Inverter versus 12v

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11th May 2018, 06:19 PM
Homestar

Induction cooktops use HUGE power - one I installed at a friends house needed 30amps total. That's over 7KW - and as mentioned, the power factor is horrendeous so without a pan on the stovetop there's a lot of VAR's to consider too. Even with one plate running you'd need ennormous battery bank to cook a meal. The ebay jobby shown uses 2KW for one plate - remember you'll need it for at least half an hour or so to cook a meal. That's over 160 amps continuous from your batteries - the cabling would need to be pretty good too.

Infrared are a little better but still huge power draw and unfortunately unrealistic to run off batteries and an inverter. Love it or hate it, gas is the only economical way of having a decent cooktop. You could use a Coleman dual fuel stove, but if carrying flamable stuff around bothers you, that's no good either.

Could run a genset while you're cooking and do it ok though.
12th May 2018, 02:26 PM
Old Farang

Quote:

Originally Posted by Mick_Marsh

Depends on which brands.
Variable Speed Drives (VSD)
They do the same thing.

They can also be referred to as VVVF drives.

Oh, I am in the industry. I used to work for a company that sells them. I now work for a company that uses them. Anything from 0.5kW metering pumps to 530kW drives. I've worked on projects that use much larger VSDs.

This may not be the correct thread to discuss this, so please move if it offends any rules.
I post it as general interest, and not trying to teach anyone to suck eggs.
…………………………………………� �…………………………………………� ��.
Bearing in mind your signature line Mr. Marsh:

I served a 5 year apprenticeship as an electrical fitter / armature winder when such training was done under the "old system", which tended to include a big sized boot! It was a commercial repair shop where we rewound and overhauled everything from electric shavers up to 500 hp motors from a coal mine. Generators, pumps, automotive, the electrical side of refrigeration, the local farmers electric fence unit, and on and on!

Following that I spent years of self study and night school obtaining marine engineers certificates, some of it while working on ships with both DC and AC systems.

I have been chief electrician on a DP Drillship that employed an automated power management system long before computers and PLC's were used. I have been chief engineer on a conventionally moored diesel electric Drillship, all of this over more than 30 years. None of this is in anyway bragging, just posted to establish where I am coming from.

The oil drilling industry has, for more years than I like to remember, used variable speed drives (VSD) Every one of them used DC traction motors in various roles such as draw works, mud pumps, rotary table, etc. The standard DC motor employed is the same motor as used in locomotive diesel electric engines, nominal 800hp.Some of them are made by EMD and others by GE.

Although the DC motors have changed very little over the years, the control systems certainly have. Have you had any experience with a Ward Leonard System? What about a magnetic amplifier and saturable reactor? Some of these systems had absolutely no AC connection, apart maybe from the prime mover. Earlier types employed DC generators with various control systems, to drive the DC motors, more common in later years were SCR drives. Some of these systems were also employed in electric cargo cranes. If you have never had the dubious pleasure of working on a LeTourneau PCM 120 electric crane I can assure you it was definitely a VSD!

All they do have in common is that they are VSD and used to control DC motors.

The onlyvariable speed AC motor that I have seen is a "Schrage", used mostly in the carpet and yarn making industry, and it is termed a VSD.

A common simple VSD is a Singer Sewing Machine with a foot control, a true VSD that works on both AC and DC if a universal motor.

By definition ,an "inverter' is changing a DC source to AC. There are several methods employed to achieve it. Briefly, if you want to supply the device with AC then it is designed to firstly convert the AC to DC before "inverting" it back to AC. The frequency of the AC depends on the design. If you are going to run it off a battery or other DC supply, then it only has to "invert" the designed voltage to AC and at whatever frequency required. The thing to watchout for with this is if the output is a pure sine wave, or a"modified" sine wave, which is more a "square wave" and not suitable for some equipment, especially electronics.

A variable frequency drive (VFD) just employs more electronics to alter the output frequency.Most, not all, also control the output voltage. In which case it is termed a VVVF. In any case, whatever it is termed it is an "inverter", not a VSD.

It could be argued that all of this is just semantics, but it is not. A VFD in whatever form, is a much more sophisticated piece of equipment than any VSD. And that is even before getting into such deviations as "vector drive".

Just to avoid any more typing, a simple reference:

https://www.metroid.net.au/engineering/vsd-vfd-vvvf-whats-difference/

Happy camping!
12th May 2018, 02:38 PM
Mick_Marsh

Quote:

Originally Posted by Old Farang

This maynot be the correct thread to discuss this, so please move if it offends anyrules.
I post itas general interest, and not trying to teach anyone to suck eggs.
…………………………………………� �…………………………………………� ��.
Bearing inmind your signature line Mr. Marsh:

I served a5 year apprenticeship as an electrical fitter / armature winder when such trainingwas done under the "old system", which tended to include a big sizedboot! It was a commercial repair shop where we rewound and overhauled everythingfrom electric shavers up to 500 hp motors from a coal mine. Generators, pumps,automotive, the electrical side of refrigeration, the local farmers electricfence unit, and on and on!

Followingthat I spent years of self study and night school obtaining marine engineerscertificates, some of it while working on ships with both DC and AC systems.

I have beenchief electrician on a DP Drillship that employed an automated power managementsystem long before computers and PLC's were used. I have been chief engineer on a conventionally mooreddiesel electric Drillship, all of this over more than 30 years. None of this isin anyway bragging, just posted to establish where I am coming from.

The oildrilling industry has, for more years than I like to remember, used variablespeed drives (VSD) Every one of them used DC traction motors in various rolessuch as draw works, mud pumps, rotary table, etc. The standard DC motor employedis the same motor as used in locomotive diesel electric engines, nominal 800hp.Some of them are made by EMD and others by GE.

Althoughthe DC motors have changed very little over the years, the control systemscertainly have. Have you had any experience with a Ward Leonard System? Whatabout a magnetic amplifier and saturable reactor? Some of these systems had absolutelyno AC connection, apart maybe from the prime mover. Earlier types employed DCgenerators with various control systems, to drive the DC motors, more common inlater years were SCR drives. Some of these systems were also employed in electriccargo cranes. If you have never had the dubious pleasure of working on a LeTourneau PCM 120 electric crane I can assure you it was definitely a VSD!

All they dohave in common is that they are VSD and used to control DC motors.

The onlyvariable speed AC motor that I have seen is a "Schrage", used mostlyin the carpet and yarn making industry, and it is termed a VSD.

A commonsimple VSD is a Singer Sewing Machine with a foot control, a true VSD thatworks on both AC and DC if a universal motor.

By definition,an "inverter' is changing a DC source to AC. There are several methods employedto achieve it. Briefly, if you want to supply the device with AC then it isdesigned to firstly convert the AC to DC before "inverting" it back toAC. The frequency of the AC depends on the design. If you are going to run itoff a battery or other DC supply, then it only has to "invert" thedesigned voltage to AC and at whatever frequency required. The thing to watchout for with this is if the output is a pure sine wave, or a"modified" sine wave, which is more a "square wave" and notsuitable for some equipment, especially electronics.

A variablefrequency drive (VFD) just employs more electronics to alter the output frequency.Most, not all, also control the output voltage. In which case it is termed aVVVF. In any case, it is termed an "inverter", not a VSD.

It could beargued that all of this is just semantics, but it is not. A VFD is a much more sophisticatedpiece of equipment than any VSD. And that is even before getting into suchdeviations as "vector drive".

Just toavoid any more typing, a simple reference:

VSD, VFD, VVVF? What’s The Difference? - Metroid Electrical Engineering

Happycamping!

Thankyou for that link you provided.
Just before the description of the VVVF drive, you'll see the words, and I'll quote from the article here,:

Quote:

Most commonly, the terms VFD and VSD are interchangeable.
13th May 2018, 01:15 AM
DrDeath

Who’d have thought Landies could provoke such marvellously interesting and learned electrical and semantical (?ish) discussions !

But then, I spose they stimulated the invention of steam, winches and tow trucks ...

I’m just a closet Electragician, vastly humbler background. Scientific Instrument Making, Systems Electrician, first almost killed myself inside a valve TV at the age of 7 ... made me the halfwit I am today ... most of my motors have been tiny to small ac & dc, brushed, brushless, VFD, VSD, exotic little constructions of esoteric automagnetic eddies and current shunts and back emf’s and all driving cardiac pacemakers and microscopic escapements inside dear little nipple hung fob watches etc ... nothing like those beautiful big industrial behemoths you gentlemen reminisce all over ... about ... with ... umm ... you know what I mean ...

Where was I ... oh yes, semantics, well said that man. Aah, the black arts of advertising ...

‘Infrared’ cooktops:
Infrared = heat = lots of electrical energy turned into heat energy = lots wasted into the air and vessels etc.
Losses (>): fuel/sunlight > electricity > chemical battery > electricity > inverted to 240VAC > cooker > air/vessel > food.

Induction: same, but less wasted in air/vessels.
Jugs: focussed, short ‘on’ times. Lotsa losses in generation, storage, inversion.
Microwaves: focussed, short ‘on’ times. Lotsa losses in generation, storage, inversion.

Conclusion: gas (or genny if you’re rich)

240 Volt AC domestic ‘inverter’ fridges:
240Volts AC > rectified to 339 Volts DC (240 x 1.414 to get DC equivalent power) > inverted back to AC at varying frequency & shaped voltage > motor (phew!).
Losses (>): Fuel/solar >> battery >> inverted to 240VAC > rectified to DC > inverted to AC (frequency/voltage shaping) > motor (mechanical/hydraulic & cabinet/ambient/front opening losses). Lots of electronics to wear out or go wrong in the inverters and fridges, not designed for unstable or vibration prone environments.

The advantage of ‘inverter’ air cons and fridges (they’re both just heat pumps) is that they can run quite slowly, rather than frequently starting and stopping and only being able to run at full speed or nothing. Their main advantage is that they don’t ‘clunk’ on/off, tend to keep temps steadier (less important in domestic fridges than air cons), and don’t draw huge currents every time they start up. The benefits of their less extreme starting currents are outweighed in vehicular or low voltage DC systems by the very large losses in producing, storing, releasing, inverting, rectifying, inverting and controlling it all.

3-way ‘fridges’: the generally available type are only ‘coolers’ that use thermal evaporation/condensation/expansion techniques to reduce temps to around 20℃ below ambient, therefore not cold enough. Good when used in cool environments. Heat from gas flames or electrical elements is hard to vent away, and adds to heat load inside vehicle/van (which can be good in cooler environments, though need for venting can negate this).

Low voltage DC fridges: designed and built with electrical and cabinet high efficiencies as primary goal, no inverter losses (usually), purpose designed motors. Can use inverter tech, but not common and still don’t have the huge losses of higher voltage gear. Cabinets are usually top opening, which avoids dumping cold air load every time door is opened.

Conclusion: purpose designed low voltage dc fridge (or 240VAC with Oka or trailer full of genny and batteries if you’re not poor)(or learn to enjoy tea again)

(and before you lot jump on my maths and physics; simplification, exaggeration and corner cutting are prerogatives of the old, so go back to calculating tubes of acne cream vs income)
13th May 2018, 07:50 AM
austastar

Love it!

Thanks, it will leave a smile on the dial all day.

Cheers
13th May 2018, 11:35 AM
DeanoH

Quote:

Originally Posted by Mick_Marsh

Thankyou for that link you provided.

Just before the description of the VVVF drive, you'll see the words, and I'll quote from the article here,

Most commonly, the terms VFD and VSD are interchangeable.:

It is also common to refer to a Koala as a Koala Bear, it doesn't mean that it is correct. :)

Tsk ....tsk Michael, selectively quoting :o

Here's the conclusion of the same article relating to the use of VSD,.VFD, VVF terminology.

So which should I use?

It’s most common for industrial control systems to be AC-powered.
In this case, the three acronyms are interchangeable and all refer to the same thing.
In the case of a DC control system, the correct term is most likely VSD.
Or, in the HVAC or mechanical services industry, AC drives might be referred to as inverters.

Deano :)
13th May 2018, 12:53 PM
Homestar

In industry, the terms VSD and VFD are interchangeable. I find that most don't know the difference and most use the term VSD, not VFD in my experience. This is despite the they are talking about AC equipment. Maybe miscommonly quoted yes, but we understand what is being discussed as DC drives are generally highly specialised these days and those talking turkey about such things will be on the same page anyway.

It's like generators - as a Specialist in this field that term amuses me as they are alternators - Generators produce DC, and my customers - and you guys as well when we discuss generators - are talking AC. I assume that when someone is talking about a generator that they mean AC, but they are technically wrong. No point getting a bee in my bonnet though, it won't change what people do.

So the term VSD is perfectly legitimate when talking AC starters in my opinion although maybe not technically correct.
13th May 2018, 03:29 PM
mike123

Quote:

Originally Posted by Pedro_The_Swift

Theres two words you dont see together very often,,
satellite internet and toaster[bigrolf]

Yes I know, the system was added too over time. I needed the internet when I could occasionally work from there and then others wanted a toaster :-(
13th May 2018, 03:51 PM
DeanoH

Back on the subject of portable/mobile fridges, I've just replaced my two Engels, one MF35 and one MF17 used as fridge and freezer respectively with an upright. After much deliberation I went for an Everkool 146 litre 2 door. The deciding factor here was 55mm insulation for the fridge and 75mm insulation for the freezer compartment.

From an efficiency viewpoint the upright design will be a minus for losing cold air when opened. I've yet to see a caravan type upright fridge with drawers or fold down doors on the shelves to reduce cool air loss, interesting when you consider my 1980's Philips upright freezer does (did) have fold down plastic doors on each shelf to help efficiency.

On the plus side I'm now running one 'new' compressor (Chinese BD35 clone) instead of two 20 yo compressors and have much better insulation. Too early to tell what the comparable efficiency's are but the doubling of capacity and accessibility is certainly a plus. :)

Deano :)
17th May 2018, 04:16 PM
nick_e

Quote:

Originally Posted by Homestar

It's like generators - as a Specialist in this field that term amuses me as they are alternators - Generators produce DC, and my customers - and you guys as well when we discuss generators - are talking AC. I assume that when someone is talking about a generator that they mean AC, but they are technically wrong. No point getting a bee in my bonnet though, it won't change what people do.
.

I think there is just ambiguity around the terms, and it's not surprising there is confusion.

A (modern) car has an alternator that uses a voltage rectifier to output DC.

A genset uses an alternator that puts out AC at mains voltage but they are marketed as 'generators'. Not sure if this is a throwback from the old days before AC took off or if its just a different, non technical use of the term generator.

Actual generators aren't used that much out of specialised applications these days as far as I am aware. Most common applications have been replaced with either AC alternatives or electronics powered by rectified AC supply.

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