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Please reccomend a shunt or inductive for measuring small current/wattages.

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Checkthisout

Solar Wizard
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Hello. On my 12 system, I want to measure small current draws (like a few watts). This does NOT have to handle full draw but maybe a max of like 10-20 amps between the equipment I want to measure and the battery.

With that said, does the victron or someone else's smart shunt catch draws that are only a few watts?

If not, what would work?
 
Not an expert on these shunts, but I think they all can measure that small. Even a few watts or less than 1A. How accurate are those measurements I don’t know.

The Victron equipment is overkill and too pricey for my use case, but the Renogy battery shunt appears to measure all this nicely on its own LCD screen, no Bluetooth phone app required like the Victron smartshunt. The smartshunt can be hooked up to an optional LCD screen but at an extra cost. The Navy uses Victron equipment, I don’t need that level of build quality lol. Not for a leisure RV.
 
You probably want a shunt if you want to accurately measure small currents.

Victron BMV712 if you want a nicer (shunt based) battery monitor that also has a built-in screen. It also has a couple other features that smartshunt doesn't.

If you add a RaspberryPi with VenusOS installed to a SmartShunt or BMV712, you get a really nice system for the money. Try setting up charts and remote monitoring with the renogy shunt? With charts, you don't just know that the batteries are dead, you know when the battery charged or discharged over time (for example, seeing that somebody used an 1800W load for 40 mins 2hrs ago that drained your batteries from 40% to 20%, not "the batteries are dead now").

Unfortunately it's really hard to get a RaspberryPi right now but you could add that part in after the supply issues clear up.
 
Checkthisout said:
With that said, does the victron or someone else's smart shunt catch draws that are only a few watts?

If not, what would work?
Click to expand...
You're in the range of precision that is hard to get outside of a lab. And if you're in the lab with that gear you to have the skills to set it up correctly and zero it out (calibrate) to get measurements reliably which is not a small task.

A shunt is the only thing that going to get you close that I can think of but keep in mind, a shunt take 2 things. The shunt and VOM and each will have thier own accuracy issues. Murphy's law tells us that errors add up, not cancel when using multiple pieces of equipment.

The Smart Shunt will get you pretty close but probably not reliably to within watts.

1665951202594.png
 
I use the Harbor Freight Ames 1000A DC clamp ammeter. On 60A range, it has resolution of 0.01A
Seems good for checking my PV panels.

I think when used for AC amps it works at several amps but shows 0.00A when current is actually 0.10A or so.
(I could use it to measure change in current from 48V battery when driving 120Vrms into transformer, but it didn't show current in transformer. My Fluke probe did show the AC current.)

Obviously for low currents you can use a large sense resistor and measure volts. AC or DC.
 
OzSolar said:
The Smart Shunt will get you pretty close but probably not reliably to within watts.
Click to expand...

You posted a chart showing the shunt based system would be accurate within +-0.12W, far better accuracy than being requested.

It's almost like there's an entire tiny laboratory inside every shunt, based on your claims that you would need a lab for this precision.
 
Lilikoi_Heavy_Industries said:
You probably want a shunt if you want to accurately measure small currents.

Victron BMV712 if you want a nicer (shunt based) battery monitor that also has a built-in screen. It also has a couple other features that smartshunt doesn't.

If you add a RaspberryPi with VenusOS installed to a SmartShunt or BMV712, you get a really nice system for the money. Try setting up charts and remote monitoring with the renogy shunt? With charts, you don't just know that the batteries are dead, you know when the battery charged or discharged over time (for example, seeing that somebody used an 1800W load for 40 mins 2hrs ago that drained your batteries from 40% to 20%, not "the batteries are dead now").

Unfortunately it's really hard to get a RaspberryPi right now but you could add that part in after the supply issues clear up.
Click to expand...

I have a mini PC I remote desktop into already to check on the generator, charge controller, modem and other stuff.
 
OzSolar said:
You're in the range of precision that is hard to get outside of a lab. And if you're in the lab with that gear you to have the skills to set it up correctly and zero it out (calibrate) to get measurements reliably which is not a small task.

A shunt is the only thing that going to get you close that I can think of but keep in mind, a shunt take 2 things. The shunt and VOM and each will have thier own accuracy issues. Murphy's law tells us that errors add up, not cancel when using multiple pieces of equipment.

The Smart Shunt will get you pretty close but probably not reliably to within watts.

View attachment 116638
Click to expand...
Well, thanks for this chart. Plus or Minus .01 amps at 12 volts means it will measure changes as low as .12 watts does it not?
 
Lilikoi_Heavy_Industries said:
You posted a chart showing the shunt based system would be accurate within +-0.12W, far better accuracy than being requested.

It's almost like there's an entire tiny laboratory inside every shunt, based on your claims that you would need a lab for this precision.
Click to expand...

Ok. So maybe I just get the victron shunt and if it doesn't deliver, I return it within the 30 day window on Amazon.

It's spendy but that's OK. If I can hook to a pc using their ve direct cable without having to have anything else between that's probably a fair bargain.
 
Checkthisout said:
I have a mini PC I remote desktop into already to check on the generator, charge controller, modem and other stuff.
Click to expand...
Oh, wow, you're really advanced. What are you using to data log and chart your system state of charge?

EDIT: Yep, you probably need the VE.Direct cable for staying connected to this. You need it for hooking it up to a raspberry pi also.

If you decide to use the renogy, you could point a webcam at it?
 
Lilikoi_Heavy_Industries said:
Oh, wow, you're really advanced. What are you using to data log and chart your system state of charge?
Click to expand...

Well, the Tycon monitor for the generator tracks and logs tbattery state of charge. The solar charge controller does this as well.

I have cameras, modem etc etc and I want to see how much each of these devices pulls and start to manage their power consumption coming into winter.

Yes I could use my fluke to do this but I definitely wouldn't mind a shunt that could show amps in out of the battery from all its charging and load sources.
 
Lilikoi_Heavy_Industries said:
Oh, wow, you're really advanced. What are you using to data log and chart your system state of charge?

EDIT: Yep, you probably need the VE.Direct cable for staying connected to this. You need it for hooking it up to a raspberry pi also.

If you decide to use the renogy, you could point a webcam at it?
Click to expand...

Don't want to detail my whole system but amps in from the MPPT are monitored by the charge controller itself.

Amps flowing in from the generator battery charger are monitored on a shunt between the charger and batteries.

I just need 1 more monitoring pint to see what's coming out of the batteries as parasitic loads from the monitoring equipment.

I traded out my netgear and Asus for a mofi and my power draw seems to have noticeably increased. I thinks it's fancy wifi is the culprit but I'm not sure hence my want for a shunt.
 
Lilikoi_Heavy_Industries said:
You posted a chart showing the shunt based system would be accurate within +-0.12W, far better accuracy than being requested.

It's almost like there's an entire tiny laboratory inside every shunt, based on your claims that you would need a lab for this precision.
Click to expand...
If it was that simple I suspect they would publish the actual wattage accuracy. Why don't they?
 
OzSolar said:
If it was that simple I suspect they would publish the actual wattage accuracy. Why don't they?
Click to expand...
Because it can be used for many different system voltages, and because inside a system voltage, there is also variation. They stated it the way that it was correct.

Since this thread is about a 12V system, it's safe to assume voltages will be between 10V-16V, which yields 0.10W to 0.16W as possible measurement variance.

If it were on a 48V system, the math is different, and it's suddenly around 0.48W instead.
 
Hedges said:
I use the Harbor Freight Ames 1000A DC clamp ammeter. On 60A range, it has resolution of 0.01A
Seems good for checking my PV panels.

I think when used for AC amps it works at several amps but shows 0.00A when current is actually 0.10A or so.
(I could use it to measure change in current from 48V battery when driving 120Vrms into transformer, but it didn't show current in transformer. My Fluke probe did show the AC current.)

Obviously for low currents you can use a large sense resistor and measure volts. AC or DC.
Click to expand...
I have a fluke 77 that does 10 amp pass through and a separate inductive clamp that I can use....I want something that's always there and hooked up.

Like most solar guys, I like to look at things just to look at them.
 
Ok. So after thinking about it, it looks like I'll get the victron. I like that I can hook it to the PC I have which means I can look at it on many different devices.
 
The downside of a shunt is that it heats up under load. Sure a 500a shunt has pretty low voltage drop but it has some and it’s always there.

A CT metering device doesn’t have and voltage drop.

For the OP what’s the max peak load of the system? Sounded like you weren’t concerned about measuring peak current, more of resolution of smaller current. If you use a shunt you’d still need to factor in peak current. Can’t have a 50amp shunt for low current high resolution, when it needs to deliver occasional 100-200amps.
 
740GLE said:
The downside of a shunt is that it heats up under load. Sure a 500a shunt has pretty low voltage drop but it has some and it’s always there.

A CT metering device doesn’t have and voltage drop.

For the OP what’s the max peak load of the system? Sounded like you weren’t concerned about measuring peak current, more of resolution of smaller current. If you use a shunt you’d still need to factor in peak current. Can’t have a 50amp shunt for low current high resolution, when it needs to deliver occasional 100-200amps.
Click to expand...

The victron is 500 Amp. I'm drawing about 2000 (~250 amps) watts max continously for a few minutes.

And only 300 watts continuous at any other time.

If the victron didn't go down to .01 resolution I could easily place a much more wimpy shunt between the loads I want to measure and the Batts.
 
My 500a Renogy shunt is garbage under .5 amps. Under two Watts and it doesn't even see it, 2-5w and it just guesses, 5-10w it starts getting more accurate.
 
A.Justice said:
My 500a Renogy shunt is garbage under .5 amps. Under two Watts and it doesn't even see it, 2-5w and it just guesses, 5-10w it starts getting more accurate.
Click to expand...

I think the other thing I like about the Victron is all the processing takes place right the shunt.

The Renogy is probably doing the measuring at the display which means the mv signal has to travel up whatever length of wire is chosen.
 
A.Justice said:
My 500a Renogy shunt is garbage under .5 amps. Under two Watts and it doesn't even see it, 2-5w and it just guesses, 5-10w it starts getting more accurate.
Click to expand...
Ok this is good to know. While it would be nice to measure the draw of a single 1W LED lamp, I think I can live without that. I've been considering the Renogy shunt over the Victron one for two reasons:

1) Price - Renogy retails for $90 (often on sale for $70-80), and the Victron 712 (one with an LCD screen so you're not tied to a smartphone app like with the SmartShunt) is $205.

2) UI - From what I've seen comparing the Victron 712 to the Renogy 500A monitor, I much prefer the UI layout of the Renogy. The Victron is made for industrial geeks who want high precision data and displayed in a way that makes the most sense to them. Renogy's market base is the opposite of that - they want something that's easy to read and understand and are less interested in lots of high-precision data. So I find the usability of the Renogy much better. This is all from reading and watching reviews, I would love to be able to test out each monitor first-hand, which might sway my current opinion.

Now I do see the AiLi monitor now has a version that looks like a knock-off of the Renogy one, for $70, but haven't researched it much to know if it's just a look-a-like with far inferior components or what, compared to the Renogy one.
 
Tomthumb62 said:
Ok this is good to know. While it would be nice to measure the draw of a single 1W LED lamp, I think I can live without that. .
Click to expand...
You run into an issue when you want to run that one LED for long periods of time. My battery sat for about 6 months with the BMS and solar charge controller on, but the draw was so low that the shunt didn't catch it, and still said my battery was full, in reality it was almost empty. It's not a huge deal if you're recharging on a regular basis, but if you have any "low and slow" loads, I would recommend another shunt.

In all fairness, it could just be my specific unit that isn't super accurate, but that's my experience.
 
A.Justice said:
You run into an issue when you want to run that one LED for long periods of time. My battery sat for about 6 months with the BMS and solar charge controller on, but the draw was so low that the shunt didn't catch it, and still said my battery was full, in reality it was almost empty. It's not a huge deal if you're recharging on a regular basis, but if you have any "low and slow" loads, I would recommend another shunt.
Click to expand...
You make a very good point! The point being is, without context and use case, we're all guessing here, often based upon our own use case. Of course, I've never assumed anything like that, lol. For example, I started a thread about a redneck way to make crimps and got pounded for it, which I deserved, because my method really wasn't safe for long-term use. Some people wanted me to buy a $200 crimp tool - what they didn't realize is I only needed to make 4 crimps. Whereas their use case is to make dozens if not hundreds. But that context and use case isn't always obvious. Assume = ass out of u and me (lol)

And you also just made me aware of the SCC drawing a small bit from the battery. I hadn't thought of that, such as during long term storage. Thanks.
 
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