Energy Monitor Killed Using Wrong Charger

[Pejayuk]

Hi there,

I have an 'Alert Me' DIS150 electricity monitor (Branded British Gas). It is usually powered via a 5V power adaptor, but also has built-in rechargeable batteries (3 x AAA NI-MH) so it can be taken from room to room. It has a wireless sensor that clips onto the meter tail and a colour LCD display.

I'd been using it in another room and when I took it back to its usual place, I accidently plugged in the wrong adaptor. (12V from my battery charger!) It was obviously running off the batteries when I plugged it in and the display stayed on for maybe a second before it died.

The charging circuit does appear to still be working and still charges the batteries to 3.8V. With the power supply connected, the board is taking 11mA without batteries connected and 20mA with batteries in.

I guess my biggest hope is that a component providing over voltage protection (If there even is voltage protection) might have gone and the main IC and display might have survived.

Any help or suggestions as to what I should check first is very much appreciated. I don't have much experience of this type of repair but am very keen to learn.

 

[kellys_eye]

The provision of an external 5V power supply usually means there is no onboard regulation and the main circuitry is powered directly - which probably means it's goosed*.

* polite word for FUBAR'd

 

[Pejayuk]

Okay thanks. I guess the designers didn't factor in that someone would be stupid enough to connect it to the wrong power adaptor - that's where I come in!!

Just to satisfy my curiosity and to hopefully learn something from this mishap, where on the board could I check voltages to prove it is either the main IC (EM250) or the LCD that has blown, rather than a minor component?

 

[kellys_eye]

Measuring a voltage won't indicate an internal fault in the main IC. If it's 'blown' then a lot of the pins that drive displays and take in voltages/signals just won't be doing what they're meant to do.

 

[Martaine2005]

I guess the designers didn't factor in that someone would be stupid enough to connect it to the wrong power adaptor

Happens all the time.
That’s why designers normally put a label (in yellow) saying “only use for this unit”.
Also, the designer doesn’t know how stupid the user is!.
Just because something fits in a hole, doesn’t mean it belongs there. She or he or it could be married!

Martin

 

[Pejayuk]

Yeah I guess so....... though in my defence, I was also a bit unlucky that I happen to have two power adaptors plugged into a 4 gang socket and just happen to pick up the wrong jack plug without thinking!

Maybe it's time to put some labels on the jack plug end of the leads so I don't get them mixed up again.

 

[kellys_eye]

It would help if manufacturers got together to keep the designs common and avoiding conflict such that all 5V adapters had only ONE size plug (i.e. they MUST be mini-USB) etc but there's a lot to be said for the 'conspiracy theory' that they design them so people CAN make errors as it only generates more sales......

 

[Martaine2005]

Maybe it's time to put some labels on the jack plug end of the leads so I don't get them mixed up again.

I couldn’t agree more.
Most of us (me) have iec connectors with 1A, 5A, 13A plug fuses.
That will dictate its use.
Others have the 5V USB cable that will power anything of 5V. BUT only .5mA or .750mA or 2A. Big difference.


Martin

 

[Harald Kapp]

Matching chargers to gadgets or matching the many cables in my storage box to different uses has led me to buy these self adhesive label strips years ago. Ever since it is so much easier to find the correct cable for any combination of gadgets and/or chargers.
A word template for labeling these with a printer is available - I simply use a sharpie.

 

[Martaine2005]

there's a lot to be said for the 'conspiracy theory' that they design them so people CAN make errors

Although true, most designers do have a label with either the “ only use with” or the voltage plus maximum Ampere per unit.
The OP agreed to being stupid and wrongly used a different adapter.
Short story, always check the voltage, polarity and the amperage.
Don’t use a 1A iPhone charger to for a 3A USB audio mixer. ( don’t know if or when this would happen).
But I am sure it does happen.

Martin

 

[Harald Kapp]

S... happens. I recently used a 5 V LED strip on a variable adapter set to 12 V. Don't ask me why. In my case I was lucky: the controller was designed for 5 V - 12 V and the LEDs survived. In the case discussed here I don't think the circuit is salvageable with reasonable effort-

 

[Pejayuk]

S... happens

You're definitely right there!

The real irony is, the power adaptor which did the damage was for my Techno-Line BL700 battery charger. The earlier versions of these were powered by 5 or 6V, but there were so many instances of people frying them by using the wrong power supply, the later ones like mine were upped to 12V.