Float of LFP

[JustMurph]

Easy answer, because, as noted by Erik in his article, very little of the charging equipment on the market is capable of managing the batteries in the way he recommends. Add that most BMSs use passive cell balancers that often require higher charge voltages.

I did just note that the latest firmware for my victron MPPTs finally lets me set the absorption time to less than 1 hour and use tail current to end that phase.

[sailingharry]

Originally Posted by JustMurph

if I swapped from this charging regime to what's recommended by Erik, how much does my battery life increase by? Do I go from 3000 cycles to 4000 cycles? 6000? That's what I want to know. Keen to hear if anyone has that data, either studies or real life experience.

We had the same issue with lead, in all its incarnations. My boat came with AGM of unknown condition. I seem to recall a date stamp around 2015. We've had the boat 5 years, and about 2 years ago, stopped stressing about 100% SOC 3 times a week. Before that, I stressed a lot and ran the engine a lot. I decided that LFP was "on the horizon" (but like sunsets at sea, every day the sun is just as far away....), and the batteries were old, and so who cares. Well, two years later, they are still doing their job. I do intend to do a capacity test this fall, unless I pull the LFP trigger instead (or maybe as a result!).

My point is, we "know" that AGM "hate" if they don't get a 100% SOC every day or two. But how much do they hate it? Same as the 50% rule -- how much does it hurt? If I buy 800Ah and run it down to 400 (50%), compared to buying 600 and running it down to 200 (30%) -- I pay 30% more for the 800, do I get 30% more life? Even if I got 40% more life, the smaller cheaper 600Ah battery might still be a better deal. Or if I I wake up at 50% and know I'll be on shore power tonight, should I run the engine just to charge, or just pull down another 20%. But no one knows!

[barcoMeCasa]

Originally Posted by JustMurph

Easy answer, because, as noted by Erik in his article, very little of the charging equipment on the market is capable of managing the batteries in the way he recommends. Add that most BMSs use passive cell balancers that often require higher charge voltages.

I did just note that the latest firmware for my victron MPPTs finally lets me set the absorption time to less than 1 hour and use tail current to end that phase.

Can most mppt solar regs really not be set to stop bulk at a voltage? Easy with victron. Why bother with any absorption time if on solar?

Not sure about BMS, quick google suggested not a problem balancing at lower voltages but maybe that was just active. can't see how they would need to "overcharge by either holding the batteries at an absorption voltage, or a float voltage that is higher than recommended" like you said.

I´ve not balanced this year & worst cells still within 17mV, do they really need balancing every single cycle?

[JustMurph]

Until this update, there was no choice, you were getting 1 hour of absorption time. Default on the lithium profile is 2, which is ridiculous.

Not all BMSs are configurable, for example the ones in my batteries. It was noted earlier they start balancing at 28V, so I do need to charge over that to ensure they balance. Do I need to balance daily, no. Is that something I want to actively manage, no. I want set and forget.

I completely agree that charging profiles in current products don't cut it, my question is, how much does it really matter?

[barcoMeCasa]

Originally Posted by JustMurph

Until this update, there was no choice, you were getting 1 hour of absorption time. Default on the lithium profile is 2, which is ridiculous.

Not all BMSs are configurable, for example the ones in my batteries. It was noted earlier they start balancing at 28V, so I do need to charge over that to ensure they balance. Do I need to balance daily, no. Is that something I want to actively manage, no. I want set and forget.

I completely agree that charging profiles in current products don't cut it, my question is, how much does it really matter?

OK, I´m more than happy with my "treat them gently" setup so stopped looking.
"Until this update, there was no choice, you were getting 1 hour of absorption time." victron smasrtsolar? Absorption time has always been configurable since I've fitted mine. Enable expert mode to get at it.

[s/v Jedi]

People asked me for the settings in expert mode. See attached screenshot. This is a 24V battery and it’s the “storage mode” settings, i.e. low absorption voltage.

As you can see, I use a fixed absorption time of 30 minutes. For my normal absorption voltage, this 30 minutes gets me to the soc% where I want to stop charging (>98%)

Also, I don’t use tail current. You can’t use that when you are also consuming power: only part of the current from the moot goes to the battery.

[barcoMeCasa]

Originally Posted by s/v Jedi

Also, I don’t use tail current. You can’t use that when you are also consuming power: only part of the current from the moot goes to the battery.

Which is good point for anyone installing, well worth using victron smartshunt or the bmv with bluetooth (or get the ve direct adaptor) , smartsolar regulators can talk to the shunt & make decisions based on what's going on at the battery, not the output of the regulator. tail current maybe not such a big deal with lithium but makes big difference in actually getting lead acid really charged all the way. Same here, I don't bother with tail current
Just stuck a fluke meter on mine, even with just 2.1a going in from the early morning sun the voltage at the regulator reads 13.56v but the regulator knows it's 13.34v at the batteries & works from that. That's with 2.5mm² cable. The voltage the smartsolar use do seem to drift around a tiny bit from the shunt though from logging data, they aren't bang on tightly coupled.

[rslifkin]

Originally Posted by s/v Jedi

Also, I don’t use tail current. You can’t use that when you are also consuming power: only part of the current from the moot goes to the battery.

As mentioned by another poster, if you've got a Victron GX device in the system and it has a shunt connected (or battery current data from a connected BMS) and you enable DVCC and Shared Current Sense, it accounts for loads. The MPTTs get info on actual battery current from the GX device.



I haven't gone LFP yet, but I'm using a setup as described above with my AGMs. The MPPTs reliably drop to float when the batteries are down to the target current acceptance regardless of load.

[s/v Jedi]

Originally Posted by barcoMeCasa

Which is good point for anyone installing, well worth using victron smartshunt or the bmv with bluetooth (or get the ve direct adaptor) , smartsolar regulators can talk to the shunt & make decisions based on what's going on at the battery, not the output of the regulator. tail current maybe not such a big deal with lithium but makes big difference in actually getting lead acid really charged all the way. Same here, I don't bother with tail current
Just stuck a fluke meter on mine, even with just 2.1a going in from the early morning sun the voltage at the regulator reads 13.56v but the regulator knows it's 13.34v at the batteries & works from that. That's with 2.5mm² cable. The voltage the smartsolar use do seem to drift around a tiny bit from the shunt though from logging data, they aren't bang on tightly coupled.

Originally Posted by rslifkin

As mentioned by another poster, if you've got a Victron GX device in the system and it has a shunt connected (or battery current data from a connected BMS) and you enable DVCC and Shared Current Sense, it accounts for loads. The MPTTs get info on actual battery current from the GX device.

I haven't gone LFP yet, but I'm using a setup as described above with my AGMs. The MPPTs reliably drop to float when the batteries are down to the target current acceptance regardless of load.

Indeed, there are two methods that I know to get accurate data to the MPPT: DVCC via a GX device or the Bluetooth smart networking. In both cases the data is sourced from a BMV or SmartShunt. There’s a SmartSense but that doesn’t have current measurement.

[barcoMeCasa]

Originally Posted by rslifkin

As mentioned by another poster, if you've got a Victron GX device in the system and it has a shunt connected (or battery current data from a connected BMS) and you enable DVCC and Shared Current Sense, it accounts for loads. The MPTTs get info on actual battery current from the GX device.



I haven't gone LFP yet, but I'm using a setup as described above with my AGMs. The MPPTs reliably drop to float when the batteries are down to the target current acceptance regardless of load.

Very good thing imho to keep posting this info, how often to you hear "I'm fully charged before lunch cos my regs have gone into float".. where in fact it's their fridges & laptops that have been charged..

[barcoMeCasa]

Going back to this post...https://www.cruisersforum.com/forums...ml#post3836281
today was a good solar day, smartshunt read 51.6% at sunset, might be back full soon...
So.. much guesswork & assumptions here but assuming the smartshunt undereads energy going back in each day by about 0.7% then "full" with voltage going up the knee looks like it might be around 56%, 78.2% was the last "full" reading 30 days ago so tomorrow would be 78.2 minus 31 days of loosing 0.7%, might hit it tomorrow if the sun & wind are similar!
(smartshunt efficiency set to 100% & peukerts set to 1)

Or not, really don't know & probably no one is interested anyway but maybe someone is & only takes a moment to share some data.
Place your bets gentlemen, what SOC reading will the top knee @ 13.8v be after a month not resetting the smartshunt? ..

[CaptainRivet]

On my and a buddies boat who have an Electrodacus BMS which measures SOC as accurate as BMV it depends how big your bank is...around 500AH around 95%, on a 1088AH around 98%SOC.

[wholybee]

Originally Posted by barcoMeCasa

Going back to this post...https://www.cruisersforum.com/forums...ml#post3836281
today was a good solar day, smartshunt read 51.6% at sunset, might be back full soon...
So.. much guesswork & assumptions here but assuming the smartshunt undereads energy going back in each day by about 0.7% then "full" with voltage going up the knee looks like it might be around 56%, 78.2% was the last "full" reading 30 days ago so tomorrow would be 78.2 minus 31 days of loosing 0.7%, might hit it tomorrow if the sun & wind are similar!
(smartshunt efficiency set to 100% & peukerts set to 1)

Or not, really don't know & probably no one is interested anyway but maybe someone is & only takes a moment to share some data.
Place your bets gentlemen, what SOC reading will the top knee @ 13.8v be after a month not resetting the smartshunt? ..

I'm not placing bets, the an LFP is not 100% efficient, nor is peukerts 1. So I would not expect a smartshunt to be accurate if that is how you set it up. It would be closer at 99% and 1.03 or 1.04.

That is close enough to 100% that many just leave it be. But over the course of time it does add up.

[barcoMeCasa]

Originally Posted by wholybee

I'm not placing bets, the an LFP is not 100% efficient, nor is peukerts 1. So I would not expect a smartshunt to be accurate if that is how you set it up. It would be closer at 99% and 1.03 or 1.04.

That is close enough to 100% that many just leave it be. But over the course of time it does add up.

Isn't that going to wrong way based on the data?

Assuming hitting the 13.8v up the knee a bit as a reliable data point for SOC (seems to be) if the smartshunt SOC isn't reset it gets lower every day. It thinks less energy is going back in and/or more energy is going out than there really is.
Will need to have a look but istm even if your generic figures are close to the mark the victron still gets it wrong and low set to 100% & peukert at 1.
Bit unsure about Peukert, discharge setting it above 1 will likely make things worse but google/google scholar didn't come up with much useful info regarding peukert when charging. Setting efficiency to less than 100% will make the error worse as well afaics.
Testing required to confirm this.
Haven't found a way to tune this out so if the daily incremental in the victron SOC can be manually tuned out reliably a bit then that would be a nice thing

[barcoMeCasa]

very happy to be wrong here, no idea how the smartshunt deals with peukerts, set it from 1 to 1.5 then back to 1 the smartshunt resets the soc instantly way higher then back again..


Thought I'd played around of both these settings to unsuccessfully try to tune out the error but obviously need to have another go
Still can't see how less efficiency would reduce the error but as the average discharge rate is far below the c rate can see now how it could work to reduce the error. Thnx