Made charging stand for BC-900 charger (JPG inside!)

[Muse]

I just bought the BC-900, and am aware of the concern about possible runaway overheating, so I made a charging stand out of very thin sheet metal, some discarded steel pallet straps, a few computer case screws, a 12v 80 mm computer case fan, a 5.2 v wall wart. Notice that the BC-900 and wall wart plug into a power strip for convenient turn on/off. At the moment I'm refreshing 3 old 700 mah AAA's.

 

[ackbar]

Re: Made charging stand for my BC-900 charger

That is awesome. I was thinking of doing something similar. Right now I have my charger on top of a old optical drive.

 

[VidPro]

Re: Made charging stand for my BC-900 charger

just a side note, cooling the batterys MIGHT change the way the charger is capable of seeing the termination thing , the Vdrop.
just soes you knows. and can check for stuff like that.

 

[bob_ninja]

Re: Made charging stand for my BC-900 charger

BTW, for charge rates 500 mA and 200 mA you don't need cooling at all. There is not much heat being generated.

 

[clintb]

Re: Made charging stand for my BC-900 charger

And on a properly operating charger (read: senses a proper deltaV and/or deltaT), you should not be using a fan at all on the charging process.

The problem arises from different cells and different chemistries (NiCd or NiMh) need higher, in the case of NiCd, or lower, in the case of NiMh, deltaV. Even cells from different manufacturers within the same chemistries can possibly need higher or lower deltaV. Confusing yet? Chargers like the BC-900 and C-9000 try their hardest to get it right and come soooo close. Yeah, that's the reason I have a Competition Electronics T35 GFX for the R/C stuff. Everything is adjustable on that baby.

 

[Muse]

Re: Made charging stand for my BC-900 charger

BTW, for charge rates 500 mA and 200 mA you don't need cooling at all. There is not much heat being generated.

Yes, I was wondering whether or not it's a good idea to have a fan on the BC-900. I believe I read posts from people who do use a fan, and that's where I got the idea. I'd think that the delta V has nothing to do with the temperature of things. I don't remember reading any technical descriptions or even nontechnical ones of what delta V charger termination entails.

Anyway, I figure cooler is better especially with a charger that could overheat. Since the 12v fan is being run at 5.2v it's not pushing a lot of air, but enough to aid heat dispersal from the cells, and some from the charger itself. I believe that the BC-900 uses delta V, not delta T.

In any case, the stand does isolate the charger in case it does "melt down." I especially like the power strip shutoff, really the last idea I got, because plugging and unplugging two plugs is way inconvenient. I always unplug any wall wart/etcetra that's not needed. Besides, La Crosse says to power off the unit when not in use. They may have a reason for this.

Anyway, while I have been cautious with charge rates on my first few experiments, I think I will be using charge rates higher than 500 ma pretty soon. Probably 1000 ma with my stronger AA's. Not sure, but some people recommend it.

 

[clintb]

Re: Made charging stand for my BC-900 charger

As quoted from the Thomas Distributing BC-900 page:

UL approved, the LaCrosse BC-900 battery charger also has safeguards that sense rechargeable battery polarity, rechargeable battery temperature and defective rechargeable batteries.

So, the BC-900 has a temperature sensor, but it is only for a charging runaway condition. Heat is a byproduct of the faster charging rates, especially when 1C+. If you cool it while charging, you are creating an environment of possible false peaks. Don't do it! If you must use the fan, do so when discharging at higher rates.

 

[Muse]

Re: Made charging stand for my BC-900 charger

As quoted from the Thomas Distributing BC-900 page:

So, the BC-900 has a temperature sensor, but it is only for a charging runaway condition. Heat is a byproduct of the faster charging rates, especially when 1C+. If you cool it while charging, you are creating an environment of possible false peaks. Don't do it! If you must use the fan, do so when discharging at higher rates.

I don't understand. The BC-900 doesn't use temperature to determine end of charge, right? Only to decide that things are getting too hot and then stop activity until temperature goes down to safe level. So, how can having a weak fan over the batteries adversely affect the functionality?

From Thomas-Distributing:

"The Temperature Sensor Circuit built in to the BC-900 will stop the charge cycle if the battery temperatures reach 127°F. As soon as the batteries have cooled the automatic charging will resume. This feature will greatly maximize the life of your rechargeable batteries when dangerous overheating is prevented."

 

[tacoal]

Re: Made charging stand for my BC-900 charger

Muse,

You are right, the BC-900 uses the thermal sensor as a safeguard.

Cooler environment is helpful for battery to generate detectable -dv/dt. This is also
helpful the MOSFET used in charger to avoid thermal runaway.

The first batch of C9000 has problems to deal with the thermal sensor so that a cooling fan will make overcharge worse. BC-900 and 'improved' C9000 don't have this problem.

I usually put the BC-900 in a slope position to make the natural air flow more easily.

 

[VidPro]

Re: Made charging stand for my BC-900 charger

Cooler environment is helpful for battery to generate detectable -dv/dt. .

i donno, your going to want to see if this is true or not, detecting the Vdrop, when the battery is COPING with the overcharge level. when the battery goes into overcharge, pressure rises, heat rises, and voltage drops, i am betting that if the first 2 dont occur, that the 3rd will be harder to detect, not easier.

 

[tacoal]

Re: Made charging stand for my BC-900 charger

i donno, your going to want to see if this is true or not, detecting the Vdrop, when the battery is COPING with the overcharge level. when the battery goes into overcharge, pressure rises, heat rises, and voltage drops, i am betting that if the first 2 dont occur, that the 3rd will be harder to detect, not easier.

Please check the document at http://panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_Overview.pdf
.
The figure at bottom right corner of page 9, shows how temperature affect the voltage curve.

 

[VidPro]

Re: Made charging stand for my BC-900 charger

sure enough, the Hump is much larger at the lower temps

edited out that other stuff.

 

[VidPro]

Re: Made charging stand for my BC-900 charger

but (always that but huh)
this is what temperature they are being charged IN, not how they are being externally cooled. so a change in temp of the battery in freezing weather, would show more deflection. say like right near the end of charge, even in the snow, that sucker starts heating up. if it STAYED the temperatures they are listing, then it wouldnt heat up.
(thats my theory

so i am saying that the change in the battery temp is what happens, if its a room temp and it does not heat up, or (according to the chart) does not CHANGE in temperaturee a lot. then mabey it doesnt display a change as much.

 

[SilverFox]

Re: Made charging stand for my BC-900 charger

Hello Muse,

Nice set up.

My personal opinion is that you should not blow are on the cells as they are charging, however I have no problems if you turn the fan around and suck warm air from the batteries and charger.

Tom

 

[wptski]

Re: Made charging stand for my BC-900 charger

Hello Muse,

Nice set up.

My personal opinion is that you should not blow are on the cells as they are charging, however I have no problems if you turn the fan around and suck warm air from the batteries and charger.

Tom

Tom:

Hmmm, does it really make any difference? After the initial startup, the air being pulled is going to be cooler anyway, I think!

 

[SilverFox]

Re: Made charging stand for my BC-900 charger

Hello Bill,

I think there may be a difference between blowing and sucking...

Blowing is more directed and sucking is more of an increased ventilation.

Tom

 

[tacoal]

Re: Made charging stand for my BC-900 charger

VidPro,

My interpretation of the figure is that the cooler the environment (or battery), the easier to generate a detactable -DeltaV.


I think it is better to suck the air for Muse's setting since this agrees with the natural air flow(hot air going up spontaneously).

 

[wptski]

Re: Made charging stand for my BC-900 charger

Hello Bill,

I think there may be a difference between blowing and sucking...

Blowing is more directed and sucking is more of an increased ventilation.

Tom

Tom:

Look how the fans work on the E-15 and D-15 chargers. They actually blow air over the cells not suck. Of course, if they sucked the heat inside the charger, that may not be so good either!!

 

[SilverFox]

Re: Made charging stand for my BC-900 charger

Hello Bill,

Good point. However, charging at 3C or higher should develop a strong -dV signal, so a little cell cooling may not make any difference. The BC-900 has a hard time getting to a 1C charge.

Tom

 

[VidPro]

Re: Made charging stand for my BC-900 charger

VidPro,

My interpretation of the figure is that the cooler the environment (or battery), the easier to generate a detactable -DeltaV.

well as long as you see the logic of what i am saying, that is all i am saying, when the overcharge state is reached the battery heats, and the voltage drops.
this effect is more visable when the battery was cold via the environment, but that doesnt nessisarily mean when the heat of the overcharge is removed from the battery.

a more sensitive Vdrop charger (like an adjustable one) or a high rate of charge, will still get the job done.

you see to my "simple" mind there is little different from any cell Boiling/bubbling at its end of charge, then the Vdrop which occurs when the pressure and heat rise in these thing. seems to me the vdrop is a result of internal damages beginning to occur.
look at the chart, its at 110-120% overcharge Already, its not Hey i am charged stop already, its Help me , i am dying here

its the same with lead acid, ni-?? and li-ion, they are all some metal plate with electrolyte battery. they all BUBBLE up when they reach overcharge (even if they dont show a easy vdrop). of course with li-ion pressure rise and heat is more critical to destruction of the battery.