[RE-wrenches] Lithium upgrade when Magnasine goes to float too soon

Tue Apr 18 14:49:56 PDT 2023

Wrenches,

Yes, some of the "Older" designed inverters/Chargers don't like the quick
rise in voltage when charging batteries.

Most LFPs with a BMS and while being charged in "Open communication" can
withstand having the voltage at 14.2 to 14.4 volts 24 hours/7 Days a week.
  As the internal BMS regulates the charge to the cells.

Make sure you contact the battery manufacturer,r as some of them need to be
charged differently, or you may need to update the charger to one that can
support LFP batteries.

I can tell you that with the Surrette "R-Series LFP," you can set the
charging voltage to 14.4 (28.8v, 57.6v) and leave it there however long you
want.   With that, generally, Lithium batteries do not like to be fully
100% charged all the time.

What we advise on the "R-Series" is you set the Bulk/Absorb Voltage to
14.4v (28.8 or 57.6), and if you see a sudden transition or surging on a
charge, then you put the Float voltage from 13.8 to 14.2 and extend the
float time to to the total expected charge time.   This is something that
you should experiment with for the first few months to get the settings
right.   If you have an Android device, you can download the Bluetooth
dashboard to check the State of charge to ensure the battery is charged.
If not, you can extend that float time to aid in getting to that full
charge.

The good news is LFP or L-Ion don't need to be fully charged. As long as
you get to that 80% to 90% ballpark, you will not lose capacity like lead
batteries.   You won't have full capacity on the battery, and you'll need
to oversize a bit more if you operate like this.

Surrette LFPs like to see the charger setup as a 2-Stage Charger, but as
mentioned above, if you can't adjust this, you will need to set the float
voltage and time to compensate for voltage surge or early transition to
float.

With all that being said, parallel string balancing is an issue we often
see in the field on batteries that do not have closed-loop communication.

If they are not communicating and the customers are cycling the battery
bank full time, I suggest balancing the battery bank strings every 3-6
months.   The harder they work them, the more balancing you will need to
do.    Another way to prevent this need for balancing is instead of
Absrobing for 15-30 mins, you extend the absorb timers and disable any end
amps settings as having the voltage at the 14.4 (28.8 or 57.6) for a more
extended period will help keep the parallel strings more balanced.

With Lead batteries... If you see this direct rise in voltage while under
charge, there is an issue...   It could be anything from a connection issue
to a dead or dying cell.

In any case, when dealing with batteries, make sure that you're wearing
your PPE gear.

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On Tue, Apr 18, 2023 at 12:55 PM Mick Abraham via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi, Mechanix~ I have several local clients with various different versions
> of Magnum pure sine inverters & all of the inverters seem to transition to
> the float stage soon after the charge cycle begins. I've observed this even
> when the inverters & batteries were brand new. I'm aware of the menus about
> adjusting the bulk time duration but even adjusting that to the longest
> setting never helped.
>
> Since these clients are all off grid with no generator automation, I
> just tweaked the float voltage to match the bulk voltage then instructed
> the clients to turn off their generator when the target voltage appears on
> their display. The batteries were always lead acid floodies.
>
> Now that some of these clients need better batteries (& I hope they can
> afford transitioning to lithium), are there any mfr's for drop in
> replacement lithium which don't care if the gen-powered charger can't shift
> downward for the float voltage? The customers' PV chargers all have a float
> function that does work right. I know that Blue Planet suggests 55.2v DC
> for all charge stages, but my Magnum systems are all either 12v nominal or
> 24v nominal, so I'll need to find a different brand that builds the lower
> voltage batteries.
>
> The clients can still shut down the generator when the target voltage is
> reached, but what if they fail to shut down soon after the setpoint is
> reached? I wouldn't want to put anybody's battery warranty at risk due to
> this strange charging quirk. Also, I'd like to know if any other Wrenchies
> have noticed this peculiarity with the Magnum inverters.
>
> Thanks in advance; the Wrench List is The Bomb!
>
> Mick Abraham, Proprietor
> www.abrahamsolar.com
>
> Landline: 970-731-4675
> Cell phone or for text messaging: 970-946-6584
> ᐧ
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