Battery Equalisation

[Bushtracker]

Could anyone advise me on settings for battery equalisation ? I have recently installed a Axpert 5 kW inverter with 6 PV panels and 4 x 200aH AGM batteries and I notice that the settings on the inverter as regards the battery equalisation is 'disabled' - is this correct? Setting 5 in WatchPower is set on AGM , and I have been lead to believe that battery equalisation is a good thing to do?

Thank you

[Jaco De Jongh]

4 hours ago, Bushtracker said:

and I have been lead to believe that battery equalisation is a good thing to do?

With Battery equalization you are sort of deliberately "Overcharging" your batteries and this is something that you should only  do if you see there is a significant difference in the Battery SG readings after they have been fully charged. This is normally done every 3 to 6 months (If Needed) . 

Battery Balancing on the other hand is something totally different and worth doing. 

4 hours ago, Bushtracker said:

Could anyone advise me on settings for battery equalisation ?

The data sheet for your batteries will show if it is allowed and what the equalization voltage should be.  

Please remember, not all AGM's can be equalized. 

[DeepBass9]

12 hours ago, Jaco de Jongh said:

Please remember, not all AGM's can be equalized. 

Is that because of the gassing?

If you are running a battery balancer, and there is no midpoint deviation, then I presume there will be no need to balance the batteries?

[Jaco De Jongh]

37 minutes ago, DeepBass9 said:

Is that because of the gassing?

What I could gather over time, the way the battery is build, with the size of the inter-cell connections ext determines if they can be equalized or not. I never went into much dept, but have looked at quite a few different AGM datasheets in the past and what was interesting is that some allowed equalization and some didn't. There are a few members that I saw knows quite a lot about batteries, maybe they can tell us more.. @Youda is one of them if I remember correctly or was it @phil.g00?

45 minutes ago, DeepBass9 said:

If you are running a battery balancer, and there is no midpoint deviation, then I presume there will be no need to balance the batteries?

This is also what I was trying to say in the above post, It will be more beneficial to do balancing than doing Equalization. 

[Bushtracker]

20 hours ago, Jaco de Jongh said:

What I could gather over time, the way the battery is build, with the size of the inter-cell connections ext determines if they can be equalized or not. I never went into much dept, but have looked at quite a few different AGM datasheets in the past and what was interesting is that some allowed equalization and some didn't. There are a few members that I saw knows quite a lot about batteries, maybe they can tell us more.. @Youda is one of them if I remember correctly or was it @phil.g00?

This is also what I was trying to say in the above post, It will be more beneficial to do balancing than doing Equalization. 

Thank you, now I will check the battery manufactures specs to find out whether equalisation is necessary. I have not learnt about battery balancing, I will check if Youda can help me?

[Jaco De Jongh]

20 minutes ago, Bushtracker said:

I have not learnt about battery balancing,

That is where you use battery balancers to balance your batteries during charging. It monitors the voltage of every battery in the bank and if one "Falls" behind it will allow a little higher charge to that specific battery to try and get him on the same voltage as the others. 

[Bushtracker]

2 hours ago, Jaco de Jongh said:

That is where you use battery balancers to balance your batteries during charging. It monitors the voltage of every battery in the bank and if one "Falls" behind it will allow a little higher charge to that specific battery to try and get him on the same voltage as the others. 

Thank you I will follow this up.

I'm still concerned about my battery health and charging! Since commissioning (one and a half months) I have only seen 1 occasion where the Inverter display says 'Fully Charged' , It is set on Charging by PV only and some days when we are away for most of the day and there is not much load the batteries still do not reach 'fully charged' on the inverter display although it does get to 100% on the Watch Power display?

Your comments would be much appreciated

[Jaco De Jongh]

19 minutes ago, Bushtracker said:

I have only seen 1 occasion where the Inverter display says 'Fully Charged' ,

Please dont look at the display for any indication of State of Charge. The unit looks at voltage and voltage cant be used to determine how "full" a battery is. You will need a proper battery monitor to tell you that. A battery monitor is the only accurate way of measuring the True SOC. Please consider investing in one. When used correctly, you will ensure that your batteries dont get over utilized. (that you dont discharge them to a point where they will be damaged)

The battery monitor measures coulombs flowing in and out of the battery and reports the precise SOC at all times. 

[Bushtracker]

1 hour ago, Jaco de Jongh said:

Please dont look at the display for any indication of State of Charge. The unit looks at voltage and voltage cant be used to determine how "full" a battery is. You will need a proper battery monitor to tell you that. A battery monitor is the only accurate way of measuring the True SOC. Please consider investing in one. When used correctly, you will ensure that your batteries dont get over utilized. (that you dont discharge them to a point where they will be damaged)

The battery monitor measures coulombs flowing in and out of the battery and reports the precise SOC at all times. 

Thank you so much for this. Is there a particular make of battery monitor that you would recommend?

[Jaco De Jongh]

3 minutes ago, Bushtracker said:

Thank you so much for this. Is there a particular make of battery monitor that you would recommend?

Victron BMV 702 or if you want Bluetooth connectivity (to monitor the batteries from your phone), look at the 712. It is more expensive and in most cases the 702 is just doing fine.  

[Bushtracker]

2 minutes ago, Jaco de Jongh said:

Victron BMV 702 or if you want Bluetooth connectivity (to monitor the batteries from your phone), look at the 712. It is more expensive and in most cases the 702 is just doing fine.  

Thank you Jaco, I will look for one. Presumably one has to check each battery individually in the bank?

[Jaco De Jongh]

11 minutes ago, Bushtracker said:

Presumably one has to check each battery individually in the bank?

Nope, with the battery monitor, you monitor the complete bank. 

[___]

Mmmmh. Equalisation is a kind of balancing. It is how we did it before Lithium batteries got in the way

So as a battery charges it starts to accept less and less current, until it accepts only a couple hundred milliamps. Now imagine if I had two batteries where one of them is full and will only accept a few hundred milliamps, but the one next to it isn't full yet and will still accept an ampere or two. If I hold this bank at float voltage for long enough the slow charging rate forced on the string by the full battery will EVENTUALLY allow the lower battery to charge fully, but this could take days... and not only that, while you're slowly trying to trickle everything to 100% full sulfation is already setting in in the lower areas.

Equalisation is the poor man's method to get past this problem. You deliberately raise the voltage high enough so that even a full cell WILL pass more current. This raises the charge current through the rest of the battery, so that all the cells gets a proper chance to charge.

Equalisation is often recommended after a deep discharge. This is because the capacity of each cell will be a little different, and this difference becomes most apparent when you're filling them up from the bottom. This is also true, by the way, for Lithium Iron Phosphate (LFP). Nothing works a BMS/balancer harder than a battery that was taken down to 0% SOC and is now approaching 100% SOC, especially if that battery also has active bottom-end balancing (that is another topic... if you don't find yourself nodding along... then just ignore this bit for now ).

This practice of deliberately forcing current through your batteries boils off some electrolyte. With flooded batteries you simply top up the electrolyte. With AGM batteries you cannot. Charging AGMs this hard tends to cause them to vent, and the water is lost forever (it cannot recombine through the battery's internal recombination systems). This is why you don't equalise AGMs... at least not regularly.

Equalisation is not needed if your cells are balanced. A good absorption charge is all you need.

Similarly, there are devices that can bypass current past a cell to help other cells to charge, thereby getting the same effect: current is forced through the loop without forcing them THROUGH full cells. These devices are called balancers (and I am preaching to the choir here ).

LFP batteries must have balancers, because an LFP cell passes almost no current once it gets full. The only way to get current through the loop is to bypass high cells (or to actively transfer charge between cells, again... ignore if you don't know what detour I'm hinting at here ). All good LFP batteries will have balancing included in the BMS.

[Bushtracker]

Thank you Plonkster, so do I conclude that a battery monitor is the way to go to balance your batteries and keep them healthy?

[Jaco De Jongh]

39 minutes ago, Bushtracker said:

so do I conclude that a battery monitor is the way to go to balance your batteries and keep them healthy?

Battery Monitor is to monitor the batteries and know its true SOC and protect their health through using that info to protect your investment. 

When you have the monitor, you will be able to see the conditions that might damage your batteries for example... 

1. Constant under charging,
2. Over or Under voltage
3. Too low discharge. 

 

 

 

Battery balancers are different equipment and will assist in keeping all the batteries in the bank balanced. You have an option between Victron and imported HA1 or something like that (Not 1000% sure about the name. ) Of the latter you will need one to balance 4 batteries. The Victron you will need 3 to balance 4 batteries. 

 

1 hour ago, plonkster said:

Similarly, there are devices that can bypass current past a cell to help other cells to charge, thereby getting the same effect: current is forced through the loop without forcing them THROUGH full cells. These devices are called balancers (and I am preaching to the choir here ).

 

[___]

1 hour ago, Bushtracker said:

Thank you Plonkster, so do I conclude that a battery monitor is the way to go to balance your batteries and keep them healthy?

What my tag-team-mate @Jaco de Jongh said

[Richard Mackay]

Another option is If you have wet batteries that you can access the electrolyte then a hydrometer is also a good indicator of battery condition.

And if you are needing a quick check for dying cells then use a non contact thermometer (infrared). This provides a temperature measurement which will indicate trouble if a cell is hotter than the rest.

[Jaco De Jongh]

15 minutes ago, Richard Mackay said:

Another option is If you have wet batteries that you can access the electrolyte then a hydrometer is also a good indicator of battery condition.

And if you are needing a quick check for dying cells then use a non contact thermometer (infrared). This provides a temperature measurement which will indicate trouble if a cell is hotter than the rest.

Sounds great, how will you know the true SOC of the battery using these meters? 

[DeepBass9]

If you want to KNOW what is going on with your batteries, a monitor and a balancer are essential. If you are going to drop R50k or R100k on batteries, spend another few bucks on understanding what is happening there.

[Richard Mackay]

1 hour ago, Jaco de Jongh said:

Sounds great, how will you know the true SOC of the battery using these meters? 

This extract is from the AEE Solar catalog: https://aeesolar.com/wp-content/uploads/2018/01/2018-AEE-Solar-Catalog.pdf  (bed time reading!)

This was the way it was done back in the 'good old days' but it still has merit from what I have gathered.

The temperature measurement is not for SOC but for a quick check on your batteries.

[Jaco De Jongh]

54 minutes ago, Richard Mackay said:

This was the way it was done back in the 'good old days' but it still has merit from what I have gathered.

Hi Richard, I think you are missing the point of what we are trying to do here. I am fully aware of the above procedure, but we are talking about constant 24/7 monitoring of your battery bank, from anywhere at any time. I cycle my batteries every single day, I can basically  be anywhere in the world and exactly know the state of charge of my battery bank and control my load accordingly to protect my battery bank. I dont have to get up every hour during the night to measure the SG and then decide to go back to grid once I reach 50% DOD. I can rely on my battery monitor to make that decisions for me and my management system will switch over to grid when its needed.  

The OP is interested in knowing the SOC of his battery bank and wants to implement that value into his control philosophy, I am sorry, but the Hydrometer will just not work in this instance.  As the 3rd last sentence in your screenshot rightfully says, "Always try and take readings after the battery  has been idle or slowly discharging for a while". On big systems we want to be able to tell the SOC while charging, idling or even discharging at 4000 watts...   

[Bushtracker]

11 hours ago, Jaco de Jongh said:

Hi Richard, I think you are missing the point of what we are trying to do here. I am fully aware of the above procedure, but we are talking about constant 24/7 monitoring of your battery bank, from anywhere at any time. I cycle my batteries every single day, I can basically  be anywhere in the world and exactly know the state of charge of my battery bank and control my load accordingly to protect my battery bank. I dont have to get up every hour during the night to measure the SG and then decide to go back to grid once I reach 50% DOD. I can rely on my battery monitor to make that decisions for me and my management system will switch over to grid when its needed.  

The OP is interested in knowing the SOC of his battery bank and wants to implement that value into his control philosophy, I am sorry, but the Hydrometer will just not work in this instance.  As the 3rd last sentence in your screenshot rightfully says, "Always try and take readings after the battery  has been idle or slowly discharging for a while". On big systems we want to be able to tell the SOC while charging, idling or even discharging at 4000 watts...   

 

13 hours ago, DeepBass9 said:

If you want to KNOW what is going on with your batteries, a monitor and a balancer are essential. If you are going to drop R50k or R100k on batteries, spend another few bucks on understanding what is happening there.

Thank you for your comments and advice - I was under the misconception that once the system was installed, it would look after itself ? How wrong I was! I guess I did not do my homework sufficiently and now it is a "catch 22" situation?!

So I need 3 balancers and a battery monitor that will take care of 4 x 200aH AGM batteries?

Any advice on which to install first or do they have to be together?

 

[Jaco De Jongh]

5 minutes ago, Bushtracker said:

Any advice on which to install first or do they have to be together?

Definitely the battery monitor.  

[DeepBass9]

The HA02 unit will balance 4 batteries at once. I'm not sure where to get that from now, there were forum members importing these. I have a BMW 712 which is nice as you can just check on an android app what is going on (links via bluetooth).

[___]

29 minutes ago, DeepBass9 said:

HA02

The HA02 is an active balancer, using DC/DC converters. We've had at least one outright failure among forum users (smoke came out) and one suspected failure of a former member (batteries went out of balance despite using the balancer). I don't know out of how many units sold that is, but I assume these are outliers. The HA02 is much cheaper than the alternative.

The alternative (the Victron balancers) is more old-school and robust. It simply shunts up to 700mA past a high cell using a good old resistor. Not much to go wrong