Voltage drop

[rvlifer]

For those looking at solar this info may help and maybe you guys who are more knowledgeable can verify i am interpreting this correctly. My solar charge controller and inverter/charger are on the inside front wall of my main storage compartment, less than 2 ft from my battery bank which is in the front storage compartment of the 5th wheel. Wiring between the battery bank and the inverter is stranded 00 gauge if i remember correctly. Wiring gauge from the solar charge controller to the inverter is smaller. The wire length from the inverter to the batteries is less than 4ft

the power comes down from the panels to the charge controller at 72v.

Here are pics of the setup. I need to do a little cable management to organize the wires again.






I have magnum's bmk plus a trimetric installed. In this pic you can see the difference in voltage they show. I think the magnum inverter is pumping 96a to the batteries from shore power. The trimetric shows 89.9a getting to the batteries. The solar panels are adding 16a which should be captured by the trimetric. Pretty substantial difference

 

[rvlifer]

The trimetric is far more accurate than the magnum. Right now the magnum bmk shows the battery voltage at 14.3v and the trimetric at 14.1v. The magnum shows soc at 99% but i know that isnt right. Right now i calculate the soc as around 55% the magnum bmk has a useful ah in/out reading that is far more useful than the soc reading.

The batteries were disconnected so the trimetric hasnt had enough time to calculate soc. The magnum generates an soc reading in far less time. The magnum bmk is useful but i trust the trimetric a lot more

 

[Lou Schneider]

Current stays constant at any point in a series circuit. If there's nothing between the TriMetric and the Magnum they should read identically.

 

[rvlifer]

The magnum bmk plugs into the inverter and does not include anything to account for temp. The trimetric connects to the shunt or batteries cant remember which and included a temp sensor. They rarely read the same. Been that way from day 1

 

[John From Detroit]

Ok. this system is confusing enough.
IF all current is passing through both the Magmum and the Tri-metric shunts then LOU is correct they SHOULD read the same key word highlightd.. but RVLifer pointed out the word Accuracy.
Some meters are better (more accurate)than others.

And if the Solar is adding (Which may or may not be happenng if the inverter is charging) then the Tri-metric should show the combined amperage.. again.. Should.

 

[rvlifer]

Ok. this system is confusing enough.
IF all current is passing through both the Magmum and the Tri-metric shunts then LOU is correct they SHOULD read the same key word highlightd.. but RVLifer pointed out the word Accuracy.
Some meters are better (more accurate)than others.

And if the Solar is adding (Which may or may not be happenng if the inverter is charging) then the Tri-metric should show the combined amperage.. again.. Should.

Both the solar charge controller and inverter bmk connect to 1 shunt. The magnum design has the magnum bmk control panel plug into the inverter. The solar power attaches to the output connector of the inverter prob cause that was the closest connection. Shouldnt affect the inverter in any way ut it does run through the shunt so both bmks should pick it up.

I suspect the bmk function is built into the inverter and the bmk module is just a remote control that displays the info sent to it from the inverter.

Either way the magnum bmk was never very accurate. This is the 2nd rv i have had it installed in so i dont suspect any issues with other components.

to make it even more complex i also mounted the plug from the portable solar panels on the rv and that is wired theough the shunt as well. It wasnt plugged in so the values in the pics arent affected by that.

There are still one or 2 things that bypass the fuse and shunt and were wired directly to the batteries. Never successfully traced those

 

[workinonit]

Pretty confusing. Especially after I read the words inverter and charging. Inverters don't charge batteries unless this is some hybrid inverter. By definition an inverter makes AC out of DC.

 

[Alaskansnowbirds]

Pretty confusing. Especially after I read the words inverter and charging. Inverters don't charge batteries unless this is some hybrid inverter. By definition an inverter makes AC out of DC.

There are pure "inverters" that do exactly what you described. There are also "inverter/chargers" that are inverters until they see external AC power then they are chargers. A lot of us just call them all "inverters".

 

[rvlifer]

Most magnum inverters are inverters/chargers. They do have a mobile line of pure inverters but mine does both.

The setup is simpler than it is to describe. Both bmk's should read the same. The magnum is a great product with a ton of features but the lack of a temp sensor probably accounts for some of the difference. The number of settings you can adjust for the inverter and charger functions is great. I wouldnt hesitate to buy another one.

The bmk function on the magnum seems more of an afterthought. I dont use these but it also has options for auto generator start and solar inputs. My solar charge controller is connected to the output lug on the inverter only as a convenient place to connect and doesnt use the magnum solar features.

The trimetric being a dedicated bmk seems more thorough than the magnum. The calculations it uses to determine soc seem more advanced and it uses more data to calculate it than the magnum.

If i only had one bmk it would be the trimetric. Having both is useful cause for one thing i see the difference between how much voltage the magnum is sending to the batteries and how much is actually getting there. The point of this thread was to show how much voltage drop there was over a short distance even with large gauge wiring. If that isnt what these numbers show then hopefully you guys can educate me on how to interpret this more accurately

 

[rvlifer]

In the pics the midnite solar charge controller and magnum bmk are showing the same battery voltage of 14.3v. The solar cc is showing that 16 amps are being sent to the batteries. The magnum inverter/charger shows 96 amps being sent to the batteries from shore power. The trimetric display is showing that a total of 89.9 amps is being added to the batteries.

Most of that wiring mess connected to the shunt is all the stuff the manufacturer wired to the batteries. Some of it was connected prior to the battery disconnect but some was directly wired to the batteries. Took a long time to trace it all and get it all behind the battery disconnect and fuses. Not fond of when they ran stuff to the battery without fuses.

the magnum, solar charge controller, and trimetric each have to be configured for the battery bank. The people who set this up reaaly seemed to know what they were doing and i let them configure everything. I took notes so i could verify all the settings or reprogram them if for any reason they reset. It is possible that some of the settings could account for the differences in readings but i couldnt begin to guess which. There are so many settings on the magnum you can tweak

 

[Lou Schneider]

Both the solar charge controller and inverter bmk connect to 1 shunt. The magnum design has the magnum bmk control panel plug into the inverter. The solar power attaches to the output connector of the inverter prob cause that was the closest connection. Shouldnt affect the inverter in any way ut it does run through the shunt so both bmks should pick it up.

This is probably the key to the differing readings. Each device should be connected to it's own shunt with both shunts connected in series so all of the current flows through both of them. The shunt produces voltage in the millivolt range and it's likely connecting two devices to a single shunt produces ground loops that introduce noise and gives erroneous readings on both.

 

[rvlifer]

This is probably the key to the differing readings. Each device should be connected to it's own shunt with both shunts connected in series so all of the current flows through both of them. The shunt produces voltage in the millivolt range and it's likely connecting two devices to a single shunt produces ground loops that introduce noise and gives erroneous readings on both.

Thanks. Good to know. I will add that to the list for when it gets to elkhart.

Would that be enough to account for that much of a difference though? Seems i should have 112 amps going to the batteries but the trimetric only shows 89.9

With 2 shunts where do you connect everything pulling from the batteries?

 

[Lou Schneider]

Thanks. Good to know. I will add that to the list for when it gets to elkhart.

Would that be enough to account for that much of a difference though? Seems i should have 112 amps going to the batteries but the trimetric only shows 89.9

With 2 shunts where do you connect everything pulling from the batteries?

Same as they are now, on the load side of the shunt pair. You just put both shunts in series in place of the one that's there now.

battery (-) === shunt 1 === shunt 2 === loads (-)

 

[rvlifer]

Same as they are now, on the load side of the shunt pair. You just put both shunts in series in place of the one that's there now.

battery (-) === shunt 1 === shunt 2 === loads (-)

Thanks. This is very helpful. Will be interesting to see how things are affected by it.

What would you do with the solar charge controller in that setup? Right now it connects to the inverter ouput lug then to the shunt. Should that be on Its own shunt?