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diy solar

Custom Shunt, combining Batrium + Victron Lynx

Firstascent

Solar Enthusiast
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Mar 7, 2020
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265
Before you say it, I know there are MUCH cheaper, and easier, ways to do this, and ways to do this without using the Victron Lynx Shunt entirely... but that wouldn't be as fun :) I'm doing this purely because I want to and for aesthetics. So keep that in mind as you read. I'm sure I'm the only one dumb enough to buy a Lynx Shunt to test this out haha.

I'm using the Batrium BMS, so their Shuntmon is required for proper functionality. I'm also using the Victron Lynx for my DC distribution which led me to want to use the Lynx Shunt for aesthetic reasons. Can't deny the Lynx is a clean setup :)

Now comes the challenge, how to use both shunts but maintain the clean appearance of the install. Obviously none of this is recommended by neither Victron or Batrium but I'm going for it.

If you're not aware, I don't need two complete shunts, all I need is one shunt but the two separate electronics of each system to function. The Lynx shunt only comes in one option, a 1000A/50mv shunt. The Batrium essentially has two options, a 500A/50mv and a 1000A/50mv shunt, they call the entire shunt package their Shuntmon. In the Batrium software you tell it which shuntmon you have.

Here is the first unknown. Batrium states they do a 10-point calibration to basically "pair" each individual circuit board with each individual shunt for better accuracy. They do have an option where you can send them in a different shunt (ie a 250A shunt or something they don't offer) and they will calibrate your shuntmon for your specific shunt. of course at a cost, and they are in Australia. Without having everything fully connected yet I can't say how accurate it will be connected to a different shunt, but should know in a few days and can compare do some comparisons. Also I should note that I currently have the 500A/50mv shunt but in software I will be telling the Batrium BMS I have a 1000A model and hoping it will calculate accordingly.

Since a shunt is measuring the voltage drop across the "resistor", aka shunt, you need a wire/lead on each side of the shunt to compare. The hole spacing of the Victron Lynx shunt and the Batrium Shuntmon are ALMOST identical! which is a huge plus. This is the next unknown I'll need to work out.
Also, the Lynx Shunt has M5 threads for screws and the holes in the circuit board of the shuntmon where the screws pass through are designed for M4 screws, which means an M5 screw is too big to fit through the holes on the circuit board. yes I checked :) Quick and dirty option would be drill out the holes in the Shuntmon circuit board just a tiny bit to allow the screw to fit through, but I don't want to do this.
So the current plant is I'm ordering some short aluminum standoffs that have an M5 male thread on one end and an M4 female thread on the other. The M5 male side will also hold down the existing small wire lugs as part of the Lynx shunt and then I'll be able to use M4 screws for the Shuntmon. I should have these standoffs on Tuesday/Wednesday so I can do some further test fitting.

Ok, now comes the last (at least for now) hurdle. The Shuntmon has terminal block connectors soldered on, a 2-pin and a 4-pin each with a 3.5mm pitch. If I place the shuntmon inside the Lynx shunt then it just barely fits WITHOUT the terminals actually connected. So this wouldn't work as-is. What I'll need to do is order and solder in new terminal blocks that have the solder terminals inline with the connector side so that when I plug it in it isn't taking up more space on either side. The photos will really help show what I'm saying here.
I did test fit that I have plenty of internal clearance so I can still fit the Lynx Shunt cover back on over everything with the Shuntmon inside.

That's where I'm at for now. Call me crazy all you want, I'm having fun :) Constructive Criticism always welcome! I'll keep this updated with further info in the next couple/few days.

Typical Lynx Distribution, nothing custom, no Batrium
IMG_5144.jpeg


Lynx Shunt close-up where the Shuntmon needs to fit
IMG_5145.jpeg

Testing clearance to fit the Shuntmon inside the Lynx Shunt
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Shuntmon showing the holes in the circuit board
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Shuntmon disassembled
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closeup of the Shuntmon circuit board
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bottom side of Shuntmon circuit board showing where I'll need to de-solder and re-solder new terminal blocks
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The current design of the terminal blocks on the Shuntmon wouldn't allow me to actually plug in the connector. The Lynx case fits right where the black rubber piece is on the busbar.
IMG_5154.jpeg

If I solder on new terminal blocks that allow me to plug in from the top side then I think this would work perfect.
IMG_5155.jpeg

This is simply the Batrium Shuntmon unscrewed from the supplied 500A/50mv shunt.
IMG_5156.jpeg
 
Ok, I thought I was the only one crazy… For my MotorHome I am using Batrium Bms with the 1000a shuntmon, then my negative wire goes into a Victron 1000a Smartshunt then into the MotorHome.

The two shunts stay very close - in voltage, amps, and battery capacity. (As you would expect) - so maybe you can recalibrate the Shuntmon (using the Victron shunt as your standard).

Good Luck! - sounds like a fun piece in the project.
 
I know that is going to be an expensive project. but I'd like the idea and look is important too..
Agreed, on both counts haha

Ok, I thought I was the only one crazy… For my MotorHome I am using Batrium Bms with the 1000a shuntmon, then my negative wire goes into a Victron 1000a Smartshunt then into the MotorHome.

The two shunts stay very close - in voltage, amps, and battery capacity. (As you would expect) - so maybe you can recalibrate the Shuntmon (using the Victron shunt as your standard).

Good Luck! - sounds like a fun piece in the project.
Oh nice, somewhat similar! why did you go with the 1000a shunts? I think for the majority of us a 500a is sufficient, and more common.

Good to know your too shunts stay close to each other. I definitely don't expect them to be exact but as long as it's close enough to have an accurate state of charge I'll be happy. and since it will have no effect on my individual cell monitors the Batrium will still keep me safe from that perspective.

and thanks! I'm really looking forward to this. My test stand-offs should be here Wednesday, that will be a big piece of the puzzle to verify.

shoot, I still need to order new terminal blocks. I just ordered a new soldering iron last night, no idea where mine is/was.
 
The reason for both shunts being 1000a is this is a 12v battery with eight 272ah Lishen cells in a 2p4s. For my MotorHome I wanted to keep the boost ability - At a 1C discharge, it could be 540a - those cells can supposedly do a 2C discharge for a few seconds- so it might start the big Diesel engine- it calls for a battery with 1000CCA. Hopefully I never have to find out, but I wanted the pieces in place just in case. (I have a 400a class T fuse protecting the battery. If I need to do a big boost - it won’t be enough- so I made a 1/4” copper busbar to replace the fuse.)
 
Ok so I did some further basic testing last night since I didn't want to wait for the little M5 standoffs I ordered (which actually just arrived a couple hours ago).

Initial tests were "OK" but between the Batrium and the Victron they were far enough off to where I will need to spend more time calibrating/adjusting or something to ensure I have good values.

Since the Shuntmon I ordered initially is a 500a/50mv shunt and the Victron uses a 1000a/50mv shunt, the first thing I had to do was tell the Batrium software that I have a 1000a/50mv shunt since I'm tying it into the Victron directly. You'll see in the photos I simple ran a quick 18ga wire lead from the Shuntmon circuit board to each side of the Victron shunt and then ran the positive reference wire on the positive busbar. I'm not sure how much it matters where the positive reference wire is placed (Batrium says at the battery) so I'll need to play with that.

Right off the bat here are the values/discrepancies between the Victron and Batrium

Victron Lynx Shunt
13.21V​
-1.50A​
-19W​

Batrium software (shuntmon connected directly to Victron Lynx Shunt)
13.26V​
-1.3A​
-17.6W​

I would like them to be a little closer together in the readouts. I don't know yet what options I have in the Batrium software to do this so will need to play with that tonight but I don't think I'm at any road blocks...yet. I am definitely not going to re-solder on new terminal blocks until I can get good readings closer to each other since as of now everything is easily reversible.

I think what I will do next is re-assemble the Batrium shuntmon in it's normal config with it's 500a/50mv shunt that it is calibrated for and install it in series withe the Victron lynx and see how the values compare (I should've done this first but didn't want to disassemble the Lynx Distributor :)
if the values are still off, I'll need to determine which is more accurate, the Batrium or Victron.
If the values are very close, then I'll know I need further adjustments somehow in the Batrium software when using the 1000a shunt.
There is still the possibility that there are some settings configured in the shuntmon circuit board preventing accuracy since again, according to Batrium they do a 10-point calibration for the specific shunt block and supplied cabling. I could see this making things more accurate, but to what level. I mean, it is only reading to hundredths

Btw, I did also set the Shuntmon back to its default of 500a/50mv while connected to the 1000a shunt and the values where about half of what they should be, so that was a good indication simply that some type of config is taking place when I select a 1000a shunt in software. You'll see that in the screenshot that shows only -8.63W of load.

I do have some accurate Fluke meters I can get some current readings from but will need to break the circuit to get a measurement, it's a good meter but will only do up to 10a continuous, so will need to make sure I don't have any loads over 10a, which is easy since this is all testing and no real loads attached.

Output from Victron Lynx Shunt
IMG_5191 (1).jpeg

Batrium software directly connected to Lynx configured for 1000a/50mv shunt (values at top right corner in green)
IMG_5192.jpeg


Batrium software directly connected to Lynx configured for 500a/50mv shunt, note the amps and Watts are half of what they should be, this is a good sign config is taking place as it should.
IMG_5193.jpeg

Batrium software where I can select from a dropdown which shunt I'm using
IMG_5194.jpeg

Initial test attached some leads to the Batrium shuntmon circuit board
IMG_5173.jpeg

back side showing attached leads for testing.
IMG_5174.jpeg

shuntmon connected to each side of the 1000a shunt block
IMG_5175.jpeg

voltage sense wire for the shuntmon
IMG_5177.jpeg

voltage sense attachment point from the shuntmon to the Lynx positive busbar. (battery is left side, all loads are right side.
IMG_5178.jpeg
 
It doesn’t surprise me that you are close, or that there is a little different either, because the resistance of the blue wires is being calculated in your whole load.
Did you run a larger load? If you are off by only a little with a large load you may be ok.
 
It doesn’t surprise me that you are close, or that there is a little different either, because the resistance of the blue wires is being calculated in your whole load.
Did you run a larger load? If you are off by only a little with a large load you may be ok.
you bring up a good point in that at the end of the day, when comparing these, I'm wondering what an acceptable level of difference would/should be. I need to decide that so I know when to stop and when close enough is good enough haha.

I haven't ran any real load on this yet only a few devices in idle state, I'll see if I can find something to wire up. worse case I can plug the inverter into a standard 15a wall receptacle, set the charger to output 10-20 amps and see how the shunts match up then. I'm going to go play around with it more right now.
 
well, tonight I learned a lot and also hit a somewhat similar roadblock but now more difficult to "fix" by myself.

I connected my Batrium Shuntmon, in it's normal setup as I received it from Batrium, in series with the Victron Lynx Shunt. I put a charge from the Inverter from 10 to 20 amps and they were pretty much spot on with each other. So that tells me they are both accurate, no surprise there but an important data point I needed to gather nonetheless.
This is about the only good thing that happened tonight haha.

I then connected the Shuntmon circuit board back onto the the lynx shunt with my new standoffs that arrived today for testing and fitment. The existing holes in the Lynx are M5 and the Shuntmon circuit board has holes for M4 bolts. I got two different types of standoffs to test, one has an M5 male thread with an M4 female thread, the other is an M5 male thread with an M3 females thread.

Due to the holes in the shuntmon circuit board not lining up exactly with the Lynx shunt, the M5 to M4 didn't work because the shuntmon was just a tad too wide to get the second bolt in :( and I didn't want to drill out the circuit board, yet. Then I tried the using the M5 to M3 standoffs and that did work. Since M3 bolts are smaller it gave me juuuuuust enough wiggle room to get both bolts in and everything secured.

At essentially no load and devices in an idle state I had fairly close values but not as close as when the two shunts were separate and in series. The shuntmon was reading about 17.5w whereas the lynx was a little over 18w. So pretty close, I thought I was on the right track.

Then I put a charge load on it at too different levels up to around 20 amps, basically the higher the load, the further apart the readings would be :( not good. You can see in the screenshots that that the Lynx shunt was reading 18.3a/245w and the shuntmon was reading 16.1a/216w, so a little over 2a difference. At a lower load the Lynx was showing 7.4a/98w whereas the shuntmon showed 6.4a/86w so as I mentioned as the load increases so does the discrepancy.

I looked through the Batrium software further and also reached out to them, there isn't any user configurable settings specifically related to the shunt config that would change the voltage/current readings. Only they can do that at a price but you have to ship your specific device to them so they can calibrate it.

So now I'm not sure what I'm going to do, I did ask them how much it costs for the custom calibration so we'll see. I imagine it's a quick process so hopefully not crazy, but would suck to ship it back and forth and the downtime in between.


Standoff adapters from M5 male thread to M3 female thread. I didn't want them this long, I looked at the wrong column in the specs when I ordered :( But the idea is still the same and it fits.
IMG_5201.jpeg

Discrepancy between the Victron and Batrium, Victron showing 18.5a
IMG_5205.jpeg

Discrepancy between the Victron and Batrium, Batrium showing 16.1a
IMG_5206.jpeg
 
I'm still waiting to hear from Batrium on a couple more questions regarding having them calibrate it to a different shunt but in the meantime I wasn't completely satisfied with the standoffs I had so I customized them and it's much better now.

First I cut the standoff in half to make it shorter. I also didn't like using the m3 screws that I had to use in order to make the shuntmon holes line up to the slightly more narrow lynx holes. When I cut the standoff in half I then had a smooth surface, a blank slate. I screwed in the new shorter standoffs, placed the shuntmon on top, then marked where the holes Should be which is slightly off center of the standoff in order to accommodate the wider spacing of the shuntmon.

I then drilled and tapped the new locations and BAM, everything is much better now with the supplied M4 screws from Batrium.
Really all that is left is to hopefully hear from Batrium that they can do this no problem, I'd ship it off to them so they can calibrate it, then once I receive it back I'd still need to re-solder in new terminal blocks and I should be good to go! It's coming along well, Unfortunately I have a lot riding on Batrium's support to recalibrate though.

Taped off where I wanted to cut each standoff with a cut-off wheel.
IMG_5211.jpeg

Placed the standoffs in my drill press and "pressed" them into sandpaper to make the surface flat and smooth from the cut-off wheel.
IMG_5213.jpeg

Before and after from the drill press
IMG_5215.jpeg

Had to order a 3.3mm drill bit specifically for this haha, best $3 I ever spent. You'll notice I'm drilling off center, this is on purpose.
IMG_5240.jpeg

M4 tap. I only used the drill press to keep things aligned. I hand spun the chuck to thread it. side note, my drill press actually has a "tap" feature but I've never used it and didn't want to practice on this one :)
IMG_5232.jpeg

Making sure an M4 screw fits :) It did.
IMG_5241.jpeg

Finished standoffs mounted to the Lynx shunt.
IMG_5234.jpeg

Fits perfectly! All of this will eventually be hidden by the Lynx cover, but I'll know it's good :)
IMG_5235.jpeg
 
Your going to cost me a lot of money.
I'm here to help :LOL:


Another update, it's not going well with Batrium. We've now exchanged a few emails and they are saying they don't want to do the re-calibration service as it's not something they really do anymore. They did it previously when they didn't offer multiple shunt options. Which is very unfortunate, they even have it on their site that it is an option. Could be easy money for them, I have no problem paying them for their service.

But just to be clear, our emails have all been friendly and professional, so this isn't meant to bash on Batrium, I'm just frustrated :) and unfortunately you have to use their shuntmon. fine, but let me use my own shunt block like your website says!

Not the end of the road by any means, just means I have to get a little more creative now. With all the customization in the software that Batrium offers I wish they would allow you to configure the shunt parameters. they allow you to do it on the cell monitors if the voltage is off, would be an easy and great feature to add for the shunt as well.
 
Just out of curiosity. Have you measured the difference on both shunts?
In what regard? If you mean the resistance of each, no I haven't. But I was actually going to today, although I know they will be different as one is a 1000a/50mv and the other is a 500a/50mv, but even if they were both 1000a/50mv shunts I'd imagine they'd have a slight difference as well.

If you mean the current measurement of each, yes. When the two shunts were in series they were both pretty much spot on with each other at loads from <1a to 20a.
 
In what regard? If you mean the resistance of each, no I haven't. But I was actually going to today, although I know they will be different as one is a 1000a/50mv and the other is a 500a/50mv, but even if they were both 1000a/50mv shunts I'd imagine they'd have a slight difference as well.

If you mean the current measurement of each, yes. When the two shunts were in series they were both pretty much spot on with each other at loads from <1a to 20a.
Sorry I meant to say resistance. For all the customization Batrium allows, it’s a shame you can’t calibrate it in the software
 
Sorry I meant to say resistance. For all the customization Batrium allows, it’s a shame you can’t calibrate it in the software
Agreed, it's a shunt, nothing fancy going on there haha. since its based off a "known" resistance value all I'd need is a field to input that value and done.
 
Back at it again with some more testing. I tried really hard with Batrium again but think I reached the end of the ‘custom calibration’ battle. So that’s not an option any longer.
So now it’s up to me to adjust the values from a physical connection standpoint. Since it’s based on resistance being a key value I played with different mounting points with some good success.

instead of connecting at my custom stand-off points, I chose a location further apart using two existing mounting screws that hold the Lynx shunt down to its case.
Doing this gave me Very close values from 1-20 amps! This so is the closest I’ve gotten the two shunts so far which is promising.
Tomorrow I’ll do further testing with higher loads to see if I get linear results at these given points. With my multiplus inverter/charger I can adjust the charge load up to 120a. If I can get consistent matches results from 1-120A then I’d say it should remain accurate at even higher loads.
Photo below shows the two blue lead wires at the new test points. If this does work I’ll also have to rethink my aluminum standoffs since it was my mount for the Batrium shuntmon as well, so I’d need a non-conductive way to mount it.
 

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I've finally come to a completion with this project where I am satisfied. Also, after thinking about what exactly I'm trying to accomplish in more detail I think I could almost do what I need to do WITHOUT the Batrium shuntmon. The reason being that I would still have SOC% with the Victron Lynx Shunt and I'm not using the Batrium for Charging, I have that configured within both the Victron Multiplus II inverter as well as the SmartSolar MPPT, the Batrium is there as a last resort.

With that being said, I did get everything connected now. Both the Victron and Batrium shunts are reading within a few watts of each other.

First step was to de-solder the 2-pin terminal connector on the Shuntmon, and re-solder on similar Vertical style so that it would fit inside the Lynx Shunt. Btw, it's a 3.5mm pitch on the terminals.

This is the Shuntmon circuit board with the factory 2-pin connector on the right. Notice how it plugs in to the side, this was an issue for fitment.
IMG_0609.jpeg

2-pin connector de-soldered/removed
IMG_0610.jpeg

New vertical style 2-pin connector soldered on
IMG_0613.jpeg

Re-assembled in the 'case'. I had to make the cutout about 5mm deeper to fit the new connector.
IMG_0616.jpeg

Custom wire made (18ga tinned copper) for one side of the shunt connection which will attach to the Lynx, see further info in next photos.
IMG_0620.jpeg

Shuntmon mounted to a custom aluminum standoff I made. there is only one standoff on the right connection point, then you can see the left connection point is connected to the shunt block with an existing screw that held the shunt block physically in place to the housing.
You'll also notice the red power wire connected to the Shuntmon, this is how the Shuntmon reads the battery pack total voltage.
IMG_0624.jpeg

Perfect fit, this is why I needed the vertical style 2-pin connector.
IMG_0626.jpeg

I passed the data cable for the Shuntmon through one of the vents so that I'd still be able to close up the Victron Lynx Shunt housing.
IMG_0630.jpeg

All sealed up with no fitment issues! (This is my test bench so ignore the mess. Everything will be getting installed in my RV shortly now that I've figured this out).
IMG_0631.jpeg

I also now have the Batrium communicating with my Victron Cerbo GX via Canbus! This is pretty awesome, I haven't played with it too much and still have some config to do but I can see all the Batrium info, including High/Low temps of EACH cell and High/Low voltages of EACH cell, pretty sweet!

The end goal will be to figure out how to configure it so the Victron controls the charging, and the Batrium is monitoring individual cells and is my last resort to shut the system down if something else (Victron) were to fail in doing so. (I have no idea how I'm going to configure it yet, so that's the next mini project, there are SO many settings in the Batrium ha!)
IMG_0640.jpeg


I hope this helps someone else some day if they get the crazy urge such as I :) If anything, I had a ton of fun during this process and stoked on the outcome. I hit lots of walls, jumped many hurdles, and finally completed it.
 
Great info , thank you for posting. I am about to try to do the same thing. I have a 1000amp lynx with the 1000amp shuntmon Do you think I Can just mount the board right on the lynx?
 
Great info , thank you for posting. I am about to try to do the same thing. I have a 1000amp lynx with the 1000amp shuntmon Do you think I Can just mount the board right on the lynx?
Do you mean you want to mount the shuntmon onto the Lynx exterior housing? If so, yes that would work as well and what I thought about doing. I decided to mount it internally simply for aesthetics :) But the actual placement won't affect anything really.

What does matter is where you connect the two leads coming from the shuntmon board. Connecting to the exact locations on the Lynx shunt that I did I believe will be critical. I tested various locations and these (as shown in my photos) gave me the most accurate readings to what the lynx shunt was saying.

I think I mentioned above as well but I think it's great that you can view one, or both, of the shunts if you ever want to confirm accuracy. So my battery level will be tracked via the Victron shunt AND the Shuntmon and I can view both easily.
 
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