Battery Monitor shunt installation on Roadtrek RS

[ahamuser]

Hi Everyone. New to Class Bs here. Just got a 2018 Roadtrek RS Adventurous and looking forward to our new journey. I'm looking for a good battery monitor and have scoured the internet for advice. The popular and most accurate ones involve installing a shunt, such as, the Trimetric and Victron. There are plenty of reviews of both of those so not looking for a comparison. However, I could not find a discussion or how-to on installing a shunt for my specific Roadtrek model. I have 2 lithium batteries (200ah each) located outside and underneath the chassis behind the wheel wells. I'm quite a DIY kinda guy and wanted to explore how any of you installed a shunt on RT w/ batteries outside. Any suggestions would be greatly appreciated.

[avanti]

I don't know anything about RTs, but unless the battery compartment is very tight, the easiest way to mount a shunt is directly onto the negative battery terminal.

Here's how I installed my Trimetric shunt:

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[ahamuser]

Thank you Avanti! I saw those pics from a previous thread. You did a fantastic job making your shunt. I will probably buy one as I need at least a 400amp shunt and don't trust myself makeing one. My problem is trying to figure out how my two batteries are wired so that I can located the most negative post and location of shunt (either inside or outside), drilling points to the rear, etc.
I'm pretty sure they are wired in parrallel as one of the labels showed 12v instead of 6v. I'm hoping someone with a Roadtrek RS has done this because the simply voltage reading that RT provides is crap.

[Stevemo]

You will need to obtain some multi-conductor cable to run to the shunt. My RT came with a Bogart and some horribly tiny Belden wire. I would get something better so that you can crimp to it.

You will put your shunt on one of the battery negative terminals where they batteries join and head to the coach/ground. You will want to run a full size negative cable back to the inverter if you have one. You should not draw 400 amps through the body of the van.

I have some videos here of two Roadtreks that may give some ideas.

Chevy batteries and shunt:

https://www.youtube.com/watch?v=d6ZsgJkWISI

Dodge batteries and no shunt:

https://www.youtube.com/watch?v=qne0ljwivHY

https://www.youtube.com/watch?v=OuVb0CIafyo

Some cable glands for the holes in the floor:
https://www.amazon.com/gp/product/B0...d9cc37c7ffb11c (affiliate link)

I would follow the shortest routing possible (probably the existing Roadtrek cable route), at 400 Amps you are going to need to be real short.

Blue Sea has some good resources.

[booster]

If I read this correctly, the OP has two 12v lithium modules, one on each side of the van, hanging under the body. The pix of 6v batteries will be inaccurate because 6v are in series and the 12 have to go in parallel.


The whole thing with the shunt placement is that all the current from both batteries has to go through the shunt which is placed in a common negative battery cable. With the batteries underneath and on opposite sides, getting a common ground and trying to get the shunt inside the van where it will stay clean can be quite an exercise. It is especially true if you try to keep equal cable lengths on the two battery negatives.


Also be aware that the monitor will not be able to see the internal parasitic losses of the modules, which can be as much as 4-5ah per hour depending on what revision level of modules you have, so would have to either manually allow for it or program it in the monitor if it has "storage loss" or similar function you can set. Some 200ah modules will self discharge in as little as a couple of days with no load on them, if they are on.



My guess would be that Roadtrek wired them with the battery negatives to the chassis, and then also has the inverter negative to the chassis, but that is just a guess. All the other negatives from 12v stuff in the van are also going to be to the chassis.



If it is that way, the OP would need to run a negative battery cable from each battery to a common binding post, hopefully inside the van, and then another cable from the other end of the shunt to van chassis to catch all the returning amps. This will give a lot of extra cable, but with the batteries that far apart, you don't have a lot of choice.


High currents through the chassis don't really seem to be much of an issue, that I have seen, and many of us run upwards of 300 amps from the alternator(s) to the coach on a regular basis, with the negative back being the chassis. Just make sure you have a good clean and bolted connections. If the inverter is close to the shunt when laying things out, running the negative of that back to shunt can minimize resistance a bit if you use very large cable, though, as it minimizes the number of connections.


The sensing wires from the shunt can be quite small, as they carry nearly no current, just stay big enough to make them not fragile. They are often furnished with the monitor kit, and should be used as a twisted pair of wires with no splices or connectors in them if possible because they are very sensitive to extra resistance.

[avanti]

Originally Posted by ahamuser

TYou did a fantastic job making your shunt. I will probably buy one as I need at least a 400amp shunt and don't trust myself makeing one.

Just to be clear: I didn't fabricate a shunt, only the copper bus bar which also serves as a mounting bracket between the shunt and the battery negative terminal. The shunt is the standard Trimetric one. 400 amps would be no problem for the copper bus.

[booster]

I don't think the OP was saying he planned on drawing 400 amps, can't imagine what he would use it for anyway all at once. Usually the charging off a big alternator would be the largest current and would be in the 2-300 amp range tops and averaging substantially less than that on a hot alternator.


I think with most monitors you get the choice of 100 or 500 amp shunts, which is good to go at 500 as you don't really want to run a shunt much above 50% capacity for very long or it will heat up too much anyway.

[avanti]

A side note about chassis grounds:
The ampacity of the chassis is huge--much larger than any practical wire. There is really no reason to be afraid of running high currents that way. For example, I use the chassis for the return from my second-engine alternator all the way back to my batteries in the far aft.

The issue is establishing high-quality and dependable ground points. I only use the engineered ground points provided by Mercedes. Assuming that the battery and the inverter are reasonably close together, it is indeed more practical to run a wire. But, it isn't because of any problem with putting high currents through the chassis.

[cruising7388]

Originally Posted by booster

If I read this correctly, the OP has two 12v lithium modules, one on each side of the van, hanging under the body. The pix of 6v batteries will be inaccurate because 6v are in series and the 12 have to go in parallel.


The whole thing with the shunt placement is that all the current from both batteries has to go through the shunt which is placed in a common negative battery cable. With the batteries underneath and on opposite sides, getting a common ground and trying to get the shunt inside the van where it will stay clean can be quite an exercise. It is especially true if you try to keep equal cable lengths on the two battery negatives.


Also be aware that the monitor will not be able to see the internal parasitic losses of the modules, which can be as much as 4-5ah per hour depending on what revision level of modules you have, so would have to either manually allow for it or program it in the monitor if it has "storage loss" or similar function you can set. Some 200ah modules will self discharge in as little as a couple of days with no load on them, if they are on.



My guess would be that Roadtrek wired them with the battery negatives to the chassis, and then also has the inverter negative to the chassis, but that is just a guess. All the other negatives from 12v stuff in the van are also going to be to the chassis.



If it is that way, the OP would need to run a negative battery cable from each battery to a common binding post, hopefully inside the van, and then another cable from the other end of the shunt to van chassis to catch all the returning amps. This will give a lot of extra cable, but with the batteries that far apart, you don't have a lot of choice.


High currents through the chassis don't really seem to be much of an issue, that I have seen, and many of us run upwards of 300 amps from the alternator(s) to the coach on a regular basis, with the negative back being the chassis. Just make sure you have a good clean and bolted connections. If the inverter is close to the shunt when laying things out, running the negative of that back to shunt can minimize resistance a bit if you use very large cable, though, as it minimizes the number of connections.


The sensing wires from the shunt can be quite small, as they carry nearly no current, just stay big enough to make them not fragile. They are often furnished with the monitor kit, and should be used as a twisted pair of wires with no splices or connectors in them if possible because they are very sensitive to extra resistance.

You make two under appreciated points:

1. Typical SOC metering utilizes a single shunt positioned in the common negative bus for all batteries being measured. However, Roadtrek scatters their batteries all over the coach and provides discrete negative leads for some if not all the batteries. Consequently there is no common negative bus to support a single shunt and to make the shunt usable would require running lengths of 4/0 cable that has a prodigious cost per foot.

There is a way around this. While the negative leads in a multiple battery array may use discrete negative leads, they all utilize a common bus for the positive leads. Blue Sea offers a model 1830 SoC meter with a shunt that can be installed on the positive bus with an insignificant loss in meter accuracy.

2. Significant internal BMS parasitic losses not recognized by the shunt seems unique to the Roadtrek lithiums. By comparison, the BMS parasitic in the Xantrex Li3 system is less than forty milliamps with an accrued 24 hour loss of less than 1 ah. The Roadtrek setup would require a meter that would permit dialing in parasitic ah losses to keep the SoC reading accurate. I'm not aware of any shunt fed meter that provides this feature.

There is an additional issue you didn't mention which is meter calibration. The SoC meter requires defining the ah capacity of the battery system. With a monolithic setup like provided with Xantrex and Volta, the total available ah capacity is fixed, so defining this in the meter is a simple input. But with the Roadtrek lithium setup, there is no invariable total ah value. It depends on how many batteries are on or off line. Since you have only a single calibration for the meter, you would have to renew the calibration each time you brought any battery on or off line. Otherwise, your SoC readings would be riddled with errors.

[booster]

Originally Posted by cruising7388

2. Significant internal BMS parasitic losses not recognized by the shunt seems unique to the Roadtrek lithiums. By comparison, the BMS parasitic in the Xantrex Li3 system is less than forty milliamps with an accrued 24 hour loss of less than 1 ah. The Roadtrek setup would require a meter that would permit dialing in parasitic ah losses to keep the SoC reading accurate. I'm not aware of any shunt fed meter that provides this feature.

There is an additional issue you didn't mention which is meter calibration. The SoC meter requires defining the ah capacity of the battery system. With a monolithic setup like provided with Xantrex and Volta, the total available ah capacity is fixed, so defining this in the meter is a simple input. But with the Roadtrek lithium setup, there is no invariable total ah value. It depends on how many batteries are on or off line. Since you have only a single calibration for the meter, you would have to renew the calibration each time you brought any battery on or off line. Otherwise, your SoC readings would be riddled with errors.

When I mentioned the setting for self discharge earlier, I had in mind a Trimetric we used to have that I think had that setting available. That was about a decade ago. They now don't show that setting in any of their literature, so I either am remembering it incorrectly or it has been removed to put more useful feature in it's place. It would be useful in the case of the big parasitic units, it it went that high. IIRC it may only have gone to 3% per month, not the 70% per day that would be needed.


Obtaining the capacity is not all that difficult as the monitor will do it for you when you run a discharge from full to the lowest voltage you are comfortable with and note the amp hours. You will have your usable AH and show zero to 100% for that usage on your meter.


Xantrex and Volta probably have a setting for the AH, even though they tell you what they are, as it is needed to be able to compensate as batteries age. 80% of original capacity is a normal place to call batteries worn out, so you would need at least that much range. They may have an automatic compensation bases on voltages and cutoffs, as they could get away with that with lithium batteries.

[booster]

I just looked at the Blue Sea site which doesn't show an 1830 monitor, but found it on Google search.



I know we have heard in the past they have a monitor for positive shunt placement, but the instructions don't say that currently.


Blue Sea used to have (maybe still do) a "shunt shifter" which was a small circuit board that mounted to the shunt and allowed it to be used on the positive cable, but I have never used one.


Found it


https://www.bluesea.com/products/824...nt_Shifter/FAQ


With this you could use any monitor in the positive cable, as far as I know.

[ahamuser]

Thank you so much for everyone's replies. This sounds more complicated than I imagined especially where my two lithiums are located (external rears)on my '18 RT RS Adventurous. Looks like I will need to hunt down a battery wiring diagram specific to my model/year so I can figure out if I have, as one of you mentioned, two grounds or one. I did, however, find a simulator wiring diagram from metrotrekkers.org that is intertesting but not sure if applicable. Here's the link: http://metrotrekkers.org/utility/electrical.htm

I'm located in the Houston,TX area. Just in case this work is beyond my pay grade, does anyone know a shop that would be able to handle installing a shunt/battery monitor for Roadtreks? I learned that most shops are not as knowledgable with class B lithium/solar electrical systems.

[Stevemo]

Avanti: When you used your chassis as the negative return how did you calculate the distance to size your positive wire? The common convention is to add the positive and negative cable lengths together to determine the overall distance and wire size.

Ahamuser: You should be able to work it out. Read some of the information in the Blue Sea catalogs and their other documents. I honestly don't use my Bogart as I don't camp in any location for more than 24 hours. What do you want to get out of yours?

[cruising7388]

Originally Posted by booster

Obtaining the capacity is not all that difficult as the monitor will do it for you when you run a discharge from full to the lowest voltage you are comfortable with and note the amp hours. You will have your usable AH and show zero to 100% for that usage on your meter.

That's true for a fixed battery supply with the meter calibrated to reflect the battery ah capacity. But the Roadtreks permit turning batteries on or off at will. For example, if equipped with four 200 ah batteries you would calibrate the meter for 800 ah and the meter would register discharge levels accurately. But if you subsequently shut down two batteries and neglect to recalibrate the meter to 400ah, I think you will be getting inaccurate meter readings.

[cruising7388]

Originally Posted by booster

I just looked at the Blue Sea site which doesn't show an 1830 monitor, but found it on Google search.



I know we have heard in the past they have a monitor for positive shunt placement, but the instructions don't say that currently.


Blue Sea used to have (maybe still do) a "shunt shifter" which was a small circuit board that mounted to the shunt and allowed it to be used on the positive cable, but I have never used one.


Found it


https://www.bluesea.com/products/824...nt_Shifter/FAQ


With this you could use any monitor in the positive cable, as far as I know.

Blue Sea makes two series of digital meters, 8248 LED and 1830 OLED. Model 1830 can be found in the OLED meters. Both types can be used with the shunt in the positive lead but the 8248 LED SoC requires the outboarded 8242 shunt shifter which is piggy backed on the meter shunt. The 1830 OLED has the shunt shifter integrated into the meter. This capability isn't described in the literature but was described to me by the engineer that designed the meter who indicated that it's shunt could be located on a positive lead with with less than 4% error.

[booster]

Originally Posted by cruising7388

That's true for a fixed battery supply with the meter calibrated to reflect the battery ah capacity. But the Roadtreks permit turning batteries on or off at will. For example, if equipped with four 200 ah batteries you would calibrate the meter for 800 ah and the meter would register discharge levels accurately. But if you subsequently shut down two batteries and neglect to recalibrate the meter to 400ah, I think you will be getting inaccurate meter readings.

The process for determining capacity was for individual modules so you know how much power you really have and wouldn't necessarily be what you put into the meter.

On a Roadtrek, I think you would need to decide how you were going to use the batteries and then set up the meter to do as well as possible.
I think there would be several options you could do, and others probably could come up with more.


* Setup the AH in the meter for one module if you only use one at a time and do 100% manual reset on it when you switch modules.


* Setup the AH for two or more at a time if that is how you use the modules with total number of module you use together


* Setup the AH for the total AH you have in all modules together as the ones that are full but not on are just like power in the ones that are on but not used yet. Full reset of the meter would be only when all are fully charged.


All the setups would work OK depending on what you like, but all are going to get screwed up by the parasitic losses in the Roadtreks, which is much more of a concern regarding accuracy. As soon as you start turning modules on and off so they don't self discharge on you, it gets harder to keep track of how much they have lost. Perhaps a resettable stopwatch on each module that runs only when the module is on would work once you check what the parasitic is per hour. It all gets to be a real PITA, I think, when it really shouldn't have that kind of losses if it had been made right in the first place.


It is interesting that I find myself never even looking at the %SOC on our system of 440ah of AGM batteries as I always use the AH in/out display which I find much more useful. They are truly the same thing and based on the same calculations that include the charge efficiency error on recharge, so no difference in accuracy, but the AH reading just seems to register better to me.

[avanti]

Originally Posted by Stevemo

Avanti: When you used your chassis as the negative return how did you calculate the distance to size your positive wire? The common convention is to add the positive and negative cable lengths together to determine the overall distance and wire size.

The reason cable length is significant is because you want to keep the voltage drop down to an acceptable level. The smaller the wire, the greater the voltage drop per meter of wire. However, the ampacity of the chassis is so large, that as a practical matter you can ignore it. If properly installed, you will never see a material voltage drop in the chassis part of the circuit. So, just look at the length of the positive cable and round up.

In my case, though, the only long high-current run is the one from my second-engine alternator to the batteries in the rear. The Balmar regulator has a remote voltage-sense input, and will adjust automatically for the voltage drop. So, in this case the only thing that matters is heat dissipation, so the length is not really relevant.

[booster]

Originally Posted by avanti

The reason cable length is significant is because you want to keep the voltage drop down to an acceptable level. The smaller the wire, the greater the voltage drop per meter of wire. However, the ampacity of the chassis is so large, that as a practical matter you can ignore it. If properly installed, you will never see a material voltage drop in the chassis part of the circuit. So, just look at the length of the positive cable and round up.

In my case, though, the only long high-current run is the one from my second-engine alternator to the batteries in the rear. The Balmar regulator has a remote voltage-sense input, and will adjust automatically for the voltage drop. So, in this case the only thing that matters is heat dissipation, so the length is not really relevant.

I would add that if you do have two batteries that are a ways apart, you are always better to try to keep even in cable length, usually by going to a central binding post between them with equal legs to each. If it is not possible to do that, you can calculate the resistances in the cables and adjust the cable size to get the same resistance with uneven lengths. Overall resistance is what determines the balance of charging and discharging in multiple batteries in parallel, so can be important.


The Blue Sea Systems "Circuit Wizard" on their website is very useful for finding wire size requirements as it lets you add things like if in sleeving, how long at high amps, etc into the search, so is good if you are worried about heat. It is very conservative and based on the very strict marine wiring rules, so certainly a safe way to go.

[engnrsrule]

I have an RS (2006) and selected the Victron Monitor with Bluetooth and it is excellent. Since the shunt actually has smaller control wires and electronics on board, I chose not to mount it in the battery compartment, but put it in the compartment with the charger inverter. This required altering the cabling to bring a direct negative terminal to the shunt. For correct operation there should be no other negative connections between the negative terminal of the battery and the negative side of the shunt. The cable on the right goes straight to the negative terminal of the battery. The two leads on the left side are from the charger and down to the vehicle ground.

I am running two GC2 lead acid 6V batteries which just fit in the stock battery compartment and deliver 235 Ah.

I also changed from the inline fuse to a mounted fuse block (for the 0.1A monitor power fuse). For the display, I relocated the water heater switch and put the display above the tank panel. The biggest challenge was running the lead behind the bathroom panelling. I made two access holes, one behind the rear passenger seat and one in the wall panel behind the sink shroud (no picture of that hole). Used a fish tape to get a pull string through.