Cycle Life - Is time a factor?

[snoobler]

Thanks for the config summary very useful!


Yeah, but I'm wondering what "100% - 80%" means for battery health in the context of degraded batteries and a calibrated scale. I guess I'm doing the best I possibly can for them, save for not using them at all!

I was also thinking....given my batteries are starter batteries, do you think it's possible that my batteries aren't actually degraded

No. A year's worth of use would degrade any lead-acid battery, deep cycle, starter, FLA, AGM, Gel, etc.

, but should be derated for solar cycle usage? I.e. 80Ah is only applicable in the context of starting an engine. Just a thought.

Probably, but derating translates to actually utilizing them less, i.e., lower currents and lower rates of discharge/charge, not just a capacity derating.

 

[jt_retro]

No. A year's worth of use would degrade any lead-acid battery, deep cycle, starter, FLA, AGM, Gel, etc

Sorry, what I meant, was that is it possible that the full derating amount isn't wholly attributable to my use (ie some/most of the derating value is due to them being starter batteries used in another context)

I've set my Ah to 336Ah (30% derate), and so far things are looking good. I'm basing this on seeing the tail current after some charging in conjunction with a SOC in the high 90s. But I'll post back when I get some more data.

 

[snoobler]

Sorry, what I meant, was that is it possible that the full derating amount isn't wholly attributable to my use (ie some/most of the derating value is due to them being starter batteries used in another context)

No. Capacity ratings are still C20, and Peukert should be about the same.

I've set my Ah to 336Ah (30% derate), and so far things are looking good. I'm basing this on seeing the tail current after some charging in conjunction with a SOC in the high 90s. But I'll post back when I get some more data.

If possible, it's probably worth taking the system offline for about 4 hours to see if resting voltage correlates to %SoC.

 

[jt_retro]

Ok I think I understand: When my batteries were new, I would have been able to draw C/20. But, because these are starter batteries and not deep cycle, they are not good at C/20 and other slow+steady currents and as such, this is why I'm seeing more degradation than I would otherwise with deep cycle batteries.

Does that sound about right?

Hopefully once I've figured out a good calibration with the BMV, I'll be able to see my true SOC and minimise too much more damage by staying above 80%

 

[jt_retro]

@snoobler ok I've set my Ah to 300 and this is what I've got this evening



Do you think this is acceptable? I left the bank for a good long adsorption charge throughout the afternoon and saw 12.8v after that. I haven't had the opportunity to do any at rest testing though.

I'm really unsure what % soc correlates to what voltage for my bank. Incidentally my bank is sitting at 12.1C right now temperature wise, so I'm not sure if today's causing the voltage to read a bit lower.

Reducing the Ah to 200 right now makes the BMV show 73%. That's seems like a very extreme derate though?!

Cheers

JT

 

[snoobler]

You're likely between 70-75% SoC. The small drain might push it to 75-80% once removed, BUT as you pointed out, temp influences it. Default is 25°C, so there should be some efficiency losses.

Given the temp, you're likely within 5-10% of actual.

 

[jt_retro]

Thanks

In the past, I have tested removing the small drain (inverter standby, btw) and the voltage increases by about 0.1V.

In your opinion, where should I set my Ah at for a reasonable reading? Setting at 250Ah gives 80%.

 

[snoobler]

I'd leave it where it is and start logging snapshots to see how it changes over time. Record SoC, current, voltage and temp. Shoot for the typical low ~1A draw.

 

[jt_retro]

@snoobler here is a reading at the start of the night this evening. Ah is set to 300 (left alone as suggested). Temp is 15.2C


I think it's safe to assume that the voltage would be 12.56V if I removed the small load. Would that line up with 89% in your opinion?

Ooc, what voltages/ voltage ranges do you personally use as a rule of thumb when estimating SOC? I see lots of different numbers online.

Thanks!

 

[Hedges]

"I have 6 x 80AH 12V AGM batteries in parallel."

Are you ever getting these up to proper absorption voltage, and holding it there for specified time?
That is what it will take to recharge. 12.46V or 12.8V won't do it.

 

[snoobler]

@snoobler here is a reading at the start of the night this evening. Ah is set to 300 (left alone as suggested). Temp is 15.2C

View attachment 47089
I think it's safe to assume that the voltage would be 12.56V if I removed the small load. Would that line up with 89% in your opinion?

Ooc, what voltages/ voltage ranges do you personally use as a rule of thumb when estimating SOC? I see lots of different numbers online.

Thanks!

Same answer as before. It's more accurate than it was. You have a more realistic baseline and should start logging the prescribed data on a weekly/monthly/whatever basis.

The only way to determine this is to conduct a full discharge test of your bank to determine how much of the 480Ah capacity it has.

"I have 6 x 80AH 12V AGM batteries in parallel."

Are you ever getting these up to proper absorption voltage, and holding it there for specified time?
That is what it will take to recharge. 12.46V or 12.8V won't do it.

We discussed that extensively on page 1.

 

[jt_retro]

Thanks Snoobler. Do you have any advice as to which voltage values I should use to determine estimated SOC?

Thanks!

 

[snoobler]

Lacking a battery model specific resource:



To state it clearly, I don't think you should do anything but use the system and periodically log SoC, voltage, current and temp. Regardless of the values, they can be the basis for identifying trends. If you notice that in two weeks, you're seeing a lower voltage for the same SoC, current and temp, you know your batteries are deteriorating.

We've confirmed that you're able to fully charge the battery @ the absorption voltage, and we've tweaked the BMV to correctly acknowledge a full charge. Those changes plus the reduction in programmed capacity and performance indicates that the SoC % is vastly more accurate than before.

If they really only have 300Ah, your batteries are likely at end of life in terms of their available capacity, and it's all downhill from here. The only remaining question is WHEN you need to replace them.