Recomendations: How to set up an extra battery for my system

[Tasmaniak]

It's rare that a car won't start at 12.3

 

[kopper69]

It's rare that a car won't start at 12.3

Not sure where this post is relating to, maybe a mistake? But it depends on the condition of the battery. A new battery at 12.3V probably would, an older battery could very easily fail to start the car if it was at 12.3V.

 

[commsirac]

It's rare that a car won't start at 12.3

As I said, in my experience, once below that voltage it can get dicey, especially when the temp gets lower and the battery gets older.
I dont know about your experience, but best not to second guess what I post.

Perhaps have a look at Car and Deep Cycle Battery Frequently Asked Questions (FAQ) Section 4 for open circuit battery voltage versus level of charge at various temps.

 

[garfa]

so what your trying to say is that there could be a difference of 0.06V if the batt is between almost 40 and 4 degrees C........
R...I...G...H...T.....
probably get a bigger voltage difference over dirty terminals.....
stop being a keyboard warrior and acting like you are the king of the hill.

 

[commsirac]

so what your trying to say is that there could be a difference of 0.06V if the batt is between almost 40 and 4 degrees C........
R...I...G...H...T.....
probably get a bigger voltage difference over dirty terminals.....
stop being a keyboard warrior and acting like you are the king of the hill.

What dont you wait for a reply before asserting yourself here, then you wont need to wipe the egg of your face.

You obviously havent taken in what I said. As the battery gets near the critical 12.3V level/50% charge level then it can be critical(not turn the starter over fast enough) with an older battery or at cold temperatures.
There is a table in that link that shows you how the voltage of battery underload drops with temperature....have a look.

 

[garfa]

reply from whom exactly, the bloody pope!
i have read the whole page, cannot find much there.
yes, temp does have an effect but less than .06 under normal australian conditions.
all that you have shown is that voltage of an LA batt is effected by temp, marginally. which we all knew.....
this does not address the issue that a batt w/ 12.3v will start a car 99/100.

 

[commsirac]

reply from whom exactly, the bloody pope!
i have read the whole page, cannot find much there.
yes, temp does have an effect but less than .06 under normal australian conditions.
all that you have shown is that voltage of an LA batt is effected by temp, marginally. which we all knew.....
this does not address the issue that a batt w/ 12.3v will start a car 99/100.

Oh dear, I only provided the link for people to verify hopefully what is generally known, and for the fact that at ~12.3V a battery is only half charged. As you can see(well maybe you cant) even when nearly discharged completely the voltage doesnt really fall below 11.8V, which makes the device that isolates an appliance 11V not really well designed, WHICH WAS THE MAJOR point under discussion that related to the thread....but some want to try and start brush fires and catch me out on details......not on this issue Im afraid.
Here is a summary of that info directly from the link:
For example, if the electrolyte is at 20° F (-6.7° C), the Open Circuit Voltage reading would be 12.696 for a 100% State-of-Charge. At 100° F (37.8° C), the Open Circuit Voltage reading would be 12.308 for 50% SoC and a reading of 11.773 or lower at 120° F (48.9° C) would indicate a discharged battery.

Most people know that a battery that is on the way out usually first struggles when its cold(how come you dont?), and its not because the open circuit voltage(Im guessing you dont know what that means) drops by 0.06V.... in simple terms, the chemical reaction in the battery doesnt go as well when it is cold.

Go back and look at the Capacity Load Test which shows battery voltage under load versus temperature, which shows how under load the difference in output is close to 1V with a 40C temp difference, that's with a battery in good condition with 80% charge. 1V difference at the starter can easily make a difference between getting the motor to spin fast enough to start.
It gives some indication of what lies in store with batteries with more travelled batteries at lower levels of charge where the voltage will drop more quickly in a start situation and further.

 

[Not_An_Abba_Fan]

Which is why I still recommend having a second battery to run accessories. The risk of having a battery drop below the critical starting voltage is all that you need when you are alone in a carpark thumping out some rad tunes.

 

[garfa]

Oh dear, I only provided the link for people to verify hopefully what is generally known, and for the fact that at ~12.3V a battery is only half charged. As you can see(well maybe you cant) even when nearly discharged completely the voltage doesnt really fall below 11.8V, which makes the device that isolates an appliance 11V not really well designed, WHICH WAS THE MAJOR point under discussion that related to the thread....but some want to try and start brush fires and catch me out on details......not on this issue Im afraid.
Here is a summary of that info directly from the link:
For example, if the electrolyte is at 20° F (-6.7° C), the Open Circuit Voltage reading would be 12.696 for a 100% State-of-Charge. At 100° F (37.8° C), the Open Circuit Voltage reading would be 12.308 for 50% SoC and a reading of 11.773 or lower at 120° F (48.9° C) would indicate a discharged battery.

Most people know that a battery that is on the way out usually first struggles when its cold(how come you dont?), and its not because the open circuit voltage(Im guessing you dont know what that means) drops by 0.06V.... in simple terms, the chemical reaction in the battery doesnt go as well when it is cold.

Go back and look at the Capacity Load Test which shows battery voltage under load versus temperature, which shows how under load the difference in output is close to 1V with a 40C temp difference, that's with a battery in good condition with 80% charge. 1V difference at the starter can easily make a difference between getting the motor to spin fast enough to start.
It gives some indication of what lies in store with batteries with more travelled batteries at lower levels of charge where the voltage will drop more quickly in a start situation and further.

No, what you brought up originally was that temp effect the batt.

Now read your chart, and you can clearly see that even if the battery went from almost -20 degrees to almost 50 degrees C the battery voltage will change LESS THAN 0.15 volts.

So a 12.3 battery will start a car regardless of temperature.

I have included your original statement below

A new battery at 12.3V probably would, an older battery could very easily fail to start the car if it was at 12.3V.

Anything to add?

 

[| evaN |]

i was running 2 deep cycle batteries with a redarc battery isolator and if you've got a decent system, the front battery wont be full enough for long enough for the isolator to which over to the rear battery to charge it. if you're going to upgrade the alternator then go duel batteries, otherwise don't bother.