Toyota prius 2016/ 12v battery recharge

whenever the car is made 'ready', the engine charges the hybrid battery through the inverter/converter when necessary, and the hybrid battery charges the 12v battery.

no alternator on a prius

 

There is no alternator. The simplest answer is the high voltage battery will maintain the 12V battery whenever the car is in READY and not in Neutral. Not in READY, all power is supplied by the 12V battery. The car will protect the 12V battery from excessive discharge by shutting down the car if left too long. In READY -> Neutral, the high voltage circuit is also disconnected, so don't stay in N too long either.

 

That is a bit too simple.
The HV batttery doesn't do that directly but through a voltage converter (commonly called an inverter).

But.....why do you ask ?

 

To be a bit more specific, there is a DC to DC converter in the inverter assembly which drops the high voltage DC from the hybrid battery to low voltage DC to maintain the charge on the 12 volt battery. When the car is in READY mode, the DC/DC converter supplies ~13.8 VDC to the 12 volt battery.

 

@zaitoun can you describe your use of the car? Are you driving a lot, most days, or short trips and multiple days where the car isn't used? Or somewhere in between?

 

Yes, @zaitoun l are you concerned the battery may be failing?

Multiple short trips daily, say adding up to at least 10 miles, and say every other day at most, your battery should be getting enough charging through use. If it's every second or third day you use it, and a single daily trip, say 2~3 miles only, then the battery may be chronically undercharged. Good for both the battery and engine to occasionally do longer trips too.

 

I think Gen 4 manages battery better than older models. Mine is 4½yrs old - and since lockdown, I'm often only driving twice a week - and it's been fine.

 

Mine is over 3 1/2 years old now and battery coping well too. It's quite common at the moment for me not to use my car for a couple of weeks and all is well. I did put my maintainer on this past weekend just to give it a little boost as I haven't used it for nearly three weeks as a precaution.

 

For those interested, it might be a good idea to start a thread for Gen4 prius 12 volt battery charging behavior much like @Rob43 started for the Prime
12v Battery Is Discharging, Re-Charge Now ! | PriusChat

I'm the second to admit I really don't know how Gen 4 - both Prime and orther Gen4 models charges / discharges the 12 volt. Rob43 was the first I've seen anyways, to admit he doesn't fully understand how it works.

My Primes 12 volt readings jump around so much and don't always behave the same way any two times after the same drive or charging session.

 

It's been well described by John Kelly, WEBER State University - here are 2 - the first specifically is on a Gen 4, but I suspect is similar to PRIME:

THIS next one refers to the OLD VERSIONS of PRIUS - but the general systems are similar, and he talks about concepts more:

 

@alanclarkeau Thanks for the video links, they explain a lot concerning the gen4 12 volt charging system.

By just looking at my Primes 12 volt flooded battery, I was not aware of the 12 volt battery's temp sensor and still don't know where it's located or the connections used to acquire it's data. <-to do list > Since the HyCam's AGM battery used in the second video John Kelly shows the temp sensor of it is right on the AGM battery.

The thing is that what's discussed in the Gen4 vidwo is mostly concerned with diagnosing the 12 volt charging system. That's typically done in temp controlled surroundings. Thus when temps are very low and the 12 volt may or may not be closer to or below the 12 volt minimum stated for the bottom end of the 12 volt battery SoC
(state of charge, after removing the surface charge) during the diagnostic, than 12 volt battery health becomes harder to diagnose And 12 volt failure tends to happen more often during very cold temps which is the season here in most of the US.

Our first night below freezing, in the morning I read 11.9x on our 12 volt. So. I'm going to keep a closer eye on 12 volt health during the coming season to try and nail down some of the variables involved. And bone up on that battery temp sensor stuff too. Not to mention, when the 12 volt is reading below 12 volt in the freezing cold, I don't really want to turn on the headlights, heat on high and defrosters just to check the 12 volts state of health.

anyone know how much those 3 flukes RMS meters + 2 clamp ons Prof John Kelly is using go for?

 

I was going to ask why you seem to be SO obsessed with your 12 Volt battery but then I remembered what forum this is in.

11.9 with no load, or a very small load, indicates that it is a bit BELOW half discharged.......so maybe you should be concerned.......now.

Harbor Freight sells a little red meter for about $8. It is more than adequate for most home uses.

 

It's the wide range of 12 volt readings that's got me stumped. Than there is the inconsistency of readings when I think they should be the same of similar. That's just freaky.

I've got a few of those HF meters one red and a couple yellow too. I also have a clampon, but not a fluke RMS meter and clamp on and I have an old Radio Shack digital multi I use on the 12 volt in the Prime

All my meters combined and an inexpensive thermocouple probably cost less than one of those fluke clamp on's. much less one of those meters, even if they're the cheap flukes

 

That was a question I had initially - I was used to - back in Dad's first car from the '50s, a voltmeter and an ammeter on the dashboard - and the volts stayed quite static once settled.

But someone, I think on PriusChat, back when I first got mine, said something like - just remember that it's not like the olden days with a voltage regulator - the computer does its own thing, playing games with High Voltage battery and 12 volts - just let it do it and ignore it.

 

I just found this thread. As I was reading along, I thought, "I guess I'm going to have to link to Professor Kelly's video on charging the Gen 4 12V." Buuuuuttttt ... ya beat me to it. Fascinating stuft, btw.

 

I don't find it freaky. My understanding is there is "smart" recharge of the 12V. When first going to READY, the DC volts is in the 14+/- range, meaning it is charging the 12V. After a little bit, the DC volts drops to around 13+/-, meaning the 12V is charged. If you continue to drive, it will increase back to 14 as needed to keep the 12V charged. You can monitor this while driving with a plug in voltmeter like this,

 

I have one of those, too. It's pretty educational. Too bad the 12V socket is in such an inconvenient place under the center arm rest on my '17 Prime.