Member postings for Robert Atkinson 2

Don't get me started on wood burning stoves. Either through ignorance or selfishness many people mis-use them, burning green wood, painted wood, chipboard and rubbish. This causes terrible local polution especially for those with respiritory problems.

Robert G8RPI

Hardening depends on the material, which you have not specified. If it is a hardenable material then laser cutting will create a thin hard "skin" Thi can be taken off with a dremel / die-grinder or similar before you bore it out.

Water jet cutting is an option that won't thermally affect material but I've no idea what cost for similar accuracy is.

Robert G8RPI.

We need to be sensible here. There are dozens of ways to run an LED off a car supply, with different pros and cons. No disrespect to the OP but if his electronics knowledge is such that h is buying "12V LEDs" with resistor already fitted he is not going to be working out a LM317 constant current design.

But a LM317 in constant current mode won't work with the LED + Resistor lights that the OP is using.

I've not been keeping up to date with this thread and there have been some misunderstandings. Andrew, the 180R nd 12 V zener was my suggestion. SOD's diagram was a little simplistic in not including the resistor (unknown value) that is part of the "LED" and had a polarity error. My suggestion was based on a presumed "LED" specification of 12 V and 20 mA. An additional 180 ohms will drop 3.6 V at 20 mA keeping the "LED" within it's 12 V rating even at 14.4 V (typical maximum charging volte for a 6 cell lead acid battery.The zener will keep the voltage at the "LED" terminals at 12 V (give or take a bit) even if the LED does not draw it's full current. It will also provide suppression of positive spikes. I did suggest in a later post that a 10 or 11 V zener would be even better. The resstor / zener combination provides very good protection against negative spikes (clamping to less than 1 V most LEDs will withstand 3-4 V). I think the most likely cause of the failures is negative spikes but unless an oscilloscope is put on the car we are just making assumptions, some based on experience, some guessing.

I'm happy to put my money on my suggestion. I'll send the OP a 180 ohm resistor, 12 V zenner to try with one of his "LEDs" on the car. If the LED fails I'll make a donation to a charity of his choice. @ Tim Stevens send me a personal message with you address and I'll post them ready wired.

To use a LM317T (or LM317L) regulator its input voltage must be at least 2 V higher than the required output (datasheet says 2.5 V). So would have to be set to 10V output to work with the battery off charge. Even worse, the LM317 is also susceptible to spkes, especially negative, on the supply, To use it safely in a car it needs additional components. As a minium it is a LM317, 0.1uF capacitior. diode and two resistors. A lot more complication for little, if any, advantage of one resistor and one zener.

This stuff is part of my day job - on aircraft.

Robert G8RPI

Hi Tim,

No you don't need a higher voltage zener. the additional 2 or 3 volts is dropped across the 180R resistor This "wastes" about 0.05 W (50 milliwatts) of power.
I think your problem is the LEDs are running at maximum at 12 V and the 13.8-14.2 V of a modern regulator plus any spikes from other loads is the last straw. The 180 ohm / 12V zenner circuit ensures the LED and resistor nver sees more than 12V (you could even go down to 10 or 11 V which will further protect the LED and reduce any flicker from voltage variation. One advantage of this simple ciricut is it protects itself. If you use a voltage regulator IC you really have to add diodes and capacitors to protect the IC.

SOD,

Thanks for doing the circuit (and credit). I looked again at the unit you linked to. It seems to be specfically for German cars and reversing cameras powered from the reversing light. It appears some models use some kind of PWM to the light. I'm guessing here, but it's probably a series diode and a electrolytic capacitior to give smooth DC at low current.

Robert G8RPI.

OK,

So the lighting regulations don't apply

Sounds like cheap LEDS running at maximum current coupled with spikes (negative as well as positive) from the generator / igintion system. Put a 180 ohm 1/4 watt resistor in series with each LED and a 12V 0.5W zener diode across each LED (on LED side of resistor) Anode to negative side of LED.

If all LEDs come on at once a single resistor and diode will work. Let me know how many LEDs you have on the circuit and I'll calculate values. I've probably got suitable parts in "stock" If so I'll send you them for postage cost.

Robert G8RPI.

Edit,  Shoulld have said, the zener is cheap, simple and protects aginst both positive spikes above 12 V and negative spikes above 0.8 V

Edited By Robert Atkinson 2 on 14/08/2020 13:07:35

Edited By Robert Atkinson 2 on 14/08/2020 13:08:06

Edited By Robert Atkinson 2 on 14/08/2020 13:08:49

Ref my earlier posts,

1/ What is the part number / suppler of the 3 mm LEDs ?

2/ What is the vehicleand how old is it ?

Robert G8RPI.

OT but LED hedlamps are legal, my car has them.

What is NOT legal is replacing the filament lamp (bulb) in any exterior car light with an LED. The only exception to this is the reversing light. The legal reason for this is car lights and replacable lamps have to meet certain standards and be tested and approved . They are "E" marked to show compliance. There is NO approved standard for LED repalcable lamps. It is possible to have a complete LED light compliant but the LEDs in it are not replaceable.

The practical reason is that LEDs have different optical characteristics to filaments so a reflector and lens desigined for a filament almost certainly won't have the same pattern and brightness with an LED fitted. It might be possible to design a LED replacement lamp that works in one, or some, lights but it is impossible to design one that will work in any because there i so much variation in light optical design. You can get legal LED replacements for sealled beam headlight units because thi is a complete light with optics, not a replacement lamp for a set of optics.

Robert G8RPI.

"ordinary" LEDs do not have an internal resistor Some do but it's not standard. Can the OP provide a part number or link for the LED they are using and then we can stop guessing!

Edit,
That "regulator/filter" could be anything, even a empty box, there is no specification at all.

Edited By Robert Atkinson 2 on 13/08/2020 21:14:16

Well as it's for sale in Germany I'd be surprised if it had a 13A plug

Edited By Robert Atkinson 2 on 12/08/2020 19:12:21

The Jaguar figures make sense to me.

Output rating 9A continuous 13.5A (150%) for 1 minute
Input 14.9A maximum so 90.6% efficency at 150% output load.

Robert G8RPI.

There are two common issues:

1/ Bleeding, which Stuart had, where the segmets get dark and blurry. seems to be caused by contamination of he liquid in the display.

2/ Weak or ghosting segments often cused by bad zebra strip directionally conductive rubber. This can be cured by removing , cleaning and resaeting the display, PCB and stip. Use a lint free cloth dampened with IPA to gently wipe the glass edge of the display, PCB and both edges of the strip. Don't wet the display or strip with solvent and don't touch the contact areas with bare fingers. Reassemble with care.

Flukes are great (I have 7 , the 8010A make a nice bench meter and the physically similar 8050A is more accurate with 4.5 digits instead of 3.5. There are a lot of Ex MOD Fluke 25's on the mrket at the moment. These are a rugged, waterproof autoranging meter that works well and is more accurate than their new basic models.

Robert G8RPI.

As said high voltage transmission of power is more effective and DC has lower losses. Once electronic converters became more economic DC transfer has many advantages.

One issue with AC that has not been mentioned is Skin Effect. This is where the alternating current causes a magnetic field that repels the electrons towards the outside of the conductor (Left Hand Rule). This is increses with frequency so is mostly seen in high frequency circuits but is significant at 50 and 60Hz at high power levels.
Basically the cener of the conductor is not carrying significant current (electrons). This means it's wasted material. In high power radio circuts it is so significant that they use copper tube with silver plating with no loss over solid bar. It's also why they can use steel strength members in the center of copper or aluminium AC HV power cables with little additional loss.

Robert G8RPI.

@ Bob Worsley

While your conclusion ".. buy a VFD same size as the motor. " is correct, your explanation is seriously flawed.
It falls over in the first 3 lines. If motors and VFDs were both rated on output power picking a VFD the same size (rating) would result in an undersized VFD.

The VFD power rating (output) should match, or be slightly greater than, the electrical power rating (input) of the motor.

I'm not even going to bother addressing the rest of your explanations flaws.

Robert G8RPI.

A micromill with chip guard and tool changer went for over £2500 on ebay earlier this year.
https://www.ebay.co.uk/itm/Denford-Novamill-Cnc-Milling-Machine-/153966150453?

A lot has changed since January though.

Robert G8RPI

Those are actually not that big and are high quality machines. Yes they have significant value.
Other will have a better idea of exact values but the small bits an pieces and accessories are important and add to value.
An adver on here might work otherwise an auction (one for each machine with any bits you can associate with it) is a good option.

+1 for not over sizing the drive.
The sellers who advcate using oversized drives are just making more money from you. In the case of lower quality drives that may have undersized heatsinks and marginal semiconductors they are also reducing their exposure to warranty claims at your expense. As others have said if parameters, particuarly urrent limits are correctly set a larger drive will not protect the motor. Less obviously, the control will not be as good. Any drive will have a dynamic range from minimum load to maximum. Minimum does not change significantly with drive size but maximum does. Modern drives are digital with a fixed number of "steps" (resolution) between min and max. Typical is 10 bits giving 1024 steps. If you us a 1kW drive on a 500W motor a most it will get to half power - 512th step. Thus you have haff the control resolution. Most users will not notice this but why pay more for poorer performance?

Robert G8RPI.

Hi,

I was very confused myself when first trying to determine the differences. Unusually, the Lathes.co.uk website did not help very much. I fianlly went back to contempary Myford documents that I found online -
http://vintagemachinery.org/pubs/detail.aspx?id=6592

Robert G8RPI.

@ Howard Lewis

Your description is incorrect

ML1 & ML2 are 3 1/8" center height (8.5" swing) and 15" between centers

ML3 & ML4 are 3 1/2" center height (10" swing) and 24" between centers

Either 3 1/8 " x 15" OR 3 1/2" x 24" not a mixture

The difference between ML1 (or ML3) and ML2 (or ML4) is that the ML2 (ML4) were "superior" models with bronze headstock bearings, ball headstock thrust races, long cross slide and quick relese tailstock.

Some later models may have a mixture of features or options. but this is the basic differences. This is taken from Myford literature, I think the Lathes.co.uk website has it wrong or written confusingly in places

Robert G8RPI. ML2 owner.

Edited By Robert Atkinson 2 on 07/08/2020 11:48:04