Prius Prime - 12V Charging System

I've never owned a Prius less than seven years old; my current one is a decade, and I parted with the last one at 15. If there's any degradation over time in the DC/DC converter output capability, it sure doesn't happen on a scale anything like two years. It pretty much keeps on ticking.

It's built roughly like a 1500 watt power supply for a computer: solid state, no moving parts, electronically regulated. If one is going to fail, it's probably more likely to just go lights-out at some point than it is to slowly drop off.

It will shut off on you if the liquid cooling pump wears out and the electronics get too hot, but usually it'll be right back in business again when it cools, all you have to do is swap the pump.

 

Can we assume that you're experiencing a 12v battery charging issue ?


Rob43

 

I now know what's wrong with your Prime, you have a weak 12v battery that's in poor shape. It's most likely on it's way out right now, the BIG problem is your "aftermarket stereo system with an amplifier". Your stereo & amp is reeking havoc on your 12v battery.

Buy a new aftermarket 12v battery and then go the extra mile by frequently putting it on a trickle charger.

12v Battery Is Discharging, Re-Charge Now ! | PriusChat


Rob43

 

Probably hit the bulls eye here. Also, if you're not driving it often & far enough, the 12V state of charge will gradually get weak. That would be aggravated by a high power stereo. And those warnings you're getting seem like ones that could come from too low voltage on the 12V buss.

 

I still highly recommend checking & occasionally trickle charging your 12v battery...even if it's brand new.



Rob43

PS, I literally just took off my 12v / 0.75 amp "Battery Tender" as you were typing. My OE 12v battery is nearing the end of its useful life.

 

Can you explain about the "100A capable charging system"? 12v battery in the PRIME needs less than 5A to charge externally, anything higher is not recommended. Why do you think the internal DC-DC charging system is using anything more to charge a 12v battery?

 

I can't comment on your car stereo needs...

As to 12v replacement, my typical 12v resting voltage is barely 12.3 volts, sometimes less. Recently I was playing with an old 12v GPS unit & killed my 12v battery down to 5.85 volts...ouch. My Prime lit up like a Christmas tree, I immediately gave it a Big Charging protocol and brought it back to life.

So probably soon-ish.


Rob43

 

We still don't know how long or frequent your drives are. Lots of people (not just Prius people) are finding nearly dead batteries from cars sitting idle for long periods due to COVID imprisonment and then only making short trips that don't charge long enough to bring the battery back up. Modern cars are only completely off if you disconnect the battery.

 

While that is true for many cars nowadays, I agree with OP that it is strange to see the error message coming back only 2-3 days after replacing 12v battery.

 

Good point. Sounds more like a larger than normal parasitic drain.

 

And, as OP commented if the aftermarket power amp is the culprit, why would it start causing the problem now especially on a brand new replacement battery that did not happen for 18 months after the installation of the amp. I don't have a good explanation, but it does seem something has changed, as OP is speculating.

 

perhaps something went bad in the amp. if the errors don't come back, i would read up on audio mods. many people have had problems over the years. read gen 3, there is a lot of good info there. and prime is even worse for 12v problems.

 

If the OP has any more problems, I'd strongly recommend the purchase of a BM2 Battery Monitor or similar. That will allow ongoing monitoring of battery voltage. Actually, I'd recommend that to any Prime owner.

The 100A output capability of the inverter was reported in the Youtube video on the Prius charging system that was posted by WeberAuto. Although it's for the Prius rather than the Prime, I think he states that they're the same. But that 100A only gives you 1200 to 1400W total for all the needs of the battery, the car, and the amp. Yes, the amp will rarely, if ever, ask for that much power, but how forgiving is the inverter when it sees an overload? Recent vintage Converter/Inverter assemblies start at around US$200 - $300 on ebay. Do you feel lucky?

I know nothing about big car stereos, but I'd be tempted to power one up through a relay so that it's totally disconnected until the car is in Ready mode. That would remove any vampire drain. I don't know if a big amp needs power to remember anything. I would also fuse it at a level that guarantees that it could never overload the inverter. Just remember that there are no guarantees!

 

+1
It makes sooooo easy to monitor and know when the battery needs to be charged.