SCC not shifting to Float Charging Mode

[Mohsin Ali]

Hello Everyone
I am trying to run a small fridge (6 cuft) on battery connected in parallel with an MPPT solar charger . The settings of the controller are
Bulk Charge Voltage 14.4
Float Charge Voltage 13.5
My load is ~140W @ 12V and I have a Lead Acid 12V 140Ah battery attached in parallel with my load and the charger.
I've noticed with the load attached, the voltage drops about ~0.45V. I've metered the battery and the charger keeps the battery at about 14.0V indefinitely in Bulk Charging Mode, If I disconnect the load, the battery reaches float instantly. I'm assuming this isn't sustainable for the health of the battery, so I would want to make sure the battery is reaching all 3 phases correctly.
I'm not sure what the next logical step should be to get this set up working? Should I program the charger myself?

 

[sunshine_eggo]

Hello Everyone
I am trying to run a small fridge (6 cuft) on battery connected in parallel with an MPPT solar charger . The settings of the controller are
Bulk Charge Voltage 14.4
Float Charge Voltage 13.5
My load is ~140W @ 12V and I have a Lead Acid 12V 140Ah battery attached in parallel with my load and the charger.
I've noticed with the load attached, the voltage drops about ~0.45V. I've metered the battery and the charger keeps the battery at about 14.0V indefinitely in Bulk Charging Mode, If I disconnect the load, the battery reaches float instantly. I'm assuming this isn't sustainable for the health of the battery, so I would want to make sure the battery is reaching all 3 phases correctly.
I'm not sure what the next logical step should be to get this set up working? Should I program the charger myself?

If you never reach bulk/absorption voltage, you'll never start the absorption phase. It will never reach termination criteria, and it will never drop to float.

Sounds to me like you have insufficient PV for your needs and/or, your wiring is woefully inadequate.

Care to elaborate?

 

[Mohsin Ali]

If you never reach bulk/absorption voltage, you'll never start the absorption phase. It will never reach termination criteria, and it will never drop to float.

Sounds to me like you have insufficient PV for your needs and/or, your wiring is woefully inadequate.

Care to elaborate?

I want to add something
1. When the load is applied, voltage drops across battery terminals despite adequate supply from PV, I can give you an example at peak power PV can provide upto 35 Amps DC @ 12volts but still if a load of 15 Amps DC is applied, a terminal voltage drop of 0.3-0.5 volt occurs, why is it so? Can you tell the reason behind this voltage drop?
2. MPPT display shows same voltages despite a drop of 0.3-0.5 volts on the terminals.
So I think PV support is adequate but wiring is not. The length of wire from PV to SCC is around 75 feets and guage is 12AWG it should be atleast 10AWG imo

 

[sunshine_eggo]

I want to add something
1. When the load is applied, voltage drops across battery terminals despite adequate supply from PV, I can give you an example at peak power PV can provide upto 35 Amps DC @ 12volts but still if a load of 15 Amps DC is applied, a terminal voltage drop of 0.3-0.5 volt occurs, why is it so? Can you tell the reason behind this voltage drop?

Look at it from the battery's perspective. It has 35A coming in, but that suddenly drops to 20A, so a voltage drop will occur as there is less current coming in.

2. MPPT display shows same voltages despite a drop of 0.3-0.5 volts on the terminals.

There are losses in the MPPT to battery connections.

So I think PV support is adequate but wiring is not. The length of wire from PV to SCC is around 75 feets and guage is 12AWG it should be atleast 10AWG imo

12awg can handle 20A, and that's PV current, not battery current. I would expect it's adequate for the array current.

Between battery and MPPT, you need at least 8awg, and you need high quality connections, i.e., no alligator clips.

The MPPT needs to "see" bulk voltage uninterrupted for its absorption duration before it will drop to float.

What controller?

What is the absorption duration?

 

[Mohsin Ali]

Look at it from the battery's perspective. It has 35A coming in, but that suddenly drops to 20A, so a voltage drop will occur as there is less current coming i

Look at it from the battery's perspective. It has 35A coming in, but that suddenly drops to 20A, so a voltage drop will occur as there is less current coming in.

But here same current is coming in and going out, I have measured with clamp meter when 15 Amps are being drawn by load the current supply also matches the demand but even then 0.3-0.5 volts are dropped across battery terminals

 

[Mohsin Ali]

Between battery and MPPT, you need at least 8awg, and you need high quality connections, i.e., no alligator clips.

Yes I have used 6AWG wire between MPPT and Battery and installed ferrules and crimped them properly

 

[Mohsin Ali]

What is the absorption duration?

1. Infinite duration with heavier loads like Fridge which takes 10~15 amps
2. Without any load or small loads like Fans or Bulbs it takes 15-20 minutes to reach float charging mode once it reaches bulk charging volts, which is 14.4 in my case

 

[sunshine_eggo]

But here same current is coming in and going out, I have measured with clamp meter when 15 Amps are being drawn by load the current supply also matches the demand but even then 0.3-0.5 volts are dropped across battery terminals

If the battery requires a current to support a given voltage, and you lower that current, the voltage will drop.

Yes I have used 6AWG wire between MPPT and Battery and installed ferrules and crimped them properly

6awg is good. Ferrules are good but can be bad:

What controller?

1. Infinite duration with heavier loads like Fridge which takes 10~15 amps
2. Without any load or small loads like Fans or Bulbs it takes 15-20 minutes to reach float charging mode once it reaches bulk charging volts, which is 14.4 in my case

My question was directed at settings, i.e., what is the MPPT set to run for absorption? Can I assume it's 20 minutes, something different, or is it based on tail current?

Summary of existing and new questions:

1. What controller?
2. What is the programmed absorption time?
3. Array power?

Please click Spoiler in my sig and check link #2.

 

[Mohsin Ali]

My question was directed at settings, i.e., what is the MPPT set to run for absorption? Can I assume it's 20 minutes, something different, or is it based on tail current?

Summary of existing and new questions:

1. What controller?
2. What is the programmed absorption time?
3. Array power?

Please click Spoiler in my sig and check link #2

1. SIMTEK® MPPT + Solar Charge Controller
2. There is no option to set absorption time only Absorption Volts and Float Volts can be set, following is my settings as per manual of Battery
1) Bulk Charge Volts= 14.4V
2) Float Charge Volts=13.5V
3) Array power is 880 watts combined (3x180watts panel & 1x330 watt panel all connected in series)

 

[Zwy]

Hello Everyone
I am trying to run a small fridge (6 cuft) on battery connected in parallel with an MPPT solar charger . The settings of the controller are
Bulk Charge Voltage 14.4
Float Charge Voltage 13.5
My load is ~140W @ 12V and I have a Lead Acid 12V 140Ah battery attached in parallel with my load and the charger.
I've noticed with the load attached, the voltage drops about ~0.45V. I've metered the battery and the charger keeps the battery at about 14.0V indefinitely in Bulk Charging Mode, If I disconnect the load, the battery reaches float instantly. I'm assuming this isn't sustainable for the health of the battery, so I would want to make sure the battery is reaching all 3 phases correctly.
I'm not sure what the next logical step should be to get this set up working? Should I program the charger myself?

I think the charger will remain in bulk as a load would be similar to a discharged battery. The MPPT switches to CV instead of CC charging mode, thus it will just hold voltage and supply the current to meet loads. It will continue charging at that set voltage until current drops to 0A.

Set bulk for desired absorption voltage. As this is lead acid, the battery internal resistance will increase as 100% SOC is reached. Lead acid is not time based charging, it is based upon internal resistance. Absorption charge voltage should be reached as much as possible as this helps reverse any soft sulfation on the plates. With never entering float, it will take more water but you also have plates that should have little sulfation.

 

[Mohsin Ali]

I think the charger will remain in bulk as a load would be similar to a discharged battery. The MPPT switches to CV instead of CC charging mode, thus it will just hold voltage and supply the current to meet loads. It will continue charging at that set voltage until current drops to 0A.

Set bulk for desired absorption voltage. As this is lead acid, the battery internal resistance will increase as 100% SOC is reached. Lead acid is not time based charging, it is based upon internal resistance. Absorption charge voltage should be reached as much as possible as this helps reverse any soft sulfation on the plates. With never entering float, it will take more water but you also have plates that should have little sulfation.

Can this higher voltage effect battery life apart from consuming more water?

 

[Zwy]

Can this higher voltage effect battery life apart from consuming more water?

At 14.4V, that is the higher end of what is considered normal absorption voltage for most lead acid. Manufacturer specs are usually best.

This is not a 3 stage charger if you can not individually set bulk, absorption and float. Most batteries use 14.8V for bulk, 14.0V to 14.4V for absorption and 13.5V for float.

I explain how I charge using a power supply in this post. Would I concern myself with 14.4V absorption? No, eventually the battery internal resistance will increase and amps will drop to basically nothing. Basically you are powering loads as the charger never hits float and the battery isn't really taking on any amps. Could this cause plate erosion? Possibly but I think you might be better off ensuring a full absorption charge is done, daily is best. The biggest killer of any lead acid battery is sulfation caused by inadequate absorption charge. With solar, getting full absorption charge on a regular basis can be difficult as the length of time to complete absorption may be longer than available sun yield.

 

[Mohsin Ali]

This is not a 3 stage charger if you can not individually set bulk, absorption and float. Most batteries use 14.8V for bulk, 14.0V to 14.4V for absorption and 13.5V for float.

I dont understand how someone can set bulk and absorption invidually when both occurs at same voltage???please explain this point. As per my knowledge bulk charging continues until battery reaches 14.4 volts, then absorption starts at constant volts of 14.4 until current drops to almost zero and then voltage is dropped to float values and stays there for rest of time.

 

[sunshine_eggo]

At 14.4V, that is the higher end of what is considered normal absorption voltage for most lead acid. Manufacturer specs are usually best.

This is not a 3 stage charger if you can not individually set bulk, absorption and float. Most batteries use 14.8V for bulk, 14.0V to 14.4V for absorption and 13.5V for float.

I don't agree with this. Power system batteries rarely specify a different voltage for Bulk and Absorption. They are just different sides of the same voltage. In fact, I can't think of a case I've ever seen it. Trojan, Rolls, etc., do not. They have two voltages: absorption and float (we're not mentioning equalization in this context).

RV converter manufacturers DO make this distinction, and it's often 14.4V bulk, 13.6-13.8V absorption and 13.2V float. This is because RVs tend to stay on shore power a lot. Float at 13.5V of FLA REQUIRES regular checking of electrotlyte. 13.2V is way less maintenance intensive.

The three stages of charging are not defined by different bulk and absorption voltages. The three stages are:

1) constant current util bulk/absoprtion voltage reached.
2) constant voltage at bulk/absorption voltage while current tapers.
3) float - holding battery at full charge.

I dont understand how someone can set bulk and absorption invidually when both occurs at same voltage???please explain this point. As per my knowledge bulk charging continues until battery reaches 14.4 volts, then absorption starts at constant volts of 14.4 until current drops to almost zero and then voltage is dropped to float values and stays there for rest of time.

Yep.

When drawing a load from your system, I suspect the absorption cycle is never meeting its end criteria - whatever that is. It's going to take some troubleshooting on your part to see if you can determine an absorption voltage that yields the desired behavior.

 

[hwy17]

I would just set bulk absorb and float to 13.75 and then you don't have to worry if it's exiting absorption or not.

 

[Zwy]

I dont understand how someone can set bulk and absorption invidually when both occurs at same voltage???please explain this point.

I'm using a power supply, not a charger.

I also have a charger that will enter a desulfation phase if required of around 15.0V.

It depends on the battery manufacturer specs and the charger.

As per my knowledge bulk charging continues until battery reaches 14.4 volts, then absorption starts at constant volts of 14.4 until current drops to almost zero and then voltage is dropped to float values and stays there for rest of time.

For your charger, that is perfectly acceptable as I already related. Your problem is the loads are causing the MPPT to not enter float. Will it harm the battery? Possible plate erosion but is less of a problem than sulfation . Trojan for example says max time at absorption is 4 hours. That is after CV is hit. If you have 8 sun hours per day, will the battery be in absorption charge for 4 hours after hitting CV? Odds are it won't.

If you are concerned about it, then use a timer. Or a MPPT that allows for timed absorption. Most solar systems using flooded lead acid suffer from not enough time for a full absorption charge. This leads to shortened battery life.

 

[Zwy]

I don't agree with this. Power system batteries rarely specify a different voltage for Bulk and Absorption. They are just different sides of the same voltage. In fact, I can't think of a case I've ever seen it. Trojan, Rolls, etc., do not. They have two voltages: absorption and float (we're not mentioning equalization in this context).

RV converter manufacturers DO make this distinction, and it's often 14.4V bulk, 13.6-13.8V absorption and 13.2V float. This is because RVs tend to stay on shore power a lot. Float at 13.5V of FLA REQUIRES regular checking of electrotlyte. 13.2V is way less maintenance intensive.

The three stages of charging are not defined by different bulk and absorption voltages. The three stages are:

1) constant current util bulk/absoprtion voltage reached.
2) constant voltage at bulk/absorption voltage while current tapers.
3) float - holding battery at full charge.



Yep.

When drawing a load from your system, I suspect the absorption cycle is never meeting its end criteria - whatever that is. It's going to take some troubleshooting on your part to see if you can determine an absorption voltage that yields the desired behavior.

It depends on the charger.

In this case, I would use it and forget about holding the battery at 14.4V. It actually might be beneficial to the battery long term as 100% SOC with full absorption is hit.

The question is whether amps actually drop to almost 0A and how much time it spends in CV.

 

[Mohsin Ali]

If you have 8 sun hours per day, will the battery be in absorption charge for 4 hours after hitting CV? Odds are it won't.

Yes you are right it hardly remains in absorption mode for 4-5 hours since at around 7:30 A.M I connect the load (refrigerator that consumes almost 10 Amp DC) and at that time only 9-10 amps are produced by solar so battery remain at around 13V and then gradually reaches 14.4 volts after 2-3 hours, then stay there until 5 P.m after that solar current starts to reduce. I remove load at 5:30 A.M so bulk charging voltage period may not be more than 4~5 hours