Opening the ELV MLE 6 Plus charger for maintenance.

Introduction

Although this battery charger really has no user servicable parts inside, still it can be necessary to split the two parts of the shell. It happened to me when I was recharging two RAM (Rechargeable Alkaline Manganese) cells from AccuCell. I put two cells in and switched the machine on at 2:30 AM. It immediately deduced the right kind of cells and started a RAM cell charge.

When I got out of bed at 7:40 AM, I noticed that one cell was rather hot. On closer inspection (after I got a burning sensation due to electrolyte spills on my chin) it became clear that the warm cell was blown. A slimy liquid was present in the shape of droplets on the cell and in the charging bay.
I first visited a doctor who gave me an ointment against burns. Later I went to work and after that home again. That evening I decided to thoroughly clean the charger.

This is my ELV charger that burned my face... :o(

Opening the ELV charger

The charger is closed with special screws. In the middle of the slot is a small hill, such that normal screwdrivers cannot engage. So I took an old screwdriver and a narrow file and made a small tool. I removed the four screws in each corner. After this, the cabinet still would not open, so I applied gentle force with my crowbar :o). The case split and the insides showed themselves to me. I was impressed.

The MLE 6 Plus charger is completely filled with electronics. It has a powerful transformer under the bulge and all the electronics are stored on a single PCB right under the LED's and the red control button.
The microprocessor in charge is a Zilog Z86E08. On the reverse side of the PCB were some SMD chips with (probably) some comparators or ADC's, but these were in rather difficult spots to read them.

At that moment I discovered that I had forgotten two screws. Underneath the big sticker on the bottomside are two more screws. You can locate these by pressing with your indexfinger on the sticker while looking for a "soft spot".

After cleaning the contaminated parts, I used normal pozidrive screws to fix the shells together.

Feedback from the Accucell company

Later, Accucell of Germany contacted me and explained that the first productionruns of the ELV MLE-6 Plus series contained a serious error such that they did not recognise the RAMcells good enough. Also they pointed out that the RAM cells are not suitable for high current applications like powerful electronic flashes (guidenumber > 32) and toys. In general, the cells will get damaged if the discharge current exceeds 400 mA for a longer time.

In such cases, and if the charger lost track, the cells get too hot and the plastic seals rupture due to enormous internal pressures, thereby expelling the excess liquid from the batteries interior.

The chemistry.

The charger made by Accucell itself. It was cheap and S L O W The liquid contains a strong alkali (caustic soda, NaOH) with some Zinc and Manganese salts. The latter are not very poisonous or harmful to your health. The alkaline solution however is very, not to say: extremely, toxic and harmful to the skin.
Sodiumhydroxide breaks down the fats and tissues of your skin (hydrolysis). For thicker skins this is no big deal. If you start rinsing within minutes, there will be only superficial damage, which will heal very fast.

If the solution however contacts thinner skin, like that of your face, the hydrolysis of the skin will proceed very fast and the damage is bigger. In such a case it is always of advise to consult a medical doctor such that (s)he can prescribe some inflamation preventing ointment.
The defective batterychargers of ELV should have been recalled in June of 2000, but apparently some slipped through the mazes.


Current situation.

I now have a real Accucell charger. the cheapest one: EUR 15 for a charger plus two Mignon (=AA) cells. It's a steal. And it's a nice charger too: as can be seen in the photo on the left!

As could be expected: I opened it up and found a transformer, 12 diodes and 2 LED's. No more. But it works. I considered to publish the diagram, but for EUR 6 (actual price of the charger) you won't even be able to get a comparable case. So why bother with fraud?
If you're about to get yourself a set of AccuCell batteries, buy an original charger! They're affordable and good. This particular one is not very fast, but who cares? I plug it in when I go to sleep. I don't mind waiting while I sleep. :o)

All in all, the AccuCell batteries are a good product. The walky talky in which they were used had a considerably longer up-time, due to the 0.6 Volt extra that these cells offer (in pairs, of course) over Ni-based rechargable batteries.

Are RAM cells my cup of tea?

That's a tough question.

RAM cells offer some distinct advantages. But they also put strict demands on the user. Therefore I have set up some statements:

  1. You are a law obiding citizen
  2. You NEVER have been speeding
  3. You NEVER skipped a red light (even in the middle of nowhere)
  4. You always do as you're told by your boss (or wife)
If all these statements apply to you, you will be the clear winner when using RAM cells. If one or more of these statements do not apply to you, just forget about RAM cells and buy a good quality of NiMH cells.

The rules for using RAM cells are:

Especially the recharging regime was too much for me. So I always discharged too deep. So I had to charge much longer and in steps. So my RAM cells died before they were old.

In general, my cells needed charging times of 10 to 24 hours. After 8 hours it might be a good idea to swap the cells in the charger. Don't ask me why, but it helps reducing charging times.
If you posess an official AccuCell charger: TRUST THE RED LIGHTS about energystate of the cells. Your charger is always right. (I could have been related to these things... :o) ).

Looking back.

Some months ago I gave my remaining cells, plus the cute charge in the bottom picture, to a friend, who probably put them in a safe place, finding them back in a decade or two. Anyway, I am using ONLY Ni MH cells nowadays. I charge them with the ELV charger of above. And for these, it's a mighty fine charger. It does a good job on NiCd and NiMH cells.

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