Member postings for Robert Atkinson 2

For clock setting you don't need a full GPSDO. Just get a Oven Controlled Crystal Oscillator (OCXO) or Temperature Compensated Crystal Oscillator (TCXO) with adjust ment and set it occasionally aginst a GPS. This is easy if you have an oscilloscope. Trigger the 'scope from the GPS 1PPS output (e.g.) put it on channel one) and monitor the output of the oscillator on one channel. The trace of the oscillator will drift across the screen. adjust it for minimum drift and it will be accurate to fractions of parts per million. you can then put the GPS away for 6 months. or more. This assumes it was already within 1Hz of nominal frequency.

Lots of OCXOs and TCXOs on ebay.

Robert G8RPI. (time nut, 5 GPSDO's, 4 Rubidium atomic frequency standards, HP 5370B etc).

You don't need the extra oscillator and phase locking for a master clock, just a divide by 30 on the 1pps output (an a flipflop to reverse the polarity every other pulse for a Gents. If you want to build a Miller style GPSDO you need one of the Jupiter receivers with a 10kHz output. I've got a couple if you are stuck. Andy G4JNT has some good info too.

Robert G8RPI.

Yes, that is a master clock. Nice find.

Robert G8RPI.

TR7? Surely it's a TR8 or haven't you told your insurers and the DVLA?

Robert G8RPI.

+1 for Wiha or stop your local Snap-On van.

Robert G8RPI.

A 12V (or better 24V e.g. truck) brushed DC motor like a wiper motor and a PWM controller would probably be a good opton for light work on a Pultra at higher speeds. PWM controllers are available on ebay and are cheaper than variacs and inherently safer being low voltage.

That controller is totally unsuitble for a lathe motor. It does not even have a power or current rating. They are intended to control small shaded pole induction motors of the type used in fans, maybe a few tens of watts maximum. They don't even do a good job of that. They effectively limit the power to the motor so it never gets to synchronous speed.
It almost certainly does not meet safety an interference regulations either.

The only way to properly vary the speed of an induction motor is to change the frequency of the power to the motor using a VFD or inverter. This will work on single phase motor over a limited range but it is much better to change to a 3 phase motor. If the single phase motor has a run capacitor theen this would have to be switched to different values for different speeds.

Robert G8RPI.

It's a really good idea to fit an isolator switch like this:

https://www.ebay.co.uk/itm/Universal-12V-Battery-Isolator-Switch-Kill-Switch-Winch-Isolator-DA2037/371193793900?epid=1326302701&hash=item566cdfcd6c:g:Z8wAAOSw0vBUbP7f&frcectupt=true
(random ebay item also available from motor factors and the like)

close to the battery.

Apart from an emergency cut out for a electrical fire or motor controller runaway they are a handy security measure. If you leave the loco for even a minute, take the key with you. You can it on an expanding key chain so you have to take it with you.

Robert G8RPI.

A really good book on energy is "A cubic mile of oil"

https://www.amazon.co.uk/Cubic-Mile-Oil-Realities-Averting/dp/0195325540

Not cheap though

There is some free info here http://global.oup.com/us/companion.websites/9780195325546/

The short term future for cars is clearly hybrids. My peronal vuew of the ideal is an electric drive train with a high efficiency IC engine running at it's peak efficiency load point driving generator. Maybe a tiny gas turbine runnnng on LP or even better hydrogen. Generator only needs to be big enough to give range extension, around te average power used by the car.

Robert G8RPI.

Back to the electric / IC comparison. Quick wed search gives a Nissan leaf at £318 pm and a Fiat Panda 5 door at £155 PM (including inital payment) Plus £12 pm road tax for the IC car gives a difference of £151 pm. Assumng about 40 MPG thats 0.11 litres per mile at £1.5o per litre (inflation allowance) thats 17p per mile so the Panda can do 880 miles per month (10,000 per year) for "free". Even at a typical mileage payment of 37p is 400 free miles per month (4900 per year) even if the Leaf was charged for free.

Robert G8RPI.

You are correct on the current, 100A is a 1 hour charge. I really must pay more attention.
There is no renewable or combination of renewables that can provide 24/7/365 supply without storage. Batteries (in "walls" or cars) are not a viable long term solution.
My car comparison was a personal situation, not generic. The diesel estate is still going strong over 4 years later. The cost of an electric would still be more than a diesel for me even for a new lease (at full price).

Robert G8RPI.

Well your 32A may be 7.3 kW draw on the mains but it's not putting 7+kW per hour into the battery. Firstly there is the charger efficiency, maybe 95% so 6.99kW out. Battery charge efficiency is 99% at best so 6.9kW (not including any loses in cables etc). This is as you say worse in winter not least because you have to heat the battery pack. Typically you would need 14-15h for a full charge. Not often you would need a full charge.

On new nuclear, it can of course provide extra capacity, you just have to build enough.

Robert G8RPI.

This is a very valid point about plug in vehicles. Rather than looking at max power look at range and batttery capacity in kWh The new Nisan leaf is 160miles and 40kWh so thats 250Wh per mile. A 2h commute at 50MPH is 100miles and 25kWh so still over 100A. for a 10h charge.
Good excuse to get a 3 phase supply laid in

There is also the question of where the electricity will come from. We need more (next generation) nuclear power.

My employer also owns a car dealership and a few years ago we were offered a deal for 50% off the lease cost of a small electric car (had to participate in research study data logger etc). I did the sums and even charging for free at work it would still be cheaper to run my 6 year old 150hp turbodiesel estate car for 4 years and then scrap it than to lease the electric.

Robert G8RPI

Edited By Robert Atkinson 2 on 08/06/2019 09:09:54

Geiger counters, other radiation detectors and radioactive material

Robert G8RPI.

I wonder if it has anything to do with IP? Snap on used square but don't seem to have patented that
**LINK**

Maybe someone in the UK had a patent on square drive?

What do you want to know, theory, practical uses, installation?

If searching, try polyphase rather than 3 phase

Try this for theory

https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-061-introduction-to-electric-power-systems-spring-2011/readings/MIT6_061S11_ch3.pdf

Mind you all that math does not turn the light on

https://www.youtube.com/watch?v=8ve23i5K334

Robert G8RPI

Edited By Robert Atkinson 2 on 07/06/2019 07:18:55

Edited By Robert Atkinson 2 on 07/06/2019 07:24:02

Ron said

"Using a digital tacho I found that two of the motors are quite close within 2-3% of each other with a third motor approx 4% slower and the fourth 5% faster. The slowest to fastest motor are within 9-10%, this is all with the motors unloaded of course. I am quite happy with that, the four smaller motors I have in the 0-4-0 are only good to within 10% and they have proved to be fine with no issues on the track."

An off-load test is not representative at all. The speed is dependent on the voltage (supply x %PWM) and load. With no external load the actual load on the motors is just the bearings and brushes and these are very variable between motors. This probably accounts for most of the speed difference you are seeing. When loaded the resistance of the motor and connecting wires will help share the load between the paralleled motors. To help this, make the parallel connection at the controller, not the motors. This means running two pairs of wires from the controller, one pair to each motor. Ideally the wires should be of similar length other wise the motor with the shorter wire will take more of the load.

Robert G8RPI.

From the photo this appears to be a basic PWM controller probably a sawtooth oscillator, variable voltage (from pot)and comparator. While two could be modified to run from one pot I don't think a simple parallel connection is advised.
There are two reversing relays and depending how they are wired they probably provide dynamic braking (also using the MOSFET source drain diode and battery) when the control switch is off. A separate double pole "off" switch or a pair of microswitches operated by a cam on the throttle control would be easier than trying to find a dual gang, 100K linear pot with a double pole switch. I found a 50K, which might be OK but it's a single pole switch so needs investigation or a relay and it looks pretty poor quality.

**LINK**

A professional modular pot and switch would be expensive.

You could try hacking one of these

**LINK**
and one of these

**LINK**

together. I.e put the switch of the single onto the double.

Where are you located? Maybe someone come and have a look at the controllers.

Robert G8RPI.

One advantage of online ordering is you can cancel it or return the item....

Another option, depending on your batteries would be to use 48V and run the motors in series/parallel on one controller. Series the two motors sharing an axle and parallel the two bogies. If you series the bogies then one slipping would "take" all the voltage and you will loose power at the other bogie.

Otherwise I concur, a dual pot is the way to go. If I had a controller to hand I'm sure a simpler control could be worked out, but I don't.

To keep it mechanical you could of course make a throttle lever and gear (ot miniature toothed belt, crank etc) to the two control pots.....

Robert G8RPI.