diy solar

diy solar

LV2424: finding the right settings

This is actually starting to become clear as time goes on... I've noticed even in the last 24 hours that the batteries like being around 25.8 to 26.6 V.

The cells will usually settle in this range.

My battery specs show this:



Is it reasonable to set these two settings based on that chart? Bulk charge to 28.8 V (14.4 V x 2) and float charge to 27.6 V (13.8 V x 2)? I get that these settings can vary and experimentation is probably the best way to optimize, but is there logic in setting them according to those specs? In other words, is that what I'm getting at, in theory?
3.65V x 8 is 29.2V. Personally, I prefer the 3.5V per cells area myself. If you top balanced you cells in parallel, do you remember how long it took at just a few watts to bring the cells to 3.65V from 3.5V? Not very long and that was at the max 3.65V. You have way more watts inputted to the cells at higher pack voltage. I prefer not running to the fringes and have one cell that is a slight runner. Much safer running in the knee area.

The 27.6V would work for float.
 
Some of us have real jobs. And I mean real jobs. 12 to 14 hour days for me. ???
I think you should shoot for 16 hours a day, 24 if you can manage it.

What has been found is that MPP and GW don't supply loads during the day from the PV array is float is set lower and batteries ended bulk charging.
That is how charge termination works generally and is not specfic to MPP or GW.

Essentially, you could enter nighttime with no PV array input and run out of battery during the night.

Yes when the sun goes down your solar harvest will be greatly diminished.

Think about this, you have really light loads during the day, the battery never dropped to the float voltage so no charging occurs after the bulk charge voltage limit was reached.
This function is generally called re-bulk or something similar as in re-entering bulk phase and will not ever trigger if the float voltage is higher and your charge source can maintain float.
Think about that.

My understanding is you set the float high and suffer the incremental voltage stress to keep your batteries full for nighttime use.
 
Last edited:
Are you estimating state of charge from voltage?

I'm using the WatchPower software to monitor the system (it shows a percentage and voltage in the dashboard). I find it handy because it's on a monitor that I can glance at in passing. It's also nice updating settings with it, as opposed to the MPP LV2424 display. But this may not be accurate as I'm relying on the User-Defined setting (for LiFePO4), which doesn't really know my exact battery specs. In fact, I can't find the SOC table for my battery, only the spec sheet. Or do pretty much all LiFePO4 batteries have similar SOCs?
 
Last edited:
I think you should shoot for 16 hours a day, 24 if you can manage it.

I used to work 120 hours a week in my younger days. Made good money too. How do you think I pay for all the solar stuff now? :)

That is how charge termination works generally and is not specfic to MPP or GW.



Yes when the sun goes down your solar harvest will be greatly diminished.


This function is generally called re-bulk or something similar as in re-entering bulk phase and will not ever trigger if the float voltage is higher and your charge source can maintain float.
Think about that.

Basically yes, you are doing the same here.

My understanding is you set the float high and suffer the incremental voltage stress to keep your batteries full for nighttime use.
Only if float is set higher than the bulk charge. All that is being done is battery voltage is kept in a range between the float level and level bulk terminated. That will not stress the battery.

Explain how it would be beneficial to the battery to run it down to a much lower SOC , then bulk comes back and charges at high amps compared to letting the battery set at let's say a range of 27.5 to 28.0V for a 24V pack while the loads are powered off the solar?

If one thinks about it, it actually increases cycle count with running the battery to lower SOC, then resuming bulk.
 
One thing you want to avoid is charge controller repeatedly reinitiating a bulk recharge cycle due to random inverter loads. It is hard on batteries and can be difficult to setup depending on your use profile and how charge controller terminates bulk cycle..

Many charge controllers trip a new bulk cycle whenever battery drops below float voltage setting. This can occur every time a moderate load is applied to inverter. Many charge controller just have a timer for time spent at bulk voltage charge cycle before dropping back to float. A better charge controller terminates bulk cycle based on charge current drop off with a timer maximum time for secondary backup criteria to drop out of bulk mode and revert back to float.

Grid tied hybrid inverter will often draw current immediately from battery when switching from bulk to float to drag battery down to float settng. A good design is a grid tied hybrid that gradually steps down from bulk to the float voltage when switching from bulk to float mode.

If all you have is a timer based bulk exiting charge controller you really have to be careful of repeated retriggering to bulk mode due to random inverter load. This could result in a lot of time spent with bulk voltage imposed on battery that is hard on battery. In this case the only option is to reduce bulk voltage setting and/or shorten the bulk time timer setting.

To complicate things more, many BMS's only balance when a cell rises above 3.4v. This can mean you only get balancing when in bulk mode so if bulk exit time is set too short time you will not get much balancing opportunity on cells. The best solution for this is a bulk setting about 3.5v x number of series cells and moderate bulk cycle timer setting. This is what Victron recommends for their charge controller settings.
 
Last edited:
I'm using the WatchPower software to monitor the system (it shows a percentage and voltage in the dashboard). I find it handy because it's on a monitor that I can glance at in passing. It's also nice updating settings with it, as opposed to the MPP LV2424 display. But this may not be accurate as I'm relying on the User-Defined setting (for LiFePO4), which doesn't really know my exact battery specs. In fact, I can't find the SOC table for my battery, only the spec sheet. Or do pretty much all LiFePO4 batteries have similar SOCs?
I have a very similar setup and I don’t recommend attempting to ascertain your battery’s state of charge using anything other than a shunt based meter. When I first got the lv2424 I was similarly confused about it’s charging cycle (I did not have or want a shunt). I found that if I flipped the breaker for my panels (on to off back to on) the lv2424 would begin a bulk cycle. Just like you, I could add load and see the input from the solar array increase. I did not understand why the lv2424 wasn’t harvesting full power from the panels all of the time or completing a bulk cycle at least once per day. Finally, I installed a shunt based monitor. They are cheap and simple to install. Now, I let my lv2424 do it’s work without fussing over its cycles or methods. The monitor assured me two things. 1. My battery can be charged to its nominal capacity without going through a bulk cycle or ever reaching a high voltage like 28.8 or 29.2 for example. 2. The lv2424 will automatically do a bulk cycle occasionally; I have theories regarding why but I won’t go into them because They are just theories. The unit is doing its job and doing it well. Something I did not believe before I had a shunt based monitor and I was very concerned that if it didn’t bring the batteries to my absorption voltage every day then I wasn’t getting a full charge. Those ideas were mostly false. On another note, I skimmed the rest of this thread, and if I’m understanding correctly, there’s been discussion about floating your battery at high voltages. I recall doing this trick on the lv2424 as well. Setting my float voltage at 28.8 in an attempt once again to force the lv2424 to bring my battery to a “full state of charge”. Unless things have changed a lot, and I don’t think they have, I don’t think that floating at a high voltage is a good idea for lifepo4. My recollection is that Will Prowse and Battleborn suggest floating at 27.2 will do no harm, but floating above that may impact longevity negatively. To me, a high state of charge and a high voltage are not synonymous. High voltage may imply a high state of charge but a high state of charge does not necessarily imply a high voltage. A shunt will make that clearer. This has been my experience. I hope it helps. Good luck!
 
Basically yes, you are doing the same here.
I have not mentioned anything about what I am doing.
Only if float is set higher than the bulk charge.
Hope you mean re-bulk.

All that is being done is battery voltage is kept in a range between the float level and level bulk terminated. That will not stress the battery.
Yes it will.
Holding a battery above full resting causes voltage stress.
I do understand why you would be willing to do that for your use case.
 
Thanks @cotrailhead. Your explanation has given me some much needed perspective. And it's starting to make more sense as I monitor my system. Clearly my understanding of batteries, especially LiFePO4, was severely lacking.

I think I'll purchase a battery monitor, as you suggested. Seems a good way to familiarize myself further and monitor the system more accurately.
 
2 x 12 V 100 Ah ExpertPower LiFePO4 batteries in series...

Reading the docs for the shunt battery monitor... Instructions say to fully charge or discharge in order to calibrate the monitor. I'm a bit unclear on how to do this.

I read that for LiFePO4, you charge at 14.6 V until current slows to stop. In theory I get this, but what's the best way to accomplish this? I tried using the LV2424 (utility priority and bumping float/bulk charge settings). It charged to about float (27.6 V) and started discharging. Is this fully charged? Or should I hook up a car battery charger and monitor voltage unti it reaches 29.2 V? Or is there a way to push to full with the MPP?

Conversely, if I want to calibrate based on fully discharged, what voltage is safe? Do I need to go down to 2.5 V per cell (10 V)?
 
Last edited:
Just like top balancing, a columb counter battery monitor needs to know what 'full' is to reset its AH consumed count to zero.

This is usually done by a user setting that specifies what battery voltage level you want monitor to reset battery to 'full'. A given monitor may have a register setting you can directly enter value or you press a 'reset to full' button when you fully charge battery. Be careful on latter as if you have overly high charged voltage, like absorb voltage, it may not hit that same voltage level on every full recharge so monitor will not reset. Usually like to have reset to full voltage a little below your absorb charge voltage level.

If you don't recharge beyond this reset voltage level then monitor works on 'dead reckoning'. It just keeps a running tally on discharge and charging currents for AH used and remaining, from last reset to full point. This degrades over time due to various measurement accuracy and other losses so it should be allowed to reset its reference periodically, by charging to defined 'full' voltage, to keep monitor accurate.

Battery capacity is a user setting also. You can put anything you want into setting. Some folks put 80% of actual battery capacity so their readout has safety margin so they don't get too close to inverter or BMS low voltage shutdown.

Some monitors have a charge efficiency user setting. For LFP use 99% This derates charge current by % specified.,

There are cheapo monitors that readout % charge based on battery voltage reading. These are close to useless for accuracy.
 
Last edited:
My setup: lv2424 (hereafter referred to as "the unit") with 2-12v, 100Ah SOK LiFePO4 batteries is series (24v system). My problem: the unit seems to be charging the batteries even though they are at "100% full" voltage of 27.2v. I hooked up the batteries and panels (2-350w panels in series) yesterday, no mains power or loads just yet. I wanted to see what the panels could do. Plenty of sun yesterday so putting out around 540W. I turned on the unit and set the bulk charge to 28.4v and float to 27v as per battery vendor recommendations. I ran the Watch Power software and it indicated 27.2v on the batteries but only 70% charge (should be 100% at that voltage). turned on the panels and it was charging the batteries. I have it set up so 20A for solar. This was indicated in the Watch Power readout (19-20A) and confimred this with a clamp style amp meter on the battery positive wire (read around 20A). So, my sssumption was that the panels were charging the batteries even though they were at 27.2v. I let it do its thing all day and a couple hours before sunset I noted that the Watch Power was stil showing 70% charge and 27.2v on batteries and still pumping 20A to the batteries (confirmed these voltage and amp readouts with meters). After sunset, the batteries dropped to 26.5v (80%). I checked this morning and still at 26.5v, athough the only load is the unit itself at around 3w. I am going to let it do its thing again today to see if it ever stops sending the full 20A to the battereis. If not, then i am concerned. So, questions: I noted much discussion aobut the float level (low versus high [near bulk]), since mine is "low" is that my problem? If my batteries' inital SOC was not balanced before i connected them to the unit, could that be my problem? I would just like to know how to get the unit to understand that my batteries seem to be fully charged and to stop charging them. Or are they really not fully charged and the unit is doing what it is supposed to do and i just need to relax and let it do its thing. Also, i know that the batteries' BMS's woudld stop an overcharge situation (set at 29.2v and can't change that) but the unit should be stopping the charge before that occurs. Any advice would be greatly appreciated. thanks.
 
My setup: lv2424 (hereafter referred to as "the unit") with 2-12v, 100Ah SOK LiFePO4 batteries is series (24v system). My problem: the unit seems to be charging the batteries even though they are at "100% full" voltage of 27.2v. I hooked up the batteries and panels (2-350w panels in series) yesterday, no mains power or loads just yet. I wanted to see what the panels could do. Plenty of sun yesterday so putting out around 540W. I turned on the unit and set the bulk charge to 28.4v and float to 27v as per battery vendor recommendations. I ran the Watch Power software and it indicated 27.2v on the batteries but only 70% charge (should be 100% at that voltage). turned on the panels and it was charging the batteries. I have it set up so 20A for solar. This was indicated in the Watch Power readout (19-20A) and confimred this with a clamp style amp meter on the battery positive wire (read around 20A). So, my sssumption was that the panels were charging the batteries even though they were at 27.2v. I let it do its thing all day and a couple hours before sunset I noted that the Watch Power was stil showing 70% charge and 27.2v on batteries and still pumping 20A to the batteries (confirmed these voltage and amp readouts with meters). After sunset, the batteries dropped to 26.5v (80%). I checked this morning and still at 26.5v, athough the only load is the unit itself at around 3w. I am going to let it do its thing again today to see if it ever stops sending the full 20A to the battereis. If not, then i am concerned. So, questions: I noted much discussion aobut the float level (low versus high [near bulk]), since mine is "low" is that my problem? If my batteries' inital SOC was not balanced before i connected them to the unit, could that be my problem? I would just like to know how to get the unit to understand that my batteries seem to be fully charged and to stop charging them. Or are they really not fully charged and the unit is doing what it is supposed to do and i just need to relax and let it do its thing. Also, i know that the batteries' BMS's woudld stop an overcharge situation (set at 29.2v and can't change that) but the unit should be stopping the charge before that occurs. Any advice would be greatly appreciated. thanks.

I've figured out in running my system for a few months that voltage is not a good metric for SOC. At 27 volts your batteries might be full but they might not.

Here's an example. My batteries might be around 40 percent or less in the morning (26 point something volts or lower). Low loads over night... Then the morning comes and on a nice day like today, once sun is blazing, I'm getting something like 900 watts from my panels. Then unit is charging fast at this point, maybe 25 amps... The battery bank voltage spikes to 27 volts or so but the SOC is just starting to climb. Maybe around 50 percent at this point. Because I'm using a coloumb counter, I just trust that and somewhat ignore voltage. This has been a very good way for me to track my batteries lately so I recommend looking into one of these meters.

For the LV2424, my experience is that it doesn't really stop charging until around the bulk charge setting, which is what I would consider 100%. And because LiFePO4 don't ever stay at that voltage without current coming in, the charger pretty much always charges if there is load. I usually draw at least an amp or two so I've never seen my unit really stop charging.

For me a float around 27.2 V and bulk up around 28.4 V has been pretty sane. Though I must admit, my LV2424 doesn't seem to be doing the periodic bulks that some folks say it should.
 
Last edited:
My setup: lv2424 (hereafter referred to as "the unit") with 2-12v, 100Ah SOK LiFePO4 batteries is series (24v system). My problem: the unit seems to be charging the batteries even though they are at "100% full" voltage of 27.2v. I hooked up the batteries and panels (2-350w panels in series) yesterday, no mains power or loads just yet. I wanted to see what the panels could do. Plenty of sun yesterday so putting out around 540W. I turned on the unit and set the bulk charge to 28.4v and float to 27v as per battery vendor recommendations. I ran the Watch Power software and it indicated 27.2v on the batteries but only 70% charge (should be 100% at that voltage). turned on the panels and it was charging the batteries. I have it set up so 20A for solar. This was indicated in the Watch Power readout (19-20A) and confimred this with a clamp style amp meter on the battery positive wire (read around 20A). So, my sssumption was that the panels were charging the batteries even though they were at 27.2v. I let it do its thing all day and a couple hours before sunset I noted that the Watch Power was stil showing 70% charge and 27.2v on batteries and still pumping 20A to the batteries (confirmed these voltage and amp readouts with meters). After sunset, the batteries dropped to 26.5v (80%). I checked this morning and still at 26.5v, athough the only load is the unit itself at around 3w. I am going to let it do its thing again today to see if it ever stops sending the full 20A to the battereis. If not, then i am concerned. So, questions: I noted much discussion aobut the float level (low versus high [near bulk]), since mine is "low" is that my problem? If my batteries' inital SOC was not balanced before i connected them to the unit, could that be my problem? I would just like to know how to get the unit to understand that my batteries seem to be fully charged and to stop charging them. Or are they really not fully charged and the unit is doing what it is supposed to do and i just need to relax and let it do its thing. Also, i know that the batteries' BMS's woudld stop an overcharge situation (set at 29.2v and can't change that) but the unit should be stopping the charge before that occurs. Any advice would be greatly appreciated. thanks.
A few things, have you ever fully cycled the batteries from full charge to low voltage cutoff by the BMS?

If you aren't a heavy user and tax the batteries fully everyday, you might just back off the voltage setting on the top end. Your cells will stay much more in balance. Originally I started with 28.0v as the charge limit but have since backed off to 27.0v bulk and 26.5v for float. Cells seem to stay closely balanced and I have plenty of reserve with the usage during the cloudy days and during night.
 
I've figured out in running my system for a few months that voltage is not a good metric for SOC. At 27 volts your batteries might be full but they might not.

Here's an example. My batteries might be around 40 percent or less in the morning (26 point something volts or lower). Low loads over night... Then the morning comes and on a nice day like today, once sun is blazing, I'm getting something like 900 watts from my panels. Then unit is charging fast at this point, maybe 25 amps... The battery bank voltage spikes to 27 volts or so but the SOC is just starting to climb. Maybe around 50 percent at this point. Because I'm using a coloumb counter, I just trust that and somewhat ignore voltage. This has been a very good way for me to track my batteries lately so I recommend looking into one of these meters.

For the LV2424, my experience is that it doesn't really stop charging until around the bulk charge setting, which is what I would consider 100%. And because LiFePO4 don't ever stay at that voltage without current coming in, the charger pretty much always charges if there is load. I usually draw at least an amp or two so I've never seen my unit really stop charging.

For me a float around 27.2 V and bulk up around 28.4 V has been pretty sane. Though I must admit, my LV2424 doesn't seem to be doing the periodic bulks that some folks say it should.
Agreed on using voltage as the metric. I did my homework and came to the same conclusion. Actually, my only problem turned out to be me and my lack of patience. The unit ended charging within the set parameters and stopped, although i agree with you about the "always charging" situation with the unit. It does seem to trickle in an amp or two like you said. Someone else told me that these units are set to AGM standards so using an LFP battery will probably confuse it into thinking that it's not at 100% but it's a non-issue since the unit does actaully stop bulk charging. The battery icon may show "charging" but once the middle green light goes solid, the batteries are charged. So, i'm good with it at this point. Thanks for your help.
 
A few things, have you ever fully cycled the batteries from full charge to low voltage cutoff by the BMS?

If you aren't a heavy user and tax the batteries fully everyday, you might just back off the voltage setting on the top end. Your cells will stay much more in balance. Originally I started with 28.0v as the charge limit but have since backed off to 27.0v bulk and 26.5v for float. Cells seem to stay closely balanced and I have plenty of reserve with the usage during the cloudy days and during night.
No i have not but plan to. i just replied to another follow up post on here and explained that my issue was my lack of patience. After the second day, the unit is behaving just fine. I do appreciate your suggestion about evnentually lowering the bulk/float. That would make sense when i'm not using it as much during certain times of the year. thanks for the help.
 
Back
Top