Heart Interface HF12-1200

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Overview

Function Description
Important Technical Specifications (for HF12-1200U)
Usage Features
Installation
Crucially, a transfer switch must be used if shore power or a generator is also available to prevent backfeeding, which will damage the unit and void the warranty
Battery Interconnections
Protection Circuits
Maintenance Features
Battery Sizing and Usage
Remote Control
Troubleshooting

The Heart Interface HF12-1200 Power Inverter is a mobile AC power system designed for converting 12 VDC battery power into 120 VAC household electricity. It is available in two models: the HF12-1200U, which features a Ground Fault Circuit Interrupter (GFCI) outlet on the front panel, and the HF12-1200UW, which lacks a front outlet but includes a 3-foot output cable terminating in a junction box for hardwiring into an electrical system. The device is designed for durability and long-term service, provided its installation and operational requirements are met.

Function Description:

The HF12-1200 operates by converting direct current (DC) from a battery bank into alternating current (AC) suitable for powering various electrical appliances. It utilizes pulse width modulation (PWM) control circuitry and Field Effect Transistors (FETs) to generate a modified sine wave output. The internal transformer is wound, dipped in lacquer, and baked for low resistance and high efficiency. The unit's chassis acts as a heat sink, with circuit boards mounted to its sides for effective heat dissipation. The control circuit board, located on the front panel, manages the FETs, maintains a stable 60 Hz frequency, and regulates the output voltage at 120 volts RMS. It also incorporates several protection circuits to ensure safe operation.

Important Technical Specifications (for HF12-1200U):

Battery Voltage: 12 volts
Battery Voltage Range: 10.2-15 volts
Low Battery Cut-Out: 10.2 volts
Voltage Regulation: 5% true RMS
Output Power (min. 30 mins): 1200 watts
Output Voltage: 120 volts AC (also available in 240 VAC, 100 VAC for export models)
Frequency Regulation: 0.5%
Wave Shape: Modified sine wave
Surge Power: Capable of starting a 1/4 HP inductive motor
Power Factor: 1 to 0.1 lagging
Efficiency: 91.3% @ 1200 watts / 96.6% @ 600 watts
No Load Drain (w/o remote): 0.07 amp
Automatic Load Demand: Standard, no time delay
Dimensions (DxWxH): 10.4" x 15" x 7.2"
Weight: 42 lbs.
Protection: Circuit breaker, electronic overload, thermal overload, high/low battery protection.
Consumer Warranty: 30 months

Usage Features:

The inverter is designed to power a wide range of appliances, including fluorescent and incandescent lights, refrigerators, freezers, computers, televisions, and electric heaters. It can handle both resistive and inductive loads, though inductive loads (like motors) may require a larger starting current. The unit features a unique load detection circuit that allows it to draw very little power (about 65 milliamps) when no significant load is present, outputting around 50 volts RMS in this idle state. It is set to detect a 7.5-watt load to come out of idle. For small inductive loads that fail to activate the unit, running a resistive load (e.g., a 15-watt light bulb) simultaneously can force it out of idle.

Installation:

Proper installation is crucial for safety and performance. The unit must be grounded to an earth ground (for stationary installations), vehicle chassis (for RVs), or vessel's grounding system (for marine applications) using an 8 AWG stranded copper wire. The CHASSIS GROUND and EQUIPMENT GROUND connectors on the back of the inverter are electrically bonded. For AC output, the HF12-1200U allows direct plugging of appliances into its GFCI outlet or can be hardwired into an existing electrical system via a 3-conductor wire. The HF12-1200UW is designed for hardwiring into the electrical system using its supplied junction box.

Crucially, a transfer switch must be used if shore power or a generator is also available to prevent backfeeding, which will damage the unit and void the warranty.

Battery connections require careful attention to polarity, as reverse polarity will damage the unit. The inverter comes with two 36-inch 1/0 (00) AWG black battery cables, with the positive cable marked with a red end. If longer cables are needed, they should not exceed 10 feet to avoid excessive voltage loss. Fusing is mandatory for UL listing and safety. For marine applications, the fuse must be within six feet of the battery, and for RV applications, within 18 inches. A Class J fuse rated at 200 amps is required for the supplied 90-degree C. rated stranded cables. The inverter can be mounted horizontally or vertically, secured to a flat surface with 1/4 inch stainless steel bolts tightened to 20-25 ft./lbs. Adequate airflow around and under the unit is necessary for cooling, especially when operating high-powered loads. It is not ignition protected and should not be mounted in hazardous locations or airtight compartments with batteries.

Battery Interconnections:

The inverter operates on a 12-volt battery bank. For 6-volt batteries, pairs must be wired in series to achieve 12 volts. For 12-volt batteries, they are connected in parallel. The amp-hour capacity of a series-connected bank is equal to one battery's capacity, while for a parallel-connected bank, it's the sum of individual battery capacities. At least 0 (1/0) gauge copper cable with proper terminals should be used for battery interconnections, ensuring clean and tight connections.

Protection Circuits:

The Heart Interface includes several protection mechanisms:

Overload Protection: A fast circuit protects against short circuits and excessive inductive loads. Activated overloads are indicated by a green LED. If the overload is removed within 10 seconds, the unit resets automatically. Persistent overloads (over 10 seconds) cause the unit to shut off, requiring manual reset by cycling the power switch.
Circuit Breaker Protection: A 10-amp circuit breaker on the front panel allows for starting inductive loads but trips if sustained output exceeds its rating. Resetting involves pushing the popped-out breaker back in.
Ground Fault Circuit Interruption (GFCI): The HF12-1200U has an integral GFCI outlet. The HF12-1200UW requires a separately supplied GFCI for branch circuits. GFCI must be tested monthly by pressing the test button; if it doesn't trip, the unit needs service. A load must be on the unit for the GFCI test to work.
Overheating Protection: A thermal sensor in the transformer shuts down the unit if internal temperatures become too high, indicated by a red overload LED. The unit requires cooling before it can be restarted.
High and Low Battery Voltage Protection: The unit operates within a 10.5 to 14.5-volt range. If battery voltage falls outside this range, the low battery LED glows red, and the unit eventually shuts down. This prevents total battery discharge and permanent damage. A time delay allows for momentary voltage dips during inductive motor starts. High battery voltage (overcharging) also triggers this protection.

Maintenance Features:

The Heart Interface is a solid-state device requiring minimal maintenance, primarily periodic cleaning with a damp cloth. It should be kept dry, and if water enters, it must be disconnected and thoroughly dried before reuse. Regular maintenance of the battery bank is essential, including checking electrolyte levels, filling with distilled water, and cleaning all battery connections to prevent self-discharge.

Battery Sizing and Usage:

The performance of the inverter depends heavily on the battery bank. Deep-cycle batteries, such as golf cart batteries, are recommended for their longevity and ability to withstand deep discharge cycles. Automotive starting batteries are not suitable. Sealed gel-cell batteries are also gaining popularity due to their maintenance-free nature and high charge current acceptance. Battery capacity is expressed in amp-hours, typically based on a 20-hour discharge cycle. Deep-cycle batteries can be discharged up to 80% without permanent damage, but shallower discharges extend battery life. Sizing the battery bank involves calculating the total watt-hours consumed by appliances between charging cycles and converting this to amp-hours, accounting for inverter inefficiency (approx. 10% extra). Monitoring battery state of charge is useful to determine when recharging is needed. This can be done with a digital volt meter, measuring battery voltage at rest (after several hours without charging or discharging). A fully charged battery reads about 12.6-12.8 volts at 80°F, while an 80% discharged battery reads about 10.5 volts. Ambient temperature affects battery performance, with reduced capacity in cold conditions. Batteries can be charged from various sources (engine alternators, solar panels, hydro/wind systems, AC battery chargers) simultaneously while the Heart Interface is operating. The inverter requires a battery bank and will not operate solely on a charging system.

Remote Control:

An optional flush-mount remote control panel (RP-9) with a 20-foot wiring harness is available for the HF12-1200U. It plugs into a 9-pin connector on the front panel and allows remote on/off/reset control and LED indication of power status, low battery, and overload. To use the remote, the power switch on the inverter itself must be in the OFF position.

Troubleshooting:

Abnormal Load Behavior: Some inductive loads may hum slightly louder due to the modified sine wave output. Sine wave filters are available if this is unacceptable. Small loads (under 7.5 watts) may not activate the load demand circuit; running a resistive load concurrently can help. Digital clocks may run faster due to the modified sine wave.
Sensitive Electronics: Starting large inductive loads (e.g., 1/3 HP motors) can interfere with sensitive electronics like computers, potentially causing them to crash. It's recommended not to operate sensitive electronics simultaneously with large motor starts.
Microwave Ovens: Microwave ovens may cook 15-25% slower on the inverter because their cooking speed depends on peak AC voltage, which is influenced by input battery voltage. Higher battery voltage can improve cooking speed.
Motors Not Starting: If motors fail to start, check battery voltage while the motor attempts to start. If voltage drops below 11.0 volts, check battery connections and state of charge, or consider a larger battery bank. If voltage remains above 11.0 volts but the motor still won't start, adding a 3 µF motor-run capacitor may help.
Output Voltage Measurement: The inverter's output voltage (119-121 AC volts RMS) can only be accurately measured with a true RMS volt meter due to its modified sine wave output. Standard volt meters may show readings between 90 and 140 volts. In idle state (no load), a standard meter will show 20-30 volts AC (true RMS is about 55 volts AC). To confirm voltage regulation, observe the brightness of an incandescent light bulb; it should appear similar to when plugged into utility power.
No Output: If there is no output voltage, first check battery voltage, dead batteries, or bad connections. If the inverter does not hum, produces no power, and continuously displays a green overload LED, contact the dealer or Heart Interface.