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Open Roads Forum  >  Tech Issues

 > Battery Type and Inverter Alarm

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BFL13

Victoria, BC

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Posted: 10/31/20 05:40pm Link  |  Quote  |  Print  |  Notify Moderator

Testing to compare with Mr Wiz's results and the Li performance with its lower IR (assuming that 3 is for 100AH at 77F)

FWC wrote:
"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"

100AH Stark AGM - 5 mOhms
100AH SiO2- =< 6.8 MOhms (when full at 77F)
? AH Li 3 mOhms

Mr Wiz wrote:

"200 ampHr Deka AGM, will handle my MW, around 1165 input Watts, 700 cooking Watts,
Amps/Watts draw varies with battery SOC
Early morning with a 75% soc around 88 amps,
But with a full charge load draw is 96 ? 101 amps , 2000w PSW inverter"

My test with my zoo of wiring and the Wet 6s: (same inverter as Mr Wiz and 800w cooking MW)

460AH full, 108amp draw-- 0.9v drop = 0.9/108 = 8.3mOhms
230AH full, 103 amp draw--1.4v drop = 1.4/103 = 13.6 mOhms

230AH at 81% SOC, amp draw initial 89amps quick drop to 83 then rapid climb to 101 amps at the end of 2 minutes. Voltage drop 1.4v same.

81%= 186AH so 1.4/89 = 15.7 mOhms so higher than the full at 13.6, which is how it should be.

So that was different from how it acted when the battery was full, as Mr Wiz noted. I don't know if he waited two minutes to see what happened next though, or why it did that.

Don't know how much of that R is IR. ISTR a pair of 6s would be 10, so 3.6 for wiring? WAG.

On more AH = less IR, confirmed with above for the Wet 6s, and that Stark 100AH AGM at 5 mOhms compares with an 8D 250AH AGM at 2 mOhms.

* This post was last edited 10/31/20 06:21pm by BFL13 *   View edit history


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pianotuna

Regina, SK, Canada

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Posted: 11/01/20 08:46am Link  |  Quote  |  Print  |  Notify Moderator

If resistance is low in Li chemistries then why is the safe rate of continuous discharge typically 1C?

Rate of continuous discharge on the SiO2 is well over 3C.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

BFL13

Victoria, BC

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Posted: 11/01/20 09:10am Link  |  Quote  |  Print  |  Notify Moderator

Must not be all about internal resistance then.

Another thing is how Wets discharge and recharge at the same rate with 25% max recommended to give the chemistry time to act same time each way.

But the SiO2 and Li have way higher discharge rates allowed than their recharge rates allowed. With Si, I am guessing it can de-crystallize way faster than it can crystallize? No idea with Li.

FWC

The Wilderness

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Posted: 11/01/20 09:30am Link  |  Quote  |  Print  |  Notify Moderator

The 1C rate is typically a BMS limit. The intrinsic discharge rate is dependent on the cell design but can range from 5C to 50C, continuous.

pianotuna wrote:

If resistance is low in Li chemistries then why is the safe rate of continuous discharge typically 1C?

Rate of continuous discharge on the SiO2 is well over 3C.


time2roll

Southern California

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Posted: 11/01/20 09:35am Link  |  Quote  |  Print  |  Notify Moderator

If you need increased amps just get more batteries.


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BFL13

Victoria, BC

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Posted: 11/01/20 09:40am Link  |  Quote  |  Print  |  Notify Moderator

My theory on crystallizing and de-crystallizing speeds seems to be shot down here.

I don't really understand about termination voltages wrt discharge current rates as explained here. Perhaps there is a similar table for Li, and the answer to PT's question might be in any differences between them?

https://www.gliderpilotshop.com/lead_crystal

pianotuna

Regina, SK, Canada

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Posted: 11/01/20 09:41am Link  |  Quote  |  Print  |  Notify Moderator

Hmmm get more batteries is fine if you have deep pockets.

3.5 c from a 100 amp-hour SiO2 vs 1 c from 3 Li is $450 =< $2700

2oldman

south

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Posted: 11/01/20 10:29am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Rate of continuous discharge on the SiO2 is well over 3C.
Not that you'd ever need that. The battery may be capable of it but what about the wires and connectors?

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