How low can the voltage get before alarms go off or things start shutting down like the fridge. The reason I ask is the 6v vs 12v threads and just what is usable AHs and reserve capacity.
If it's below the level that a 12v bank can be discharged safely then it gives the 6v bank of equal AHs a advantage, maybe more so depending on charge density.
Charge density to me is this. The peak charge burns off fast and then the closer you get to rated charge the slower the voltage drops. So the drop from 12.2 (50% for a 12v bank) to even 11.9v on a 6v bank could represent a considerable AH increase.
I get this concept from my RC packs that were tested between each flight. I got more flights between 4.8v and 4.9v than I got from 4.9v to the peak of say 5.4v
This all make little (but some) difference if you must maintain 12v.
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I think your question is would 12 volt batteries serve you just as well as 6 volt batteries. The difference between two 12 volt and two six volt batteries has been discussed here in detail many times, but I sense your question is focused on the voltage readings as the batteries discharge. Deep cycling is just not good for 12 volt batteries due to the size of the plates. That's why they are used for short bursts of power as needed to start the engine.
Long battery life of wet cell batteries (like most of us use in our RVs) requires you to stay above 11.9 volts. A fully charged battery will give you a reading of 12.5, more or less. If you test the voltage while the battery is connected, then the parasite load will drop the reading slightly, even if it is fully charged. I have no idea if the rate of voltage drop would match the percentage of amperage left in the battery. Logic tells me it would be close, but I have no idea if that is correct.
I suspect some alarms may go off at 12 volts, or 11.9, but some appliances will continue to draw power until the batteries are dead. It just depends on the appliance.
I don't know how this would relate to lithium batteries used in RC packs.
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ASSUMING equal quality of construction, and equal total capacity, there is no difference between two 6 VDC batteries in series and a single 12VDC battery.
In fact, think of the two 6 VDC batteries in series as "a 12 VDC battery in two separate cases".
Voltage at particular depths of discharge for either (since they are both wired for 12 VDC) is the same.
One of the primary reason to consider 6 VDC golf cart batteries is that they are manufactured in such volume that they are a very good value in a deep cycle battery. Because there are fewer 12 VDC batteries of the same quality, they are more expensive per amp-hr.
The question confuses two issues. SOC and its related resting voltage, which we try to stay above 50% etc. But when at 50% and you run the microwave so voltage drops into the low 11s, this is not a battery-killer.
The inverter will alarm at 11v but keep running the appliance until voltage sags to 10.5. If you don't mind the screaming alarm while you finish what you are doing! This still isn't the same thing as "going below 50% before recharging." That is because when you finish with the inverter job, the voltage bounces back to go with the SOC near 50%.
Now the other thing that arises is whether 6v have more of a voltage sag under load than 12s, so 12s will go down more in SOC before the inverter alarm goes off. There is some evidence in favour of 12s for that situation, but the difference does not matter.
I find that with four 6s I can run the microwave on inverter at 50% SOC and voltage stays over 11 so it does not alarm. However when doing that with only a pair of 6s, SOC has to be above 75% to not alarm off. So now we are looking at battery bank ah capacity needed to keep the voltage from sagging below 11 at 50% SOC.
I was able to do that ok with a bank of three 27s at approx 330ah so the real story is you can get away with three 12s but need four 6s (but only because you can't have three 6s) and two of either isn't enough.
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Everything will operate down to 10.5 volts... some things a bit lower.
But that will be 100% discharged and a bit hard on the battery.
IMO for full timers 12.2 12.3 is about minimum for long battery life. For part time use 11.6 11.8 is plenty low and very important to get a 100% tip top charge before storage. These are voltages under moderate load.
YMMV. Maintaining higher voltage is always better when possible.
It all depends on what is the safe voltage of discharge of each battery and the shut down point of my fridge.
At this level the difference is small and conceptual for me. My TT came with a grp 27 95 ah battery that I will bank with a match. That will be double my needs on a bad day.
450 watts of solar should be able to replace what we use even in less than idea conditions. The Champion will take over if it can't.
I would get 6v GC jars if I had to replace both but only because of the longevity vs cost. I've thought about 3 12v but for the added cost and tongue weight I don't get much benefit unless the solar goes down.
* This post was
edited 05/06/12 03:28pm by JiminDenver *
Radiated 2 hours 600 RADS, no radiation at present time.
When did the alarm go off? When should it have gone off?
That's what the thread is about, is it not?
Remember Chernobyl? A long line of volunteers was formed to shovel chunks of irradiated graphite off the roof of adjacent reactor buildings that were still functioning. The drill gave one man a shovel at a time. He raced out into 600 RADS/hr radiation (think of it as say a 400 amp draw on a battery bank) shoveled one single chunk onto the shovel, raced to the edge of the building, dropped it over the side, then raced to the lead-lined door, was admitted then bussed off the property forever. The hero that absorbed 600 RADS/hr for hours sitting on the edge of the blowout, got radiated so badly his skin turned to leather and they buried him in a lead casket. This parallel is designed as a corollary of battery DAMAGE not discharge DAMAGE! to the amplitude of discharge, and length of time in a discharged state. To wit: How many negative amp hours from full charge have accumulated OVER WHAT TOTAL SPAN OF TIME. Think of it another way, when would you, personally, have an alarm sound? How much hysteresis, to be built in? How would you construct your algorithm? Remember, we are talking about alarm not merely singular digital data.
If there are any techhies out there that want to blow this around a bit, please PM me.