Parasitic drain on 12V battery

[Joningy]

That is a new and very interesting approach, but if MG is capable of the 12v auxiliary battery being topped up from the HV traction battery whilst locked and asleep, why isn't it?

This leads me to think perhaps, what I was told that MG does NOT support this is correct, I'm thoroughly confused.

But meanwhile the small 12volt backup jump starter is proving extremely useful and practice for when it happens in the darkness!

I regularly used the ismart app on my previous MG4 without ever having a problem, so what is different to on my S5 to the MG4?

 

[marcbesty]

Thanks for all of the comments. Some of them far too technical for me .

AA boosted the car again on Saturday, left it on the drive in Ready mode for 2-3 hours, took it for a 45 minute drive and charged the car overnight.

Went to use the car this evening and got an error message as I opened the car saying battery is low. Kept it on the drive for an hour in Ready and then went for a 45 minute drive but still had the error pop up when I locked the car. I've got the car on charge overnight so hopefully that gives it some charge.

In terms of apps, I have the MG app and the car is connected to the Fuse Energy app. I get kicked out of the MG app whenever I log in after a few minutes guessing that is due to being logged in to the Fuse App.

 

[stevedee]

So this might be of interest.

I don't have a system battery problem, but I've been pulling data from the car via the API this evening and noticed this...

Note that the time between samples is 10 minutes, so you wont see the second-by-second complete picture of what is happening.

But look at the system battery column on the far right. When the battery drops down to some point below 12.3V, the car steps in and charges the system battery, from the traction battery, for between 10- 30 mins (...again, can't be more specific due to the 10min update interval).

The voltage then drops back below 14V (no longer charging) and slowly falls from 13V to 12.5V.

The important point here is that the car appears to be monitoring the system 12V battery, and topping it up with a short charge if it drops below some preset limit. It doesn't wait until the car's traction battery is being charged.

My guess is that cars which suffer from flat 12V batteries, have a problem with this auto-charging mechanism.

 

[Joningy]

So this might be of interest.

I don't have a system battery problem, but I've been pulling data from the car via the API this evening and noticed this...

View attachment 42666

Note that the time between samples is 10 minutes, so you wont see the second-by-second complete picture of what is happening.

But look at the system battery column on the far right. When the battery drops down to some point below 12.3V, the car steps in and charges the system battery, from the traction battery, for between 10- 30 mins (...again, can't be more specific due to the 10min update interval).

The voltage then drops back below 14V (no longer charging) and slowly falls from 13V to 12.5V.

The important point here is that the car appears to be monitoring the system 12V battery, and topping it up with a short charge if it drops below some preset limit. It doesn't wait until the car's traction battery is being charged.

My guess is that cars which suffer from flat 12V batteries, have a problem with this auto-charging mechanism.

So from this can we positively say the High voltage traction battery is definitely charging the auxiliary battery when it drop to or below 12.3 volts?
Knowing if this is correct, helps when my car goes in for diagnostic checks on Wednesday, I also suspect the charging system is possibly faulty.

As I mentioned earlier, I have emailed MG Customer Support and had an automated reply today, purely acknowledging receipt of my email, but no answer to my question asking if the HV traction battery actually charges the 12v auxiliary battery whilst locked and turned off.

 

[TimothyN]

Has a Chinese programmer used the expression "Not too shabby"?

 

[Lovemyev]

@emmrecs
Although I do use the App myself, I would say that my usage is what you might class as fairly normal ?.
At a guess, I would say an average of once every couple of days or less.
In cold weather, you may use it a couple of times in a day to turn on cabin heating etc.
But then I can go days, or sometimes a week without using it.
I would expected that your usage would have to be very excessive to cause a completely flat battery surely ?.
Like checking it every hour, seven hours a day !.
I mean, who the hell does that.
My wall box is a pre-smart unit, so there is no fear of any interaction between the box and the car.
I was cleaning my car at the weekend and had the hatchback and doors open for about 2 hours.
Therefore the electrics / modules where all alive.
The car was not in ready mode, so not putting any charge into the 12 volt battery.
The following morning, straight after boot up, I checked the 12 volt battery status.
It was still displaying 14 volts.

 

[decrep]

So from this can we positively say the High voltage traction battery is definitely charging the auxiliary battery when it drop to or below 12.3 volts?

I think so, you can see the traction battery drops at the same time as the system battery goes up. This is expected behavior even if MG deny it

 

[stevedee]

No one should be worrying that their actions are causing the system 12V battery to go flat.

Its laughable to think that any EV manufacturer would design a car where the 'little' battery is allowed to go flat, while there is a gurt big source of power strapped to the underside of the car.

Without the 12V battery, the car is truly useless. Without the 12V battery, you won't even be able to listen to Radio Caroline while you wait for the AA to rescue you!

The design requirements of the EV 12V battery are completely different to those for a traditional car. (BTW; never fit such a battery in an EV).

The EV 12V battery is maintained in a 'partial state of charge' by the traction battery via a controller (e.g. high voltage DC to low voltage DC).

From my overnight check, my car (under current local conditions) is being 'trickle charged' from traction battery approx every 5hrs.

Without that frequent charge, it would soon be too low to be useful. Its never fully (100%) charged because we want it to enjoy a long & happy life!

If the guys in the service workshop tell you they are looking for faulty components that may be draining the battery, they either 1) don't understand how the car works or, more likely 2) are taking the piss, because they find it hilarious to talk rubbish to customers (many of the mechanic friends I've had over the years have been category 2).

I hope this helps. It represents my current understanding of the situation and how I believe the system works. But remember, your warranty is with MG, not me!

 

[T1 Terry]

No one should be worrying that their actions are causing the system 12V battery to go flat.

Its laughable to think that any EV manufacturer would design a car where the 'little' battery is allowed to go flat, while there is a gurt big source of power strapped to the underside of the car.

Without the 12V battery, the car is truly useless. Without the 12V battery, you won't even be able to listen to Radio Caroline while you wait for the AA to rescue you!

The design requirements of the EV 12V battery are completely different to those for a traditional car. (BTW; never fit such a battery in an EV).

The EV 12V battery is maintained in a 'partial state of charge' by the traction battery via a controller (e.g. high voltage DC to low voltage DC).

From my overnight check, my car (under current local conditions) is being 'trickle charged' from traction battery approx every 5hrs.

Without that frequent charge, it would soon be too low to be useful. Its never fully (100%) charged because we want it to enjoy a long & happy life!

If the guys in the service workshop tell you they are looking for faulty components that may be draining the battery, they either 1) don't understand how the car works or, more likely 2) are taking the piss, because they find it hilarious to talk rubbish to customers (many of the mechanic friends I've had over the years have been category 2).

I hope this helps. It represents my current understanding of the situation and how I believe the system works. But remember, your warranty is with MG, not me!

Its never fully (100%) charged because we want it to enjoy a long & happy life!
I hope you are not referring to the lead acid battery with that statement, because the opposite is true.
Not fully charging and holding it there for some time, will result in the plates sulphation, reducing the batteries plate surface area to convert the sulphur out of the lead and back into the acid.
This sulphating is compounding problem. Each bit of sulphation blocks the conversion process resulting in less capacity and a faster rise to the preset charging voltage .... resulting in more sulphation.

T1 Terry

 

[stevedee]

Has a Chinese programmer used the expression "Not too shabby"?

The classifications I've included in my code for 'efficiency' also include; " well done!", "in a hurry, are we?", " Lead foot!", so I can't blame our Chinese friends.

I had a couple of attempts at providing some kind of indication on how well the car was being driven, but have settled on the figures used by ev-database.org. So 100% matches their range figure, and obviously >100 is better, <100 is worse ...but its just a guide.

 

[Lovemyev]

If the guys in the service workshop tell you they are looking for faulty components that may be draining the battery,

Unless the car has a large parasitic drain of course, that could be as a result of a relay etc not unlatching correctly, then even if the car receives a top up charge from the traction battery every 5 hours, then this may not be enough to replace the charge to full capacity.
Over time the battery is loosing more and more from its stored state, until eventually it is depleted.
Unless the the system is intelligent enough to keep charging the 12 volt until it reaches a satisfactory level.
The small 12 volt battery in these cars are man enough to do the job, when everything is working “as they should” and the battery condition is 100% perfect, but any excessive over use or even a small drain leaves the car stranded.
There is no “fat” left to spare with regards to its capacity unfortunately.
They are going to be an item that will need replacing by their owners more frequently than you might expect tbh.
Purely based on the fact they have to almost 100% perfect or we are going to get caught out.
Better quality and more capacity, means extra cost and increased weight.
Both are avoided by all manufacturers!.

 

[T1 Terry]

Being a lead acid battery, only 50% of the fully charge capacity can be drawn for the battery to remain above 12vdc. A brand new 35Ah lead acid battery has 17.5 useable capacity before it drops below 12v, at the point, I think I read that the HV battery will not attempt to charge it back up. It the HV to 12v battery recharge is every 5 hrs as I saw mentioned somewhere here, that allows 3.5Ah each hr over the 5 hr period, or a 3.5 amp continuous load, would see a brand new 35Ah, fully charged, drop to the 12v cut off over a 5 hr period .....

This is all predicated on the lead acid battery actually having 35Ah.
With an LFP quality cell battery, the same 35Ah is all useable and should hold above 12v until all 35Ah are drained from it.
Added to that, the HV battery charging the 12v battery will have it very close to fully charged by the time the 14.4v cut off is reached.

It doesn't need a bigger battery, it needs a battery with a better chemistry.

The Sodium ion (Na+) alternative, wouldn't be fully charged at 14.4v, if the same 35Ah is required, a larger capacity Na+ capacity battery would be needed. If the full 17.5Ah the lead acid battery would have been capable of delivering when new, was enough, then the same 35Ah Na+ battery would also do the job far better than the lead acid battery.
Both of these choices would have better than a 10 yr life span, so equivalent to replacing the lead acid battery 5 times at least.
The part where the Na+ battery really shines is, absolutely no damage being dragged down to 0V in each cell, it will simply recharge and carry on life as usual

T1 Terry

 

[stevedee]

Unless the car has a large parasitic drain of course, that could be as a result of a relay etc not unlatching correctly, then even if the car receives a top up charge from the traction battery every 5 hours, then this may not be enough to replace the charge enough ?.
Over time the battery is loosing more and more from its stored state...

I'm sorry, I completely disagree with you.

I tried to be clear that I was NOT saying the MG S5 EV recharged its 12V battery every 5hrs, only that mine is doing this, at the moment.

Recharging happens when the system determines that a charge is required; this is when the required battery voltage is less than some preset limit (certainly less than 12.3Volts).

I disagree that this problem hinges on heavy battery drain for a number of reasons. I may be mistaken, but I think we are talking about relatively new cars & in some cases, the batteries concerned have passed a few simple tests.

>> Even if these batteries needed charging every hour, the system would still cope. <<<

 

[Lovemyev]

I may be mistaken, but I think we are talking about relatively new cars & in some cases, the batteries concerned have passed a few simple tests.

The car maybe new or nearly new, but this does not necessarily mean that a parasitic drain is not totally out of the question.
Having worked in a car assembly plant on a secondment for about 18 months, you maybe a little surprised to see just how many items get replaced on brand new cars per shift, due to manufacturing faults within them.
Being new, does not necessarily mean every component is going to be 100% perfect.
A new car is made up of thousands of so called new components, the law of averages states that it only takes one of those parts to malfunction intermittently and you have an issue on your hands.
If this was not the case, then manufacturers would not be offering warranty cover to millions of their customers.
Anything in possible on a so called new car.
In certain cases, customers just end up loose faith in their new cars.
Those that continue to have issues that the dealers are just unable to correct.
So these cars end up being traded in prematurely as a result of the customers total frustrations.
Typically know as “Friday afternoon or lemon cars”.

 

[stevedee]

...If the HV to 12v battery recharge is every 5 hrs as I saw mentioned somewhere here.....

...Added to that, the HV battery charging the 12v battery will have it very close to fully charged by the time the 14.4v cut off is reached.

It doesn't need a bigger battery, it needs a battery with a better chemistry...

Not every 5hrs, see my earlier comments.

No, the 12V battery is not fully charged, its given a short, low current, 'trickle charge'. A full charge is not possible in such a short time.

Its not like a petrol engine battery; its designed to deliver a relatively low & steady current for the car's instrumentation, and not designed for very heavy, very short term loads (like starting a petrol engine).

EV batteries typically suffer 'sudden collapse', that's the more common failure mode. In an ideal world (where we, as consumers have plenty of cash-to-splash) a ***-ion battery would be a good choice. But an EV lead/acid battery is more than adequate for this job.

I guess people will believe, what people want to believe. This discussion thread is called "Parasitic drain on 12V battery" so there is already a presumption that this is the problem, are some are suggesting its a combination of poor design & battery failure.

All I've tried to do is to inject a degree of technical reasoning, using my industrial background.

 

[T1 Terry]

I'm sorry, I completely disagree with you.

I tried to be clear that I was NOT saying the MG S5 EV recharged its 12V battery every 5hrs, only that mine is doing this, at the moment.

Recharging happens when the system determines that a charge is required; this is when the required battery voltage is less than some preset limit (certainly less than 12.3Volts).

I disagree that this problem hinges on heavy battery drain for a number of reasons. I may be mistaken, but I think we are talking about relatively new cars & in some cases, the batteries concerned have passed a few simple tests.

When you say, completely disagree with you:
1) You don't agree that an LFP battery could deliver twice as much electrical energy as a lead acid battery of the same capacity before the 12v terminal voltage is reached?

2) You don't agree that if the full 35Ah needs to be delivered from an Na+ battery, it will need to be a greater capacity than 35Ah if only charged to 14.4v

3)You don't agree the Na+ 35Ah battery charged to 14.4v could deliver the same 17.5Ah while remaining above 12v as the new and in good condition lead acid battery should be able to deliver?

As far as what was said in your post, I clearly misunderstood what you were saying ..... but after re-reading it a few times .... I'm not really sure what you were saying ..... the predetermined 12v terminal voltage that triggers a top up is an unknown, but you believe it is less than 12.3v .... but past there you lost me ....

T1 Terry

 

[T1 Terry]

The car maybe new or nearly new, but this does not necessarily mean that a parasitic drain is not out of the question.
Having worked in a car assembly plant on a secondment for about 18 months, you maybe a little surprised to see just how many items get replaced on brand new cars due to manufacturing faults.
Being new does not necessarily mean every component is going to be 100% perfect.
A new car is made up of thousands of components, the law of averages state that one of those parts could well have an issue.
If this was not the case, then manufacturers would not be offering warranty cover to customers.
Anything in possible on a so called new car.
I certain cases, customers loose faith in new cars that continue to have issues that the dealers are just unable to correct.
So these cars end up being traded in prematurely as a result of the customers frustrations.
Typically know as “Friday afternoon or lemon cars”.

The sampling rate of product, reflects both quality and price. With the lead acid battery we are talking about, I doubt it is even charged after assembly and filled with electrolyte.
I remember some 55 yrs ago, I worked afternoons, Saturday and holidays at an old time garage, they had batteries in a cardboard box along with a bottle of electrolyte. When a battery was sold, it was my job to put the electrolyte into the battery, then put it on a charger until the specific gravity of the electrolyte reached a certain level ... at that point it was fully charged.

Roll on forward to now, you can't even get to the electrolyte and even if you could, I doubt there would be enough in each cell to fill the hydrometer to get a reading ....
The battery is assembled and the electrolyte fed in on an automated production line.
There just isn't enough money to be made to actually pay workers to assemble the batteries. The freight from the factory to the vehicle assembly line probably eats half of the profit margin

T1 Terry

 

[stevedee]

When you say, completely disagree with you...

Sorry T1 Terry, I didn't say I disagreed with you. That was a response to another post.
I referred you to that post only with regards to the 5hr charging confusion ...I should have just typed it out again.

My understanding of AGM batteries (as used on EVs) is that they use very little electrolyte, and its all absorbed into a fiber mat (so not sloshing around).

Anyway, I think I'm done with this thread, its not my problem at the moment (thank goodness).

I'm trying to work out why my Intelligent Octopus Go tariff is not longer Intelligent; its stopped charging my car!