Should my 2 lithiums be balanced?

[Langloan]

Hi all I have 2 x 100a Renology lithiums and their MPPT controller / 100 w solar panel.

Not on EHU in France now for over a week.

Last night the system shut down in the middle of the night and my Sargent controller flashed Leisure battery “Dangerously Low”. Turned on the van engine for 2 mins and all weirdly returned to normal

However I notice my batteries have quite different charge %? Is this normal?

Also I am getting Error 4 on both - do I need to do anything?

Thanks for any advice

 

[AdrianChen]

Mmm - I'm sure an expert will be along shortly to help, but my observations are:

With a voltage on both batteries of 12.4v, and no current draw I think the batteries are at around 15% SOC, so the BMS seems to have become out of kilter with the real SOC.

I guess the 100w solar panel isn't keeping up with your usage?

When you start the engine the alternator either via a SCR or more likely a B2B will provide a charging current to the batteries of up to 14.2ish amps, so the panel, and possibly the battery will see that charge current and be happy, but the effect will disappear quickly after the engine is turned off.

I would find some EHU, and fully charge the batteries ensuring the charger gets to float voltage so, if it is properly setup, you know the batteries have had time to do their cell balancing at which point the BMS should reset to 100%.

The battery BMS will often drift slowly from being accurate because they often don't measure current below an amp or so and can be fooled by very large currents from an inverter for example, and if the battery isn't fully charged they cannot reset to 100% so the inaccuracies get bigger... A properly configured shunt is the most accurate/practical means to monitor batteries I think. My shunt will measure down to 0.1amp, and up to 500.

 

[Kannon Fodda]

Something a bit odd there. Voltages on the battery, 12.4V is low for lithium. Implies the state of charge could be as little as 10% compared to the indicated 50% or 80%.

Many BMS systems aren't good at measuring small discharge currents so over time the SoC reading indicated could become incorrect. A shunt may give a better picture.

Your batteries may charge / discharge unequally especially if the wiring offers different lengths to create slight different resistance.

Your batteries need a complete full charge cycle including lengthy absorption phase so that BMS can rebalance all the cells. The BMS app may have other settings that show if the cells are all in similar voltage or not.

 

[MichaelT]

Your batteries may charge / discharge unequally especially if the wiring offers different lengths to create slight different resistance.

Yes should connect them to bus bars with exact same length wire.

 

[Langloan]

Many thanks to both of you for your info. Unfortunately the reason that I am on 12v is that my EHU isn’t working ( see separate thread)

I am here for 5 more days and then a long drive back to UK will recharge both to 100%

Once home I may also upgrade my solar from 100% to 200w as Renology seem to have a good promotion at £122

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[AdrianChen]

Many thanks to both of you for your info. Unfortunately the reason that I am on 12v is that my EHU isn’t working ( see separate thread)

I am here for 5 more days and then a long drive back to UK will recharge both to 100%

Once home I may also upgrade my solar from 100% to 200w as Renology seem to have a good promotion at £122



View attachment 940027

Can you get hold of a cheapo or borrowed charger? At least then even if the SOC is wrong you could get some power into them......

 

[Kannon Fodda]

Hmm, I'm wondering if your EHU issues and battery shut down are related? If your batteries are low the Sargent on EHU could be getting overloaded especially as can happen on some sites that the mains supply is limited current and the expected supply voltage has dropped from poor mains wiring.

You have a Sargent unit. What model? Does it have a proper lithium setting? Some are very basic, even on vans that are quite recent build and the charging function is barely suited to lead acid let alone lithium (my now 5 year old system is horrid with a hopeless 13.8V flat rate of charge, so I've effectively bypassed it).

Do you have any form of B2B charger for running on engine or still rely on the Sargent? Same for hook up. If the Sargent is as pants as I fear it's charging voltages would not get your lithium to a good SoC either driving or on mains, and you don't have enough solar for that to do the heavy lifting.

 

[Langloan]

Van is Autotrail Arapaho 2010 with Sargent 325 power unit

 

[Kannon Fodda]

Van is Autotrail Arapaho 2010 with Sargent 325 power unit

Arghh. I hope you have a B2B fitted to bypass that thing.

Assuming I am reading the manual I can find correctly, the battery charging systems buried in the Sargent EC325 has a flat 13.5V output. That is useless for Life-PO4 leisure batteries which fully charged rest at 13.6V. So whilst driving or on hook up if you have the EC325 as your sole means of charging, the battery can never get to a full SoC.

Many lithium batteries have been sold as "drop in". They sort of work, but do rely that the vehicle into which they were dropped had some adequate means of charging.

 

[Langloan]

Arghh. I hope you have a B2B fitted to bypass that thing.

Assuming I am reading the manual I can find correctly, the battery charging systems buried in the Sargent EC325 has a flat 13.5V output. That is useless for Life-PO4 leisure batteries which fully charged rest at 13.6V. So whilst driving or on hook up if you have the EC325 as your sole means of charging, the battery can never get to a full SoC.

Many lithium batteries have been sold as "drop in". They sort of work, but do rely that the vehicle into which they were dropped had some adequate means of charging.

Thanks - I have a Renology MPPT

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