Tag Archives: TPMS

Under pressure

External TPMS sensor

The TPMS monitor arrived. The packaging looked like it was opened along the way going through customs.

It was fairly easy to install. Replace tire stem caps with little knobs. An alarm went off almost immediately as I put one on. I changed the units of measurement so the pressure and temperature were set to PSI and Fahrenheit.

TPMS host display

My tires were setting around 20 psi. The maximum pressure for the tires is rated at 51 psi.

I did some quick research and found most cars have a pressure around 32 psi, and that the door should have a sticker with the recommended tire pressure. I only saw the sticker with the VIN on it. I dug through the owners manual and found that Sebring-Vanguard recommended a tire pressure of 32 psi. Inflated the tires to 35 psi.


The recommended tire pressure for standard and radial tires, front and rear is 32 psi. A lower tire pressure will give a softer ride, but a lower speed and ranger a higher tire pressure gives better speed and range.

CitiCar 1976½ Owners Manual, Sebring-Vanguard page 24

Power Transmission

Along with receiving the majority of parts by the end of next week, I’ve been researching battery cables. The first thing was to identify the amps going through everything.

Battery Monitor350500
4 Battery Modules4 * 250
4 * 400
Battery Switch350
600@5 min
1200@30 sec
Contact Solenoid650650
Motor Controller380
420@5 min
500@2 min
Reversing Contactor400400
Max Amps Allowed350400
Amperage that devices can produce, handle, or draw in the circuit

The fuse does not allow any more than 400 amps supplying the motor. From here, I was able to get a general idea of how large the battery cables need to be.

In addition to amps, I also had to take voltage drop into consideration. To do this, you need to know the length of the full path in circuit – battery to motor, and back again. I took some string and laid it out in a large loop around the bench seat. It came out to roughly nine feet.

The parameters are 48 volts @ 400 amps running along nine feet of cable. I found a calculator and put in the following:

Gauge2/0 AWG
00 AWG
Voltage48 VDC
1-way circuit length4.5 feet
Load400 amps
0.288 VDCVoltage Drop
47.712 VDCVoltage at Load
0.6%Voltage Drop
circular mils
Wire cross section

It appears 2/0 AWG wire will handle the maximum load the fuse will allow with a minimal voltage drop.

In other resources, I’m finding that 00 gauge is often rated for a maximum current of 186 amps, and that you should never exceed 80% of the rating (148.8 amps). Even a 4/0 wire will only be rated for 380 amps max.

In this scenario, it feels like the wire will melt before the fuse breaks. Things that confuse me are that the information that I’m finding is often for bringing electric into a house. I often look at how golf carts are wired up, but they are often working with 2 AWG wire, which is much smaller than 2/0 AWG.

To support 400 amps, I think I would need 500 kcml / 500 mcm of copper wire rated for 90°C. It looks like it costs roughly $14/foot. The wire is thick – as in power lines on telephone poles. I wouldn’t have the ability to afford tools to cut, crimp, and bend the stuff. Besides speed, I think modern EV’s go with higher voltage systems to reduce the amps needed, thus reducing the size of the wire.

The motor controller supports current limiting, so I could force it to use no more than 148.8 amps if I desired.

Someone local that I met on the maiden voyage has a few tools and supplies to help out with that they had used on their own EV.

In other news

  • D & D Motor Systems is shipping my motor.
  • Popular Science, June 1975 has been shipped
  • The portable EVSE has been shipped
  • I need to do some research on plug breaking / dynamic braking
  • I may need to contact D & D Motor Systems or Alltrax to see if they have a field map for my specific motor / controller.