Big Data for a Tiny Trailer: Battery Monitor Installation: Victron BMV-700

Coolparrot

Great! Thanks for the info. I'm excited to do this install. I have decided to just wire it to the battery directly. I manufacture T@B accessories and we are coming out with a dual battery upgrade kit that allows 2 group 24s or 6vs in the oem propane tub. With dual battteries, I'm definitely not worried about any drain from the  shunt when the main power switch is off while in storage. I'll post pics of my install once complete  Waiting on parts now. 

Coolparrot

One last question.  If using dual 12v batteries wired in parallel configuration, do I need to use the Victron 702 or will the 700 work? 

BrianZ

@Coolparrot, it is my understanding that the 702/712, which have a second input at the shunt, can use it for a second voltage reading from either a second battery/battery bank midpoint or a battery temperature sensor.  If you had two 6V batteries in series, the second input could monitor the midpoint voltage for detecting an imbalance between the two.  It could also monitor a separate 12V battery, but I do not see how it could monitor both separately when connected in parallel. 

You could use the second input for a temperature sensor at the positive terminal of one or the other battery, so it seems to me that would be the only additional benefit you'd get from a 702/712.  Maybe @jkjenn or somebody can confirm.

I got the 712 for the built-in bluetooth plus temperature sensor, but we only use one battery.  Temperature allows more accurate indication of battery status, plus can be shared with a Victron solar charge controller via bluetooth for fine tuning charging voltages.  Some use a second 12V as a spare to avoid accidentally depleting both.

jkjenn

Coolparrot said:

One last question.  If using dual 12v batteries wired in parallel configuration, do I need to use the Victron 702 or will the 700 work? 

Either should work, just fine, as you are still measuring the strength of 12v dc.

pthomas745

I bought my trailer a Victron 712 for Christmas.  I've read this thread over and it makes more sense with the shunt in your hands!

Anyone else who tackles this:  I've discovered the ring terminals that came with the trailer are too small for the shunt, so I'm crimping on 12-10 ring terminals to the trailer's negative battery connector.

One thing I need to make certain of:

The Zamp negative cable goes to the "Load And Charger" side of the shunt?  This is the sentence that is getting to me:

"It actually does matter because the monitor won't see it if it is on the battery side. You want it on the trailer side."

So, the "trailer side" is the stock trailer cable harness that connects to the "Load and Charger" part of the shunt and disappears into the trailer?

It seems kinda obvious, I bet, but when electricity is involved I become an OCD cryptologist and try to decode every hieroglyph!

Sharon_is_SAM

@pthomas745, the trailer side of the shunt is circled in my picture.  That end of the shunt goes to the junction box.  If you wire something on the negative lead before the shunt (directly on the negative terminal) the battery display monitor will not reflect a true reading.  Hence, everything should come after the shunt.  We had our charge controller wired by nuCamp this summer.  The positive battery lead stayed on the battery, but the negative lead was wired at the junction box - after the shunt.

pthomas745

Thank everyone in this thread again.  The connections went extremely easy and I've been Victronning all day.  An amazing device and tool.

pthomas745

One more Victron question.  It has been running for 10 days now, and I've had my solar panel connected and the trailer on to watch the display on the 712.

This was the display this morning.  I've set the Victron to the stock battery size of 70AH, which, in theory gives me 35AH to use.  I've used 7 amp hours, and the state of charge is still reading 95%.  The battery voltage is 12.38

Does the battery voltage on the Victron fall under the dictum that the only way to get a good voltage readout is from a "rested" battery?  Or, is 12.38 the "real time" voltage, with no resting needed?

And the state of charge number:  is the 95 percent computed from the entire 70AH battery setting? And, if the voltage number needs a rested battery, this will always be the more reliable number?

I think I have this straight in my head, but I would like to have an experienced user tell me if I'm right or wrong.

jkjenn

In your settings, under Relay, do you have SOC Relay set to 50%?

https://youtu.be/KIVeffHqXu4

pthomas745

Yes, it is at 50%.  I went to the AM Solar page and set the Charge Voltage parameter to 14.2.  That was the only thing I changed on the battery setting page.

Edit: with the Victron manual in my hand, they suggest the Charge Voltage parameter should be 13.2.

Sharon_is_SAM

 My understanding is that the BMV voltage read out is real time and the SOC accounts for multiple factors, unlike a simple 12v plug in monitor that reads the voltage after the shunt.  

The SOC considers the entire battery capacity and they make a point of saying to rely on this number - not voltage as the BMV SOC compensates for charge efficiency and temperature.  But, the Time Remaining is the time to the discharge floor (50%) and is suspect when viewed under a heavily, fluctuating load.  So, stick to reading the SOC.

One thing to remember, if you disconnect the (+) supply to the BMV (like with changing the battery fuse) you need to resynchronize.  The standard factory battery disconnect on the positive lead will not interrupt the supply.

jkjenn

Sharon_is_SAM said:

 My understanding is that the BMV voltage read out is real time and the SOC accounts for multiple factors, unlike a simple 12v plug in monitor that reads the voltage after the shunt.  

Yes, this correct. 

ajordan

Has anyone moved a lithium battery to an inside location and if so, do you have a wiring diagram showing how you moved the wiring to the new location?