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Open Roads Forum  >  Tech Issues

 > Solar MPPT and lithium batteries

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alpen1

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Posted: 03/08/22 12:16pm Link  |  Quote  |  Print  |  Notify Moderator

I switched my AGM batteries to lithium's. I can't get a definitive answer on MPPT charge parameters, except to "user define" which I have done. My question is: since MPPT chargers rely on voltage drop to start the charging process, and lithium batteries maintain a consistent voltage until depleted, how will the controller know when to charge?
The "user defined" parameter settings seem like a work around, but spending a week and watching the voltage stay the same, but capacity drop with minimal amperage charging from the solar panels, I wonder how long before they are depleted? Is there a solar charger that uses capacity drop to start the charging process?

pianotuna

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Posted: 03/08/22 12:30pm Link  |  Quote  |  Print  |  Notify Moderator

Hi,

Find out the recommended charge voltage for the Li batteries. Set the charging voltage to that number, or slightly lower.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

LittleBill

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Posted: 03/08/22 12:36pm Link  |  Quote  |  Print  |  Notify Moderator

lithium battery's drop voltage. not sure who told you they don't... a standard 18650 cell is charged to 4.2 volts, it can drop all the way to 2.75 to be considered dead. thats over a volt difference.

there are multiple chargers that charge lithium, simply match one of them, lithium are some of the simplest batteries to charge.





2oldman

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Posted: 03/08/22 12:40pm Link  |  Quote  |  Print  |  Notify Moderator

LittleBill wrote:

lithium battery's drop voltage. not sure who told you they don't...
There seems to be this misconception they do not, but they do.

Actually I'm not sure if it's the BMS or the controller that's more in 'charge' of the charging. I set my Outback controller to the voltages specified, set Absorb to as near zero as possible, and it works fine.

The voltage will vary quite a bit when charging.. at least mine do.

* This post was edited 03/08/22 12:50pm by 2oldman *

naturist

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Posted: 03/08/22 12:47pm Link  |  Quote  |  Print  |  Notify Moderator

It's not that lithium batteries' voltage doesn't drop, it's that it drops much more gradually until the battery is almost dead, when it drops like a rock.





LittleBill

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Posted: 03/08/22 01:42pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

LittleBill wrote:

lithium battery's drop voltage. not sure who told you they don't...
There seems to be this misconception they do not, but they do.

Actually I'm not sure if it's the BMS or the controller that's more in 'charge' of the charging. I set my Outback controller to the voltages specified, set Absorb to as near zero as possible, and it works fine.

The voltage will vary quite a bit when charging.. at least mine do.


the bms is safety system. its not suppose to engage unless there is an issue. that being overvoltage, undervoltage, temperature, cell voltage deviation and amperage.

the charger does all the charging. period.

time2roll

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Posted: 03/08/22 01:59pm Link  |  Quote  |  Print  |  Notify Moderator

alpen1 wrote:

I switched my AGM batteries to lithium's. I can't get a definitive answer on MPPT charge parameters, except to "user define" which I have done. My question is: since MPPT chargers rely on voltage drop to start the charging process, and lithium batteries maintain a consistent voltage until depleted, how will the controller know when to charge?
The "user defined" parameter settings seem like a work around, but spending a week and watching the voltage stay the same, but capacity drop with minimal amperage charging from the solar panels, I wonder how long before they are depleted? Is there a solar charger that uses capacity drop to start the charging process?
Might help to post the controller make and model.

Also post your user defined settings.

My Morningstar MPPT 60 wakes up with the sun every day and puts 13.8 volts into the battery and then drops to float at 13.0 volts. Yes the battery will rest at about 13.4 13.3 all day never getting power from float. Next day controller pushes the battery back up to 13.8 volts. No issues.


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vermilye

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Posted: 03/08/22 03:07pm Link  |  Quote  |  Print  |  Notify Moderator

My Victron 100/50 with parameters set for lithium also starts each morning in the bulk mode, charges until the charging voltage hits around 14.3V, switches to absorption and brings them up to 14.5V while balancing the battery cells. After absorption, it switches to float at 13.6V. Throughout a typical night, using 30 - 40 amp hours, the battery bank typically drops to 12.8V by morning. Bank is 3 100 amp hour Battleborns.

* This post was edited 03/08/22 05:00pm by vermilye *


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3 tons

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Posted: 03/08/22 03:19pm Link  |  Quote  |  Print  |  Notify Moderator

LittleBill wrote:



the bms is safety system. its not suppose to engage unless there is an issue. that being overvoltage, undervoltage, temperature, cell voltage deviation and amperage.

the charger does all the charging. period.


Exactly, unlike PWM, MPPT is a more sophisticated dc-to-dc type charger (utilizing surplus voltage), but no need to be concerned by that - just set the charge voltage at 14.x volts, but not to exceed 14.6v… Float (say, 13.6v) is unnecessary but nor will it hurt, and forget equalizations…

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Itinerant1

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Posted: 03/08/22 06:19pm Link  |  Quote  |  Print  |  Notify Moderator

I'm in the boat as most charging lfp, mppt wakes up when the sun hits the front panels ( Bulk mode). Charges to 14.1v, absorbs for 6 minutes then floats at 13.6v till the sun goes down and the SCC goes into sleep mode. Rinse and repeated now for 6 years.

* This post was edited 03/09/22 08:07am by Itinerant1 *


12v 500ah (5,120Wh usable), 20 cells_ 4s5p (GBS LFMP battery system). 8 CTI 160 watt panels (1,280 watts)2s4p,Panels mounted flat. Magnum PT100 SCC, Magnum 3012 hybrid inverter, ME-ARC 50. Installed 4/2016 been on 24/7/365, daily 35-45% DOD 2,000+ cycles.

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