Battery sense for Victron solar controllers

[sailingharry]

I've just done an upgrade on the solar on my boat. It includes a pair of 195W rigid panels each going to a Victron 15 amp mppt controller. There is another 300W of smaller panels going through individual Genasun mppt controllers. I have seen over 30 amps to the batteries which is good! The controllers are less than 5 ft from the batteries and use #6 conductors for the combined outputs.

I also have a Victron Multiplus inverter charger with the Bluetooth dongle that connects to the batteries. All of the Victron equipment has Bluetooth ability, which leads to the question.

When pumping 20 or 30 amps into the batteries, the Victron controllers are reporting a quarter volt more battery voltage. The problem is they are seeing it at the controller and not the battery. The inverter, sitting idle, is reading the actual battery voltage.

It would be just fabulous if the Victron dongle on the Multiplus would report that voltage to the Victron mppt controllers. Alternatively, it would be wonderful if the Victron controllers had a voltage sense lead.

Remote sense is such a well-established and long-standing tradition. Is there any way to implement this on a modern piece of equipment? Raising the output of the solar controllers so that the charging voltage is higher would potentially improve my charge rate.

[noelex 77]

Victron make an inexpensive and easy to install device called the Smart Battery Sense. It will communicate the true battery voltage and temperature to the Victron Smartsolar MPPT controllers. Purchase the newer long range unit rather than the older (black) version.

There are alternatives to the above products. Some of the Victron battery monitors have a similar ability.

[jordanbigel]

Originally Posted by noelex 77

Victron make an inexpensive and easy to install device called the Smart Battery Sense. It will communicate the true battery voltage and temperature to the Victron Smartsolar MPPT controllers. Purchase the newer long range unit rather than the older (black) version.

There are alternatives to the above products. Some of the Victron battery monitors have a similar ability.

Unfortunately, as I discovered myself, if you accidentally bought the MPPT 75/15 without bluetooth, this device is useless. I dont believe there is a way for the non-bluetooth version to get the temp sense. If I had known this, I would have spent the extra bucks for the BT version. But I stupidly assumed that using the VE.Direct cable with a CerboGX would provide all the data needed, and that the BT was only for viewing data on your phone - dumb mistake. Partly Victron's fault for not adequently highlighting the deficiencies of the non-BT unit. At this point I am considering selling them on bay (2 of them) and buying the BT units.

[wholybee]

Also, if you have a victron smart battery monitor like the BVM-712, it will provide voltage and (i think) current information to the solar controller. No need for a separate battery sense.

[dfelsent]

I have 3 mppt 75/15 and a bmv712 all Bluetooth. I have an inherent lack of trust in networked, Bluetooth or otherwise, devices. These have worked for me for the last year flawlessly. The bmv provides the voltage sense.
My only complaint is that from time to time my phone app insists on upgrading the firmware on one unit or another. That’s a risk.
But all in all I am VERY pleased with the devices. they seem to do exactly what they claim to do.

[GILow]

Originally Posted by sailingharry

...
When pumping 20 or 30 amps into the batteries, the Victron controllers are reporting a quarter volt more battery voltage. The problem is they are seeing it at the controller and not the battery. The inverter, sitting idle, is reading the actual battery voltage.
...

Actually, what you describe suggests there may be some resistance between the controllers and the battery, resulting in lost charging capacity.

Using V=IR, or 0.25 = 30R gives us about 0.008 ohms, not huge, but relevant.

More importantly, P=I^2R tells us you may be losing P=(30)^2 x 0.008 = 7.5 watts.

OK, not the end of the world, but worth chasing down of you can.

[sailingharry]

Originally Posted by wholybee

Also, if you have a victron smart battery monitor like the BVM-712, it will provide voltage and (i think) current information to the solar controller. No need for a separate battery sense.

The Bluetooth dongle for the inverter directly reads battery voltage (at the battery). Sure would be nice if it shared it amongst the Victron devices!

[sailingharry]

Originally Posted by GILow

Actually, what you describe suggests there may be some resistance between the controllers and the battery, resulting in lost charging capacity.

Using V=IR, or 0.25 = 30R gives us about 0.008 ohms, not huge, but relevant.

More importantly, P=I^2R tells us you may be losing P=(30)^2 x 0.008 = 7.5 watts.

OK, not the end of the world, but worth chasing down of you can.

The resistance and the associated voltage drop are almost exactly what is predicted. Using the voltage drop calculator at customcables.com, the old genuinedeals, shows a .23 volt drop for 30 amps running 10 ft through #6 cable. If I upsize it to #4, that drops to .14V -- but those cables get hard to handle and hard to terminate in the small terminal screw sizes.

[Jetx]

Originally Posted by jordanbigel

But I stupidly assumed that using the VE.Direct cable with a CerboGX would provide all the data needed, and that the BT was only for viewing data on your phone - dumb mistake. Partly Victron's fault for not adequently highlighting the deficiencies of the non-BT unit. At this point I am considering selling them on bay (2 of them) and buying the BT units.

Bluetooth does make programming/configuring the controllers super-easy, which is nice if you have to tweak settings a few times to get everything playing nicely together. BUT you may not need it in this case… If the Multiplus is connected to the CerboGX, you just need to enable DVCC (distributed voltage and current control) on the Cerbo, and it will share the Multiplus’s sensed voltage with the MPPT’s.

Unless the non-Bluetooth MPPT models also do not support DVCC, but I bet they do.

[GILow]

Originally Posted by sailingharry

The resistance and the associated voltage drop are almost exactly what is predicted. Using the voltage drop calculator at customcables.com, the old genuinedeals, shows a .23 volt drop for 30 amps running 10 ft through #6 cable. If I upsize it to #4, that drops to .14V -- but those cables get hard to handle and hard to terminate in the small terminal screw sizes.

Ah, right. Yep, 10 feet of wire will do that. No chance you could move the controllers closer to the batteries? (Looking for a cheap solution here.)

[sailingharry]

Originally Posted by GILow

Ah, right. Yep, 10 feet of wire will do that. No chance you could move the controllers closer to the batteries? (Looking for a cheap solution here.)

Actually, 10 ft of wire is only 5 ft from the batteries.

Ironically, they are actually only one foot from the batteries. But I have a serious philosophical problem with connecting anything to 800Ah of AGM without a big fuse before it. So they each run about 1-2 ft in #10 to a 6-way blade fuse panel, then run about 3 ft to my main distribution panel, through an 80 amp MIDI fuse, through a class T fuse, and then 4/0 about 4' back to the batteries. The ground run is somewhat similar, but a little shorter and no fuses. So 6 ft of #6 plus a few more feet of something larger.

[swampbush]

Since it did a firmware upgrade last year mine sends voltage info to the Bluetooth network.

[sailingharry]

Originally Posted by swampbush

Since it did a firmware upgrade last year mine sends voltage info to the Bluetooth network.Attachment 258713

Very interesting. Does the Bluetooth Network include the solar controllers? It seems insane to buy a second Bluetooth device to tie to the same wires that the first one is to transmit to the solar controllers.

[swampbush]

Originally Posted by sailingharry

Very interesting. Does the Bluetooth Network include the solar controllers? It seems insane to buy a second Bluetooth device to tie to the same wires that the first one is to transmit to the solar controllers.

Yes it does. It seems to read 0.1 volts higher than the my bmv700 with Bluetooth dongle. Solar controllers charge to the voltage of the bmv700 which seems to have priority. If I unplug the bmv dongle then the inverter dongle supplies voltage. It also supplies temp data to the mppts.

[smac999]

enable dvcc in the cerbo

it will use data from the bvm or the inverter if they are all connected to the cerbo.

I have found glitches with dvcc though. like if you set the inverter shut off voltage to 11v. it still uses the inverter post voltage and not the battery voltage. even though the inverter will show the battery voltage. IE the BVM will show 11.5v, the inverter voltage shows 11.5, but the inverter still errors and shuts off because it's 11v at the inverter posts.