How important is V-Sense to the health of my system?

[KevinC_63559]

Have a newly installed Victron Multiplus II and am awaiting delivery of some wire to rig a V-Sense cable for it. Unit appears to function just fine without it, and the battery BMSes showed a near perfect (0.034V delta) balance after things ran for awhile.

I hit the Victron Community and searched a bit and came across some concerns about the Multiplus electronics being fed via the V-Sense cable that was ever so slightly concerning. Other posts seemed to imply the V-Sense was important if I was every charging under a heavy load, due to voltage drop across the main battery cables.

Curious what this community thinks? Should I hook up the V-Sense cable or just let is pass? No biggie to do so, just curious if most feel its necessary.

Note my system is lightly loaded, peaking around 800W on my 12/3000/120 (normally around 350W), with the batteries only being used in power outage situations. I'd load level a bit, just for fun, but believe the minimum setting for shore power is 9.7A. I'd need to set it down to 5 or so to clip peek demand.

 

[sunshine_eggo]

I have V-sense hooked up, but then I have my BMS passing voltage to the entire system effectively overriding it.

High current charges will enter absorption sooner thus lengthening total charge time.

High current discharges may trigger premature cut-off even when OCV or SoC is acceptable.

If the lack of a V-sense value does NOT cause any operational issues, it's not needed.

 

[timselectric]

I've never heard of it. So, I'm guessing that it's not that important. lol

 

[sunshine_eggo]

I've never heard of it. So, I'm guessing that it's not that important. lol

Victron inverters have a V-sense terminal where you simply connect to battery (+) and (-) for OCV measurement.

 

[KevinC_63559]

Victron inverters have a V-sense terminal where you simply connect to battery (+) and (-) for OCV measurement.

(Typically with 18 gauge wire, since its voltage sensing only, but some report the inverter will power itself off this connection bypassing any main on/off switch if it doesn't sense power from the batteries (due to that switch))

 

[sunshine_eggo]

(Typically with 18 gauge wire, since its voltage sensing only, but some report the inverter will power itself off this connection bypassing any main on/off switch if it doesn't sense power from the batteries (due to that switch))

I didn't have it installed for the first year, and that never happened to me.

 

[KevinC_63559]

I didn't have it installed for the first year, and that never happened to me.

Bad language choice on my part. Should not have said "power itself off" but rather "power itself from".

 

[740GLE]

As a good blue koolaid drinker, you should already have a smart shunt, and a Bluetooth dongle for that MPII, it’s not the 90s, go wireless!!

 

[KevinC_63559]

As a good blue koolaid drinker, you should already have a smart shunt, and a Bluetooth dongle for that MPII, it’s not the 90s, go wireless!!

90s or not, nothing beats hard wired.

 

[HighTechLab]

Never had a customer have an issue not using one. I’d only use it if you have extremely long cable runs.

 

[KevinC_63559]

Never had a customer have an issue not using one. I’d only use it if you have extremely long cable runs.

Thanks!

 

[Dooug]

Would a cerbo/smart shunt/multiplus combo running dvcc shared voltage be the same as the V-sense wire? I think the shunt be the most accurate voltage and share it with the multiplus and mppts.

 

[KevinC_63559]

Would a cerbo/smart shunt/multiplus combo running dvcc shared voltage be the same as the V-sense wire? I think the shunt be the most accurate voltage and share it with the multiplus and mppts.

Virtually by definition the most accurate measurement of battery voltage would be via a reading at the battery terminals. The V-Sense wire does just that, bypassing any voltage drop due to load through the main battery connections or any issues between the main battery connections and the Multiplus (loose connections, bad fuses, etc.) since its a direct run from those terminals into the Multiplus theoretically without any load on the wires.

 

[EvanC]

....minimum setting for shore power is 9.7A. I'd need to set it down to 5 or so to clip peek demand.

I just set my 12/2000 AC input down to 2 or 3 amps the other day. I'm pretty sure it goes down all the way to 0 in 1 amp increments. Maybe even 0.5

I was on a PC with the USB cable/adapter. Maybe you are wireless and it doesn't allow as much flexibility? I would assume your capabilities would be the same.

I wouldn't personally care about the V sense. If you were trying to push 3kva from the battery 24hrs a day or something maybe it could be nice to have, since that is when your large wires are providing the least accurate voltage maybe? If your using it in "passthru" most of the time and only using battery for grid backup, I wouldn't see the need.

 

[sunshine_eggo]

Would a cerbo/smart shunt/multiplus combo running dvcc shared voltage be the same as the V-sense wire? I think the shunt be the most accurate voltage and share it with the multiplus and mppts.

It would simply depend on which device is more accurate - the V-sense terminal or the smart shunt.

I just set my 12/2000 AC input down to 2 or 3 amps the other day. I'm pretty sure it goes down all the way to 0 in 1 amp increments. Maybe even 0.5

The issue is with PowerAssist being enabled. If disabled, there is no lower limit. If powerassist is enabled, there is a minimum configurable input current limit for reliable operation, and it varies by model power AND output voltage. If you have a standard MP 12/2000, your lower limit is 5.5A.

For the MP 12/3000, the limit is 7.5A. For the MP-II 12/3000, the limit is 9.5A.

"These limits are based on the current default calibration values and will slightly vary in practice."

These values are published in a spreadsheet on the victron professional site.

Victron Energy - Victron Professional

professional.victronenergy.com

You can obtain it by signing up for a free account.

I wouldn't personally care about the V sense. If you were trying to push 3kva from the battery 24hrs a day or something maybe it could be nice to have, since that is when your large wires are providing the least accurate voltage maybe? If your using it in "passthru" most of the time and only using battery for grid backup, I wouldn't see the need.

If the lack of a V-sense value does NOT cause any operational issues, it's not needed.

 

[EvanC]

The issue is with PowerAssist being enabled. If disabled, there is no lower limit. If powerassist is enabled, there is a minimum configurable input current limit for reliable operation, and it varies by model power AND output voltage. If you have a standard MP 12/2000, your lower limit is 5.5A.

Interesting! Totally not how I remember it working. Thanks for the resource.

 

[sunshine_eggo]

Interesting! Totally not how I remember it working. Thanks for the resource.

That limitation has bitten people in the butt at times. There was one guy that wanted to feed his Q with the AC output of a hydro system, but it was well below the threshold, and the Q wouldn't boost when needed.

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