Wiring Victron Smart Battery Sense

[gerry mcg]

Quick question.
I'm wiring in a victron smart battery BT voltage and temperature sensor.
The wiring is simple and pre fitted A fused red live wire with ring terminal and a black ground wire with ring terminal.
I have a Victron BMV700 Shunt fitted.
Common wisdom is all grounds come off the negative terminal of the Shunt.

Does this apply to the victron Battery Sense too? Or should it be connected to the negative terminal of the battery (as it is reporting the battery temperature? (How does it do this? Is it simply reporting ambient temperature in the vicinity of the battery by direct contact of the smart sense unit? Or by some form of electrical sensing via wires?)

I guess it is not critical as the power draw of the BT is negligible

And secondly if it should be directly wired to the battery, as I have 2x95Ah batteries, should I wire it across both or simply to one?

Thanks
G

 

[Two on Tour]

I connected my Victron Smart Battery Sense directly to our leisure battery rather than going through our BMV 712 as it only draws 1.6mA.
You will get a slight SOC drift over time, but I reset our SOC regularly as recommended by Victron anyway.
Personally if practical, I would connect it across both of your batteries, but across just one should make little odds unless one of your leisure batteries is on its way out.
I also fitted a Victron Smart Battery Sense to our starter battery as well to keep an eye on what that is doing.

​

 

[gerry mcg]

^ thanks, that is what i have done ..
wired across both batteries and not onto shunt negative

 

[RM_Marine]

I did mine like this

 

[autorouter]

These SmartSense units are intended to be literally stuck on the side of the battery, because they measure temperature by contact. That's a bit of a problem with some battery spaces, but as near the battery as possible is best.

In theory the positive and negative sense wires should be where the charger (MPPT etc) is connected to the battery. The idea is that it reports back the exact battery voltage, without any voltage drops in the main supply cables, so that the MPPT can adjust the battery voltage back to the correct value. For two batteries that's usually the negative of one and the positive of the other.

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[autorouter]

I connected my Victron Smart Battery Sense directly to our leisure battery rather than going through our BMV 712

I am under the impression that a SmartSense unit is not necessary with a BMV712, which can measure current, voltage and temperature with a temperature sensor, and can report its readings via Bluetooth. The SmartSense was intended for MPPTs etc, that already know the amps passing through, so just need voltage and temperature.

 

[Newfie]

You can download the wiring diagrams I& you know uou4 model number from Victron

Lynx Smart BMS - Victron Energy

The Lynx Smart BMS is a dedicated Battery Management System for Victron Lithium Smart Batteries. There are multiple BMS-es available for our Smart Lithium...

www.victronenergy.com

 

[gerry mcg]

I've stuck it once the battery

 

[Two on Tour]

I am under the impression that a SmartSense unit is not necessary with a BMV712, which can measure current, voltage and temperature with a temperature sensor, and can report its readings via Bluetooth. The SmartSense was intended for MPPTs etc, that already know the amps passing through, so just need voltage and temperature.

I was originally running a BMV700 with a BT dongle that used the VE.Direct port on the BMV700 and used a SmartSense on our LifePo4 leisure battery to measure the leisure battery temperature and cut the solar charging below 5c via the VE.Direct network.
When I set up a Raspberry Pi to monitor our two Victron MPPT solar charge controllers and the shunt remotely via the VRM, I needed the VE.Direct port on the BMV700 readout for the VE.Direct to USB cable to the Pi.
Now with no BT on the BMV700 I could not access it with the Victron connect app to change it's parameters, I swapped out the BMV700 for a BMV712 with the BT built-in and used second data connection on the BMV712 shunt to monitor the starter battery as I was already using the SmartSense to monitor the leisure battery temperature I did not need to fork out another £25 for the Victron temperature sensor for the BMV712.
I just left the SmartSense on the starter battery as it's doing no harm there.

 

[EML]

^ thanks, that is what i have done ..
wired across both batteries and not onto shunt negative

Shouldn't really do that, but it's not the end of the world.

First off, there's no 'negative' on a shunt, so your post was pretty confusing. Victron calls one terminal 'Battery only', which is the terminal you connect to the battery negative post, with nothing else connected to that post. They call the other terminal 'Load and charger', which is where you connect the ground points of all your equipment. In practice, the 'load and charger' will be a fraction of a volt higher than 'battery only', so I suppose 'battery only' is 'negative' in some sense.

A shunt only works if all the load currents in your van are returned to the battery negative post through the shunt. It needs to be the choke point, to let it see/measure everything. If you connect your sensor directly to the battery you're bypassing this. It won't make a huge difference to your readings, but it does make the shunt a bit pointless.

For your sensor positive terminal, It doesn't really matter which battery positive post you connect to in a dual-battery setup. The two posts will be at almost exactly the same voltage.

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[Two on Tour]

Shouldn't really do that, but it's not the end of the world.

First off, there's no 'negative' on a shunt, so your post was pretty confusing. Victron calls one terminal 'Battery only', which is the terminal you connect to the battery negative post, with nothing else connected to that post. They call the other terminal 'Load and charger', which is where you connect the ground points of all your equipment. In practice, the 'load and charger' will be a fraction of a volt higher than 'battery only', so I suppose 'battery only' is 'negative' in some sense.

A shunt only works if all the load currents in your van are returned to the battery negative post through the shunt. It needs to be the choke point, to let it see/measure everything. If you connect your sensor directly to the battery you're bypassing this. It won't make a huge difference to your readings, but it does make the shunt a bit pointless.

For your sensor positive terminal, It doesn't really matter which battery positive post you connect to in a dual-battery setup. The two posts will be at almost exactly the same voltage.

So which post are you referring to. ?

 

[deleted79651]

So which post are you referring to. ?

Looks like Post #3

Steve

 

[Two on Tour]

Looks like Post #3

Steve

Looks like I'm on somebody's ignore list then as there is no post #3 for me.

Edit : and post #8, looks like the OP, have I upset him ?

 

[EML]

So which post are you referring to. ?

Sorry, should have quoted. Gerry says in post #1:

Common wisdom is all grounds come off the negative terminal of the Shunt.

And post #3:

^ thanks, that is what i have done ..
wired across both batteries and not onto shunt negative

And the pic in post #8 appears to show the sensor negative terminal wired direct to the battery negative "post" (or whatever it's actually called...)

Post #1 is confusing because there is no "negative terminal of the shunt", and post #3 is confusing for the same reason and because it's inconsistent with post #1, and post #8 is plain wrong.

Clearer?

 

[autorouter]

I wouldn't worry too much about it. There is always an inherent conflict when you are trying to measure both amps and volts to high accuracy.

If you put the SmartSense on the battery negative terminal, you get accurate voltage but the BMV shunt misses some of the amps (only a very tiny amount).
If you put the Smartsense on the BMV shunt load terminal, you get an accurate amps reading but the SmartSense misses the voltage drop across the shunt (again only a tiny amount).

If it was a digital system you could get the computer chip to add voltages together and also read the amps, to give you much better accuracy. But for battery cable voltage drop compensation that's just not necessary.

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[EML]

If you put the SmartSense on the battery negative terminal, you get accurate voltage but the BMV shunt misses some of the amps (only a very tiny amount).
If you put the Smartsense on the BMV shunt load terminal, you get an accurate amps reading but the SmartSense misses the voltage drop across the shunt (again only a tiny amount).

Good point. What's confusing is that, if it's just a voltmeter, it should be drawing about a microamp, not 1.6mA, as Gerry said. If it's just a meter it should obviously just go to the battery post. But,as you say, I wouldn't worry about it.

 

[gerry mcg]

even at 1.6mA current draw (i.e. in 24hrs that 0.039A / 39mA when on VEnetwork, its hardly going to make a dent in the battery capacity

 

[EML]

even at 1.6mA current draw (i.e. in 24hrs that 0.039A / 39mA when on VEnetwork, its hardly going to make a dent in the battery capacity

No, it's pretty trivial. It does mean that the system isn't properly zero'd, though, and can't tell when there's no current draw. OTOH, the shunt isn't magic, and almost certainly can't detect 1.6mA anyway, so even that isn't a good argument (unless you've got very sophisticated shunt electronics).

OTOH... I've just checked the spec for Victron's 'Smart Battery Sense', and it doesn't say what the shunt actually is. So, it might be a cheap one at, maybe, 50 mOhm (0.05R). This would be useless, and your battery reading could be over a volt out when charging. Unless you actually know it's 1mOhm or less, ignore everything I said, and connect directly to the negative post...

And, having now read the manual, I've found this...

Connect the two eyelets to your battery terminals and attach the unit directly onto the battery-body using its self-adhesive strip.

For banks of batteries Smart Battery Sense may be connected to any one of the individual batteries.

 

[autorouter]

Unless you actually know it's 1mOhm or less,

It's a 500A 50mV shunt (sense resistor). That makes its resistance (R = V/I) 50mV/500A = 0.1mOhm. Victron shunts are good quality items. The voltage drop will usually be a lot less than 50mV.