Turbo-charging Motorhome Electrics

[xsilvergs]

@wildebus
Why not use Node-Red to control the relay which will disconnect the lithiums?

Does the LiFePo4 really worry about the absorption voltage? Those that don't use B2B's and charge direct from the alternator aren't.

Long absorption periods would ensure the lithium batteries balance and their cells balance.

So many lithiums are advertised as drop in replacements and have long warranties, is the manufacturer worried about absorption times?

From my experience with a pair of Ecotree lithiums in parallel I was surprised to see how equally they consume a 60 amp charge, each taking close to 30 amps. I do see that minutes after the MPPTs go into absorption there charge current drops to near zero.

 

[PeteS]

I dont think the absorption time is an issue, the BMS controls the charge, mine starts to reduce at 3.45v/cell and the tail current falls to below 1Amp around that voltage such that Absorption for my Lithium setup on average lasts around 6 minutes then it drops to float.

 

[wildebus]

@wildebus
Why not use Node-Red to control the relay which will disconnect the lithiums?

Does the LiFePo4 really worry about the absorption voltage? Those that don't use B2B's and charge direct from the alternator aren't.

Long absorption periods would ensure the lithium batteries balance and their cells balance.

So many lithiums are advertised as drop in replacements and have long warranties, is the manufacturer worried about absorption times?

From my experience with a pair of Ecotree lithiums in parallel I was surprised to see how equally they consume a 60 amp charge, each taking close to 30 amps. I do see that minutes after the MPPTs go into absorption there charge current drops to near zero.

Well.... A few things here.
Lead-Acid batteries require a higher charge voltage and also temperature compensation so the colder they are, the greater the charge voltage. In the winter you can hit 15V on the charger.
Why am I talking about Lead-Acid charging parameters? Because I have the Lithium and Lead connected together so when the lithium is charged but the Lead still needs charging, the voltage would be too high.
You can't really relate the settings I need for my Hybrid Battery setup to that of a 100% Lithium Bank - different needs, different configurations.

Do you want a long absorption time anyway. I say no. The battery cells balance internally and don't need an absorption level type of voltage to do so, and so there is no advantage to having that. You might want to do that occasionally for top-balancing but I find the cells equalise over a time following a charge or discharge.

Ref Node-red, there is no advantage to using that for that function, but actually a disadvantage as it brings additional complexity and componentry into the equation.
Say I was going to use what I have permenantly ... With node-red I would need the BMV to send a signal via its low-current relay to the high-current power relay, but have the Venus OS device running and Code Red active and programmed to read the voltage and issue the command via the BMV (which would be set as a Remote Relay). Extra components that if not running will stop it working. I see no advantage to that when you can just set the parameters direct in the BMV. What I missing that Node-Red would add?

Why are Lithiums advertised as drop-in replacements? Because if they were not, people wouldn't buy them. Lithiums are NOT drop-in replacements in truth. You have to have the right charging setup and monitoring setup for them. They WILL work as direct drop-ins, but not optimally.

On your setup, you see the MPPTs go into absorption and then charge drops to zero minutes after. That is correct as the charger is in bulk mode all the time the batteries are really taking a charge. Lithium doesn't have an absorption mode requirement and what you are seeing is demonstrating that. Your charger should drop to float very soon after it is in absorption mode, and the float is pretty well just the resting voltage of the battery and ideally should be disconnected.
When it comes to charging from the alternator rather than via a B2B, you will find that the relay gets (in correctly configured setups) disconnected once the Batteries are full and the battery is not sitting at whatever voltage the alternator is putting out.

 

[wildebus]

I dont think the absorption time is an issue, the BMS controls the charge, mine starts to reduce at 3.45v/cell and the tail current falls to below 1Amp around that voltage such that Absorption for my Lithium setup on average lasts around 6 minutes then it drops to float.

It isn't. Voltage is.

 

[xsilvergs]

Typical charge cycle for my Ecotree batteries. Charge current goes to zero as the MPPT's go to Absorption.

Can cell balancing take place while the battery is being charged? Balancing, should we say "Top Balancing" isn't this usually done at a fixed voltage? Or are we talking about some other type of balancing?

I have seen my batteries disconnect themselves if the charge voltage goes higher than the manufacturers recommendations.

From a quick look at the Cerbo it only has digital inputs and sadly no digital outputs, am I correct?

 

[wildebus]

Your charging is typical of LiFePO4 Batteries - all looks normal there.
Top Balancing is pretty unusual I would say and generally can be ignored I would say. I have found cell balancing carried out by the batteries internal BMS takes time and is when the battery is generally pretty inactive. Your batteries will disconnect themselves - high voltage protection feature in the BMS - which is why you don't want them sitting at a high voltage of course. Always best to avoid the error in the first place as when your batteries disconnect, you presumably lose battery power and are dead? A bit inconvenient?

The Cerbo has 4 digital IO ports, but you are quite correct - they are in fact only Digital Inputs and NOT Digital Input/Output.
You could consider the two relays as Digital Outputs I guess and control those via Node-Red if you wanted. I am using those two relays for other purposes however.
If you had a Pi I guess you could use a GPIO port to send a control signal to a Power Relay, but I don't see a reason when you have a method to control it more directly and reliably from the device that is supplying you already with the voltage information that you would use as the basis to issue the signal.

 

[xsilvergs]

Your charging is typical of LiFePO4 Batteries - all looks normal there.
Top Balancing is pretty unusual I would say and generally can be ignored I would say. I have found cell balancing carried out by the batteries internal BMS takes time and is when the battery is generally pretty inactive. Your batteries will disconnect themselves - high voltage protection feature in the BMS - which is why you don't want them sitting at a high voltage of course. Always best to avoid the error in the first place as when your batteries disconnect, you presumably lose battery power and are dead? A bit inconvenient?

The Cerbo has 4 digital IO ports, but you are quite correct - they are in fact only Digital Inputs and NOT Digital Input/Output.
You could consider the two relays as Digital Outputs I guess and control those via Node-Red if you wanted. I am using those two relays for other purposes however.
If you had a Pi I guess you could use a GPIO port to send a control signal to a Power Relay, but I don't see a reason when you have a method to control it more directly and reliably from the device that is supplying you already with the voltage information that you would use as the basis to issue the signal.

I know my batteries look normal I don't need you to tell me that.

Your understanding of battery balancing seems to differ from mine.

A win for the cheaper RPi over the Victron product I guess.

 

[wildebus]

I know my batteries look normal I don't need you to tell me that.

Your understanding of battery balancing seems to differ from mine.

A win for the cheaper RPi over the Victron product I guess.

I am still not getting the advantage of Node-Red to activate the relay?

 

[xsilvergs]

I am still not getting the advantage of Node-Red to activate the relay?

As your Cerbo has no digital outputs and if it doesn't have a spare relay output there probably is no point to using Node-Red.

There may be no "advantage" to using Node-Red (did I say there was?), it could be an alternative, a 21st century option.

 

[wildebus]

Where Node-Red could come in useful is if the batteries themselves were compatible with a Node-Red interface. Using Node-Red in this situation however would just add an additional layer to the components that were already in place so IMO is not an alternative but just an unneccesary complexity. (Node Red in a Victron setup I personally see much more as a information and analysis tool rather than a control one)

The actual solution once delivered will actually not need Node-Red, An RPi, a Cerbo or even a BMV to provide an automated and programmable Lithium Disconnect. This is important as it means it is suitable for installations which are not Victron-based in any way and any kind of Lead Acid Battery and any kind of Battery Charger - in other words, it makes a Lithium Battery truely a Drop-in, and not just a Replacement but an Addition.

The use of a dedicated Lithium BMV with the VSDR Lithium Controller extends the flexibility as you can if you want decide how charged you want the Lithium to be in a Hybrid Bank - there is a theory that charging only to 80% doubles the life. Is that right? no one actually knows. Does it matter? who cares if you get an extra 10 years from the bank if a replacement after the normal lifespan maybe 1/4 the price you originally paid and you would have had that extra 20% of capacity available to you all that time. But the option is there for those who are interested.

 

[xsilvergs]

(Node Red in a Victron setup I personally see much more as a information and analysis tool rather than a control one)

Great shame. Find to time and explore its capabilities you may be very surprised what can be achieved.

 

[wildebus]

Great shame. Find to time and explore its capabilities you may be very surprised what can be achieved.

Rely on something that may not be running after a restart and you may be disappointed at the results.

Node-Red is good - but you cannot run the interface - at least the Victron implementation within the OS Large - on a Tablet or Phone*. Kind of limits the usability of the product in a mobile environment I would say. THAT is the great shame as it removes it from being a product that can be relied on.


*You may have found a way to do so, in which case please share how on the Victron Community where this is a common question and so far no one has posted a solution,

 

[xsilvergs]

Rely on something that may not be running after a restart and you may be disappointed at the results.

If it's not running I guess your Cerbo won't be running either.

If your results with Node-Red have been disappointing perhaps the problem isn't with Node-Red.

 

[wildebus]

If it's not running I guess your Cerbo won't be running either.

If your results with Node-Red have been disappointing perhaps the problem isn't with Node-Red.

Exactly. If the Cerbo or other Venus OS device such as an RPi fails to start up correctly, everything it CONTROLS does not run. This is why I have failsafe options such as override switches in place. If you are MONITORING something, it is far less critical.

As I stated, Node-Red cannot be run via a Tablet or Phone. THAT is disappointing and maybe the problem IS with Node-Red as it cannot be run that way - unless you know better on that one and my dissapointment on that front can be alleviated?

 

[xsilvergs]

Exactly. If the Cerbo or other Venus OS device such as an RPi fails to start up correctly, everything it CONTROLS does not run. This is why I have failsafe options such as override switches in place. If you are MONITORING something, it is far less critical.

As I stated, Node-Red cannot be run via a Tablet or Phone. THAT is disappointing and maybe the problem IS with Node-Red as it cannot be run that way - unless you know better on that one and my dissapointment on that front can be alleviated?

If you login to the VRM portal on a PC, phone or tablet device, select Advanced from the menu. In the url bar delete the last part of the url which should be "advanced" and replace it with "proxy/" (e.g. vrm.victronenergy.com/installation/xxxxx/advanced becomes vrm.victronenergy.com/installation/xxxxx/proxy/), the backslash at the end is important. You should see a button "Node-Red Editor". Selecting this will allow you to create and edit the flows. Selecting the little square box with the arrow (far right of image) opens up the GUI you've created to allow remote control.

It's possible to remotely reboot or power down a Pi, I'm not sure if this can be done on a Cerbo. There would be the possibility for example to read the state of your MoHo lights via the Cerbo digital inputs and turn them on remotely from your phone.

 

[wildebus]

If you login to the VRM portal on a PC, phone or tablet device, select Advanced from the menu. In the url bar delete the last part of the url which should be "advanced" and replace it with "proxy/" (e.g. vrm.victronenergy.com/installation/xxxxx/advanced becomes vrm.victronenergy.com/installation/xxxxx/proxy/), the backslash at the end is important. You should see a button "Node-Red Editor". Selecting this will allow you to create and edit the flows. Selecting the little square box with the arrow (far right of image) opens up the GUI you've created to allow remote control.

View attachment 4712

It's possible to remotely reboot or power down a Pi, I'm not sure if this can be done on a Cerbo. There would be the possibility for example to read the state of your MoHo lights via the Cerbo digital inputs and turn them on remotely from your phone.

How did you get run the certificate problem? I don't know how to and going by the posts on the Victron community, no one on there seems to know either.

 

[xsilvergs]

I'm sure I have seen this (must have been early days) and just pressed CANCEL as I've never installed a certificate.

 

[wildebus]

And if you haven't got access via the Tablet or Phone and don't have a PC with you, you are screwed if you need to reboot the Venus Unit as after a reboot, Node Red does not load automatically, you have to manually click the button to start it. That is NOT a robust control system (unless you know a way to have it auto-exectute Node Red? might be a secret option?)

 

[wildebus]

I'm sure I have seen this (must have been early days) and just pressed CANCEL as I've never installed a certificate.

Cancel takes you back to the previous VRM page.

 

[xsilvergs]

I truly don't have any of these problems to mention. I power up the RPi, Node-Red starts moments after the RPi and runs for months. I've not read of problems like you seem to suffer.

If your Cerbo repeatedly crashes or Node-Red crashes or doesn't start I suggest you reinstall the firmware again, if problems still persist contact mpvader via the victron community.