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Battery terminals. Who is right?!


powerbow1415
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Hi guys…this is gonna sound like a real dumb-***** question….I want to remove my battery to charge it, then replace it back in the car…I have always done red first then black, then black/red on re-connecting…but some say it’s the other way round, black/red then red/black…who is actually right??…then I reset the battery by way of, pushing rear fog 5 times, then hazards 3 times, all in the space of 10 seconds…the battery light will flash 3 times to confirm successful battery reset.

🤔🙂

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Always disconnect the earth (BLACK) first

Always reconnect the earth (BLACK) last

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The manual says disconnect black first. Then when reconnecting connect black last. It’s so that you don’t accidentally short yourself through the body of the car when handling the red terminal. 

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The correct method for safety reasons is:

  • Disconnect the negative (black) lead first and then the positive (red)
  • Reconnecting should be positive first and then the negative.

As far as does it make any difference from an electrical point of view to the operation of the car, the answer is doesn't matter. The reason for this method being the preferred order is that once the negative lead is disconnect from the chassis it eliminates the risk of an accidental short-circuit when using a spanner, by it touching the bodywork while working on the positive terminal.

Unfortunately on a great number of car these days this method is often impossible. As the battery is mounted so far back under the scuttle panel that the negative terminal can not be reached until the battery is pulled forward and almost out of the battery tray. This forces the situation that the positive lead has to be removed first (and reconnected last). So when this is the case extreme care must be taken to ensure that a spanner or other tool never accidentally comes in to contact with the bodywork while working on the positive terminal. Place a cloth or similar over the positive terminal to protect it while removing or fitting the battery when the negative lead is connected. 

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Thanks guys….I have a 10mm plastic spanner….yep, neg’ term’ is right under scuttle panel..what I will have to do is use the plastic spanner on both terminals and will have to do Red/black then b/r, but by using the plastic spanner, thus should eliminate any risk of a short…does this sound a sensible option?.

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10 hours ago, powerbow1415 said:

this is gonna sound like a real dumb-***** question…

Another dumb question - could you not just charge the battery in situ?

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Tried that, but cannot access neg term…tried to ground the nt on bare piece of metal, but had no effect

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Attention !!

The battery on a 2015 Kuga is intended to be recharged while still fitted and connected.

  • The positive charger lead should be connected directly to the positive battery terminal.
  • The negative charger lead should be connected to the chassis main earth point - NOT the battery terminal.

This allows the Battery Monitor System (BMS) to correctly measure the charge current going back in to the battery. When charging is complete do NOT reset the BMS or the State Of Charge (SOC) data will be lost and the days in service 'clock' for the battery will be wiped out.

 

earth.JPG

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Cheers buddy, much appreciated…your image above is the exact earth point I used…the battery is the EFB type, not an AGM. So I put my charger on the EFB setting, then left it for 24 hours, but no substantial charge appeared to be apparent…I used my noco 10 charger…all I saw was the charge indicator lights going through to green, then restarting the cycle again from red, continuously…my multimeter reading showed no more than a 2volt increase, from 12.1V…my noco also had a repair mode on it but I could not use that until the battery was fully charged…I thought 24 hours would be enough with a 10 amp charger….either I was doing something wrong, or the battery didn’t need charging, i suspect the former.

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4 hours ago, powerbow1415 said:

I thought 24 hours would be enough with a 10 amp charger….either I was doing something wrong, or the battery didn’t need charging, i suspect the former.

I think that (like a great many) your understanding of how a battery recharges is perhaps misunderstood.

Current can not be 'pushed' in to any battery. The current has to be drawn by the battery. This means that you could have a 500Amp charger but the battery will still only draw a current up to the maximum constraints of the battery type and chemical condition that it is currently in.

For a 'battery charger' to get a 'battery' to draw a higher charge current, the charger must increase the output voltage to a level higher than that of the battery.

For example if you have a battery which is at 12.0V then the battery charger may output a voltage of 14.0V and for the purposes of this example we will say that the battery will draw a current of 2 Amps. In order to get the battery to draw a higher current the charger would have to increase the voltage to say 16.0V which would perhaps then get the battery to draw a current of 4 Amps. Of course the charger can not just go on increasing the voltage forever otherwise the battery will overheat and burn out.

A typical Smart battery charge will output a maximum of 4 Amps. Even if you have a 10 amp charger the current taken by the battery is determined by the battery. Should the battery state of charge be in a very low condition it may initially draw 9 or 10 Amps for 10 or 15 minutes but that will very quickly decrease to a steady current of less than 4 Amps.

To fully recharge a very flat battery and to restore its state of charge to 90% or better can take 48 hours. After the first 24 hours it will have a SOC of around 70%

SOC.JPG

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4 hours ago, powerbow1415 said:

…I used my noco 10 charger…all I saw was the charge indicator lights going through to green, then restarting the cycle again from red,

That doesn't sound right. I have a Noco Genius 5.  That goes through the indicators from red through amber to green and when it's gone through the full cycle and the battery is fully charged but the charger is still connected to the mains, it goes into "maintenance" mode with the green indicator pulsing occasionally. According to the Noco website the 10 should do the same.

 

 

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1 hour ago, alexp999 said:

Voltage is the push. 😉

Correct and Current is pull 👍

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57 minutes ago, Eric Bloodaxe said:

That doesn't sound right

I agree. If the battery Colin has on his 2015 is the original then it's around 7 years old and very possibly defective.

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2 hours ago, unofix said:

I agree. If the battery Colin has on his 2015 is the original then it's around 7 years old and very possibly defective.

Or it could be as simple as not getting a good contact when connecting the black terminal of the charger to the chassis? I find both the Noco and the C-tek I have can be a bit sensitive to this.

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3 minutes ago, Eric Bloodaxe said:

I find both the Noco and the C-tek I have can be a bit sensitive to this.

Would never have that problem with a Maypole 🤣

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13 hours ago, unofix said:

Correct and Current is pull 👍

The voltage is also the pull (the negative terminal). Current is just a measure of how many electrons are passing through, it’s the resistance that stops it being infinite current. But a 15V charging voltage across a battery with a resting voltage of 12.5V is only raising the voltage inside the battery by 2.5V (that’s only 0.4v per cell) the current that can flow is determined by the internal resistance of the battery. That’s why the car can control the current being applied by adjusting the voltage. But the resistance of the battery changes with age and temperature. That’s why we have these BMS sensors. 
 

Current = Voltage / Resistance. 

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2 hours ago, alexp999 said:

The voltage is also the pull (the negative terminal)

Wrong. Voltage is never pull, and if you actually check the real flow of electrons is from the negative terminal to the positive terminal. This assumption of the flow of electrons being from positive to negative was caused way back in the very early days of electricity and was actually a pure guess. By the time it was possible to measure the direction of the flow of electrons through a circuit it was too late as the convention had been established. To change it would have lead to much confusion in an industry that was still in it's infancy and so it was agreed to leave the accepted convention as it was. Many decades latter this has been a major problem in the semiconductor industry.

It is the internal resistance of the battery cell that limits the flow of current. The internal resistance of the battery changes constantly and hence for a fixed charging voltage the current flow will change as the resistance of the cells also change. There are two methods of charging batteries and the chemical composition of the cell determines which method should be used (a) Constant voltage, and (b) Constant current.

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The problem is trying to make analogies. It can be easier for people to think of the voltage as causing the “push” / “pull” around a circuit. Current is just a measure of “flow” there is no pull of current only resistance to it. Hence high current in something not designed for it generates excess heat. 
 

But we’ve probably gone a bit off topic now lol. If I’d have read OPs message fully I should have just replied with charge it in situ no need to take it out and don’t reset BMS in my first reply. Instead of only picking out the question. 

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Thanks guys…really appreciate your inputs 👍🙂

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