New battery voltage 12.2V

D

doningtonphil

Member
VIP Member
T6 Pro
Hello.

I just replaced my battery. The previous one failed.
However, with the engine running OBDeleven showed battery voltage 14.4 volts - obviously the alternator charging.

I just coded in the battery, but one I do an OBDeleven scan it showed the battery as on being 12.2 volts, but then more recently 12.5 volts. Is this because the smart alternator doesn't need to charge or should the alternator always charge when the engine is running (thus 14.4)volts and I have a problem?

Also, do batteries normally get delivered fully charged or should I have charged before fitting?
 
doningtonphil said:
Hello.

I just replaced my battery. The previous one failed.
However, with the engine running OBDeleven showed battery voltage 14.4 volts - obviously the alternator charging.

I just coded in the battery, but one I do an OBDeleven scan it showed the battery as on being 12.2 volts, but then more recently 12.5 volts. Is this because the smart alternator doesn't need to charge or should the alternator always charge when the engine is running (thus 14.4)volts and I have a problem?

Also, do batteries normally get delivered fully charged or should I have charged before fitting?
Click to expand...
Don’t forget that the battery will be held at around 80% charge due to the stop/start system. My battery is usually around 12.43-12.5V
 
OK. As long as approx 12.5 is OK.
It was logical to me to see 14.4 which showed the alternator was running, but happy to hear 12.5 is OK.
Why only 80% and not 100%?
 
To allow for regeneration - when you apply the brakes, part of the energy to be lost will be absorbed by the alternator charging up the battery - so sparing your brakes a little but more importantly storing some of that lost energy as useful energy within the battery.
 
Missing volts

i have hooked up the MPPT to the Vehicle Battery via a fused line and make after break switching but for a long time now I cannot fathom why the MPPT output voltage is not shown at the battery so today I took some readings:

Volts across battery: 12.6v terminal to terminal
MPPT output: 13.5v

Removed the inline fuse, fuse receptor terminals read as above

Checked continuity of fuse, in line fuse no more than 20cm from battery. All good. No or minimal cable losses

Checked continuity of battery side of fuse, all good (otherwise there would be zero volts reading at the fuse anyway)

Checked if BMS is limiting voltage/current with negative to chassis and positive measurement either side of BMS: 12.6v

fuse back in. MPPT still reading 13.5v with float charge of 0.1amps, battery still showing 12.6v.

Engine was off for the readings but battery voltage climbs to 14v when alternator does its thing.

the only thing i have not done is measured the resistance of the full cable run from the battery to the mppt terminal which is less than 2m on a 10awg cable

can anyone account for why the battery does not show 13.5v
 
dcpen43 said:
Missing volts

i have hooked up the MPPT to the Vehicle Battery via a fused line and make after break switching but for a long time now I cannot fathom why the MPPT output voltage is not shown at the battery so today I took some readings:

Volts across battery: 12.6v terminal to terminal
MPPT output: 13.5v

Removed the inline fuse, fuse receptor terminals read as above

Checked continuity of fuse, in line fuse no more than 20cm from battery. All good. No or minimal cable losses

Checked continuity of battery side of fuse, all good (otherwise there would be zero volts reading at the fuse anyway)

Checked if BMS is limiting voltage/current with negative to chassis and positive measurement either side of BMS: 12.6v

fuse back in. MPPT still reading 13.5v with float charge of 0.1amps, battery still showing 12.6v.

Engine was off for the readings but battery voltage climbs to 14v when alternator does its thing.

the only thing i have not done is measured the resistance of the full cable run from the battery to the mppt terminal which is less than 2m on a 10awg cable

can anyone account for why the battery does not show 13.5v
Click to expand...

Check ground continuity.
 
t0mb0 said:
Check ground continuity.
Click to expand...
forgot to add that. Did a negative continuity check and ground too yesterday while tidying a messy tow bar installation for or by the previous owners.
 
I recently replaced my starter battery, the battery specialists that supplied it stated that modern cars charging systems (smart alternators) combined with ever increasing loads is resulting in reduced battery life.
They recommend putting an external charger on the battery every 3 months.
 
If you've checked for continuity on both positive and ground sides of the circuit then my guess is you technically have continuity but with high resistance which is causing high voltage drop. If you measure the voltage whilst the MPPT is active (and engine turned off) from negative battery terminal to positive MPPT output and then compare that to the voltage from negative MPPT to positive MPPT, the difference should give you an idea of the voltage drop across the ground connection. Alternatively you could measure the voltage drop or resistance of the negative to negative run directly.
 
dcpen43 said:
forgot to add that. Did a negative continuity check and ground too yesterday while tidying a messy tow bar installation for or by the previous owners.
Click to expand...
just checked the
t0mb0 said:
If you've checked for continuity on both positive and ground sides of the circuit then my guess is you technically have continuity but with high resistance which is causing high voltage drop. If you measure the voltage whilst the MPPT is active (and engine turned off) from negative battery terminal to positive MPPT output and then compare that to the voltage from negative MPPT to positive MPPT, the difference should give you an idea of the voltage drop across the ground connection. Alternatively you could measure the voltage drop or resistance of the negative to negative run directly.
Click to expand...
will give that a go. Just calculated cable voltage drop at 15amps over 2m of AWG10 and it looks to be less than 1% so that looks ok. will get the multimeter out again
 
dcpen43 said:
just checked the

will give that a go. Just calculated cable voltage drop at 15amps over 2m of AWG10 and it looks to be less than 1% so that looks ok. will get the multimeter out again
Click to expand...

Yeah, it’s the grounding I’d be most suspicious of if the positive is basically a single run of decent cable.
 
Last edited:
dcpen43 said:
just checked the

will give that a go. Just calculated cable voltage drop at 15amps over 2m of AWG10 and it looks to be less than 1% so that looks ok. will get the multimeter out again
Click to expand...

t0mb0 said:
Yeah, it’s the grounding I’d be most suspicious of if the positive is basically a single run of decent cable.
Click to expand...
think i have found the culprit there is an intermittent resistance of 1.7ohms on the negative path. will track the bugger down tomorrow starting with the terminal crimp and working backwards
 
dcpen43 said:
think i have found the culprit there is an intermittent resistance of 1.7ohms on the negative path. will track the bugger down tomorrow starting with the terminal crimp and working backwards
Click to expand...
The engine grounding connection to the RH side of the timing belt cover is a known issue, corrosion within the cable termination.
 
dcpen43 said:
Missing volts

i have hooked up the MPPT to the Vehicle Battery via a fused line and make after break switching but for a long time now I cannot fathom why the MPPT output voltage is not shown at the battery so today I took some readings:

Volts across battery: 12.6v terminal to terminal
MPPT output: 13.5v

Removed the inline fuse, fuse receptor terminals read as above

Checked continuity of fuse, in line fuse no more than 20cm from battery. All good. No or minimal cable losses

Checked continuity of battery side of fuse, all good (otherwise there would be zero volts reading at the fuse anyway)

Checked if BMS is limiting voltage/current with negative to chassis and positive measurement either side of BMS: 12.6v

fuse back in. MPPT still reading 13.5v with float charge of 0.1amps, battery still showing 12.6v.

Engine was off for the readings but battery voltage climbs to 14v when alternator does its thing.

the only thing i have not done is measured the resistance of the full cable run from the battery to the mppt terminal which is less than 2m on a 10awg cable

can anyone account for why the battery does not show 13.5v
Click to expand...
That's because the solar controller doesn't have enough power to raise the battery voltage...and that's normal.the mppt 13.5v odd will be pulled down to the battery voltage of say 12.2v

But over time the battery will charge.... slowly.

It's like filling a leaky bucket with a dripping tap...the bucket won't fill unless the drip can over come the leak .

Volt drop over the battery cable will also cause a drop in voltage from mppt to battery.


Anyhow.

What size solar panel.

What size mppt.

How long cables to battery and connections etc.

As always post some pics to see what's what. And make sure you use a chassis ground and don't go across the battery NEG post.
 
Dellmassive said:
:) That's because the solar controller doesn't have enough power to raise the battery voltage...and that's normal.the mppt 13.5v odd will be pulled down to the battery voltage of say 12.2v

But over time the battery will charge.... slowly.

It's like filling a leaky bucket with a dripping tap...the bucket won't fill unless the drip can over come the leak .

Volt drop over the battery cable will also cause a drop in voltage from mppt to battery.


Anyhow.

What size solar panel.

What size mppt.

How long cables to battery and connections etc.

As always post some pics to see what's what. And make sure you use a chassis ground and don't go across the battery NEG post.
Click to expand...
love the analogy

175w 75/15 and approx 2m and it does you chassis ground.

If the MPPT is being pulled down i would expect to see the battery voltage at the MPPT terminals, which strangely I dont. That suggests a high ressistance somewhere in the neg line. Did find a 1ohm intermittent res yesterday.

the problem i have is that its such a beautiful day and one give our seasonal track record that should not be squandered on Dubs no matter how much we love them. :):)
 
Time to post some pics of the setup.

And screenshots from the app..

A 175w on a 75/15 should get you at least 6-10A charge on a low battery.....

So turn all you loads on and track some pics...


Lovely sunny day at.


Eg from now....

400w. 100/20. 300ah. lifepo4.



Screenshot_20240510_080223.jpg
 
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