Plugin but without adding batteries??

One point not mentioned on this thread is: Suppose you have a green battery upon leaving home. Whether the car has no or 20 extra batteries, the system and engine must go thru its warm-up period for the first five minutes. I have left my garage in the morning with a full green battery and seemingly drove in stealth, however the first bar never wavered and always showed 25-35mpg. So the engine was running whether I liked it or not! You can't get around the Prius computers, if you could you would probably be working for Toyota.:rockon:

 

An EV button takes care of this issue.

Tom

 

So, in EV mode, engine warm-up is precluded and nonexistent?

 

Warm up is held off until the ICE needs to run.

Tom

 

OK, I guess it works.

 

Nothing commercial, but some people have jury rigged things for bench testing.

As already has been said - doing so will very probably significantly impact the life of the stock battery. It's not designed to be taken repeatedly from full to empty.

 

I don't get it. Not all energy comes from the ICE - some of it comes from braking. I've been able to go from 3 to 5 bars just in a braking cycle alone. It is not fair to say that not ALL energy comes form the ICE. Secondly, when I get stuck in stage 3, my average mpg is around 30-35. When I get to stage 4 and the car allows me to drive off the battery at times, my average mpg jumps up to 55. I'm not talking instantaneous, but cummulative average.

 

How did you get your car up to speed so that you could brake and recover some of that energy?

It would be more efficient if you did not use the brakes at all - brake regeneration only recovers a fraction of the energy at best due to losses in the generators, inverters and batteries.

 

I'm not a gearhead, but I never got this either. There are always times when I'm going to use the ICE regardless, so why not use battery when you can? My MPG always went up (over the long haul) when I batteried down a particular parkway on my morning commute.

 

Something like what you are asking for could be done, but would have very limited appeal and significant cost. If you want to try and figure something out, I would spend a lot of time reading up on the cal-cars method of PHEV conversion. This is an open-source project, so there is a lot of info out there. Theoretically, you could use the same basic idea they use. You'd need the car to be on, you'd need a CAN-View controller to read the battery SOC from the CAN bus. You'd need a power-supply capable of producing ~242-260V, preferably with a current limited output. You'd need a series of relays and contactors to connect and disconnect the charger from the battery and provide battery cooling/ventilation while charging. All that would probably run you in the range of $1200-$1500, but would be reasonably safe since you are keeping all the normal Prius safety and battery protection systems relatively intact.

IMHO, while the above may seem overly complicated its one of the few fairly safe ways to try and accomplish what you are trying to do. Part of the trick is if you don't use the Priuses built in systems to protect and monitor the battery, you have to have a very smart charger. NimH is very difficult to charge safely, as its voltage is not a good indicator of SOC. In fact, as it approaches full charge its voltage can actually go down as it heats up rapidly. This can result in a runaway condition and explosion if the charging system is not smart enough to recognize this condition and shut down. A big part of this challenge is that this effect does not happen at any specific voltage, its highly dependent on a number of factors including temperature. A number of pretty smart folks in the PHEV development community have already experienced catastrophic battery failure in this fashion.

Another issue is you have to outsmart the battery controller. If the controller is powered off, and you charge up the battery, when you power the car back on it will still show the same pre-charge SOC. Since it cannot rely on voltage, it mainly uses a coulomb counting or current integration approach to estimating SOC. If it wasn't there to watch current come into the battery, it doesn't recognize that its there and doesn't update SOC. If you try to charge the battery through the current sensor with the controller power on, it will throw a fault and shut down. The HV system works kind of like a GFI outlet, if the current into/outof every point of the system isn't identical (within a few mA) it disconnects itself assuming there could be a short somewhere. The trick people figured out is to charge the battery with the controller on, but without the charge coming through the current sensor. The controller will not register the incoming current, but when the battery voltage rises above 242V it will trigger a recalibration routine to recalculate SOC. The Can-View will monitor the SOC, and once it starts to recalibrate upward will automatically disconnect the charger once the SOC passes a certain predetermined (but programmable) SOC. By default this is ~73%, as thats the ideal SOC for encouraging the HV controller to use more electric and less gas at higher speeds. In a PHEV, the CAN-View will keep conencting and disconnecting the power source (the big battery) to keep the SOC within a few % of this ideal point. You'd probably want to program it higher, maybe up to 80% although at somepoint I believe EV is locked out due to too high an SOC.

For this reason, even if you had a fancy charger that would safely charge the battery to exactly 80%, it might not do you any good. The battery controller would still think it was at 60%, or wherever it started, and when it drained enough current to get to 40% it would start the ICE ignoring the fact that it was still really higher than that. PHEV conversions like aminor's (I think) get around this by using SOC spoofing. Rather than charging up the battery to a high enough voltage to get it to recalibrate the SOC, they have a controller that broadcasts a fake SOC value. The new version of the cal-cars system is also heading in this direction, replacing the CAN-View with a dedicated SOC spoofing controller.

The bottom line is the Prius and its battery are very complex pieces of hardware, and I don't think there are really any cheap/simple ways to fool them. If you are really interested in this sort of thing, I would strong consider looking at a DIY PHEV conversion, which should be $2500-3500 particularly with your minimal range requirements. Actually this might be ideal for a lead acid conversion, as you could use even smaller/lighter batteries, and discharge them much less deeply making them last a lot longer.

Links:
Electric Auto Association main page on PHEVs:
Main Page - EAA-PHEV

EAA page focussed on cal-cars open source conversion:
PriusPlus - EAA-PHEV

Maker of CAN-View controller, and the PHEV system Aminor is using:
CAN-view index

Seller of a complete kit based on cal-cars, available with no batteries for somewhere around $3500, with 20Ah lead acid for $5000, and with Li-ion for $8500-$15000
Products - Plug-In Supply Inc of Petaluma California

 

Whether directly or indirectly, it ultimately comes from the ICE. As Drees suggests, you wouldn't have the opportunity for regenerative braking without ICE energy having been expended to move the car in the first place. So as a couple of us have suggested, better is to just let the kinetic energy go directly to work for you to keep the car moving rather than losing some of it through regeneration. That's part of what "pulse and glide" is designed to do as a driving technique.

Your stage 4 mileage is better than stage 3 because the ICE is free to shut off when not needed for propulsion. It won't consistently do that in stage 3. When I'm in stage 4 I easily get 60-80 MPG, sometimes even more in summer.

You pay for it eventually. The battery eventually has to be replenished, and again, that power comes from the ICE with conversion losses along the way.

I'm not a gearhead either, so it took awhile for this to sink in. Trust those of us who avoid the battery as much as possible (and get 60-80 MPG): Deliberately using the battery will hurt fuel economy in the long run, unless (to tie back in to the original post) there would be some way to plug it in.

 

When you need to buy something, do you always get a cash advance from your credit card. You might as well, since you will need to pay off the card at the end of the month. I certainly hope not, since the cost of that cash advance is not free. Credit card companies charge interest on advances.

The same thing is true when using the battery on the Prius. There is a cost involved with putting energy into the battery and taking it back out again. It's better than losing it, but there is a cost. Regenerated energy is like free money. It's better to use it instead of losing it. However, it's not really free, since you paid for it in advance by getting the car up to speed.

The best mileage comes from never using the battery.

Tom

 

I use the battery when I am maintaining speed when I have a hill to climb ahead. My thinking is, the ICE has fixed losses when it is running. The friction of the internals is not a great deal more when the ICE is putting out (numbers about to be pulled out of thin air) 30kW than when it is putting out 20kW. If I deplete the battery some then it recharges when the ICE would be running anyway am I in front? I think I might be. I can travel maybe 1 or 2 kilometres with a little electric help with the ICE off on flat ground which at that time consumes no petrol then when I climb the hill, not a steep hill but it requires the ICE to run, I recharge with maybe 95% efficiency ICE as it would be running anyway so friction and thermal losses will happen anyway instead of having the ICE running on the flat at no better than 39% efficient. I might lose 20% in electrical conversion but that is better than 60%.
What do people think?

 

That was what I was trying to get at. I don't have a problem with the general theory of avoiding conversion losses, but is there really no time when making deliberate use of the battery could save gas in the long run, such as when you are absolutely certain that you will be running the ice in any case immediately after a long battery run? I do try to do mild pulse and glide, but anything more than that seems like way more trouble than it's worth.

 

If you can get over 2000km out of a tank it might be worth it but I won't be doing anything that radical any time soon athough it has been done.

 

Forgive me... I must comment!

While I realize that the NiMH modules in the Rav4EV are not the same as in the Prius, they are at least the same chemistry. And while full charge cycles do recue the life of the battery, I think calling it "greatly" may be over-stating things. We are seeing livetimes of 10 years and 150,000 miles on the NiMH batteries in the Rav, and these things are charged to full every day, and are regularly emptied.

Again, I'm sure it will shorten the life. I just wonder about the "significance." At some point there is a trade off. You've built the battery. It cost energy and money and pollution to create. If you don't use all of its capacity, it may last longer. But how much more benefit could you get out of its shortened life if you used more of it?

Fortunately there are guys who get paid to think about this. I only offer the Rav4EV experience (energy packs vs power packs) as a data point.

Except for the poor energy density, that's the truth. We're getting closer to that ideal every day though!

 

Sorry it's taken me so long to reply, but there was a question about the special battery charger I had made for my PHEV prius.

It's a Zivan NG3 charger, which has been programmed by the UK Zivan agent Zapi to charge NiMH batteries. In order to safely charge the prius pack the specs are as follows:

Zivan NG3, SX curve. 238V cut-off voltage (the charger will stop when it reaches this voltage). A maximum charge of 4A gives a nice smooth easy charge.



Any other questions, please don't hesistate to ask!

Regarding charging - I'd agree with Daryll's comments about the Rav4 and Prius battery chemistries. I'd add that using a single Prius pack will put more strain on the system than mutiple packs, as with multiple parallel packs you share out the current demand between the multiple packs, meaning lower current drain on each pack.

Nikki.

 

Just because you are running the ICE doesn't mean you get to charge the battery for free. Charging the battery draws power from the ICE either way.

As for your general question, yes, there are special conditions where it makes sense from a fuel economy standpoint to use the battery:

1) When moving the car a very short distance. It makes no sense to turn on and warm up the ICE when it will be immediately shut off.

2) When creeping in stop and go traffic, but you know that you will soon be driving at speed. In this case it makes sense to forestall the recharge so that the ICE can run efficiently at higher loads for a longer time while it both moves the car and recharges the battery. This assumes that the moving speed will be moderate so as to avoid wide open throttle conditions, where the ICE is not as efficient.

3) When coming to a long downhill, where energy will be regenerated in too large a quantity for the battery at its present SOC. In other words, if you are going to do a lot of regenerative braking, it's a good idea to have some room in the battery.

A typical rechargeable battery that will go for over 100,000 partial cycles will be unusable after 1,000 complete cycles. That's a fairly significant difference. Obviously it all depends on what you consider a full cycle and what is a partial cycle, and also on the type of battery. As you point out, battery technology is improving all of the time, where full cycling is getting to be less of a problem.

Tom