Prioritising solar panels and wind turbines over mains chargers

[SpitfireJay1]

Just registered, thanks to the administrative officer for quoting a Kantian ethic. First time poster, so please be gentle lol. Ok I have an old ferro endurance and am trying to go off grid, not just because of higher bills but I like the independence . I have now six 90ah agm batteries, powered by an old Rutland 913 and currently in possession of four 100w explorer solar panel. Not sure if you allowed to mention brand or companies on here, but I'm sure the moderators will put me right, but when generic terms will suffice I will use them. Ok so 400w of solar and when I have built the new gantry 200w more plus whatever the variable outputs of the wind turbine is. So 600w plus say 30 for the turbine. Apparently my very cool ctek m200 does not push out the 14.7 that agms need, so I now have a victron ip65 and 50amp victron mppt charge controller en route....... phew. Ok my question is, how do I prioritise the solar and wind as the primary contributor to the charging system, rather than the mains charger. Up till now I have been turning off the mains charger during the day, then back on at night. Now I'm just leaving it on all the time. A shunt when finances allow. Will the smart chargers talk to each other and do it automatically the most frugal way or what ?

 

[jwfrary]

Umm short answer is no.

Long answer is there's some workarounds but they require a bit of extra wiring and complication.

Option 1

The Mppt you bought may have a load output, this could be used with a relay to turn your charger on when it's dark and off when it's sunny.

Option 2

Use a slightly lower charge voltage on your shore power charger than on your solar there by prioriting solar, less complication but it also means the shorepower wont give quite as Fuller charge.

To do this set the float absorbtion and bulk voltages in the chargers at. 0.1v from each other. In practice you will also need to account for voltage drop in the cables for each of the two chargers.

You Could also do both to cover all your options

 

[Gumpy]

Its been easy for me with just two sources to prioritise solar over a mains charger, However you do need to be able to set the charge voltages on both the MPPT and the charger
I have 500w of solar with an EPever MPPT and a Victron Multiplus.
I set the charge voltages on the MPPT 0.2v higher than the charger *
Charger
Float voltage is 13.4v Absorption 14.2v
MPPT
Float is 13.6v Absorption 14.4v
The charger sits there most of the time when its sunny doing nothing when the sun goes in it takes over the float charge duties.
The only time its a problem is if there is a power cut when the MPPT is in float mode and the charger then goes through its cycle which is set to be less than one hour.
I've been running it this way for a couple of years now.


* voltages are correct for my sealed batteries if you have AGM or FLA voltages will be different.

 

[SpitfireJay1]

Thank you both for your replies. Yes I do have AGM batteries as advised by my supplier as I am on a sailboat and will when launched, heel over quite a bit and will receive some vibration, which I was informed AGM's are more capable of dealing with because the acid is in packages and not free flowing, bit like my old waterbed lol. Apparently AGM need 14.7 input and the mains victron is Bluetooth and so is the victron charge controller I will receive next week and both have apps and controllable usability so I may be able to prioritise that way. Apparently I will need a shunt later as well and I'm hoping that buying the latest types from the same manufacturer will mean better controllability. I really do want off grid as much as possible so will buy an inverter briefcase generator to power the mains charger. This is all beyond me but I am slowly learning and applying from research and now help from this forum but still might require a professional marine electrician . Thank you.

 

[Gumpy]

If charging using Victron kit then there is another thing to be considered.
I would turn off adaptive charging in the Victron and set a fixed absorption charge time since the charger will drop into float way to early when using adaptive charging leading to under charging of the batteries. Its not so bad when you have solar but in winter its a big consideration .

 

[SpitfireJay1]

If charging using Victron kit then there is another thing to be considered.
I would turn off adaptive charging in the Victron and set a fixed absorption charge time since the charger will drop into float way to early when using adaptive charging leading to under charging of the batteries. Its not so bad when you have solar but in winter its a big consideration .

Thank you for time and understanding. Best wishes. Jay.

 

[noelex]

If charging using Victron kit then there is another thing to be considered.
I would turn off adaptive charging in the Victron and set a fixed absorption charge time since the charger will drop into float way to early when using adaptive charging leading to under charging of the batteries. Its not so bad when you have solar but in winter its a big consideration .

Adaptive charging is a good feature. I would be reluctant to disable this setting.

If the charger is dropping to float early you are much better to simply extend the absorption time. This will fix the issue without disrupting the charge algorithm.

 

[Gumpy]

Adaptive charging is a good feature. I would be reluctant to disable this setting.

If the charger is dropping to float early you are much better to simply extend the absorption time. This will fix the issue without disrupting the charge algorithm.

Except that, unless they have changed the software, the absorption time is set by the algorithm, all you can do is set the maximum time which doesn't extend the time it just limits it.

 

[noelex]

Except that, unless they have changed the software, the absorption time is set by the algorithm, all you can do is set the maximum time which doesn't extend the time it just limits it.

The adaptive charging measures the battery voltage at start up and adjusts the absorption time. The idea is if the battery voltage low the absorption time will be extended beyond the normal fixed 2 hrs used by most chargers.

The default settings give a 6 hr absorption time if the battery voltage is below 11.9 v ( for a 12v system). 4hrs for a voltage between 11.9 v and 12.2v. 2 hrs for a voltage between 12.2 v and 12.6 v and 1hr for a start up voltage above 12.6v.

It is sensible system, smarter than the fixed ( usually 2 hr) adsorption time used by most chargers. Disabling this feature is not a good idea for most installations, although there are some rare exceptions.

If the default absorption time is too short (which is unusual ) it can easily be increased. Increasing the the absorption time on the Victron units will always do just what it implies even with the adaptive charging feature enabled and the absorption time will extend. For example if the default absorption time is doubled the times quoted in the second paragraph will also double.

It is more common for the default absorption times to be too long. If this is the case it can easily be reduced while still retaining the adaptive feature. The adaptive nature of the absorption time will work to automatically extend the absorption time on those occasions where the battery is more deeply discharged than normal.

if the absorption time is abnormally short a more likely culprit is the tail current feature. This can occasionally result in a much shorter than desirable adsorption times for some installations. Generally this feature is better disabled on marine systems, especially with multiple charge sources. This can done easily on most Victron equipment via the software.

 

[Gumpy]

The adaptive charging measures the battery voltage at start up and adjusts the absorption time. The idea is if the battery voltage low the absorption time will be extended beyond the normal fixed 2 hrs used by most chargers.

AIUI the absorption time is calculated from the time that bulk takes to complete nothing to do with the voltage, for adaptive charging to work it also needs to know the battery bank size, is there a setting for it within Victron?

 

[Gumpy]

Just checked on my Victron adaptive charging time is generated from the Bulk time so nothing to do with voltage

A theory on why adaptive charging can't work!

Adaptive charging is fundamentally flawed unless the charger knows the size of the battery bank it is charging. There are many very complex issues that interact to mess the whole idea up.

Assume the charger does *not* know the size of the battery bank.

If the battery is very deeply discharged then the bulk stage will take a long time. If it isn't deeply discharged the bulk stage will be very quick.

From this the assumption is made that if the bulk stage took a long time (and hence the batteries were deeply discharged) then the acceptance cycle is made long. If the bulk stage was short, (and hence the batteries were not deeply discharged and merely required a "bit of a top up") then the acceptance cycle is made short. So the acceptance cycle time is calculated as being proportional to the bulk cycle time.

This leads to an anomoly.....

Assume a battery discharged to 50%. The charger goes into bulk and it takes 5 hours to reach acceptance. From this it calculates it needs a (say) 3 hour acceptance cycle (it doesn't matter what figures we actually use).

Now put the same charger on a battery bank half the size. The bulk cycle will last roughly half as long. So it caculates an acceptance cycle of a shorter time than the one above, let's say it calculates 1.5 hours.

In the first case the charger was smaller in relation to the batteries than in the second case yes?

This means that when the acceptance voltage was reached in the first example, the batteries would actually be in a higher state of charge than when the acceptance voltage was reached in the second example.

Think about it. If you put a 1000 amp charger on a 10Ahr battery the acceptance voltage will be reached *instantly* even though the battery is nowhere near charged.

This means that the required acceptance time in the first example is actually *shorter* than that required in the second example, not longer as the charger calculated. So in this case the charger calculated *exactly* what was *not* needed.

So we can turn it round. The acceptance cycle time becomes *inversely* proportional to the bulk time.

If we discharge the original battery to 50%, it takes 5 hours for the bulk cycle, calculates 3 hours for the acceptance.

Now discharge the same battery to 75% state of charge. The bulk cycle will last roughly 2.5 hours and the charger calculates a *longer* acceptance cycle, say 6 hours. This is also clearly wrong!

Both are wrong. An acceptance cycle time proportional to bulk cycle time fails in the case of different battery capacities.

An acceptance cycle time *inversely* proprtion to the bulk cycle time fails in the case of different state of charge levels on the same battry bank.

Unless the charger knows the size of the battery bank *and* knows how much current is going into the batteries as opposed to into the loads *and* knows the state of charge of the batteries at the beginning of the charge cycle, adaptive charging is fundamentally flawed.

There is no way round the fact that a fixed time period for the acceptance cycle is the best way to go. And it has to be a lot longer than many chargers run it for.
The only way to tell when the batteries are nearing fully charged is when the tail current drops and steadies at about 1-2% of battery capacity.

 

[noelex]

Ah, I see the confusion. When you suggested that SpitfireJay 1 turn off adaptive charging on his “Victron Kit” I understood this advice to include his Victron 50amp mppt charge controller. Perhaps you meant only the mains charger?

The adaptive charging for the Victron 50amp mppt charge controller works in the manner I indicated in post #9. Turning off adaptive charging would be counterproductive.

The Victron mains chargers use a different adaptive system based on bulk time, as you have indicated. But I do not agree this is a bad system. Nor do Victron (and other manufacturers with a similar system), otherwise they would not incorporate a complex feature and would simply use a simpler dumb charging algorithm with a fixed absorption time.

The system is not complex to understand. A longer bulk time (if nothing else is changed) indicates a lower SOC and therefore the need for longer absorption time. Most users will have experienced this for themselves. Charging a near full charged battery results in a short bulk time (which will also need a short absorption time) conversly a well discharged battery needs a long bulk time.

 

[Gumpy]

I did mean the mains charger.
Sorry for the confusion on that.
As explained the mains charger adaptive charging is not the best ?
Despite that I have a multiplus on the boat and a charger in the caravan.

 

[SpitfireJay1]

Thank you all for your Response's, it truly brings a tear to the eye for this old Kantian to see so many people taking the time to help me who has little or no knowledge of this subject. I will keep this page open and although I am unlikely to have the knowledge to help with many marine based issues. If any railway or psychology issues need answering, my time will become your time. Thank you again. I understood 90% of that, which is enough when my shunt is purchased to make a system that should work very well, although my bank account is itchy and sore lol.