In my camper van, I currently have a full Victron 12V setup, designed for high current draws, mainly for my MultiPlus-II 12/3000/120-32. Currently, I have two AGM Super Cycle 12V/170Ah batteries connected in parallel, giving me a battery bank of 340Ah.
When designing the setup, I thought that one day, I will upgrade the batteries to two or maybe three Superpack 12 V 100 Ah - High Current. Those are capable of continuous 100A discharge each, which means that with only two batteries in parallel, I could draw 200A, aka roughly 2400W through my MultiPlus, giving me the ability to safely use an induction cooktop or other larger appliances. With three batteries I could even theoretically draw 300A, even tho 250A is the max my MultiPlus would ever need.
Now my question is the following. What kind of current can I continuously draw from the AGM setup I have now installed in the van ? When I say continuously, I mean for about 20-30min, the time to cook for example. I understand that higher current draws decrease the number of life cycles you are able to get out of your batteries. But taking that apart, what can I actually draw from my setup ? Are we talking 70A max or are we talking 140A max or can I even safely draw 200A ?
I would rather use my actual setup with an appropriate induction cooktop, than change perfectly fine working batteries for no reason if I can draw appropriate current from them.
These batteries are rated for CCA of 600A, so parallel would be 1200A, but this will be limited by the wiring. How long you can draw this current for depends on the state of charge of the battery.
Drawing 250 - 300A from the pair for 30min would give a discharge of ~150Ah, Due to the Pukert coefficient, your batteries capacity at this current will be limited - the 170Ah is at c/20, this discharge is ~1C. Capacity is likely to be~100Ah at that current, so you will be discharging say 150/200Ah. (75%).
Use your existing batteries until they fail, then upgrade.
Where and how did you find the info of the CCA of 600A ? Been looking for that kind of numbers and never found it… Obviously my wiring is set up for the 250-300A of continuous current that the MultiPlus can handle. And I get that the battery works the longer when fully charged
But, as I understand it, Cold Cranking Amps refers to the amount of electrical current a battery can deliver at 0°F (-17.8°C) for 30 seconds, which has little to do with continuous discharge. Mathematically we could calculate anything, such as how the battery could be drained in half a minute, integrating the Pukert effect and telling us what the amperage should be to do so… But in the real world, those batteries have physical limitations due to internal components, the chemistry used, etc. I guess there should be a way to calculate a max current output, just as the lithium ones gives us, instead of CCA which is little to useless to my usage ?
Also, when you say to use them until they fail… how exactly are they supposed to fail ? Would rather avoid a fire or an explosion
CCA is published in the battery data sheet. I found that on the Victron website.
CCa indicates the max current the battery can sustain without damage, ie buckling of the plates & thermal distortion. This is somewhat temperature dependent, but the CCA rating is that normally used for limiting current.
Use until fail: Normally, the capacity degrades below a useful level before there is any danger of explosion.Typical hard fail mode is a cell goes short circuit internally, and the rest of the battery gets warm and gasses off during charging, terminal voltage is low - i.e.12V instead of 14.4 on full charge.
