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

[orange4boy]

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?

[bwilson4web]

My first hack was to install a 1 kW, modified sine wave inverter. This schematic shows the 12 VDC system:

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

[orange4boy]

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

[bwilson4web]

Originally Posted by orange4boy

. . .
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.
. . .

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

[MetroMPG]

Originally Posted by orange4boy

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.

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.

[MetroMPG]

Originally Posted by bwilson4web

If I can make a table, I'd like to start a separate thread discussing NHW11 mods and the price-performance tradeoffs.

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

[orange4boy]

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

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

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.

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.

[bwilson4web]

Originally Posted by orange4boy

. . .
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

[orange4boy]

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.

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

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.

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.

[orange4boy]

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