12V Aux Battery Charging

[AndyH]

I'm going to see how the 2018 PHEV charges the 12V aux battery when it's healthy. I'll use a LaMantia BA402 battery analyzer as a voltage logger and try to capture an entire charge cycle. I'll cross-check with my EVSE to see how much energy the system uses when it charges. This should also tell us if the charge process is fully charging the sealed lead acid battery. Nissan, at least, is undercharging the 12V battery in the LEAF and this is leading to premature failure.

The battery in the US spec car is a GS Yausa S46B24L(S) and appears to be a proper deep cycle battery with a 45 Ah capacity.

Step 1... I confirmed that the car does run a charge cycle at 1400 every day when plugged-in.

Step 2... I arranged access to the aux battery, connected the analyzer and laptop to power, and made sure I could capture good data.

Step 3... Charge profile for healthy battery when connected to EVSE

The initial spike when connecting the EVSE only drew 1WH. The car did not activate the traction battery charger or draw power through the EVSE after the initial spike. It's a nice looking charge profile - it looks like Mitsubishi's properly charging the battery.

Step 4... (find out of aux battery is charged when the car is not plugged-in)
It doesn't appear that the car will run a 2pm charge session for the 12V battery if the car's not plugged-in.

Step 5... (discharge battery to about 50% and see what happens)

 

[generaltso]

Looking forward to your results!

 

[HHL]

I don't think there is much going in and out.....
Had mine parked for a month last year and it wasn't plugged in. Mine does not have the wi-fi, so it doesn't periodically charge from the traction battery. It booted right away after 4 weeks....
The only time it discharges significantly is when you power on the car without the pressing the brake pedal, and leave it like that to run the radio, turn on the lights...
Otherwise the aux battery never has to supply power for longer than a second or two.

 

[AndyH]

I don't think there is much going in and out.....

At the very least, with a perfect battery and zero load, the 45 Ah battery will lose about 5% per month from normal self-discharge - 2.25 Ah/month. Even without WiFi, enough of the electronics have to be on 24/7 to catch the radio signal from the key. It's not a lot, but over time can prematurely age a battery.

 

[AndyH]

Charge profile chart added.

 

[generaltso]

Interesting. So the charge cycle ran for about 20 minutes at 2pm with the EVSE plugged in? Was the drive battery fully charged when this cycle started? If so, did it draw power from the EVSE to charge the 12v battery?

 

[AndyH]

Interesting. So the charge cycle ran for about 20 minutes at 2pm with the EVSE plugged in? Was the drive battery fully charged when this cycle started? If so, did it draw power from the EVSE to charge the 12v battery?

Yes, this was a 2pm charge and the EVSE was plugged in. The drive battery was fully charged. No power was drawn from the EVSE during the 12V battery charge.

 

[generaltso]

Interesting. So the charge cycle ran for about 20 minutes at 2pm with the EVSE plugged in? Was the drive battery fully charged when this cycle started? If so, did it draw power from the EVSE to charge the 12v battery?

Yes, this was a 2pm charge and the EVSE was plugged in. The drive battery was fully charged. No power was drawn from the EVSE during the 12V battery charge.

So I guess the power must be drawn from the drive battery regardless of whether the EVSE is plugged in. It must not have been enough for the drive battery to start charging again though.

 

[AndyH]

Interesting. So the charge cycle ran for about 20 minutes at 2pm with the EVSE plugged in? Was the drive battery fully charged when this cycle started? If so, did it draw power from the EVSE to charge the 12v battery?

Yes, this was a 2pm charge and the EVSE was plugged in. The drive battery was fully charged. No power was drawn from the EVSE during the 12V battery charge.

So I guess the power must be drawn from the drive battery regardless of whether the EVSE is plugged in. It must not have been enough for the drive battery to start charging again though.

Exactly - it's charged with a DC-DC converter from the traction battery.

Steps 4 and 5 are designed to test the hypothesis that our friend from Australia is losing traction battery charge due to having a failing aux battery.

https://youtu.be/BBHfQYKPLcY

 

[Bert]

... following this with very very great interest.

Your friend from Australia

 

[AndyH]

I've checked my car for the past 3 days - it doesn't run a 2pm charge session when it's not plugged in. Has anyone seen their car run a 2pm session when it's not been connected to an EVSE?

 

[generaltso]

I've checked my car for the past 3 days - it doesn't run a 2pm charge session when it's not plugged in. Has anyone seen their car run a 2pm session when it's not been connected to an EVSE?

That’s odd considering it’s not taking the charge from the EVSE anyway.

 

[PHEV07]

I don't think there is much going in and out.....

At the very least, with a perfect battery and zero load, the 45 Ah battery will lose about 5% per month from normal self-discharge - 2.25 Ah/month. Even without WiFi, enough of the electronics have to be on 24/7 to catch the radio signal from the key. It's not a lot, but over time can prematurely age a battery.

Have you determine what the Drive Battery Voltage is. I read somewhere it was 300VDC and a few other places say it is as Hi as 360VDC.

With this value of high Voltage, to charge the 12V Aux bat rated at 45Ah from 12.6V to 14.6V state of charge the Current from the Drive battery would be minimal enough not to require the EVSE to initiate a charge it it was off at the time I wouldn't think (14.6/360= 0.04 or around 1.8 Ah).

 

[AndyH]

I've checked my car for the past 3 days - it doesn't run a 2pm charge session when it's not plugged in. Has anyone seen their car run a 2pm session when it's not been connected to an EVSE?

That’s odd considering it’s not taking the charge from the EVSE anyway.

I'm thinking it'll have to charge it at some point if the car's not plugged-in - there are people that 'never' plug in. I may have to discharge the battery some and put a logger on it for 24 hours and see if anything happens.

 

[HappyHeyoka]

I'm thinking it'll have to charge it at some point if the car's not plugged-in - there are people that 'never' plug in.

I'm maybe forgetting the details but from memory the 2PM thing only happens when the WiFi is (a) installed and (b) enabled.

I did see (or rather, hear and was very suprised by) by the 2PM charging thing early on when I actually used the WiFi and the phone app. Now I don't use those and because it's a PITA I just leave the WiFi off and I don't see the 2PM thing any more.

Even without WiFi, enough of the electronics have to be on 24/7 to catch the radio signal from the key. It's not a lot, but over time can prematurely age a battery.

You're kind of in my bailiwick there: the key fob receiver is likely to draw microamps (as in, millionths of an Amp); it probably wakes up and does something if it sees a valid code sequence but you'd have to be sitting there all week pushing the button on your keys to draw significant power (not withstanding lock solenoids etc).

 

[PHEV07]

I'm thinking it'll have to charge it at some point if the car's not plugged-in - there are people that 'never' plug in.

I'm maybe forgetting the details but from memory the 2PM thing only happens when the WiFi is (a) installed and (b) enabled.

I did see (or rather, hear and was very suprised by) by the 2PM charging thing early on when I actually used the WiFi and the phone app. Now I don't use those and because it's a PITA I just leave the WiFi off and I don't see the 2PM thing any more.

Even without WiFi, enough of the electronics have to be on 24/7 to catch the radio signal from the key. It's not a lot, but over time can prematurely age a battery.

You're kind of in my bailiwick there: the key fob receiver is likely to draw microamps (as in, millionths of an Amp); it probably wakes up and does something if it sees a valid code sequence but you'd have to be sitting there all week pushing the button on your keys to draw significant power (not withstanding lock solenoids etc).

I am sure the Head Lights are powered by the 12V Aux Battery. 2018 PHEV uses LED lights but they would still draw some Current. High Beams use Filament or Halogen so those puppies are sure to drain the 12 Volt Battery with in a few Hours.

Just a thought on how to drain that 12V Aux Battery

 

[Bert]

Step 4... (find out of aux battery is charged when the car is not plugged-in)
It doesn't appear that the car will run a 2pm charge session for the 12V battery if the car's not plugged-in.

Step 5... (discharge battery to about 50% and see what happens)

This seems to be my problem at the moment. Could you see if the the aux battery is ever charged when the car is turned off and not plugged in? What happened once you discharged the aux battery, did the DC/DC converter kick in at some stage?

That could be the missing piece in solving my loss of capacity while parking drama...

Thanks Andy from Andy.

 

[AndyH]

Step 4... (find out of aux battery is charged when the car is not plugged-in)
It doesn't appear that the car will run a 2pm charge session for the 12V battery if the car's not plugged-in.

Step 5... (discharge battery to about 50% and see what happens)

This seems to be my problem at the moment. Could you see if the the aux battery is ever charged when the car is turned off and not plugged in? What happened once you discharged the aux battery, did the DC/DC converter kick in at some stage?

That could be the missing piece in solving my loss of capacity while parking drama...

Thanks Andy from Andy.

Hi Andy,

I haven't connected the battery analyzer and let the car sit for 24 hours to see what happens. I guess I should do that in the next fortnight while I still have my smart. It goes back to Mercedes mid-month.

Separately, I'm curious about how and when the car cools the battery. I'll be in your situation in a few months - with weather approaching 43°C. Heating the battery isn't my primary concern.

Tschuess, Andy

 

[HappyHeyoka]

This seems to be my problem at the moment. Could you see if the the aux battery is ever charged when the car is turned off and not plugged in? What happened once you discharged the aux battery, did the DC/DC converter kick in at some stage?

A non-invasive current measurement device (clamp on hall effect?) would be really handy to deploy around your car... something with data logging would be great to try and pin down when it happens.
If that's not something you are familiar with, it's time to get friendly with a local electronics nut or electrical engineer. It's not the kind of gear an auto electrician is likely to have (although I'm sure some have a nice clamp meter that might have bluetooth or something)

And I say "you" because obviously something is going on with your car that isn't, for example, happening with mine - also an Australian 2014.5; I have watched the videos and your frustration is obvious.
I've got lots of 12v accessories, the car sits for days at a time, sometimes a week (I work from home, if I am busy I don't go anywhere).
Never had a problem.

I'm sure I could attach something to _my_ car to do this, but it's not actually useful diagnostic data about _your_ problem.

 

[Bert]

A non-invasive current measurement device (clamp on hall effect?) would be really handy to deploy around your car... something with data logging would be great to try and pin down when it happens.
If that's not something you are familiar with, it's time to get friendly with a local electronics nut or electrical engineer. It's not the kind of gear an auto electrician is likely to have (although I'm sure some have a nice clamp meter that might have bluetooth or something)

And I say "you" because obviously something is going on with your car that isn't, for example, happening with mine - also an Australian 2014.5; I have watched the videos and your frustration is obvious.
I've got lots of 12v accessories, the car sits for days at a time, sometimes a week (I work from home, if I am busy I don't go anywhere).
Never had a problem.

I'm sure I could attach something to _my_ car to do this, but it's not actually useful diagnostic data about _your_ problem.

I'm electrician with a specialisation in electronics and computing, so yeah... a clamp amp with logger is quite expensive though and I have hesitated to buy one just for this purpose yet. I will hook up my normal amp meter (20A) and see what is going on on the weekend.
At the moment it looks like the aux battery is getting charged while the car is parked, the voltage increases slowly even with the standby load of the car. So it must be related to that.
I would spend the money and buy a new aux battery for testing purposes. I feel the loss during the day is getting worse (2.5Ah and 5/6km down is now almost the rule). So there is a good reason it could be related to a dying aux bat... although all measurements seem to be fine and don't point to a faulty 12V battery.