Oversized temperature-sensor lugs on battery terminals?

AaronD

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Aug 10, 2014
723
Catalina 22 9874 Newberg, OR / Olympia, WA
Is it safe to mount a charger's temperature-sensor on a smaller terminal bolt? Reading @Maine Sail's charger-installation article , I see: "Any terminal mounted temperature sensor also needs to be connected directly to a negative terminal, and not the positive terminal." I hadn't thought about it before, but that makes good sense.

My Lifeline batteries use asymmetric terminal bolts (M10 ~3/8" for the positive and M8 ~5/16 for the negative). And my temperature sensors' lugs are for 3/8" (both the Rogue solar controller and Sterling shore power charger). So I had mounted to the positive; I'll definitely change that.

IMG_1978.JPG

It's generally bad form to use an oversized lug on any terminal. For any other wire, I'd cut off the lug and replace it with the right size. But I can't do that to a temp-sensor :()

Is there some form of adapter I should know about? Or is this an exception to the always 'use the right size lug' rule? Naturally, the sensor lugs go on last (highest current first, and lowest current last - these are 0 current, so definitely on top). Is that safe in this case? Or will the oversized lugs prevent a solid connection for the current-carrying lug on the bottom of the stack?

Or do I just tape the sensors to the side of a battery? (That seems trouble-prone too).
 
Jan 11, 2014
11,401
Sabre 362 113 Fair Haven, NY
The temp sensors should go on top of the stack of connectors. They are not current carrying so a little slop shouldn't be an issue.
 

PJL

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Apr 22, 2014
47
Hunter 42 Nuevo Vallarta, Mexico
Is there some reason you can't simply use a washer under the bolt's head?
 
Jun 25, 2019
27
Hunter 28 Treasure Island Marina, Kingst
I could not reply yesterday so here is my comment: I am a mechanic and I would advise to use one 5/16" flat washer under the terminal, and one over it to make the best possible contact.
 
Jun 25, 2019
27
Hunter 28 Treasure Island Marina, Kingst
The reason for the difference in battery terminals, is that you do not invert polarities when you connect batteries. That is with the right size terminal on each of the cables.
 
Jan 11, 2014
11,401
Sabre 362 113 Fair Haven, NY
I could not reply yesterday so here is my comment: I am a mechanic and I would advise to use one 5/16" flat washer under the terminal, and one over it to make the best possible contact.
Placing a SS washer under any terminal connections on a battery is not a good practice. SS is a poor conductor of electricity and heat. This will increase the resistance in the circuit and reduce the efficiency of the system. It may also cause the battery to overheat with unfortunate consequences.
 

AaronD

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Aug 10, 2014
723
Catalina 22 9874 Newberg, OR / Olympia, WA
I was mostly offline for a few days. Coming back, I see nobody has offered a credible reason why these oversized lugs will start a fire or find another way to kill me. :)

I thought of adding a copper washer or two, but couldn't think of a way that would really help either. So I elected to just follow @dlochner's advice, ignore the slop (on the smaller negative bolts), and put it all back together.
 
Jan 11, 2014
11,401
Sabre 362 113 Fair Haven, NY
I was mostly offline for a few days. Coming back, I see nobody has offered a credible reason why these oversized lugs will start a fire or find another way to kill me. :)

I thought of adding a copper washer or two, but couldn't think of a way that would really help either. So I elected to just follow @dlochner's advice, ignore the slop (on the smaller negative bolts), and put it all back together.
Just be certain the temp sensors are on top of the stack.