Battery Current Sensors ~ worth knowing

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When installing electrical accessories (lights, winches, etc.) on newer vehicles, be careful not to make electrical connections so close to the battery terminals that you inadvertently bypass a Battery Current Sensor. The computer increases or decreases alternator output based on the amount of electrical current it sees being drawn through the Battery Current Sensor. When new electrical connections are made directly to the battery terminals, the current going to the new accessory is unseen by the computer, alternator output is kept low and the battery eventually goes dead.

See the Battery Current Sensor for your specific vehicle under "Electrical" in the RockAuto.com catalog. The repair manual (found under "Literature) or owners manual can also help determine if your vehicle's Battery Current Sensor is on the positive or negative side. Battery current sensors are most commonly part of the negative battery cable circuit. On those vehicles, grounding a new electrical accessory to the body or engine block rather than directly to the negative battery terminal is all it takes to avoid bypassing the Battery Current Sensor.


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The computer and its Battery Current Sensor also change how to use a multimeter to check alternator output. To maximize fuel economy, the computer may use the Battery Current Sensor signal to keep alternator output as low as possible. That means a multimeter's probes placed on the battery terminals may show less than 13 volts when the engine is idling. That low voltage does not mean the alternator is bad. It may just mean the computer has not increased alternator output because there is not enough current going through the Battery Current Sensor. Turn on the headlights, rear window defroster or some other significant electrical load. The computer will respond by increasing alternator output, and the multimeter will read ~14 volts at the battery terminals.

Tom Taylor,
RockAuto.com
 
Hi.

Interesting. So that is how the ECU obtains its information to control the variable alternator current output. Clever.

Interesting also to note that the current sensor is usually on the negative circuit to ground. So as you mention additional electrical accessories that are grounded via chassis or engine earth will have their current demand sensed via the sensor.

Cheers.
 
“Battery current sensors are most commonly part of the negative battery cable circuit. On those vehicles, grounding a new electrical accessory to the body or engine block rather than directly to the negative battery terminal is all it takes to avoid bypassing the Battery Current Sensor.”

I think Tom’s got this backwards. If you connect accessory direct to the neg. terminal of the battery, that would bypass the sensor.
 
Tom says not to connect to the negative battery terminal but to the engine body etc. i.e. negative battery circuit is the way I read it in his article. I don't think anyone has it backwards.
One does not want to bypass the Battery Current Sensor otherwise the alternator [ECU] is not able to read the correct load so will be, in the case of additional accessories, under or not charging the battery.
I get a monthly newsletter from RockAuto that often has up to date tech info worth absorbing.
The original post was not my work but straight out of this newsletter & noted @ the bottom of Tom's quote.
What I learned I thought worthy of passing along to others, who may be interested. JG.
 
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Just checked & my old Scenic 1 & it has a BCS on the positive terminal, so I doubt Peugeot doesn't have the same or similar.
The POS terminal is covered by a red plastic enclosure. It's under there.
I know every Astra I've had & that's about 5 had them also. I buy cheapies needing a roadworthy, get them right, register & on sell them.

My take with Tim's article is that accessories need to be plumbed into either the ground [or positive] circuit, that the BCS is part of, BUT NOT @ the battery terminal itself as that negates the BSC operation. Is that others understanding?

More in depth BCS info:
 
My take with Tim's article is that accessories need to be plumbed into either the ground [or positive] circuit, that the BCS is part of, BUT NOT @ the battery terminal itself as that negates the BSC operation. Is that others understanding?
Hi.

That is my understanding also. But the original article could have written differently with more clarity; as it is slightly confusing due to the long sentence and phrasing structure.

Cheers.
 
The sensor on an RHH engine battery in a C5 - the small black box on the negative earth terminal on the right
rhh.JPG
 
Hi.

That is my understanding also. But the original article could have written differently with more clarity; as it is slightly confusing due to the long sentence and phrasing structure.

Cheers.
Exactly Whippet, poor grammar on Tom's part.
Cheers
 
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