Battery voltage between 13.6 - 14.4 concidered fully charged?

[teddysx3]

Hello everyone,

I'm curious about these voltages 13.6-14.4. My charges is set to 14.4 to charge bulk/absorb and 13.6 float.

I have hooked up 3 batteries in parallel, before connecting them I charged all of them to 14.4, and left them to rest 1-2 days. These were their voltages before connecting them - 13.25, 13.25 13.49. Is the 13.49 a little too off?

Anyway when I connected them they gave a 13.33 avarage which I think is ok. I charged it to 14.4.

What I see is when I leave the float to drop to 13.6 while the charger is connected and floating, it drops much faster to 13.6 from 14.4 then If I charge it to 14.4 and right when the charger goes to float turn off the charger. After the charger is off and have not waited for the charger to bring it down to 13.6, I see that the voltage drops much slower when not waiting for the float to drop it, is this normal? Actually I'm not sure if it will ever drop to 13.6, if not left on the float setting to make it drop, correct?

Is anywhere from 13.6-14.4 voltage concidered fully charged? And I should not worry that the battery bank is not at 13.6, instead at 14.07 like at the moment?

Thanks.

 

[MichaelK]

You are confusing charging voltage with battery voltage. Because of the laws of physics, a battery can never charge at it's voltage potential, it must be charged at greater than it's final potential. Perhaps potential is not the technically proper word.

For a lead-acid battery, it's charging at 14.4V, but once fully charged, the resting voltage of the battery itself will drop back down to about ~12.7V. This depends on battery chemistry, and other factors like ambient temperature. Li has a more flat voltage curve, so voltage is not as good an indicator of charge as for lead-acid. BTW, for lead-acid, even voltage is only considered a mediocre why of determining charge state.

 

[teddysx3]

You are confusing charging voltage with battery voltage. Because of the laws of physics, a battery can never charge at it's voltage potential, it must be charged at greater than it's final potential. Perhaps potential is not the technically proper word.

For a lead-acid battery, it's charging at 14.4V, but once fully charged, the resting voltage of the battery itself will drop back down to about ~12.7V. This depends on battery chemistry, and other factors like ambient temperature. Li has a more flat voltage curve, so voltage is not as good an indicator of charge as for lead-acid. BTW, for lead-acid, even voltage is only considered a mediocre why of determining charge state.

Hey, yes I understand. I forgot to mention I have LifePo4 batteries.

I know the 14.4 volts are used for charging, but then when do I know when the resting voltage is the actual voltage of the battery fully charged? How many hours does it need to rest for the voltage to drop to the fully charged battery volatage, and to not have static voltage left.

 

[MichaelK]

Hey, yes I understand. I forgot to mention I have LifePo4 batteries.

I know the 14.4 volts are used for charging, but then when do I know when the resting voltage is the actual voltage of the battery fully charged? How many hours does it need to rest for the voltage to drop to the fully charged battery volatage, and to not have static voltage left.

Resting the battery really only applies to lead-acid. Voltage of Li batteries is so flat, that you really can not use voltage as a guide at all. Here is where a battery shunt comes into play to measure the total amps going through.

 

[sunshine_eggo]

It really depends on the size of the cells. The big 280Ah cells can hold 3.50V for a long time after being charged to 3.65V. It's very useful to burn off any surface charge, i.e., hit it with a moderate load for about 30 seconds where you know you're not consuming more than 1% of the battery capacity.

Pretty reliable after about 30 minutes, but it's best taken with a grain of salt. Note that 13.1 to 13.2V cover 30% of the charge range... pretty worthless there.

As mentioned above... a battery monitor is best.

 

[teddysx3]

Hey guys,

I have it all, all victron equipment.

I charged each battery to 14.4, then float brought it down to 13.6, did that to the 2 betteries. The third one I charged to 14.4, then did not wait for the float voltages to bring it back down to 13.6. The 2 batteries that had 13.6 float were are 13.3, but the other was at 13.5ish. I don't think that the batteries for 1-2 days could have dropped to 70% discharge with no loads connected (13.3)?

Should I cylcle the 3 batteries again one by one to 14.4 and let the float bring it down to 13.6, and then connect them in parallel to make sure the voltages are balanaced? They are now connected and I have ran a charge cycle to 14.4 with all 3 in parallel. Am I overthinking it?

 

[sunshine_eggo]

14.4V at the battery terminals must typically be maintained for about 30 minutes to ensure full charge. You know you're fully charged when current as dropped to 0.05C (5A for a 100Ah battery).

Something that may occur with LFP is BMS over-voltage protection. Are you certain this didn't happen with the two 13.3V batteries?

If you're worried about them being balanced, they're in parallel, so it's pretty much impossible that they're not at the same voltage. If you're worried about internal cell balance, hold them at about 14.4V for a day, completely disconnect them and let them sit overnight. See what the resting voltages do.

 

[teddysx3]

14.4V at the battery terminals must typically be maintained for about 30 minutes to ensure full charge. You know you're fully charged when current as dropped to 0.05C (5A for a 100Ah battery).

Something that may occur with LFP is BMS over-voltage protection. Are you certain this didn't happen with the two 13.3V batteries?

If you're worried about them being balanced, they're in parallel, so it's pretty much impossible that they're not at the same voltage. If you're worried about internal cell balance, hold them at about 14.4V for a day, completely disconnect them and let them sit overnight. See what the resting voltages do.

I'm not sure about the over-voltage protection, I thought it was normal for the voltage to drop a little after them being disconnected from the charger, now having to think about it, 13.3-13.25 is a little low and strange.

I have absorbtion set for 1 hour at 14.4 volts so I was under the impression that I charged all the batteries...I hooked them up in parallel and also did a full chargin cycle 1 hour 14.4, so I hope they are full of charge one way or another.

They are renogy 100ah batteries, and I don't have access to their BMS, I have a smart shunt installed.

 

[sunshine_eggo]

I'm not sure about the over-voltage protection, I thought it was normal for the voltage to drop a little after them being disconnected from the charger, now having to think about it, 13.3-13.25 is a little low and strange.

I'm not liking that at all.

I have absorbtion set for 1 hour at 14.4 volts so I was under the impression that I charged all the batteries...I hooked them up in parallel and also did a full chargin cycle 1 hour 14.4, so I hope they are full of charge one way or another.

They are renogy 100ah batteries, and I don't have access to their BMS, I have a smart shunt installed.

Enable voltage and current in the Victron Smartshunt trends tab. With recent firmware update, they enabled it to keep 45 days of history even when app is closed.

Discharge the batteries a little and then charge again. Set absorption to 14.4V and tail current to 0.1A. Once it indicates 14.4V, you should see a smooth taper from the max current down to to 0.1A and then shut off. If you see an abrupt step down in current, that means a battery has likely entered protection mode.

 

[teddysx3]

I'm not liking that at all.



Enable voltage and current in the Victron Smartshunt trends tab. With recent firmware update, they enabled it to keep 45 days of history even when app is closed.

Discharge the batteries a little and then charge again. Set absorption to 14.4V and tail current to 0.1A. Once it indicates 14.4V, you should see a smooth taper from the max current down to to 0.1A and then shut off. If you see an abrupt step down in current, that means a battery has likely entered protection mode.

Thank for the tip.

So my findings. I charged a few days ago all 3 battery banks to 14.4, then 13.6 float was activated. Disconnected the bank from the system via a switch, 0w load from the smarshunt so no parasitic draw. I went today to check on it, and the voltage of the bank was 13.25, which from my understanding is 70-80% charge, in a few days? That's really strange, with 0w load...

I have now charged again to 14.4, float 13.6 and disconnected each battery bank from each other, so no cables connected to any battery, only the raw terminals, I will see what will happen in a couple of days, and see if any of the battery has drained this much in voltage. They should not have a .3-.4 voltage drop with no loads only for a couple of days, should they? The only thing have hooked up before the on/off switch is the smart shunts positive cable, so I have monitor the voltage of the bank even when the I have switched the power to off. Could the little LED blue light from the shunt draw that much power in just a couple of days?, I don't think so...

As for the smart shunt trends, I now activated voltage and current while charging to 14.4 and float 13.6, and saw a smooth curve from 14.4 to 13.6. But! My battery setting in the shunt were:
Charging voltage: 13.2 (default)In the image below shows 13.6, but I changed it just now, it was 13.2. Should this voltage be a little below float(13.6), or a littlbe below absorbtion(14.4).I dont' think this could have been the issue today that the batteries were again 13.25, I meseared them with a multimeter, It's just used to calculate SOC right?

Tail current: 4.00% - I'm only able to put in a % for the trail current, not 0.1a like you suggested and the lowest is 0.5%, which if my calculations are correct from 100ah, 0.5% is .5amps.

 

[TomC4306]

Try only charging to 14v, then disconnect and check a few hours later and see if they don't settle at a higher voltage

 

[TomC4306]

0.05C (most cell spec sheet tail current) is 5%.
For a 100ah battery that's 5amps.
For a 280ah battery it's 14 amps.

 

[sunshine_eggo]

Thank for the tip.

Can you include snapshots of the trends? Smooth increase to 14.4V and smooth taper of current?

If charging from solar, it's critical that you set charged voltage to 0.2V below absorption. Tail current 6%.

 

[teddysx3]

Can you include snapshots of the trends? Smooth increase to 14.4V and smooth taper of current?

If charging from solar, it's critical that you set charged voltage to 0.2V below absorption. Tail current 6%.

Thanks for keeping me informed.

I will get you the screenshots tomorrow.

At the moment, I'm charging with a Multiplus 3000va, I have limited to 40a current for the 300ah battery bank.

I also charge with solar but not at the moment.

Do you think every time I change from solar and ac when I'm charging, I need to edit the shunts settings or can I input some kind of "best of both worlds" setting?

Thank you!

 

[sunshine_eggo]

Thanks for keeping me informed.

I will get you the screenshots tomorrow.

At the moment, I'm charging with a Multiplus 3000va, I have limited to 40a current for the 300ah battery bank.

I also charge with solar but not at the moment.

Do you think every time I change from solar and ac when I'm charging, I need to edit the shunts settings or can I input some kind of "best of both worlds" setting?

Thank you!

AC charging is consistent and reliable current-wise - following a very predictable pattern. That's why the float voltage sync setting works.

PV charging can regularly cause false sync to 100% by maintaining a voltage above float but allows current to drop below 6% or whatever.

Summary:
PV charging with AC charged settings runs significant risk of false 100%.
AC charging with PV charged setting runs slight risk of small inaccuracies.

If both or inconsistent, PV settings left alone is the best choice unless you want to bother with changing them back and forth. IMHO, PV settings and forget it.

 

[teddysx3]

AC charging is consistent and reliable current-wise - following a very predictable pattern. That's why the float voltage sync setting works.

PV charging can regularly cause false sync to 100% by maintaining a voltage above float but allows current to drop below 6% or whatever.

Summary:
PV charging with AC charged settings runs significant risk of false 100%.
AC charging with PV charged setting runs slight risk of small inaccuracies.

If both or inconsistent, PV settings left alone is the best choice unless you want to bother with changing them back and forth. IMHO, PV settings and forget it.

Now I understand that you are talking about initial chargin to 100% SOC correct? It will be AC for sure, as I want to be sure I have pushed a big amount of current at a stable voltage. I'm using PV charging when I'm off grid to top them off, but having them charged to 100% SOC initially with AC, it's not a problem I assume.

For PV and AC, what settings do you purpose, charged voltage and tail current? And what tail current in % should I put to show you the graphs when charging from AC?

Thanks you !!!

 

[sunshine_eggo]

Now I understand that you are talking about initial chargin to 100% SOC correct?

yes.

It will be AC for sure, as I want to be sure I have pushed a big amount of current at a stable voltage. I'm using PV charging when I'm off grid to top them off, but having them charged to 100% SOC initially with AC, it's not a problem I assume.

For PV and AC, what settings do you purpose, charged voltage and tail current?

0.2V below absorption (14.4) and 6%. If you set for 0.2V below float and charge with PV, your SoC will likely jump to 100% when it's actually lower. I assume you'd want max accuracy when off grid.

I'm still not convinced this voltage drop isn't a cell balance issue. Try setting float to 13.8V and hold for 24 hours.

 

[teddysx3]

0.2V below absorption (14.4) and 6%. If you set for 0.2V below float and charge with PV, your SoC will likely jump to 100% when it's actually lower. I assume you'd want max accuracy when off grid.

I'm still not convinced this voltage drop isn't a cell balance issue. Try setting float to 13.8V and hold for 24 hours.

It was 13.2 by default and I have not changed it, that's why I was wondering sometimes why the 100% SOC was off, thanks for that!!

I'm also not sure it's cell ballance issue, they should be balanced from the manufacturer, they ahve RJ45 ports for auto-balancing between parallel connection. I will let you know tomorrow the status of the batteries after 24 rest, and will do a cycle of discharge and charge to get the trends.

Thanks!

 

[sunshine_eggo]

It was 13.2 by default and I have not changed it, that's why I was wondering sometimes why the 100% SOC was off, thanks for that!!

I'm also not sure it's cell ballance issue, they should be balanced from the manufacturer,

I'm guessing you have missed the 100s of posts about brand new batteries not being balanced from the manufacturer.

Renogy is not known for their technical acumen or their quality.

they ahve RJ45 ports for auto-balancing between parallel connection. I will let you know tomorrow the status of the batteries after 24 rest, and will do a cycle of discharge and charge to get the trends.

Thanks!

 

[teddysx3]

I'm guessing you have missed the 100s of posts about brand new batteries not being balanced from the manufacturer.

Renogy is not known for their technical acumen or their quality.

Well yeah...I assume there could be a imbalance in cells inside, they use pouch cells actually as far as I know...

So how would I balance them if needed, keep the absorb or float at a certain voltage for a longer period of time? Since It's not a self built battery, and I cannot balance each cell, they are pre-balanced pouch cells, so the only way maybe is..?