Is 12.2 volts TOO LOW???

cupcake · May 2014

Hi guys - I have a quick question:

Since adding a refrigerator to the off-grid system I've noticed my daily 'min' voltage reading is 12.2 volts according to the controllers memory settings...
Before the fridge my 'min' was 12.5

The fridge cycles on an off through the night (normal operation) -- so my question - as far as battery-life is concerned is 12.2 volts OK during 'semi load' overnight on a continual basis? Or is 12.2 not accurate because its under a semi-constant load? (with the fridge compressor cycling on and off all night long)

FYI, during the day the bank gets a full charge...

I have 5, 100ah batteries in parallel..

So is 12.2 at night worry? or no-worry??

Thanks guys!

--cups-of-cake

BB. · May 2014

Re: Is 12.2 volts TOO LOW???

Do you have a hydrometer?

-Bill

cupcake · May 2014

(repost) Is 12.2 volts too low..??

Somehow my original thread got locked/closed ..perhaps by mistake?

I have SEALED batteries, I cannot use a hydrometer. My original question/post is below -- THANKS AGAIN!

Hi guys - I have a quick question:

Since adding a refrigerator to the off-grid system I've noticed my daily 'min' voltage reading is 12.2 volts according to the controllers memory settings...
Before the fridge my 'min' was 12.5

The fridge cycles on an off through the night (normal operation) -- so my question - as far as battery-life is concerned is 12.2 volts OK during 'semi load' overnight on a continual basis? Or is 12.2 not accurate because its under a semi-constant load? (with the fridge compressor cycling on and off all night long)

FYI, during the day the bank gets a full charge...

I have 5, 100ah batteries in parallel..

So is 12.2 at night worry? or no-worry??

Thanks guys!

--cups-of-cake

Blackcherry04 · May 2014

Re: (repost) Is 12.2 volts too low..??

Sounds about right. A lot voltage sag depends on your wiring to the inverter and the batteries ability to satisfy the current needed. Standing voltage and loaded voltage will always be different. Somewhere around 11.9V standing voltage ( unloaded ) is 50% DOD. Yours sounds good to me.

cupcake · May 2014

Re: (repost) Is 12.2 volts too low..??

Blackcherry04 wrote: »

Sounds about right. A lot voltage sag depends on your wiring to the inverter and the batteries ability to satisfy the current needed. Standing voltage and loaded voltage will always be different. Somewhere around 11.9V standing voltage ( unloaded ) is 50% DOD. Yours sounds good to me.

Thanks! - I appreciate your help... I know 12.2 on 'the chart' says 50%... but my nighttime 12.2 overnight reading is when there is a fluctuating load (refrigerator)...

So I just wanted to make sure...

I appreciate your help

--cake

BB. · May 2014

Re: Is 12.2 volts TOO LOW???

Sorry Cake,

Doing posts on my touch screen phone and clicked thread lock.

-Bill

Cariboocoot · May 2014

Re: (repost) Is 12.2 volts too low..??

Under load system nominal Voltage is about as low as you want to get (i.e. 12 Volts). If you've got two tenths over this by morning you're still in good range.

Blackcherry04 · May 2014

Re: Is 12.2 volts TOO LOW???

There lot's of charts that say a lot of things. Using the SG readings are the best, even they have a range because it does not change instantaneously. Second would be a battery monitor with a shunt and knowing the amp hrs removed if your peukert exponent is correct. Volt meters are another issue if you do not know the correct battery voltage. Reading to .1 you do not know if the voltage is 12.29 or 12.21, depending on the size of a bank that makes a difference. Another is dip and recovery ( Coup de Fouet ) to the load, the initial surge of starting a refrigerator may cause a voltage dip that takes awhile to recover from while under load.

vtmaps · May 2014

Re: Is 12.2 volts TOO LOW???

cupcake wrote: »

Since adding a refrigerator to the off-grid system I've noticed my daily 'min' voltage reading is 12.2 volts according to the controllers memory settings...
Before the fridge my 'min' was 12.5

I'm not sure what you are describing... is 12.2 the voltage in the morning? Or is the morning voltage higher than 12.2 (but the monitor tells you that the voltage sagged to a 12.2 minimum during the night)?

What counts is your voltage in the morning. If your morning voltage is 12.5 under your normal baseline loads, it doesn't matter that the voltage sagged for an instant to 12.2 when the freezer compressor switched on. Different voltmeters will 'capture' different values for the minimum... it depends on how many times per second they read the voltage. The transient sag is very brief... to brief for many meters to measure.

If your actual morning voltage is 12.2, that means you are using more power overnight and your battery has a lower voltage because it is at a lower SOC.

--vtMaps

cupcake · May 2014

Re: Is 12.2 volts TOO LOW???

vtmaps wrote: »

I'm not sure what you are describing... is 12.2 the voltage in the morning? Or is the morning voltage higher than 12.2 (but the monitor tells you that the voltage sagged to a 12.2 minimum during the night)?

What counts is your voltage in the morning. If your morning voltage is 12.5 under your normal baseline loads, it doesn't matter that the voltage sagged for an instant to 12.2 when the freezer compressor switched on. Different voltmeters will 'capture' different values for the minimum... it depends on how many times per second they read the voltage. The transient sag is very brief... to brief for many meters to measure.

If your actual morning voltage is 12.2, that means you are using more power overnight and your battery has a lower voltage because it is at a lower SOC.

--vtMaps

^ Thank you -- good points and excellent info:

To answer your inqusitions:

My MORNING voltage is 12.5 or 12.8 according to my wife who gets in the control-room at 7am each morning.

The "12.2" is the controllers 'log' of the overall 'miniumum' voltage... which begs the question: does the controller just log the minium voltage for that day OR the *average minimum voltage for the day... THAT would tell me a lot!

The controller is the moringstar MPPT-60 cotroller...

if its NOT the 'average minumum' for the day then it would make sense that the compressor 'surge' would kick it down to 12.2 momentarily...

Thanks for all your help - all of you...

--cup-o-kake

waynefromnscanada · June 2014

Re: Is 12.2 volts TOO LOW???

cupcake wrote: »

I have 5, 100ah batteries in parallel..

OUCH!!! Not good.

Desert Rat · June 2014

Re: Is 12.2 volts TOO LOW???

I've noticed the same thing with my Morningstar TS-MPPT-60 controller--the logged Battery Vmin is always lower than the observed morning battery voltage. I've always figured that the logged number represents an instantaneous dip when my chest freezer kicks on during the night.

DMJ72 · June 2014

Re: Is 12.2 volts TOO LOW???

cupcake wrote: »

^ Thank you -- good points and excellent info:

To answer your inqusitions:

My MORNING voltage is 12.5 or 12.8 according to my wife who gets in the control-room at 7am each morning.

The "12.2" is the controllers 'log' of the overall 'miniumum' voltage... which begs the question: does the controller just log the minium voltage for that day OR the *average minimum voltage for the day... THAT would tell me a lot!

The controller is the moringstar MPPT-60 cotroller...

if its NOT the 'average minumum' for the day then it would make sense that the compressor 'surge' would kick it down to 12.2 momentarily...

Thanks for all your help - all of you...

--cup-o-kake

I have / had that same controller in my first solar setup, it ran a 13 cu. ft fridge. I know what you mean, I would get up and look on the logs, and see V-minimums of 23.6- 23.2 volts (even though my pre-sunrise voltage was 24.6+ on the meter-display). The first time it happened, i rushed outside and did a hydrometer reading .. its was 70%+ SOC. Turns out my fridge loved defrosting cycles @ 3am approx.. = load voltage sag.

Slappy · June 2014

Re: Is 12.2 volts TOO LOW???

Check batts with a volt meter before the sun comes up. Then compare your log for min volt.

mike95490 · June 2014

Re: Is 12.2 volts TOO LOW???

Slappy wrote: »

Check batts with a volt meter before the sun comes up. Then compare your log for min volt.

That does not work, I can chart my minute interval logs, and see as loads come and go at night, the battery sags, and then recovers a fair amount over an hour, when the load (fridge) shuts off.

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

waynefromnscanada wrote: »

OUCH!!! Not good.

Why not??

--cake

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

Desert Rat wrote: »

I've noticed the same thing with my Morningstar TS-MPPT-60 controller--the logged Battery Vmin is always lower than the observed morning battery voltage. I've always figured that the logged number represents an instantaneous dip when my chest freezer kicks on during the night.

Yeah... this is basically what I'm exepreincing... a low 'logged' Vmin voltage (12.2)... I guess I'll get up before sunrise to read the actual voltage....

--CC

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

Slappy wrote: »

Check batts with a volt meter before the sun comes up. Then compare your log for min volt.

I will do this tomorrow morning - thank you...

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

mike95490 wrote: »

That does not work, I can chart my minute interval logs, and see as loads come and go at night, the battery sags, and then recovers a fair amount over an hour, when the load (fridge) shuts off.

So basically you're saying if I get up at the crack-of-dawn tomorrow AM and the fridge just got done the compressor cycle, the batteries might show a false low voltage?

--cakey

zoneblue · June 2014

Re: Is 12.2 volts TOO LOW???

AGMS + no SOC monitor = tricky to tell whats going on. You can get familiar, and you will over time, with the morning rest voltage. I did for a year, and soon got a feel for SOC from it. Technically true rest voltage should be after several hours of no loads. A fridge cycling will thus make the voltage read a tad low, but not excessively so in my experience. Our bank never gets much exercise, and morning rest is usually 24.7V. However turn on a 1kW load like an iron or blender, then itll dip to 12.4V alright.

vtmaps · June 2014

Re: Is 12.2 volts TOO LOW???

cupcake wrote: »

I have 5, 100ah batteries in parallel..

waynefromnscanada wrote: »

OUCH!!! Not good.

cupcake wrote: »

Why not??

Parallel battery systems are problematic because when you charge them the current does not divide up equally among them. They will have a shorter life. You have 5 times as many battery cells as you need to have. The chance of having an outlier weak cell is almost 5 times greater than if you had just one string of battery cells, and your entire battery bank is no better than the weakest cell.

short discussion here: http://www.wind-sun.com/ForumVB/showthread.php?14674
more recent discussion here: http://forum.solar-electric.com/showthread.php?23600

--vtMaps

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

vtmaps wrote: »

Parallel battery systems are problematic because when you charge them the current does not divide up equally among them. They will have a shorter life. You have 5 times as many battery cells as you need to have. The chance of having an outlier weak cell is almost 5 times greater than if you had just one string of battery cells, and your entire battery bank is no better than the weakest cell.

short discussion here: http://www.wind-sun.com/ForumVB/showthread.php?14674
more recent discussion here: http://forum.solar-electric.com/showthread.php?23600

--vtMaps

^ Alrighty,... I am all ears.... so what do you suggests as an optimal battery setup for a 12-volt system such as mine??:

2X280w panels --> monningstar mpp6-60 controller --> 5 'deep cycle' batteries from autozone (yes, I know..) all in PARALLEL --> Samlex PST-2000w-12v inverter hardwired to --> standard AC panel box...

all off grid FYI... and in the desert (ie no cloud cover issues..ever)

Thank you...

-cake cups

Cariboocoot · June 2014

Re: Is 12.2 volts TOO LOW???

cupcake wrote: »

^ Alrighty,... I am all ears.... so what do you suggests as an optimal battery setup for a 12-volt system such as mine??:

2X280w panels --> monningstar mpp6-60 controller --> 5 'deep cycle' batteries from autozone (yes, I know..) all in PARALLEL --> Samlex PST-2000w-12v inverter hardwired to --> standard AC panel box...

all off grid FYI... and in the desert (ie no cloud cover issues..ever)

Thank you...

-cake cups

You've got a total of 560 Watts of panel. Expect about 36 Amps of peak current. That means a maximum battery bank capacity of 720 Amp hours, which you won't like because the charging would be far too slow to be practical. 360 Amp hours would be 'ideal' but there don't happen to be any batteries right at that level.

Some options:
Two parallel strings of GC2's giving 440 Amp hours @ 12 Volts (four batteries). 8% peak charge rate, only two parallel connections, very inexpensive batteries. Approximately 2.6 kW hours total.
Two L16 320 Amp hour 6 Volt batteries in series. 11% peak charge rate, only one battery string, more expensive batteries. Approximately 1.6 kW hours total.
Two L16 390 Amp hour 6 Volt batteries in series. 9% peak charge rate, only one battery string, more expensive batteries. Approximately 2.3 kW hours total.

Important thing to do: look and see what sort of real deep cycle batteries are available locally.

Blackcherry04 · June 2014

Re: Is 12.2 volts TOO LOW???

You could always get 6 , 2 volt custom batteries made to size for about $250 + each. or do like the all my customers do, put 8-10 Sams golf cart batteries in parallel for $84 each and get 4-6 years out of them and smile all the way to the bank.

Slappy · June 2014

Re: Is 12.2 volts TOO LOW???

Do you have your battery sense wires hooked up. It does make a difference on the controller reading.

zoneblue · June 2014

Re: Is 12.2 volts TOO LOW???

Just goes to show that theres always an exception to every rule.

Blackcherry04 wrote: »

You could always get 6 , 2 volt custom batteries made to size for about $250 + each. or do like the all my customers do, put 8-10 Sams golf cart batteries in parallel for $84 each and get 4-6 years out of them and smile all the way to the bank.

cupcake · June 2014

Re: Is 12.2 volts TOO LOW???

Slappy wrote: »

Do you have your battery sense wires hooked up. It does make a difference on the controller reading.

No I don't -- that's a good point though - I probably should hook up the battery sense wire.....

Thanks

--cake in a cup

Blackcherry04 · June 2014

Re: Is 12.2 volts TOO LOW???

zoneblue wrote: »

Just goes to show that theres always an exception to every rule.

Thats why you always look for the source of the " Rule ". Most are repeated often, but they are not necessarily true.

Is 12.2 volts TOO LOW???

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