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

One of the things I'd like to try is powering the 12V load on my Prius with a deep cycle battery pack like I do with the Golden Egg. This would take a load off the ICE without having to do a big, expensive PHEV conversion which can't be done on the NHW11 in any event. For instance, running the heater fan can cause the ICE to start when it would otherwise be off.

Bob, I saw in a post you made on Green Hybrid, your idea of a turbo alternator. So you were thinking along those lines, sort of, although you may have been thinking more along the lines of supplying the main pack.

Has anyone done a DC-DC 12V bypass or parallel with a battery pack? I would think there were some good FE gains to be had there. How is the 12V regulated and is this hack possible?

My first hack was to install a 1 kW, modified sine wave inverter. This schematic shows the 12 VDC system:
http://hiwaay.net/~bzwilson/prius/priups_00.jpg
The "HVC" is the vehicle inverter operated by the hybrid vehicle ECU. I believe there is a voltage sensor that runs from the trunk mounted 12 VDC battery to the front. The nominal 12 VDC voltage when the vehicle is running is 13.8 VDC. Be careful with the 12 VDC system as several Prius have had their control computers fried by accidental, reverse polarity during a jump.

The measured 12 VDC load runs ~450 W although others have reported as low as 350 W. Regardless, it is a significant load. You can get a feel for it by reprogramming the Graham scanner. Since the maximum, battery module voltage differences are ~0.1 V, they can be replaced for your study:

• cycle so the line to be replaced is on the display
• tap the middle MODE so the first data item blinks
• tap left and right until the first desired value shows up
• tap middle MODE so second data item blinks
• tap left and right until desired data value shows up
• hit middle MODE until back to the select line to display
• hit right or left until the line to replace is showing with the original values
• hold the right button for a slow count of 3 to replace the displayed values - the new values will show up
• if you don't want to keep these values, hit "RESET"
• if you want to keep these value, turn the car off and it will save them for the next power on

I would recommend changing to monitor traction battery voltage and current. Then turn the car on, not running, and use the current and voltage to calculate the overhead load of the car. My memory is ~450 W. Turn on the head lights (Ok, the tail lights to work with the daylight running lights) and use brights and the cabin fans to see the additional load. For fun, press the brakes and see the power draw.

I would recommend getting the electrical diagram manual as your circuit road map. Given the 450W, ~ 1/2 hp, 12 VDC electrical load, it should make a significant improvement.

If I can make a table, I'd like to start a separate thread discussing NHW11 mods and the price-performance tradeoffs. Experimentation is good and hopefully this may give some ideas.

Bob Wilson

Thanks for the info, Bob.

I knew you would understand what I meant.

I'm trying to figure out a way of describing this and writing a good thread title so other hybrid owners would understand. In the ICE crowd you would just call it an alternator delete and everyone gets it. The Prius is a different animal

Some title ideas:

Running Prius 12V system with deep cycle batteries.
DC-DC bypass: Plug in 12V system for Prius.
Improving Prius MPG: 12V load supplied by plug-in pack.

I think the first one is the clearest.

p.s. I'll probably do the UPS Prius too at some point. We have a lot of outages here. The other day I brought my deep cycles and inverter over to my Honey's work so they could keep open during an outage. An extention cord from the car would be easier and very slick:cool:

If I were doing it, I would probably approach using a step-up, power supply rated at say 600 W (~45 A @13.8 VDC). It would use a current regulating circuit to tickle the voltage up and displace the inverter load. As soon as the target current from the deep storage battery was reached, hold it there.

The advantage is you won't have to break any circuits and it should minimize worry about open-loop, voltage feedback. You may run into some feedback instability but current sense regulators at these voltages and current levels should be standard parts.

One risk is the slightly higher voltage may lead to incandescent lights being a little "bright" and possibly shorter life. ... Tradeoffs.

Bob Wilson

I do too, but I'd juice it up by adding something like: DIY "mild" plug-in Prius: powering the 12v system from the grid/deep cycle batts" :)

I love that you're already planning further efficiency mods.

The forum software isn't terribly table-friendy, but it is doable.

See this thread for information: http://ecomodder.com/forum/showthrea...aces-6412.html

Ha Ha, I basjoosed my headlights and weather stripped the engine compartment yesterday. CAN'T. STOP. ECOMODDING. HELP.

If I knew more about electronics, I would probably agree with that approach. I will look into a current regulator and see if it's something I can handle. I was hoping for a simpler approach but I suppose I should start the new thread to describe what I hope to do.

Please never let my suggestions be anything other than that ... there is more than one way to 'skin that cat.' <GRINS>

The "Toyota Prius Electrical Wiring Diagram, 2003 Model" is publication EWD893U would be an excellent guide. Looking on pp. 50 and pp. 59, it looks like the main inverter 12 VDC supply and sense lines are:

• C5 connector, pin 1 - main supply, WHITE
• C4 connector, pin 3 - sense or secondary 5A line from aux B+ terminal, BLACK with RED STRIPE
• C4 connector, pin 1 - IGCT unknown, WHITE with GREEN stripe to all ECUs
• C4 connector, pin 2 - IDH unknown, YELLOW to A/C amplifier

Understand you are in new territory and I tend to be a conservative engineer. So I would probably do a lot of checking before trying to substitute a nominal 12.x VDC battery for the 13.8 VDC generated by the inverter. One wild thought, a 24 VDC deep discharge battery could be stepped down using a switching power supply to just about any lower voltage fairly easily and efficiently.

Bob Wilson

This has been done before so hopefully I will be able to get some specific info before I do anything:
http://www.veva.bc.ca/articles/PHCdemoArticle080211.pdf

I will try to get some information from the owner, who is a member of VEVA and has rebuilt several Prii:
http://peopleshybrid.com/index.htm

I like that idea better. 24V is better because it seems to be easier to find and implement a down converter than a boost converter. Also, I will need at least 2 batteries if the overhead is indeed 300+ watts. I'm not concerned about the extra weight because it's well known that cutting ICE electrical overhead outweighs the added weight of batteries. Ha Ha.

Questions to be answered assuming a 12V nominal system:

Will the lower voltage (under 13.5V) set codes? My guess is that it might if it gets too low. Prii with dying 12V batteries exhibit all kinds of strange behaviours. Although a dying battery will probably be sub 10V under load. The graham scanner sees 11.3 on mine with the hybrid system off so there seems to be some flexibility.

I noticed, from the EWD that there seem to be quite a few different blocks or busses. I was thinking, If there was a simple way to keep the DC-DC happy by leaving it to run the ECU's, or at least the engine bus then it would be less likely to set any codes. I have noticed on my van that some sensors (eg. coolant temp) read low when the voltage gets low.

What is the electrical efficiency of the THS from ICE (35%eff) to MG(?%Eff) to battery(?%Eff) to DC-DC(?%Eff) to 12V? How does it compare to a regular ICE(20%Eff) belt(?%Eff) Alternator(45%Eff) 12V?

Is the DC-DC a simple load based unit? Will it just supply what is asked of it and no more?

What happens to a stock Prius if the DC-DC goes offline while driving? If the car still operates then we know it would be possible to simply substitute the 12V supply. (better if 13.5V)

Will it be a simple/desireable thing to supply some blocks with 12V and some with the DC-DC?

Should I have a relay set up to switch between systems for long trips when the batteries get low?

Fun stuff.

Another interesting idea:

Take some Prius battery modules and make a series of parallel (2X7.2V) 14.4V packs. Would possibly need a custom charger (beyond me) and a custom clamp system. (Simple job for me).

Don't know how they would stand up to repeated deep cycles.

If I'm not mistaken a Gen1 pack, rewired, would yield 19 - 14.4V blocks @ 6.5ah = 123.5 Ah. If you could get one cheap, that is.

My lead acids are 120Ah each for $49 a piece and I already have chargers.

Lead acid: 30-40 Wh/kg
Prius NiMH: 46 Wh/kg

Excellent! I always enjoy using the fruits of proven technology ... <GRINS>
My old man's brain may not always be the swiftest ... but occasionally even a blind pig finds an acorn. <GRINS>
Once the car starts, the inverter provides enough voltage to run without a battery. Good Prius friend Hobbit performed that experiment.

That is the funny thing. We find intermittent problems that suddenly disappear when a good aux battery is installed. My OEM battery lasted until January of this year ... 4 years? I had to change it before flying to Detroit in January.

All the right questions.

To the best of my knowledge, no one has done a through job of researching this. I have fuel consumption figures for my inverter setup but I've not tried to work the problem back to the source(s).

Once I start drawing 1 kW, the voltage drops off keeping the 1 kW power but now with more amps and less volts.

Fun stuff indeed! I've not tried that experiment but you are asking the right questions. <GRINS>

GOOD LUCK!
Bob Wilson

Thanks for the above, Bob.

I've been studying the EWDs and there are some mysteries. One thing that seems obvious is that the inverter powers two main branches, One with the 12V on it with some basic functions and another, isolated from the 12V battery with a much higher total load. It may turn out they are all on a communal bus, but that is how it looks from here. It somehow does not seem logical, on reflection because it would mean that the DC-DC has two isolated output branches. Possible for redundancy but not likely.

I need to find out what the function is of the three leads which are mentioned below...

One is apparently a sense lead but for what? Why does the DC-DC need that when it has the main line right there? Just thinking out loud.

Back to the diagrams...

The area of concern:

http://ecomodder.com/forum/member-or...-prius-ewd.jpg

Mystery one solved.

The green/black wire from the 12V battery block is the main ignition relay wire.

Mystery two:

There is only one main power wire from the DC-DC: White.

What else would the DC-DC wires be?

1) 5A black/red: Main start up power? Battery charging wire? This would only make sense if the battery could be isolated. Most alternator systems just vary the whole system voltage which the battery happens to be attached to.

2) Voltage sense wire.

3) amp sense wire.

4) HV supply. This must be the shielded HV wires.

5) Temperature sense wire.

Exciting news!

I tried a few simple experiments with the NHW11.

I disconnected the main 12V supply wire from the inverter. The larger grey connector/white wire below the MG2 main cables at the back of the inverter. Started the car and got P3004 Power Cable Malfunction (Prius), P3125 Converter & Inverter Assembly Malfunction (Prius), triangle etc. Still ran.

Hooked up my 50A switch mode battery charger to the 12V battery and set it to 50A. ~ 14.5V Codes and triangle remained. Cleared codes with Graham scanner:D... turned off car and started again... Ran fine, no codes, no triangle.

Running load showed a little less than 20 amps. I tried fans and lights and some other loads which added to that but not as much as my van. Apparently they have designed some pretty efficient electrics in the Prius. I will try to do a detailed study of the loads if there is no other reference.

Then I shut off the car, disconnected the charger and started it on the 12V battery alone. It worked and the codes did not come back. All the way down to 11.3V

Then turned off the car and plugged the inverter connector back in. All good and showing 13.8V at the battery.

My question is why did the codes not come back when I ran with just the 12V battery the second time? Does the ECU ignore faults for a while after you clear them?

Conclusion: The car runs on just the 12V battery with the main inverter supply wire disconnected. This means it should be a fairly simple thing to supply the 12V system with plug in juice. I may ultimately need a good 100A DC-DC converter for whichever battery pack I decide to use. Hopefully the voltage is the trigger in which case one simply must keep the supply above x-volts to keep the ECU happy.

We shall see.

Excellent news!

If you get a chance, see what the Graham scanner reports for the traction battery current with and without the inverter 20 A. (14.5 * 20 = 290 W.) A detailed load study is an excellent idea. You wouldn't want the control computers to 'lose their mind' if someone flipped on a high current load, say window defrosters and windshield wipers, at the same time. Probably anything with a fuse greater than the 20 A. would be a good candidate and as well as the brakes (electric accumulator.) You are also in a position to see how low the 12 VDC system can go before obvious codes are throw.

Hummmm, 290/745 ~= ~.39 hp, nominal savings.

GOOD WORK!

LATE THOUGHT:
This mode, where the deep discharge battery and charger provides the operating current provides a 'fail safe' with one risk ... over charging the existing AUX battery. I had a generator voltage regulator once fail and the 12 VDC battery got hot enough to emit acidic steam ... an interesting problem.

Bob Wilson

Driving into work, it occurred to me there is a very simple circuit that could easily work:

1. 100 A diode - inverter output to 'white wire' - this will typically drop about 1.2 V making the output voltage closer to 12.6 VDC if any current flows from the inverter
2. 13.9 VDC DC-DC converter output voltage - except for any possible voltage drop, the deep-discharge battery should provide the bulk of the power. Then when it goes 'dead', the vehicle inverter picks up the load.

You'd still need some sort of indicator that the deep-discharge battery is drained. Also, you'll need a 12 V. battery to provide starting power if the deep-discharge battery is 'out of juice.' ... Just a thought.

Bob Wilson

I did think of this and have had the issue before. I was experimenting with alternator delete and supplying 14.5V to the system so I installed a battery isolating solenoid to take it out of the system. But that's a manual system. If the voltage was kept =or<13.5V then you would not have to worry about overcharging. Perhaps another big diode on the 12V battery?

Your idea is more elegant, simpler and provides some measure of automation. Would the voltage after the diode still be lower when the Prius converter takes over? I'm sure there is a way to design a circuit that would solve that problem automatically but I'm not the man for that design although I could build it, given a diagram. That could be done later when we get proof of concept. The math is good but the real world always has the final say. As the kids say..."Reality bites".

I think the People's Hybrid system used 4 x 50 amp DC-DC converters in parallel which might make the whole thing cheaper. I've tried to find high amp converters and they are $$$$$ but lower ones are $.

Now if we could find out where the ECU get's it's Voltage signal and leave the Prius converter hooked up to that then we don't need any $$$ converters.

This is why I was hoping for efficiency numbers on the MGs and converter. In a standard stone age system, it's more than double.

Oh, right...(smacks forehead) Form the current draw on the traction battery I could figure the efficiency of the DC-DC. That's one down...

Terribly exciting. Not as sexy as a PHEV conversion but massively easier and cheaper.

I was thinking about this at lunch and realized the deep-cycle battery only has to provide the 90% load over the time, vehicle base load, and let the vehicle inverter with diode handle the peak loads (aka., rear window defroster, windshield wipers, night driving lights and brake.) Anything over that would drop the output voltage and the inverter would then provide the make-up or peak power. For example, you measured ~20 A. in your first test. Add whatever you consider to be additional, standard load plus 5-10% and that would be your deep-cycle battery DC-DC converter design goal << 100 A. <grins>

This also, in theory, means we can lighten up the power diode, forward current limit and use a less expensive part. However, there are tons of automotive alternator diodes out there that should easily be within this range and quite affordable.

One other thing, the vehicle ECUs use 'cheap' DRAM for persistent memory. What this means is losing the 12 VDC wipes out not only the clock and radio stations but also the ICE Lambda constants. Many have noticed that it takes a couple of runs before the Prius 'relearns' these values and becomes more efficient again.

Bob Wilson

ps. CBS3502412 (300W) or CBS3504812 (348W) would be a very nice converter and Allied sells them $171.53 ... <hummm> Also, the TI PT7750, 15A is another nice part. Then there is is Ebay part: 160381658887 ... sounds too good to be true.

More good ideas.

This only happens when the 12V is disconnected though right? Not if it just drops below 12v.

For now I'm going to test it with my 12V batteries - 750 watt inverter - 50 amp switch-mode charger - 12V Prius. Some losses from the batteries there but it's all the same to the Prius.

In the meantime I should be on the lookout for some big-ass diodes and hopefully a similarly big-ass DC-DC. The diodes reside in the voltage regulators, yes? Or are they mounted on the alternator?

Is the diode simply wired in line with the Prius DC-DC main wire? Which way should the "ring" face.

I'm going to need block heaters to get decent mileage in the winter here. I just did two trips to the Cove and back and the Km/100 bars traced a hyperbolic curve down from the cold drive to the warm.

Excellent approach. You'll get a rough-order feedback on the potential fuel savings without putting a lot of money in the project. If it looks good after and "A" "B" "A" test, then an optimized design makes sense.
It varies. I was looking at Ebay and saw a Ford and Chyrsler external set set of 100 A diodes but I haven't checked Digikey, Allied and Mouser, yet. What really surprised me were some Schottky diodes. These have an unusually low forward voltage drop.
The 'ring' should be the direction the "+" charges exit. Just check it with a battery and VOM. The positive charges pass in the direction of the arrow towards the base.

In the USA we have to order block heaters from Canadian dealers.

Bob Wilson

Ouch!

I think that's the favourite of the DIY EV controller builders.

Found another too good to be true:DC 24V to 13.8V 65A Switching Power Converter H3800-65A on eBay (end time 07-Nov-09 09:28:30 GMT)

That's only $65 Can. Perhaps they mean 6.5 amps.

Interesting. I've seen more and more Chinese knock-offs but after the 48 V charger for my Ebike failed and I had a chance to see what they built, I'm uneasy with their quality. Sad to say, I've been frustrated at not getting a clean set of specs from the Chinese importers. Still, it might have some excellent parts.

You might ask the seller if they can share the "User's Guide." If so, look carefully for any power up order limitations (what caught me) or cautions about static charge protection. Still, nice specs and a great price ... almost too good.

Bob Wilson

Traced another few wires down.

(IGSW) Is the Main hybrid ECU power signal. (Not in the posted diagram) This wire traces from the hybrid ECU through the ignition key switch to the battery/DC-DC block.

(IGCT) The white/green in the EWD I posted seems to be the common power signal to all ECUs plus the converter. I traced it to an IGCT (ignition switch) relay controlled by the main hybrid ECU. The switch closes to a 12V battery/DC-DC common block.

(S) Black-red seems to be the supply power to the DC-DC. Fused. Goes back to the battery block #2. Not switched. If the battery were isolated by a relay then I would guess this to be the charging wire.

(NODD) The L-O ( blue orange? ) may be the amp or voltage lead. My bet is on Voltage since it is stated in the manual that the ECU judges a fault by comparing DC-DC output voltage to line voltage.

The yellow (IDH) which goes to the A/C amplifier may be a different voltage or perhaps the A/C is designed to shut down if the DC-DC fails to save battery power. Not important in any event

Also terminal block #1 on the right hand side of the engine compartment houses the 100A DC-DC fuse in the top left corner. Unfortunately difficult to remove because it's screwed to the block from below so the inverter has to come out to get to it.

Those are my best guesses.

Bob, Do you know if the Prius block heater is the same between models? I'm imagining some astronomical price for the Gen 1 and I know the Dealer will tell me they are different regarldess.

Then NHW11 and NHW20 have the same 1.5L engine block and the heater plugs into an obscure hole between the block and the firewall. The Echo and 1.5L Scions use the same block.

If you can get a hold of Wayne Mitchell, "firengineer" (?), at PriusChat, he would be the definitive source. Search the forums and you should locate him soon enough.

BTW, I like your circuit analysis. It makes sense that the other ECUs are only power enabled after the hybrid vehicle ECU comes up. Now there are two that probably have to be on 24x7:

• ignition key reader - queries the RFID and lets the HV ECU know it is "OK." I believe it is in the 'A/C amplifier' circuit.
• HV ECU - must respond to the "key is OK" signal to bring up the car

Bob Wilson

I did a bit of research to find out how efficient the Toyota Prius electrical system is.

For now I have had to rely on generic information, not Toyota's

This is interesting but I wonder if this is for full charge. Typically full charge has higher losses and partial charge can be very efficient such as in lead acid. Since the Prius uses "micro cycles" I would imagine the battery to be more efficient than 66%

At which rates does the Prius battery typically charge and discharge? I guess this could be figured from the Graham scanner by graphing battery current in and out.

My guesstimated electrical efficiency of the THS from ICE (35%eff) to MG(90%Eff) to battery(75%Eff) to DC-DC(85%Eff) to 12V?

So a 450 watt load requires very roughly 711 watts to produce from the 35% efficient engine-MG-battery-DC-DC-12v. Some of that is recovered energy though so there are too many variables to be accurate. For instance, It would be much more efficient if it came directly from the MGs.

How does it compare to a regular ICE(20%Eff) belt(?%Eff) Alternator(45%Eff) 12V? It's better. A 450 watt load requires roughly 837 watts from the 20% efficient engine.

Still, in both cases, the running electrical load is a substantial drain on the system.

Hi,

My refurbishment experiments suggests the health and status of the modules has a lot to do with NiMH battery efficiency:
http://hiwaay.net/~bzwilson/prius/pri_batt_300.jpg

It is enough that after replacing a traction battery pack, there is a period of 3-4 months where the MPG shows about a +2-4 MPG over the following, years of performance. I saw this first in the Dept. of Energy Prius fleet studies and later in Patrick Wong's data.

Bob Wilson

That's great. I also read that the generators are about 90-95% efficient which is about as good as production electric motors get.

What would be interesting is a test to see if there's a difference in mileage between no accessories and a slew of some measurable ones on. The Prius is a bit different because the HV battery is so variable that it may not show up quickly but taking stock of SOC might help.

That would give me some indication of the efficiency and what I can expect. The calculated electrical load numbers on ICE cars correspond nicely to the MPG numbers.

I can't do a good test here because of all the hills though. Any takers?

From the below graph we can see that at 45mph the NHW11 requires ~10 hp. If the running draw is 1 hp including all losses, that's 10% just like a regular ICE car.

The graham scanner reports the HV battey is supplying 1.5 to 2.5 amps of ~270 Volts to the DC-DC converter to run the basic requirements. that's .54 to .9 horsepower before calculating in the generator and battery losses, which means that the engine has to come up with a bit more than that accumulated power somewhere in the driving cycle. Since that draw is constant during ready mode, that's quite a few of watts all told.


http://hiwaay.net/~bzwilson/prius/ca..._MPG_Rev_B.jpg

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.

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.

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

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.

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.

Good stuff Marcus. Keep us updated. 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

lol Bob, lets not get all dramatic. :p

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

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

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