Powertech MI-5702 Inverter

       I have had a few cheap medium power pure sine wave inverters (<500W) and they all failed so I looked for a better built one.

       I found this one on a second hand store, the price was about $50 and a couple screws missing on the top cover so I was able to take a peek inside before buying it. It worked when they tested it so I took it home.

The box

The inverter. It was in decent shape, no dings or scratches except for a couple missing screws on the top cover.

DC input terminal block. Has nice beefy terminals that could take about 4ga cable. Holes are 9mm dia.

Australian outlet. It is 230V AC 50Hz

Removing the top cover, Internals look decent.

All big caps are Capxon brand but should be fine for general use.

Input terminals are big but the wires going to the PCB are thin. Around 10-12ga.

All wires have color coded plugs.

Back of the outlet. Ground is connected to chassis. Output wires have a ferrite core for filtering.

Battery cables also have a ferrite core for noise suppression.

USB 5V output has a proper DC-DC supply using an MC34063.

Current transformer is used to sense output current load.

Main output inductor looks nice. It is varnished so the windings do not move.

Another view of the input side. The cables are very flexible.

These are a pain, output H bridge transistors clipped to the chassis.

Input switchers are mounted on a separate heatsink with a thermistor nearby. Fan is thermally controlled.

There are four single diode TO-220 devices.

Isolated supply for the HV side circuitry. The input and output are galvanically isolated only connected by a few low value capacitors for noise.

SPWM control sub PCB. This uses a PIC micro and IR2110 mosfet drivers.

Back of the SPWM board.

Atmel Mega8A for the housekeeping duties and a TL494 for the step up converter.

Lots of noise filtering on the output side.

Took a universal outlet from a broken inverter. That's not gonna work.

Hole is too big.

Bent the side tabs and it just might work.

Hotmelt glue is your friend.

Doesn't look too bad.

At first power on, the SMPS goes into hiccup mode drawing short bursts and consumes very little average power.

When there is a load detected, SMPS goes into continuous mode and draws a steady idle 5.5W.

Yellow is the live pin, blue is the neutral pin. Typical waveforms of an SPWM modulated pure sine inverter.

       This appears to be an old unit, online stores show it is discontinued. We shall see how long it will last in my use.

Page created and copyright R.Quan ©16 Oct 2017