It’s not as it warms up, it’s as the battery needs less after the big draw of the starter. This is done with a voltage regulator. It’s noting as complicated as say the charging system on say a BMW. At least that is my take on it.

 

Thanks for the reply. I think the issue is the input that the voltage regulator receives.

Observations on my 2016 Camry seem to indicate that temperature of the alternator is the only input.

Many cars today have a Hall effect current sensor on the negative battery lead. There may be a temperature sensor for the battery. An electronic control unit controls the voltage regulator setting based on all inputs. Float voltage is maintained after the initial charge cycle completes.

My car appears to be very light on charging especially after a warm start. I'm just curious if Toyota has implemented any kind of smart charging system.

My understanding is that alternators with internal voltage regulators have controlled battery charging based only on temperature going back many decades.

 

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Thanks for the reply. I think the issue is the input that the voltage regulator receives.

could be the regulator is on its way out.

Observations on my 2016 Camry seem to indicate that temperature of the alternator is the only input

no sir the regulator is not heat controlled

Many cars today have a Hall effect current sensor on the negative battery lead. There may be a temperature sensor for the battery.

never seen either on Toyota’s

I'm just curious if Toyota has implemented any kind of smart charging system.

not that I know of

My understanding is that alternators with internal voltage regulators have controlled battery charging based only on temperature going back many decades.

You need to research and read up on alternators and regulators, none are solely based on temp.

 

Current sensing does not require anything complex outside of what is already in the voltage regulator of the alternator. Some vehicles in the past like a lot of modern Chrysler had varistors near the battery to detect battery temp. and adjust accordingly. Some Cadillac's with remote battery under the seat also had them.

None of this is a must have. The same sort of circuitry that you see in a Midtronics battery tester can and is sometimes included in some more complex European designs but almost always works against long-term durability.

Most Toyota's that are driven 20 miles a day with out demanding additional loads like ham radio amp, car audio or the like get very long battery life with even average to cheap lead acid batteries. The problems arise with vehicle that see 2 mile trips and or demanding electrical loads.

A lot of fords have the mystery wire no one seems to understand that goes from the CPU to the alternator and controls charging. When I was downsized from the large domestic full line automotive manufacture and I went to work for Autozone as a store manager and later a regional manager I had to stop people from tossing alternators at Fords with this system. 50% of the time that wire was bad and needed to be repaired it was not the alternator. Complicated systems especialy if they require the CAN bus to operate are BAD designs.

Some Rolls Royce's the starting circuit depends on the alternator to function properly so if the alternator is slightly bad they will not start. They used a GM alternator. If you did not know that you could waste a lot of time trouble shooting why the vehicle will not start.

On a daily driver that is not hybrid or all electric I would never want a digital control system for charging. I would want analog system and very basic since you gain nothing adding complexity. I routinely get between 7 to 11 years out of Walmart Everstart Maxx batteries. I have never gotten less than 5 years out their value line what ever they call that on a Toyota.

My Mom often had issues because she had a company car for decades. So her personal car's got driven 2 to 4 miles a day if that and it was all inner city.

 

Current sensing does not require anything complex outside of what is already in the voltage regulator of the alternator. Some vehicles in the past like a lot of modern Chrysler had varistors near the battery to detect battery temp. and adjust accordingly. Some Cadillac's with remote battery under the seat also had them.

None of this is a must have. The same sort of circuitry that you see in a Midtronics battery tester can and is sometimes included in some more complex European designs but almost always works against long-term durability.

Most Toyota's that are driven 20 miles a day with out demanding additional loads like ham radio amp, car audio or the like get very long battery life with even average to cheap lead acid batteries. The problems arise with vehicle that see 2 mile trips and or demanding electrical loads.

A lot of fords have the mystery wire no one seems to understand that goes from the CPU to the alternator and controls charging. When I was downsized from the large domestic full line automotive manufacture and I went to work for Autozone as a store manager and later a regional manager I had to stop people from tossing alternators at Fords with this system. 50% of the time that wire was bad and needed to be repaired it was not the alternator. Complicated systems especialy if they require the CAN bus to operate are BAD designs.

Some Rolls Royce's the starting circuit depends on the alternator to function properly so if the alternator is slightly bad they will not start. They used a GM alternator. If you did not know that you could waste a lot of time trouble shooting why the vehicle will not start.

On a daily driver that is not hybrid or all electric I would never want a digital control system for charging. I would want analog system and very basic since you gain nothing adding complexity. I routinely get between 7 to 11 years out of Walmart Everstart Maxx batteries. I have never gotten less than 5 years out their value line what ever they call that on a Toyota.

My Mom often had issues because she had a company car for decades. So her personal car's got driven 2 to 4 miles a day if that and it was all inner city.

Since Rolls comes with a lifetime warranty and road service for the original owner, the only time you waste is waiting for the mechanic to come to you. What your car is doing doesn't seemtobe a problem. Looking at it like that is the problem.

 

Thanks all for the replies and helpful information. It is much appreciated.

It looks like the Toyota RAV4 does have a smart charging system. Take a look at the information and features at the two links below. They do use a Hall effect device for the current sensor. The key feature is that the Electronic Control Module is involved with charging of the battery.

Charging Control General - Toyota RAV4 Car Features

This system lowers the generated voltage when the vehicle is idling or is being driven at a constant speed, and raises the generated voltage when the vehicle

www.toyotaguru.us

Battery Current Sensor - Toyota RAV4 Car Features

Installed on the negative terminal of the battery, this sensor detects the amount of charging and discharging amperage of the battery and sends signal to the

www.toyotaguru.us

The Camry charges the battery adequately if driven three or more times per week. However, I'd still like to see a better charging system. I may not drive the car for a week or two and have to use a battery maintainer. Many cars today are very light on charging to help meet the corporate fuel economy standards.

 

Smart charging systems do have advantages over traditional systems. I have an F-150 and it has the smart charging system and it's original battery has lasted longer than any of the other 7 vehicles I've owned, over 5 years. I live in the gulf south and the long summer heat kills batteries. I recently replaced it for peace of mind and it was starting to form corrosion, but it was still starting the truck with ease. My Camry was 3 years old when I bought it and had it's original battery that died less than a week after I bought it.

The Ford's smart charging system has the PCM telling the alternator how much voltage to put out. The PCM uses the battery monitoring system to monitor electrical load along with ambient temperature, battery state of charge and battery age to determine how much power is needed from the alternator by communicating with it. To increase battery life it doesn't charge the battery to 100%. Just like any rechargeable battery it's happiest at about 80% charge. However, as the battery ages and it's ability to hold a charge reduces the system compensates by maintaining a higher battery SOC. This also means you have to reset the BMS in the computer when you change the battery so it knows it's a new battery. So, a simple battery change isn't as simple as the Camry.

If the battery is charged sufficiently and the electrical load is low the PCM can command less than 13 volts from the alternator just to maintain the battery's SOC. This gives a slight increase in fuel economy because the alternator's drag on the engine is reduced. Conversely, on a cold, rainy night when you have the heater, seat heaters, rear defroster, lights and wipers on the PCM can command sustained maximum output from the alternator to meet demand. And since it's all controlled by the PCM, it will assist the alternator by increasing engine idle speed. It also takes temperature into consideration when charging the battery. In cold weather it charges the battery at lower voltages and slowly ramps up as the battery warms up. This avoids the rapid increase in battery temperature when charged at higher voltages which reduces battery life. And just like the A/C compressor, the PCM will not turn on the alternator during startup to reduce drag on the engine for easier startups.

 

Thanks for the information on the Ford F-150 Smart Charging. That is a very impressive system. I've tried searches on Smart Charging and there is a lot of interesting information available.

My concern is primarily the need to use a battery maintainer if the car is driven less frequently. It has been stated that cars today are designed to maintain batteries but not charge them following anything other than a modest discharge.

I experienced that myself after getting a jump start. The car was driven more than 20 miles and a check on the specific gravity of the cells showed essentially no change.

A big factor today is the parasitic current drain seen in all newer vehicles. It looks like discharge can accumulate from week to week if the car is not driven long enough. The car may not start after accumulating some level of discharge if it then sits for a week or two.

 

Your car is approximately 6 years old. I would start by changing the battery since a six year old battery is going to be pretty weak.
Which could be causing the higher voltage at startup since it can't recharge as fast as new battery.

I find it very interesting you commented about cars not being designed to recharge a battery that was drawn down to a low voltage. Most modern cars have a alternator in the 200 amp range while most car sized batteries will only pull at most 20 amps and that drops rapidly as the battery recharged .

You can change a battery faster with higher voltage but that significantly reduces battery life.

The only time I would consider a trickle charger is, if I would need to let the car sit for over a month since mine normally only gets used Saturday and Sunday and has sat for 2 weeks several times never needing to be jumped I'm not concerned about it.

 

14 SE - I came across an interesting thread stating that Toyota alternators have a low output voltage and are not aggressive charging systems. That confirms my experience. The thread mentions a diode addition done in the fuse box that increases the alternator charge voltage.

Alternator Question: 2017 4Runner

On the subject of automotive charging systems being designed to maintain but not charge batteries beyond a certain point, here is a very informative thread.

Can a dead car battery be completely recharged by just jump starting the car and driving around?

Look for the posts from Jim McIlvaine and Steve Porter. There is also quite a bit of misinformation in the thread.

It is also helpful to understand the proper method to recharge lead acid batteries using a three stage constant current, constant voltage, and float charger. Three stage chargers of this type typically charge at 14.2 to 14.5 volts in the constant voltage phase. That is generally not available from a standard alternator except for a short period of time before it goes to float voltage.

The 14.2 volts from my alternator after a cold start is normal for a battery in any condition. That is the period of time where most of the charging takes place. The voltage regulator in a standard alternator includes temperature compensation and the voltage drifts down as the alternator and battery warm up. I believe that serves two purposes. It takes the charging voltage to a high float state and it also prevents overcharging of the battery at higher temperatures.

I was interested in your comment that batteries may only pull 20 amps initially followed by a steady decline. If you have any additional information please pass it along. I have been looking for a chart where someone has actually taken measurements. There are many variables including the battery state of charge, the internal series resistance, the voltage regulator setting, and other loads on the alternator.

 

I don't have any solid data on charging amps I said that based off my experience working with machinery and occasionally needed to charge something that was sitting all winter or diagnosing starting issues.

Diesel pickups usually have 2 batteries do you will see a higher amp draw on them but most passenger cars have very small batteries compared to what I'm used to working on.

 

Here is a document showing how to estimate lead-acid battery charge current based on state of charge and charge voltage. Look for "Batteries Chargers Alternators" in the lower right section of the web page below. Refer to Figure 2 in the document.

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As an example, consider a 60 Ah car battery at 80% state of charge and an alternator voltage of 14.2 volts.

Figure 2 shows a charge rate of C/5 for 80% state of charge and 14.2 volts. 60 Ah divided by 5 is 12 amps.

You can then see the charge rate drop to C/10 after the battery reaches 90% state of charge. 60 Ah divided by 10 is 6 amps.

At 100% state of charge, the charge rate drops to C/20 for a charge current of 3 amps.

Higher charge voltages are required for higher charge currents. At 90% state of charge, 15.2 volts would be required for a charge rate of C/5 or 12 amps.

Unfortunately, the chart does not cover cases with a deeply discharged battery and an alternator voltage of 14.2 volts.