La Crosse BC-900 Charger Warning

[tacoal]

Hi jtr1962,

You are welcome!

The resistance of the thermistors in my BC-900 is measured only about 9.2K at 70F. 12.2K is about 30% above the 9.2K. This might be another factor causing the melting down.

I also checked the waveform around the thermistors. It seems it measures the time charging a capacitor (near the hole) from 0V to about 1.2V through each of the thermistors or the reference resistor to check if the temperature is higher than the reference.

I also noticed that there will be a gap between the metal plate and the battery if it is not well installed. This would make the charger think the temperature there lower than real one.

 

[SilverFox]

Hello Jtr,

I have also noticed that the thermocouple contact with the metal strips may be in question. I believe someone (on the German camera site) mentioned modifying the thermocouple placement to insure better contact.

Mine has a bit of thermal paste as well. When I put my unit back together, I added additional thermal paste to insure good heat transfer.

Tom

 

[wptski]

Well, add me to the growing list of La Crosse BC900 meltdowns!

I had just purchased sixteen Duracell 2300mAh AA made in China. These had been formed on a Sirius Pro Former and cycled four times on various RC chargers. This is the third batch that I was running a Test Mode(1000ma/350ma) on. I had been watching the unit and this was the first cell to complete the discharge showing 2.37Ah which is about the same as the others from this batch that I've tested.

A few minutes later I looked closer and noticed the it's button had dropped! I started to smell something burning and the LCD on that slot started to turn black. So I quickly pulled the plug. Funny as the cells aren't warm or anything!

Just took it apart and the button is melted and stuck to the circuit board!

The worst part of this is that I'm one of the first CPF'r to get this charger from J.S. Burly's and I'm sure that's over a year ago!

EDIT: As it turns out, my PayPal shows payment on 1/16/2005! Can't cut it any closer than that! :wow:

 

[SilverFox]

Hello Bill,

Wow, this is not good news at all...

When you contact La Crosse, ask them what they think is going on. I would be interested to hear what they have to say.

Tom

 

[wptski]

Tom:

I'll be calling them tomorrow!

I did think of something else too. As I mentioned this was the third set of DuraCell 2300mAh cells that I ran in 1000ma/350ma Test Mode. I was having trouble with the Mode button while trying to get to the Test Mode and I believe it started with the second batch too.

I finished charging those four cells in a MAHA MH-C401FS in fast(1000ma) mode because of all this talk about charging at 1C with these larger cells. I also have two MAHA MH-C204W which do two cells at 2000ma or four at 700ma with -DeltaV, zero DeltaV, Temperature and Time cutoff. I think that I'll start using these at 2000ma for those DuraCells.

 

[jtr1962]

A few minutes later I looked closer and noticed the it's button had dropped! I started to smell something burning and the LCD on that slot started to turn black. So I quickly pulled the plug. Funny as the cells aren't warm or anything!

It seems that the MOSFETs on the board generate enough heat sometimes to cause the buttons to drop. For that reason I recommend using a fan if you're operating the charger over 500 mA.

On a more positive note, I did the temperature modification as I described (and checked the thermal coupling of the thermistors as Tom recommended), and refreshed 48 cells at 1000 mA without a fan. The charger stopped charging when the cells were about 120°F (warm to the touch but I can keep my hand on them continuously). Before the cells would get hot enough that I couldn't keep my hand on them for more than a few seconds. I still recommend using a fan at higher charge currents to prevent charging from being stopped due to overheating. Also, the charger seems to pick up the end of charge signal better with cool cells. No need for a huge fan. An 80 or 120 mm PC case type fan either set on top of the charger or on the side is enough cooling.

 

[wptski]

It seems that the MOSFETs on the board generate enough heat sometimes to cause the buttons to drop. For that reason I recommend using a fan if you're operating the charger over 500 mA.

On a more positive note, I did the temperature modification as I described (and checked the thermal coupling of the thermistors as Tom recommended), and refreshed 48 cells at 1000 mA without a fan. The charger stopped charging when the cells were about 120°F (warm to the touch but I can keep my hand on them continuously). Before the cells would get hot enough that I couldn't keep my hand on them for more than a few seconds. I still recommend using a fan at higher charge currents to prevent charging from being stopped due to overheating. Also, the charger seems to pick up the end of charge signal better with cool cells. No need for a huge fan. An 80 or 120 mm PC case type fan either set on top of the charger or on the side is enough cooling.

jtr1962:

A bit late for mods! This was the largest capacity cells that I've ever used in the BC-900. What capacity are the 48 cells that you refreshed? What about your recommended power supply?

I just charged two of the 2300mAh Duracells in a MAHA MH-C204W at 2A with a dual input temperature probe monitoring both cells. They both got just over 140F before it finished charging. The highest temperature was 143.3F I'm running a second set right now. The highest I read on the BC-900 at 1.8A was 130F.

Your BC-900 stops at 120F with your mod, so what happens after it restarts, does it still complete the cycle?

 

[jtr1962]

A bit late for mods!

Agreed in your case since the damage is done.

What capacity are the 48 cells that you refreshed? What about your recommended power supply?

Nexcell 1800 mAH. I purchased them about 2 years ago. I did the test with the stock supply but the alternate supply can be purchased here. I noticed the charger does get a little warmer internally with the alternate supply since it's 3.3V instead of 3V. If I can get the alternate supplies open I might be able to find an adjustment pot to bring them down to 3V.

Your BC-900 stops at 120F with your mod, so what happens after it restarts, does it still complete the cycle?

Yes, it will reset, start charging again, and eventually complete the cycle. The problem is that with lots of starts and stops it takes way longer. For that reason I recommended using a fan.

 

[wptski]

Agreed in your case since the damage is done.


Nexcell 1800 mAH. I purchased them about 2 years ago. I did the test with the stock supply but the alternate supply can be purchased here. I noticed the charger does get a little warmer internally with the alternate supply since it's 3.3V instead of 3V. If I can get the alternate supplies open I might be able to find an adjustment pot to bring them down to 3V.


Yes, it will reset, start charging again, and eventually complete the cycle. The problem is that with lots of starts and stops it takes way longer. For that reason I recommended using a fan.

jtr1962:

I was hoping that you tested with some 2300mAh or larger cells.

High temperature cutoff is a safety feature and not something that should happen frequently! I wondering if the cycle is interrupted too close to the termination point, it may cause problems? These larger cells need higher charge rates to insure proper detection of termination voltage drop but now were generating more heat! I think that we need some new designs for these new generation cells.

I once had a problem with a third party cellphone battery charger and called Tech Support. They had instructed me to just stop the cycle and restart it again! Darn thing never worked the same after that!!

 

[jtr1962]

I also have 14 2300 mAh Nexcells. I'll try recharging them at 1000 mA without a fan and see if there are any problems.

Yes, I did hear that if the charging cycle is interrupted there may be problems detecting end of charge when it resumes. That might be one reason LaCrosse set the cutoff temperature so high-so that it would be a backup in case the -dV/dt detection failed, but normally wouldn't come on. I only had a problem with two of my cells. They kept starting and stopping from overheating. I finally took them out when the charger said that 2.7 AH had been pumped into them even though they were still charging. I figured they were plenty charged by then.

 

[tacoal]

The current sampling resistors will generate more heat than those MOSFETs. The On-state resistance for NTGS3443, the MOSFET in BC-900, is about 0.1 ohm; the sampling resistor is 0.2 ohm.

One thing happened this afternoon when I charged the Rayovac 2000mah battery in 700ma refreshing mode. Since this is the second time to change these batteries, I checked them about 20 minute. At time, when it is in charge mode, the battery and charge is very hot when I put the charger in flat wood surface. The surface is hot too. Then, I elevate the battery end of the charger about 2 in by something, i.e. the charger is in a sloping position. After this, the batteries and the charger stay cool even in charge mode.

So it is a good practice to put a fan against the charger or put the charge in a sloping position so that the air circulation could bring away more heat from the charger to keep it stay cool.

jtr1962:

Did you measure the shutdown temperature before you did the mod?

 

[jtr1962]

jtr1962:

Did you measure the shutdown temperature before you did the mod?

Just by feel. I've done a lot of experiments with thermoelectric modules where I measured temperatures of hot and cold plates, so I have a pretty good idea of what various temperatures feel like. Before the mod, the cells were getting to about 140°F. Afterwards, roughly 120°F. Granted, this is all just by feel, but it agrees pretty well with the actual measurements in the article you linked to earlier.

 

[SilverFox]

Hello Tacoal,

I have been using a small rock to elevate the back sides of my BC-900 and Energizer 15 minute chargers. It seems to help a lot.

Tom

 

[BVH]

Does anyone have a source for a very quiet, 120 volt, miniature fan that moves just enough air to cool the charger/batts?

 

[SilverFox]

Hello Jtr,

There seems to be two firmware versions of the BC-900. I believe most of the problems we have been hearing about are with version 32. The Germans have been discussing version 33, which seems to shut things down at about 127 F (about 53 C).

Does your charger have version 32?

Tom

 

[wptski]

I wonder if the user in this thread:BC-900 Meltdown ever got his replacement and what version it is, 32/33?

I tried calling La Crosse about my BC-900 twice and got dumped after a few minutes to voicemail! I left a message the second time. They might be closed today because of the holiday!

EDIT: I emailed them also!

 

[tacoal]

Just by feel. I've done a lot of experiments with thermoelectric modules where I measured temperatures of hot and cold plates, so I have a pretty good idea of what various temperatures feel like. Before the mod, the cells were getting to about 140°F. Afterwards, roughly 120°F. Granted, this is all just by feel, but it agrees pretty well with the actual measurements in the article you linked to earlier.

I see. Thank you for the info.

 

[jtr1962]

Does your charger have version 32?

Yes, version 32 like pretty much everyone's here. I wonder if they did a board redesign with version 33 or just a software change.

 

[nuggett]

In my version 33 manual, it states the charger will shut down if temps exceed 127 deg, then restart after cooling

 

[wptski]

In my version 33 manual, it states the charger will shut down if temps exceed 127 deg, then restart after cooling

nuggett:

How long have you had your BC-900?