====== Modifications ======

<WRAP important>
**Legal note:** anything that lets the motor push a C5 faster than 15.5 mph, uses a motor rated above 250 W, or removes the pedals takes it outside the EAPC rules. It then becomes a motor vehicle for road-use purposes. See [[guides:the_law|Legislation]].
</WRAP>

===== Battery and power wiring =====
  * **Modern batteries.**
    * Owners commonly replace the long-dead Oldham battery with a car or leisure battery.
    * A **LiFePO4** pack is a popular upgrade. A 12 V 20 Ah golf-trolley pack weighs about 2.5 kg against about 15 kg for lead-acid, and owners report much better acceleration and climbing. One reported about 7 miles of motor-heavy use from 20 Ah.
  * **C5Alive "QR" Quick-Release Power Wiring kit** (v2, Feb 2006). This replaces the key-switch power block with:
    * quick-release battery clamps;
    * a relay;
    * a replacement dual-pole **light switch** that switches both main power and the lights. The lights are therefore always on when the C5 is on, so fit **LED bulbs**.

Fitting outline:
    - Remove the boot and the control box cover. Use 7 mm and 8 mm long-reach sockets on the two 7 mm and two 8 mm power nuts, and unplug the brown +12 V from **X5**.
    - Swap the light switch, wiring it exactly as the guide shows. Wrong wiring damages the control box and pod.
    - Run the new red/black leads through the seat grommet: **red where brown went, black where blue went**.

**Don't drop nuts or washers into the control box.**
  * **3D-printed key-switch adapter** (c5owners.com). This lets the original key switch sit on any battery using quick-release clamps. The original charger can still be used on a lead-acid car battery.

===== Simplified relay controls (John Wilson, c5owners.com) =====
Use this to get a C5 running when the pod or control box is dead or missing, or after a reverse-polarity disaster.

  * **12 V twin-relay circuit:**
    * Use **two 70 A automotive relays**.
    * The handlebar switch, through a 5 A fuse, energises relay 1, which energises relay 2, which switches the motor.
    * Fit a **5 A diode** across the circuit as shown, with the silver band towards relay pin 85.
    * Use 6 mm² cable for the motor circuit. Cheap 100 A jump leads work, or reuse the original brown (= +) and blue (= −) leads.
    * Keep the original **orange-wire thermal switch** in the circuit as the only motor protection, and add an **80 mm 12 V PC fan** on the motor.
    * Optionally add a kill switch and a key switch.
  * **Keeping the original lights, indicators and horn:** feed 12 V to the original control-box terminals just inside its inspection cover. The box is already fused.
  * **Instrumentation:** add a **shunt with a combined volt/ammeter** in a modified pod housing.
    * Current guide: about **29–30 A** on the flat; about 40 A climbing while pedalling; under 5 A means coast.
    * Voltage guide: about 13.5–14.4 V full. **Stop at 10.5 V.** The voltage recovers to about 11.5 V after a rest, enough for a mile or two home.
  * **Optional extras:** hazard-warning wiring with 5 A diodes, an LED-compatible flasher, and a relay-driven motorcycle or car horn.
  * A **24 V version** uses a **4QD Porter 10** speed controller.

===== 24 V conversions =====
  * 24 V conversions have been done since soon after launch. They make the C5 noticeably faster, so it is **no longer an EAPC on the road**.
  * **Usual approach:** two 12 V batteries in series (one in each footwell), a PWM controller, a **throttle** in place of the push button, and a **motor cooling fan**. The original pod and control box are removed or bypassed.
    * Controllers: the **4QD Uni-8**, later discontinued; its replacement the **4QD Porter 10**, rated 12–48 V; and others.
    * Owners report **36 V** is possible with good motor ventilation.
  * **The Sinclair designers' own notes** (Unofficial Service Manual) on running the original electronics at 24 V:
    * pod: R17 doubled to 94 kΩ and C12 uprated;
    * control box: C2 uprated, a bigger heatsink on IC1, and a resistor in series with the relay coil.
  * **C5Alive 24 V kit** (v2, Feb 2006). Instruction sheets W1–W6 and S1–S8, plus a cooling-fan bracket sheet:
    * battery 1 positive goes through a relay (switched by the C5 light switch) to the controller +B and the fan;
    * a link wire runs from battery 1 negative to battery 2 positive;
    * battery 2 negative goes to controller B−;
    * controller M+ and M− go to the motor brushes A and B;
    * the throttle cable runs down the steering column.

Notes from the kit:
    * The original thermistor (purple/grey) and thermal lock-out (orange) become redundant, so tie them back.
    * The lighting circuit is lost with this kit.
    * Some early "2-battery" C5s already have a square cut-out in the right-hand moulding for the second battery's wiring.
  * **Cooling fan:** C5Alive's kit clamps a 12 V fan to the motor with 3–4 brackets and a jubilee clip, set diagonally to clear the seat. 3D-printed fan connectors for 90 mm and 120 mm fans are available from C5owners.

===== Gearbox and drivetrain upgrades =====
  * **Metal gearbox insert:** an alloy insert with a toothed ring and the large bearing fitted. You reuse the original 3 cogs and posts. It was offered by "Sinclair C5 Chas" (about £65 in 2013) and used on 24 V machines.
  * **Reproduction plastic gearbox cogs:** moulded or 3D-printed.
  * **Disc brakes:** front and rear conversions are documented in forum threads.
  * **Wider or upgraded tyres:** Schwalbe Big Apple or City Jet on the rear.

===== Electronics replacements (c5owners.com projects, now unsupported) =====

^ Project ^ What it does ^
| **POD ULA replacement module** | An Arduino Nano on an adapter PCB that plugs into the **ULA socket**. No other changes are needed and it's fully reversible. Right bar: battery gauge. Left bar becomes a **motor temperature gauge** (two green when cool; two red above 60 °C; tone and lock-out at **70 °C**). Low-battery tone and lock-out. **Motor-current display is not reproduced.** |
| **C5duino** | An Arduino Nano control box. It monitors battery voltage, ambient and motor temperature, motor current and speed (via a reed switch). It runs a variable-speed fan, software flasher and hazards, mileage, a PIN lock, **pedelec mode** and "Smart Drive". Lock-outs at 70 °C, below 10.0 V, and above 120 A sustained. V2 supports 24 V with a Uni-8. |
| **C5 Touch / LCD touchscreen** | A touchscreen dashboard (Arduino Mega) that talks to the C5duino over serial. |
| **X-POD** | A complete replacement pod and control box with a touchscreen. Shows time and date, a pedalling indicator and pedelec mode, motor state, battery volts and a 5-segment gauge, motor and ambient temperature graphs, speed, mileage and drive/pedal/coast charts. Controls lights and indicators, a PIN lock, a variable fan from 30 °C, and cut-out at 70 °C. 3D-printed case. |
| **Pedelec mode** | A reed switch on the crank, so the motor only runs while you pedal. Optional speed window. |
| **Journey data logger, LED grid display** | Smaller experiments. |

Firmware and PCB files were published on c5owners.com and its 3D-model download site.

===== 3D-printed reproduction parts (C5owners STL library) =====
  * **Original-pattern parts:**
    * Hi-Viz mast caps; pod caps holder; pod washer;
    * rear wheel centre caps;
    * chain-tensioner chassis clip;
    * light-switch bracket; handlebar switch bracket; handlebar grommet;
    * boot clips; rear frame inserts;
    * indicator template;
    * motor heat-sensor holder;
    * bulb access housing and top;
    * toolkit cap;
    * side-panel clips;
    * wing-mirror brackets;
    * battery stop bar.
  * **New designs:**
    * cooling-fan connectors for 90 mm, 90 mm extra-long and 120 mm fans;
    * X-POD case and control box;
    * mudflaps (X-POD style);
    * a replacement boot lock;
    * rear-brake bearing bracket;
    * key-switch and battery adapter.
  * If you sell prints, C5owners asks for credit in your listing.

===== Extreme builds =====
  * **Adam Harper's record C5s** reached up to **150 mph**, with 0–60 mph in about 5 s, and drove through a 70 ft tunnel of fire.
  * Other owners have fitted jet engines, bigger wheels and high-powered motors. These are for track and private-land use only.

===== Sources =====
  * c5owners.com: "Simplified Relay Controls" (John Wilson); projects pages (POD ULA Replacement, C5duino, X-POD, Pedelec Mode, 24V Conversion); 3D printing pages; forum threads 23, 31, 53, 271, 317.
  * C5Alive.co.uk downloads: 24V kit instructions (v2, 06-02-06); QR Power Wiring Fitting Guide (v2, 24-02-06); cooling fan mounting instructions (v1.01, 30-9-05).
  * //The Unofficial Sinclair C5 Service Manual//, "Application of C5 instrumentation system to other vehicles".
  * //Twist & Go// magazine, p. 50 (Adam Harper).