26650 custom charger

[matt_o]

I made this for charging my two 26650's that I always use together in my ROP.

My question is if I put a jumper in between the two dummy cells would this charge the batteries in parallel and balance the charge? They should always be at the same voltage coming out of the light. I could hook both batteries to one dummy cell but then would it take twice as long to charge? Is it correct to assume that if I jump the two bays it will still take the same amount of time to charge as if I charged them separately?

 

[kaptain_zero]

Assuming the charger is charging each battery to the same voltage, there is no reason to bridge them. If they do not charge to the same voltage, that becomes a reason NOT to bridge them, but rather to start looking for a better charger that works properly. (And yes, the charging time would remain the same, even if you bridged them)

These two batteries may be used together, but that does not mean they will discharge evenly. One cell may age more quickly than the other or have slightly more or less chemicals etc. By charging them separately, each on it's own circuit, you are bringing them back to the same full charge voltage, even though one cell might require more charging than the other. Bridging them would cause the charger to stop charging when the first battery reaches full voltage BUT that is highly unlikely as the charging circuits were not designed to work if bridged this way.

So, keep it as is and use a verified/calibrated volt meter to verify that everything is fine when fully charged.

And for the record, a verified/calibrated volt meter in this case means that if you use a cheap DMM (I use 2x $10.00 ones myself), have it checked against a known meter or two so you know where you're at. I had both mine checked against 3 high end DMM's and a calibrated test bench unit (none of them were dead accurate except for the test bench unit) and it showed that one of my units read 0.01V low and the other 0.04V high. Neither is an issue, once I know for sure. I just add or subtract from the reading I get to give me the actual reading.

Regards

Christian

 

[kramer5150]

Your setup is correct and optimal for these cells. No need to jump anything, and no need to parallel charge. The WF-1139 has completely independent charge bays that monitor each cell individually.

 

[Billy Ram]

One thing is it's going to take a long time to charge 4ah batterys with a charger that only puts out .375ah. Keep a watch that it shuts off when they are charged. It may not shut off.
Billy

 

[bigchelis]

If you stick the IMR 26650 in the charger and jam a piece of aluminum foil in the (-) side of the cell at the bottom it charges too.

I topped off an IMR 26650 yesterday to try it out like the lighthound.com pictures show it and it works great.

 

[bigchelis]

Here is a picture of the way I been charging my IMR 26650 lately:

 

[matt_o]

I charged them like that one at a time the first time I charged them only I had to make a shim for the positive side. If I charge two at a time, as in my setup, will it charge them both in the same amount of time it takes to charge one in your setup?

 

[fivemega]

The WF-1139 has completely independent charge bays that monitor each cell individually.

That is true but two bays are not necessarily charge both cells equaly.
I do have exact same charger. Left bay allways stops charging at about 4.19 and right bay stops at about 4.21 volts. Not a big deal but not exactly same.
In this case, I switch the cells from two bays, for top off undercharged cell. Right bay continue charging lower voltage cell but left bay light stays green because battery voltage is higher than cut off voltage.

 

[kaptain_zero]

That is true but two bays are not necessarily charge both cells equaly.
I do have exact same charger. Left bay allways stops charging at about 4.19 and right bay stops at about 4.21 volts.

The difference between these two channels works out to approximately 0.5% which is well within acceptable tolerances and is negligible in the greater scheme of things.

Regards

Christian

 

[kaptain_zero]

I charged them like that one at a time the first time I charged them only I had to make a shim for the positive side. If I charge two at a time, as in my setup, will it charge them both in the same amount of time it takes to charge one in your setup?

Charging two batteries as you have shown in your original post will charge in the same amount of time as it takes to charge one battery shown charged inside the charger using some aluminum foil to make the contact.....

Your setup is correct and the most efficient you can hope for.

Regards

Christian

 

[mrartillery]

Ive used both ways and either way works fine. It does take a bit longer to charge them in the wf-139 but it gets the job done. Keep a multimeter close by as well and check the voltage often.

 

[matt_o]

I do check the voltage regularly during charging. Every time I have pulled them off before the green lights turn on. I try to do this around 4.18-4.2, however the last time it was 4.21 and still charging when I removed them. They seem to drop a little bit after a couple of hours off the charger though.

 

[kaptain_zero]

How accurate is your meter?!?!? Don't forget that most inexpensive DMM's are not accurate at all when it comes to measuring mV. I believe bargain meters are built to around 20% accuracy, high end DMM's such as Fluke etc. are held to 5% and Certified Bench type analog meters are around 1%. If you do not test a typical $10 to $50 meter against a known, calibrated professional meter or three... you really don't know what you are getting.

Example, my older Chinese made DMM reads 4mV high so I can go to 4.24V off the charger and I'm dead on 4.2V actual. Then add in the fact that you have a 5% leeway on full charge and I could be reading 4.3+V with that meter and still not have to worry.

On the other hand, my newest meter reads low.... If it reads 4.2V it's actually 4.21V and of course that's still not a problem, but only because I took the time to have it tested and KNOW it's error rate and so I can adjust for it. Any of these meters could be out waaay more.... but you never know until you have it checked by a reliable technician.

We complain a lot about these cheap $10 Chinese made chargers by checking it with a $10 Chinese DMM..... who's to say which, if any, is correct without calibrating one of them to a known level.

Regards

Christian

 

[matt_o]

I have a Fluke 115 which isn't as accurate as the more expensive ones but should be respectable. I do need to get a know voltage to compare it to though. At any rate it isn't a cheap $10 Chinese meter.

 

[kaptain_zero]

Ok, sounds like you have a decent meter, but still.... and this is the tech I talk to, "DMM's are NOT the ideal piece of equipment for testing such small voltage differences." I would, if I were you, have that meter checked against a few other meters or even a bench unit that has been recently calibrated to be sure of where your unit is reading. Something as simple as holding the battery in your hand during measurement can cause the voltage to drift several mV as does the actual temp of the battery when you take the measurement, which accounts for the slight settling of the voltage a couple of hours after charging. And don't forget the 5% leeway on the 4.2V ideal...... there is some fudging room.... not a lot, but there IS some.

How high does your charger go if you let it go until the lights turn green?

Regards

Christian

 

[matt_o]

I've never let it charge long enough for the lights to turn green.