How far can we run a battery down to ?

iana · Guru

How far can we run a battery down to ?

Moonraker · Senior Member

I think best to not go below 50% and keep the batteries on float charge all the time when not being used.

LLD · Guru

Definitely try not to go below 20%. My power regulator shuts down below 20% so I have no 12V power down in the red. Although I can easily charge the battery back up to 100%, I have to disconnect the power regulator for it to reset itself. My battery goes into the yellow a bit.

swamp · Senior Member

HI
Buy yourself a LOW VOLT DISCONNECT LVD . Preferably a 12.ooV cut off with inbuilt time delay. Projecta do 2 either a 30 or 50amp unit with different voltages .

Fit a master ON/OFF isolater that shuts down every thing 100% chargers /displays / solar can all draw small amounts of power and eventually flattening battery .

50% discharge is a good balance between cost vs perf

Peter_n_Margaret · Guru

Moonraker wrote:
I think best to not go below 50% and keep the batteries on float charge all the time when not being used.

Sorry but the 50% often quoted as a maximum discharge to avoid damage is a common urban myth. You will not find that supported by any battery manufacturer's life data. It is often justified using the number of cycles obtainable, but that is a misleading way of establishing battery life. Battery life is best expressed as a total Ahs of output (or more precisely, Whrs). If you make that calculation, you will find that depth of discharge makes only a little difference to the total life.

It can be looked at from a different perspective - Vis - If you have 2 batteries and discharge them to 40% DOD EVERY time, they will last almost exactly twice as many cycles than if you had one battery and discharged it to 80% DOD EVERY time, but one will cost half as much and weigh half as much as two (and have less reserve capacity).

Yes, it is important to recharge lead acid batteries fully as soon as possible after use. Leaving them in a partly charged state is not a good plan and charging them at appropriate voltages (according to the manufacturer's recommendations (with temperature compensation) will avoid damage and get the best life from them.

Cheers,

Peter

-- Edited by Peter_n_Margaret on Friday 7th of December 2018 04:56:49 PM

Whenarewethere · Guru

I can't fit any more batteries in my car, 3 x 26AH. I going to run then down as much as they can take to do the job if I can't charge them. On average that generally does not happen so it is only a small % or the cycle numbers. Then I will replace them in a couple of years. Not worth stressing over a bit of extra life as the amortized value of the batteries is not worth saving extra cycles. The value in cold food is more than battery cycles.

Izabarack · Guru

iana wrote:
........, how far can I regularly run the batteries down to, without damaging them.

Are you planning to regularly discharge/use the batteries down to some SOC before recharging?

Any cycling down from full charge reduces the life of a LA battery. Best or longest life will/be obtained by keeping them topped up rather than trying to establish some number at which damage occurs. There is no number above which no damage or reduction in life occurs. As Peter says above, concentrating on depth of discharge and cycles has been shown to be of not much use. Manufactures of named Deep Cycle batteries tout the design specifically aimed at deep discharge capable while still giving long life.

Iza

Jaahn · Guru

Hi Iana smile

I agree with the discussion so far. Usefull ideas to guide you. I wanted to add that the voltage you measure as the battery is being used will not be the voltage shown in that table ! That table is the resting voltage but as you use power the voltage is pulled down lower than that table. It depends on how much current you draw out of the battery so you should be aware of that. Using a high current, say for example for an inverter, will pull the voltage down a few volts perhaps. When you stop using the power the voltage comes back up to the resting figure eventually. hmm

But you should get an idea of what is happening if you observe the voltage and know what is being powered up at the time. After a while you can see what is the trend and know when you should stop. biggrin

Jaahn

PS Please do not come on and tell us how much better some other batteries are and start a sh*t fight.

-- Edited by Jaahn on Saturday 8th of December 2018 08:35:21 AM

-- Edited by Jaahn on Saturday 8th of December 2018 10:41:53 AM

Peter_n_Margaret · Guru

Izabarack wrote:
Best or longest life will/be obtained by keeping them topped up rather than trying to establish some number at which damage occurs. There is no number above which no damage or reduction in life occurs.

Yep.

It is worth mentioning that if you are charging at (say) 10A from your solar (or some other charger) at the same time that you are running a (say) 6A load, then NONE of the 6A is coming out of the batteries (it is all coming out of the charge source directly) and therefore NONE of that load is "wearing" the batteries out.

Cheers,

Peter

iana · Guru

Izabarack wrote:

Are you planning to regularly discharge/use the batteries down to some SOC before recharging?
Any cycling down from full charge reduces the life of a LA battery. Best or longest life will/be obtained by keeping them topped up rather than trying to establish some number at which damage occurs. There is no number above which no damage or reduction in life occurs. As Peter says above, concentrating on depth of discharge and cycles has been shown to be of not much use. Manufactures of named Deep Cycle batteries tout the design specifically aimed at deep discharge capable while still giving long life.

Iza

Yes, free camping, as I said in the initial post, we are totally 12v, including the fridge which will draw 7.5A every hour all through the night.

I have a "Threshold Voltage Switch" kit which I will set to a voltage determined by maybe the comments on here to alert us when the voltage gets too low. Which usually happens about 3-4am.

Probably the max load will be 20A if the fridge is on, and we are using the TV and vast set-up. But that would only be for short periods.

Peter_n_Margaret · Guru

What sort of fridge?
7.5A continuous for 14 hours (at least, between the sun shining) is over 100Ah. That is HUGE.

I run 2 compressor units, one fridge and one freezer and combined they use about 25Ah over night (about 3.5A each, when running, which is not much over night) and although mine are well insulated, your consumption seems abnormally high.
Might be an opportunity there to reduce your power consumption.
Cheers,
Peter

rockylizard · Guru

Gday...

I can understand your concern about how far 'down' can one regularly run a battery.

However, and I do know you are fully aware, it is more a case of making sure you have enough solar to re-charge the battery/s to restore the power consumption of the night during daylight hours.

Without sufficient solar panels to restore the battery SOC by around midday, one will be constantly running on poorly charged batteries - with the additional problem of quite probably shorter battery life as a result.

It is a really a calculation of how much will be taken out of the battery each night (and therefore have a battery that has sufficient Ahrs to allow that without dropping below quite probably 50%) and then sufficient solar to restore that battery's SOC so that the cycle can begin all over again.

Cheers - John

[edit: if the usual amount of power required to make it through the night is such that it drains the battery/s below eg 50%, then it would seem there are two choices. Either reduce the amount of power required for the night/s or invest in a battery with sufficient capacity to match that consumption. By corollary, that then leads to having sufficient solar to restore that battery's SOC by around mid-day the following day to ensure longevity of the battery.]

-- Edited by rockylizard on Saturday 8th of December 2018 09:45:06 AM

iana · Guru

Sorry my mistake, once an hour for five minutes. How ever my post is about determining a set point for the battery voltage so we can manage the batteries and get max life from them, within reason.

Peter_n_Margaret · Guru

Best battery life comes from maximising your solar and minimising your loads (especially loads when the solar is not working) and fully charging ASAP at the appropriate voltages (with temperature compensation).
Cheers,
Peter

Jaahn · Guru

Hi Iana smile

Great productive discussion this morning on a topic that other people will be interested in generally too. biggrin biggrin

Another thing that might help your overnight fridge use is to put some extra bottles of water(even beer) in there, and during the day when the solar is putting in power, they get cold and then 'store the cold' during the night to help the fridge stay cool. This works well in the summer with lots of solar and hot nights. hmm

Sometimes I turn the fridge off in the night when I get up, if I see the meter looking a bit lowish. Then turn it on first thing in the morning again. It does not get much less cold than normal. Our battery is getting a bit down now. cry

Jaahn

-- Edited by Jaahn on Saturday 8th of December 2018 12:51:05 PM

Peter_n_Margaret · Guru

Yes Jaahn. This is "power shifting". Trying to use more power when you have plenty of charge capability and less when you don't, even when the batteries are full.
We bake bread in a bread maker. It is great to wake up to fresh bread for breakfast, but it is better for battery life to have it for lunch.
The other option is to choose your appliances carefully, especially those that get used after the sun goes down like lights, TV, fridge, computer, heaters.
All these things will improve battery life.
More solar is much cheaper and last longer than more or replacement batteries.
Cheers,
Peter

DMaxer · Guru

I have just replaced my battery and now find the new one is not recharging through the solar and regulator. Do I need to turn off regulator and reset it. If so how do I turn it off and how does one reset it?

Jaahn · Guru

Hi DMaxer smile

Could I humbly suggest you start a new thread for this. This discussion is going well now. See at the top "Start A New Topic" just as easy as joining this one !

We cannot reply to your question without knowing more details, the type of regulator etc. The more details on the battery and solar the easier to answer.

Jaahn

-- Edited by Jaahn on Saturday 8th of December 2018 12:59:10 PM

LLD · Guru

The monitor in my van. When it gets to the red I have to re-boot my Omaglec Controller (disconnect battery). Hence I avoid going there. Unless battery is actually on charge (good sunny day or on mains), the monitor is in the yellow.

Van - Battery Monitor.JPG

Jaahn · Guru

Hi LLD smile

I have a dual model of these great meters in my MH. It is the best thing I have ever seen for battery voltage monitoring. Our previous MH had one and I purchased another one for the new one when I set it up. Does both the vehicle and the house batteries. biggrin SWMBO can see what the batteries are doing too !!

They look simple but if you look carefully the voltage steps are not all the same and are matched to the different parts of the battery voltage curve you need to see. It can be checked at a glance any time and instantly tells me if the solar, or the motor charging is working and at night if the battery is holding up OK or if it's time for bed confuse

Having the vehicle battery also monitored I see instantly if, say, I left the lights on or something else is flattening it. smile

Jaahn

Warren-Pat_01 · Guru

Hi everyone,
I see on the excellent monitor above that 10% capacity is equal to around 11.4v. My Trailblazer fridge has a cutout set at 10.6v - far too low for my thinking.

A female friend in our bird club bought a $400 AGM battery to run her small fridge while out bush on a survey. She put it on a concrete floor an arrival home & forgot about it. Cutting a long story short, when I got the battery it had 0v in it! Another friend's 20A smart charger would not touch it. Using an old 1960's vintage battery charger, a pair of old 37w solar panels & later a smart charger, it took three weeks to bring it back to life.

She now uses it wisely. An older battery would probably be a boat anchor now as batteries do not like severe discharges.

Tony Bev · Guru

There are different rule of thumb measurements, for the (SOC) State of charge, of batteries, Ian

Below is what I have been using, as I had been unable to find one for Bosch AGM batteries

My understanding is that it is better to try and not let them get below 50% capacity

After saying that, it is a brave man indeed, who is prepared to tell the better half, she is using too much power
smile On the other hand, if you are nimble on your feet, and know how to weave and duck, you may get away with it smile

Battery SOC.png

T1 Terry · Guru

True battery voltage is measured under load, not rested. The rested voltage can be effected by plate sulphation and not give an accurate assessment of just how much there is left in the battery. Try to avoid pulling the battery below 12v under load, no matter what battery chemistry, they will all do it but it does effect cycle life. If you can't run the loads you want to run without the battery dropping below 12v then you do not have enough battery capacity available. This can be the caused by sulphated plates, simply not enough base capacity or just how the batteries are wired. In any event, if the load regularly draws the battery below 12v it should be investigated to determine the cause.

T1 Terry

Peter_n_Margaret · Guru

Warren-Pat_01 wrote:
Hi everyone,
I see on the excellent monitor above that 10% capacity is equal to around 11.4v. My Trailblazer fridge has a cutout set at 10.6v - far too low for my thinking.

Fullriver quote 10.5V as zero state of charge.

Secop/Danfoss compressors will run down to 10.4V in standard configuration and can be configured to run at less than that.

Cheers,

Peter

oldtrack123 · Guru

Peter_n_Margaret wrote:
Warren-Pat_01 wrote:
Hi everyone,
I see on the excellent monitor above that 10% capacity is equal to around 11.4v. My Trailblazer fridge has a cutout set at 10.6v - far too low for my thinking.
Fullriver quote 10.5V as zero state of charge.
Secop/Danfoss compressors will run down to 10.4V in standard configuration and can be configured to run at less than that.
Cheers,
Peter

The low voltage cutout with Danfoss units is more to protect the Danfoss unit from undervoltage, the same with all Waecos.

Unless it is required to be that low ,to compensate for voltage drop in the feed lines ,it should be set higher for battery protection

A simple change of a resistor.

Peter_n_Margaret · Guru

Yep. Don't disagree.
Waeco = Danfoss.
Cheers,
Peter

Cloak · Guru

Disappointing to see the industry still mucking around with measuring voltage as the main determination of a battery's charge.

Shunt monitors are much more accurate and prolong battery life.

iana · Guru

Thanks for the input everyone, I think I will set the alarm threshold at about 12.05 to 12.02 volts, at that point if required I will turn off the house batteries and plug in the vehicle auxillary. So far the new batteries have been performing fine, but then again, no TV or many lights. Will see how we get on when winter comes and the sun is low on the horizon and over cast days, until then perfect solar charging weather.

Jaahn · Guru

Cloak wrote:
Disappointing to see the industry still mucking around with measuring voltage as the main determination of a battery's charge.

Shunt monitors are much more accurate and prolong battery life.

Hi Cloak smile

I believe the answer is that people do not see the need to spend the big bucks to get a decent meter that will read the totals in and out. Some do and are happy with them. biggrin

But if you use the voltage which is always readily available and observe it for a while under different usage conditions, most people can get a good idea of what is happening. If you find that you cannot do that then spend the extra money. hmm

Also another solar panel or two will be cheaper than the totaling meter and will possibly solve any problems anyway. aww

Jaahn

oldtrack123 · Guru

Jaahn wrote:
Cloak wrote:
Disappointing to see the industry still mucking around with measuring voltage as the main determination of a battery's charge.

Shunt monitors are much more accurate and prolong battery life.

Hi Cloak
I believe the answer is that people do not see the need to spend the big bucks to get a decent meter that will read the totals in and out. Some do and are happy with them.
But if you use the voltage which is always readily available and observe it for a while under different usage conditions, most people can get a good idea of what is happening. If you find that you cannot do that then spend the extra money.
Also another solar panel or two will be cheaper than the totaling meter and will possibly solve any problems anyway.
Jaahn

Two things are all you need

A low voltage disconnect plus a good [permanently wired in direct to the battery] voltmeter with that you have a max discharge voltage set & observation of the voltmeter will soon show you how the battery is performing under differing loads.

Knowledge speaks, but wisdom listens.