DX Li-ion "C" cells?

[sb_pete]

Apologies if this has come up before - I did try to search quite a bit and came up dry.

Anyone have any experience with these DX 25500 "C" cells?
http://www.dealextreme.com/details.dx/sku.5035

I know the capacity is marketing nonsense, but someone posted on DX that he measured 3000-31000 mah at 1A discharge so still better than a 18650 cell. I also know that AW's would be better quality and I think these are unprotected while his are protected. But these are just under 50mm meaning they would fit in a 2c without an extension.

Question is:
1. Anyone tried em?
2. How would one go about retrofitting a protection circuit onto them (hopefully still being able to fit a pair in an otherwise stock mag 2c)?

I am thinking that if this could work then one could have a 2c using rechargeable li-ions but with the ability to fall back on cr123's if necessary.

Thanks as always everyone.
-Pete

 

[DM51]

I had a quick look at that page, and unless I missed something I think you are right to assume these are unprotected cells.

It is possible to buy separate protection circuits, although I have not looked into where to get them to fit "C" cells.

However retro-fitting a protection circuit, even assuming you could find some with the correct settings and do the fitting yourself, would not solve the length problem. The reason the AW "C" cells are 53mm long is because the protection circuit takes up that extra 3mm - it sits on the end of the cell. So these DX things would end up the same size.

And then (the clincher for me) there is the question of cell quality...

 

[Gunnerboy]

I am using two of these to drive a ROP LO. Since these are unprotected, I don't want to try them with either ROP HI or 5761 bulbs.

I have quite a few AW li-ion C's, which are the benchmark, but I bought a couple of these out of curiousity. These are great for the price and I will be buying another pair to use in another ROP LO I plan to keep in my truck.

Cheers,
Gary

 

[DM51]

I am using two of these to drive a ROP LO. Since these are unprotected, I don't want to try them with either ROP HI or 5761 bulbs.

I have quite a few AW li-ion C's, which are the benchmark, but I bought a couple of these out of curiousity. These are great for the price and I will be buying another pair to use in another ROP LO I plan to keep in my truck.

Cheers,
Gary

Paradoxically, you would be safer using them with a high-load application, rather than a low-load one.

This is because you will notice more quickly that the cells are running low - the rate at which the light dims will be quicker and therefore more noticeable. At the first sign of dimming, obviously, you should switch the light off and recharge the cells.

It goes without saying that you should be extremely careful with these cells - they pack a lot of punch, in more ways than one, and if they fail for any reason and then blow up, they will constitute a very real danger. It is most emphatically not advisable for those who do not have a thorough knowledge of good practice and correct procedures with Li-Ion cells to use unprotected ones.

This is especially true where cheap cells are concerned, and I would repeat that the quality of these particular cells, and the degree of quality control exercised in their manufacture, is unknown.

Please BE VERY CAREFUL INDEED with them.

 

[Gunnerboy]

Thanks DM51. I will use caution with these cells.

I meant that since these unprotected cells deliver slightly more voltage to the bulb than AW's I didn't want to risk insta-flashing my 5761, which may be operating right on the edge with protected cells.

Gary

 

[DM51]

They will deliver the same voltage as AW "C" cells (max 4.2 volts if you charge the cells correctly). Voltage is not affected by protection (except obviously for over-charging and over-discharging).

"C" Li-Ions will work with the 5761, but there are 2 problems - instaflash from high voltage (problem is eliminated by using an NTC and limiting charge to 4.1 volts) and high current draw (~5.5A is quite a lot for the "C" Li-Ion, and the high discharge protection on AW cells is set at about that figure IIRC). I think it was the current (not voltage) that you meant when you mentioned "operating on the edge".

jimjones3630 has done quite a lot of work with the 5761 - you could do a search to find out more. He favours using Emolis or A123s with this bulb.

 

[Gunner12]

The main danger of Li-ion batteries happen in charging. You can probably discharge the cell to 1V safely, but don't try to charge the cell or

Just be careful with them.

 

[VidPro]

Paradoxically, you would be safer using them with a high-load application, rather than a low-load one.

.

Reverse paradox is if the light gets accidentally left on, gets bumped and turns itself on, some normal consumer uses it, like your kids when your not home.
lots of LED lights would at least stop when the voltage is not high enough, but the high drain incadscent knows no bounds, it will shred your cell all the way down to zero given the chance..
then you still got a dead cell, that heats more on the charger :-(

as long as the user is totally aware, or just keeps topping off, ya might get away with it

 

[sb_pete]

Just out of curiosity: I know very little about how PCB's work - Maybe somebody could point me to a good tutorial type thread on this?

On another note, I know that you can put a single protection circuit onto a battery pack so what about doing something like putting a protection circuit into the light housing. No protection against charging issues obviously but this would pre-empt them from getting to that point right?

Is this even possibe?
Thanks,
-Pet

 

[VidPro]

protection is simple
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=711
geesh look at all of them well it was simple.
battery goes into protection curcuit, Load and charge go into other side, they often have a similar ground, although it might not be the cathode (-)

most of the ones i got even came with connection instructions, amasing.

you can put protection curcuits in flashlights, packs about anything. a cool one i did was with 4x 14500s with the protection stuffed into the center (fits a D size hole). kinda hard to do with D cells, but there is sufficent space in your average mag for a protection curcuit, but not always for the wiring to go to each seperated cell :-(
that is where protected cells come in handy, cause they have the wiring on them, and its only a bit fatter/taller than normal.

 

[sb_pete]

OK, so just to check: Using the ultrafire smart charger and the "C" adapter they would charge just fine b/c that charger would stop the charge at 4.2v.

The real problem is that if you have over-discharged them, they are dangerous to charge, right? So as long as you used a multi-meter to check the voltage everytime before you charged them, you would be fine right?

What is the rule for overdischarging? How much until the battery becomes dangerous? <3v?
How much until you will affect long term life of battery, but not make it dangerous?

Thanks,
-Pete

 

[DM51]

The Ultrafire WF-139 will take >7 hrs to charge a "C" Li-Ion. It will NOT necessarily stop the charge at 4.2v. And if you leave the battery on the charger it will keep on overcharging an unprotected cell until it blows up.

If the battery reads 4.2v it is full. Any more than that, and it is over-charged.

At 3.5v resting, it is effectively empty. To take a resting voltage, measure the cell after leaving it to rest (i.e. not in use) for ~15 mins.

If it measures below 3.0v resting, it has been over-discharged and has probably been damaged. Attempting to recharge an over-discharged cell can be very dangerous.

It is not necessary to discharge the cell fully each time. It is not good for the cell either. You can top it up any time you want.

 

[SilverFox]

Hello DM51,

A point of clarification...

Leaving a cell charging on the Ultrafire WF-130 will eventually allow the cell to come very close to the open circuit voltage of the charger. This charger does not shut off when the cell is fully charged, but continues to charge until the voltage of the cell is the same as the voltage of the charger. I don't recall what the open circuit voltage of the charger is, but I believe it is around 4.3 volts. At 4.3 volts, you have certainly overcharged the cell and have done damage to it, but I don't believe it will "blow up."

Tom

 

[DM51]

Thanks Tom - by open circuit voltage, do you mean the voltage across the 2 terminals in the bay without a cell in it?

 

[SilverFox]

Hello DM51,

That is correct.

Tom

 

[DM51]

Oooooh... Well, mine reads 4.65v on each bay...!!!

I'm just wondering if it's possible that this voltage actually drops under load. If it doesn't, then that is reason enough never to use this charger with unprotected cells.

I ran a test on it with an unprotected 18650 some time ago, but my nerve failed me when the cell reached 4.28v and the light still hadn't turned green, and I pulled it.

 

[SilverFox]

Hello Dm51,

Oops, I stand corrected... 4.65 volts may indeed cause things to go poof.

Yes, the voltage will drop under the load of charging, but if the cell has very low internal resistance and is left in the charger for an extended period of time, it will continue to charge until it reaches close to the open circuit voltage of the charger. The higher the internal resistance of the cell, the more the voltage will drop. It could be that this charger was designed to work with the added resistance of the protection circuit. This may bring the voltage down to only a case of mild overcharge.

Caution: If you are financially forced to use this charger, do so with caution.

Tom

 

[DM51]

I think that must be the case, that the protection circuit helps to reduce the voltage. That, and the protection itself stopping over-charging anyway.

I'm going to go through a bunch of old DC power supply units I have stored away somewhere (if I can find them) and try some different voltages into the 12v DC input on the WF-139, and see what that does to the output voltage. I don't expect much to come of this that would be of any practical use - it's just curiosity.

In the meantime, for all users (especially sb_pete with DX "C"-cells) - as Tom says, use this charger with CAUTION!

 

[VidPro]

Hello Dm51,

Oops, I stand corrected... 4.65 volts may indeed cause things to go poof.


Tom

geesh, that is bad. a charger like that might have been Demanding a Protected cell, and attempting to rely apon protection of the cell.

i remember somone mentioning that the original PILA charger would go high too, and was also dependant on pila protected cells.

because some protections (even made/used today) can have a wery high cutoff like 4.35, some protections would not be good on chargers like that either. the protection on lots of small lowcap pack items was not intended as a charger cutoff, but more like emergency cutoff for last chance survival>
According to the spec stuff, chargers are supposed to have proper cutoff, reguardless of cell protection.

 

[sb_pete]

The Ultrafire WF-139 will take >7 hrs to charge a "C" Li-Ion. It will NOT necessarily stop the charge at 4.2v. And if you leave the battery on the charger it will keep on overcharging an unprotected cell until it blows up.

:thinking: I thought these were "smart" chargers and did stop the charge. According to AW's sales thread

This UltraFire LiIon intelligent charger ( model WF-139 ) has two independent charging channels for 18650/17670s. With its spring loaded -ve contacts, it will also charge 18500/17500/14500s. Charging current is 450mA per channel. Worldwide voltage 100-240V ( 50/60Hz ). The stopping voltage of this charger is 4.17-4.23V.

Original post by AW in CPF marketplace here (marketplace thread id=142521

Is this info incorrect?
If that is the case, what charger would you recommend for charging li-ion 14500 thru 18650 cells that does cut off the charging current?

Thanks guys,
-Pete