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

[orange4boy]

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

Ouch!

What really surprised me were some Schottky diodes. These have an unusually low forward voltage drop.

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

[orange4boy]

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.

[bwilson4web]

Originally Posted by orange4boy

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

[orange4boy]

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.

[orange4boy]

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.

[bwilson4web]

Originally Posted by orange4boy

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

[orange4boy]

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

The coulometric charging efficiency of nickel metal hydride batteries is typically 66%, meaning that you must put 150 amp hours into the battery for every 100 amp hours you get out. The faster you charge the worse this gets.

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%

Using a C/10 rate for charge and discharge I have found that almost every NiMH battery yields a ~98% cycle efficiency.

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.

[bwilson4web]

Hi,

My refurbishment experiments suggests the health and status of the modules has a lot to do with NiMH battery efficiency:


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

[orange4boy]

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?

[orange4boy]

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.