Solar charging in Storage

[PeteS]

I have a Victron SmartSolar 75/15 MPPT controller installed in the motorhome, Its been installed for around a month and I topped the leisure battery up a fair amount today more than I have had in the past and I last did it in June so it maybe overcharging and I'm thinking I need a storage preset for the battery which will only ever float the battery at 13.2V to maintain it.
My history shows it gong into Bulk then Absorption then float every day when the sun come up and as its temperature compensated voltages are up a 14.56v, I think this is unnessecary when its in storage.
So my question is does anybody know for sure how to eliminate the absorption mode.?
Currently I have it set to 13.0V and 0 mins duration, is that going to do it?

The Q&A on the Victron Community have an answer which suggests doing what I'm after doing but doesnt state how to achieve it.

I already disable the solar controller when on EHU as the two compete againt each other.

 

[wildebus]

The way the Absorption works by default on the SmartSolar is it will go into that mode for a set period based on the voltage level at the time the contoller wakes up. If the battery voltage is >12.6V (which is likely the case for you) then the Absorption time is 1/6th the duration you have set. I have not tried setting a time of 0 mins, but I guess if it accepts 0 Mins, then the absorption mode will kick in and instantly switch into float mode (I would expect it must enter absorption, even if momentarily, to get to float as that is the programmed charge cycle and you cannot specifically bypass one mode to go direct to float from bulk).

If you setup the absorption to effectively bypass that mode, you are really eliminating a key charging cycle and not using the controller to its full capability, but what you have setup as you have described it will do what you are wanting I would think.

The battery voltage you have setup for the Absorption Mode (also called CV or Constant Voltage) will be the voltage it will put out when the battery is at 25C. In the UK we will be below that temp almost always and so the voltage will be higher as it compensates by increasing the voltage as the temp is lower (and vice-versa). As an example, one day when the interior temp started creeping up and reached 38C, the batteries were still at a steady 20C.
The Victron MPPT by default only checks the temp once - when it 'wakes up' - and the voltage for ABS mode assumes that temp all day (and also assumes the MPPT Controller is by the batteries). If you feel the voltage is too high and the compensation is wrong, you could just lower the initial voltage. You can also change or even remove the temperature compensation voltage adjustment in the setup of the SmartSolar.

Ref Solar and EHU competing against each other - this is a pretty common situation and the Solar typically loses out as the AC Charger output is so regular (This is my feeling on why the EHU tends to win). What I have done to make the Solar the primary charge (may as well use the free sun energy instead of paying for power into the AC Charger) is to make the MPPT Absorption Voltage slightly higher than the AC Charger (or alternatively set the AC Charger voltage slightly lower than the MPPT) . That way the AC charger sees a voltage above what it is configured for and will not put any power in, and the MPPT Controller will provide the power. This method works pretty well when the van is just sitting on the driveway - and so effectively 'in storage'.

Finally, I think maybe you are overly worrying about the batteries being overcharged. A Smart Charger (Solar, Mains, B2B, whatever) is designed to essentially cut out (so go to Float or Storage) when the battery needs no charge and I would setup the parameters in the MPPT to suit what the battery manufacturer recommends and leave it as that.


Hope this was of some interest and help.

 

[PeteS]

Thanks for that, I have the Smart Battery sense so the controller takes its temp from that throughout the day. I was just concerned and trying to eliminate electrolyte loss during storage, the battery is taking 90W every day to maintain itself which is good but I think it could do it via float and not by elevating the charge voltage when I know its not going to be used.
The presets are available so I was just experimenting I guess to see how it gets on.

 

[wildebus]

Thanks for that, I have the Smart Battery sense so the controller takes its temp from that throughout the day. I was just concerned and trying to eliminate electrolyte loss during storage, the battery is taking 90W every day to maintain itself which is good but I think it could do it via float and not by elevating the charge voltage when I know its not going to be used.
The presets are available so I was just experimenting I guess to see how it gets on.

The Smart Battery Sense can be a useful addition (and especially so when the Controller is located away from the battery). The idea of the absorption time automatically getting reduced depending on voltage level would I have thought accommodated your idea of mimizing the time at that stage when in storage. TBH, I've never used the presets on the SmartSolar as switched to the user input option and entered the parameters myself.

When you have set 0 mins in ABS mode, how long do you see the controller actually in ABS mode? I do think it is not something you can actually specifically bypass as the route is pre-programmed in regardless and all you can do is change the time spent in each stage (I don't know this for sure, just my belief)
I will try setting 0 mins on one of my SmartSolar MPPTs and see what it does

 

[PeteS]

Tbh I’ve only just set it 0 mins and it seemed to change certainly within a minute but that’s only once. I will keep monitoring it and see

 

[WildThingsKev]

I don't know about your controller but I'm certain that leaving solar charging in storage did for my previous batteries. I always disconnect solar when I'm not using the van now and just give the (gel) leisure batteries a top uk once a month, starter once a fortnight.

 

[PeteS]

This morning I realised I'd set Absorbtion voltage below Float voltage so unit was in Bulk at 13.1V so was going nowhere fast. I increased the Abs voltage to 13.4 and once the Bulk V reached that Voltage it switched to Absorption mode, took around 15seconds. It then stayed in Abs mode and I've noticed this before, I disconnected the link and reconnected and it was in Float.
So did it swap to Float while I was disconnected, about 3 seconds or does the mode not refresh as often as the voltage/current. I'll have to monitor that out of curiosity.
So after 1 night I have achieved what I wanted which is a small maintenance charge, we are away today for a few days so it will be out of storage mode and back into 'Normal' while we are away.
Time to monitor how it interacts with the mains charger which is a Ctek M300 which has no user settings but is temperature compensated at the battery.

For info I changed my solar controller because it wasn't temperature compensated and the M300 at temps below 0C would cause the over voltage alarm on the Solar to go off, mainly at night when the heating was on as the charger would put out over 15v in Absorbtion mode.

 

[wildebus]

Sounds good. For Absorption Mode, I would personally be inclined to set at a few minutes rather than zero (zero would be very unusual setting and maybe not actully act as expected?). choose 6 minutes and then you can also check the way the start voltage cuts the set time e.g. set at 6 minutes, and if the start of day voltage is >12.6V, you will have absorption for 1 minute; if 12.5V, absorption will be 2 minutes. While you are concerned about excessive absorption times, doing that would 1) confirm the controller is working as it is programmed and 2) give you such a short absorption time it should not be of concern?

It looks like you will have two different groups of settings you want to use then? I don't know if you utilize the feature or not, but you can save different settings to a file and then instead of going in and changing the various bits and pieces, you could just load up the appropriate file. So you could have say one file called "Storage" and another "On the Road" and load whichever is right for the situation.

 

[SquirrellCook]

So now you have me worried Pete, I'm using the Victron Smartsolar 100/30. It's permanently looking after 2 Trojan T105 6volt batteries.
I haven't checked the electrolyte since setting up for this seasons adventures. Sadly the vehicle is parked up/stored more than it's used.
I had a very short life out of my previous batteries, can't remember what they were of hand, but not cheap.
This prompted me to install the Victron kit. I've noticed after a big discharge and poor solar it can fail to reach 100% charge, unless bullied.
The next day if no load is taken it soon gets to 100%.
I have resisted camping beside it to watch what it does, but according to it's history around 50watts are used per day maintaining it and running the box of tricks. 12.75 being minimum voltage and 14.73 being the max. At the moment it's 13.32 and in Float.
About once a week I use the solar to change the engine start batteries as being a Merc there is always a load on them.
To date I'm happy in my ignorance, in two weeks we venture of for a week, the nocturnal fridge consumption will be a test for the batteries.
Fingers crossed.

 

[wildebus]

This is one of the things with the Victron Controller ... it will stay in Absorption mode for a set time - and that time may not be enough to fully charge the battery if the solar harvest is poor and below what the battery could take.
(I say the Victron controller there and other makes are different, but it is the battery maker that specifies the recommened maximum Absorption time and the Victron MPPTs can be set to that, but other makes don't have that setting available - so it is not really a Victron limitation. You could set an fixed absorption time of 24 hours if you wanted to)

 

[PeteS]

I do indeed save the stings in different files to load as required. The abs time I have set at 1 minute and 13.4 volts with a float of 13.2 for storage.
At the moment I’m turning solar controller off when on hook up to avoid it going through a bulk/absorption charge cycle when the solar wakes up. I might change some settings to overcome that in the coming weeks

 

[wildebus]

Hi Pete,
I raised a question (to myself mainly) about can the controller skip the absorption mode and go from Bulk to Float? I have that answer now from my own setup ....

I have set my controller to have a fixed 6Hr Absorption Time (I'm not using the variable time based on voltage method at the moment).
This was reached just before 15:00 and later on when a load meant the battery voltage dropped enough to revert back to bulk, the Absorption phase got skipped as all that time was used up earlier in the day

 

[PeteS]

That’s interesting because really it should go back through absorption to float as you have taken a fair amount of energy out the battery.
I have set my float to be slightly lower than the charger so it just sits there quite happily in float mode until it switches off. I wanted a fall back if we had a powercut rather than turn solar off.
I’ll see what happens in the morning.

 

[PeteS]

So I awoke this morning to find the solar in Bulk mode at 14.56V even though the mains charger had been keeping it in float at 13.72V all night.
That in my mind is wrong.
Ive looked back through the history now that I have worked out I can get a CSV file of it and whilst in storage it has had 2 hours of bulk and 2 hours of Absorption everyday on average over the last 30 days. That is not good on a battery that is not in use.

I need to see over the coming weeks when it is back in storage how the new settings fair, but 4 hours of 14.6v is just going to cause gassing on a FLA battery.
The SmartSolar is turned off for now whilst on hook up

 

[wildebus]

What is the mains charger set to in terms of voltage compared to the MPPT controller?

Out if interest, the graph I posted showing the timeline of the MPPT state? I also have a mains charger plugged in.

The way your controller is working sounds normal to me though. Your battery is at 13.7V. The MPPT Controller WITH the compensation is set to run at higher than 13.7V so when it wakes up at first light it will start it's charging routine and try and take the battery to the programmed voltage that you have set it (13.4V + temp compensation increase). Why are you thinking this is incorrect?


I would suggest as a test that you have the MPPT lower than the Mains Charger (this is already done), disable the temperature compensation fully and then see what happens next morning.

 

[wildebus]

One quickie ... what value have you got for temperature voltage compensation? If you have set the MPPT Absorption voltage to 13.4V and you see the MPPT controller outputing 14.56V, that is a massive compensation increase for Temperature (and also Voltage drop) adjustment.
The set voltage assumes a battery temp of 25C, and then the default setting is 12mV/C increase as it drops below the 25C default. If I look at my MPPT setting, I have the Absorption Voltage set at 14.2V and the maximum I have got today is 14.27V when the battery temp was 16C (that reading is from my mains charger temp probe, so the SBS connected to the MPPT could have a slightly different value. I haven't cross-checked)
If you were using the 12mV/C value for example, the maximum increase if the battery was at Zero C would be 0.3V, so your >1V is very strange (especially as I assume your battery is nowhere near 0C!) and is a massive adjustment (some of that could be calculated voltage drop as well of course).
I wonder if either the voltage temp compensation is not set correctly, or the SBS is relaying false information to the MPPT (especially on the voltage side which is causing the MPPT to boost the voltage to compensate for the apparent voltage drop?).
I think I would be inclined to disconnect the SBS and see what happens. This time of year, a big battery lump will hardly vary in temperature to really care about, especially when it is not actually being used hardly.

 

[PeteS]

Thanks for the reply, I don't think it's incorrect just not what I would like when the battery is fully charged. I need to adjust the settings to compensate. I hadn't appreciated that when the controller wakes up it automatically goes into bulk mode (I assume) irrespective of where the battery is sitting in relation to float voltage. Now I realise that I can adjust some settings.
I had been compensating by adjusting the float voltage assuming it checked that first as my float voltage on the controller is lower than the charger.

 

[PeteS]

My temperature compensation is set at 16.2mV/C which is the default in the FLA preset. battery is currently at 18C

The 14.56 at 18C is 14.4 + 113mv almost so I think the compensation is right.

I'm learning very rapidly how this controller thinks, I'm going to set the abs voltage to be lower than the charger float voltage which hopefully will stop the solar going into bulk mode when it wakes up, I think thats what you have suggested.

Thanks again

 

[wildebus]

My temperature compensation is set at 16.2mV/C which is the default in the FLA preset. battery is currently at 18C

The 14.56 at 18C is 14.4 + 113mv almost so I think the compensation is right.

I'm learning very rapidly how this controller thinks, I'm going to set the abs voltage to be lower than the charger float voltage which hopefully will stop the solar going into bulk mode when it wakes up, I think thats what you have suggested.

Thanks again

Ah, ok. That sounds right then. I was concerned due to an earlier post (#11) where you had said ....

....The abs time I have set at 1 minute and 13.4 volts with a float of 13.2 for storage....

I am now guessing the 13.4V was a typo and you meant 14.4V? (I thought the 13.4V setting might have been to try and force the controller to never to anything but a float charge)

I mentioned that I also have the same MPPT (and SBS) and am also plugged into mains at the same time, so a pretty similar configuation. I looked at my data and this may be of interest to your setup? (Please do tell me if you want me to 'cease and desist' - I do tend to get overly into this kind of discussion!)

So this is what the AC Mains Unit did from midnight to midnight yesterday (values in Watts, the peaks are the fridge compressor surges and heater )


This is the MPPT Controller output (again in Watts)


And if you overlay the two, you can see how the Mains Unit provides the background float power during night time, as soon as the MPPT unit wakes up, it is that that provides the background power and the Mains unit, even thought it never varies from float in terms of charging mode, it does drop its DC output as the MPPT takes over (and in the usual dip from 3-4PM (big tree blocks panels) the Mains comes back in as the MPPT drops off)


This to my mind is just as you would want it, with the "free" energy from the Solar taking priority over the grid power from the AC Mains Charger,

 

[PeteS]

Ah, ok. That sounds right then. I was concerned due to an earlier post (#11) where you had said ....

I am now guessing the 13.4V was a typo and you meant 14.4V? (I thought the 13.4V setting might have been to try and force the controller to never to anything but a float charge)

No I did mean 13.4V but that's for a storage setting file, that one seems to work ok.

At the moment I'm working with the FLA preset and adjusting settings in that to allow it to work alongside the mains charger which is set to 14.4 for Bulk and Abs and 13.6v for float with the same temp compensation. (I cannot change those values.

To prevent the solar going into bulk/abs while the mains is present I was going to set Solar ABS to 13.5v with a float of 13.4 and see what happens in the morning.

It would be nice for them to work together but the charger is also a 20A power supply so it can provide quite a lot of power at Float voltage before it takes anything from the battery. So I don't think they are ever going to work in harmony............

Really happy for this discussion to carry on, I'm trying to find a solution to this, I have an electronics background and its good to bounce ideas.
I'm really trying to get my battery to work as it should, its a Banner FLA which I know is much maligned but for all the wrong reasons.

Thanks for the help so far.