Lithium battery question.

[SCTN]

I agree rick. I’ve been in touch with Sportsmobile and once our shelter in place is over and it seems smart to move again I’m going to have them take a look. I’ll do some further research on my battery’s and the soc monitor and see if there is something else I can do.

But I’m the meantime I have 20% more battery, that’s going to be super helpful...I don’t know what I’m gonna do if I can use all 80%! Thanks for all your help.

[rsamco]

OK, another possibility is that one of the batteries isn't participating (e.g., is disconnected). And I'd visually check out that the Relion battery monitor's battery shunt is correctly installed -- should be on the batteries' negative post(s) so the ALL current to/from BOTH batteries passes through that shunt. It was a little tricky fabricating a shunt mount for my single battery situation...I can imagine it being quite a bit more difficult for your two battery situation.

I'd measure both battery voltages both after "shutoff" & when you think that they are both fully charged. Are both in agreement? Note that a lithium battery voltage does drop significantly as its SOC approaches 0%. Unfortunately, you'll probably have to isolate each battery from the other to get correct individual measurements (recommend using a digital VOM). Oh ya, I'd first use the VOM to see if both batteries are connected together -- no resistance between two positive battery posts & then measure between negative posts!

I would not assume that SMB-W has enough lithium experience to know what's going on. Maybe they've come a lot further in the past year since my build out, but I wouldn't assume that. As you'll see in my upcoming lithium system post, I had to significantly "tune" my setup. Other than setting charging profiles to lithium on the 3 charging "controllers" (alternator+regulator, solar, & inverter/charger), SMB-W left all other settings at their manufacturer defaults. So they weren't in sync with each other and none were optimum for my Relion battery. It all worked, but not optimally.

I'd recommend that you also contact Expion to see if there are any subtleties with using two of their batteries in tandem. For example, I'm wondering if there are any potential gotchas re the two batteries' BMSs balancing of all their internal cells during float/constant-voltage charging phase.

Lastly, for the time being, I'd assume that your "shutoffs" are being caused by one or both of your batteries fully discharging to 0% SOC. This is definitely not at all good for long term battery health. So, I'd minimize those "shutoffs" until you really figure out what's going on! For example, turn off all van loads like the fridge and/or keep van on shore power.

[Scalf77]

I agree with Rick, it sounds like one of your batteries is not working, connected, etc. I too would have concerns with discharging to shut off as you are degrading your number of life cycles.

-greg

[SCTN]

Exactly! That’s my concern.

Originally Posted by Scalf77

I agree with Rick, it sounds like one of your batteries is not working, connected, etc. I too would have concerns with discharging to shut off as you are degrading your number of life cycles.

-greg

[SCTN]

I’ll turn everything off until I figure this out. Thanks for the suggestion. So glad I have you guys.

[Twoxentrix]

Been interesting to read through the diagnostic recommendations...good info.

Not to state the obvious; but if in fact the system wasn't prepped correctly for you when installed, I'd consider reaching out to start negotiations for a new set of batteries - pretty sure you've shortened the life span if you've been discharging one or both completely.

[rsamco]

I probably wouldn't worry too much about lost battery life. Most modern Lithium batteries are pretty tolerant to deep discharges compared to a few year's ago. Here's a graph published by Relion (although I can't find it on their website now):



You'd have to have many tens of complete discharges before it would make a sizable dent in the battery's overall life expectancy IMO. Of course, Expion may be different, but I suspect not.

[SCTN]

After a lot of reading. I wanted to ensure my soc monitor was set up properly. It was set up to the correct ah, 240. But I’m not too sure about the correct battery percentage. According to relion soc directions the batteries need to be full at time of connection so it can “learn” this. I don’t know how but that was my understanding. My system as it was set up could never have gotten it to full due to the settings in the cc/cv menu in controller. My hunch is a full expion 360 will have a voltage of 14.4/14.6, that according to expion360 manual. I emailed to confirm this is in fact a way to read or measure a battery to ensure it is full.

Sound thinking?

I don’t believe my batteries we’re ever full and my soc monitor was giving me a false percentage reading. I never paid attention to the voltage when I turned system on after shut down.

Anyway, I know more about my system than I did 3 days ago so this has been a great learning experience.

Update: My thinking was not sound. From what I can find my batteries will never reach 14 volts. Still figuring this out.

[rsamco]

My understanding of your situation is that your battery monitor setting/calibration of 240 Ah is too high for your CURRENT situation. Your battery(s) is dead when it's showing still 50% (=120 Ah) calculated capacity still left. That's why I believe that one battery is "off-line" right now. The good news is that both batteries were online & probably at 100% SOC at the time the battery monitor was programmed! So, something has taken one of your batteries off-line since the battery monitor was set to 240 Ah & 100%. Maybe something happened that caused the Expion BMS to tripped a battery offline and there is a reset action you can do. Or maybe both batteries are separately fused (hopefully externally) and a fuse blew. Again, I'd use a VOM to first see what voltage is at each battery. If the voltage is exactly the same (I mean EXACTLY) then the two batteries are probably correctly wired together; and one of them is dead/off-line.** To find out which one, disconnect one of the batteries and measure both battery voltages again. I suspect one will be zero (i.e., tripped off-line).

If the two battery voltages were NOT EXACTLY the same, then there is probably a cable-break/blown-fuse on a battery cable. I'd measure continuity/resistance for the ground cable from the van's 12V fuse/distribution panel back to the cable at the negative battery post on each battery. If no problem there (i.e., full ground continuity on both battery neg cables), do the same for the positive circuit/cables. If the problem/break is outside of a battery, one circuit will measure open; just physically follow it to find a blown fuse or ???

Lithium batteries are typically at about 13.2V when fully charged. They are typically charged in the 4.1-14.4V range -- that's the voltage the charger is putting out, not the battery's voltage without the charger. So, the battery voltage starts at ~13.2V at 100% SOC and only drops by 0.2V all the way down to 30% SOC (~13.0V there). And that voltage can vary a bit depending upon instaneous load/draw on the battery! That's why you can't measure a lithium battery's current SOC by voltage, but actually must keep a running audit/integration of amps out or in over time.

Good luck (& keep learning :>)


**footnote: For this test I'm assuming the two battery SOCs are different since they have been disconnected from one another for awhile. Either there's a cabling problem or an internal battery problem. If cabling, then you should see slightly different battery voltages because the batteries are isolated from one another by the cabling problem and have a SOC difference (very low probability that they'd be the same). If the problem is instead internal to a battery, then that battery should have no voltage and the measured voltage at its posts will simply be the other battery's voltage. In which case, the measured voltage will measure EXACTLY the same, down to the 2nd decimal place on the digital VOM.

[Klompen]

Originally Posted by rsamco

My Isotherm 85 Cruise fridge consumed per day ~30Ah @ ~80F cabin temp before adding more insulation and ~20Ah/day after +insulation (I'll post specifics later over in Starr's thread in this forum).

I would love to see your write-up on insulating your fridge. We have as Isotherm 65 that I am sure would benefit from a similar treatment.