Overriding a "smart" battery management system

circuitsmith

circuitsmith

Joined
Dec 17, 2009
Messages
1,277
Location
Wash, DC
Like many modern cars the 2017 Hyundai Tucson reduces battery voltage when it decides the battery is charged “well enough”.
It does this to mainly save a little fuel and also avoid over charging the battery.

I have a voltmeter plugged into a 12V port so I can monitor system voltage while driving.

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When the battery is full (or nearly full) system voltage drops to 12.6V, with 4 exceptions.
When steady cruising it raises the voltage to 13.x or 14.x (varies with temperature) volts for a few minutes every hour or so.
When coasting and no throttle input it rises to 14.x, similar concept as regenerative braking, capturing wasted energy.
Turning the HVAC blower to high raises the voltage to 14.x.
Turning on the headlights raises the voltage to 14.x, we don’t want headlight brightness changing up and down.

I’m a low mileage driver, about 5-6000 miles per year. I don’t drive to work.
With COVID I’m driving even less. Few visits to family, no road trips.
Some weeks I only drive to the grocery store, one mile each way.
Takes me up to 2 months to burn half a tank of gas.

For 2 years I’ve kept a 10 watt solar panel on the dashboard to help keep the battery full.
I park on a city street; no plug-in access for a battery maintainer.
It does a good job, bringing battery voltage as high as 13.5V after a few hours in the sun.
But with long winter shadows coming and cloudy days it would be nice to get a little extra charging.

What I’ve started doing is turn the headlights on for trips 30 minutes or less, or turn them on for the last part of longer trips.
That keeps the voltage at 14.x volts for some extra charging time.
 
Most modern cars do this. This form of management does not seem reduce battery life or capacity in any way.

It's good to know that a flooded lead acid battery is fully charged at 12.6 V and that's a great place for float charging. Make sure to measure the voltage at the battery terminals, and not the cigarette lighter. You may find 2 tenths more voltage at the terminals.

It's also good to know that pumping more power into a battery will not increase it's capacity.
 
Last edited:
Hi,
First I would ensure I understand the distinction between Potential Difference and EMF. I would measure current with a clamp meter. I would determine what battery chemistry I had.
If I was then smarter than A BMS I would design my own.
As mentioned above, measure at the center of battery terminals to at least get believable voltage readings.

Aha! I see you are only joking:
"
What I’ve started doing is turn the headlights on for trips 30 minutes or less, or turn them on for the last part of longer trips.
That keeps the voltage at 14.x volts for some extra charging time.
"
 
There was a TSB issues for my 15 Legacy because its BMS logic was killing batteries. It would still behave as you describe, and was similar to my previous ‘08 Civic in its behavior. Like the Civic I planned deal with the low voltage by turning on the parking lights, which is all that was required to raise voltage to low-mid 14s.

One thing of note, is that the Civic idled noticeably poorer at 12.X volts, whereas the Legacy you couldn’t tell at all.

Anyway, the Legacy spends most of its time at 14.3-14.4VDC now that the TSB has been implemented and I’m all the happier for it. Regardless I still put a charger on both of the batteries every weekend or two or three.

Good on you for setting up a solar charger. Hopefully that’ll limit the degradation from sitting and give you longer service life.
 
Cujet said:
Most modern cars do this. This form of management does not seem reduce battery life or capacity in any way.

It's good to know that a flooded lead acid battery is fully charged at 12.6 V and that's a great place for float charging. Make sure to measure the voltage at the battery terminals, and not the cigarette lighter. You may find 2 tenths more voltage at the terminals.

It's also good to know that pumping more power into a battery will not increase it's capacity.
Click to expand...

Are you joking? Tongue in cheek response, maybe? Serious question.
 
gathermewool said:
Hopefully that’ll limit the degradation from sitting and give you longer service life.
Click to expand...
With my previous car I would remove the battery every 3 months and charge it overnight on an adjustable supply set to 14V.
I replaced the battery at 9 y.o., going strong. I didn't trust it for a tenth winter.

Did that a couple times with the Tucson. Decided to try something more convenient.
I'm hoping in a few years an ultra-capacitor jump starter will cost less than a new battery.
With that stowed away I can be a little more ambitious stretching out battery life.
 
Last edited:
This just seems like a solution in search of a problem.
Why do anything at all besides just driving the venue.
Replace the battery every 4-5 years (like the rest of the general public) and move on with ones life.
 
Leo99 said:
care to explain?
Click to expand...


First and foremost... How has your back been feeling? ?

Hope that it has been good for you.

He is right though leo99.... These new charging algorithms keep batteries typically 90 to 80 percent charged... That is not helpful to battery longevity. With all the parasitic draws on them too it really is not the best for them.
 
Ha! I was just about to create a post similar to this. Fiance picked up a lease 2019 Sentra back in January and it isn't getting driven much with the shutdowns. I have put the most miles on using it to do local short tripping and one or two trips to my parents ... because it needs to be driven.

It has a smart alternator. Can definitely tell the battery is struggling. Unlike my Subaru, running the HVAC on high won't allow the alternator to work. You can tell because the HVAC blower speeds up when letting off the throttle. It was weird running the 12v commpressor off the battery to get the winter tires inflated. The compressor would speed up and slow down as the alternator would kick it up to 12 volts. No where near 14v though can hear the compressor was running slower than normal even when it kicked up.

It has been run for more than 20 minutes in the last 3 months I bet. This morning I went to use it and it barely cranked over and started.

If it was like my American vehicles with a 12v outlet that was always live, I could rig up a battery tender or even a solar battery tender to keep the battery happy. I'd rather not have to open the hood to connect and disconnect when it's driven around town a lot.

Ultimately, I think I am just going to have to put the regular charger on it every few weeks.
 
bbhero said:
First and foremost... How has your back been feeling? ?

Hope that it has been good for you.

He is right though leo99.... These new charging algorithms keep batteries typically 90 to 80 percent charged... That is not helpful to battery longevity. With all the parasitic draws on them too it really is not the best for them.
Click to expand...

Back is doing great! Playing golf 1 to 3 times a week. Thanks for asking.

I'm ignorant about these smart battery charging systems and therefore inclined to just let the car do whatever it wants and replace the battery every 4 to 5 years. I would not drive 30 minutes extra once a week just to charge it up to make it last a couple years longer. But my drives tend to be 30 to 40 minutes so even though I drive a lot less these days, I still drive enough that I'm not worried about the battery.

My in laws have about 60,000 miles on their '96 Corolla and no battery issues. Wonder if they'd have issues with this new technology.
 
circuitsmith said:
...What I’ve started doing is turn the headlights on for trips 30 minutes or less, or turn them on for the last part of longer trips.
That keeps the voltage at 14.x volts for some extra charging time.
Click to expand...
Can you get the same effect by turning on only the parking lights? That's an easy solution, and wastes less power and bulb life than leaving headlights on.

The DC-DC converter of my Prius behaves similarly. It applies the higher of two voltages if the lights are on, if the battery is cold, if the transmission is not in "D", for a few minutes (temperature dependent) after a cold start, and possibly under some other circumstance(s). Otherwise, it drops to the lower charging voltage to save energy. To slightly better charge the 12-volt battery in winter, I might finish a trip with the parking lights on, or sit parked in "P" briefly at the end of a trip.
 
Leo99 said:
Back is doing great! Playing golf 1 to 3 times a week. Thanks for asking.

I'm ignorant about these smart battery charging systems and therefore inclined to just let the car do whatever it wants and replace the battery every 4 to 5 years. I would not drive 30 minutes extra once a week just to charge it up to make it last a couple years longer. But my drives tend to be 30 to 40 minutes so even though I drive a lot less these days, I still drive enough that I'm not worried about the battery.

My in laws have about 60,000 miles on their '96 Corolla and no battery issues. Wonder if they'd have issues with this new technology.
Click to expand...


Yeah I wonder too... My lady's Camry which is a 98 really charges a battery quite well and normally... Just like your in laws 96 Corolla... Tell you what I noticed though... I think the starter on that Camry is a little weak potentially... And always has been.. That car even with a brand new AGM battery in it started a touch sluggish last year when the temp was on the upper teens. Just made me think the starter on those mid to late 90s Toyotas were a bit undersized.. But has you know they are tremendously great and well built cars and trucks...

Glad to hear that your back has been good...

People don't realize just how hard and terribly debilitating a back injury or pain can be to someone... I came to the belief back pain, shoulder pain and knee pain can all three be considered the worst types of chronic type pain to try to deal with.

Be careful out there playing golf... Don't try to over swing... Ain't no shame in laying up.... Trying to play a 2 iron like a young Tiger Woods may not be the best idea... Like Clint Eastwood said... " Every man has got to know his limitations." Any sport that requires a lot of hip and back rotation can be hard on someone with a pre-existing injury or healed previous injury. Trust me I know that too.. playing volleyball is like that. And when I really tweaked my lower back bad in 2007... It was something else. Eventually started playing again after getting done with school in late spring 2009... And the first couple of times it tightened up on me rather good. Then it just went away and I was back to normal... And I was hammering the ball like old times and felt perfect doing so.
 
Miller88 said:
If it was like my American vehicles with a 12v outlet that was always live, I could rig up a battery tender or even a solar battery tender to keep the battery happy
Click to expand...
What I did was find an "always hot" wire under the dash, wire in a connector (I like Anderson PowerPole) that can be reached, but not dangling in the way, plus a matching connector on the panel.
For someone who can't DIY a shop that installs sound systems or alarms could do this.
 
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