Adventure EV

Wiring It All Up

by on Nov.09, 2010, under Design, Electrical, EV Land Rover

HV Circuit Control Box

The main battery pack powers more than just the motor, it also provides electricity for the ceramic-element, cabin heaters, as well as feeding a DC-DC converter (replacing the role of the original alternator) that transforms the 200+ volts to a more conventional 12 volts for the rest of the vehicle’s accessories (headlights, turn signals, etc).

All of these individual circuits need switching and fuse protection.  I created a custom, water-tight box full of these odds and ends;  main switch contactor, fuse blocks, and solid-state relays.

AccessoryControlBox_v02

Watertight NEMA-rated cable glands used for all cable transfers. GM Weatherpack and Anderson Power Pole connectors used for all connections

Accessory Control Box

High Voltage circuits. Clockwise from top left; power distribution blocks, heater element solid-state relays with heatsinks, blue Belktronix voltage prescaler for LinkPRO battery monitor gauge, fuses, Kilovac EV200 contactor

A contactor is essentially a giant relay designed to switch high-power circuits through the use of a safer, low power circuit.  Normally, special circuitry is needed to protect the motor controller circuit from an in-rush of high current when switching it on and off.  The Soliton-1 motor controller comes with a contactor and pre-charge resistor circuit built in, so I don’t have to worry about it.  Handy.

The Kilovac EV200 contactor pictured in the lower left of the box is designed to switch the HV accessory circuits.  Power from the main battery pack comes into the control box, is controlled by the contactor, and then goes to a set of distribution blocks.  Power is split to individual high-voltage rated fuses which then feed the particular accessory circuit:

2 x 12 amp fuses for the two solid-state relays (SSR) controlling the two ceramic heater matrixes for cabin heat.

1 x 30 amp fuse for the DC-DC converter

1 x 1 amp fuse for the HV ammeter wiring

1 x 2 amp fuse for the HV voltmeter wiring

Battery Pack Monitoring

While I can’t monitor individual battery cells without an advanced battery management system (BMS), I can keep track of the entire pack relatively easily with a battery monitor such as the Xantrex Link PRO.  Normally used for monitoring the state of batteries used for marine applications, the LinkPRO seems to work quite well for EV use.  It comes in a handy gauge form-factor, monitors voltage, and the flow of current (amps).

Xantrex Link PRO Battery Monitor

Keeping track of current flow is particularly useful.  Lithium chemistries have a very flat discharge curve.  That is, the voltage when a cell is full doesn’t differ greatly from an empty one.  This is great for performance as the power out of a lithium cell won’t seem to reduce very much as the battery drains.  Conventional lead-acid batteries have a steeper discharge curve.  It’s pretty easy to tell the charge state just by reading the voltage output.  Concurrently, the performance of the vehicle will diminish over time.

While the performance benefits tilt in favor of lithium, the danger is not knowing where empty really is.  When the cell actually hits empty, the voltage will drop off very rapidly, possibly rendering the cell dead.  A more reliable way of measuring the amount of electricity left in a lithium cell is to track the amount that was extracted from it.  The LinkPRO  keeps track of amp usage over time (amp-hours) which gives me a pretty good “fuel-gauge”.  A side-benefit to measuring the amount of current flowing is that it works both ways.  When I charge the battery pack the gauge runs in “reverse” to fill up.  If there was ever an error in the charging process, the gauge would reflect the true amount of charge in the cells.

The LinkPRO is not designed for high-voltage battery systems.  It works to a maximum of 35 vdc, so also located in the accessory box is a Belktronix voltage pre-scaler.  This device takes the high voltage from the main battery pack and scales it down by 10x to match the 0-35 vdc input range of the monitor, 205 volts becomes 20.5 volts, for example.  Software within the gauge multiplies the result by 10 to display the correct battery voltage.  The gauge itself is powered by a small 12v DC-DC converter that takes its power from the 12v accessory side.  Its presence is merely to isolate the gauge from the 200+ volt traction pack for safety.

Current measurement is handled by a big, beefy 1000 amp shunt inline with the main battery pack.

Deltec 1000 amp / 50mV Shunt

Finalizing Installation

The main power cables transferring power amongst the four battery boxes and the motor controller are made up of flexible, orange 2/0 gauge welding cable.  Welding cable is ideal due to the large number of fine strands of copper.  It remains very flexible while allowing great current load.

Two giant Ferraz-Shawmut 500A/300vdc fuses protect the HV circuit.  One is mounted on the rear battery box, the other in the front bay.  While an essential safety element, hopefully these never see use.

Ferraz-Shawmut 500 amp / 300vdc Fuse - Image courtesy KTA-EV

A large, Anderson-style disconnect ensures that the HV electrical path can be easily broken for safety and maintenance.  Clear-acrylic is used to cover the engine-bay battery box and to offer spectators a peek of what the battery system looks like.

FinalBayTop_v01

An Elcon PFC-5000 5kw charger sits onboard under the motor controller (hard to see).  The charger is very flexible, capable of working with 220v or 110v input, and since it’s onboard I can charge anywhere I can get power.  220v circuits, such as those found at home or in RV parks will produce 5kw of charging power capable of filling a completely depleted pack (32.8 kwh) in about 7 hours.  If used on a smaller 110v circuit, output is reduced to 2kw, which would take 16 hours to charge.  However, the pack should never really be taken below 80% usage, and I predict that regular, predicted use will be more in the realm of 50-60% making for very reasonable charge times of only a handful of hours.

Elcon PFC 5000 Charger

Since the 12v accessory circuit is mostly powered by the DC-DC converter (currently an Iota, but will probably change to a  sealed Chennic converter… if they ever get back to me), a smaller than normal accessory battery can be used to provide backup power.  An Odyssey PC625 AGM normally used in powersports applications (snowmobile, jetski,etc) is mounted in front of the main battery box.

Final Motor Bay Side View

Here it is, mostly finished.  I’ve run out of time this round, but I discovered late in the installation that the white control box needs to be re-mounted lower to provide enough room for the bonnet.  This should also help clean up the wiring a bit.

Final Bay Top View

Unfortunately, I don’t have a picture of what it all looks like with the side wings and grille on.  Testing is done with the bonnet off.

Next up… first drive impressions!


3 Comments for this entry

  • Michael Hudson

    Excellent write-up, as always. I can’t wait until you’re posting videos of driving around in this behemoth! 🙂

  • Richard Ovenburg

    I was wondering how the unstraped battery pack is working out for you.
    I’m in the same situation and I think I’ll follow your lead if it is causing no problems
    Rich in Portland

  • jeffg

    Good question. Unfortunately, I don’t have a good answer. My EV remains off the road until mid-spring, when I can get back to it.

    However, other peoples’ experience indicates that the cells shouldn’t swell under normal usage. They tend to plump up when overcharged. Regardless, they’re all packed pretty tightly in the steel battery boxes.

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