Installed BMK

[Scotty Hutto]

I installed a Battery Maintenance Kit (BMK) on my Magnum Inverter today. The BMK is a single battery bank amp-hour meter that monitors and provides important information about the condition of the battery. This information will let you know how much energy you have available, and let you plan your electrical usage to ensure the battery is not being over-discharged.

My understanding is that the BMK will allow the inverter to compute a fairly accurate State Of Charge (SOC).  As we intend to travel more and will occasionally boondock (at Harvest Hosts and the like), I wanted more insight into how my battery bank is holding up.  

Instructions are pretty straightforward forward to install. Annoyingly, Magnum does not include two items required to complete the installation.  It would be nice if Magnum (or someone) offered these already made up as an option with the BMK kit.

1. A short negative battery cable.

2. 12v black/red power wiring with a 2A fuse to power the BMK.  

If you decide to install a BMK, make sure you have those items on hand.

Install took about an hour (I made up the battery cable and power wiring prior to starting the install.)

Install area before shunt installation:

 

With shunt installed. Blue and orange wires run to BMK. Short negative battery cable run from shunt to negative distribution stud  

BMK installed by inverter (next to MagWeb, which broadcasts inverter data via the internet to my phone.)

[Dr4Film]

Scotty,

I have one to install myself but that won't happen until I return to Florida for the winter. I was planning to install it next to the inverted ceiling mounted Magnum Inverter in my rear storage bay.

I thought I read in the instructions that they stated NOT to install it in the battery bay.

CAUTION: Do not mount the ME-BMK Sense Module in a closed
battery compartment, or in an area where water or any other liquid
can enter the ME-BMK Sense Module and cause shorting or corro-
sion. The internal circuit board is conformal coated to help prevent
corrosion, but this failure is not covered by the warranty.

[Tom Cherry]

OK…GOOD DEAL.  Now are you willing to do a simple experiment.  I assume you understand or have read Battery 101.  Trojan (and others) prints up a chart on SOC based on SG as well as DC voltage.  BUT, the battery (s) must have been exercised and reasonably good condition..  

In order to compare the BMK SOC with the accepted Trojan method, you exercise the batteries.  Then when they reach 50 or so percent SOC or are discharged to that level….which is a smidge above or around 11.9/12.0, then you let them sit for a few minutes with NO drain, save a minor parasitic.  Then turn off the disconnect switch and pull the jumpers.  Wait another few minutes and they will “revive”.  Whatever that SG and/or VDC, then you read that on the chart.  That is the REAL OFFICIAL SOC of that baattery.

NOW….my question is always been….with the BMK, are you getting an exact SOC or just a better measurement (guess?).  What I have learned, verified with both Trojan and Magnum, the Magnum remote tends to NOT be that accurate.  Case in point.  My remote reads about 0.15/0.20 VDC LOWER than when you have a constant readout on the batteries themselves….using a DVM.  OK….then one would set the discharge or AGC voltage to maybe 11.7/11.8.  So you run them down to a hypothetical 40%.  In reality, the batteries are actually at 50%, under a controlled and proper load.

BUT….then you have to let the batteries recover and pop back or revive. THAT revived voltage is the TRUE SOC.  I KNOW from experimenting, that the batteries will pop back at least 0.1 VDC.  OMG….then one would set their Magnum AGS to 11.6.  BLASPHEMY….you are KILLING them.  Not SO.  

OK….my question….when the BMK says 50%….and you turn off the batteries….pull the jumpers and measure the voltages….what is the chart telling you the SOC is?  That is the BIBLE.  Magnum is a little coy about just HOW accurate the BMK is and Trojan says that the ONLY real method is to let the battery revive and then measure SG and Volts…

I guess I spent too much time as a process engineer validating the instruments so you could make an intelligent decison….

Thanks in advance.  The installation and description is top drawer.  Cut and paste to a PDF and @Frank McElroy could include in the files.

 

[Scotty Hutto]

7 hours ago, Dr4Film said:

Scotty,

I have one to install myself but that won't happen until I return to Florida for the winter. I was planning to install it next to the inverted ceiling mounted Magnum Inverter in my rear storage bay.

I thought I read in the instructions that they stated NOT to install it in the battery bay.

That is correct.  My shunt is in the battery bay (as it must be!), but the sense module is in the next bay over in the inverter bay. 

[Dr4Film]

Thanks for the clarification. You are fortunate having the battery bay adjacent to the Inverter bay.

I will have to mount everything near the Inverter as the battery bay is too far away. My Inverter is in the last storage bay on the passenger side. Going towards the rear end. Then, I have the Aqua-Hot and tank bay followed with two axles, drive and tag and then the battery bay just after the tag axle. That's well over 20 feet.

I don't have a choice!

[Scotty Hutto]

Yeah, because the shunt is not supposed to be more than 5’ from the sense module.  I guess you could mount the shunt in the battery cable coming to the inverter, then use a short battery cable from the shunt to the inverter?

I’m sure others with a similar year Dynasty / Executive / Signature have done it; hopefully someone will chime in…

[pwhittle]

I mounted my BMK shunt by the inverter.

Paul