My ZAP Xebra PK electric pickup truck
Web Links about the A123-Systems/Hymotion Plug-In Conversion
Problem with the Prius 12-volts auxillary battery
Occasional Problem Starting the Hymotion System
EV Switch
State of Charge
PSD Lubrication Issue
Performance
Publicity
On 1-2 October 2008 I converted my 2005 Prius (35,500 miles) to the A123 Systems' Hymotion plug-in. The work was excellently done by Fitzergerald's Lakeforest Toyota of Gaithersburg, MD. They did an excellent job and were very helpful with all my needs. I was able to view the vehicle at various stages of the installation. It took about 6 hours to install the system. I arrived at noon and left before noon the next day; that allowed fully charging overnight the new additional 5.45-kWh battery. (It takes about 5 hours to charge it when it is empty.) (The Prius traction battery is 1.32 kWh capacity.)
I have CANView version-3 installed, which displays on the Prius MFD (Multi-Function Display). When Hymotion goes into EV mode, the MFD jumps back and forth between the CANView screen and the Prius energy display. I found this disconcerting, so I removed CANView for now. I plan to upgrade to CANView version-4 with its own touch screen in the distant future.
I have ScanGauge. It and CANView are both connected to the OBD-II plug below the steering wheel by means of a OBD Y-cable.
I had run down the auxiliary 12-volts battery in my Hymotion Prius by leaving lights on inside two times before the Hymotion installation. It ran down the installation night at Fitzgerald Toyota because the tail lights shine during charging. If the auxilliary battery gets to some voltage below 11 volts, the car will not start; there is a slightly higher cutoff voltage for the Hymotion system to turn on. It ran down again the next night while I was charging the Hymotion battery, because the tail lights are on while charging; they turn off after charging. I bought a new Toyota Prius 12-V battery and started to put it in myself, but decided that I do not have the right tools to get it out of the tight space it is in; so I had my Toyota dealer do it. (Advance Auto did not have the proper battery; I bought it from my Toyota dealer.) Shelor Toyota in Christiansburg did the installation; they told me that they had to un-attach the Hymotion battery to slide it over a little in order to get the auxiliary out. Perhaps Hymotion can redesign the location of their battery to allow the auxiliary battery to be removed without having to move the Hymotion battery.
Another Hymotion owner and I are occasionally having a starting problem: Sometimes when the car is started after being fully charged the triangular ! sign, the check engine icon, sometimes the ABS icon or other icons shine and the Hymotion battery is not in effect. It happens more often after charging during a cold night. The Prius runs normally despite all those icon shining. Sometimes the Hymotion light above the Hymotion switch blinks 13 times at the same time, which is an indication of a low auxiliary battery, sometimes not. If I drive a mile or so and then turn the system off and then back on, it goes back to normal Hymotion operation.
The problem is that charging the Hymotion battery runs the auxiliary battery down. I have been able to stop the problem from occurring by using a trickle charger that plugs into the cigarette lighter when the Hymotion battery is charging. The cigarette lighter has to be wired to always be hot; I bought a kit from http://www.coastaletech.com/power_outlet_mod.htm to do that.
I purchased a multimeter at Radio Shack that can log data onto a PC, and it comes with MeterView software for a PC. I used it to get graphs below by connecting it through the cigarette lighter with connectors from Radio Shack. It has an RS232 connection to a computer; min ViewSonic tablet PC only has USB, so I had to use an RS232->USB converter.
Here are some results that show that the Prius auxiliary battery is slightly discharging when the Hymotion battery is charging, but not when it is not charging:
Auxiliary battery voltage when the Hymotion battery is NOT charging:
Notice that the voltage is rock solid for 17 minutes.
Auxiliary battery voltage when the Hymotion battery is charging:
The hybrid system was on and then turned off. After about 2 minutes after the hybrid-system transients died down, the Hymotion battery was started charging. After the commotion of turning off the hybrid system died down, the auxiliary-battery voltage leveled off at 12.66 volts. Then it started to drop when the Hymotion battery charging began. You can see the constant voltage here before the Hymotion charging began:
At about 11:30 the charging was complete and the auxiliary-battery voltage remained constant at about 12.5 volts. The decline in the auxiliary battery voltage over a period of almost 2 hours is quite obvious.
Since there is no sudden drop in auxiliary-battery voltage when the Hymotion-battery charging is started, the auxiliary battery is not involved in lighting the tail lights. Something else is causing the gradual drop in the auxiliary-battery voltage. The initial gradual voltage drop is about 0.1 volts every 15 minutes; it decrease with time.
In the case above the Hymotion battery was about ¼ discharged when the charging began.
The A123-Systems/Hymotion plug-in conversion automatically puts the hybrid system in EV mode when the system starts, which keeps the ICE from turning on in 7 seconds after starting. However, once the vehicle reaches 34 mph the ICE turns on to warm up. After some ICE warm up and the vehicle slows down to a rather low speed, the EV mode is actuated again.
To get high mpg in around-town driving, one needs an EV switch to keep the gasoline engine (ICE) from turning on to get itself warm:
What gain is there by installing a manual EV switch? TheForce on priuschat.com: "You would gain control on when you need to use EV mode. Once you know when is the best time to use the button and when not to, a manual button would be better than letting Hymotion control it." "You would gain control on when you need to use EV mode. Once you know when the best time to use the button and when not to a manual button would be better than letting Hymotion battery control it. If you want to install your own button you will have to bypass the Hymotion connection or install a switch inline to select between the two." I do not know how to bypass the Hymotion connection.
However, Norm of hybridinterfaces.ca says: "Any EV module of any make just enables EV mode manually, just as Hymotion does automatically. So [putting in a manual EV switch would not allow] change to the EV cut-off speed. You would need the 52-mph hack that some outfits are promoting, but I do not as it requires you to pull over, stop and re-start before the ICE can run again which I feel is a major safety hazard. You can however right now maintain stealth up to 42 mph which is almost as good as EV mode. Doesn't help much downhill with Hymotion because they can't employ regen with their system. Remember there are any number of conditions that prevent EV mode and, just because you can press EV manually when the Hymotion doesn't, does not mean the Prius will accept that EV command."
There is an issue about the need for the ICE to run occasionally to properly lubricate the power-split-device (PSD or transaxle):
"See this pic and this diagram. The pump is at the opposite
end of the transaxle from the engine, and sends a gentle flow
of transmission fluid down the assembly of shafts where small
holes let some out into the bearings along the way as well as
the final-drive chain. It doesn't seem to go much of anywhere
else, just ensures that those parts stay lubricated. The pump
is paradoxically turned by the *ICE* shaft which passes [in
two pieces] all the way through the middle."
"It is already pretty clear that the bearings [the majority of
which are ball or needle, so they're already very low-friction]
stay adequately lubricated over long periods of engine-off time.
The transmission fluid isn't involved in actual power transmission
like it is in a normal A/T; it's just a lubricant which is one
reason its service interval is so long. The jury is still out
on *very* longterm lubrication issues, such as when weeks on
end go by and someone's commuting to work under EV only and
avoiding even the brief warmup run by invoking EV mode early
enough and staying under 34 mph. Just one shot of ICE-run now
and again is enough to circulate some fresh fluid down the
shaft assembly."
So, one should let the ICE run occasionally during drives where it is not needed for propulsion. Perhaps it is best to not use the EV switch until the ICE runs for a few minutes after starting the hybrid system.
With about 200 miles of around-town driving the Roper Prius is getting about 50% to 75% better gas mileage compared to what it got before the conversion. Another way to say it is that the mpg is increased by 20 to 40 mpg.
After running the Hymotion battery all the way down, here are some amounts of energy it took to fill it: 4.61 kWh.
2008 Green Living and Energy Expo:
L. David Roper, http://arts.bev.net/RoperLDavid/
