Design challenge for a Prius

[Connecteur]

The Prius hybrid has an annoying feature. When the 12V battery falls below (I think, 11.5V) the car is effectively dead, and will not start.  The only options are a boost or a dealer service call, even though the main hybrid battery may have plenty of charge in it.

What should happen is this:  Pressing the start button should activate a controller which reads the charge level of both batteries, and if necessary, it should activate the DC to DC converter, delivering normal voltage to the 12 V system, thus allowing the car to start.

It would have to read the charge level of the 220 V hybrid battery to guard against allowing its charge level to fall below its lower threshold, before activating the DC-DC converter. If the 12V battery is completely dead, the controller could draw its small power requirement from either an on-board battery, or through a switch-mode power supply, drawing power from the hybrid battery.

It seems to me that someone who could design such a controller would have a very lucrative financial opportunity.  There are millions of Prius hybrids out there with this problem.  Parasitic drain is unavoidable and unpredictable with these cars, and I for one would welcome such a solution.

[uer166]

I can't speak for Prius, but will speculate why that might be from Tesla knowledge: some cars precharge the HV DC bus from the 12V battery before closing the contactors. It can be done via the DCDC simply by making it bidirectional and boosting 12V to 200-400V or whatever the HV bus is.

If that is the case then it's a hardware limitation, not a controls one. Pure speculation though..

[Connecteur]

I can't speak for Prius, but will speculate why that might be from Tesla knowledge: some cars precharge the HV DC bus from the 12V battery before closing the contactors. It can be done via the DCDC simply by making it bidirectional and boosting 12V to 200-400V or whatever the HV bus is.

If that is the case then it's a hardware limitation, not a controls one. Pure speculation though..

I've owned several Priuses, and having a dead 12V battery is a constant worry.  Many people seem to think that charging the main hybrid battery should also keep the 12V battery charged also, but that's not true for most models. 

I think Toyota could have easily solved this problem, but it was probably a marketing decision not to do so.  A service call to the dealer might be the preferred option (says the conspiracy-minded me).

[tszaboo]

I can't speak for Prius, but will speculate why that might be from Tesla knowledge: some cars precharge the HV DC bus from the 12V battery before closing the contactors. It can be done via the DCDC simply by making it bidirectional and boosting 12V to 200-400V or whatever the HV bus is.

If that is the case then it's a hardware limitation, not a controls one. Pure speculation though..

I've owned several Priuses, and having a dead 12V battery is a constant worry.  Many people seem to think that charging the main hybrid battery should also keep the 12V battery charged also, but that's not true for most models. 

I think Toyota could have easily solved this problem, but it was probably a marketing decision not to do so.  A service call to the dealer might be the preferred option (says the conspiracy-minded me).

Is it? I had dead battery 3 times, 2 times because I left the lights on for sure, and once probably also because I left the lights on.
I wouldn't say it's a constant worry. Also you can just start the car even from a 12V power tool battery if needed.
And when I had a service call to Toyota, to boost the car (it was in an underground garage with no people around) they just left without letting me pay for it.

[Connecteur]

I can't speak for Prius, but will speculate why that might be from Tesla knowledge: some cars precharge the HV DC bus from the 12V battery before closing the contactors. It can be done via the DCDC simply by making it bidirectional and boosting 12V to 200-400V or whatever the HV bus is.

If that is the case then it's a hardware limitation, not a controls one. Pure speculation though..

I've owned several Priuses, and having a dead 12V battery is a constant worry.  Many people seem to think that charging the main hybrid battery should also keep the 12V battery charged also, but that's not true for most models. 

I think Toyota could have easily solved this problem, but it was probably a marketing decision not to do so.  A service call to the dealer might be the preferred option (says the conspiracy-minded me).

Is it? I had dead battery 3 times, 2 times because I left the lights on for sure, and once probably also because I left the lights on.
I wouldn't say it's a constant worry. Also you can just start the car even from a 12V power tool battery if needed.
And when I had a service call to Toyota, to boost the car (it was in an underground garage with no people around) they just left without letting me pay for it.

My Priuses never got a dead battery from leaving the lights on, because they all had a timer on the headlights.  The problem is parasitic drain, which I have measured and the only solution I have found is to use a battery maintainer.  Of course that's not an option when I'm not near an outlet.

My newest Prius does software updates over the air, and I have experienced a dead battery in as little as 2 hours when parked.  I suspect it has something to do with poor cell reception in certain areas.

[tszaboo]

I can't speak for Prius, but will speculate why that might be from Tesla knowledge: some cars precharge the HV DC bus from the 12V battery before closing the contactors. It can be done via the DCDC simply by making it bidirectional and boosting 12V to 200-400V or whatever the HV bus is.

If that is the case then it's a hardware limitation, not a controls one. Pure speculation though..

I've owned several Priuses, and having a dead 12V battery is a constant worry.  Many people seem to think that charging the main hybrid battery should also keep the 12V battery charged also, but that's not true for most models. 

I think Toyota could have easily solved this problem, but it was probably a marketing decision not to do so.  A service call to the dealer might be the preferred option (says the conspiracy-minded me).

Is it? I had dead battery 3 times, 2 times because I left the lights on for sure, and once probably also because I left the lights on.
I wouldn't say it's a constant worry. Also you can just start the car even from a 12V power tool battery if needed.
And when I had a service call to Toyota, to boost the car (it was in an underground garage with no people around) they just left without letting me pay for it.

My Priuses never got a dead battery from leaving the lights on, because they all had a timer on the headlights.  The problem is parasitic drain, which I have measured and the only solution I have found is to use a battery maintainer.  Of course that's not an option when I'm not near an outlet.

It was the internal lights.
You also have to replace the 12V battery same as any other ICE car, ~6 years or so, whatever the service manual said.

[globoy]

It's probably going to be pretty hard to get access to the traction battery for a 3rd party add-on since for safety's sake the battery is disconnected outside its protective enclosure until the contactor is energized.  Energizing the contactor is a pretty involved process by the main ECU doing such things as precharging the inverter capacitor before switching on the HV.

I know some people handle this worry by getting a 12V battery emergency start kit and keep that in the car. 

I have an EV that has a feature where it will energize the HV system and recharge the 12V battery when it is too low.  The disappointing thing about that is the feature kicks in at a voltage level below which the car has started to shed loads on the 12V system such as proximity unlock and remote (cellular) access.  It's a bit of a bummer in the winter, when you'd like to turn on the heat before going out to the car (and of course the 12V battery is performing its worst in the cold).  This coming winter I plan to add a small MPPT charger and 20-30W solar panel (as a sunshade) to see if I can improve that situation.

[Connecteur]

It was the internal lights.

It was not. I checked. And they are on timers also

[Connecteur]

It's probably going to be pretty hard to get access to the traction battery for a 3rd party add-on since for safety's sake the battery is disconnected outside its protective enclosure until the contactor is energized.  Energizing the contactor is a pretty involved process by the main ECU doing such things as precharging the inverter capacitor before switching on the HV.

I know some people handle this worry by getting a 12V battery emergency start kit and keep that in the car. 

I have an EV that has a feature where it will energize the HV system and recharge the 12V battery when it is too low.  The disappointing thing about that is the feature kicks in at a voltage level below which the car has started to shed loads on the 12V system such as proximity unlock and remote (cellular) access.  It's a bit of a bummer in the winter, when you'd like to turn on the heat before going out to the car (and of course the 12V battery is performing its worst in the cold).  This coming winter I plan to add a small MPPT charger and 20-30W solar panel (as a sunshade) to see if I can improve that situation.

I realize that special instructions will be required for safe installation, but there are already mod kits that connect to the HV battery, and have been done so safely.

[globoy]

but there are already mod kits that connect to the HV battery, and have been done so safely.

Interesting.  Can you link to one?

[Connecteur]

but there are already mod kits that connect to the HV battery, and have been done so safely.

Interesting.  Can you link to one?

I know of one that converts the power of the hybrid battery to standby power using a large inverter.
I can't recall the name.

[edpalmer42]

I have a Prius Prime.  It seems that many versions and ages of the Prius family have a weak 12V system.  The 2023 and newer models might be worse than older models.

When you push the power button, the 12V battery is used to boot up all the control modules throughout the car.  They perform various 'pre-flight checks' and then, if, and only if, all those checks passed, the hybrid system (i.e. the high voltage batteries, main inverter and dc-dc converter) is brought online.  Your idea would require bypassing most or all of those safety checks and would result in many vehicle fires.

It might be possible to reduce or eliminate this issue if Toyota optimized their 12V charging algorithm and bootup procedure, but they don't seem interested in that.  They certainly aren't interested in improving the performance of older cars.  Only new models would receive those improvements.

P.S.  Wouldn't this topic fit better in the Power/Renewable Energy/EV's area?

[Connecteur]

When I took delivery of my 2012 Prius, I was disappointed to get only about 5 minutes on ACC mode.  I took it to the dealer, and they said they were surprised that the 12V battery tested bad.  I got a new battery, but I found that when the car was parked for more than a week, the 12V battery would be dead.  I think a fairly high parasitic drain was the reason.  A battery disconnect was not an option for me because it's a pain to reset everything.

The car had been in the dealer showroom for several months, with the hybrid battery charger plugged in.  I think they assumed it would keep the 12V battery charged, but it did not.  Repeated use by customers and sales staff required it to be boosted many times, causing it to fail.  That's why I took delivery of a new car with a bad 12V battery.

[tszaboo]

It was the internal lights.

It was not. I checked. And they are on timers also

How can you tell, how I drained the battery of my car? Were you there?

[Connecteur]

It was the internal lights.

It was not. I checked. And they are on timers also

How can you tell, how I drained the battery of my car? Were you there?

I thought you were explaining why mine did.

[Siwastaja]

The problem is parasitic drain, which I have measured

I won't question that. However, are you certain that
(A) it isn't cause by some aftermarket mod? Some added device? Poorly designed alarm systems, car radios, radar detectors etc. are classic examples with decades of legacy in killing batteries
(B) the car isn't somehow faulty, i.e. some internal module draining more than it should?

[TimFox]

The problem is parasitic drain, which I have measured

I won't question that. However, are you certain that
(A) it isn't cause by some aftermarket mod? Some added device? Poorly designed alarm systems, car radios, radar detectors etc. are classic examples with decades of legacy in killing batteries
(B) the car isn't somehow faulty, i.e. some internal module draining more than it should?

How high a parasitic drain did you measure?

[Connecteur]

The problem is parasitic drain, which I have measured

I won't question that. However, are you certain that
(A) it isn't cause by some aftermarket mod? Some added device? Poorly designed alarm systems, car radios, radar detectors etc. are classic examples with decades of legacy in killing batteries
(B) the car isn't somehow faulty, i.e. some internal module draining more than it should?

How high a parasitic drain did you measure?

330 mA at one point, but it's all over the map.

[Connecteur]

The problem is parasitic drain, which I have measured

I won't question that. However, are you certain that
(A) it isn't cause by some aftermarket mod? Some added device? Poorly designed alarm systems, car radios, radar detectors etc. are classic examples with decades of legacy in killing batteries
(B) the car isn't somehow faulty, i.e. some internal module draining more than it should?

I've spent considerable time on this problem. I believe it's the module that does the live updates.

[TimFox]

The problem is parasitic drain, which I have measured

I won't question that. However, are you certain that
(A) it isn't cause by some aftermarket mod? Some added device? Poorly designed alarm systems, car radios, radar detectors etc. are classic examples with decades of legacy in killing batteries
(B) the car isn't somehow faulty, i.e. some internal module draining more than it should?

How high a parasitic drain did you measure?

330 mA at one point, but it's all over the map.

That's huge!

[bson]

A battery switch mounted under a wheel panel or with a remote sounds like an easier solution... after parking and locking, when walking away, disconnect the battery.  When returning, reconnect it and unlock and get in as  usual.  You could probably just buy an off-the-shelf kill switch.

[globoy]

That's huge!

Yup.  This is the known problem with the 12V battery in EVs (not only an issue for the Prius).  These cars always have a cell modem used for remote access and for the vehicle to telemetry info back to the manufacturer.  They also often have other convenience features such as proximity keyfob detection and security cameras (e.g. Tesla) that can take power.  In fact IIRC a Tesla can put up to a 50W load on its 12V battery just sitting there (it also wakes the HV system frequently to recharge this battery).  It's my experience that this is all managed by some reasonably heavy on-board computer (e.g. not a deeply embedded controller) that takes far more current than you'd expect.  They clearly do power management (mine will start shedding loads as the 12V battery voltage falls) but most manufacturers warn against leaving the vehicle just sitting too long.  Then over time, of course, the 12V battery itself fails. 

[Gyro]

My Kia Niro hybrid has a '12V Battery Reset' button for this. The need for manual operation takes out a lot of the safely related issues associated with automatic operation. I've only ever had to use it once, tailgate not fully shut.

[Connecteur]

It's not a large battery. Only 38 Ah.

[Siwastaja]

330mA is not even close to normal. The car either has some aftermarket mod installed in it, or the car is broken. Nothing new needs to be engineered; just the car fixed.