Does using solar degrade my batteries?

[KompetentKrew]

12V is 90% discharged.

I'm surprised to learn that - when I got my boat I googled "battery voltage state of charge" and found charts like the below. Consequently I too have always used 12v as a limit.

 

[PaulRainbow]

Imagine it like this ...

The solar charger and the batteries are providing a pool of energy, and the inverter is drawing from that pool to power your devices.

For arguments sake, we can ignore conversion losses and say that your fryer is drawing 1500W and your grill another 1500w from the pool.

The battery will be providing 3000W minus what is currently coming in due to solar, for simplicity sake lets say 1000W of solar.

3000W(Load)-1000W(Solar)=2000W which must come from the battery.

For arguments sake, lets say your house bank is 3 x 220Ah batteries @12V in parallel.

This means each battery will be providing 2000W/3= 666W each, which at 12V is 666/12= 55A

You have 220Ah available, so the battery will go from 100% to dead in 220/55 = 4 hours.

Slightly picky.....

We know the OP has 660Ah, so keeping above 50% = 330Ah usable.

2000W through the inverter will draw 200A from the batteries. 1.5 hours and he's down to 50% (ish).

With no solar the inverter will draw 300A, batteries down to 50% in an hour.

You don't really want to discharge to zero as it damages the batteries, realistically keep them above 50% ... so you have 2 hours when your solar is working hard before your batteries are dead, you can do the sums again with no solar (evenings) .... the load then will be closer to 80A and you'll have 2 3/4 hours to empty ... this is indeed verging on abuse of leisure batteries.

The inverter is rated to run your loads, but the batteries are under-specced for using the full capability of your inverter.

Run the generator when cooking IMO - especially if there is little solar and you want to use more than one of your AC loads.

 

[PaulRainbow]

I'm surprised to learn that - when I got my boat I googled "battery voltage state of charge" and found charts like the below. Consequently I too have always used 12v as a limit.

You're right, i was posting in a hurry and quoted for LifePO4, my bad.

 

[noelex]

If you post gobbledygook how do you expect anyone to understand it ?

Paul, instead of posting derogatory comments as you frequently do, explain what is wrong with the post.

As a professional, you should know better than post #2 see below :

12V is 90% discharged.

The voltage under load is not a predictor of SOC without taking the factors I indicated into consideration.

I notice you tried to clear up the mistake in post #4 and correctly pointed out that this only applies to resting voltage, not the voltage under load that the OP was referring to.

Nevertheless, you did not mention other factors that make a difference, such as battery temperature. You also seemingly failed to grasp there is relationship between the voltage, SOC and discharge rate. See the useful graph below:




Below is a link you may find educational, but really you should already understand these basics of how lead acid batteries perform:

https://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

 

[PaulRainbow]

Paul, instead of posting derogatory comments as you frequently do, explain what is wrong with the post.

As a professional, you should know better than post #2 see below :

The voltage under load is not a predictor of SOC without taking the factors I indicated into consideration.

I notice you tried to clear up the mistake in post #4 and correctly pointed out that this only applies to resting voltage, not the voltage under load that the OP was referring to.

In post #13 you claim "A 660Ah lead-acid battery bank should not be regularly dropping below 12.0V with the loads you describe. The most likely cause would be a low battery state of charge, loads that are too high, a battery or batteries performing poorly, a wiring problem upstream of where the voltage is measured, or a combination of these factors."

Clearly not the case, as already explained, the terminal voltage returns to 13+V when the load is off. Only reason the Victron app shows a voltage of 12V is because the load is high. Bow thrusters routinely lower the terminal voltage to about 10.5V, doesn't mean any of your claims are true.

 

[Irish Rover]

Paul, instead of posting derogatory comments as you frequently do, explain what is wrong with the post.

In fairness, you were the first person on the thread to post something which could be described as derogatory.
I've described myself on the forum previously as a tech numpty. I sometimes ask basic, if not stupid, questions and there are a few generous posters like @PaulRainbow who go out of their way to answer in terms even I can understand, and not try to make me feel stupid or embarrassed. Your post was gobbledegook to me but I just said I didn't understand it. Your subsequent put-down was uncalled for, but I let it pass.

 

[Refueler]

Am I really "flogging" the batteries? I boil the kettle 3 or 4 times per day, use the airfryer or the grill for approx half an hour and a few other smaller low wattage appliances occasionally.

Depends on the format of the batterys ....

At say 100A+ which your batts are likely being subjected to .... if cranking batts / dual purpose leisure batts ... they can take that ampage draw ...

But get a true Deep Discharge battery that is designed for low amp demand - and repeated 100A+ draw can stress the plates such that life of battery is shortened - basically a plate could buckle ..

 

[noelex]

Bow thrusters routinely lower the terminal voltage to about 10.5V, doesn't mean any of your claims are true.

But these loads are only for a very short duration. The loads from the air fryer are over half an hour.

The original question from the OP was "Does this power inflow/outflow degrade the batteries?”

The inflow does not, but the outflow does, as you correctly concede in post #20:

They might not last quite as long as if you only used them for powering a few low current devices,

I don’t think the OP’s decision to accept this load is unreasonable (around 240A ) with both the kettle and air fryer running, but, I would be happier to run these devices separately, as you and others have pointed out. This will reduce the stress on the batteries. The voltage will not drop below 12.0V and this likely remove the need to run a generator when the voltage drops too low for the inverter.

 

[Irish Rover]

Depends on the format of the batterys ....

At say 100A+ which your batts are likely being subjected to .... if cranking batts / dual purpose leisure batts ... they can take that ampage draw ...

But get a true Deep Discharge battery that is designed for low amp demand - and repeated 100A+ draw can stress the plates such that life of battery is shortened - basically a plate could buckle ..

Batteries are 3 x Varta 210ah AGM - my bank is total 630 not 660 as previously stated.

 

[Irish Rover]

but, I would be happier to run these devices separately,

I get that, but then my chip butty would be gone cold before the tea was ready or vice versa

 

[noelex]

In fairness, you were the first person on the thread to post something which could be described as derogatory.
I've described myself on the forum previously as a tech numpty. I sometimes ask basic, if not stupid, questions and

I took your comment "PS - I'm not sure I understood anything else in your post" to indicate my post was unhelpful, wrong, or poorly written. This is not nice when someone has taken the trouble to answer your question.

Now I understand your confusion; please accept my apologies.

 

[Baggywrinkle]

Just to throw even more confusion into the mix, battery capacity is quoted in relation to a discharge current.

Batteries have a "C" quoted on them and this has a number after the C ... usually 10 or 20. (Not to be confused with 1C or 10C which has the number in front of the C and is normally used in relation to charge rates)

C=the quoted battery capacity, e.g. for a 210Ah, C=210 and the C-- value indicates the conditions for which this capacity is being quoted. The number following the C is hours, so "C10" refers to the current to discharge the battery in 10 hours. 210/10=21A.

C5 is the current that would drain the battery in 5 hours. So you would think a 210Ah battery will drain in 5 hours with a current draw of 210/5 = 42A but it doesn't work like that.

The higher the discharge current, the less capacity the battery has.

To estimate the capacity of a 210Ah C10 battery at C5 there is a factor which reduces the capacity.

The formula is C5=0.86*C10 .... so your 210Ah battery is only a 210*0,86=180.6Ah ..... and will actually deplete in 5 hours with a current of 36A, not 42.

With C10 as a reference, the table of conversion factors looks like this ....

C120=1.29*C10
C100=1.25*C10
C20=1.08*C10
C10=1*C10
C5=0.86*C10
C1=0.65*C10

So your 210AH C10 AGM Deep Cycle battery will only be a 136Ah C1 ... and a current of 136A will completely discharge it in 1 hour.

It's probably better explained here ..... What is the C Rate for AGM & LiFePO4 Battery? - Sunon Battery

 

[PaulRainbow]

Just to throw even more confusion into the mix, battery capacity is quoted in relation to a discharge current.

Batteries have a "C" quoted on them and this has a number after the C ... usually 10 or 20. (Not to be confused with 1C or 10C which has the number in front of the C and is normally used in relation to charge rates)

C=the quoted battery capacity, e.g. for a 210Ah, C=210 and the C-- value indicates the conditions for which this capacity is being quoted. The number following the C is hours, so "C10" refers to the current to discharge the battery in 10 hours. 210/10=21A.

C5 is the current that would drain the battery in 5 hours. So you would think a 210Ah battery will drain in 5 hours with a current draw of 210/5 = 42A but it doesn't work like that.

The higher the discharge current, the less capacity the battery has.

To estimate the capacity of a 210Ah C10 battery at C5 there is a factor which reduces the capacity.

The formula is C5=0.86*C10 .... so your 210Ah battery is only a 210*0,86=180.6Ah ..... and will actually deplete in 5 hours with a current of 36A, not 42.

With C10 as a reference, the table of conversion factors looks like this ....

C120=1.29*C10
C100=1.25*C10
C20=1.08*C10
C10=1*C10
C5=0.86*C10
C1=0.65*C10

So your 210AH C10 AGM Deep Cycle battery will only be a 136Ah C1 ... and a current of 136A will completely discharge it in 1 hour.

It's probably better explained here ..... What is the C Rate for AGM & LiFePO4 Battery? - Sunon Battery

Good point, which is why i suggested keeping the load as light as possible

 

[William_H]

OP 's original question has an answer of variable quantities. Certainly as said solar will contribute to the 12v DC to the inverter. Reducing the load on the battery to an unknown degree but my guess at about 20 amps good sunshine. 3000w inverter at full load is going to draw about 260 amps. So 240 amps from battery. suggesting perhaps an hour or so of safe drain on batteries from fully charged and in good condition. (probably less)
So it is the drain on the batteries that will shorten their lives. Just how much is a variable answer. As said run a generator at the same time to help.
Now just waffling here and no help to OP but 24 v system and batteries would be far more suitable to this amount of load of an inverter. Perhaps even 48 v system.
One of the real problems of 12v system at high loads is the volt drop of wiring switches fuses etc. It is quite likely that OP measure of 12v under load is a function of both volt drop in batteries and in the wiring itself.
Advice to OP Try to minimise power load on inverter and time that power is used. But sytem obviously works so carry on just be mindful of batteries. (which quite likely are not as good as new_) ol'will

 

[thinwater]

Oh dear. Going all-electric, in a big boat with generators, and believing it's green. .

 

[Irish Rover]

Oh dear. Going all-electric, in a big boat with generators, and believing it's green. .

I'm not sure what it is you're trying to say?

 

[Refueler]

Batteries are 3 x Varta 210ah AGM - my bank is total 630 not 660 as previously stated.

FLA or AGM doesn't really say anything ...

What I use for determining the battery are the specs :

Voltage / composition .. ie SLA - FLA - AGM etc
Capacity - to cover the use I expect
Cranking Amps - if I am expecting to start engine with it.

If the batterys do not show CCA (Cranking Amps) then its likely unsuited to starting an engine - and is a leisure battery not designed for high load demands.

 

[Irish Rover]

FLA or AGM doesn't really say anything ...

What I use for determining the battery are the specs :

Voltage / composition .. ie SLA - FLA - AGM etc
Capacity - to cover the use I expect
Cranking Amps - if I am expecting to start engine with it.

If the batterys do not show CCA (Cranking Amps) then its likely unsuited to starting an engine - and is a leisure battery not designed for high load demands.

I think you're just taking advantages of me now because I said I was a tech numpty .
Anyway, these are what I have
ProMotive AGM

 

[PaulRainbow]

Oh dear. Going all-electric, in a big boat with generators, and believing it's green. .

No one mentioned being green, but the OP has said, more than once, he doesn't like to run the generator.

 

[PaulRainbow]

OP 's original question has an answer of variable quantities. Certainly as said solar will contribute to the 12v DC to the inverter. Reducing the load on the battery to an unknown degree but my guess at about 20 amps good sunshine. 3000w inverter at full load is going to draw about 260 amps. So 240 amps from battery. suggesting perhaps an hour or so of safe drain on batteries from fully charged and in good condition. (probably less)

The current draw from a 3000W inverter, it's about 300A, not anything like 260A.

So it is the drain on the batteries that will shorten their lives. Just how much is a variable answer. As said run a generator at the same time to help.
Now just waffling here and no help to OP but 24 v system and batteries would be far more suitable to this amount of load of an inverter. Perhaps even 48 v system.

Indeed. My boat is 24V and i also have a 3000W inverter, this only draws 150A at full current.

One of the real problems of 12v system at high loads is the volt drop of wiring switches fuses etc. It is quite likely that OP measure of 12v under load is a function of both volt drop in batteries and in the wiring itself.
Advice to OP Try to minimise power load on inverter and time that power is used. But sytem obviously works so carry on just be mindful of batteries. (which quite likely are not as good as new_) ol'will

The OP says he's getting the reading from the Victron app, that should be more or less directly from the batteries.