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Need an inverter recommendation: Best of the worst?


Tasemu

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43 minutes ago, rusty69 said:

Ah, you sound like an hexpert. 

 

How does the current carrying capacity of the finer strand stuff compare with the bigger, fewer conductor stuff?

 

I assume more copper = more current carrying capacity . But then how can they both be described as 70mm2. 

You take the radius of the individual strand and multiply by 3.142 'squared' to get the area of the strand.

Then count the number of strands in the total 'core'.

Multiply the number by the CSA (cross sectional area) of one strand and you have the total area (mm2) of the cable.

 

As an example ( for a standard  1mm2 cable) you could have 

1) 32 strands of 0.2mm diameter (32/0.2)

2) 14 strands of 0.3mm diameter (14/0.3)

3) any other permutation.

 

The current carrying capacity is determined by the total CSA of the conductor.

 

The voltage rating is determined by the insulation thickness / type.

 

(I had 10 years as a cable designer and wrote cable specifications for the NCB, British Aerospace etc. I have several patents in my name, with the most notable being - 40 years ago -  a Fire Resistant cable to replace PYRO)

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4 minutes ago, Alan de Enfield said:

(I had 10 years as a cable designer and wrote cable specifications for the NCB, British Aerospace etc. I have several patents in my name, with the most notable being - 40 years ago -  a Fire Resistant cable to replace PYRO)

Thank you. I hated pyro. 

 

A question for anyone who might know... elsewhere I was criticised for recommending welding cable for battery connects with the comment that the insulation wasn’t resistant to the kinds of fluids that might be found in an engine room. Quite apart from the fact that most folks don’t spray their bank with assorted fluids is there any truth to that assertion?

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2 minutes ago, Alan de Enfield said:

Unfortunately 'new' materials have replaced it and I cannot even find the patent now, but it was this stuff "CalFlam" which was almost as flexible as 'flexible' mains leads.

 

https://www.farnell.com/datasheets/100664.pdf

I’ve seen that (or something like it) used although I’ve never used it myself. My last bit of pyro cabling was in the mid-70s. 

 

Someone nicked my bag of pyro tools and I thought at the time “good riddance”. 

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19 minutes ago, Alan de Enfield said:

You take the radius of the individual strand and multiply by 3.142 'squared' to get the area of the strand.

So, is the overall diameter of the cable the same for different number of strands of the same overall CSA? Cuthounds post suggests not.

 

Its too early and my brain hurts.

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We used FP200 for fire resistant cabling after we gave up with Pyro.

I was never happy with either.

Pyro was a lot of messing about and we had lots that had been installed 5 or 6 years previously and had failed insulation tests, some of the alarm installers at the time were terrible cowboys.

FP200 was easier to use but the soft silicone insulation had to be treated with respect, staff training had to be strict if we were to avoid installation errors.

Never saw Calflam, it sounds interesting

 

Sorry, getting a long way from the topic.

3 minutes ago, rusty69 said:

So, is the overall diameter of the cable the same for different number of strands of the same overall CSA? Cuthounds post suggests not.

 

Its too early and my brain hurts.

No, it comes out slightly smaller with the finer strands, that's the difficulty with getting the correct fit of the crimps. And getting every strand in the crimp take smore care.

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12 minutes ago, Boater Sam said:

 

 

Sorry, getting a long way from the topic.

No, it comes out slightly smaller with the finer strands, that's the difficulty with getting the correct fit of the crimps. And getting every strand in the crimp take smore care.

Ah, ok. so the crimp diameter is the same? Can you get slightly smaller crimps for the welding cable, or just squeeze a bit harder on the crimper?

Edited by rusty69
removed a bit cos it was rubbish
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20 minutes ago, rusty69 said:

Ah, ok. so the crimp diameter is the same? Can you get slightly smaller crimps for the welding cable, or just squeeze a bit harder on the crimper?

Crimping is to a standard pressure, so no, more pressure is not the simple answer. The copper bundle has to fit the crimp correctly before crimping. I have not found any different size crimps for odd sized cable bundles but used to pack the notional size crimp with a strand or twe of copper until it was full before crimping. The hex type crimpers are much better than the crude dent in the back type in my opinion.

Probably a non approved way but I don't have failures.

Soldering is not recommended as getting rid of all the flux is near impossible.

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3 minutes ago, Boater Sam said:

Crimping is to a standard pressure, so no, more pressure is not the simple answer. The copper bundle has to fit the crimp correctly before crimping. I have not found any different size crimps for odd sized cable bundles but used to pack the notional size crimp with a strand or twe of copper until it was full before crimping. The hex type crimpers are much better than the crude dent in the back type in my opinion.

Probably a non approved way but I don't have failures.

Soldering is not recommended as getting rid of all the flux is near impossible.

That seems odd to me, given that a standard pressure is used on the same size crimp terminals on differing overall diameter of cables. I would have thought different size crimp terminals would be available.........rushes off to have a look.

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1 hour ago, rusty69 said:

So, is the overall diameter of the cable the same for different number of strands of the same overall CSA? Cuthounds post suggests not.

 

Its too early and my brain hurts.

 

I didn't say it was the overall diameter of the cable, I said it was the csa, but it seems my spellchecker changed it to can. ?

 

The overall diameter of standard 70mm2 cable is larger than 70mm2 welding cable because there are bigger minute gaps between the larger individual strands than there are between smaller individual strands, plus the insulation is a different thickness.

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1 hour ago, WotEver said:

A question for anyone who might know... elsewhere I was criticised for recommending welding cable for battery connects with the comment that the insulation wasn’t resistant to the kinds of fluids that might be found in an engine room. Quite apart from the fact that most folks don’t spray their bank with assorted fluids is there any truth to that assertion?

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3 hours ago, Boater Sam said:

 

 

It is easier to use but crimping rings onto it is more difficult due the the size of the wire bundle and it has to have a pin crimp on the terminal end because it is poor in screw up terminals.

It carries current better than 19 strand cable due to the phenomena that most of the current is carried on the outside of each strand, strange but true.

Not true at mains frequency for cables like this. The cause is skin effect, but at 50Hz skin depth in copper is about 10mm, so the strands would have to be about 20mm in diameter for this to have any effect. It matters for solid cables on electricity pylons, but not for any stranded mains cable.

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2 minutes ago, IanD said:

Not true at mains frequency for cables like this.

And not at all true for DC

 

And it’s why RF aerials are generally tubes as opposed to solid wires.  

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1 minute ago, WotEver said:

And not at all true for DC

Indeed. But don't forget that the current into an inverter isn't DC, it's a 100Hz sinewave sitting on top of a DC current because the power out of the inverter varies over the mains cycle from zero to 2x the average. Incidentally this increases the RMS input current (which is what heats up cables and blows fuses) by about 20%, so the fuse rating does need to be higher than that worked out just from inverter power output... ?

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2 hours ago, IanD said:

Not true at mains frequency for cables like this. The cause is skin effect, but at 50Hz skin depth in copper is about 10mm, so the strands would have to be about 20mm in diameter for this to have any effect. It matters for solid cables on electricity pylons, but not for any stranded mains cable.

I thought pylon cables were steel rope (for strength)over wrapped with aluminium strands (for conductivity) and coated in heavy grease, or am I showing my age again as it has all changed?

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1 hour ago, Chewbacka said:

I thought pylon cables were steel rope (for strength)over wrapped with aluminium strands (for conductivity) and coated in heavy grease, or am I showing my age again as it has all changed?

 

They used to be made (as you say) of a few very thick aluminium strands wrapped over a steel core (ACSR, ~5mm strands); the skin effect thickness limit then applies to the strands, which are still very thick compared to normal stranded cable. Modern ones often have a carbon fibre core (ACCC) where the "strands" are flattened into trapezoidal segments which leave almost no gaps, in this case the skin thickness limit applies to the overall core since the gaps are too small to have any effect. Since the conductor then appears like a tube, the "wall thickness" is then what matters. See pictures here:

 

https://en.wikipedia.org/wiki/Overhead_power_line

Edited by IanD
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On 18/03/2019 at 20:01, sirweste said:

I wouldn't have thought the motor uses that power, it will be the heating element surely - which obviously won't really care about the waveform it sees. 

 

A motor takes a huge belt as it starts up (that's why electric cars accelerate so well from a standstill).

 

N

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On 22/03/2019 at 11:01, cuthound said:

The overall diameter of standard 70mm2 cable is larger than 70mm2 welding cable because there are bigger minute gaps between the larger individual strands than there are between smaller individual strands

 

While the minute gaps might be bigger between the larger strands, on the other hand there will be fewer of them....

 

 

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58 minutes ago, Mike the Boilerman said:

 

Don't be silly, electrons are round and they'd get all wedged up in square strands...

I think you will find the square electron was discovered along with the Higgs Boson. It has been named a sqelectron and has a charge of 1.60217662 × 10⁺¹⁹ coulombs.

 

There are twice as many electrons as sqelectrons so they are cancelled out and non detectable.

Edited by rusty69
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On 19/03/2019 at 00:20, Boater Sam said:

Never said it does. Of course its the heater that takes a lot of current, we all know that, but the motor has to start and run at the same time in the wash program.

I'm surprised if the max rating of the washer is only 1500 W.

It definitely seemed like you did say that the motor would use the rated power:

On 18/03/2019 at 11:58, Boater Sam said:

That washer only 1500 Watts? Remember that motors take more whilst starting, 1800 Watts may be better.

 

But I guess that's not what you meant then. 

 

On 23/03/2019 at 09:37, Theo said:

A motor takes a huge belt as it starts up (that's why electric cars accelerate so well from a standstill).

 

N

Yes an electric motor has a very very high acceleration from standstill, when compared to an IC engine.  However the "huge belt" of energy usage at initial startup, of the electric motor, is not as high as running a heating element.

So as stated, the element will use the 1500 W, if used on cold cycle the power required will be much less.

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