Victron MPPT Battery Charging Algorithm

[noelex 77]

The Victron MPPT regulates the battery very differently to all other solar controllers. Although some aspects of the algorithm are used by other brands, the net effect is the Victron solar regulator uses a very different method to determine if the regulator should be in bulk, absorption or float.

I have used solar as the primary means of battery charging on boats for more than 30 years with many controllers. The last 10 years we have been cruising full time so this provided plenty of time to study how various controllers perform. I have only lived with the Victron for a short time so the conclusions below are provisional, but hopefully through this thread any errors I have made will be pointed out.

My controllers are the Smartsolar 100/20 models.
These are some of the things I have discoved so far:

The absorption timer does not count up when the battery voltage is only at the absorption voltage. This may seem like a minor point, but this is the cornerstone of how most regulators work. After the bulk cycle the Victron regulators count “absorption time” continously irrespective of the battery voltage unless the voltage drops below the float voltage for 1 minute. This will trigger another bulk cycle. So rather than displaying time actually spent at absorption voltage, the “absorption time” Victron is displaying is actually “elaspsed time after bulk”.

Victron's “maximium absorption time” set by the user is modified by the start up voltage when the regulator first wakes up. If the start up voltage is 11.9v or below, the “elapsed time after bulk” will be the “maximum absorption time set by the user”. If the start up voltage is between 11.9v and 12.2v the “elapsed time after bulk” will be 2/3 of the “maximum absorption time set by the user”. If the start up voltage is between 12.2v and 12.6v the “elapsed time after bulk” will be 1/3 of the “maximum absorption time set by the user”. If the start up voltage is over 12.6v the “elapsed time after bulk” will be 1/6 of the “maximum absorption time set by the user”.

So if you operate an appliance with a high current drain such as an electric kettle just before solar start up, your absorption time will be very different compared to operating the same kettle later in the cycle.

The Victron regulators will initiate another bulk/absorption/float cycle much more readily than other regulators. For most regulators the bulk return voltage is around 12.2v (for a 12v system). For the Victon regulator it is float voltage (with a 1 minute delay) so it is likely to be around 13.8v. There is an enormous difference between the likelhood of the voltage dropping below 12.2v during the solar day compared to likehood of the voltage dropping below 13.8v. The bulk return voltage is not adjustable on the Victron regulators.

Finally, if the total current drops below a set value and the voltage targets are being met, the regulator will drop down to float. This set value depends on the size of the regulator, but is the same for 12 or 24v systems. For my 100/20 regulator the set value is 1A. This is a major nuisance if you have a multiple controller set up and I hope Victon can introduce a change in the software so this fuction can be disabled or the value modified by the user.

The most important question is how well does this very different algorithm perform in the real world. Unfortunately, I will have to need a longer evaluation period. First I want to understand how it works.

[Pete7]

Probably going to need to sit down and read that again when on board looking at the Victron display and the manual in hand.

However, John one question for the time being, how good is the default set up out of the box for these MPPT charge controllers? I have a pair of them set for FLA batteries with the default charging algorithm.


Pete

[Greg4cocokai]

I just installed to Victron 100/30 charge controllers for my 2x300w panels. When nearing 100%SOC, the controllers would bounce back and forth, with one putting out max and the other 20% of that.

I added a pic of my color controller, what are the setting at the bottom right?

[noelex 77]

Originally Posted by Pete7

However, John one question for the time being, how good is the default set up out of the box for these MPPT charge controllers?

It is worth the trouble to check if the default settings are correct.

Firstly check the battery set points for absorption, float and equalisation. The best guide is from the battery manufacturer, but if you post your battery type someone will probably already know the answer. My three Victron regulators measure voltage accurately, but if you have a well calibrated multimeter this is worth checking. Some other models I have looked at can be 0.2v or more out, which is enough to be very significant.

The above voltages need modifying for temperature. The Victron temp sensor on the smaller controllers is not external, so is not a great deal of use (although they have recently released an external device that will do this with some models). Personally, I have disabled this temperate measurement and manually measured a typical battery temperate and modified the voltage set points to take this into account. This only needs to be redone for different seasons and locations, small temperature differences are not important. If you have a very high power charging system (big alternator or solar array relative to the battery capacity) it is worth checking how much the batteries heat up when charging.

Then there is absorption time. The default setting on the Victron is 6hrs, but this will be modified by the start up voltage and the actual time will be between 1 and 6 hours. It is important to realise this is not a true absorption time, but simply the net time after bulk. On most systems this will be conservative, and especially with flooded batteries I would increase this to around 12 hours. Better again is to measure the battery return amps or sometimes called end amps. This is the net current entering the battery just before the regulator drops down to float. The correct value should be around 0.5 to 1% of the capacity. In other words if you have a 400AHr battery bank if the absorption time is correct, the current entering the battery when the absorption voltage is being maintained should be 2 to 4 A depending on who you believe. In practice, the current drops off quickly so there is not as much difference between 2 or 4 amps. Lets use 3A as a reasonable number. If the current entering the battery is more than 3A just before the absorption cycle ends, the absorption time is too short and should be increased. If it less than 3A the absorption time is too long and should be shortened.

It is better to monitor a few charge cycles. Don’t get too concerned getting it exactly right. With flooded batteries you can be quite aggressive. With gel batteries you need to be a little conservative and with AGM you should make a more serious effort to set things exactly right.

[noelex 77]

The other interesting, and I think very good feature is that if a new cycle (bulk absorption and float) is initiated, the absorption time for the subsequent cycles is much shorter than the original cycle.

About a quarter of the absorption duration seems typical. This is not mentioned anywhere in the documentation, but seems one of the fundamental keys that makes the algorithm work. Most regulators rarely initiate a second cycle and if they do the absorption time is the same as the first cycle. The Victron very readily starts subsequent cycles, but reduces the chances of overcharging by reducing the absorption time on these cycles.

Very interesting.

[noelex 77]

Originally Posted by Greg4cocokai

I just installed to Victron 100/30 charge controllers for my 2x300w panels. When nearing 100%SOC, the controllers would bounce back and forth, with one putting out max and the other 20% of that.

That is normal, Greg. Providing the batteries are kept at the required set point it is not a problem.

For example, if you are in absorption mode with a voltage set point of 14.6v and the batteries and load require 5A to maintain this voltage, it does not matter to the batteries if all the 5A is supplied by either one controller or the other, or if 2.5A is supplied by one controller and 2.5A by the other, or any combination.

As far as the batteries are concerned, as long as they are at the set point of 14.6v and have the required 5A to maintain this voltage all is OK.

Sorry, I haven't used the Victron colour controller so I am not familiar with the settings, but I am sure someone will know.

Nice avatar BTW. I am partial to mermaids .

[travellerw]

Originally Posted by Pete7

Probably going to need to sit down and read that again when on board looking at the Victron display and the manual in hand.

However, John one question for the time being, how good is the default set up out of the box for these MPPT charge controllers? I have a pair of them set for FLA batteries with the default charging algorithm.


Pete

I found the default settings were not sufficient for my standard golf cart FLA bank. All three of my controllers were off by about 0.2V when checked at the battery terminals with a multimeter. I'm guessing some of that was do to wiring and buss bar loses.

I bumped my absortion voltage to 15V and my absorbtion time to 10 hours. We have been using these settings for about 9 months of full time cruising. The batteries get all the way to 14.8V at the terminals.

I have also mounted my controllers right next to the batteries (actually attached to the sealed battery box). This helps the controllers do acurrate temperature compensation.

So far we have been very happy with our Victron controllers. We had EPEVER controllers for our first 2 years of cruising (killed by lightening). While they worked well, the Victron's are better. Our batteries generally seem to be happier and we are waking up to higher voltages. The batteries also seem to be using less water than with the previous controllers.

[john61ct]

I have a lot of faith in the Dutch engineers at Victron, but have to say I'm surprised that their algorithm isn't better documented. Perhaps they are being opaque for competitive reasons.

In any case, until we fully understand the decision tree flowchart, I'm willing to treat it as a Black Box.

I consider "Absorb Hold Time" to be from when Bulk ends until Float starts.

______
Isolated from any loads, starting with my bank at 50% SoC, what does trailing current read when the SC drops to Float?

If that amps measurement is near ballpark for my target endAmps, great. If not, bump it up and iterate testing until it is.

Then repeat the above with normal loads connected up.

Obviously, the more consistent your setup's usage patterns are, the more regularly you will hit target endAmps without risking overcharging, which is important for GEL, also AGM, but less of a concern with a FLA bank.

In fact with FLA, as long as you keep water topped up, some may just set Float to the Absorb voltage while the bank is in regular use cycling mode. They just need to remember to set it back to normal (or lower) when the bank is in storage, or at least not being cycled.

As beaten to death in this thread: http://www.cruisersforum.com/forums/....php?p=2646786

[chris in SG]

Originally Posted by Greg4cocokai

I just installed to Victron 100/30 charge controllers for my 2x300w panels. When nearing 100%SOC, the controllers would bounce back and forth, with one putting out max and the other 20% of that.

I added a pic of my color controller, what are the setting at the bottom right?Attachment 171544

I was scrolling through threads and posts looking for queries and advice on what I would call 'interaction and interference' between solar charge controllers working in tandem. I was hoping this (quoted) post would have prompted more feedback but it seems not.

I'm sure my situation can't be unusual - the result of adding solar panels which are different specs and therefore require separate controllers. I have two 325W 24V panels and one 300W 24V panel for a 12V system. The twin panels are controlled by a Bluesky controller (which I chose because I liked the integrated battery monitor) and the 300W panel is controlled by a Victron 100/30 smart controller. I find that the controllers get confused by the apparent battery voltage which is actually the solar voltage from the other controller. If Victron sold a controller or a network which could address this problem then I would invest in another Victron controller and use the bluesky hardware for battery monitoring only. BUT I don't see Victron advertising any system which would address my problem. If I have two 100/30 controllers, they will still be 'confused', it seems to me. Then I see Greg's post and photo of the colour monitor thingy (which I always thought seemed a bit gimmicky) and I wonder if the screen reference to "standalone or parallel" touches on the issue I'm concerned about.

Any views on this anyone?

[john61ct]

My view is what you see as confusion should not result in any serious issues, the bank does end up getting charged to full when it's sunny, if there's enough panels.

There are systems that coordinate multiple controllers, and suspect Victron has them, have you contacted them to ask how?

At the high end with the add-ons they can get expensive but. . .

I suggest you start a new thread giving detailed observations of the specific behaviour you consider a problem.

[travellerw]

Originally Posted by chris in SG

I was scrolling through threads and posts looking for queries and advice on what I would call 'interaction and interference' between solar charge controllers working in tandem. I was hoping this (quoted) post would have prompted more feedback but it seems not.

I'm sure my situation can't be unusual - the result of adding solar panels which are different specs and therefore require separate controllers. I have two 325W 24V panels and one 300W 24V panel for a 12V system. The twin panels are controlled by a Bluesky controller (which I chose because I liked the integrated battery monitor) and the 300W panel is controlled by a Victron 100/30 smart controller. I find that the controllers get confused by the apparent battery voltage which is actually the solar voltage from the other controller. If Victron sold a controller or a network which could address this problem then I would invest in another Victron controller and use the bluesky hardware for battery monitoring only. BUT I don't see Victron advertising any system which would address my problem. If I have two 100/30 controllers, they will still be 'confused', it seems to me. Then I see Greg's post and photo of the colour monitor thingy (which I always thought seemed a bit gimmicky) and I wonder if the screen reference to "standalone or parallel" touches on the issue I'm concerned about.

Any views on this anyone?

We run 3 Victron MPPT controllers and a single cheap Chinese brand MPPT to charge our single 12V battery bank. All three controllers terminate to the same spot on the buss bar. We don't have any 'confused' issues at all. They all play nice until the upper portion of the 'Absorbtion' phase. At that point randomly 1 of the three will stay in Absorbtion while the other 3 will drop to Float. Eventually the forth unit will drop to float.

[john61ct]

Originally Posted by chris in SG

If Victron sold a controller or a network which could address this problem then I would invest in another Victron controller

Google for their VE. can protocol.

Looks like CCGX is an enabling piece.

One starting point https://www.victronenergy.com/blog/2...controllers-2/

But again, if you're on a budget, unnecessary bells & whistles IMO

[chris in SG]

Thanks for your suggestions. Yes, I should contact Victron and see how helpful they can be. I suspect they may suggest that I should only be using Victron controllers, then they will work together without deliberate networking. That seems to be travellerw's experience.

[noelex 77]

Originally Posted by travellerw

They all play nice until the upper portion of the 'Absorbtion' phase. At that point randomly 1 of the three will stay in Absorbtion while the other 3 will drop to Float. Eventually the forth unit will drop to float.

Ideally all the controllers should terminate the absorption phase at (or roughly at) the same time. The Victron algorithm bases the time after bulk (it is not true absorption time) on the voltage at startup. So with my start up voltage this morning (25.8v) and my “maximum absorption time setting” of 12 hrs the controllers should have stayed in “absorption” mode for exactly 2 hours. One of the controllers did exactly this. One controlled dropped down to float at only 47 min and one dropped down to float at 1hr 5 mins.

This early termination of the absorption phase by two of the controllers is not desirable. The early termination is due to the “Tail current cut off feature”. If this could be disabled, the other two controllers would have stayed in the “absorption” phase of the same two hours as the first controller.

The early termination of the two controllers is of no consequence providing the solar power is enough for the one solar panel to maintain the absorption voltage. However, if the sunlight level drops or the loads increase, the battery voltage can drop well below the absorption voltage and stay there without the other two controllers offering any power, which is not ideal.

[travellerw]

Originally Posted by noelex 77

Ideally all the controllers should terminate the absorption phase at (or roughly at) the same time. The Victron algorithm bases the time after bulk (it is not true absorption time) on the voltage at startup. So with my start up voltage this morning (25.8v) and my “maximum absorption time setting” of 12 hrs the controllers should have stayed in “absorption” mode for exactly 2 hours. One of the controllers did exactly this. One controlled dropped down to float at only 47 min and one dropped down to float at 1hr 5 mins.

This early termination of the absorption phase by two of the controllers is not desirable. The early termination is due to the “Tail current cut off feature”. If this could be disabled, the other two controllers would have stayed in the “absorption” phase of the same two hours as the first controller.

The early termination of the two controllers is of no consequence providing the solar power is enough for the one solar panel to maintain the absorption voltage. However, if the sunlight level drops or the loads increase, the battery voltage can drop well below the absorption voltage and stay there without the other two controllers offering any power, which is not ideal.

That is interesting, mine are usually only a few minutes apart from Absorbtion to Float (max I would say 10 minutes). I wonder if this is due to my solar arrays being very physically close together. They all must "wake up" at the same time.

The other thing my controllers do. If the voltage drops due to load increase or sun loss, then they switch back to Bulk really quickly (within a min or so). At that point all three will go back to Bulk and begin putting in power. They do this even if all 3 are sitting in Float and I kick on my water heater. This seems to line up exactly with your first post.