Friday, July 12, 2013

eBay can kill you

A few posts ago, I wrote here about how we replaced our 120-volt marine electric range with an induction cooktop from Europe, which required 230-volt power. That project took longer than expected, in part because of a hiccup with the power setup. I wanted to write this separate post to talk about that, because I think I will end up linking to it at some point in the future. Also, that post was already way too long.

To refresh your memory, we wanted to have an induction cooktop on the boat, because they work so much better than conventional resistive electric burners, rivaling gas in the level of control and speed of response. They also use less energy, which is important to us because we plan to run it with the inverter on battery power while we are at anchor.

Were it not for this desire to power the cooktop from the inverter, we could simply have connected it to a 240-volt circuit; both the shore power and generator supply 240 volts, split phase. Our inverter, however, is a 120-volt only model. We briefly considered getting, instead, the 240-volt split-phase version of the same unit (a Magnum Energy Magna-Sine 4024), but that version is not marine-rated, has no neutral-ground bonding relay, and, most importantly, can only supply about 80% of rated output when used for strictly 120-volt loads -- the majority of our planned usage.

Another option was to forgo the dual-burner unit I had my eye on, and instead get two single-burner, US-spec 120-volt induction units. The problem here was that our very limited counter space could not accommodate two units front-to-back, and if we put them side-by-side one unit would be partly under a fairly low overhead cabinet, creating a possible fire hazard as well as the possibility of damaging the cabinet with steam and other cooking fumes.

Instead I opted to convert the 120-volt inverter output to 240 volts just for the cooktop circuit. This is a pretty straightforward process, done all the time in industrial settings by using a simple device known as an autotransformer. This is nothing more than a transformer where the primary and secondary sides share a common winding, and these can be used to step voltage up, from say 120 to 240 volts, or, by connecting the same device the other way around, to step voltage down, for example from 240 volts to 120 volts.

Commercial autotransformers in the three kilowatt range, what we needed for our cooktop, can be quite pricey, so instead I bought mine on eBay. I chose a vendor with a shipping warehouse in the U.S., but there was no question that I was buying product from China, almost directly. In fact, I buy quite a few items direct from China when I need them -- some of the quality is actually quite good, and there are bargains to be had. And it's not as if one can buy, for example, a video camera made in the U.S. -- it just doesn't exist.

The brand turned out to be "Seven Star," even though the seller had carefully blocked that out on his listing photos. There were quite a few auctions for what appeared to be identical units, and I am guessing any seller I chose would have shipped me the same "Seven Star" model.

I tested the unit as soon as it arrived, carefully checking input and output parameters such as voltage, and I even boiled some water on the induction cooktop to make sure it would all work together. Then I set it all aside until I was ready to install the cooktop.

As part of the cooktop project, I had to source a circuit breaker and some appropriately rated wire to hook up the whole system. I wanted a toggle-type breaker mounted near the unit, so we could shut off power to the transformer itself when the cooktop is not in use. Otherwise, the transformer would be using a small amount of power all the time, even with the cooktop off, dissipated as waste heat -- not where you want your battery power to be going.

It was then that I realized that the European-style power cord on the transformer, which also came with an adapter to connect it to North American outlets, was suspiciously thin. The size stamped on the cord was 2mm2 (the rest of the world sizes wire in square millimeters of cross-section), which works out to around 15 AWG. That's about right, at 240 volts, to carry the transformer's rated 3,000 watts, which would be just over 12 amps. But the way this particular model works, the cord is used on the input side for both step-down and step-up modes, with a selector switch determining which mode is operative. At 120 volts, this cord could be carrying as much as 25 amps.

By any standards of safety, that much current requires at least 12 AWG (4mm2), double what was provided. Here in the US, code mandates that it actually be 10 AWG (6mm2), treble what was provided. I decided it would be unsafe to use the transformer as delivered, but I hoped I could resolve the issue simply by replacing the power cord with 10-gauge boat cable. I had already planned to cut the plug off the cord and hard-wire it anyway.

The real surprise came when I opened the unit up to replace the cord. What I found inside was appalling. For starters, not only was the cord 2mm2, but so too was all the internal wiring between the cord, the switch, the fuse holder, and the outlet built into the back side of the unit. This outlet is a "dual mode" type, which will accept both European style 220-230 volt plugs (two round pins) or North American style plugs with two blades and an optional ground pin.

It gets worse. As long as I had the unit open, I had a careful look at all the parts. The transformer windings themselves looked fine, and the transformer pigtail looked to be about 12-gauge, acceptable as AWM. The aforementioned selector switch, which, by its very nature is involved in both the high current and low current side of the equation, was rated at just 3 amps at 125 volts, or 2 amps at 250. That would be suitable for a device capable of, at most, 500 watts -- just one sixth of the intended capacity of the transformer. Worse, the rating in our intended use, in the step-up mode, is just 375 watts, one eighth of what we need.

To top all this off, the inline fuse holder, providing a false sense of security to any unsuspecting consumer, is rated at just 15 amps, but was pre-equipped with a 30-amp fuse. Two 30-amp fuses were supplied as spares. The 15-amp rating would be fine for 3,000 watts in step-down mode, but then the fuse should also be at most 15 amps. The installation of the 30-amp fuse confirms that the manufacturer well understood that the unit would be expected to carry 25 amps in the step-up mode. Yet they deliberately chose significantly undersized components in the assembly.

To make matters worse, the (undersized) wire connecting all these items was merely soldered to the tangs, as you can see in the photos. It was not first twisted through holes or in any other way mechanically secured before soldering. This would pretty much guarantee that, in a prolonged 3,000-watt usage episode, the tiny connecting wires and maybe even the undersized parts themselves would heat up to the point of softening the solder considerably, which might lead to an internal wire coming loose and possibly creating a short circuit.

In short, this transformer is a serious hazard, possibly a death trap. I've broken the warranty by opening up the case, so I am stuck with it, but I did alert the seller through eBay's system. He was blasé, telling me simply to "contact the manufacturer" (yeah, right -- in China), you know, the one whose name he deliberately obscured in his listing. And I have a good mind to file a complaint with the CPSC.

As for my own application, I opted to completely remove both the under-rated switch and fuse holder, and run my 10 AWG boat cable directly to the transformer inputs. We don't need the switch because we will only use the transformer in one mode (step-up) and the fuse is redundant for the magnetic-hydraulic circuit breaker I've installed in line with the supply wiring. I added better case grounding to the unit, but left the output wiring alone as it was sufficient for the lower current on the output side. We needed the special outlet to accept the European plug from the induction cooktop -- I did not want to void another warranty by cutting the plug off that, too.

I will remain a bit nervous about this until we have a solid track record of use. In the interim, I will keep an eye on things using my infrared pyrometer, ensuring that operating temperatures remain in an acceptable range. I also made sure to install the case with plenty of free air space around it.

The lesson here, of course, is caveat emptor. There are plenty of unscrupulous sellers on eBay, and plenty of off-shore manufacturers, out of reach of US laws and codes, willing to supply them with inferior and outright dangerous products.  eBay does have some buyer protection policies in place, but the average consumer would have no way of looking at this product, without disassembling it, and knowing just how dangerous it is.


  1. Wow - I've run into some under-sized wiring component issues in the past, but your example takes the prize. This unit - as delivered - is merely waiting to surprise anyone who would use it anywhere near its full rating.

    I agree with your approach: I suspect that the transformer windings themselves - based on your inspection - are up to the task. I'll wager the transformer probably came from a different factory than the final, completed unit. The transformer factory likely supplies units for many different applications, some of which will draw the full current rating - so they're configured to meet standards that other assembly-only entities don't bother to meet.

    I applaud your intent of notifying the supplier, but I'd sadly agree that the manufacturer cares little.

    Once again: Thanks for going to the trouble to share what you learn on each project. I pay close attention, and plan to make use of these lessons in the future!

  2. How long can you cook without depleting the batteries?

    1. That's a great question. The answer depends on what we're cooking. I expect that, as now, we will seldom use both burners together, and even the single burner will rarely be on its maximum setting (1,500 watts). Typical usage is more like 500 watts, which comes out to about 23 amps at 24 volts (accounting for losses). As the batteries, once they are replaced, should give us about 700 amp-hours, of which 80% is usable, that would let us cook at that rate for a full 24 hours continuously. Alternatively, if we cranked both burners up to the full 3,000 watts, we could cook for four straight hours on a full charge, assuming nothing else is using any power.

      In practice, on the bus, with a single 1,300-watt induction hob, we never worried about its effect on the battery capacity. Cooking for a half hour or so is just in the noise level. When we want to cook longer that that, we are probably using the crock pot anyway, which uses maybe 100 watts or so. Again, eight hours of crock pot cooking is almost in the noise level, but, generally, we were under way anyway, and the juice was coming from the engine alternator.

  3. You should see chinese cell phone chargers ;) Almost as bad

  4. Sean
    Thanks for the detailed account of your adventure.
    If you still need a standard EU socket I have a few and could send you one for shipping costs.
    We are out in our Motorhome and won't be back to our fixed home for about 2 weeks.

    1. Thanks. To clarify, there is already an EU receptacle on the transformer (on the side opposite the one pictured above, with the instructions and ratings on it), and that's all we need. The transformer is mounted in the cabinet below the cooktop so that the cord reaches easily.

  5. Very timely. I am getting ready to buy a step-up transformer through Ebay probably. I have installed a 230 volt mini-split AC on my Cityliner. The Cityliner is set-up primarily for 115 volt with a Trace 4024 and a Honda 6010 although I will have a couple of 230 volt circuits when it is available on the pole. The mini-split draws 8 to 10 amps with 13 on rotor lock-up. I am planning on a 5,000 watt transformer and will probably hard wire the transformer its self after you experience.



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