12 Volt Battery Low

Yes.

 

charging the traction battery with the evse, will charge the 12v accessory battery, but it is unlikely to put enough power to it to recharge it completely. it is more likely just a small charge. enough to maintain a full battery but not enough to bring back a battery that is low...

 

A couple of points:
A so-called 12 volt battery is actually fully charged at 12.7 volts. 12.0 volts (at 70 degrees F) is under 25%.
Is there an alternator on our Primes? I don't think so. The 12v battery is charged by an electronic system from the traction battery.

So...
(1) Check that the battery cable connections are clean and tight. Include the ends away from the battery on the positive and negative cables. Check that the cells have electrolyte at least covering the grids. Top off with distilled water, if needed, up to the indicators.
(2) Fully charge the 12v battery and have any shop run a load test. Many battery retailers will do this for free. It'll show the condition of the battery. If the battery is shown to be good by the load test, then...
(3) Put an ammeter on one of the battery cables. Look for current that should not be there. If there is current showing, something is drawing down the battery when it shouldn't. The dealership can try to find and fix this.
(4) Or, there is a malfunction in the charging circuit from the traction battery--another dealership repair.

By the way, 40 to 80 amps would be a very big load on this little battery. 40 amps for 12vdc would require #8 gauge cable. 80 amps would require #4 gauge cable--(check any DC ampacity table).

 

I came to this thread because the same thing just happened to me. I just got my 2017 Prime last week and been messing around with it in the past couple of days learning and reading the manual which is gigantic. So I’ve spent a lot of time with the car in ACC mode or turned on in EV mode.

I always assumed that the traction battery would maintain the 12V charged if the car is turned on. But you say there is no alternator on these cars. So how does it charge the 12V battery? Can’t the gas engine charge it? If it is the traction battery that charges it, why did mine get discharged when I had the ignition on?

I thought that with a Prius having such big batteries, they would design it in a way to prevent such an old problem from happening. I have plenty of charge in my traction battery as the panel indicates, but there’s no way for the car to turn itself on from the traction battery, and from what I am reading the AC 120V charger is no help either? This doesn’t make sense to me.

 

They have a DC/DC converter that supplies power to the 12 v battery and accessories (lights, fans, etc.).

I should add, the DC/DC converter is tied to the traction battery.
Unsupervised!
iPhone ?

 

the 12v is charged by the hybrid battery through the inverter/converter. the hybrid battery is charged by the engine if you run out of wall charge.
this only takes place when the car is made 'ready'. otherwise, the hybrid battery is disconnected from the car.
this is a safety feature so no one will get electrocuted, and so you can't run down the hybrid battery without the ability of the engine to recharge it.
also, the 12v gets charged when the evse is charging the hybrid battery.

 

If your car does not start, you may need to jump, as many who has had weak or dead 12 v battery. If that jumping does not help, you may need to replace the 12V. You said, you just got the car, but the car is 2017, correct? It seems on both Gen4 and PRIME early demise of 12v battery is happening quite often. We don't know if that is due to charging system problem or bad batch of batteries on those cars.

 

Without an engine turning over to clue you in, it is easy to mistake being in accessory mode for being in ready, and thus draining down the 12 volt battery without being aware.

Teslas are the only car I know of that will use the traction pack to maintain the 12 volt while unplugged.

The Ioniq hybrid 12 volt is a module on the traction battery. If it is dead, it can be 'jumped' by just a push of a button.

 

The screen in front of me displays "ACCESSORY" when the car is in ACC mode, but when you press the POWER button a second time the display says "Ignition ON" and the full panel illuminates. I had it like this most of the time but the 12V discharged anyway. I admit this was all my fault, but then again, I am still learning to own a hybrid. I was under the assumption the traction battery was being used while the panel says "Ignition ON". What I didn't notice is if the "READY" indicator was illuminated, and probably it was not showing READY because I had not pressed the brake to turn it on. Perhaps the only way to leave the car on and prevent 12V battery discharge is to turn it on completely by pressing the brake pedal while pressing the POWER button? Am I correct in that?

I went ahead and plugged in the car to the 120V AC outlet and I was able to immediately turn on the car (Ignition ON). So to me this indicates that the AC charger also charges the 12V battery? Correct? However, since it is charging still (as I write this) the READY indicator does not turn on as expected. I turned off the vehicle to let it charge normally. But later tonight after it is done charging I will try to see if I can start the car without the AC charger.

Also, another question, if I change the vehicle to "charge mode" will that charge the 12V battery? This is the mode where the gas engine kicks in and stays running all the time.

 

The car isn't started with Ignition on. With the classic key ignition, the ignition on corresponds to the position just before the one that starts the engine. Once started, the key pops back to that ignition on position.

When the Prius is in that mode, more electrical systems are turned on than in Accessory, but the traction battery is still disconnected. To turn the 'engine' on have the battery connected, the car needs to be in READY mode. That is entered by depressing the brake pedal while pushing the engine button.

Once the car is actually running, the 12 volt will be charged, but it takes time to fully charge a battery that has died, and it is best for lead acids to be fully charged. Using a charger would be best to get the most life out of a discharged battery. That applies to all cars, not just hybrids.

 

Interesting question. As noted above, there is no alternator on the engine, so just running the engine does not directly charge the 12V battery. Running the Prime engine in charge mode charges the traction battery. Whether or not the system then lets the traction battery charge the 12V battery....?

You may be able to test this if you have a volt meter. I'd measure the voltage on the 12V battery with the car off. While in Park start the car and switch to charge mode (If it will do that in Park???). Measure the voltage at the 12V battery again. If it measures higher, yep, it's charging the 12V.

 

Thanks Trollbait for that great explanation. That answered all my questions. I was able to verify that the electrical AC charger also charges the 12V battery. I was able to start and drive the vehicle after it finished charging the traction batt. Interestingly, I found that "charge mode" is not available when the traction battery is fully charged.

As Trollbait stated, if the hybrid system is ON (not just in "ignition ON"), meaning you are able to drive the car, the traction battery sends charge to the 12V battery. I presume that using "charge mode" won't make any difference since the traction battery will still charge the 12V battery as long as the hybrid system is ON whether or not the "charge mode" is active.

Basically, in any other regular gas-only car, if you run it in ACC or Ignition ON and the engine is not running, your 12V batt will deplete from overuse. For me, this is lesson learned. Thanks for all your feedback!

 

Charge mode is a fast DC charge. Because that heats up the battery quicker than charging from an outlet, the software limits the max charge from it to 80%.

 

So if I understand you correctly, the "charge mode" which is when we force the gas engine to run to charge the traction battery, also charges the 12V battery at a faster rate than the 120V AC outlet. How much faster is "charge mode" to charge the 12V battery than just having the hybrid system running in EV mode?

 

I don't believe this is the case. As long as the traction battery has power and the car is in READY mode, it will power the DC-DC converter and that charges the 12V battery. This is regardless of whether the ICE is charging the traction battery or not. The rate of charge into the traction battery does not impact the charge rate of the 12V battery.

 

Adding to that, the DC-DC converter isn't like an alternator in that its output is in no way related to engine rpms.

 

i would not trust your newly recharged 12v battery just charged from the evse or from the charge it gets from the traction battery while the car is running.
get a dedicated 12 v charger or maintainer and recharge that battery before it is permanently discharged.
can just plug it in overnight if its the automatic type and fully recharge the 12v battery.
the evse charge, and tiny bit the traction battery supplies when its engaged, are only enough to maintain the 12v, not recharge it.
others will disagree. but thats my .02 cents.
your battery was likely neglected before you got it, and you sapped even more voltage from it during your learning phase.
these little batteries dont have any spare capacity, and are only used to run the electronics on the prius, thus barely need 10.5 volts (guesstimate) to wake up the system. by then the battery is so weak its beyond saving. people dont know they are running with weaker and weaker battery until its REALLY dead. you just crossed that threshold. maybe just you overdid it, it just happened, and a good recharge /recondition will recover full capacity to 12.7 volts. but chances are it was a weak battery, and you just made it even weaker. relying on the evse unknown charging regimen, is likely going to lead to you having a dead battery again very soon.

 

force charging has nothing to do with the 12v. it will recharge the traction battery by running the gas engine. at that time you happen to get the 13.1-13.9 V that the traction battery supplies to the 12v battery. thats it. you also get that 13.1-13.9 V as long as you are in the IG ON mode, aka driving somewhere. so its nothing special. that 13.1 to 13.9 is anemic, wont charge your phone, wont operate many electronics, so likely was designed to preserve as much energy as possible for driving. to get that 133 mpgE. the voltage is just enough to keep the computers happy, and not have the 12v slowly discharge. it might be getting 20 amps in, but all 20 amps are going right back out, so no spare capacity for anything else, like recharging a discharged battery...

 

A phone charges from 5V, so any good quality 12V-5V converter will do fine. The problem with the Prius is that the USB port they installed does not provide the necessary current to charge a phone of any size, and that is a limitation of that specific device. I have had as many as four devices running/charging on two Anker 12V dual USB chargers at the same time - no problems. I ran in this configuration for a trip of 3500 miles. That's a Go Pro, a Samsung Tablet, an iPhone 7 and an iPad Pro all charging at the same time from 12V power.

The problem is not with the voltage of the 12V battery system.

 

In addition to charging the 12V battery from the traction battery when in READY mode from a 12V power supply in the inverter-converter, I seem to recall that some of the experts here have determined that there is a separate 12 power supply driven from the charging cable, so the 12V battery gets some charging (but not much) while charging the traction battery. This is done so that the 12V load of the charger circuity does not drain the 12 battery while charging the traction battery.