Battle Born Lithium

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I think we have had this discussion previously - a gel battery is a lead acid battery where the sulfuric acid electrolyte is absorbed into SiO2 powder. I am not sure how an 'SiO2' battery differs from this, besides marketing?

Gel/AGM/SiO2 are all valve regulated lead acid batteries (VRLA, ie sealed) so I guess you could claim they are all modified versions of each other.

A higher quality AGM like Odyssey/Northstar have internal resistance around 2-3 mOhms, cheaper ones like Renogy are around 4-5 mOhms. LiFePO4 (eg Lithionics) are at about 3 mOhms. In these cases you will have 30 - 60% lower voltage drop under load.

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Gel electrolyte batteries typically have a higher internal resistance than AGMs, so you would expect 'SiO2' batteries to have a higher internal resistance and higher voltage drop under load. Furthermore, the internal resistance rises as the SOC decreases (all batteries) and lead acid voltage decreases rapidly with decreasing SOC, leading to the shutdowns you are seeing.

LiFePO4 has a lower internal resistance to start with (although the BMS can add some resistance), higher starting voltage and very little decrease of voltage with decreasing SOC, making it better suited to high load situations.

There seems to be more to different battery types and inverter alarming than I realized.

Li has a flat internal resistance curve on discharge and voltage stays up (so no alarm) while lead acid batts have a linear increase in internal resistance as SOC goes down along with dropping voltage (so it alarms) I don't know what SiO2 is like in comparison (yet).

Meanwhile, Mr Wiz recently posted that his inverter pulls fewer amps running his MW at 75% SOC than it does at 95% SOC with his AGM (lead acid), BUT--the usual story is that the inverter will draw more amps as voltage drops in order to maintain the watts. He has a PSW inverter.

There might be something there between MSW and PSW for how they act, don't know (yet) Or something I have not noticed in how mine acts (same model of inverter, but with Wet 6s)

The usual story is that more AH bank means lower internal resistance, so you can do same MW down to a lower SOC with a bigger bank before it alarms.

In my SiO2 test, I ran the battery down with a nearly continuous 65% draw, and the inverter alarmed at 11.1 volts with SOC 60% (measured later as resting voltage) . What I did not test for, and perhaps makes a difference, is intermittent shorter time high draws where the battery can recover after each episode. More like real life camping. That might let you get farther down in SOC, don't know ( have to wait for some real life camping to learn that)

Anyway, there seems to be more to all this than I have always thought.

As interesting of a test that may be all my testing is done in real life in a day to day living off the system, besides the 3000w inverter might react badly trying to pull a load that large.

The largest loads that I have used are 200-235a nearing 2,900w and that is only because we forget at times that we're boondocking.

Looking back through my notes.... this was making the pot of coffee, using the microwave, humidifier, laptop/ phone/ phone booster plugged in.

37% SOC, lfp bank 12.65v, inverting 12.2v (235a)

Or this one at a higher SOC.

72% SOC, lfp bank 12.92v, inverting 12.5v (231a)

We're going into our 5th winter season of boondocking which is what really exercises the SOC range or should I call it the partial SOC range with lows of 25% to 90% for weeks at a time before either solar catches up or a boost charge from the generator is needed, 2 hours of run time to put 200ah in. ;)

Itinerant said he can run his MW down to 30% SOC, but note his bank of Li batts is 500AH. If his MW causes a draw of 150 amps that is a 30% draw.

I have a single 100AH SiO2 and a draw of 65 amps that sets the inverter alarm off 11.1 volts at 60% SOC, but note that is a 65% draw.

I don't know the relative abilities of Li and Si for sustained high draw, but the comparison should be at the same percentage of draw in amps per 100AH of bank. At 500AH bank 65% would be 325 amps.

So all Itinerant has to do as a little test, so we know more about Li, ie, get the 500AH bank full and then run a load of 325 amps for 37 minutes straight. If the inverter has not yet alarmed, keep going until it does!

"Usable" for that level of work might be more with the Li with its flatter voltage curve over that range of SOC, so it might even get to as low an SOC as is prudent before the inverter alarms.

We have lots of popcorn to sustain us while he reports in from time to time on how the test is going. :)

BFL13 wrote:
Gottaluv "usable"! My wiring etc has my SiO2 set off the inverter alarm when it gets down to 60% SOC running the MW. That means I have another 40% of SOC down to say 20% I can't use for the MW.

I can still run lights etc farther down in SOC below 60%, but it is not "usable" below that for MW work.

I might be able to improve that a bit with better wiring, but not much.

Same thing with Wet 6s really. Can run the MW with one pair of 6s down to 75%. Needs a second pair to run it while down to 50%. So what does "usable" mean? It Depends! :)

Consider a Panasonic inverter microwave to use the lower settings that get down to about 500 watts.

Itinerant11,

That's a nice feature.

One thing that I do when I have had hookups is turn the inverter charger to standby so all charging is done by solar. I'll let the batteries carry the minimum 12v DC loads and the 120 AC passes through to the entire 5th wheel. The inverter is set to standby incase there was a 120v power lose in the campground.