Brent S
Top Poster
I just got these mini LED’s too. A 30pack for 10.00. Again, amazon is awesome. I’m starting to feel like I should be getting paid endorsements from them 
Lithium Solar Power!
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TexasFreedom
A True Doomsday Prepper
That's what I've been trying to say. As I said, I think we were talking past each other. A little detail, after the 'rated' cycles, it's not that it 'starts to wear out'. I'm not sure how they rate it, but I suspect at that point the battery might have 25% of capacity left, at most 50%, or maybe only 10%. But the premise is that it's "useful life" is over. But assume 25%. So your example, a 100a-hr battery rated 80% for 500 cycles. Roughly assuming the degrading is linear, after 250 cycles, the battery will only have 5/8ths its original capacity. So at that point 'fully charged' will be 62.5 a-hr. An important point, "80%" then will only be 50 a-hrs. After all it would be impossible to get 80 a-hrs out of a battery only able to hold 62.5 a-hrs.
Are we now saying the same thing?
Yes, that capacity slowly decreases over time. So that you will only get 100 amp hours from a new battery, and that capacity will diminish over time. Same thing with the lithium battery in my phone. It only has 5000 miliamp hours of capacity when it's new. And every time it goes through a discharge/charge cycle that is degraded somewhat.
Here is a chart showing the relationship between voltage and remaining capacity of lead acid batteries. The voltage is for batteries that have been at rest for 3 hours. I have a meter that will tell me DC amp hours used. So I need to test my batteries, which are all several years old, and see how many actual amp hours I get before the battery falls to the 50% voltage level. Then multiply by two and that should tell me how many total amp hours the battery will actually deliver.
But there is a Catch-22: Obviously I need to discharge at the appropriate 20 hour rate, but then if the capacity is degraded, I don't really know what the 20 hour rate is until I determine the capacity by testing it at the 20 hour rate.
Here is a chart showing the relationship between voltage and remaining capacity of lead acid batteries. The voltage is for batteries that have been at rest for 3 hours. I have a meter that will tell me DC amp hours used. So I need to test my batteries, which are all several years old, and see how many actual amp hours I get before the battery falls to the 50% voltage level. Then multiply by two and that should tell me how many total amp hours the battery will actually deliver.
But there is a Catch-22: Obviously I need to discharge at the appropriate 20 hour rate, but then if the capacity is degraded, I don't really know what the 20 hour rate is until I determine the capacity by testing it at the 20 hour rate.
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And BTW, SoC (State of Charge) is simply 100%-DoD (Depth of Discharge) So if the first column were DoD instead of SoC, the top number would be 0% and the bottom number would be 100%.
Those say 30 amps, I hope you got some with a MUCH MUCH higher current rating! Minimum for your setup would be 150 amps if you have one on each battery, or 300 amps if you only have one for both batteries.
Brent S
Top Poster
That’s not for the primary line to the camper. I am putting fuses everywhere! I’ve seen what a shorted battery is capable of. I’ve even welded with a 12v battery before. (Just to see if it could really be done).
Shorted one today...
And right on the bolt threads too. I had to file the bolt threads down to get the nut off.
I discovered that the chart doesn't work for AGMs, not even close.
I let a 125 amp hour battery rest for 3 hours, then ran it at 54 amps until the meter said I had used 25 amp hours. Then let it rest and measured the voltage again. Starting voltage was 13.2, final voltage was 12.8 - SoC of over 100% according to the chart after running 25 amp hours off of it.
And right on the bolt threads too. I had to file the bolt threads down to get the nut off.
I discovered that the chart doesn't work for AGMs, not even close.
I let a 125 amp hour battery rest for 3 hours, then ran it at 54 amps until the meter said I had used 25 amp hours. Then let it rest and measured the voltage again. Starting voltage was 13.2, final voltage was 12.8 - SoC of over 100% according to the chart after running 25 amp hours off of it.
TexasFreedom
A True Doomsday Prepper
Doc,
OK, there are other factors. That chart is at a certain environment, change temperature & it changes.
Another way to check your level is to do a partial discharge. So fully charge the battery. I like to run a light load just to knock the 'overcharge' off the battery. Let's say it's a 12v / 150 a-hr battery. Run a 10 amp load for an hour. Let the battery sit a few hours. BTW, this test must be done in a constant-conditions environment (inside the house?). Measure the voltage (V1). Now run a 10% load for 2 hours. In this case, that is a 15 amp load. You could run a 5% load for 4 hours, but you want a total of about 20% of the rated capacity. Make sure it is a constant-load. Let's say you run lights, measure the current a minute after you start, and again 10 minutes later, and again 10 minutes later, just to make sure it's constant. Remove the load and wait a couple more hours. Measure the voltage again (V2).
The nice thing is that this test is fairly independent of a number of variables. Use your table above. See where V1 and V2 sit on your table. If this battery has full capacity, you would see a proper 20% degradation. But if you see a 30% degradation, that means your battery's capacity is only 2/3rds of its original capacity (100 a-hr, not 150 a-hr).
As a battery degrades, it's top voltage drops. So on your chart, a 'new' battery will be 12.7, but if that battery is degraded to 70%, it's max voltage will be 12.32v.
OK, there are other factors. That chart is at a certain environment, change temperature & it changes.
Another way to check your level is to do a partial discharge. So fully charge the battery. I like to run a light load just to knock the 'overcharge' off the battery. Let's say it's a 12v / 150 a-hr battery. Run a 10 amp load for an hour. Let the battery sit a few hours. BTW, this test must be done in a constant-conditions environment (inside the house?). Measure the voltage (V1). Now run a 10% load for 2 hours. In this case, that is a 15 amp load. You could run a 5% load for 4 hours, but you want a total of about 20% of the rated capacity. Make sure it is a constant-load. Let's say you run lights, measure the current a minute after you start, and again 10 minutes later, and again 10 minutes later, just to make sure it's constant. Remove the load and wait a couple more hours. Measure the voltage again (V2).
The nice thing is that this test is fairly independent of a number of variables. Use your table above. See where V1 and V2 sit on your table. If this battery has full capacity, you would see a proper 20% degradation. But if you see a 30% degradation, that means your battery's capacity is only 2/3rds of its original capacity (100 a-hr, not 150 a-hr).
As a battery degrades, it's top voltage drops. So on your chart, a 'new' battery will be 12.7, but if that battery is degraded to 70%, it's max voltage will be 12.32v.
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