Long time since last tech related post! Today continued the test to find Argon drive power limits (see earlier tests here). This time I loaded drive’s internal AC to DC power supply with an old room heater while simultaneously measuring transmitted power from AC and DC lines.

The heater pulled 1.53 kW from drive HV DC bus for about 45 minutes continuously with only passive cooling of the drive. Temperatures were measured from multiple points of drive along PSU current path (components & PCB traces) to find out if anything is overheating. I’m happy to report that everything stayed relatively cool which means the drive is capable of at least 1.5 kW output continuously! The hottests parts inside were 8 Amp fuses which is easily helped by using larger fuses.

Today I got first results from the accredited testing service for compliance of power drive safety standard EN 61800-5-1. They did good job and found few issues:

1. Isolating transformer between user touchable and hazardous voltage side doesn’t meet reinforced isolation requirements
2. Clearance from power stage & bridge rectifier mounting screws to PCB tracks not large enough
3. On one side of the enclosure the vent holes are too large to meet IP30

Logic power isolating transformer (blue) has 3 kV isolation spec but still doesn’t meet the strictest interpretation of  the safety standard

Luckily none of them is hard to fix but finding them early was very important!

Update

By contacting transformer manufacturer we learned that the blue winding consists triple insulated teflon wire which fulfills the reinforced isolation standards. If we can confirm that, we save few days of isolated PSU circuit redesign & testing!

Lately I have been concentrating on finding the current & power limits of the Argon drive. I have used the artificial load unit as test load.

Testing has gone well and has revealed things I didn’t know about Argon. The most positive surprise is that the drive seems to be able to deliver a lot more continuous power than calculated. The first anticipated limiting factor in the design was the equivalent series resistance (ESR) of the bulk capacitors. ESR sets the limit to the maximum ripple current that AC-to-DC power supply can handle because current flowing through capacitor’s internal resistance will heat them up and eventually make them reach their maximum safe temperature.

By calculating maximum ripple current & power based on capacitor specs I came up with figure of 700W continuous power before capacitors get too hot (105⁰C). However, by testing I found out that even at 1200W continuous output the caps didn’t get warmer than 37⁰C. I think capacitors either are way better than specified or their ESR is specified at 105⁰C which may be much higher than the ESR in room temperature. So 700W is probably the limit when capacitors already run hot (needs very high ambient temperature) and at least 1.2kW may be extracted at room temperature.

Oops! Artificial load unit power resistor wire terminals desoldered them selves under little bit too much pressure

We finally have received the samples of enclosure consisting steel sheet metal cover and aluminum heat sink plates. So the front panel art comes with trees as voted best in the previous posts. My thanks to everyone giving comments to that post! It really helped us to make the best choice.

Argon prototypes with industrially made covers. LED numbering texts (above the RJ45 sockets) were mistakenly forgotten from the front panel art.

The cover slips on smoothly unlike the first self made prototype which required bending one side in order to install it on the device. The realized design looks and feels very solid and leaves only little space for improvement. However, few improvements will be carried out mainly to help assembly, most of them being related to threading for mounting screws and adding more accuracy to bends.

To the final design I’m also considering to add an placeholder hole for possible extension port that could be installed inside the drive as stack-on circuit board. Extension boards could be made by end users, third parties and of course by us.

Today I went into the lab to repeat some surge tests that let the smoke out of Argon’s on-board voltage regulator the last time. This time some circuit modifications were made as attempts to enhance the surge voltage & current handling. Surge test attempts to emulate a lightning strike.

Total of 12 a bit different surge pulse tests cases had to be carried out to meet the EN 61000-6-2 and EN 61000-4-5 industry standards. In the list below are the open circuit voltage and series resistance that are shot to the target voltage supply lines:

• + and – 500V 2Ω between 24V and 0V (DC supply)
• + and – 500V 12Ω between  +24V input and chassis (DC supply)
• + and – 500V 12Ω between 0V input and chassis (DC supply)
• + and – 1000V 2Ω between L and N (AC input)
• + and – 2000V 12Ω between L and chassis (AC input)
• + and – 2000V 12Ω between N and chassis (AC input)

The surge tests are typically more difficult to pass than ESD & EFT due to high injected energy and currents. For instance 500V and 2Ω  produces current of 250A and 1000V 2Ω yields whopping 500 Amperes. That will heat up the overvoltage protectors quite extremely and weaker components simply explode.

Now all tests passed without damage and motor was servoing simultaneously through the whole test. Changes will be brought to the PCB design which makes a big step closer to the final design.

I hope our followers have had a restful Cristmas break and joyful beginning of the new year! Anyway, time to get back to the business.

The photo below shows the artificial load unit to be used in Argon production testing process. In other words it will be used to simulate heavy load for drive power stage electronics to separate the wheat from the chaff.

Artificial load (work in progress). The most of energy goes into the flat power resistors mounted on the sides of the heat sink block.

The unit consists of three inductors and three power resistors forming a 3 phase load that simulates a motor stator. In the same high density heat sink there is also a fourth power resistor that provides load for regenerative resistor IGBT switch.

Other stuff inside provides power for cooling fans and contactor that safely disconnects the load in case of over heating. The two fans in the heat sink are installed in push-pull configuration for maximum air flow.

A day in a EMC lab yielded over 40 radiated emission measurements and lots of useful data about how to install the device to minimize interference.

GTEM type EMC chamber

Inside the chamber

Few radiated emission test results shown below. The green line represents the limit to meet IEC 61000-6-4 limits in industrial environments, so any spike above it would mean that device is not compliant.

Chamber & measurement equipment background noise. The small spikes in GSM frequencies can be seen beyond 900 MHz. Notice that graph has different scale than the ones below.

These tests were carried out while drive was executing 10 Hz high current square wave torque command which was found to produce the worst case scenario.

Driving square wave torque command without any added filters on cabling

By experimenting we found out that a ferrite bead core on 3-phase output leads (as common mode filter) before motor cable makes a quite significant difference. The graph below shows a success in emission test. This test was repeated several times in different ways to eliminate the possibility of error.

Same as above but with a ferrite bead filter on phase leads. A spike visible at 360 MHz is probably a third harmonic from the 120 MHz CPU.

In addition to emission tests, also radiation immunity test was carried out. No sign of disturbance was noticed on drive operation or communication to PC, so immunity test was passed as well.

Next up: ESD & EFT tests. But first I’m going to visit Germany and SPS IPC DRIVES fair in Nuremberg. See you there!

Tomorrow will be a big day for Argon; it will be tested for EMC (electromagnetic compatibility) standards in a test laboratory. The tests consists several measurements: radiated emissions, conducted emissions, radiated interference survival, electrostatic discharge and surge current tests.

Argon will be tested against the most stringent standards that the CE regulations specify ensuring (if passed) that it may be installed in virtually every environment without violating the regulations. For example different cable length classes exists. Some classes require testing up to 3 meter cables but I chose to use the class that requires passing all tests with 30 meter cables in addition to 1 meter cables. In some cases 1 m cables may give worse results so testing with a such short cables is also a requirement.

Milled enclosure sheet metal

The device under test has a self rolled enclosure milled with a self made JV2 CNC router. The sole purpose of this prototype is to check fitting and provide EMI shielding during the tests. The final enclosure will have more professional finish.

Argon testing with work-in-progress enclosure