question

How to confirm accuracy of a DMM?
Aside from returning the DMM to the manufacturer to perfrom calibration you can use another instrument that is known to be calibrated to calibrate your DMM.

The products number/model number of the voltage meters in Victron products?
You would have to email victron and ask, but they may not provide this information and just provide you with details of accuracy.

My question about how you can all guarantee the accuracy of Victron voltage meters when you all told me that unless a DMM is calibrated every year its not guarantee accurate, so I clearly asked how and why the Victron units can/are still considered accurate when they aren't calibrated every year?

DMMs can recieve a lot of accidental abuse when used for testing, and can be introduced to a lot of risks that can cause harm to the DMM. It is less of a concern for a static instrument that is not introduced to unknown environments and conditions.

• How can Victron products be guaranteed to have accurate Voltage if they're not regularly calibrated?

If we are talking about Shunts, they are quite accurate and generally quite stable over a wide temperature range, they achieve this by using manganese alloys for the resistive elements that you see as 'fins' of metal between the posts of a shunt. The fins also serve as extra surface area to help cool the shunt because as the shunt gets warmer it is less capable of carrying its rated current.
So this helps stabilize the temperature. In addition to those most shunts are remote from a BMS or monitor and you have to worry about voltage drop in the Kelvin wires that measure between the posts and can lead to inaccuracy, with the SmartShunt one advantage is that this concern is virtually eliminated because the measuring electronics are mounted directly at the Shunt.

In addition whilst they are manufacturing and calibrating the shunt a small amount of material from the fins will be milled out to make sure the voltage drop is as accurate as possible to their reference, this is because shunts are so sensitive these kind of discrepancies have to be accounted for in manufacturing.

Even with all of these provisions to retain accuracy even shunts can stray over time, that is why Victron have the option to perform a zero calibration of the shunt from within the app if you suspect a problem.

Of course I have only talked about SmartShunts here because any other type of voltage measurement from an MPPT or Charger, or Voltage sense is widely understood to be worthless, and is more an 'indicator' rather than a 'measure'.

• Exactly what accuracy percentage does a Digital Multimeter need to have to be considered accurate enought to perform testing?

For the SmartShunt the resoultion is +/- 0.01V with an accuracy of +/- 0.3%. So more accurate than that.

Hi @Not a hard question to answer

Some Victron products such as the SmartShunt are intended as measuring equipment. These products have their accuracy listed in their data sheet, see this example for the SmartShunt, with a resolution of +-0.01V, and accuracy of +-0.3%

Other products make use of a built in voltage reading to serve their primary function, such as battery charging or inverting. The built in precision and accuracy of their measurements is sufficient for that task (which are intended to be functional, and not absolute), but will vary, and has additional installation dependant variables.

There is a quality of power called Ohms law, basically there is a relationship between voltage, current and resistance. The power electronics that draw, or push current will cause the voltage to drop, or rise.

If the product uses these same wires to sense the voltage, then it can appear that the voltage is higher or lower than it will appear at the battery terminals taken from a voltage sensing device that is not drawing or pushing any current.

Further to that, the size of the wires that are selected by the installer on site will also affect this current carrying voltage reading for these charging or load products. There is a lot more detail about these effects (and how significant they can be in certain circumstances) in the Ohms Law chapter of the Victron book Wiring Unlimited here.

For the most part our equipment will do it's best compensate for these variations to the amount that is required to perform the job reliably (such charging a battery, or turning off an inverter before a battery is totally flat). In some cases, users might want the extra accuracy that can be provided by a dedicated piece of measuring equipment, with a defined resolution at accuracy and we make that possible too.

This is not essential from Victron's perspective, and most users are happy to accept our design and some level of variation. It's a complex dynamic, but from our experience the variables and tolerances are acceptable as long as all the specifications in the product manuals are followed correctly. As an example, in a battery charger when the battery is full the charging current is reduced and the voltage reading will be more accurate.

For those that DO want the extra precision, there is a variety of ways to do so.

For example installing a SmartShunt and then setting up a VE.Smart Network, and then sharing the voltage from the battery terminals with a paired SmartSolar MPPT.

For the MultiPlus, you can wire in a dedicated voltage sensing wire connection (that doesn't carry any current, just the voltage, providing a more accurate reading).

Or enabling Distributed Voltage and Current Control (DVCC) with a Victron GX device, and connecting all the system components to that.

Again, all of these are optional improvements for those that want to improve the accuracy of things, but may or may not be necessary from Victron's perspective and dependant on the installer to assess. They may decide a very long wire run will cause sufficient issues to warrant additional equipment in one installation, while a very short and thick wire run in another does not.

In some regions these requirements are dictated by specific local standards that govern the acceptable amount of voltage drop between a source and an appliance - while in another region a different installer may choose to manage that variation in other ways.

We consider our equipment reliable and accurate enough to use as is out of the box, as long as it is installed by a suitably qualified and trained installer.

@Not a hard question to answer and @Guy Stewart (Victron Community Manager)

I have found this type of behaviour from time to time. This is not the first forum to have trouble like this. Though, I would offer a few points of contention. When you are rude to someone do not get offended when you are handled in kind, not only that, but refrain from "ganging up" This is not only childish or child like, but, this serves no purpose and does not solve,

1: A legitimate question that was asked.

2: A legitimate control of appliance measurement.

When dealing with a situation such as this I would ask the forum moderators to not choose sides but to instead rather try to "de-fuse" such occurrences by messaging parties and making sure that conduct is becoming. Having a certificate or diploma does not make you the best engineer or accountant, this only serves to say you went on a course teaching you the in's and out's, experience in my books far outweighs ANY certificate or diploma when it comes to the real world, and so, this means that more often than not the number crunchers who do a lot of the legwork need to listen to the folks actually USING the equipment, I mean sorry, but, setting up an MPPT does not need a rocket scientist. But, it takes some very talented programmers to allow hardware and software to be able to talk to one another. And, when you have a whole host of Victron equipment that has readings scattered over fractions of a volt when idle, means that there will be questions asked.

This should be foreseen by you and should pretty much be a given that there will be questions asked.

And, therefore, if you task yourself with answering someones question about this, it need not end in being called an invalid....

Victron can't assure any type of concrete accuracy in the field under many types of installations not under their direct control...

That being said, I have 2 MPPT's that are connected to the same battery via breakers that are reading a minimum of 0.5V difference between them. Same model, same make and same output wiring to battery. Using MY DMM I have found that there is no perceivable voltage drop on my cabling as these runs are far to short to be able to influence a 0.5V drop between devices... My cable run from battery to bus bar is 1.5M...... The MPPT's to bus bar are less than a meter..... So, why the voltage discrepancies? My DMM reads the same voltage at any given part of my DC system, (NO load conditions) all readings taken on the respective devices terminals. Yet, between the two MPPT's there is a 0.5V discrepancy (In software) and an almost 0.7V difference on the multiplus(In software).... And this is comparing my DMM reading to any of the devices in software....

What would be nice is if we could get a software fix to "offset" voltage readings under the devices tabs in software. These discrepancies do not bother me at all, because I have verified this physically to my DMM, thereby proving device measurement faults. I personally have just told my system to take any and all voltage measurements from my batteries BMS.

That works for me, I have found that this is an endless rabbit hole that one can get sucked into when chasing voltage discrepancy faults, If you are unsure, put a constant load on your DC bus system and measure with your DMM, any glaringly obvious faults hardware wise or installation wise will show up in this fashion when metered out.

Any engineer worth his salt will tell you outright, that having multiple points of measurement will ALWAYS end in a greater % of error, this is due to more than one reason, the type of silicone used, minor differences in point to point connections and many many more..... What these points are used for is not accuracy but more to see any big problems that may be rearing their heads..... On a solar install, with that much switching noise...... 0.7V not a major problem for me.

In the end, we all have our own opinions, and you know what they say: Opinions are like buttholes..... Everyone has one.....

I guess though, that it all comes down to how you talk to someone that will show who you are.....

Have a great day!