Reply
 
Thread Tools Display Modes
 
Old 09-07-2019, 02:35 PM   #21
Silver Member
 
Join Date: Feb 2018
Location: VA
Posts: 69
Default On Topic(?) and Current based regulation

As the originator of the post I do not mind (and actually appreciate) drifting into topics related to the overall addition of battery monitoring and solar challenges.

I followed up with Victron Energy on the sharing of the shunt with a "current based" solar controller. They said they had no knowledge of this application. Blue Sky offers a Solar Controller that includes a shunt but it is billed as a 3-stage MPPT and its literature makes no mention of current based charging, so I assume the functionality of the shunt is to support current measurement of the accompanying display, which includes current, SOC and other functions similar to the Victron. From the Blue Sky description - "It protects battery from deep discharge (via load output), and it has Battery Temperature Compensation (with external battery temp. sensor)." So it may be that the monitoring functions serve to prevent overcharge in some way.
__________________

engnrsrule is offline   Reply With Quote
Old 09-07-2019, 02:53 PM   #22
Platinum Member
 
Join Date: Aug 2010
Location: Minnesota
Posts: 7,678
Default

Quote:
Originally Posted by engnrsrule View Post
As the originator of the post I do not mind (and actually appreciate) drifting into topics related to the overall addition of battery monitoring and solar challenges.

I followed up with Victron Energy on the sharing of the shunt with a "current based" solar controller. They said they had no knowledge of this application. Blue Sky offers a Solar Controller that includes a shunt but it is billed as a 3-stage MPPT and its literature makes no mention of current based charging, so I assume the functionality of the shunt is to support current measurement of the accompanying display, which includes current, SOC and other functions similar to the Victron. From the Blue Sky description - "It protects battery from deep discharge (via load output), and it has Battery Temperature Compensation (with external battery temp. sensor)." So it may be that the monitoring functions serve to prevent overcharge in some way.

On the Blue Sky all of the advanced features are handled by using the Pro Remote. Without the remote you get the default timer stuff and internal amp and volt readings. Here is the Pro Remote manual. Look at page 8 which has the menu map for the amp setting for float transition and you can also find everything else that that can be set.


https://sunforgellc.com/wp-content/t...anual_(EN).pdf


We do shart a Blue Sky 2512HV with our Magnum shore charger without issue.
__________________

booster is online now   Reply With Quote
Old 09-08-2019, 05:39 PM   #23
Silver Member
 
Join Date: Jun 2017
Location: California
Posts: 60
Default Optimizing battery charge

Booster, this has been a very useful discussion, one that led me to look deeper into how tail-current is used by the BMV. That led me to the conclusion I don't understand all of the inner-workings of how a BMV712 communicates with the AC chargers and solar controllers.

According to the BMV712 bluetooth User interface, Victron Smart Networking transmits three pieces of data onto the wireless network: Battery Voltage, Battery Temperature (measured at the positive post), and one data box that's not identified by name (possibly a software error in the interface, or a legitimate piece of data that just doesn't have a label).

So if I assume the unlabeled data structure is void, a solar controller listening to the network only knows battery voltage and temperature, and its own internal current measurement that it sends to the battery node. But the total battery current can significantly differ from this because of other sources and loads tied to the same battery post.

There's also a 'lithium setting' in the solar controller to shut down charging based on temperature. It does not have a programmable value, simply a check-box.

Then there's a bistable relay inside the BMV712 which has N.O. and N.C. contacts, that are programmable to respond to high voltage, low voltage, low SOC, high and low temperature. I use this to disconnect the solar controller PV inputs, and to inhibit the 120VAC charger during fault conditions. My AC charger power supply and its secondary current regulator/voltage limiter are not Victron products, they're all OTS commercial products purchased from Amazon.

So as it sits now, my solar controller followings the Victron charging algorithm adjusted to my Li-ion settings, with an additional hardware safety feature of having the PV input SSR disconnect the panels in case of OV, UV, and temp. I don't use low SOC since that's when it should charge.

But my 120VAC charger is... "homebrew." It's a 24 volt, 600 watt supply adjusted to 28 volts for headroom required by the downstream current regulator, which regulates the current to keep the power supply from shutting down by its fold-back current limiter. It also limits the Li-ion charging voltage, and is set to 24.4 volts. I added an opto-coupler so the BMV712 can shut it down, but later realized it didn't need to be isolated, I could have just driven the shut-down node directly to ground through the 712's contacts.

I don't provide any float voltage as of yet, just the power supply tapers off in constant voltage mode. With Li-ion's low self-discharge, I may not even need to float when everything is disconnected, but the BMV, inverter, battery protects and solar controllers do have some quiescent power draw, so sooner or later it will cycle back and charge again.

That all said, in the Victron eco-system, there's another way to communicate using VE Direct cables that I'm not currently using. More data can be sent to wired Victron devices, and it's very likely the big Phoenix AC chargers have a more sophisticated algorithm that uses more than voltage and temperature, so you might look into this. There's also a low cost Venus-GX (Linux based) control box that can connect several components and provide even more functionality, and a couple more very useful relay outputs.

So this seems worth looking into further. If you're optimizing your system to squeeze the most charge capacity you can out of lead-acid batteries, remember using more of a battery's capacity is always a trade-off with battery life. And that may somewhat explain why default Victron settings use values generalized for a variety of applications and they let the user set them according to their needs.

One final comment; if this is too much effort for most of you RV owners, adding one more battery to your system can negate the need for so much optimization. It buys you extra storage and longer life for the whole battery bank.
Nic7320 is offline   Reply With Quote
Old 09-08-2019, 09:50 PM   #24
Platinum Member
 
Join Date: Aug 2010
Location: Minnesota
Posts: 7,678
Default

Quote:
Originally Posted by Nic7320 View Post
Booster, this has been a very useful discussion, one that led me to look deeper into how tail-current is used by the BMV. That led me to the conclusion I don't understand all of the inner-workings of how a BMV712 communicates with the AC chargers and solar controllers.

According to the BMV712 bluetooth User interface, Victron Smart Networking transmits three pieces of data onto the wireless network: Battery Voltage, Battery Temperature (measured at the positive post), and one data box that's not identified by name (possibly a software error in the interface, or a legitimate piece of data that just doesn't have a label).

So if I assume the unlabeled data structure is void, a solar controller listening to the network only knows battery voltage and temperature, and its own internal current measurement that it sends to the battery node. But the total battery current can significantly differ from this because of other sources and loads tied to the same battery post.

There's also a 'lithium setting' in the solar controller to shut down charging based on temperature. It does not have a programmable value, simply a check-box.

Then there's a bistable relay inside the BMV712 which has N.O. and N.C. contacts, that are programmable to respond to high voltage, low voltage, low SOC, high and low temperature. I use this to disconnect the solar controller PV inputs, and to inhibit the 120VAC charger during fault conditions. My AC charger power supply and its secondary current regulator/voltage limiter are not Victron products, they're all OTS commercial products purchased from Amazon.

So as it sits now, my solar controller followings the Victron charging algorithm adjusted to my Li-ion settings, with an additional hardware safety feature of having the PV input SSR disconnect the panels in case of OV, UV, and temp. I don't use low SOC since that's when it should charge.

But my 120VAC charger is... "homebrew." It's a 24 volt, 600 watt supply adjusted to 28 volts for headroom required by the downstream current regulator, which regulates the current to keep the power supply from shutting down by its fold-back current limiter. It also limits the Li-ion charging voltage, and is set to 24.4 volts. I added an opto-coupler so the BMV712 can shut it down, but later realized it didn't need to be isolated, I could have just driven the shut-down node directly to ground through the 712's contacts.

I don't provide any float voltage as of yet, just the power supply tapers off in constant voltage mode. With Li-ion's low self-discharge, I may not even need to float when everything is disconnected, but the BMV, inverter, battery protects and solar controllers do have some quiescent power draw, so sooner or later it will cycle back and charge again.

That all said, in the Victron eco-system, there's another way to communicate using VE Direct cables that I'm not currently using. More data can be sent to wired Victron devices, and it's very likely the big Phoenix AC chargers have a more sophisticated algorithm that uses more than voltage and temperature, so you might look into this. There's also a low cost Venus-GX (Linux based) control box that can connect several components and provide even more functionality, and a couple more very useful relay outputs.

So this seems worth looking into further. If you're optimizing your system to squeeze the most charge capacity you can out of lead-acid batteries, remember using more of a battery's capacity is always a trade-off with battery life. And that may somewhat explain why default Victron settings use values generalized for a variety of applications and they let the user set them according to their needs.

One final comment; if this is too much effort for most of you RV owners, adding one more battery to your system can negate the need for so much optimization. It buys you extra storage and longer life for the whole battery bank.

That is kind of what I found when I did a quick look at Victron a few times over the years, not obvious how it works or exactly what the capability is. The used to have some layouts that showed all the charging sources and shunt tied to a central control(?) unit,but never explained. They are big on having one of their design dealers do alll that stuff.


No need to opitmize our system as we have all three charging sources controlled by the tail amps so as good as it gets for us. I do like to keep up with what is possible, though.


One thing about getting absolutely full batteries by using tail amps, properly set, is that the extra capacity comes with no downside, only upsides, once you have system. The extra capacity you get actually will significantly INCREASE battery life, not decrease it like doing deeper discharges would. Using the Victron defaults with low charge voltage and 4%C tail current would not give max capacity or life in naerly all systems, even if you had a system that would actually do it.



I need to look at Charles' website again as it has been a while. They also showed integrated controls like Victron, and some of the Charles equipment may also be used by Victron depending on who you believe.
booster is online now   Reply With Quote
Old 09-08-2019, 10:13 PM   #25
Silver Member
 
Join Date: Jun 2017
Location: California
Posts: 60
Default

Quote:
Originally Posted by booster View Post
One thing about getting absolutely full batteries by using tail amps, properly set, is that the extra capacity comes with no downside, only upsides, once you have system. The extra capacity you get actually will significantly INCREASE battery life, not decrease it like doing deeper discharges would. Using the Victron defaults with low charge voltage and 4%C tail current would not give max capacity or life in naerly all systems, even if you had a system that would actually do it.
I would like to see verification of this for lithium-ion, because i've always heard pushing cells to the maximum charge has a penalty. Let's ask Tesla!
Nic7320 is offline   Reply With Quote
Old 09-08-2019, 10:32 PM   #26
Platinum Member
 
Join Date: Aug 2010
Location: Minnesota
Posts: 7,678
Default

Quote:
Originally Posted by Nic7320 View Post
I would like to see verification of this for lithium-ion, because i've always heard pushing cells to the maximum charge has a penalty. Let's ask Tesla!

No, not true for lithium. I have been only referring to lead acid charging. You certainly can use tail amps for lithium, and it is probably marginally more accurate than using voltage, but you would stop at some amount under 100% full. How much under is up for grabs, yet, I think. We hear "knee of the curv", 90%, 97% etc, but I have seen very little real test data of how much space is needed.
__________________

booster is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 12:30 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×