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Lithium SOC


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#1 Cpt Davenport

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Posted 04 August 2022 - 03:47 PM

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.


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#2 pvstoy

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Posted 04 August 2022 - 11:55 PM

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


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#3 Vic Harder

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Posted 05 August 2022 - 02:02 AM

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.


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#4 Cpt Davenport

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Posted 06 August 2022 - 02:06 PM

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?


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#5 Vic Harder

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Posted 06 August 2022 - 08:40 PM

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.
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2012 ATC Puma Shell build - https://www.wanderth...012-puma-build/

Power considerations thread - https://www.wanderth...e-power-scotty/

Building out an electrical system - So, you want to setup a good electrical system in your camper? - Electrical, Charging, Solar, Batteries and Generators - Wander the West


#6 todgru

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Posted 06 August 2022 - 09:43 PM

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/
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#7 PaulT

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Posted 07 August 2022 - 02:34 AM

Time to consider calibrating your digital voltmeter?

 

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#8 Cpt Davenport

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Posted 07 August 2022 - 02:48 PM

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.


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#9 heinphoto

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Posted 07 August 2022 - 07:39 PM

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


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#10 Dadocut

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Posted 08 August 2022 - 07:20 AM

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....qE4gxMgK8SrMvs .  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.

 


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