Website for Turnkey Solar Solutions in Arizona

Frequently asked questions (FAQ).

History has shown that one of the more reliable charge controller designs is the Pulse Width Modulated (PWM) Switching Shunt Regulator, covered by U.S. Patent # 4,661,758 and held by the President of ETA Engineering, Inc. The patent includes a PV current source, a Shunt Switch, Blocking Diode, Pulse Width Generator, Voltage Comparator, a Temperature Sense Reference Voltage and a Battery with Load. The comprehensive Patent includes seven claims and provides a means where the battery temperature and battery charging response actually control the final charging rate to maximize battery recharging with minimal water loss.

ETA Engineering incorporates multiple methods to protect the control electronics in the charge regulator. The logic power supply is one-way diode protected with a current draw of only about 1 milli-amp. The internal power supply is filtered, giving immunity to all types of transients and RF energy. The basic control circuitry includes a delay circuit that prevents high-speed oscillation if the battery is left disconnected while the PV module or array is still connected. This delay circuit also prevents excessive heating due to switching losses. All of ETA Engineering's charge regulators incorporate temperature compensated charging with limits set for the given battery chemistry used. The use of this charging philosophy and circuitry maximizes battery life and performance and is now a standard across the industry.

The input to the charge regulator from the PV module is normally the most common source of lightning induced transients. ETA Engineering protects it's regulators with a high bandwidth ceramic filter capacitor (.047 µF) in parallel with a 1.5 Joule Avalanche Breakdown Diode designed for transient clamping within 1ns (1 billionth of a Second). Speed is essential since the Power FET(s) normally used as the switching element(s) can be destroyed with a high voltage pulse of only a few nanoseconds. Input surge current is limited by the inductance of the wiring coming from the PV source to a value within the range of the suppression diode. It should be noted that lightning strikes are measured in milliseconds and induce pulses for even shorter periods. For this reason, fuses (even the fast-blow type) are not effective in protecting PV charge regulators from lightning induced transients. A fuse has a response time measured in seconds. This is due to the fuse's excessive thermal or mechanical inertia, and reduces the fuse's ability to react to a quick event, such as a nearby lightning strike. Charge regulators that depend on fuses for transient protection will fail when exposed to transient surges due to the characteristics of the fuse.

Power FET components used in ETA Engineering's complete line of charge regulators have current ratings several times that of the expected regulator operating levels. This minimizes heating while giving a wide safety margin. ETA's charge regulators will take twice their rated current for 20 seconds without harm. It should be noted this rating gives four times the rated power dissipation! Power dissipation in a Power FET is proportional to the square of the current through the device.

ETA Engineering's regulators are potted in a two-part Epoxy Resin to maximize environmental protection. Extruded aluminum heat-sinks are used in all of the regulators, with exception to the Low-current PBR, to minimize any temperature rise while charging. The charge regulator terminal connectors are designed to accept up to two #10 AWG bare wires, thus eliminating crimp terminals that can be a reliability problem when not crimped to standards.

For reliable system operation, the PV module frames should always be grounded with adequately designed ground rod(s) and cable. The wire diameter of the ground cable should be greater than the largest wiring used for PV module connection to the charge regulator. This gives lower inductance for the ground cable than for the PV leads. The ground cable should be as close to vertical as possible with no turns or sharp angles to significantly increase wiring inductance. When lightning strikes the module frame(s) it is shunted to ground, minimizing its effects on the system when a ground rod connection to the frame is included. The charge regulator and battery should not be grounded, thereby reducing "ground loops" and discouraging the lightning from "jumping" over to the PV leads and finding ground through the system.

ETA Engineering believes that true reliability comes from proper engineering design. Our charge regulator designs are based on long term field experience and sound engineering design practices. Our two Senior Electronic/Electrical Engineers have over 70 years of solid state circuit design and Quality Control experience. This combination of field and design experience result in reliable and effective charge regulators.