What does the "Sensing Charging Cable" do?

[farmer.leo]

The alternator wire charges the batteries, but there is another wire called the Sensing Charging Cable which I could guess allows the regulator part of the alternator adjust the charging voltage.

If that assumption is correct, why would you have a separate cable to measure the same battery? I may be missing something, but isn't this cable connected to the same battery, and would have the same voltage, as the alternator wire?

How would you connect the alternator wire & sensing charging cable if you want a house battery and separate starting batter?

 

[pvb]

It allows the alternator to sense the actual voltage at the battery terminals, and therefore compensates for any voltage drop in the wiring, for example, or due to a diode splitter. The sensing cable is usually attached to the domestic bank, as these are the batteries most in need of charge.

 

[VicS]

The alternator wire charges the batteries, but there is another wire called the Sensing Charging Cable which I could guess allows the regulator part of the alternator adjust the charging voltage.

If that assumption is correct, why would you have a separate cable to measure the same battery? I may be missing something, but isn't this cable connected to the same battery, and would have the same voltage, as the alternator wire?

How would you connect the alternator wire & sensing charging cable if you want a house battery and separate starting batter?

What PVB says but it is important that the battery with the sensing wire connected to it is not disconnected in some way otherwise the alternator will go to its maximum possible output volts in a fruitless attempt to get the right reading on the sense wire and overcharge the other battery(ies) in doing so

If you do not need the battery sensing capability connect the sensing wire to the main output terminal.

 

[matthewriches]

I can stress the importance of ensuring the cable cannot become accidentally isolated or disconnected. I have a really good photo of a battery bank where the tops have blown off due to having a huge amount of juice shoved into full batteries!

 

[William_H]

How would you connect the alternator wire & sensing charging cable if you want a house battery and separate starting batter?

Both batteries are connected to the alternator for charging. But need to be separated for discharge /use so that engine start battery is quarantined from discharge. This can be done by a single switch (or often the 1,2,both,off switch) But you have to remember to set the switch to both for engine running (charge) and to 1 or 2 for discharge. However an arrangement of diodes can direct the charge current to both batteries without permitting discharge or a voltage sensing relay can be set up to only charge both batteries when engine is running. (charging) olewill