I have a Jetbeam RRT-01 XM-L T6 flashlight and I was doing some tail cap current tests with it. I picked up an AW IMR 18350, since this light supports those batteries to see if it would last longer than a 16340 of the same capacity due to it being able to hold voltage at higher current draws.
The batteries I tested with:
AW IMR 18350 - 700mAh - Max discharge 6A - tested 740mAh at .2A on my Thunder AC680 hobby charger
Solarforce ICR 16340 - 880mAh - Protected - tested 759mAh at .2A on my Thunder AC680 hobby charger
I put the light at maximum output using the control ring and ran my Extech EX320 DMM leads from the back of the battery to the driver pill, with the button top of the battery directly connected to the positive contact on the light.
Here are the readings I got:
AW IMR 18350 - 2.67A
Solarforce 16340 - 2.03A
Besides the fact that 2A seems like a lot for a 16340 (violates the 2C rule), I decided to run a discharge test with my Thunder AC680 hobby charger to see which battery would keep the light in regulation longer, ignoring the fact that the AW battery allows more current draw.
I hooked up my Solarforce 16340 to the AC680, and set the discharging profile to NiMH, 2.8v, 2.0A. When I start the test, the current just stays at zero and never changes. I assume that means that the charger is tripping the protection circuit on the battery.
So how is it that my Jetbeam RRT-01 can pull 2.03A from the battery, but my hobby charger cannot discharge it at the same current?
I don’t have a hobby charger, but maybe it’s because you set the discharging profile to nimh.
I really have no clue what I’m saying, but that just sticks out to me.
Well, the only difference between NiMH and LiPo on a hobby charger for discharging is that NiMH lets you select 2.8v, whereas with LiPo, you can only go down to 3v. I use NiMH because the industry standard is to discharge at .2C to 2.8v to determine capacity.
Hobby chargers have a fair bit of voltage detection circuitry built into them. I'm not familiar with the AC680, but when you set it to NiMH discharge, and it senses 4 volts or more on the cell, it may refuse to run the discharge. Also, unless the cell is rated to be discharged that low and you plan to use it that way, the relatively little capacity between 2.8 and 3.0 volts won't be very important.
As an aside, there is no "industry standard" voltage for testing cell capacity. Within a particular cell chemistry you might say that, but newer designs are rated down to 2.5 volts while other designs are not. You're probably better off letting your use case determine your cutoff voltage for discharge testing. For example, if your light will shut off at 3.0, 3.3 or 3.5 volts, that shutoff voltage would be a better choice for testing purposes, because you would get a better indication of your actual run time.
During the discharge via the hobby charger, what voltage does it read?
If the protection circuit has tripped, the charger would terminate the charge cycle because the voltage drops to zero.
I’ll try doing a 2.0A discharge on my Ultrafire 16340’s.
Edit: Yeah, it tripped the protection circuit at about 1.6A, and the charger said “connection break down” which essentially meant the voltage was zero.
I haven’t used your a charger of your model, but I assume it should do the same when the protection is tripped.
I think the voltage sag of the battery is reaching the set cut off point before the charger can get to a 2 amp discharge. I have had cheap 18650 trustfires that couldn’t be discharge at 3 amps because the voltage sag. The load voltage was less than 3 volts at about 2.5 amps causing the hobby charger to trip.
Here is a screenshot of the raw data for my AC680 with it set to LiPo Discharge 3.0v(1S) with the amps set to 2.0A. You can see that the current drops to zero after ramping up to 1.4A. The last voltage reading was 3.77v, which is definitely not low enough to trip the protection circuit. I have discharged these down to 2.8v with no problems. Strange that it doesn’t show a battery disconnect like yours. I’m assuming yours is also a Turnigy AC6 based charger since, basically, every hobby charger on the market is…
The charger might not be outputting a “connection breakdown” message when the protection trips.
Two things you can do to clear things up:
1. During a 1.0A discharge, could you unplug the connections very briefly to simulate the circuit tripping? I’m curious how the charger will interpret that.
2. Can you hold a multimeter against the cell and verify that the protection circuit is tripping?
When mine trips, the voltage of the 16340 does not come back up to 4.1V until I remove the discharge/charge leads from the battery. Yours might be resetting instantly, confusing the charger. As you probably know, hobby chargers focused towards RC batteries, which don’t have protection circuits and can easily discharge 50A.
Nevermind. I just hooked up a brand new, freshly charged MNKE 3500mAh IMR 26650 to my charger and set it to 2.0A and it did the same exact thing. I guess even though it says it can support a 2.0A discharge and lets you go that high, it fails out. Oh well. Time to buy a CBA IV…
The max discharge for a turnigy accucel 6 is 5 watts. If you where discharging a Nimh then it would handle 2a. That might explain it.
I have the accucel 8, good for 5 amps with a single li-ion.
I think you've found the problem. Most chargers advertise having 50 or even 80 watts of charging power. But they usually only handle 5 watts discharge. You can see in your log that at :09 seconds the discharge power hit 5.24 watts and then it shutdown. Unless you really want to do a lot of serious discharge testing, for the same $100+ you could get one of the iChargers that will handle 20 or even 30 watts. Some allow adding an outboard power resistor that will increase discharge capacity even further.
I wouldn’t be opposed to buying an iCharger, but I hate the idea of external power supplies, both of the hobby chargers I have (Thunder AC680 and Hitec x4 AC Plus) have built in AC power supplies.
I think if I were going to get an iCharger, it would only be for the purposes of discharge testing batteries and a CBA IV is $160, so after buying an iCharger and a power supply, I would probably just buy the CBA IV instead.
