Question about parallel/series Li-Ion batteries

[idlplumb]

I'm gathering up materials for a mag XM-L build and I'm wondering about batteries. I have a 4D mag that I will be using for this and I have plenty of 18650's laying around.

Question is this.....for max runtime I would want to parallel 4 18650's, correct?

If this is the case, I plan on building one or two "packs" with the batts wired and heatshrinked and all that good stuff, but my concern is charging. Should I go with a standard 18650 charger and go with the adapter with the magnets? OOOOrrrr, is there a way to get the cells in a standard mag and somehow wire up a charging port?

I think I prefer the magnet adapter since it'll give the batteries breathing room as they charge so they don't overheat.

Any thoughts? Suggestions? Maybe a good DIY or two someone can point me to?

 

[lightseeker2009]

I wonder if in this case would four NIMH D-Cells not be a better bet? With four 12 000 mah D-cells you will get more voltage and runtime than you will get with four 18650's in parallel. And you would need to bore the mag for the 18650's, not so with the D-cells..

 

[VegasF6]

Your batteries will be capable of producing the same amount of energy wired in series or parallel. It comes down to the efficiency of your circuit how that energy is used. It would certainly be easier to series connect them.

 

[moderator007]

As lightseeker2009 said a 4d nimh setup would be much easier. You could use the shiningbeam amc7135 2800 ma driver. I believe hes out of stock right now because i dont see them on his site. You could email bryan at shiningbeam to see when they will be available. Or look around. The 3 mode driver he sells works very well. And no strobes.

You could shrink wrap the 4D's together just leaving the ends open for contact. Then you could charge them all together with a external port wired in.

If you choose the 18650 setup you will have to bore the light to get the batterys side by side in the light. The driver you could use would need a 8.4v input if you configured it as a 2s2p pack. You would still have lots of dead space in a 4D that wasnt used. If you used all the 18650's in series just like the D configuration. You will need a driver with over 16.8v input. Harder to find. The extra length of the 18650's may not work. Charging these 18650's in the light is another discussion.

As for a charger i would consider a hobby charger either way you go. They are way better at charging packs. Hobbyking has lots to look at. They can charge alot of different types of batterys.

 

[idlplumb]

The more I think about it, the more I like the sound of NiMH cells. Safer than lithium and very easy as they would be D cells anyway.

Would it be worth building a pack? Or should I just charge them separately?

 

[moderator007]

It will be what ever way you prefer. If you had a hobby charger you could charge as a pack all at once. Or if you seperate them you can still charge them all together in a normal charge that excepts 4 D's. If you are going to make a external charging port the hobby charger is the way to go. Hobby chargers just have so many different uses. They do alot more than just charge batterys.

 

[45/70]

Would it be worth building a pack? Or should I just charge them separately?

It's almost always better to charge NiMh cells individually, if possible. Unless the cells have been very carefully matched in performance, before assembling the "pack", some cells will be consistently overcharged and some undercharged, when charged in series, eg. with a hobby charger. This will result in some of the cells in the pack failing much sooner, than if the cells were charged individually.

Even when cells are well matched, such as in welded R/C, or tool packs, where you have no choice as to how to charge them, it's a good idea to run a 0.1C "forming charge" every 5 or so charge cycles. This forming charge helps to balance the cells, and will extend pack life. Again, in order for this to work, the cells have to be very well matched from the start. Assembling NiMh cells of varying performance levels into a battery pack, will almost always result in short pack life. This is generally why less expensive battery packs don't last as long as the more expensive ones, ie. the packmaker didn't take the extra time needed to match the cells.

Dave

 

[idlplumb]

So my easiest option and probably cheapest is to just go with 4 NiMH 1.2v D cells like the light was meant to take and get a charger to charge them individually outside the light. Correct?

I actualy could get a little more runtime out of my 18650s since they're 3800mah but it seems like too much work.

 

[moderator007]

In the first post the op made, op was asking if there was a way to wire in a charging port. You will have to charge the batterys all together in order to do that. As 45/70 said they may not last as long as charging individually.

Yes 4 D's would be easier. 4 Nimh 10,000mah d's will give you a run time of a little over 3 hours at full brightness with the shiningbeam i mentioned early. If you buy a 2D maglite then you could run 2 18650's with a little work.

 

[lightseeker2009]

So my easiest option and probably cheapest is to just go with 4 NiMH 1.2v D cells like the light was meant to take and get a charger to charge them individually outside the light. Correct?

I actualy could get a little more runtime out of my 18650s since they're 3800mah but it seems like too much work.

I don't have as much experience in testing batteries like 99% of the guys here... But I see no problem in charging them in series in the light itself. Just make sure you buy batteries that are in the same condition and age and I bet you will be fine. If you get 10 000 mah batteries charge them at 1000 mah if in series. You can always take them out lets say every 3rd time when they need charging and charge them seperately to equalise them better. Once or twice in series in your light I'm sure will do no harm.

Just to backup my statement. I've got a 3300mah 7.2V RC car battery pack. Its more than 6 years old. Admittedly, its only used maybe twice or even once a month. But when used its almost fully discharged. And when charged I charge it with a car charger in the field. It fully recharges the pack in less than 20 minutes. That means its charging at a very high rate and its charging the cells in series, everytime.. The battery still works perfectly with no memory loss etc. I even use this pack in one of my LED Lanterns of which the led used to run with two 16850's. Its always ready and charged. When I put it in my sons RC truck I dont even top it up. I just take it out of the light in put it in the truck. So just charge them in the light if you prefer.
Just my 2C:)

I'd say go with the D-cells. Try to get the best while your at it. You do get LSD D-Cells. But My experience with LSD cells is that if you are going to charge the light not less than once in lets say every four months, then you dont need LSD cells anyway.

I've done a practical test comparing a Unicross 2700mah AA to a 2000mah Eneloop. I fully charged them, left them for 4 months and tested the runtime in my Olight T15 on the high setting. The Eneloops lasted 73 minutes, the 2700's lasted 84 minutes. Granted, after a year the eneloops would have won. But like I said, if you are going to recharge regularly, dont bother with LSD cells if they are far more expensive than regular D-Cells.

I hope to see your build soon

 

[lightseeker2009]

I have an Imax B6 and it works perfectly with everything I charge. I should have taken the model with the build-in power supply though... Now I must hook it up to my jumpstart kit as a power source.

 

[moderator007]

As far as charging the cells in the light, does anyone know of any DIYs for building a charging port into the light itself? A plug in the tailcap seems the most reasonable as there seems to be enough space in there.

I would say the best place to put the charging port would be just before the switch on the side of the body. As you can get to and make your connections right on the switch terminals to your port. Your ground will be the screw to the body in the switch. And your positive will have to come from the bottom contact of the switch that makes the connection to the positive of the batterys bypassing the switch.

If the port was in the tail cap you would have to have a wire or some type of connection to go back up the tube to the positive end of the batterys. The tail cap is ground.

 

[carl]

Did you land up installing the external charger port? If so, I'm interested in the same thing.

Some ideas:

1) A port just ahead of the on-off switch is better. A tailcap hole would cause a water leak path, even if o-rings were used. So a hole through the battery tube, just ahead of the plastic switch assembly, not at the top of the tube where rain could go down it but maybe on the side or bottom. Also, any wiring toward the tailcap can get twisted or caught up in the tailcap spring when unscrewing the tailcap. Not good.

2) The ground wire should be soldered to the nut on the back side of the port inside the tube. The positive wire should go through the switch toward the positive end of the battery pack, thus bypassing the on-off mechanism.

One question is whether the charger port will always be 'hot' and ready to short with one drop of water.

Any corrections or suggestions?


thanks