WA8LMF Home Page | Main Ham Page | Mail Mobile Page |Updated 19 March 2009  

Mobile Installation In 2005 Toyota Prius

 Photos of the installation are below.

  • The Prius main electric system is a 240 VDC MNiH battery pack that powers a 440VAC 3-phase 60 Hp water-cooled electric motor.  (The electric motor is plumbed into the radiator just like the gas engine.)  A 240VDC to 440 VAC inverter is integral to the electric motor.   This HIGH-POWER DC-AC conversion creates LOTS of broadband white noise on the HF bands (S9 plus on all bands 40 through 10 meters and about S6 on 6 meters) which gets worse when you step on the brakes (Energy is partly reclaimed by making the motor run backwards as a generator to recharge the battery when you step on the brakes. Normally, the drag of the motor-cum-generator provides nearly all the braking effect. Unless you push the brakes all the way down in a panic stop, the mechanical brakes and linings almost never engage. ).  

    The high white noise level makes HF operation (except for the extremely strong signals of 15M and 10M band openings) nearly impossible. The noise shows up even at VHF where it registers about S-1 or S-2 on the Kenwood D700's S-meter.
  • The  Prius 12 VDC system is a very vestigial affair intended to power just the radio, lights and computer display.  It uses a 240VDC-to-12 VDC stepdown converter that can provide about 40-50A but the 12 VDC battery is a 20 AH device that looks like it came from a motorcycle.  It's main purpose to power up the computer electronics that need to boot in order to start the hybrid power system.  (In the Prius, EVERYTHING is fly-by-wire.  The power steering, the water pump, the power brakes and the air conditioning are all powered electrically off the 240 VDC system which in turn is controlled by the 12 VDC powered computer systems.)

    In my install in a 2005 Prius, I installed a second 50AH deep-cycle battery with an intelligent voltage-sensitive isolator to run the computer and radios engine-off.   The DC-DC converter has no problem charging the second battery, especially because the power-FET-based Hellroaring Technology battery isolator has inrush limitation. Details on the Hellroaring isolator are here:
          http://hellroaring.com .  

    The isolator and second battery hookup is similar to the one shown on this page:
  • I have observed no interference problems TO the Prius' complex electronics FROM transmitters at all, even with 100W on HF or 2M.
  • On the other hand, there is plenty of interference FROM the hybrid power system TO the radios. Based on my experience, it is almost useless to try to receive on a frequency below about 2 meters in the Prius.   On bands below 2M, receive is masked by a continuous S9 white noise level.  This is NOT discrete "birdies" such as you get from computers or TV horizontal sweeps.  It is broadband white noise hiss that sounds exactly like an empty channel except at S9 instead of S0, on any of the HF bands. 

    [  My hypothesis is that this is simple diode noise from the very large amounts of DC current flowing through semiconductor junctions in the hybrid power converter system; not switching transients from the DC-to-AC power inverters which would tend to be harmonics of a discrete frequency that would repeat every so many KHz as you dial across the band. ]

  • When  you park, but don't shut down the hybrid power system (you don't start this car; rather you boot it), the gas engine shuts down but the control systems remain live if you don't push the "OFF" button.
    In turn, you can continue to run the electrically-powered air-conditioning or other devices from the 240 v battery.  Every time the battery drops to about 210 volts, the gas engine will start up by itself, run for a minute or two to recharge the battery and then shut off again.   It can repeat this process endlessly.   The 240-to-12VDC down converter continues to run, making available 30 amps continuously. This is very handy when operating mobile-at-halt for some special event, without having to continuously idle the engine for power.   I've actually slept overnight in the car in air-conditioned comfort (in Iowa in August!) with the APRS laptop and radio running,  and used only about a half-gallon of gas.   
  • This has some interest emergency power potential.  The website

        http://priups.com     [ As in "Prius UPS"]

    explains how many high-power computer-room UPS systems actually use 240 VDC batteries. By connecting one of these devices (without it's battery) across the Prius 240V battery, you can extract a continuous 10-15KW of AC power ( ! ) from the Prius elecrical system. Again, every time the battery pack drops to 210 VDC or so, the gas engine just starts up and recharges it.   [And the Prius gas engine at idle is virtually silent unlike most gas-powered generator sets.]
  • A third-party adapter is available that can allow the car's color LCD "multi-function" display to display external NTSC video sources; i.e. a built-in monitor for my mobile SSTV LiveCAM.

Click on thumbnails for full-size pictures.  (Pictures open in separate windows.)

View from driver's seat of mounted control heads for Kenwood TM-D700 APRS radio and Yaesu FT-100 HF transceiver.  The laptop, running UIview and MapPoint, is supported by a commercial Ram Mounts "RamPod" mounting system.  This tripod system uses soft-drawn 5/8 inch aluminum rods that can be bent by hand to fit any installation.  The bottom of the rods lock into brackets with setscrews that slip under the seat rails. 
View of mounted control heads from passenger side.  There is a lot of room between the front of the console and the underside of the dashboard for mounting hardware.  Note the GE mobile radio speaker mounted behind the radio control heads. The device at the left is the tripod head and ball-joint of the RamPod mount for the computer.

The bracket, bent from .090" aluminum, is bolted to the underside of  the plastic dash with a single 1/4" bolt and nut.  The screw head, inside the dash, is re-enforced with a 2-inch diameter fender washer to avoid cracking the plastic surface. The surface of the bracket that is against the plastic dash has a piece of ribbed  industrial rubber matting glued to it to provide friction to prevent it from rotating.

Click Here to download a drawing with the dimensions of this bracket, in Acrobat .PDF format
View of the RamPod "foot" mount. This view is of the left rail of the passenger seat. The seat is pushed all the way to the rear to expose the hardware. Normally the aluminum rod is covered with a piece of black cable loom for a more finished appearance.  The black box behind the rod is a DC-DC converter to provide 19VDC for the laptop computer from the 12 VDC system.
This is the trunk area of the car. A second, hidden, storage area is located under the removable floor panel. . 
The hidden "lower trunk" is lined with a polyethylene "tub". I cut an aluminum plate to exactly fit this tub and mounted all the radio hardware on it.  This plate, insulated from the car's chassis by the plastic tub) also serves as a common point ground for all equipment powered by the second battery (An Optima Spiracell Yellowtop deep-cycle AGM). The objective was to avoid having the 20-30 amps of DC current used by the ham gear from circulating on the car's chassis and possibly interfering with the car's complex electronic control systems.  The car's own 12 volt battery system is located in the right-rear corner of the trunk.  As a result, I had a very short cable run to connect my added battery system to the OEM battery via a Hellroaring Technology battery isolator switch.  The carpeted panel over the front edge of the opening covers the 240 VDC hybrid battery.

The main chassis of the Yaesu FT100 is at the left side of the picture.  The Kenwood D700 chassis is located under the passenger seat.  The layout on the plate was planned with the possibility of accommodating the main chassis of a Kenwood TS2000 in the future.
Two antennas installed with no-holes hard mounts. A Yaesu ATAS-100 mini-screwdriver for 40 through 6M is on the left side. A Comet SB-14 6-2-450 antenna is mounted to the right.  The details of the home-brew brackets are shown in the next two pictures. 
These home-brew mounting brackets are bent from .090 mild steel. Each one has a piece of rubber cut from an old inner tube glued to it to avoid scratching the surface it is bolted to. The horizontal surface  of the "wing" is punched with a suitable hole (5/8" for a SO-232 bulkhead connector for mounting the ATAS-100, or 3/4" for installing an NMO mount for the VHF/UHF antenna).

Click Here to download a drawing with the dimensions of this bracket, in Acrobat .PDF format
The antenna mount bracket installed.  You remove the two bolts securing the hatch lifter rod bottom end, slip the antenna mount between the hatch sidewall and the lifter, and re-insert the bolts.  (Prop up the hatch door with an old broom handle or stick before unbolting the support.)  There is just enough clearance between the trunk lid and the sides of the hatch opening for the mounts to not interfere with the movement of the trunk lid.