Trouble charging AW IMR 26500's on wf-139?

[Swagg]

Is there an alternative to using the UltraFire WF-139? I haven't had any issues before, but the last battery I just received just won't charge on this charger. I know the charger is working fine, and Ive also been using some strips of copper to help make contact. Anybody know of a better charger or method?

 

[TooManyGizmos]

~

The Pila IBC 2-bay charger is the most common answer you will get.

$50.00 ..... but considered by most to be worth it .

( rather than going thru many cheaper chargers that fail )

Or you could move into more versatile "Hobby" chargers for just a little more money .

~

 

[kramer5150]

Whats the voltage of the cell? The WF-139 will not attempt to charge a cell thats less than 2.7V.

Hobby charger and a cell cradle would be my suggestion.

 

[Justin Case]

For some reason, with the IMR26500s, I've had problems making electrical contact between the cell's terminals and the WF-139 charger's contact points. But I have been able to charge a 26650 cell in the WF-139. Go figure.

The usual solution is to connect a C-cell holder to a contact spacer that fits into the charger. CPF is filled with all sorts of clever methods. Here is one approach:

 

[Swagg]

Yeah Justin Case, that's the approach I was planning on, where did you get those cradles? I was thinking about getting the cheap ones at radio shack but is there a problem with those?

 

[Justin Case]

I've used the Radio Shack holders. They work, they are readily available, and they are inexpensive. But IMO they don't work as well as the Bulgin holders shown. The issue seems to be higher resistance in the Radio Shack holders due to various crimps, springs, and skinny wires. Nothing that can't be fixed via low resistance mods to the holder. Also, it might not matter that much when charging at low rates like with the WF-139.

You can find Bulgin C cell holders from Allied Electronics, Mouser, and Digikey.

I made my spacers to be AA length so that I could also use the holders with a AA NiMH charger.

 

[Swagg]

I've used the Radio Shack holders. They work, they are readily available, and they are inexpensive. But IMO they don't work as well as the Bulgin holders shown. The issue seems to be higher resistance in the Radio Shack holders due to various crimps, springs, and skinny wires. Nothing that can't be fixed via low resistance mods to the holder. Also, it might not matter that much when charging at low rates like with the WF-139.

You can find Bulgin C cell holders from Allied Electronics, Mouser, and Digikey.

I made my spacers to be AA length so that I could also use the holders with a AA NiMH charger.

Thanks man! Yeah those spacers are pretty sweet. I'm not super savvy here, any advice on making spacers?

 

[kramer5150]

Heres something similar I made for another member. As mentioned, the WF-139 does not charge at a high enough current to overheat the electrical contacts.

 

[Swagg]

Whoa Kramer5150 that's pretty sweet! I just ordered the heavy duty C trays from Mouser that Justin Case mentioned, thanks again Justin. Now I gotta get something like those spacers set up...

 

[hoongern]

~

Or you could move into more versatile "Hobby" chargers for just a little more money .

~

In fact, budget hobby chargers such as the Turnigy Accucell-6 only cost ~ $20, and are REALLY versatile - you can charge your cells at any current you want (much faster than the wf-139), with proper CC/CV charging algorithm.

Of course, there are other options as well.

But when I did have my wf-139, I connected the charging bays to an external D-cell holder in which I placed the 26500s. It "worked", but took a long time to charge. After a little while, I decided to go with a hobby charger and haven't looked back since!

 

[kramer5150]

Whoa Kramer5150 that's pretty sweet! I just ordered the heavy duty C trays from Mouser that Justin Case mentioned, thanks again Justin. Now I gotta get something like those spacers set up...

I just used brass bar stock, and pressed it into the wood. Soldered the 18 AWG onto it. Brass soaks up solder very easy.

 

[Swagg]

In fact, budget hobby chargers such as the Turnigy Accucell-6 only cost ~ $20, and are REALLY versatile - you can charge your cells at any current you want (much faster than the wf-139), with proper CC/CV charging algorithm.

Of course, there are other options as well.

But when I did have my wf-139, I connected the charging bays to an external D-cell holder in which I placed the 26500s. It "worked", but took a long time to charge. After a little while, I decided to go with a hobby charger and haven't looked back since!

Ok so now I'm getting in over my head, I looked at that charger, looks pretty cool. So I'm guessing you attach the c battery bays to the charger, how many bays at once? And when you say faster, how much faster does it charge? And when you start talking algorithms that intimidates me a little...

 

[mdocod]

For anyone already charging in external cradles, it makes way more sense to just pick up a hobby charger as suggested. Spend as much as you are willing to spend and read some reviews and such before pulling the trigger. Though it does seem that even the cheap hobby chargers do a better job than any of the cheap "flashlight" market oriented chargers.

Swagg,

Many hobby chargers are either going to be single or double channel. And most can charge 4 or more li-ion cells in series through the use of balance taps to even out the cells. Through the use of series charging with balance taps, you can maximize the available wattage available from the charger more easily. In series wired stacks, you wire everything up in series with balance taps in-between each cell connection, and then select a charging rate that is appropriate for 1 cells rate.

Any single channel on a charger like that can be used to charge as many li-ion cells as you want in parallel, provided they are in a similar state of charge when put together in that parallel pack. You can technically speaking even charge different capacity cells, different size, and different chemistry within the li-ion group with them all wired in parallel as long as they are all supposed to have the same charge termination. The charge rate with cells in parallel is the combined ideal charge rate of all of the cels in the parallel configuration combined. Set the charger to "1 cell li-ion" mode for this, because all you would be doing is making a huge 3.7V battery out of many cells whose capacity will combine in parallel.

Most chargers will have a maximum current, and maximum voltage, and maximum wattage total they can operate at, and they will very rarely be able to deliver anywhere near their peak power delivery into a 3.7V parallel stack of cell, so the fastest charging options will usually be thorough a series arranged pack.

There is a ton of flexibility with that type of charger, once you learn all that can be done and start coming up with charging cradles for all your cells you'll probably really come to appreciate it.

Eric

 

[Swagg]

Hey Eric, thanks for the reply, definitely getting me on the right track. I'll be doing more research before I feel comfortable buying a better charger which is what I want to do.

For now, Kramer, would you be willing to set me up with a setup like that? Of course I'll be willing to cover whatever it is cost wise.

 

[Justin Case]

The concept for these sorts of spacers is to find some suitable cylindrical insulator and figure out a way to attach some metal contacts on each end of the insulator.

I used hollow plastic tube. As an expedient, you can use a Papermate ball point pen body. The metal contacts are epoxied into the ends of the tube. The contacts themselves consist of a brass screw, brass nut, and AMP/Tyco crimp-on ring terminal. You can either crimp or solder your wire to the ring terminal. Slide the ring terminal onto the brass screw. Then thread on the brass nut to hold the ring terminal in place. Epoxy the end of the brass screw in the hollow plastic tube.

I actually cut my plastic tube slightly overlength (by about 1mm-2mm). That allowed me to file a flat on each brass screw head to increase the contact area. After filing, the overall length of the spacer was exactly AA length.

Kramer's approach also looks simple, using readily available materials. You can get brass rod from onlinemetals.com. In fact, you could even dispense with the brass rod. You can use some brass wood screws at each end of the wood spacer.

If you go with a hobby charger and decide to set up a parallel charging cradle arrangement, here is an example using Bulgin holders:

I used Deans 12 gauge noodle wire to connect the Bulgin holders in parallel. The noodle wires terminate in 15A banana plugs, which plug into the output jacks on your typical hobby charger.

The main issue with using a relatively low powered hobby charger is that you may run into difficulty charging at 1C if you want to charge many cells at the same time (e.g., 5xIMR26500). A 1C charge rate for an IMR26500 is 2.3A. Five IMR26500s in parallel means that your hobby charger needs to deliver 5*2.3A = 11.5A. If your charge rate can't hack it, then you kind of defeat the purpose of the whole arrangement -- rapid recharging of multiple Li-ions. If the hobby charger's max charge current is only 5A, for example, then you'd charge 5xIMR26500 at about 0.4C, not 1C.

If you plan to charge only a couple of cells in parallel, then most likely any hobby charger has enough "oomph".

You also typically need to supply an external power supply to run the hobby charger. Think of the hobby charger in the same way as a flashlight DC-DC converter. The hobby charger has a certain "driver efficiency".

For example, you might have to feed the charger 20V and 3A so that the charger can deliver 11.5A and up to 4.20V to 5xIMR26500. Bottom line is that your power supply has to be able to deliver more power than what the charger sends to the cells because the charger isn't 100% efficient. In the notional example above, you need a 60W power supply to charge 5xIMR26500, even though the max power that gets sent to the IMRs is only 48W.