Does MPPT charge controller damages a battery ?

[Mohsin Ali]

Hello everyone,
I heard from someone that MPPT charge controllers provide all the current or you can say raw power generated from solar panels to the battery regardless its capacity of absorbing charge specially during bulk charging stage, we can only control the current by decreaing/increasing installed capacity... Is it right?
And secondly if battery is fully charged and we connect a load to the battery (mppt is also connected in parallel) then what will happen? Load will run directly from mppt or through battery?

 

[RCinFLA]

MPPT controller have a power conversion DC to DC converter. They can provide most of the total PV power possible but just like any other charger they will back off when battery fully charged state is reached.

 

[400bird]

Hello everyone,
I heard from someone that MPPT charge controllers provide all the current or you can say raw power generated from solar panels to the battery regardless its capacity of absorbing charge specially during bulk charging stage, we can only control the current by decreaing/increasing installed capacity... Is it right?

That's how a PWM charge controller works. It just connects the panels straight to your battery until the voltage conditions are met, then it starts PWM to limit the voltage and still flow some power.

A good MPPT has settings and can limit charge current, but not all MPPTs have this feature, as most people want all the energy they can get from the sun.

And secondly if battery is fully charged and we connect a load to the battery (mppt is also connected in parallel) then what will happen? Load will run directly from mppt or through battery?

Depends on your settings. If you're in float, the MPPT should attempt to power the load.

 

[Mattb4]

You were told wrong. A solar charge controller whether PWM of MPPT job is to charge the battery. It does this by loading the solar panels until the battery reaches the settings for voltage and or SOC.

If your battery is fully charged, and the SCC has shut off, connecting a load to the battery will draw from the battery until your SCC reaches voltage settings to start charging again. Once it does the amount it delivers will be up to the capacity of the panels (and the SCC). Loads always draw their power needs first before any extra goes to the battery. Say yoru panels and SCC can deliver 200w to the common DC charging bus. Loads of less than 200w would mean extra going to battery. Loads greater than 200w would mean the battery picks up the amount above 200w.

ETA: BTW yes, a poorly functioning or improperly setup SCC, can damage a battery. Batteries have specific charging requirements.

 

[Mohsin Ali]

But suppose I have 400 watts of solar panels installed with a 12v 100ah lead acid battery then if all power generated is transferred to battery (it will be around I=400/12=33 amps) the battery will be damaged as it can absorb only 10~15 amps max.

 

[Mattb4]

But suppose I have 400 watts of solar panels installed with a 12v 100ah lead acid battery then if all power generated is transferred to battery (it will be around I=400/12=33 amps) the battery will be damaged as it can absorb only 10~15 amps max.

If your SCC has no ability to set charge amperage you need to select one that has the right level. For a 10 amp charge you will only draw ~120w from the panels.

 

[Q-Dog]

But suppose I have 400 watts of solar panels installed with a 12v 100ah lead acid battery then if all power generated is transferred to battery (it will be around I=400/12=33 amps) the battery will be damaged as it can absorb only 10~15 amps max.

This is the reason there are different sized charge controllers. You need to match the charger to the battery capacity. Some chargers can limit their output.

 

[Mohsin Ali]

If your SCC has no ability to set charge amperage you need to select one that has the right level. For a 10 amp charge you will only draw ~120w from the panels.

My question is whether the SCC limits the power to 120 watts or just delivers what it gets?

 

[Zwy]

But suppose I have 400 watts of solar panels installed with a 12v 100ah lead acid battery then if all power generated is transferred to battery (it will be around I=400/12=33 amps) the battery will be damaged as it can absorb only 10~15 amps max.

A lead acid battery's internal resistance increases as full SOC is reached. The charger should be set for the battery manufacturer specified charging voltage, around 14.5V. As the battery charge advances to 100% SOC, the amps will be reduced due to the increased resistance of the battery. The charger will hold the set charge voltage during the absorption charge until either a specified time set in the charger settings or until amps reach close to 0A.

The charger will then float the battery at the voltage setting you input.

 

[Zwy]

A lead acid battery charging rate decreases as the internal resistance increases. The problem with using solar with lead acid batteries is the absorption charge period is quite long as the battery internal resistance increases. This leads to never completing absorption charge and the result will be sulfation of the plates over time and resulting capacity loss.

 

[Mohsin Ali]

A lead acid battery's internal resistance increases as full SOC is reached. The charger should be set for the battery manufacturer specified charging voltage, around 14.5V. As the battery charge advances to 100% SOC, the amps will be reduced due to the increased resistance of the battery. The charger will hold the set charge voltage during the absorption charge until either a specified time set in the charger settings or until amps reach close to 0A.

The charger will then float the battery at the voltage setting you input.

Yes in my mppt Charge controller Bulk and Float Charging Volts can be set, and when battery volts reach bulk voltages then it reduces current and charges at constant voltages until battery is fully charged. But my concern is rate of charge during bulk charging stage, it should be 10 hours for Lead Acid batteries but if battery is charged at above this rate then will it be damaged?

 

[Mattb4]

My question is whether the SCC limits the power to 120 watts or just delivers what it gets?

If it is a 10a SCC than it only can load the panels by that amount. You seem to be stuck thinking panels are pushing power. Loads draw power from the panels. The SCC is limited by its max battery charge rate and if the panels can give it that amount. Any extra potential of the solar panels is simply not used.

 

[Zwy]

Yes in my mppt Charge controller Bulk and Float Charging Volts can be set, and when battery volts reach bulk voltages then it reduces current and charges at constant voltages until battery is fully charged. But my concern is rate of charge during bulk charging stage, it should be 10 hours for Lead Acid batteries but if battery is charged at above this rate then will it be damaged?

What MPPT do you have? And what battery?

Only time possible for peak power output of PV is during peak sun. If you are unable to set charger output amps, which I'm sure you will be able to, you can add more batteries in parallel. This reduces the amperage into each battery.

Lead acid is high internal resistance even at lower state of charge. One can also reduce the bulk charging voltage, this slows down the amperage as the battery internal resistance has to be overcome by the charger. However, the reduced voltage may not be the manufacturer recommended charging voltage and sulfation will result. As the internal resistance of lead acid is higher than let's say LFP in comparison, it will not charge at the max rate as the LFP.

Hook up the charger and observe the charge amperage, it will probably be below 10A. One has to increase charging voltage considerably to really push high amperage into a lead acid battery.

 

[Mohsin Ali]

If it is a 10a SCC than it only can load the panels by that amount. You seem to be stuck thinking panels are pushing power. Loads draw power from the panels. The SCC is limited by its max battery charge rate and if the panels can give it that amount. Any extra potential of the solar panels is simply not used.

Suppose if its an 80A SCC , panels also has the potential to provide this current and battery is small like 12 volts 100 Ah, then what will happen? Will the battery be charged with 80 amps?

 

[Q-Dog]

Suppose if its an 80A SCC , panels also has the potential to provide this current and battery is small like 12 volts 100 Ah, then what will happen? Will the battery be charged with 80 amps?

Yes, it would charge at 80 apms if the panels can supply that. Unless you can tell the charge to limit charging to something less. But why would you get such a large charge controller if you don't need that much charging?

 

[Mohsin Ali]

Yes, it would charge at 80 apms if the panels can supply that. Unless you can tell the charge to limit charging to something less. But why would you get such a large charge controller if you don't need that much charging?

Because I want to run DC load in the daytime and charge battery

 

[Mohsin Ali]

Because I want to run DC load in the daytime and charge battery

It has no settings to limit output current, only Voltage levels can be set

 

[Q-Dog]

It is possible to limit battery charging and still power DC loads within the Victron ecosystem, but that would require shunts, and a GX device with DVCC configured, and likely a smart battery BMS that can talk to the GX device.

 

[Hedges]

My question is whether the SCC limits the power to 120 watts or just delivers what it gets?

It has no settings to limit output current, only Voltage levels can be set

Most have adjustable voltage and time, operate CV/full power until absorption voltage reached, hold at absorption for a period of time, drop to float voltage.

Some, I think, can operate CV/CC. Most wouldn't know if a load was taking some of the current. Midnight Classic + Whiz Bang Jr, or Victron + Cerbo, can measure battery current and deliver extra for loads.

In your case, I think you need to pick SCC & battery to match each other for desired charge rate. Then you can over-panel to maintain current under less than full sun. You can reduce amount of PV to limit current but then it will drop off with less sun.

Is your battery FLA or AGM? FLA wants a particular charge rate, maybe 0.12C. AGM can accept higher. My AGM prefers at least 0.2C, can handle more.

 

[Mohsin Ali]

Most have adjustable voltage and time, operate CV/full power until absorption voltage reached, hold at absorption for a period of time, drop to float voltage.

Some, I think, can operate CV/CC. Most wouldn't know if a load was taking some of the current. Midnight Classic + Whiz Bang Jr, or Victron + Cerbo, can measure battery current and deliver extra for loads.

In your case, I think you need to pick SCC & battery to match each other for desired charge rate. Then you can over-panel to maintain current under less than full sun. You can reduce amount of PV to limit current but then it will drop off with less sun.

Is your battery FLA or AGM? FLA wants a particular charge rate, maybe 0.12C. AGM can accept higher. My AGM prefers at least 0.2C, can handle more.

Battery is Flooded Lead Acid, 12 volts 145 Ah , Solar panels are 880 watts combine and 80a SCC ( Max PV input is 1500 watts)