Help me understand the Prius electrical system

There was a post on the Prius Technical Stuff Yahoo group a while back with typical current draws for the 12 volt system. And yes, it would be possible to supplement the 12 volt system with a solar panel if you connect at the 12v battery so the inverter sense wire can see the voltage.

Wayne

 

Keep in mind if you are trying to help with overall fuel consumption, it is better to put a real PV array on the roof of your house and forget about carrying one around on your Prius. If you want to do it for fun or show, then that's a different story.

Tom

 

Fair enough. You are correct that any 12V power supplied by a PV panel is power not drawn from the HV bus and ultimately from gasoline. The amount is small at best, and probably does not justify the cost and weight of a PV panel.

Several of us have talked about just this idea in regard to the new 2010 and the integrated PV panel. If you have it on the car anyway, it might be fun to tie it into the 12V system.

Tom

 

Perhaps the most practical use for an integrated PV on the car, asides from ensuring the 12 vdc battery is kept fully charged, is to power a fan.

That way, when the car is parked in the boiling hot sun, at least it won't be a solar oven inside

As far as overall "footprint" a home PV makes a lot more sense, and has more potential to make a difference. Say when small desirable EV commuter cars are finally mainstream

:flypig:

You could charge the batteries with the home PV system

 

I disagree with your assertion that the onboard electronics cumulatively draw 1A from the 13.8VDC bus. That implies that the ECUs in total require 14 watts of power. Recall that power steering/brakes are also powered by this bus, as is the rear window defroster, the cabin ventilation fan, two PTC electric heaters, and vehicle lighting.

Although I haven't measured the current draw, my guess is that the ongoing power requirement would be more like 20A-30A without having the defroster, cabin fan, and lighting on. Remember that Prius has many ECUs: engine, hybrid vehicle, traction battery, skid control, power steering, air conditioning, transaxle gear select, immobilizer, body, smart, etc. With all electrical accessories on, the cumulative current draw might be as high as 70A-80A.

Therefore, the contribution that a roof-mounted solar array might provide is quite minor compared to the ongoing electrical draw upon the system and the cost of such array. The only use that Toyota can make of its 2010 roof-mounted solar array is to spin the cabin ventilation fan when the car is IG-OFF, which probably requires current of 3A-5A.

 

According to Hobbit, the base load is 300-400W - 25-35A at nominal 12V.

 

OK, since the 12V bus operates at ~13.8V, then current flow will be 22A-29A.

 

Shoot, you can't even run a small microwave oven on that.

Tom

 

That would be the base load while operating. The best a 15W panel could do would be to top off the 12V battery when parked in Sunlight. The MPG savings would be negligible, surely much less than 1%.

 

Anyone with a scangauge can see the hybrid battery current with
the car in READY and stopped. Between 1.2 and 1.5 amps, if I
remember off the top of my head. [I monitor my current with an
analog meter and so rarely see a fine-resolution figure.] Do
the math to translate from ~ 230V to 13.8, and there's your
watts in the 12V system.
.
If you feel the top of the MFD after everything's been on for
a while and *not* in the sunlight, it's easy to believe that
all those little boxes taken together, and the inverter pump
and whatever else, is pulling 350+ watts all told.
.
_H*

 

Sure, summer driving at night, that area is downright toasty