Member postings for Robert Atkinson 2

Edited By Robert Atkinson 2 on 13/12/2019 21:32:19

Sorry, too far for me, Cambrdge.

Hi,
Standard lead free electronic solder has a melting point of around 215-227 deg C depending on alloy. (old tin / lead is about 188). The rosin flux is fine for clean steel. Available from various online sellers.

Robert G8RPI.

There is no difference electrically between a VFD and a "digital phase converter" (DPC). The DPC seems to have been "invented" to tap into a specific market with limited knowledge of power electronics. Their power ratings are disingenuous at best. If thery are going to rate a motor drive in horse power then it should be able to start up a motor of that horse power, not need over 300% overrating. This is purely down to the cost/quality of the components used in the converter. Full load continuous ratings are mainly based on thermal capacity, short term capability (in order of seconds) is mainly limited by cross sectional area of conductors and solid state devices. The thermal mass allows some overload before they overheat. If the particular unit will only start a 2hp motor then its a 2hp motor drive not a 5hp.
For the particular case of a machine with one large main motor and a number of smaller ones there is even a case for a "proper" VFD on the main drive motor, with the benefits of soft start, variable speed etc and a second, small VFD (or even DPC) set for fixed output for the auxiliary motors. The smaller motors could also be changed to single phase, torque smoothness is not a big issue for a coolant pump.
Yes there may be some re-wiring required but that is once, you save money and get the long-term benefits of a VFD on the main drive.

Robert G8RPI.

Robert G8RPI.

Using a 5 HP drive to power a 1.5 HP motor is just wasteful. The supplier is not giving good advice but why would they? Buy saying you need a bigger drive they are protecting themselves aginst failures bue to poorly rated components and making more money for themselves. £1500 is a hell of a lot for a "no-name" VFD just to save setting up.
Where are you located? Maybe I could help with a better solution.

Robert G8RPI.

AFAIK the only difference between a phase converter and a VFD is the PC is non adjustable. Even if you use it at fixed speed a VFD would be a better choice for a single machine as it can "soft-start" so does not need to be over-sized.

What PC are you looking at (link) and why don't you want a VFD?

Robert G8RPI.

I think you are both correct, it depends on the condition of the system. The pressure is only constant throughout the system when it is STATIC. If anything is moving there are pressure differentials in the system.

On pressure testing with gas v liquid there is a worse case than gas, using a fluid that is gas at ambient and liquid at test pressure e.g. water over 100 deg C or LPG. With these when the pressure is released the liquid flash "boils" and expands elesing even more energy than the same volume and pressure of gas. There is a name for it "BLEVE" Boiling Liquid Expanding Vapour Explosion. Very nasty indeed especially if the fluid itself is flammable.

Robert G8RPI.

Hi Bob,

Where did you get the burner?
Can you post a close-up, infocus picture of the tank fitting?
What is the ID of the tank fitting.

Robert G8RPI.

Looks like an adaptation of a brushless DC motor similar to those used for hard disk drive spindles or possibly just a stepper. Torque looks pretty low. At about £300 per motor I don't think it is very cost effective. It is also aimed at those with low or no technical skill and no metalworking capability which is a bit of an antithesis for this forum.

Robert G8RPI.

I covered the tender (non-constant flow) case in my post, what is your point?

If we are restricting this to tender ppework why are you talking about about half mile long pipes? If point is picking at other peoples posts, there is no "potential difference" (voltage) across the pipe and even the pressure drop is not constant, it will vary as the water level in the tender drops, reducing the available pressure head and flow rate.

It depends on what the water source is.

If it's constant pressure source like a head of water or non -positive displacement pump then the flow will be less with the smaller section in place.

If it is a constant flow source e.g. a positive displacement pump, then the flow will not reduce with the restriction in place. However the pressure upstream of the restriction will be higher. This works up to the point where the pipe bursts or pump fails.

Robert G8RPI.

I did say "and correctly set-up" open loop system. Stepper systems appear very simple but actually require quite a lot of care to get optimum performance. A closed loop system may well hide much much of this from the user. A closed loop sytem that is missing steps will be out of phase because it can't correct until a step is missed so best case will be at least one step "behind". More sophisticated closed loop controllers can auto-tune the system settings but it's not clear to me if the cheap systems can do this. Correction for lost steps does not have to be done by the stepper driver. If an encoder is fitted to the leadscrew the ELS controller can monitor for lost steps and correct accordingly. One thing that can make a big difference to stepper motor performance in this type of application where resonances are not constant is an inertial damper. Basically a flexibly mounted mass on the motor shaft. https://www.phytron.eu/products/mechanics-equipment/dmp-20-29-37-inertial-damper-for-stepper-motors/

Robert G8RPI.

You are correct that if the motor is large enough and properly set-up then closed loop should not be required. The advantage of closed loop is that it corrects for any lost steps. This keeps the positions correct to the end but would not correct any surface finish issues caused by the missed steps. A correctly sized and set-up open loop motor that does not miss steps is better than a closed loop one that does but corrects. These units are not strictly servo systems, they are steppers with monitoring and automatic correction.

Edited By Robert Atkinson 2 on 07/12/2019 11:08:04

The other good one is that despite restricting the sale of military items, including most military vehicles, ebay have a category for military vehicles.

Thrust SSC had a Martin Baker ejection seat rocket motor mounted "upside" down in the nose. The intention was that if the nose started to lift it would fire keeping it on the ground long enough for the hydraulic ride height control to jack the rear end up and generate aerodynamic downforce and drag. The test firing was pretty impressivebut diddn't sound like a sonic boom. The main seat "gun" cartridges might sound a bit like it though. I've worked on a Skyvan (a 3A) and several 330's and 360's It's no coincidence that Shorts were asked to build the Miles Aerovan a couple of years before staring work on the Skyvan. It's was more a case of what not to do rather than copying it.

Robert G8RPI.

We used to hear the tail end of Concords supersonic runs up the bay of Biscay all the way in Christchurch on cool quiet evenings.
And I did of course hear the booms from Thrust SSC back in 1997. The car went supersonic 5 times. One of these was unintentional. The car was to run to a predetermined indicated airspeed which should hav been just below Mach 1, There was however a clear boom. The first suspect was the airspeed indicator calibration (which was my responsibility, I built the speedometer and Mach meter for the car) but it turned out that when calculating the target speed they forgot to allow for the affect of altitude on Mach number. The Black Rock desert is at about 3900ft above sea level.

Robert G8RPI.

No,

1 kW electrical energy input PUMPS about 4kW of ambient energy from outside to inside. about half the input electrical energy is also transfered so in heating mode you get 4.5kW of heating. an outside looses 4kW. Cooling mode only gives ((in this example) 3.5 kW of cooling.

No magic, works just like a fridge.

Robert G8RPI

The clue is in the proper name - heat pump These transfer energy from one unit to the other with a delta in temperature. They are more efficent when heating indors because a proportino of the electrical input is converted to heat nd adds to the wantd heating. I've had them in two homes now. Hitachi in last about 15 years ago and Daikin in the current. The Daikin will work below -20 outdoors.

Highly recommended.

Robert G8RPI.

A genuine Huang Yang VFD is OK, but many of the ones on ebay etc are clones or fakes.

With these types of cheap clones and fakes (not just VFDs) they save costs by not including components that do not affect basic operation but often have a safety or protection function. These include overheat and overload detection, filtering transient protection etc. They also often use under-rated componens like DC bus capacitors an output transistors. This means they work with nominal supply voltage and less than full load but may not perform or fail if fully loaded. Poor quality components and shoddy construction can also lead to electric shock and fire hazards. When operaing machine tools even a minor shock can have severe consequences as muscle contraction or reflex may result in body parts touching moving prats or sharp tools. I saw someone get a really badly cut hand from a stationary but sharp cutter on a bridgeport because they were changing the lamp in the work light. They pulled away because it was hot (power was off) but the effect was the same.

Robert G8RPI.

If you want to turn thin wall bearings accurately then how you hold them is important. Make sure that the lathe you buy can accommodate a collet chuck of suitable size. The SC2 will take one

**LINK**

**LINK**

The collet chuck can also hold an arbour to mount the bearing while you turn the outside diameter.

Robert G8RPI.