie et retirez tous les fragments du noyau magnétique, il doit être sûr. Assurez-vous que le chargeur a été débranché pendant une longue période avant de l’ouvrir, cependant.

      En: You understood correctly. If you open the battery charger and remove all fragments of the magnetic core, it should be safe. Make sure the charger has been unplugged for a long time before opening it, though.

      Cordialement, Robert

      Reply
      • Emma

         /  January 18, 2012

        Thanks a lot.
        I was going to throw it .. Luckily i found this website.

        Bye

        Reply
  3. Martin

     /  January 31, 2012

    Hello. Do you have the schematics ?
    I have a charger with another fault.
    Best regards.

    Reply
    • Robert

       /  January 31, 2012

      Hi Martin,

      Sorry, I don’t have the full schematics; the partial circuit diagram I provided was just reverse-engineered from looking at the PCB.

      — Robert

      Reply
  4. Thompson

     /  March 2, 2012

    Hej, Thanks for describing the problem so well. The same happened to my friends camera. I tried to fix it, but it did not work. Maybe because we plugged it prior repair eventough there was the rattling. Guess some components got damaged by a short circuit. Best greetings from Denmark!

    Reply
  5. Feliksa

     /  May 1, 2012

    Hallo, I have a problem with Nikon Battery Charger MH-24. I never drop down, but is not charging my battery. I try with my fredns battery and it is ok. Light is showing prosses but is never charge. What I have to do with it?

    Reply
    • Robert

       /  May 1, 2012

      Hi Feliksa,

      If the charger works perfectly with your friend’s battery, but it doesn’t work with your battery, then your battery is probably faulty. Apart from checking that the terminals are clean, there’s nothing you can really do to fix a battery. Unfortunately, you’ll probably need to take it back and get it replaced.

      Reply
  6. RAJDEEP DUTTA

     /  June 28, 2012

    Dear Friends,

    I bought a Nikon D5100 last April 2012 and charge my battery not more than 5 times. But now this charger not charging my battery. My battery is ok because its charging with my friends charger. Can you please give me some info where is the fault in my charger? Details:
    after plug in , the charger light blinking dull and continuous never stop nor even the charging light blinking with bold light. If you identify me which part is faulty in my charger circuit board then i will replace that & really i gives you a big thanks.

    Kind regards,
    Rajdeep Dutta
    India.

    Reply
  7. hi! my charging was working perfectly until today, when i charged my battery a sudden short little tiny spark lit when i plugged it in, the led lamp lit up, but when i looked at i again after a few minutes, the light was off,this never happened to my mh18a, what couldve possibly happened? and what can i do? my battery says i still have 3 percent,andi have a shoot tomorrow,what should i do? thanks

    Reply
    • Robert

       /  August 16, 2012

      It’s not unusual for there to be a little spark when you plug something into the wall. Regarding the battery not charging, check that the contacts of the battery are clean and the contacts on the charger are clean and not bent. The only way to deduce whether the problem is with battery or charger is by finding a known good battery and charger, and trying different combinations to identify the weak link.

      Generally, these things aren’t worth the time to try and fix, unfortunately — my broken inductor core was a very easy-to-diagnose case!

      Reply
  8. Mike

     /  November 7, 2012

    hi I have the same problem but mine just stop working.. 🙁 it did not fall or have this rattling sound.. what do you think is the problem? fuse?

    and one more thing mate could send me pics how to disassemble it?

    cheers,

    Mike

    Reply
    • Robert

       /  November 7, 2012

      Hey, unfortunately I can’t take a guess at what the problem might be from here. To disassemble the charger, simply remove the sticker on the bottom (which is hiding one of the screws) and undo the two screws. The screws are designed to take a funny 6-point star driver, but fortunately a plain small flathead screwdriver did the trick for me.

      I’ll update the post to include this info.

      Reply
  9. Hi Robert,

    I was following your instructions and first, I removed the two screws which are visible (i.e NOT covered by the sticker). But I was feeling around the sticker for a third screw and can not find any, I am reluctant to peel off that sticker as the only reason I am trying to open my charger is to get rid of the rattle that I have (same as your problem) but my charger still actually works perfectly. Why open it up then – you ask? Because I am selling my D700 and I have to have a charger in good condition to go with it. The shop where I am trading it in will not accept it with the rattle even though its in perfect working order. The charger appears totally sealed shut even when the two screws are removed. I would expect (even if there was one screw holding it together) that it would loosen, its like its welded / sealed shut. Any suggestions? If I remove the sticker, Im sure the shop where I’m trading it in will not accept it. If I knew where the screw was i could pierce a small hole to get at it.
    Thanks
    -Tommy

    Reply
    • Robert

       /  December 5, 2013

      Hi Tommy,

      The third screw is indeed under the sticker. You should be able to feel where it is through the sticker; I don’t have that charger on hand at the moment sorry.

      If the same thing happened to you as happened to me, you’ve got a piece of conductive metal just rattling freely around inside the charger. I wouldn’t like take the chance of having that short out the components inside, and I’d be even less comfortable forcing someone else to take that chance.

      Whether it’s even OK to sell it when you know the inductor core is missing is a little questionable.

      Reply
      • Ok thanks for the advice and good point about selling it on. Will just have to get a new one I reckon.

        Reply
  10. FERNANDO

     /  January 4, 2014

    HI, I just left my batteries to drain, then after a long time I connected the batterie to the MH-18… at first the light blinked like it used to do it normally, then nothing, its off… do you know what can be the problem, or have you heard anything like this?

    Reply
  11. Wolfgang

     /  June 22, 2014

    I don’t have the MH-18a but the MH-18 Charger by Nikon. I removed the two screws which were visible from the bottom, but I can’t get it open. Is there a third screw covered by the sticker (which I didn’t remove), or do I just have to pull harder to get it open?

    Thanks for this great page
    – Wolfgang

    Reply
    • Robert

       /  June 22, 2014

      I don’t know of the MH-18, but I had to remove part of the sticker to open my MH-18a, so I can only presume the same will be true for you. Stickers are a bit flexible, so if you gently poke around you should be able to tell whether there’s a void that might be hiding a screw under the sticker.

      Reply
  12. javier

     /  August 15, 2016

    apology, in my case inductor filaments broke and it becomes impossible to rebuild , I can bypass directly ? excuse my English

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *