BTS questions spurred by high temp batt fault

nicknick Registered Users Posts: 10 ✭✭
Hi everyone,

Hoping to get some insight on battery temperature sensors, and whether having more than one installed could lead to problems. I'm a beginner, so easy on the super-technical stuff if possible! Apologies in advance that this is a rather long post.

Our setup:
Three 250W Kyocera panels
Midnite classic charge controller + whizzbang
Four 6v 305 amp-hr Sun Xtender AGM batteries in series (outside house in a wooden box)
Magnum 4024 inverter
Magnum remote control (the basic one)

We have the Magnum BTS installed (on the battery lug) and also the Midnite BTS installed (stuck onto the side of a battery). We have set charging voltages, times, etc via the Midnite charge controller. When you check these settings via the Magnum remote control, the information has already been drawn in. So it seems like the system talks to itself.

We've been using this setup to power our house for the last six months and it has worked like a dream. But yesterday, while I was not at home, my wife texted to say the Magnum remote in the house was displaying a fault: high batt temp. A few minutes later, without doing anything, the fault light went off and everything seemed back to normal. She thinks the power might have temporarily cut out, because the internet stopped working for a few minutes (there was nothing else on that could have signified a loss of power).

According to the manual, this fault indicates inverter/charger has shut down because BTS has reached a temperature greater than 54C / 129 F. Once the BTS cools, the system automatically switches back on.

Question 1: What is the BTS measuring? The internal temp of the battery (which I assume is kind of an extrapolation), or the air around it? Because if the latter, I don't see how it could get to 54C. (We live in Sonoma county, CA.)

When I got home I checked the batteries and they looked fine and were not hot, and the system was working as normal. But the temperature shown for the BTS on the Magnum remote control was 151C / 303F, which seemed way off. I can't remember what the Midnite was showing, but it was more like 22 C.

Looking today, at time of writing the Magnum sensor still shows 151, whereas the Midnite shows: Remote 36.8, Battery 21.7, FETS 47.8, PCB 49.2.

Question 2: What are these readings? I can't find an explanation anywhere in the Midnite manual, and looking online didn't help much. Best guess is FETS and PCB are internal circuit temps or something? But what is the difference between remote and battery?

My working assumption is that there's a fault with our Magnum BTS. The manual suggests removing it from the inverter port and seeing what happens to the reading as a way of troubleshooting that. I'll do so—just need to get the tools.

But I'm now wondering if having two battery temperature sensors is confusing things. Which one does the system follow? Presumably it's not that the Magnum sensor is used by the inverter, and the Midnite sensor by the charge controller, because they are all part of the same system. 

Question 3: Do we need both BTS installed, or would one be sufficient? If one, would that be the Midnite one? (Just because the charge settings and everything else were entered via the Midnite.)

Thank you so much in advance for any help or general advice.

Cheers, Nick.


  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    No problem with two sensors (I have two), one for the controller and one for the inverter/charger.   The magnum sensor attaches to the battery lug.  The lug temperature is supposed to represent the internal temp of the battery, and I suppose it does.... but a loose connection, bad crimp, corrosion, etc can cause local heat right at the battery lug. 

    My advice: first thing check all the connections around the sensor.   If you have an infrared camera or probe you can look for heat differences at the lugs.  The heat will only be generated when there is current flow... either charging or discharging.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • VicVic Solar Expert Posts: 2,938 ✭✭✭✭

    Hi nick,

    It looks like there is something wrong with the Magnum BTS.  You might try unplugging it and plugging it back in several times (assume that this BTS uses the relatively common Phone jack/plug).

    You might visually inspect the Magnum BTS cable,  and particularly the part that is near the battery terminal,  as sometimes,  things happen to the exposed parts (have seen too many BTS cables that appear to have been gnawed by rodents,  on other folks' systems.

    Originally had thought that perhaps there was a loose battery cable connection on the battery lug that the BTS was mounted onto,  BUT  the reported temperature is SO high,  that this is probably not the case.

    The Magnum and the Classic are not communicating to each other.

    EVERY charge source should have its own BTS,  unless it is known that the system communicates this data among all devices that need it.   There is NO such communication between the Classic,  and the Magnum inverter (at this time,  am certain).

    Your Magnum inverter probably has Default settings,  which most products that can charge batteries are shipped with.  Usually,  these Defaults are fairly cautions,  and you should check to make sure that these settings are optimum for your batteries/system.

    The Classic's Temps menu paged shows the battery temp on the lower left of the screen  -- Bat temp (or similar).  Believe that on the WBjr Status page shows a "Remote temp".   This is the measured temperature of the WBjr circuit board.

    Later,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nicknick Registered Users Posts: 10 ✭✭
    Thanks for the responses. I will check the connections again, and try the unplug routine. 

    Good to know that having two battery sensors is ok. The reason I thought they were talking to each other was that when we first set the system up I specified the specific bulk and absorb voltages via the charge controller. When I went to the same section on the inverter remote, the profile read as custom and the correct voltages had been inputted. I didn't do that myself, and it seems unlikely that would be the default. I didn't mention it before, but everything runs through a Magnum Mini Panel, so maybe that's how they are able to communicate?

    Either way, I'm glad I now know that having two sensors is fine. And it's good to know that it's likely a problem with the magnum sensor rather than anything else.

    Cheers, Nick.
  • VicVic Solar Expert Posts: 2,938 ✭✭✭✭

    Hi Nick,

    OK,  I know absolutely nothing of the Magnum MMP.   Believe that this is just similar to the MidNite MiniDC and e-Panels.   A place where essentially all DC and some/most/all AC connections and breakers come together in a single box.

    Is the Classic's Ethernet port plugged into the MMP,  or into the Magnum Remote,  or the inverter?

    You could try one thing;   Change the Absorption voltage on the Classic,  and see if it changes for the Magnum,  as well.

    It would not be a trivial task for either of these two companies to allow this communication,  and there does not seem that there would be a real benefit for either Magnum or MidNite to go to the trouble to allow this cross-talking,  just because it might be cool ...   dunno.

    Does the Magnum do ModBus-like communication?

    You might ask Magnum about the temperature error,  as if it does cause the inverter to shutdown,  this is not a good situation  (yea,  this is obvious).

    FWIW,    Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nicknick Registered Users Posts: 10 ✭✭
    Hi Vic,

    I believe you are correct re: the MMP basically being the same as the MidNite panels.

    I think the Classic's ethernet port is plugged into the MMP, though I'll have to check that once I get the cover off. (Currently have literally no tools, which is not ideal.) Will change the Classic absorb setting to confirm what happens, and let you know. 

    Not sure what ModBus-like communication means, sorry.

    My next step needs to be to unplug the Magnum sensor ethernet and see if that resets the temp rating, and to go from there.

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