LaCrosse BC-9009 / BC-900 - The Melt-Downs Continue...

[Russel]

Specs: http://www.onsemi.com/pub_link/Collateral/NTGS3443T1-D.PDF

I see that the MOSFET component is only rated for 0.5 watts of heat dissipation. But isn't it being switched completely on and off?

How much heat is dissipated through it?

And how does a slight increase in input voltage affect it?
(Input voltage apparently does affect it, as LaCrosse is replacing AC adapters due to high output voltage.)

 

[uk_caver]

So the components were always hovering close to the edge of failure, and only needed a minimal change in input voltage to ramp up the failure rate from the level it was previously at?

 

[NutSAK]

LaCrosse claims to have identified the meltdown issue and is voluntarily replacing the affected AC adapters.

Link here

I don't see any suggestion to terminate usage of the recalled adapter until it is replaced....

 

[uk_caver]

I see that the MOSFET component is only rated for 0.5 watts of heat dissipation. But isn't it being switched completely on and off?

How much heat is dissipated through it?

And how does a slight increase in input voltage affect it?

The other thread linked by bones suggested it was being used in linear mode.

If that was the case, then if there was a fairly small current-sense resistor, that could mean the FET was having something around 1.6V to deal with, given a 3V supply.
However, that'd mean that a supply increase of 0.2V would only be about a 12% increase in heat, which isn't exactly a great amount - charging somewhere vaguely warm with a 3V supply might end up with hotter components than charging somewhere cool with a 3.2V supply.

 

[Mr Happy]

The other thread linked by bones suggested it was being used in linear mode.

If that was the case, then if there was a fairly small current-sense resistor, that could mean the FET was having something around 1.6V to deal with, given a 3V supply.
However, that'd mean that a supply increase of 0.2V would only be about a 12% increase in heat, which isn't exactly a great amount - charging somewhere vaguely warm with a 3V supply might end up with hotter components than charging somewhere cool with a 3.2V supply.

Hmm. By my calculations an increase of 0.2 V on 1.6 V dropped leads to an increase in power dissipation of

[(1.6+0.2)/1.6]^2 = 1.27

That would make it an increase of slightly over 25%. If a component was right at the edge that could be significant.

 

[uk_caver]

Hmm. By my calculations an increase of 0.2 V on 1.6 V dropped leads to an increase in power dissipation of

[(1.6+0.2)/1.6]^2 = 1.27

That would make it an increase of slightly over 25%. If a component was right at the edge that could be significant.

If the [average] current is constant, isn't the power increase proportional to the voltage increase?

 

[Russel]

The other thread linked by bones suggested it was being used in linear mode...

I am no expert, but wouldn't that be very inefficient? I thought the device pulsed on and off to charge batteries. My impression was that PWM allowed a smaller switching device because it didn't have to disipate the excess energy. Of course, the switching on and off generates heat in the device, but not nearly as much as using it in a linear fashion.

 

[uk_caver]

If average current control was by pure PWM, then presumably there'd need to be a resistor of reasonable size in the circuit to limit peak current to a decent value, not overloading the PSU when multiple channels were operating?
A 50mOhm FET, a ~0R25 load resistor and a single AA cell would pull quite a current from the supply.

Also, if the transistor was just going on/off, unless it had a pretty poor drive circuit, then it shouldn't be getting particularly hot, or significantly hotter with a slightly higher PSU voltage.
If there was a weak drive, if the frequency stayed the same, and minimal heat was dissipated when the FET was on, the heat dissipation in the FET should presumably be similar at all the different power levels, since it would only be dissipating during transitions between zero and the same peak current.

I suppose that with a known 3V supply, it would be possible to design a drive circuit that used the FET in linear mode, but which had a ballast resistor which in combination with the sense resistor would soak up most of the excess voltage in the case of a full (~1.5V) cell at full drive current (1A)

In that case with a properly tweaked design, the FET might normally only have to deal with a small voltage. Even when a pretty flat cell was inserted, its voltage would fairly quickly rise to ~1.2V (or maybe be rejected), or could be dealt with by starting flat cells on a lower charge current.
That kind of circuit possibly would be highly sensitive to small increases in supply voltage, since the dissipation in the FET could increase substantially, but I got the impression that that wasn't how the BC-900 worked

 

[TakeTheActive]

La Crosse BC-9009 / BC-900 MOSFET (SOT23) Thermal Runaway and/or Failure

jtr1962 had the answer in 2006: BC-900 power supply discovery

Now that we know WHAT La Crosse changed:

...La Crosse Technology recently switched to a new AC adapter that meets California Energy Commission (CEC) requirements.

La Crosse Technology has discovered that this new AC adapter has an increased voltage output;...

Reference

 

[MarioJP]

The question is what is going to happen now?

 

[r1gm1n]

The question is what is going to happen now?

La Crosse is replacing, free of charge, the adapters purchased between October 01, 2009 and January 15, 2010.

Click here: https://www.lacrossetechnology.com/support/bc9009/

 

[DarkNova]

My BC-700 AC adapter has the "IV" symbol, although it is listed as manufactured by "Ktec".

 

[Bones]

My BC-700 AC adapter has the "IV" symbol, although it is listed as manufactured by "Ktec".

Presumably, this indicates that the adapter for your BC-700 has also been brought into accordance with CEC requirements DarkNova:

La Crosse Technology recently switched to a new AC adapter that meets California Energy Commission (CEC) requirements.

...can be identified by the Roman number IV on the adapter.

...

If you have a way to measure, it would be interesting to learn whether the output voltage of your adapter is comparable to Russel's, especially if his happens to be a pre-IV version:

That is interesting.

Just out of curiosity, I measured the voltage from the BC-900 and BC-700 AC adapters I have.

BC-900 3.037 volts

BC-700 3.153 volts

AC supply to adapters 119.7 volts AC
...

 

[Nite]

Well I had just bought two of these...love the batteries. However the form only allows me to order one charger.... but i have two power supplys with the bad IV symbol on them.

Definitely need to call them. One of the chargers 4 bays is bad.

I hear they have good customer support.anyone know where to buy these cells and what brand they really are if not made by la crosse?

 

[Russel]

My BC-700 AC adapter has the "IV" symbol, although it is listed as manufactured by "Ktec".

I had to look again, mine is also made by Ktec, but no "IV" symbol.

Bones reply to DarkNova (quoted above the photo)

If you have a way to measure, it would be interesting to learn whether the output voltage of your adapter is comparable to Russel's, especially if his happens to be a pre-IV version:

I am also interested in what voltage the "IV" version BC-700 AC adapter puts out.


Again, for reference, the output of the BC-700 AC adapter in the photograph above:

BC-700 3.153 volts
AC supply to adapters 119.7 volts AC

 

[DarkNova]

I had to look again, mine is also made by Ktec, but no "IV" symbol.

I am also interested in what voltage the "IV" version BC-700 AC adapter puts out.


Again, for reference, the output of the BC-700 AC adapter in the photograph above:

BC-700 3.153 volts
AC supply to adapters 119.7 volts AC

My BC-700 IV adapter puts out 3.157 V (unloaded) with the AC supply currently at 122.3 V, so that seems pretty similar to yours.

My adapter also looks identical to yours, except there is a "IV" with a circle around it in the lower right corner, next to the plus sign, and below it it says "80BH". These markings are identical to the one on the LaCrosse page talking about the recalled adapter, so I don't know if I should be concerned or not. All the other numbers are the same as in your picture.

 

[KiwiMark]

I just checked my power adapters - one is bang on 3.00V and the other is about 3.03V, they are plugged into 240V 50Hz AC power. I guess I should be fine, mine are both older than 1 year old.

 

[Russel]

My BC-700 IV adapter puts out 3.157 V (unloaded) with the AC supply currently at 122.3 V, so that seems pretty similar to yours.

...I don't know if I should be concerned or not. All the other numbers are the same as in your picture.

I alway charge AA cells at 700ma with my BC-700. I have used mine dozens of times without any problems. Also, I don't think there have been any reports of meltdowns with the BC-700, so I would say your charger is fine.

 

[Russel]

I just checked my power adapters - one is bang on 3.00V and the other is about 3.03V, they are plugged into 240V 50Hz AC power. I guess I should be fine, mine are both older than 1 year old.

What model charger BC-700, BC-900, or BC-9009?

 

[Apollo Cree]

I'm rather concerned if 3.2V vs. 3.0 volts makes the charger melt down. That's not really a very large voltage variation. Of course, maybe the IV supply occasionally varies to an even higher voltage.