Do 12v Accessories Drain Traction Or Starting Battery When Prius "ON"?

I've run the electric cooler in a non-Prius vehicle and been OK for a couple hours but killed the battery after 5 or so hours. I've heard the Prius 12v battery is not very big so I'd be cautious on this. I'm sure others here can provide more details than I can.

 

blew head gaskets?.. in your prius?... really?...

you CAN run it off the 12v battery.. but it Really is easier to just leave the car in READY mode... so the big battery can feed your 12v line.. and cycle the engine on and off when necessary. expect to burn about a gallon every 10 to 12 hours... otherwise the 12v battery is 20 amps ( i faintly recall )... so... without droping below a decent starting voltage.. you'll probably only get an hour or two before forced to start the car.

so... yeah.. leave it in READY mode.

i used my car as a generator while i had a spark plug failure.. the car was not happy to be running but was functional.. also burnt about 2x the amount of fuel.... so worse case scenario... you'll just waste a little more fuel.

it beats using a generator since they are loud.. and constantly on.

 

He didn't blow the head gaskets in his Prius, he did in his Westfalia Vanagon. Since he can't drive it, he wants to take the Prius.


I'm not sure, but I would suspect with the power ON in the accessory mode, it would engage the hybrid battery.

 

uhhh... you don't want to drain the hybrid battery unless the engine is able to kick in to recharge it... it can't turn unless it has a charge... so.. keep it in ready mode. a 12v battery requires a jump to start the car. a drained hybrid battery requires a flat bed truck and a painful trip to your toyota dealer.

in ready mode..... your battery gets used... but the engine can turn on and recharge it. plus.. accessory mode has a timer.. er.. does in my gen II. 30 mins i think.

yes.. the car draws more power in ready mode... something like a couple hundred watts.. but... it's either fuel burnt or the chance of getting stranded.

 

I don't think the OP's question has been answered: If you have the Prius in Ready, 12V power is supplied by the HV battery. The engine will start as necessary to charge the battery as long as the shifter isn't in N.

Tom

 

The Prius has several potential power states that it can be set to. I think it would help if we can be precise about those power states:

IG-OFF where the vehicle is powered off.

ACC-ON where the MFD is on, instrument panel lights are off, and you can power up the stereo. The auxiliary 12V sockets are active.

IG-ON where the MFD is on, the instrument panel warning lights are on, and you can operate all electrical accessories including the power windows. Electrical current drain is quite high in this mode, do not leave the Prius in this condition for any lengthy period of time.

READY where the car can be driven. In this mode the DC to DC converter is providing 13.8VDC to the 12V bus, and keeping the 12V auxiliary battery charged.

Starting from IG-OFF, to switch to ACC-ON, press the POWER button once without depressing the brake pedal. Press the POWER button again without depressing the brake pedal to switch to IG-ON. Press the POWER button again to switch to IG-OFF.

Depress the brake pedal while pressing the POWER button to switch from IG-OFF (or the other ON modes) to READY.

The capacity of the 2G 12V auxiliary battery when new is in the mid 30 AH range if you have the Smart system, or 28 AH if you have a base model. The battery should not be drained below 50% capacity in the interest of maintaining a long service life. Hence if the OP wants to use a 4A load while the Prius is ACC-ON, the vehicle should be left in that state no more than four hours assuming the 12V battery is fully-charged.

If the OP leaves the Prius READY, then the only operating constraints are the amount of available fuel, the noise produced by the ICE, and the extent to which the vehicle is emitting hydrocarbons into the campsite.

 

Thanks for the update, glad to hear your camping trip was successful.

Looks like leaking head gaskets are common on that VW model:
vanagon.com - Wasserboxer Head Replacement
vanagon.com - Head Gasket Leaks

 

Thanks, very informative. I had 2 problems last year starting my Prius. Two were after leaving on Dome lights over night. The first was a deeper discharge by leaving lights, radio on, and doors open.

I assume that the starting battery ran down, and could not be charged because the car was off. But he dome lights can't be much of a load. 1/2 Amp???? Battery is 4 years old only. Maybe it was damaged from my first deep discharge???

 

Four years is a normal service life for a 12V battery in a Prius. The 12V batteries are fairly small, and fully discharging one takes some of its life.

When you say "could not be charged because the car was off" do you mean that it could not be charged by the car? In that case, no, it could not. You should be able to recharge using an external charger attached to the battery or jump points under the hood.

Tom

 

One additional piece of information (I have used one of these coolers for over 5 years in my 2004 Prius). It pulls about 4 amps (50 watts) from the 12v circuit which is not a problem for short time intervals in ACC mode as the 200v traction battery reliably has about 200 to 500 WattHours of energy available. Longer times (more than a couple of hours) do require that the Prius be in ready mode and in park (not neutral) or driving so that the ICE can supply the requires energy.

A Prius ICE averages about 20-30 hp (1.5 to 2.2 kWatts) of output when cruising at highway speed. The 50 watts used by the cooler is about 2.5% of that output so you should expect to see a 2.5% reduction in MPG (1 MPG) while running the cooler on a trip.

JeffD

 

The capacity of a new Prius 12V auxiliary battery is around 35 Ah. Since your battery is four years old its capacity has deteriorated, and might be 15-20Ah, or less by now.

How many lights were on? The front ceiling fixture has three lamps while the rear has one and the hatch has one. The front doors have courtesy lamps as well.

Suppose two 7W lights were on. That will draw ~1Ah. If you left the lights on from 6 PM until 7 AM the following day, that would be 13 hours or 13Ah. If you discharge the battery more than 50% of its capacity, it may not recover.