Controller Performance in Alternator/Load Situation

[DLTooley]

A bit of destructive battery testing with my new 12v compressor fridge brings up a number of controller performance questions when operating with a load in addition to a charge and/or alternator supplementation.

I was attempting to run the refrigerator during daylight hours only to reduce the battery demand with a minimal bank, in order to delay my battery upgrade.  It didn't work. Curiously, the worst drains seemed to be when I was driving in sunny conditions.  The simple solution seems to be to disconnect the solar and alternator charging systems, but I'd like to know the details of what is going on and I'm not 100% confident of my diagnosis.  I have a PWM controller.  My starting battery is a 35 AH AGM and seems to be unaffected.  I hard disconnect the house battery, a Wally World Marine, when under night time, no solar, load.

Here's some Q's:  

Will alternator current cause the solar controller to shut off?

Will a significant load, aprox. 2/3 of the panel wattage, interfere with battery charging?

Can a load be drawn from the controller in shady/dusk conditions that produce more than 12v, but less than charging voltage?

What is the impact of differing batteries in a solar/alternator setup?  (You are supposed to keep house batteries as a set, but, de facto, the house and starter batteries are always going to differ substantially.)

The panel is an upgraded 100 watt, I still have the 50 watt.  I'm hoping to use this as a windshield mounted supplement when camped and when lithium batteries meet my price a separate charging system.

 

[frater secessus]

Forgive my rambling answers.  I am super tired after this week at work.  Feel free to skip any/all.


> I was attempting to run the refrigerator during daylight hours only to reduce the battery demand with a minimal bank, in order to delay my battery upgrade.  It didn't work.  

Can you check the water level in the cells, or is it sealed?

If the controller has a LOAD output and low voltage disconnect for it, it'd be easier to let the controller handled shutting off the load.    Since it's a marine batt rather than deep cycle I'd probably take to to 75%-80% state of charge.  

Can anyone out there report good results from deep cycling a marine battery?   I'd be interested to learn how long they last under such conditions.  


> Curiously, the worst drains seemed to be when I was driving in sunny conditions.  

I don't have an explanation for that, unless the fridge is getting heated from something when underway and running continuously.


> The simple solution seems to be to disconnect the solar and alternator charging systems, 

Shouldn't be necessary.


>I hard disconnect the house battery, a Wally World Marine, when under night time, no solar, load.

Shouldn't be necessary.  Maybe there's a short somewhere or the controller has an internal problem causing massive drain, but I think it's something simpler.  A clip-on ammeter should show what wires are carrying power when nothing should be powered.


> Will alternator current cause the solar controller to shut off?

Generally speaking, when the battery is near charged the charge controller will be outputting higher voltage (except in Float maybe) and so will "win".  When the battery is deeply discharged the alternator will likely be putting out higher voltage.


> Will a significant load, aprox. 2/3 of the panel wattage, interfere with battery charging?

Depends on how much power charging is consuming. In this example if <= 1/3rd of available power is needed to charge then consuming the other 2/3s in load would make zero difference. If charging required > 1/3rd available power then charging would compete with load for power and charging would likely take longer.  You can, to some degree, bias the system toward charging the battery before running loads by setting LOAD reconnect to a fairly high voltage.  Until the voltage reaches that reconnect setpoint the battery would get everything.  

> Can a load be drawn from the controller in shady/dusk conditions that produce more than 12v, but less than charging voltage?

Not sure I understand.  Load can be drawn from the battery at any time (LVD notwithstanding).    



> What is the impact of differing batteries in a solar/alternator setup?  (You are supposed to keep house batteries as a set, but, de facto, the house and starter batteries are always going to differ substantially.)

The only time it really gets weird IMO is if you have a house bank chemistry that could be overcharged by normal alternator voltages in the 14s.  LiFePO4 or maybe AGM.  I've seen my chassis electrical voltage hit 15.1v a few times although it settles down to 13.x pretty soon.  

I haven't talked about this yet but I am doing an experiment to disconnect alt charging when the house system gets to 13.7v.  This would protect Li from the alternator, and while I'm running lead-acid protect the chassis from high voltage during an accidental (or careless) equalization or, to a lesser degree, high absorption.

> The panel is an upgraded 100 watt, I still have the 50 watt.  I'm hoping to use this as a windshield mounted supplement when camped 
> and when lithium batteries meet my price a separate charging system.

Could run a 2nd PWM controller on the 50w fer cheap.  Like $15 cheap.

 

[John61CT]

The panel is an upgraded 100 watt, I still have the 50 watt.

100w is not enough in most situations, and best for all panels per controller to match, especially voltage.

I was attempting to run the refrigerator during daylight hours only to reduce the battery demand with a minimal bank, in order to delay my battery upgrade.

That will both endanger food safety and use more energy per 24 hours. Most efficient is let it cycle as designed.

Also, a smaller than optimal bank size just requires more frequent charging, going below 50% just murders even a robust true deep cycle bank.

I hard disconnect the house battery, a Wally World Marine, when under night time, no solar, load.

Why? That batt won't last long anyway, but why lug it around if you're not using it?

Will alternator current cause the solar controller to shut off?

No, only as a result of setpoints and SoC climbing.

Will a significant load, aprox. 2/3 of the panel wattage, interfere with battery charging?

If you're outputting 3.5A and the fridge is running at 3A, then only .5 is remaining for charging.

Can a load be drawn from the controller in shady/dusk conditions that produce more than 12v, but less than charging voltage?

Depends on the SC, many don't even start or keep working unless input is X volts above batt V.

What is the impact of differing batteries in a solar/alternator setup?  (You are supposed to keep house batteries as a set, but, de facto, the house and starter batteries are always going to differ substantially.)

Just means the combined bank only performs as well and lasts as long as the weakest link. Best to dedicate Starter to cranking and other vehicle running loads. If driving regularly no need to combine when not driving.

There is another design where part of House bank is isolated as SoC drops, but more complex and then all batts should be identical true deep cycling.

when lithium batteries meet my price a separate charging system.

IMO LFP cells will be rising in price as demand takes off.

Meantime $180 per pair of Duracell 6V GCs from Sam's Club or Batteries+ at 200+AH is excellent value for true deep cycling

 

[John61CT]

Since it's a marine batt rather than deep cycle I'd probably take to to 75%-80% state of charge.  

Can anyone out there report good results from deep cycling a marine battery?   I'd be interested to learn how long they last under such conditions.

Depends on mfg / model quality and depth of discharge. Figure way less than half of true deep cycling all else being equal. Normally abusive conditions big box cr^p maybe a year max.

 

[John61CT]

> Curiously, the worst drains seemed to be when I was driving in sunny conditions.  

I don't have an explanation for that, unless the fridge is getting heated from something when underway and running continuously.

Turning it off overnight without eutectic holding mass causes that.

 

[John61CT]

> Will alternator current cause the solar controller to shut off?

Generally speaking, when the battery is near charged the charge controller will be outputting higher voltage (except in Float maybe) and so will "win".  When the battery is deeply discharged the alternator will likely be putting out higher voltage.

In Bulk alt is only striving for Absorb, only gets there when SoC gets to say 70%

 

[DLTooley]

Forgive my rambling answers.  I am super tired after this week at work.  Feel free to skip any/all.


> I was attempting to run the refrigerator during daylight hours only to reduce the battery demand with a minimal bank, in order to delay my battery upgrade.  It didn't work.  

Can you check the water level in the cells, or is it sealed?

If the controller has a LOAD output and low voltage disconnect for it, it'd be easier to let the controller handled shutting off the load.    Since it's a marine batt rather than deep cycle I'd probably take to to 75%-80% state of charge.  

Can anyone out there report good results from deep cycling a marine battery?   I'd be interested to learn how long they last under such conditions.  

It does have a load input, but the load is wired to the house battery, then to the charger - by far the longest run.  Definitely something to consider depending on how substantially I redo the system.

I originally designed my system for average 80% DoD, and am probably a bit above that.  I've run it for three nights in inclement weather without problem.

I was attempting to avoid a deeper discharge with the new load as an experiment as the other option would be to replace the battery bank regardless.

 

[DLTooley]

> Curiously, the worst drains seemed to be when I was driving in sunny conditions.  

I don't have an explanation for that, unless the fridge is getting heated from something when underway and running continuously.


> The simple solution seems to be to disconnect the solar and alternator charging systems, 

Shouldn't be necessary.


>I hard disconnect the house battery, a Wally World Marine, when under night time, no solar, load.

Shouldn't be necessary.  Maybe there's a short somewhere or the controller has an internal problem causing massive drain, but I think it's something simpler.  A clip-on ammeter should show what wires are carrying power when nothing should be powered.

It was running continuously, under a canopy in the pickup bed.  The Dometic **CC** 40 is the b-grade model and has a smaller compressor.

I do the hard disconnect in lieu of a solenoid or switch.  I'm thinking of upgrading my controller to MPPT.

 

[DLTooley]

> What is the impact of differing batteries in a solar/alternator setup?  (You are supposed to keep house batteries as a set, but, de facto, the house and starter batteries are always going to differ substantially.)

The only time it really gets weird IMO is if you have a house bank chemistry that could be overcharged by normal alternator voltages in the 14s.  LiFePO4 or maybe AGM.  I've seen my chassis electrical voltage hit 15.1v a few times although it settles down to 13.x pretty soon.  

I haven't talked about this yet but I am doing an experiment to disconnect alt charging when the house system gets to 13.7v.  This would protect Li from the alternator, and while I'm running lead-acid protect the chassis from high voltage during an accidental (or careless) equalization or, to a lesser degree, high absorption.

> The panel is an upgraded 100 watt, I still have the 50 watt.  I'm hoping to use this as a windshield mounted supplement when camped 
> and when lithium batteries meet my price a separate charging system.

Could run a 2nd PWM controller on the 50w fer cheap.  Like $15 cheap.

Or upgrade to a MPPT for my main charger and use the PWM for the 50 watt.  Great suggestion.

The solar panel does put out greater than expected voltages being used at altitude.  ~20v at 8k feet.  When the engine is running in sunlight it approaches 22v.  There is a voltage drop when the compressor is running, but I haven't figured out the matrix of those drops.

 

[DLTooley]

John61CT


That will both endanger food safety and use more energy per 24 hours.  Most efficient is let it cycle as designed.


Also, a smaller than optimal bank size just requires more frequent charging,  going below 50% just murders even a robust true deep cycle bank.

>The idea was to do a test of running the compressor under solar only, the alternative being to replace the battery bank anyway.  It didn't work, but the reasons why are not clear.***


If you're outputting 3.5A and the fridge is running at 3A, then only .5 is remaining for charging.

> The compressor is 5.5a, 66 watts.  The single panel is 100 watts, but it was at altitude running up to near 20v.

Depends on the SC, many don't even start or keep working unless input is X volts above batt V.

>And the particular controller.  Connecting to the load output on the controller might help, but I'd need to relocate the controller.

Just means the combined bank only performs as well and lasts as long as the weakest link. Best to dedicate Starter to cranking and other vehicle running loads. If driving regularly no need to combine when not driving.

> The system is connected under charging, and WAS disconnected under load.  The new compressor load is ~ double the previous load and is ONLY applied when solar is available and everything was connected.

There is another design where part of House bank is isolated as SoC drops,  but more complex and then all batts should be identical true deep cycling.
> Does MPPT vs. PWM make a difference in that regard?

IMO LFP cells will be rising in price as demand takes off.

Meantime $180 per pair of Duracell 6V GCs from Sam's Club or Batteries+ at 200+AH is excellent value for true deep cycling

>It looks like that's what I'll be doing, but I fear the same problem will destroy those.

 

[DLTooley]

Turning it off overnight without eutectic holding mass causes that.

Eutectic - that's a new word for me!  Yes, I was expecting longer run times during the day, the hope was I could avoid all **battery** drain by running solely off the panel.

 

[DLTooley]

In Bulk alt is only striving for Absorb,  only gets there when SoC gets to say 70%

Could I be running my house battery down to 70% in the combined system?

 

[frater secessus]

That will both endanger food safety and use more energy per 24 hours.  

Some folks use a cooler for beer and water.  Beer at 50F is a crisis but not dangerous. 

 

[John61CT]

Could I be running my house battery down to 70% in the combined system?

Sorry I don't understand, please clarify the question.

 

[John61CT]

There is no problem putting multiple charge sources in parallel on a bank.

 

[DLTooley]

Sorry I don't understand,  please clarify the question.

It was stated that alternators focus on getting a battery back to 70% SoC, then cutting back.  I'm wondering if I'm only getting recharged to 70%, kind of a brainstorm kinda thing.

Perhaps more likely is that the load in charge conditions is dropping the voltage low enough to prevent recharging.  In that case my observation that it was worse while driving was just a coincidence and not relevant to the core problem.

 

[tx2sturgis]

Will alternator current cause the solar controller to shut off?

Shut off, no, stop charging, yes.

Will a significant load, aprox. 2/3 of the panel wattage, interfere with battery charging?

Yep. Most of the current is diverted to the load. There appears to be little reserve for charging.

Your solar/battery system is simply undersized for the load you are powering.

 

[Weight]

You have two problems with equipment. Marine batteries suck for true deep cycle use, and are quickly wrecked. 100 watts of solar is not enough. I run my fridge, fans, lights, and inverter from the battery bank. Multiple EGC2 batteries. I use my charging systems to restore the battery bank.

 

[John61CT]

It was stated that alternators focus on getting a battery back to 70% SoC, then cutting back.  I'm wondering if I'm only getting recharged to 70%, kind of a brainstorm kinda thing.

No, nothing like that, you misunderstood. I said

> In Bulk alt is only **striving** for Absorb V, only gets there when SoC gets to say 70%

My point was that alt only gets to the voltage setpoint **after** bank SoC has reached that point. Before that, in Bulk stage, V is lower.

After Absorb stage starts, V is constant until bank is full. At least supposed to work that way, many charge sources go to Float stage way too early.

With multiple sources, the one with the higher voltage will keep working after the other one drops out.

 

[John61CT]

Yes, I was expecting longer run times during the day, the hope was I could avoid all **battery** drain by running solely off the panel.

So now you see you just prevented batt charging by increasing the daytime load. Run the fridge 24*7, and get more energy input, more solar or a little genny, or frequent overnights on shore power.