Battery temperature sensor

[wincrasher]

Thanks. Got it.

[cruising7388]

Originally Posted by avanti

The shunt MUST be at the negative terminal of battery #2. ALL current must pass through it with the exception of the ground wire that goes to battery #1.

The current between the two batteries is only half that of the current that goes to the load. The battery interconnect wires don't have to be as big as the load wires.

No question that to ensure an accurate reading that all current paths have to go through the shunt. But, isn't the positioning of the shunt at the negative terminal necessary for compatability only with digital current shunt fed devices? Wouldn't an analog meter be indifferent to the physical location of the shunt as long as it captures all currents?

Actually, properly set up, even digital current metering can be used with a shunt on the source side rather than the chassis side. I measure alternator voltage and current with a shunt looking directly at the alternator. It's a Blue Sea digital volt/ammeter with a shunt that has a Blue Sea accessory shunt shifter module that enables the meter to display coherent values.

[avanti]

Originally Posted by cruising7388

No question that to ensure an accurate reading that all current paths have to go through the shunt. But, isn't the positioning of the shunt at the negative terminal necessary for compatability only with digital current shunt fed devices? Wouldn't an analog meter be indifferent to the physical location of the shunt as long as it captures all currents?

Actually, properly set up, even digital current metering can be used with a shunt on the source side rather than the chassis side. I measure alternator voltage and current with a shunt looking directly at the alternator. It's a Blue Sea digital volt/ammeter with a shunt that has a Blue Sea accessory shunt shifter module that enables the meter to display coherent values.

Yes. The only issue with a digital (actually, any powered) meter has to do with powering the meter from the same source that is being measured. A passive ohmmeter (or a battery-powered one) wouldn't care. You could also make it work with a DC-DC converter to isolate the systems.

[gregmchugh]

I believe it is possible to install the shunt for the Trimetric on the positive end of the battery bank, don't know about the Victron.

[wincrasher]

Originally Posted by avanti

Yes. The only issue with a digital (actually, any powered) meter has to do with powering the meter from the same source that is being measured. A passive ohmmeter (or a battery-powered one) wouldn't care. You could also make it work with a DC-DC converter to isolate the systems.

Yes, the Victron creates a power draw in the 4mA range. So they warn you about leaving the batteries without a charger. Since my new charger can turn itself on and off, I'm not too worried about leaving the van in storage with the shore cord plugged in. It would probably take several weeks for the draw to be enough to engage the charger.

Another option is to put in an all-weather switch under the van to disengage this parasitic draw. That may be the better option.

[wincrasher]

Has anyone used one of these? 200A is probably borderline in my case.

https://www.amazon.com/Side-Battery-...erminal+switch

[avanti]

Originally Posted by wincrasher

Has anyone used one of these? 200A is probably borderline in my case.

https://www.amazon.com/Side-Battery-...erminal+switch

I have a similar one (probably not the same brand) on the starter battery of a car that often sits in storage for long periods. It allows us to start the car after many months of storage without any issue. You have to make sure it is very tight. Sometimes it vibrates loose such that the lights still work but it won't transmit high currents during starting. Always scares me when it happens until I remember to go out and retighten.

[booster]

Originally Posted by wincrasher

Has anyone used one of these? 200A is probably borderline in my case.

https://www.amazon.com/Side-Battery-...erminal+switch

I had them on all the power sources on our previous battery and charger setup. They connect and disconnect OK, but the contact area is actually pretty small. Even at 20-30 amp loads, I was seeing upwards of 1/2 volt drop across them. They also got worse over time, so they must also get dirty or corroded to some degree. I removed all of them except the one on the starting battery when I upgraded.

If you do use them, you have to be careful about getting the cables tied down well, as the extra weight and leverage of the disconnect can make it very easy to wind up with a loose connection at the battery post.

[wincrasher]

Originally Posted by avanti

I have a similar one (probably not the same brand) on the starter battery of a car that often sits in storage for long periods. It allows us to start the car after many months of storage without any issue. You have to make sure it is very tight. Sometimes it vibrates loose such that the lights still work but it won't transmit high currents during starting. Always scares me when it happens until I remember to go out and retighten.

I was wondering how they actually work, as it's not a typical switch. If I'm guessing right, the knob squeezes the plates together and makes a connection. If it wiggle loose, I suppose you'd get some arching, which would not be good for my lithium batteries.

[gregmchugh]

It has a nylon block (or something like nylon) that keeps the plates apart and compresses when you tighten the knob allowing contact.

[Boxster1971]

Originally Posted by wincrasher

Has anyone used one of these? 200A is probably borderline in my case.



https://www.amazon.com/Side-Battery-...erminal+switch

I've looked at those battery terminal switches at my local auto parts store and concluded they where junk.


- - Mike
2013 Airstream Interstate on 2012 Sprinter

[booster]

Originally Posted by gregmchugh

It has a nylon block (or something like nylon) that keeps the plates apart and compresses when you tighten the knob allowing contact.

I grabbed one of the old ones I have to look how it was actually built.

As Greg said, two brass plates with plastic between them, that float a bit until clamped with the screw and knob. The plates never do contact each other, though, when clamped. The only current path is actually through the screw itself, with the only contact area on one plate being the area under the screw head, and on the other plate it is just the thread conducting. There is a plastic sleeve around the screw diameter to insulate it when not clamped.

Very small contact for 200 amps, no wonder they got pretty hot.