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Old 04-20-2019, 01:43 PM   #1
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Question-Wiring Magnum battery monitor shunt

I have a relatively new Sportsmobile with three 92 A/Hr Deka AGM batteries, a Magnum MS2000 inverter with both the ME-BMK battery monitor and the ME-RC50 remote panel. I don't have solar; the batteries are charged either via a shore power connection or via my second alternator (Nations-270XP).

My problem is that I can't seem to get the State of Charge (SOC) meter on the Magnum inverter remote to display correctly. It was forever in the "Think'n" state even after being connected to shore power to reach full charge and then being run down before being charged fully via shore power again. After consulting with the manual I saw that it recommended inputting, via the settings, a slightly smaller battery capacity in Amp/Hrs. I noticed that while my three 92 A/Hr batteries only give me a total of 276 A/Hrs that the capacity in the settings had been entered as 300 A/Hr. I lowered that to 270 A/Hr and shortly after that, my SOC meter on the remote seemed to be working. It displayed 100% after being connected to shore power and it slowly dropped as I used the batteries.

I thought I had fixed my issue, but then I noticed that the SOC never increased UNLESS I was charging via shore power. The battery monitor's SOC didn't seem to notice the charge added to the batteries by the alternator, but it did display the increased voltage after charging via the alternator.

So I looked at the wiring diagram for both the Magnum 2000 inverter and their battery monitor. I noticed that my system isn't wired as shown in the manual. The manual shows the battery monitor shunt between the negative terminal of the battery and the negative connection to the inverter. My battery monitor shunt is between the vehicle ground on one side and the negative battery connection and negative connection from the inverter. (see diagrams)

Maybe there is a very good reason for it to be connected this way, but it doesn't match the wiring diagram in the manual. Then again, the wiring diagram doesn't show a vehicle ground either, so I can't directly compare it with what I'm seeing in my van.

To me it looks like I would need to move the negative terminal from the battery to the other side of the shunt so that the shunt is between the negative connection from the battery and the negative connection from the inverter.

Any thoughts?



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Old 04-20-2019, 01:59 PM   #2
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It looks backwards to me, but does not match what you explain as your issue, from that diagram I would expect the battery monitor to be capturing the Alternator charge current but not catch any of charge from the magnum inverter/charger. I assume the shore power charger you are talking about is from from the Magnum unit.

-greg
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Old 04-20-2019, 02:08 PM   #3
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It looks backwards to me, but does not match what you explain as your issue, from that diagram I would expect the battery monitor to be capturing the Alternator charge current but not catch any of charge from the magnum inverter/charger. I assume the shore power charger you are talking about is from from the Magnum unit.

-greg
Oh, I agree. Given how it is wired I wouldn’t expect the shunt to measure anything including the charge added by the shore power, which comes in via the inverter/charger.

I’m quite confused and will be sending this question on to Sportsmobile North on Monday, but I thought I’d see if anyone here had any ideas first.
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Old 04-20-2019, 02:38 PM   #4
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I agree with Greg - Certainly looks like the negative to inverter cable needs to be shifted to the terminal with vehicle ground.

The battery side of the shunt should have only the one cable, that goes directly to the negative battery terminal and should be the only connection to the negative battery terminal. All current then flows through the shunt. As wired now, any current through the inverter/charger is bypassing the shunt and not being measured.
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Old 04-20-2019, 10:02 PM   #5
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I agree with Greg - Certainly looks like the negative to inverter cable needs to be shifted to the terminal with vehicle ground.

The battery side of the shunt should have only the one cable, that goes directly to the negative battery terminal and should be the only connection to the negative battery terminal. All current then flows through the shunt. As wired now, any current through the inverter/charger is bypassing the shunt and not being measured.
Thanks, that's what I am thinking. The negative from the battery should be moved to the side of the shunt where the vehicle ground is connected. I'm pretty sure it is OK to leave the vehicle ground connection on the left side of the shunt and just move the neg cable from the battery to that same post on the shunt. That would place the negative cable from the battery and the negative to the inverter on different sides of the shunt, as shown in the manual.

Unfortunately, it doesn't look like I can simply disconnect that negative line and move it. The MS2000 inverter manual states "To remove battery power from the inverter, disconnect the positive connection before the negative connection." So before I can move that negative cable from the battery to the other side of the shunt it certainly sounds like I need to first disconnect the positive cable from the inverter before I can move that negative cable on the shunt since I'll be breaking the negative path to the battery bank in the process of moving the negative cable at the shunt.

I'll see what Sportsmobile North says before I go moving anything. If I lived closer to them I'd simply have them make the connection swap; no matter how much I read the manuals, I'm still afraid I'm going to miss something and end up frying part of my electrical system (or myself).
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Old 04-21-2019, 06:43 AM   #6
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You would need to place the negative from the inverter on the same side as the frame to ground connection. There should be no connection from shunt to battery. SMB frequently ties circuits to the frame for ground, none of those circuits would be read from the shunt, if you connect it with frame and battery ground directly together.

This somewhat goes back to my original answer, the way it looks like it is wired in your picture, the only thing that I would expect that shunt wouldn't have wouldn't have read was what was going in and out of the magnum inverter/charger. As the connection was on the battery side of the shunt.

Your second alternator if grounded via the frame should have gone through the the shunt and thus you should see current being increased when the van is running. Of course that depends on the how the positive output of the alternator is wired.

So I am still confused as the picture doesn't match what I would expect. Our you sure you have been reading the BMK when the remote. The inverter it self does put out charge data?

You should be able to find very large fuse "Class T" going from the inverter to back to the battery. Removing this should be the same as disconnecting the inverter from the positive side of the battery.





It would be interesting to see where the alternator connects to your positive side. Our you sure it is a second alternator versus a larger alternator with a separator or ACR. If you did get a second alternator did you get the Balmar regulator with it? It is possible that you have two separate issues.

-greg
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Old 04-21-2019, 08:03 AM   #7
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You would need to place the negative from the inverter on the same side as the frame to ground connection. There should be no connection from shunt to battery. SMB frequently ties circuits to the frame for ground, none of those circuits would be read from the shunt, if you connect it with frame and battery ground directly together.

This somewhat goes back to my original answer, the way it looks like it is wired in your picture, the only thing that I would expect that shunt wouldn't have wouldn't have read was what was going in and out of the magnum inverter/charger. As the connection was on the battery side of the shunt.

Your second alternator if grounded via the frame should have gone through the the shunt and thus you should see current being increased when the van is running. Of course that depends on the how the positive output of the alternator is wired.

So I am still confused as the picture doesn't match what I would expect. Our you sure you have been reading the BMK when the remote. The inverter it self does put out charge data?

You should be able to find very large fuse "Class T" going from the inverter to back to the battery. Removing this should be the same as disconnecting the inverter from the positive side of the battery.





It would be interesting to see where the alternator connects to your positive side. Our you sure it is a second alternator versus a larger alternator with a separator or ACR. If you did get a second alternator did you get the Balmar regulator with it? It is possible that you have two separate issues.

-greg
Thanks for the info.

I am NOT sure that the battery monitor is reading the voltage; that could be the voltage put out by the inverter as you stated. I suppose I could test that by disconnecting the communication cable going from the battery monitor to the inverter and seeing if the battery voltage is still reported to the remote.

I do have a large fuse in the positive battery line between the battery bank and the inverter. I also have a cutoff switch between that fuse and the inverter so I was thinking I'd just turn that switch off to kill power to the inverter before I move the negative connection at the shunt.

The charge cable from the second alternator runs from the alternator, under the van, then up through the floor, just outboard of the three battery boxes. I haven't opened the battery boxes to see exactly where it connects, but it appears it is connecting directly to the battery bank from the alternator.

The Sportsmobile manual mentions that a battery regulator is installed between the alternator and the battery bank in instances where lithium batteries are used. Apparently, they don't install one if you use regular AGM batteries; at least I couldn't find one when I traced the line coming from the alternator. Something I made note of needing if I ever want to upgrade to lithium at some point.

I'm going to pull the van up in front of the garage today and plug into shore power to see if I can replicate what I was seeing on my last trip: The SOC reading on the remote reached 100% when charging via shore power. The SOC slowly dropped after I disconnected shore power and used power from the batteries. The SOC would not increase even when driving the van for hours on my return trip.
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Old 04-21-2019, 08:45 AM   #8
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The voltage reading for the BMK does not go thru the shunt, it is a separate wire that attaches to the house battery, it supplies both power and the reading for the house battery. Any current that is read must go thru the shunt, that would be for both amps and amp-hrs. I honestly don't see how the SOC could ever read that the Magnum Inverter charged the battery. Two of the components are based on current readings from the shunt.
  • The charging voltage has stabilized over a period of time.
  • The charging current has decreased to a low percentage of the amphour capacity – normally less than 2%.
  • The amp-hours that were removed from the battery are within 1% of fully being returned.

When the van is running do you see the voltage increase on the house battery? I am not sure if you already stated that.

The BMK will be able to see current being used by other devices in the rig, like refrigerator, lights, etc, just not the inverter. I would also expect that it will read current going into the battery via second alternator. It is possible that the alternator will not meet the requirements of the BMK to claim full charge, but I would expect it to go up when driving.

You should also be able to dial in the correct AMPHR setting for your batteries. Be careful, there are two areas to set battery bank size, and only one of them is for BMK. The BMK bank capacity can be directly set.

While true you need the regulator for Lithium, they could have installed for your AGM setup, it would have turned the second alternator into a three stage charger, which would have been a good thing.

-greg
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Old 04-21-2019, 01:24 PM   #9
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The voltage reading for the BMK does not go thru the shunt, it is a separate wire that attaches to the house battery, it supplies both power and the reading for the house battery. Any current that is read must go thru the shunt, that would be for both amps and amp-hrs. I honestly don't see how the SOC could ever read that the Magnum Inverter charged the battery. Two of the components are based on current readings from the shunt.
  • The charging voltage has stabilized over a period of time.
  • The charging current has decreased to a low percentage of the amphour capacity – normally less than 2%.
  • The amp-hours that were removed from the battery are within 1% of fully being returned.

When the van is running do you see the voltage increase on the house battery? I am not sure if you already stated that.

The BMK will be able to see current being used by other devices in the rig, like refrigerator, lights, etc, just not the inverter. I would also expect that it will read current going into the battery via second alternator. It is possible that the alternator will not meet the requirements of the BMK to claim full charge, but I would expect it to go up when driving.

You should also be able to dial in the correct AMPHR setting for your batteries. Be careful, there are two areas to set battery bank size, and only one of them is for BMK. The BMK bank capacity can be directly set.

While true you need the regulator for Lithium, they could have installed for your AGM setup, it would have turned the second alternator into a three stage charger, which would have been a good thing.

-greg
I agree, I shouldn't be seeing any increase in SOC regardless of how I'm charging the batteries given how that shunt is connected. That is why I am experimenting today. I have never seen the SOC reading increase slowly. It simply went from "Think'n" to a SOC reading of 100% after leaving it connected to shore power overnight at the campground. I have now had my van connected to shore power most of the day and the SOC reading is stuck at 0% even though the charger has switched to float charge and if I disconnect the shore power the battery voltage is reading 13.2 V before slowly settling to about 12.8 V.

After running the van, I do see an increase in voltage displayed on the remote monitor. Again, it will eventually stabilize at 12.8 volts once the surface charge dissipates.

I verified that I did have the battery bank set for 270 AH under the battery monitor menu of the remote. This is close to the sticker claim of 92 AH * 3 batteries = 276 AH.

I do recall that when getting my walk trough of the van's systems the builder told me he hadn't tested the SOC reading on the remote, but he assured me that if I left it in "Think'n" mode it would eventually start reading the SOC after going through a few cycles where it reached full charge and then was depleted somewhat. That never happened until I lowered the battery AH setting from 300 AH to 270 AH in the battery monitor menu and then left the van plugged into shore power overnight.

Currently, I am thinking that in order to remedy this, I need to disconnect power to the inverter using the battery disconnect wired into the positive cable between the large fuse and the inverter. Then I can disconnect the negative battery cable from the right side (load side) of the shunt and move it to the left side (battery side) of the shunt, where the vehicle ground is currently attached. I still plan to wait to see what Sportsmobile North says first before I go moving the cable, but I simply can't see how the shunt would work given how it is connected presently.
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Old 04-22-2019, 01:05 PM   #10
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OK, so I emailed Sportsmobile North about this issue and included the two photos I've posted in this thread. I received an emailed invitation to call the tech who did the work on my van, so I did that.

The tech stated that the way my van's battery monitor shunt is wired is by design. He stated that they had wired the shunt as shown in the manual's diagram on past builds and had trouble with the SOC not working. He contacted Magnum (inverter and battery monitor manufacturer) and sought guidance.

From what the tech said, magnum said that because this is an install in a vehicle, with a vehicle ground, that he should try installing it so that the ground is on one side of the shunt and the negative battery cable and the negative line to the inverter are on the shunt. The tech stated that they tried that on previous installs and it worked fine and that's the way they've been doing it since.

I don't know how the shunt can be reading current flow with both the battery cable and the inverter cable on the same side of the shunt though. I asked him about that, but he didn't honestly have an answer aside from his statement that it does work like the way mine is wired on other builds. He did suggest that maybe the shunt itself is bad or even the battery monitor module itself. I told him that the battery module does appear to be working given that the green LED on the unit is on.

My next steps are to verify that the communication cable from the battery monitor to the inverter is connected correctly. If that is OK, then I am going to power down the inverter by using the disconnect switch inline in the positive cable between the big protection fuse and the inverter itself. Then I'll go ahead and move the negative battery cable to the other side of the shunt and see if that fixes the issue.

If that doesn't fix the issue then I'll disconnect everything from the shunt so I can put a multimeter across it and seen if the shunt itself is bad.

Fortunately, this isn't a critical thing as everything aside from the SOC meter appears to be working and I can estimate the state of the battery bank from its displayed voltage. Saying that, it sure would be nice to get this working properly.
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