Karen’s Victa

Karen purchased a Victa lawnmower many years ago, and it has expired.

Victa was Australian, but now owned by Briggs & Stratton. The engine is different to most two stroke small engines, the notable differences are:

  • Victa’s G4 plastic carburettor; and
  • the engine is built “upside down”, the flywheel is underneath (ie on the PTO end), and there is no main crankshaft bearing above the big end, the crankshaft is supported by two bearings below the big end.

This article describes the service work to get the mower into good working order.

First checks / observations

The handle bolts and handwheels don’t work, someone has replaced a cup head bolt with a screw and it does not locate in the tube, so a screwdriver is needed to tighten the handle. The lower bolts are loose and need tightening.

The mower takes a lot of effort to push, the wheels are jammed up with string and stuff binding the bearings.

The blades are beyond service life, chipped and blunt, and the blade carrier and mower base are caked with wet decaying grass clippings.

Fuel tank contaminated with solids and water.

This is an air cooled engine, and the cooling fins and cooling fan were caked with oily grass / dust residue. This leads to higher operating temperature, shorter engine life, and performance problems.

Above, the air filter is filthy and will cause rich running which results in carbon build up in the combustion chamber and blocked muffler. Continue reading Karen’s Victa

dB loss is always negative… right???

A recent online posting set out to inform the masses:

The concept of free space path loss (FSPL) is widely misunderstood. Some university lectures and even texts get it wrong. …

The result is some dB of loss which is the ratio of the power received to the power transmitted expressed in dB form.

Errr no! Continue reading dB loss is always negative… right???

Neewer Macro LED Ring Light Flash RF550 – Guide Number

I purchased a Neewer Macro LED Ring Light Flash online for a modest price (~$50).

It was described with specifications, but specifications for Chinese product are not to be trusted… so it deserves measurement (though shortfall would become evident in use in short time).

This article reports measurements of the flash mode characteristics. Continue reading Neewer Macro LED Ring Light Flash RF550 – Guide Number

Digital display for DIY 25W dummy load – part 3

Digital display for DIY 25W dummy load – part 1 described a  digital display for a DIY 25W dummy load / digital wattmeter. The original research tested implementations on an Arduino Nano (ATmega328P) and Arduino Mini Zero (ATSAMD21). Though the Zero appears the better chip (32bits, better ADC resolution etc), the dev board is so noisy (ADC wise) that the Nano produces better results.

This article documents tests on three other dev board alternatives:

  • Arduino Nano Every (genuine);
  • Wemos SAMD21G board; and
  • Seeed XIAO mini Zero.

Baseline: Arduino Nano v3.0 (clone)

Above is the initial prototype Arduino Nano v3.0 (16MHz ATmega328P) with OLED display. This clone has a CP210x serial chip, clones with a claimed FTDI chip are probably fakes, ones with CH340x chips are probably ok. Continue reading Digital display for DIY 25W dummy load – part 3

FT37-43 for a 49:1 EFHW transformer enquiry

A correspondent asked whether Sontheimer coupler – transformer issues – an alternative design – FT37-43 could be used to inform design of a 49:1 EFHW transformer based on the same core, but with a 2 or 3t primary.

In the case of the Sontheimer coupler the winding with the higher number of turns appears in shunt with the nominal 50Ω load, and its effect on InsertionVSWR and the core loss can be predicted reasonably well and confirmed by measurements as in the referenced article.

In that instance, a 7t winding in shunt with the nominal 50Ω load causes excessive core heating, a 3t winding will be worse, and 2t worse again.

The case of an EFHW transformer is somewhat similar, the difference is now that the winding with less turns in approximately in shunt with the nominal 50Ω primary referred load. The same Simsmith model can be used to predict likely InsertionVSWR due to primary magnetising admittance, and the core loss.

Let’s try the 3t case first, with the experience of the referenced article we can expect it will have insufficient turns for good performance.

Above is the Simsmith model of a Fair-rite 5943000201 core (equivalent dimensions to FT37-43) with a 3t winding. Note this does not apply to Amidon #43 as their material is significantly different in characteristic. Continue reading FT37-43 for a 49:1 EFHW transformer enquiry

Making a jtag2updi adapter

This article is about selection and reprogramming of an adapter to make a jtag2updi adapter using the code published at https://github.com/ElTangas/jtag2updi.

The purpose is for programming some of the newer AVR chips that use UPDI.

Above is a JTAG ICE that I purchased, but I did not check the pics carefully enough and fell foul of the Chinese Cheats. The chip arrowed is the USB-RS232TTL chip, it is a PL2303HX which will not work in Windows 10 since the driver was poisoned many years ago. Continue reading Making a jtag2updi adapter

LED plate driver failure – 24W round plate

This article documents failure of a 24W LED oyster. The luminaire was purchased complete on eBay for about $45.

After about two years use, the light became sensitive to switching transients on the mains, visibly blinking when other appliances were turn off or on. After some time, this progressed to oscillating on and off for a few seconds on a cold startup, but on hot startup it was stable. Continue reading LED plate driver failure – 24W round plate

Hot water woes

A recent episode where the 170l gas storage hot water service relieved itself through the pressure / temperature relief valve sent me on a quest to understand the problem.

At the time, a ‘full rate’ discharge of 95° water was holding the valve open, and even with the gas turned off, the flow continued for some time until I closed the water isolation valve to let the system cool down.

So, was this simply a thermostat failure, temporary or permanent, or perhaps the result of ‘stacking’.

Stacking is caused by repeated very short draws of hot water, which cool the bottom of the tank near the thermostat, triggering heat input which can cause the top of the tank to reach temperatures considerably higher than the set point of the thermostat.

Another question that was of interest in choosing a replacement if needed, was how much heat is lost from the heater, what is the running cost of heat leakage alone.

Heat leakage

The heater was allowed to reach ‘normal’ operating temperature and stabilise, and the gas valve was closed which would allow the unit to cool.

A variation on my IoT water tank telemetry project was configured to use a type K thermocouple and 4-20mA converter to provide a temperature logger, a type K thermocouple was inserted between the insulation blanket and tank at the top of the tank. The 4-20mA converter does not incorporate cold junction compensation, but the logger incorporates an ambient temperature measurement facility which will be used for approximate compensation.

Above is the improvised data logger setup. Continue reading Hot water woes