Triton discharge - seem to be getting early Li-ion cutoff (?)

[photon fiddler]

I have a Triton (original-green dot) and a new 2400mah Li-ion pack from BatterySpace. From what I've read here, I believe this pack uses LG 18650's, which appear to have tested well in several posts (typ. ~2250 to 2300) and with good consistency from cell to cell.

After seeing only 2062ma @1.0a on my first full discharge, I decided to try a couple more cycles and record the data. I've read here that the Triton tends to undercharge slightly, which fits (I think?) with the pack coming off the charger at 16.70 - 16.73, but my real question is about the voltage reading at cutoff.

Shouldn't the Triton's readout actually reach its specified cutoff voltage (12v) or at least very near just as the discharge ends? I didn't note the ending voltage on that first discharge, but subsequently I recorded the following: (voltage shown is what the Triton displayed right before cutoff.)

(subsequent charges - end v 16.7)
2061ma @1.0a 12.9v 2028ma
2034ma @0.5a 13.0v 2045ma
2007ma @0.5a 13.7v 2045ma

The pack doesn't get even the slightest bit warm during charges (.5C) or discharges. Capacity is *worse* at the lower discharge rate and (displayed) cutoff voltage is rising??? The resting/recovery voltage after the first discharge was 14.0v and 14.4 after the second. (forgot to record the 3rd) I have not had this problem with NiMH, but this is my first Li-ion pack.

Anyone? Anyone? Bueller?

 

[photon fiddler]

Hmmm... the actual post squished my data columns together. The "(subsequent charges...)" applies to the second column of ma numbers.

 

[SilverFox]

Hello Photon fiddler,

Welcome to CPF.

The end of the discharge of a Li-Ion pack has voltage dropping like a rock. It may be that the Triton was unable to update its display quick enough during the last few moments of the discharge.

I believe the discharge cut off voltage for the Triton is fixed at 3.0 volts per cell.

You would have to hook up a volt meter and track your packs voltage during a discharge to verify this.

Your cells may, or may not be LG cells. You would have to take the pack apart to determine this. Also, I believe LG makes some 2200 mAh cells. Perhaps this is what was used in your pack.

Tom

 

[photon fiddler]

Thanks for the reply Tom.

BatterySpace sells 2200 and 2400mah packs with the 2400 at a distinct premium and a picture at the bottom of my model page showing an unwrapped pack having gray cells with numbers beginning with LG. (Oddly enough, I hadn't scrolled down far enough until just now to see that picture! My pack is the brick configuration; the page for the flat configuration shows a wrapped pack.) Also there is a link to a single cell page that says in the features section "Made in South Korea - brand name is available by calling..." They might have gotten a bit of heat earlier; originally they had a link directly to an LG data sheet; now the data sheet has been "modified". :naughty:

You are correct that cutoff is fixed at 3.0v. I was actually monitoring the the display voltage for the last 15 -20 minutes on the last two discharges. There was no significant acceleration in the drop rate (right near the end) either time. Especially on the last one (ending at 13.7v), with a low 0.5a (~.2C) discharge rate I would think there would be at least tens of seconds to get from there to 12v. (or so it would appear on the graphs from other posts.) That would certainly be enough time for the Triton to update the display and give *some* indication of the "last gasp".

Since I'm using relatively low discharge rates, if there was one cell that was weak, could it reach 2.4 volts and trip the PCB without revealing itself by heating up? Or do I (likely) have a perfectly good pack and I'm just mistaken in thinking that the difference in terminating at 16.7v vs 16.8v shouldn't equate to such a large (2050 vs 2250) difference in capacity?

I'll do a voltage monitored discharge when I have time and see if it matches up with the Triton's display. The other obvious thing is to measure the cell voltage inidividually, but I'm reluctant to take the shrinkwrap off until I've communicated with BSpace. (We'll see how that goes... no reply so far.)