Review, Teardown: HIP-300 300w Pure Sine Wave Power Inverter

If you look at the post number, you will realize that this post actually got started a long time back, but didn’t see the light of day for a while. The main reason for that was because I didn’t want to spoil the surprise that I was doing a RoadTest of the Tektronix PA1000. Now that the review has been published, now I can unveil this …

Readers of the RoadTest will realize just how problematic mains electricity is for IEC 62301 Ed.2 standby power testing. The requirements are very stringent, including that the voltage and frequency be of the nominal value for the region (230v, 50Hz for Australia) and remain within a 1% window. This means the voltage should remain between 227.7v and 232.3v throughout a test, and the frequency should remain between 49.5Hz to 50.5Hz. The frequency is easy, as such large frequency excursions on the grid often mean catastrophic blackouts are going to be happening soon, but the voltage is not so easy …

VRMS-Histo

As excerpted from my RoadTest, the voltage histogram for >24 hours logging at my house gave me this. There’s a very high probability that the voltage is somewhere between 243 to 247v, roughly, which is way too high. This can be fixed with a variable autotransformer, also known as a Variac. That would “scale down” the voltages, however, that doesn’t fix the range issue. The voltage can be seen varying a span of around 10v, which is way too much. You might be able to get a run here and there (15-minute periods) where it stays stable enough, but often, it will not.

The other requirement includes the Total Harmonic Content of the first 13 harmonics be less than 2%, which occasionally gets exceeded due to industrial loads nearby. The crest factor is also a bit low at 1.39-ish, due to peak-flattening (lots of switchmode supplies).

In order to get a chance to do proper IEC 62301 standards test reports, the easiest way is to use a synthetic mains source. Unfortunately, high end laboratory grade power synthesizers cost an arm and a leg, so I decided to “cheap out” and give a low cost pure-sine-wave inverter a try.

The Unit

hip-300-inverter-box-front

This particular unit doesn’t have a visible branding on the front, and is rated as a 300 watt (600 watt surge) pure sine wave inverter. Such units are commonly used by campers, field technicians and by people who want to use a mains appliance in a car without worrying about buying an automotive-adapter (e.g. those running a laptop using its originally supplied adapter).

Such units have been reducing in price quite a lot over the years, and initially, only modified sine wave units could be purchased at reasonable prices. Modified sine wave inverters put out a “rectangular” wave, which isn’t anything like a sine wave (more on this later) and is not suitable for standby testing. It can also cause connected appliances to be stressed by the harmonics and fast-rise of the waveform, and cause them to buzz and hum. Sensitive electronics are best suited for Pure Sine Wave units.

The synthesis of a pure sine wave is most commonly done through pulse-width-modulation (PWM) methods, which switches the voltage at many multiples of the actual output frequency, and restores a sine wave out of “pulses” by smoothing it through a filter (commonly inductor-capacitor based). It is possible to generate fairly good outputs this way, although the harmonic content could be troublesome if the filter is poorly designed!

hip-300-inverter-box-rear

On the back of the box, there is some basic specifications – as far as I know, this unit is a 12v input with 220-240v AC output. It claims an efficiency of >90% and >85% full load efficiency with over-discharge warning at 10.5 +/- 0.5v, and switch-off at 10 +/- 0.5v. It claims overloading, short circuit and thermal protections, which are pretty common claims for inverters.

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The actual applicable specs are ticked on the bottom. Note that it does claim to have a 240v output and a 50Hz +/- 5% output.

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Internally, the unit is a rectangular brick, with an aluminium body and steel plate ends. The top is emblazoned with a label, with a model number of HIP-300, which suggests this inverter was made by Ningbo Honghui Electrical Appliance, although this exact model isn’t visible in their list.

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The underside of the unit seems to have a serial number but is otherwise bare.

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The front has two LEDs, one indicating power on status, and the other indicating error. One socket is provided, as is a slightly-flimsy feeling power switch. A vent grille is visible, and a large inductor wound on a toroid is visible through the grille. This may form part of the output filtering circuitry.

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The rear of the unit has a fan output with grille for cooling, with the screws slightly rusted, and two binding posts for power connection. Unfortunately, these weren’t of the banana-combination type which would have made it easy for me to use banana to banana cables to hook it up to my power supply.

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There are screws on both sides, where it is ribbed, which implies that the casing of the inverter is used as a heatsink, which is a very common arrangement.

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The unit is supplied with a manual, and a bundle that includes two cables – one is a cigarette lighter to spades (unfused) with thinner wire and a warning to limit draw to 150w maximum, whereas the other is a thicker clips to spades cable which allows for you to directly connect it to a battery.

Teardown

Taking this thing apart was quite simple, mainly because the rectangular aluminium shell around the inverter is not a single piece. To take it apart, you can remove the four screws on the power-plug end, tilt the panel away from you and slide off the top cover entirely.

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The internals consist of one PCB which slides into the rails in the bottom chassis, and a vertical PCB which is soldered to that one (which is likely the controller itself, and is changed when the unit is manufactured as a modified sine wave or true sine wave model).

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Visible on the left is the binding post inputs, and the fairly powerful fan. The input is routed to a pair of electrolytic capacitors, a high 35A rating soldered fuse-clips and a reverse polarity “crowbar” diode (which should blow the fuse given a source with low enough internal resistance).

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There is a pair of transistors at the bottom, and two pairs of transistors at the top. I am thinking the bottom pair handles the DC chopping into high voltage DC, through the main transformer core, which is then stored in the large capacitor which is approximately near the middle of the screen with the Pass QC3 label on it.The capacitor doesn’t seem to be of any reputable brand, it seems.

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The top two pairs handle chopping that DC into AC with PWM, with the two transistors to the left possibly being the drive transistors that drive the two pairs. This is then filtered through the polyester caps and large inductor, and again filtered through the isolation transformer (next to the capacitor) before becoming the output.

On the bottom PCB, there are two visible ICs, an ST LM324N quad op-amp and an AC08AA. There are also three precision trim-pots and a buzzer for warning. It is quite possible that the trimmers control the output voltage, and a variac might not be needed, but I wasn’t going to play with it and potentially destroy it. Near the vertical PCB, an opto-isolator is visible too for feedback.

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The vertical PCB houses a PIC16F716 microcontroller, and a pair of International Rectifier IR2110 MOSFET/IGBT drivers. There’s a third HA17393 comparator IC as well. The top right corner seems to show a 3.9v zener diode, which may provide a voltage for comparison.

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One of the units I received, also had a cracked ceramic capacitor behind the vertical PCB. The unit still seemed to work, so I kept it, but it;s a sign of very rough handling or poor construction techniques.

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Specifically of interest is that the ground pin is connected to the inverter chassis. I suppose “you have to connect it somewhere”, and it’s better than connecting it to the battery negative (which could make a whole car “live”), but if anything does go wrong with your appliance, touching the inverter shell is probably not a wise idea.

Will it Work?

From an initial glance, this unit has a few features which could make it problematic as a power source for standby energy testing. For one, the output voltage is claimed to be higher than the 230v nominal harmonized line voltage of Australia, so some voltage adjustment might be necessary. The tolerance of the frequency at 5% is much bigger than the 1% required by the standard. Likewise, the quality of the power highly depends on the quality of the filtering on the output. There are many variables which all need to align for this to work!

As the cost of the unit was only about AU$50, it was a pretty good deal for a pure-sine-wave unit even if it wasn’t suitable for standby testing, so I took the plunge. In fact, I took the plunge twice, as I decided to get two units, and one of the units came with a rattling transformer core, and diminished efficiency, but was still meeting specifications. I suppose you get unlucky sometimes … especially when postage is concerned.

Output Check

The first thing to do was to power the inverter up. As I would like to use it nearly continuously, using it on a battery wasn’t a good option. Instead, I hooked it up directly to a high-powered (20A) Manson benchtop switch-mode power supply. By using it to provide AC to DC, and having the inverter then change the DC back into AC, we achieve a level of isolation, which should mean that mains variations shouldn’t affect the output voltage at all, or as much.

It also improves safety, as the output of the inverter is current limited, and the total power output can never exceed the amount of power the Manson power supply can deliver, which is only 276w (minus a little bit for efficiency of converter). Overall, a large inverter isn’t necessary for standby power consumption checking as we want to measure loads which “sip” roughly 1w or less!

So, how does the output look like?

measure-graph-waveform-puresine measure-graph-harmonic-1 measure-graph-harmonic-2

The waveform is a true sine wave, no doubt about that. Looking at the harmonic graphs, there isn’t too much energy in harmonics, although there is more energy in the upper harmonics than in real mains electricity and this comes down to the fact that this is PWM generated (rich in high frequency components that need to be filtered out). You can compare this to a modified sine wave inverter below (ringing is due to the test instrument having limited harmonic data):

measure-graph-waveform-modsine

The raw numbers which are relevant to IEC 62301:

Parameter Modified Sine Wave True Sine Wave
Vrms (V) 244.61 233.52
Freq (Hz) 49.573 50.056
Vcf 1.3666 1.4496
Vthd (%) 36.735 0.55652

It’s pretty interesting, because it shows that the modified sine wave inverter I have is pretty lousy at keeping voltage regulated as well. Anyhow, the true sine wave inverter doesn’t look like a 240v model, but it is a little high for 230v, so a variac is needed. I actually built a 1A variac based on an open frame unit so as to trim the voltage. The frequency, is good as I would expect – as it’s likely to be generated by microcontroller based on the crystal input which generally only varies a few hundred ppm. The crest factor is pretty close to ideal (1.4142) and well within range.

Using it for standby power consumption runs worked fine provided the unit was left to warm up for 10-20 minutes before starting. It seems that as it warms up, the output voltage can make ~2-3% jumps but it’s all fine once it’s reached temperature. The fan itself doesn’t seem to be thermostatically controlled, and is instead activated dependent on load. For small loads below about 10w, it’s not uncommon to see the fan never spin up, but the transformer inside does get quite hot. There hasn’t been any failure to date though, so I suppose it’s okay.

Under heavy loads (120w+) the fan starts to spin quite loudly and it seems effective as I’ve run a computer off of this setup for hours with no trouble either.

Definitely a cheap fix to a potentially expensive problem, chalk this one up to a “hack”.

Conclusion

Despite my initial reservations as to how good a low cost pure-sine wave inverter could be at being a synthesized mains source for IEC 62301 Ed.2 standby power testing, my experience seems to have proven me wrong. Using the inverter connected back-to-back with a benchtop power supply produced an isolated output which was relatively insensitive to mains variations. It worked a treat, provided the output voltage was trimmed with a variac and the unit was left to warm up initially. A cheap hack, sure, but I don’t think the manufacturer of the unit intended it for this use anyway. At least it allowed me to evaluate many appliances under IEC 62301 for my own interests and give the Tektronix PA1000 a good run.

About lui_gough

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14 Responses to Review, Teardown: HIP-300 300w Pure Sine Wave Power Inverter

  1. Pingback: Investigation: How Accurate is that 3.5 digit Multimeter? | Gough's Tech Zone

  2. Tom says:

    I am interested in knowing the input current with no output load?

    • lui_gough says:

      The quiescent current for my units seem to vary depending on the temperature. One unit uses about 0.6A with no load, the other uses about 0.8A, but can be up to 1.1A when first started, and falls as it warms up. As it goes for inverters, compared to modified sine wave units, it’s actually fairly high (those can sometimes go below 0.35A), but I suppose it’s always been the case that true sine wave inverters are slightly less efficient.

      Hope that answers your question.

      – Gough

      • Tom says:

        Thanks so much for the info, Gough.
        It does seem rather high for a 300W inverter, and annoying because I couldn’t just leave it turned on all the time. Also, with the 7 to 10 watts of permanent draw, very inefficient for small loads like a fully charged laptop or a small stereo, assuming the inverter’s draw would be the quiescent power draw plus about 110% of the output to the load. I think I’ll keep looking for other possibilities. Thanks again!
        (FYI, I frequent an area of PNG where there are frequent blackouts – sometimes lasting for days. I have a small generator, a 20 amp battery charger and a 50 AHr deep cycle battery. I want to replace my 200W square wave inverter).

  3. Old Techo says:

    Very well done and thank you for your efforts 🙂

    I have the HIP-600 model and it looks very similar inside to yours. Mine has worked well for a couple of years but now prematurely immediately shuts down on a load of 400 watts. I suspect it is due to incorrect sensing of either the AC load or DC input voltage. Re the latter, during tests it never drops below 11.7 volts and the spec says will work down to 11.0 volts.

    I too spotted the 3 pots and figured they are the adjustments I need to tinker with. I’ll try them one at a time whilst monitoring AC voltage on no and light load for starters to see if I can eliminate some. Will report later.

    • lui_gough says:

      I haven’t done any testing regarding the three pots, but I one of them may have to do with transistor biasing as well, where incorrect adjustments are likely to be detrimental to efficiency or waveform quality. I would probably keep an eye on quiescent current consumed by the inverter as well in light of that.

      But more specifically, there is a potential that the low-cost/low-quality capacitors have degraded over time especially due to heat exposure. As the load of switchmode converters is very “pulse” driven (esp in PWM systems), a dying capacitor with high ESR would not be able to effectively filter these transients. The dips may actually be short to the point of not registering on the multimeter, but enough to trigger the under-voltage protection. Maybe a replace-and-see is worthwhile, or probe with an oscilloscope, but my main concern would be mainly the high voltage DC cap (400v), and the input filter caps.

      Aside from that, there isn’t much to it. Good luck!

      – Gough

  4. Old Techo says:

    Testing only. My subscription seems to have failed???

  5. Old Techo says:

    Gough, some follow-up.

    I tried the CRO but didn’t learn much so then I ordered new Caps. Eventually they arrived and I replaced all 4, remembering that my unit is the 600 watter. Although I agreed in principle about tired Caps I felt mine were not old enough – but I still thought it worth doing first before tinkering with the mystery pots.

    Testing with the same load i.e. 250 watt soldering iron then switching in a 150 watt lamp, it failed exactly as before. Happy that the Caps were not contributing I then tackled the 3 trimpots.

    Using the same load, the constant 250 and flicking on the extra 150 watt lamp I moved each trimpot 1 turn in both directions, tested and carefully returned them to original. I realised that trimpot backlash may introduce a small error. Only one trimpot had an effect and the anticlock single turn caused the invertor to shutdown just on the 250 watt load.

    Armed with this logic I turned this trimpot clockwise, one turn at a time, and found after 4 turns the invertor would for the first time support the load of 400 watts. Adding a 300 watt soldering iron gave me load options of 150, 250, 300 and combinations.

    At 5 turns of trimpot it would support 450 watts but no more. At 6 turns it supported the total of 700 watts, so I left it there.

    If I knew how to add a pic here I could identify the trimpot.

    • lui_gough says:

      Interesting result and definitely seems a little strange that you should have to move a trimpot so far in its adjustment range to restore the expected load. I’m not sure, but I really wonder if the unit will survive in the long run with such a big adjustment – I’d treat it with some care at least, because it could be a sign something else has gone bad somewhere. My normal suspicion is the caps, but since you have ruled that out, I have no idea what it might be.

      As for the subscription/comment subscription – I have no idea, but for some reason, sometimes it works, and sometimes it doesn’t. Some users seem to report not receiving follow up replies via e-mail, whereas others do. It may be an upstream spam filter blocking e-mail, or something wrong with the sendmail on my web host. Sadly, I don’t have much time to investigate this but it has been noted. I have subscribed myself to some of my own postings which seems to work … so *shrug*?

      – Gough

  6. A.Rahmani says:

    Hi. I have a similar device (made in china) and i want to fix and repair it. Chinese factory cleared details of 4 pairs transistors at the bottom, and 2 pairs of transistors at the top of board. (Transistors that were connected to the metalic frame body as heatsink) I want to know what is the name and model of this 6 transistors.

    Thanks.

  7. Australian Camper says:

    Great review and enjoyable read!

    I’m considering buying the 1000 W version of this inverter. It’s to be used while camping to power a sandwich press (nameplate information says 950-1000 W but others I’ve found are 750W). It’s a no fire zone so we need an electrical option to cook something.

    I’ve no experience using these devices. My main concern is how long it will take for the inverter to “warm up” before the appliance connected will be ready to be used. I’m assuming my car engine will need to be running while the inverter is used?

    Keep up the good work

    • lui_gough says:

      Generally an inverter doesn’t need to “warm up” as such, as its output is practically available as soon as the switch is flipped. However, the voltage may not be quite as stable initially, but it will depend on the load and how sensitive your equipment is. In general, heating elements are one of the least sensitive devices, so it really doesn’t matter, you can take it as almost instantaneous.

      Using a 1000W inverter to power a 1000W device is a pretty bad idea in general. The main reason is that most heating elements have a high in-rush when they are turned on, and may not settle to the nameplate rating until they do get warm, often consuming much more than the expected power. I’ve seen curling irons rated at 60W consume 130W when first started. As a result, it’s unlikely a 1000W inverter could power a 1000W sandwich press as the cold current could be higher than nameplate and trip the over-current protection on the inverter. Don’t be fooled by the “surge” rating of the inverter – this is the peak current that’s normally only sustained for a few cycles (less than 20 milliseconds generally). The other thing is that running an inverter at its maximum load will inevitably cause it to run at its maximum expected operating temperature, so lifetime will be impacted.

      As a rule of thumb, for continuous operation, you should aim to size your load to be about 60% of the inverter rating, or even up to 80% at the most. The reason behind this is several fold:
      – Inverters which are too large for the load are operated at too light of a loading, which results in poor electrical efficiency and hence wasted energy.
      – AC appliance nameplate wattage ratings are taken as their real consumed power, but if their power factor (ratio of real to apparent power) is not unity (i.e. 1), then the actual apparent power required is higher than the nameplate power. An inverter has to supply the apparent power, not just the real power. For example, a CFL rated at 20W with a power factor of 0.5 (your average cheapie in the shop) will need 40W of inverter capacity to run. A mixed load generally sees better power factors, as heating devices are generally very close to 1 (0.999 or above), and electronic devices are mixed depending on their design.
      – Lifetime and heating issues as mentioned above.
      – You might still want to further oversize and take the hit on efficiency especially if you wish to turn appliances on and off at your whim, or risk momentary power interruption during switching on heavy appliances.

      As you have no experience using these devices, I will have to provide a big cautionary warning here. Inverters, especially above 300W, are not toys. They draw MASSIVE currents at full load which need GOOD connections and enough current capacity to back them up, or they will fail to operate correctly and melt cables/connectors etc.

      Consider a 1000W inverter, at full load. Lets assume it’s a good product with a 90% efficiency, the power required from a car would be 1111W. If you’ve got a 12v system as a small/medium car does, the current needed is 92.6 Amps (or half that for a 24v system, e.g. 4WD/truck). This is a royal crapload of current that requires very thick cable and a definite “bolt in” to the battery terminals directly. Worst still is that this current is likely to cause you major problems pretty quickly because:
      – This is pretty close to 100A. The cable thickness required to connect that to a battery is roughly the size of jumper leads. Don’t be fooled, most 200/300A jumper leads are sized for starting operation, rather than continuous 100A flow, so it’s going to be pretty big. A terminal upgrade would not be unexpected, but skimp on the leads and you’ll find the voltage drop to the inverter will trip the under-voltage protection (complaining of a low battery) and the device will fail to operate.
      – For a point of reference, many sedans have starter motors of about 800-1200W rating – so think of your sandwich press as taking a load pretty similar to continually cranking the car … this starts to put the power into perspective.
      – An average car alternator is somewhere in the range of 40-60A, when the engine is running at some very quick speeds. When idling, the output could be quite low, say 8A or so. Of course, having the engine running and revving mildly gives your battery a bit of a break, but in itself, isn’t quite enough to offset the actual draw, so regardless, your battery is definitely going to be under stress.
      – Most car batteries are somewhere between 30-60Ah in capacity, so a load of 92.6A will definitely drain the battery in half an hour to flat. Most car batteries are not rated for deep cycling and will die a premature death if emptied below 10% or so, which really doesn’t give you much run-time (lets say, roughly 4 mins tops).
      – Get this wrong and you might get stranded, or need a push …

      That’s why most recreational people will prefer to use less energy intensive appliances, or have a dedicated bank of relatively expensive deep cycle cells for appliances only, to avoid reliance on the starting battery. Otherwise, they make use of camp-ground power supplies at caravan parks for these appliances.

      – Gough

    • Old Techo says:

      No arguments with anything Gough has stated. I have a 2500 watt invertor that I ran tests on using a nominal 2,400 watt fan heater as a load. I measured output voltage and power, input voltage and current (clamp-meter). The latter was around 270 amps from memory.

      Primarily I use the invertor, when needed, connected directly under the bonnet to my Prado twin batteries via large brass wing nuts I installed. The Prado batteries are typical large 4WD sized. As cranking bats these days are rated only in CCA I’m guessing close to 100 Ah each. I parallel them with a homemade brass knife-switch.

      My normal use is to power a nuker (microwave oven) in our caravan and that consumes about 1,500 watts. I also use the invertor at home connected to a single ex-Prado battery to power a 1,300 watt electric power-drill that I use to start my 5 kVA generator. It has an 11 HP petrol motor and I am getting too old to be able to pull-start it so I diced the recoil starter and now crank it with my drill via the sprag clutch on the end of the crankshaft.

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