Trace Engineering DR Series User Manual

Trace Engineering DR Series Owner’s Manual - Version 3.2 - 9/7/98 - Page 37
Applications
Resistive Loads
These are the loads that the inverter finds the simplest and most efficient to drive. Voltage and
current are in phase, or in step with one another. Resistive loads usually generate heat in order to
accomplish their tasks. Toasters, coffee pots and incandescent lights are typical resistive loads.
Larger resistive loads—such as electric stoves and water heaters—are usually impractical to run
from an inverter. Even if the inverter could accommodate the load, the size of battery bank
required would be impractical.
Inductive Loads
Any device that has a coil of wire in it probably has an inductive load characteristic. Most electronics
have transformers (TV’s, stereos, etc.) and are therefore inductive. Typically, the most inductive loads
are motors. The most difficult load for the inverter to drive will be the largest motor you manage to
start. With inductive loads, the rise in voltage applied to the load is not accompanied by a
simultaneous rise in current. The current is delayed. The length of the delay is a measure of
inductance. The current makes up for its slow start by continuing to flow after the inverter stops
delivering a voltage signal. How the inverter handles current that is delivered to it while it is essentially
“turned off”, affects its efficiency and “friendliness” with inductive loads. The best place for this out of
phase current is in the load, and Trace’s “impulse phase correction” circuitry routes it there.
Inductive loads, by their nature, require more current to operate than a resistive load of the same
wattage rating, regardless of whether power is being supplied by an inverter, a generator or grid.
Induction motors (motors without brushes) require 2 to 6 times their running current on start-up. The
most demanding are those that start under load, e.g.. compressors and pumps. Of the capacitor start
motors, typical in drill presses, band saws, etc., the largest you may expect to run is ½ to 1 hp.
Universal motors are generally easier to start. Since motor characteristics vary, only testing will
determine if a specific load can be started and how long it can be run.
If a motor fails to start within a few seconds, or it begins to lose power after running for a time , it
should be turned off. When the inverter attempts to start a load that is greater than it can handle, it will
turn itself off after about 10 seconds.
Submersible Well Pumps
The well pump is often the hardest load to start for inverter system. Submersible pump motors are
particularly hard because the motor is very narrow (in order to fit down the well) and draws extremely
high starting current.
When selecting a pump, check the
LOCKED ROTOR AMPS in the motor specifications. This is
usually the best guide to the maximum load the pump will place on the inverter. It must be less than
the
Max. AC Current listed in the specifications at the end of this manual. Pump suppliers and well
drillers often oversize the pump considerably in order to reduce complaints of poor pressure, low flow,
etc. Get several quotations and explain that you are very concerned about the inverter being able to
power the pump. It makes sense to operate a smaller pump longer instead of a larger pump for a
shorter period of time when you are powering it from batteries or a solar electric system.
When buying a pump, select a three wire type. This refers to the electrical configuration of the power
and starting windings in the pump motor. A three wire pump requires a separate box at the top of the
well for the starting circuit - a two wire pump has the start electronics built inside. The separate
starting box is preferred. If possible, select a relay type starting box instead of an all electronic type -
the relay types have been found to work better with inverters and generators.
The relay type also allow use of a larger or additional starting capacitor - it may help if the inverter
has a hard time starting the pump. Consult your pump supplier for more information.

Trace Engineering DR Series Specifications

General

Brand	Trace Engineering
Model	DR Series
Category	Inverter
Language	English