DIY "Mild" Plug-in Prius Project: Grid-powering the 12v side w/ deep cycle batteries

[orange4boy]

Some current accounting: NHW11

I just figured out the rough efficiency of the DC-DC but it's based on the headlights being 55 watts each.

As per the Graham scanner showing ~300V Low beams draw @ .51 Amps that's 153 watts. 55 x 2 = 110 watts leaving 43 extra watts. That works out to ~72% efficiency.

Other electrical loads. 2003 NHW11.
Running lights: .12 A / 36 watts
Headlights: .57 A / 171 watts high beams .51 A / 153 watts low beams.
Brake lights: .37 A / 111 watts
Rear defrost 1 A / 300 watts
Fan setting in amps: 1) .21 / 63 watts 2) .34 / 102 watts 3) .52 / 156 watts 4) .65 / 195 watts
Steering draws about 1A / 300 watts only while turning wheel, stopped, on gravel.

[orange4boy]

I just disconnected the DC-DC converter output and hooked up a deep cycle battery. Ouch! The Prius is an electricity pig. This may give greater returns than I expected.

Normally on my Previa, with a fully charged battery, the voltage stays above 12V for a couple of miles before it settles around 11.8 and slowly drops from there.

The Prius sucked it down to 11.4 right off the bat and below 11 with the low beams on.

The ECU seems to decide to throw a code only after the voltage drops below 12. I will have to try this again and see if hooking up a 14.4 v battery to the sense wire does the trick. That way I don't need a DC-DC up converter to get 14.4 out of the 12V deep cycles.

Then, the next time I'm under the inverter I will install a big old disconnect in there so I can fire up the DC - DC when the deep cycles are flat.

[bwilson4web]

One NHW11 trick to avoid having the daylight running lights on is to set the parking brake before starting the car. They stay off until the car is put in gear and the parking brake released.

Also, you may want to double check some of the braking loads. The power assisted brakes are motor driven. Static testing may be a little tricky but I would expect similar loads to the steering test. Perhaps have the parking brake on, shift into gear and then repeat the brake test with significant force.

Bob Wilson

[orange4boy]

The brake pump ran a couple of times. Seemed like about an amp for a few seconds.

I did the DRL disable a couple of days ago. so I'm set there.

I drove it today for the first time with the DC-DC disconnected and a deep cycle battery in the trunk. Once the initial code is erased, it keeps quiet. I forgot to reset the MFD trip mileage tho. *palm head* Without the driveway I get 4.3, with it ~5.3

The most noticeable thing was the SOC increased a bit. Usually it goes from 56% to 60% then back to 56% but today it just kept climbing and ended at 62.5% Too soon to know if that's because of the reduced demands or not but some of it must be.

I think the electric assist was working more too but I'm not sure of that. I don't EV on the flat parts anymore to save the SOC for the driveway.

[orange4boy]

It's going well so far. The HV pack builds up on each trip if I don't use EV on the flat part of the road. When I EV on the road section I end up with 4.8 L/100 when I don't I get about 5 L/100.

The battery is waking up nicely. It's been sitting around for a couple of months. It dips to about 11.8 - 12.2. It sure would be nice to have the extra 2 volts. The headlights are a bit dimmer than normal. The oncoming traffic is probably happier though.

It does make an FE difference. At this point I would guess 5-10%. Those numbers seem to match the calculations I did, roughly anyhow. More runs will tell.

[Daox]

Good stuff Marcus. Keep us updated. It really does seem like the Prius is an energy hog sadly.

[bwilson4web]

Originally Posted by Daox

. . . It really does seem like the Prius is an energy hog sadly.

Guess I'll have to drag my sorry carcass back to work at a miserable 50+ MPG. Woe is me.

Next week, I might as well trade-in my 'energy hog' Prius and get one of those energy thrifty, GM SUVs, like they tell us in the commercial.

Bob Wilson

[Daox]

lol Bob, lets not get all dramatic.

That is a significant draw. And, while I expected the Prius to draw more than the average econobox, it seems a fair amount more.

[bwilson4web]

I was just teasing but the point is well taken about the vehicle idle overhead considering:

• electric power steering - instead of a mechanical hydraulic pump
• electric assisted braking - instead of a manifold vacuum and bellows
• electric air conditioner compressor - instead of belt driven
• electric water pump - instead of belt driven

Each of these loads will have peak values but even my 2003, NHW11 with daylight running lights on draws ~1.6A @275 V ~= 440 W. (the amps vary.) I haven't tried to measure the ZVW30, engine off load, yet, but from what I've seen of the systems, I suspect it is in the same range.

So putting things in perspective, the rule of thumb I use is ~250 wHr/mile for most vehicles. In an hour, the Prius idle electrical load would be almost 2 miles of travel. But I would caution that the additional load of power steering, braking, air conditioner and intermittent water pump could easily dwarf the idle overhead. A vehicle designer might see these as predominant and not think of the idle overhead as being significant.

Bob Wilson

[Daox]

Do you know which of chose major devices run off 12V vs the HV pack?