Lithium SOC

[CPT Davenport]

Just finished 5 days running my new lithium set up. I ran the 85 liter fridge, heater, lights, hot water and charged my devices. I do not have a way to read the SOC like you all that are waving your dongles around. I did find some numbers online and was wondering if they sound accurate to the group.

Volts Capacity
14.6 100% (charging)
13.6 100% (resting)
13.4 99%
13.3 90%
13.2 70%
13.1 40%
13.0 30%
12.9 20%

Even with cloudy conditions during the day I would wake up to 13.1-13.2 and during the day I would get back up into the 14 range. I disconnected my lead to the alternator so only charging was from solar.

 

[pvstoy]

Don't have a comment but you ran the heater??? Where were you?

 

[Vic Harder]

Just finished 5 days running my new lithium set up. I ran the 85 liter fridge, heater, lights, hot water and charged my devices. I do not have a way to read the SOC like you all that are waving your dongles around. I did find some numbers online and was wondering if they sound accurate to the group.

Volts Capacity
14.6 100% (charging)
13.6 100% (resting)
13.4 99%
13.3 90%
13.2 70%
13.1 40%
13.0 30%
12.9 20%

Even with cloudy conditions during the day I would wake up to 13.1-13.2 and during the day I would get back up into the 14 range. I disconnected my lead to the alternator so only charging was from solar.

Incredibly hard to tell SOC on lithium batteries without a dongle, waving or not.

 

[CPT Davenport]

Don't have a comment but you ran the heater??? Where were you?

Up in Humboldt on the coast. Wasn't that cold (50 F) but after being in the ocean all day it was nice to get nice and toasty.

Incredibly hard to tell SOC on lithium batteries without a dongle, waving or not.

So Vic, do you think there is any validity to these numbers?

 

[Vic Harder]

Up in Humboldt on the coast. Wasn't that cold (50 F) but after being in the ocean all day it was nice to get nice and toasty.

So Vic, do you think there is any validity to these numbers?

I did run my batteries down to 10% on my last trip (parked in the shade and using my induction cooktop for a few days). I did not notice the voltage being that low. I think my 3000w Pure sine inverter would have complained if they were though.

Voltage must be measured when the batteries are at “rest”. That is hard to achieve in a working camper. And I hate guessing. The Victron Dongle is really not that expensive.

 

[todgru]

Those voltages are similar to what the manual states for my cheap AmpereTime lithium batteries. The battery has to be at rest and disconnected from any current draw or charge to be a good gauge for estimating. Like Vic said, that’s hard to do in an active camper situation.

I threw some of this info up on my website for future reference. https://todgru.com/camper/electrical/

 

[PaulT]

Time to consider calibrating your digital voltmeter?

Paul

 

[CPT Davenport]

I looks as if adding the Victron Smart Shunt 500 is the cheapest/easiest way to gain access to my SOC. Is this the correct unit to complement my Victron 100/20 MPPT? I don't really want a display in the camper and prefer to just use my phone.

 

[heinphoto]

I looks as if adding the Victron Smart Shunt 500 is the cheapest/easiest way to gain access to my SOC. Is this the correct unit to complement my Victron 100/20 MPPT? I don't really want a display in the camper and prefer to just use my phone.

That's what I installed and it has worked just fine (I'm using the SmartSolar 100/30 mppt). The only down side is that the bluetooth range isn't great - you typically have to be in or near the camper to connect. If your mppt is a SmartSolar, then this combination has the added advantage that you can set up a bluetooth "Smart Network". The mppt controller will then use the voltage and current reported by the SmartShunt to control charging. You can also add a temperature sensor to the SmartShunt, which allows much better temperature compensation. The SmartShunt is pretty easy to install (I managed to do it without destroying anything). The main thing is to make sure that the SmartShunt is the only thing connected to the negative terminal of the battery in order for it to monitor the current accurately.

-Scott

 

[Dadocut]

I assume you're talking about a 12v LiFePO4 battery.

I follow the DIY Solar Power Forum, a great source of lithium battery information. The forum pointed me to a great spreadsheet showing state of charge as a function of voltage: https://docs.google.com/spreadsheets/d/1SyzKUZ5_KxLB6megSLTXYv_1LlbcFqE4gxMgK8SrMvs . The spreedsheet matches my experience. It seems to be a bit different from what you posted at the start of this thread.

Note you really need to measure the battery voltage at rest, i.e. not charging, not discharging. I'm not sure how long of a rest is needed, but an hour would be a guess.

I built a 4 cell 230 Ah battery pack for my truck camper and used a battery management system that includes a shunt and bluetooth interface. It's a much easier way to measure state of charge than using the voltmeter. I don't have experience with the Victron products but I'm sure they'd work too (I installed a Bogart trimetric analyzer & shunt when I first bought the camper). The bluetooth in my battery pack lets me check the state of charge from inside the truck, inside the camper and even in my house about 40' away from where I park the camper. The Overkill Solar BMS & bluetooth that I used is not applicable to your application though.

Hope this helps.

 

[CPT Davenport]

The main thing is to make sure that the SmartShunt is the only thing connected to the negative terminal of the battery in order for it to monitor the current accurately.

-Scott

I'm assuming you mean anything extra to the negative right? As of now I have the wire from the FWC and a wire from the charge controller to the negative terminal.

 

[CPT Davenport]

I assume you're talking about a 12v LiFePO4 battery.

I follow the DIY Solar Power Forum, a great source of lithium battery information. The forum pointed me to a great spreadsheet showing state of charge as a function of voltage: https://docs.google.com/spreadsheets/d/1SyzKUZ5_KxLB6megSLTXYv_1LlbcFqE4gxMgK8SrMvs . The spreedsheet matches my experience. It seems to be a bit different from what you posted at the start of this thread.


Hope this helps.

Great information and thank you for confirming your SOC and the corresponding volts. The numbers they provided are quite close to the numbers I have. Both sources show 70% @ 13.2v and 20% @ 12.8v (mine shows 12.9). I think it is safe to say that if we see anything in the 12s, it is time to find some bulk charging.

 

[heinphoto]

I'm assuming you mean anything extra to the negative right? As of now I have the wire from the FWC and a wire from the charge controller to the negative terminal.

The SmartSunt has two terminals labeled, "To System Minus" and "To Battery Minus". In your case the negative from the charge controller and from the FWC electrical system would be connected to "To System Minus". "To Battery Minus" is the only thing that should be connected to the negative terminal of the battery. If you add any other devices in the future, their negative connections would also be attached to "To System Minus". You want to make sure all current flows through the shunt and doesn't bypass it, which is what happens if you make any other connections directly to the negative battery terminal.

 

[CPT Davenport]

The SmartSunt has two terminals labeled, "To System Minus" and "To Battery Minus". In your case the negative from the charge controller and from the FWC electrical system would be connected to "To System Minus". "To Battery Minus" is the only thing that should be connected to the negative terminal of the battery. If you add any other devices in the future, their negative connections would also be attached to "To System Minus". You want to make sure all current flows through the shunt and doesn't bypass it, which is what happens if you make any other connections directly to the negative battery terminal.

Got it! Thanks

 

[Stokeme]

Timely topic for me. I run a 100Ah & a 50Ah (lfp4), circa 2018, in parallel. They both had individual BT which I loved. Early this year they, the 100 first followed by the 50, both lost BT transmission. The batteries seem fine otherwise, as the charging parameters, which I follow with a SmartVictron 100/30, have remained consistent. I prefer not to mount or run a monitor. I liked BT on my phone. This Smartshunt seems like my answer.
Since I have to run a negative (parallel) cable from the 100 to the 50, it will share attachment with the shunt cable. I think it’s best to attach the shunt to the 100ah battery. It’s ok to have the parallel cable & the shunt cable mounted together, correct? As long as I attach nothing else to the “battery minus”?
Will the shunt display only the 100ah SOC? It probably would display two 100ah in parallel (200ah) as a battery bank? But will it display SOC for a 150ah bank since the batteries are not equal ah? Thoughts?
I have a simple battery box setup, connection to solar panels, connection to camper power. I do not have an inverter. I’d like to confirm my recipe for shunt hookup. Thanks ahead for any input.

 

[Vic Harder]

Timely topic for me. I run a 100Ah & a 50Ah (lfp4), circa 2018, in parallel. They both had individual BT which I loved. Early this year they, the 100 first followed by the 50, both lost BT transmission. The batteries seem fine otherwise, as the charging parameters, which I follow with a SmartVictron 100/30, have remained consistent. I prefer not to mount or run a monitor. I liked BT on my phone. This Smartshunt seems like my answer.
Since I have to run a negative (parallel) cable from the 100 to the 50, it will share attachment with the shunt cable. I think it’s best to attach the shunt to the 100ah battery. It’s ok to have the parallel cable & the shunt cable mounted together, correct? As long as I attach nothing else to the “battery minus”?
Will the shunt display only the 100ah SOC? It probably would display two 100ah in parallel (200ah) as a battery bank? But will it display SOC for a 150ah bank since the batteries are not equal ah? Thoughts?
I have a simple battery box setup, connection to solar panels, connection to camper power. I do not have an inverter. I’d like to confirm my recipe for shunt hookup. Thanks ahead for any input.

You will set the battery parameters in the BT app for 150AH. The two batteries are in parallel, so there will always be (nice fat) wires between the positive terminals of each, and the negative terminals of each. Once those are in place, you basically think of the two batteries as ONE 150AH battery. OK?

Now, on one battery, you will add the shunt between its negative post and all the ground wires running to buss bars and other things in the camper. There should be NO other wires attaching to the battery negative post on either battery (other than the fat ones that make the two ONE 150AH battery).

I would attach all loads to the other battery's positive terminal. Just to ensure that AH are being drawn from both batteries.

Ideally, you would have two shunts, one for each battery, but I think this will work ok too.

 

[Stokeme]

https://www.wanderthewest.com/forum/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=33658

Hey Vic, thanks so much for taking the time to reply. The link above is a good view of my current overall setup. I forgot that the 100Ah negative terminal also contains my solar controller attachment. How does that play into this equation?

Can l please be specific … where does my parallel negative cable attach -as it relates to my 100Ah battery? To the shunt, system minus? To the negative terminal on my 100ah battery? (I think the shunt battery minus would not be correct)
Where does the (outgoing) negative cable from my solar controller attach? To one end of the shunt or to the negative terminal on my 100ah battery?

 

[PaulT]

On my Hawk, I used a BlueSea busbar for all the grounds/returns.
https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs

All 4 studs can take multiple cables so something like the linked busbar above should accommodate all your grounds and are electrically the same connection. Use another cable to go from this busbar to the shunt and another cable to go from the other end of the shunt to the battery negative post.

The solar negative lead should be attached to the busbar, also, so that the battery monitor will see the energy going into the battery and indicate increasing state of charge.

There is a plastic cover available for this busbar that would protect it from accidental shorting from a hot lead when you are working on your electrical system.

Paul

 

[Vic Harder]

+1 to what Paul said. As for your question "Can l please be specific … where does my parallel negative cable attach -as it relates to my 100Ah battery? "

If I look at your picture, I would put an imaginary wall between the two batteries, and pretend that there is just this one 50AH battery in your setup. Attached to that battery would be those nice fat wires that go to their partners on the 100AH battery behind the "wall". With me so far? Behind the wall, there is nothing else attached to the battery posts on that 100AH battery except for those two fat wires coming forward to the 50AH battery. Good?

OK, now. As Paul suggested, all the ground wires in the system, including from the MPPT, and your fusebox, etc, will go to the load side of the shunt. And from the Batt- side of the shunt there will be a nice fat short wire going to the negative post of the 50AH battery.

Nothing will work yet though, because you have no wire attached to the +ve of the 50ah battery. All your positives could also go to a buss bar and from there to the 50AH battery's positive post.

That should do it. If that isn't clear, please try me again.

 

[Stokeme]

Helpful info from the above two posts is greatly appreciated.
Paul, I can see a bus bar would be really useful. Do I need a 600A bar? Would 250A suffice? I do not see my system getting any larger. Looking at these …
https://www.amazon.com/Post-Power-Distribution-Block-Pair/dp/B07THLYYH3/ref=sr_1_11?crid=2JRLDDK6PMI34&keywords=600+amp+bus+bar&qid=1660316879&s=automotive&sprefix=%2Cautomotive%2C113&sr=1-11

Vic, why are the “business end” of the connections conducted on the 50Ah battery, instead of the 100Ah battery? Location of the battery? Does it really matter, re - 100 vs 50? I could possibly reverse the location setup.

Lastly, I see my original setup had everything going to the 100Ah battery. I do not remember why, either ignorance or advice? One of the leads should have been on the 50, correct? That would be the norm for a 100 + 100 setup, correct? Maybe because my batteries were different Ah, it was suggested everything go thru the 100 to the 50. Not sure now.