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Peltier element controller method, 20Amps bidirectional current

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That and a number of us would love to know what company you work for and how you have yet to ever be fired for gross incompetence of your current job.
I instantly confess that my gross, utter incompetence staggers even myself, though i abide in, and indeed am from, Britain, a country which has virtually deliberately de-skilled itself over the years, so there's often little competition for me and others like me......

By the way, i find SMPS v(out) control easy......how would you say the control of temperature with a peltier sytem with an smps compares in difficulty level?

The suicide of UK owned industry from 1952 to present day (2017)

In the early 1950s, the UK was an industrial giant. Today, it is an industrial pygmy. In 1952, UK owned companies made a quarter of the world’s manufacturing exports. Today (2016), the UK makes up less than 2 per cent of the world’s manufacturing exports, and even that percentage is mostly made up from foreign owned companies operating within the UK.

The UK now has a National Debt of 1.7 trillion pounds, and has been spending much more than it earns for every year over the 33 years up to 2016, and its trade deficit is dramatically worsening. The supply of North Sea Oil on which UK has become reliant is about to run out. >50% of UK industry is foreign owned; >40% of UK vital services (electricity, gas, infrastructure etc) are foreign owned; >66% of the fuel for the UK economy is foreign owned. UK is not capable of building its own nuclear power stations but relies on China to do it whilst China is already busy building islands just off the coasts of Vietnam, Brunei, Malaysia, Taiwan and Phillipines. >90% of UK schoolchildren stop progressing in maths & science at the age of 16. The OECD recently declared that a quarter of UK’s adults have the maths skills of a 10 year old. The brunt of the UK’s Naval fleet is powered by Electric Motors & Drives designed and built by the French. In the UK in 2016, >70% of London’s ‘zone 1’ office space is foreign owned.

The UK’s downward slide is moving at an alarming pace....In 1952, the UK was an industrial powerhouse. In 1952, UK brought out the world’s first commercial airliner, and was a close second to the USA in the development of the computer. In 1956, UK was amongst the first to bring out a Nuclear power station. In the 1950’s, Britain invented nuclear power, led the world in its application and developed enough stations to sustain a sizeable home-grown industry with a strong skills base. In the 1950s, UK owned companies were the second-largest manufacturers of cars in the world (after the United States) and the world’s largest exporter of cars.

The UK’s Sir Frank Whittle invented the turbojet engine in the 1930’s. In 1940, the UK had developed a Cavity Magnetron a thousand times more powerful than anything in the USA. The Mini, as developed by the British Motor Corporation in the 1960’s was voted the 2nd most influential car of the 20th century.

However, the UK flogged most of Rolls Royce to the Germans, Jaguar Land Rover to India, Bentley to the Germans, Rover to the Germans, Triumph to the Germans, and now has virtually no car industry of its own (Some Morgan cars have BMW, or Ford engines and current Morgans are not stated as having British built engines). The UK has 25.8 million cars on its roads, and each one represents lots of money flowing overseas, worsening the already disastrous UK trade deficit. The UK cannot blame the arrival of the Far East into the world economy for UK’s poor performance, because after all Germany is managing just fine. In 2014, Germany was the world’s biggest exporter by Capital value.

The UK privatised its rail network so as to bring the benefits of private ownership...but then the German government bought a huge chunk of it (Arriva trains)...so its back into state-ownership...but owned by the state of a foreign country. In December 2015, the UK derived 17% of its energy from wind power. In Oct 2016, there were 6594 wind turbines in the UK. None of these wind turbines is designed or manufactured in the UK. Virtually all of them are designed and manufactured by Siemens of Germany or other foreign companies.


The UK payed £4.4bn net to the EU in 2009/10, but this rose to £8.8bn in 2014/15....the EU actually took 12.8 billion from UK, but gave back £4bn to be spent in ways decided entirely by the EU. The UK recently flogged off Admiralty Arch (the glorious gateway to Buckingham Palace) and The Old War Office (on Whitehall) to Spain & India respectively, for conversion into Hotels/Flats. In 2002, the UK came up with the "Enterprise Act", freeing its government from the duty of intervention when its own UK owned industries of great value were about to be sold into Foreign ownership...subsequently, from 1997 to 2007, foreign ownership of the UK’s firms rose from a third to a half, and foreign ownership of its vital services (electricity, gas infrastructure etc) rose to 40 per cent. Other countries (eg USA, Germany, France, Spain etc etc) have legislation which stops them from selling off their country’s prized assets in the way that the UK does.

Foreign companies acquired £30billion worth of the UK's enterprises in 2009. In 2010, that rose to a value of £54.5 billion. In 2016, the UK flogged off the magnificent ARM company to the Japanese for £24.3 billion, this had been the jewel in the UK's crown, one of the greatest electronics companies in the world. The UK flogged Boots the Chemists to the Italians, and Boots stores remain in the UK, and then the UK found that under Italian ownership, the UK received just £9 million in Tax from Boots, rather than the £90 million per year that it received before flogging it off (due to Boots getting "brass plated" by the Italians to Zug in Switzerland)......The same story of reduced Tax revenue is prevalent with most of the UK's other multitudinous industrial sales to foreign companies. In 2016, the Chief Advisor to the Turkish Prime Minister indicated that all the UK now does is to “Produce Cadbury’s chocolates and Maltesers”. (But in fact, Cadbury’s actually was sold to the Kraft foods company of the USA in 2010). In 2012, Nikolas Sarkozy, Prime Minister of France, declared that “The United Kingdom has no industry any more”. England is the 5th (fifth) most densely populated country in the world.
Between 2002 and 2008 the UK suffered a 50% drop in the number of its own domiciled school leavers opting for Electronics/Electrical Engineering degrees. Each year much less than 500 of UK school leavers "enrol" for an electronics degree, the majority of these choose all software modules or transfer to the School of Computer Science at the end of year two. In UK it is virtually impossible for almost anyone to assert the exact number of UK_citizen school leavers that end up actually graduating with an electronics degree each year....As far as Electronics Hardware centred graduates are concerned, the number is thought to be under 100 per year. A paltry amount.

When foreign owned companies in UK are a success, the profits flow overseas, when they do less well, there are more likely to be job losses. R&D spending gets notably less when UK industries get sold overseas. Tax revenue to UK is dramatically less. The UK is poorly placed to pay off its huge National Debt, since it has shed the once UK owned Engineering industry so desperately needed to pay off its debt.

The UK National Debt of UK is 1.7 trillion pounds in 2016. However, this figure is often “watered down” by expressing it as “National Debt as a percentage of GDP”. This comes out as 90% for UK…hardly a cause for comfort in itself, but in any case, GDP has dubious meaning for a country like UK, where >50% of industry & services are foreign owned. This is partly because for instance, GDP does not take into account profits earned in a nation by overseas companies that are remitted back to foreign investors. This can overstate a country's actual economic output.

Like in no other country, Britain has sold off more than half of its companies to Foreign owners (stated by Alex Brummer in book “Britain for Sale”). Nearly two thirds of UK manufacturing businesses that employ over 500 are now owned by foreign companies claimed business minister Baroness Neville-Rolfe in 2016.
 
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I for one think that it's great to have some contributors bringing interesting real-world engineering problems to the table here, and also that there are people working in industry who are not too proud - or to worried about what their boss might think if they found out - to bring these problems for discussion in an open forum.

Let's try to keep it polite, constructive and technical.
 
Hello,
Do you think the attached Peltier current controller topology is the most optimal?
(pdf schematic and LTspice simulation attached)
It’s just a Full Bridge where the Duty Cycle of each diagonal pair determines the direction (& magnitude) of current.
Each diagonal pair is driven by an output of a synchronous Buck driver IC.

The difference between the two current monitor outputs gives the magnitude of current.
As you can see, this topology could easily be commanded to give any magnitude of current in either direction, with a little more circuitry.

Putting this into a frequency compensated feedback loop closed on the temperature is more challenging. If the feedback loop could be done in an “iterative” set/check/modify manner then it would be very simple. All we would need to do is just increment/decrement the current, then read temperature then either increment/decrement the current again, and so on and so forth.

Do you agree that this is the simplest way to do it?

This document appears to suggest that a fully dynamic frequency compensated feedback loop must be implemented for a Peltier system...
https://www.maximintegrated.com/en/a...ex.mvp/id/3318

Page 15 of this...
https://www.analog.com/media/en/technical-documentation/data-sheets/ADN8830.pdf
.....states that Peltier resistance can be a few ohms, and with a few amps flowing through that, it would heat up no matter which way the current was flowing, so i am surprised that these Peltiers are at all useful for cooling things?
 

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So you are going to stay with bidirectional?
Why do you need to know the current?
Why not turn on the power them temp>x and off when temp<x?
 
Does the diode need to be regulated at a particular temperature or does it need to be cooled to prevent burning up? If the later, listen to what everybody here is telling you.
 
I suspect all that's required here is a simple bi-metallic switch :D

I'd be surprised if the peltier device is even needed at all. :rolleyes:

To require a "20 amp" (at 12 volts?) peltier device to cool something means that laser is putting out a lot of heat or has a unusually low working temperature limit.

Plus whatever heat sink that heat, including the now 240 or more watts the peltier is generating itself, has to dissipate just adds to the thermal control problems.

Self inflicted ΔT runaway simply due to poor understanding of basic thermal engineering practices? :facepalm:
 
thanks, these are great thoughts, i wish id spoken to you b4 i met the client on friday. They said they want a peltier solution for every occasion that they may have in future, so dont want an ic, therefore i propose the above solution in #23.
 
The key unanswered question is: Does the diode need only cooling or does it require temperature regulation?

The usual case is cooling only. If that's all that's needed here, you have an extremely complex solution to a simple problem. If temperature regulation is required, you should have explained that a long time ago.
 
it must be regulation because they said definetely bidirectional current needed. They told me the first job is a laser that is on for a ridiculously low duty cycle, so the power it takes on average is almost nothing.
 
Would not a simple temperature control to turn it on and off suffice? Is there EVER a need to HEAT the diode?
 
it must be regulation because they said definetely bidirectional current needed. They told me the first job is a laser that is on for a ridiculously low duty cycle, so the power it takes on average is almost nothing.

So your going throw '20 amps DC biased PWMed AC' at whatever voltage into both heating and cooling a peltier unit at the same time to achieve a net zero temperature differential for the vast majority of the time being the laser itself is not even on and generating heat itself. :rolleyes:

To me this sounds like your customer has no clue what they are doing or what other than they like to toss around technical terms they don't understand themselves and see who will follow them. (probably why you got assigned the project (like working with like)). :facepalm:

How powerful is this laser and what is it expected duty cycle?
 
Yes they sometimes want to heat the diode. I am not sure about the laser diode power.., they are saying they are coy about talking about particular lasers since they want a system that can be adapted to various laser diodes in different apps....

In my full bridge peltier current controller (attached here in pdf schematic and LTspice simulation) , giving the fets 50% duty cycle does not necessarily mean zero current in the peltier because of the voltage source which effectively exists in the peltier. So it seems that a Peltier is actually effectively modelled as a unipolar voltage source of a volt or two in series with a resistance of an ohm or two.

In fact, in one direction of current flow, the overall voltage across the peltier element could be zero, as the voltage of the voltage source, and the voltage across the series resistance could cancel, do you agree?

The attached shows two different Peltiers, one with 1A flowing in one direction, and one with 1A flowing in the opposite direction. Even though the magnitude of the current is the same in each case, the duty cycles which produce these currents are not conveniently symmetrical around 50% for the two cases.

This is going to cause problems……because its not going to be possible, due to peltier tolerances, to know exactly which duty cycle will give zero Peltier current….and so there is the chance that any control loop could start off with a duty cycle which puts current say in the heating direction when this was not wanted.

Do you know how this can be mitigated? I mean, it’s not the end of the world, but we really don’t want to ever (even temporarily) put current in the heating direction when we want to cool it. What we want to do is start with a duty cycle that gives zero peltier current, and then gradually increment/decrement it until we have the right system temperature. The thing is, how do we know exactly which duty cycle causes zero current?
 

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The same question still applies:

Does the laser diode require precise temperature control?

The general (with the exception of you) consensus here it that it does not. With this understanding in mind, I believe everyone here (again, with the exception of you) believes your approach is wrong, so any comments on your design will be less than helpful.

Perhaps you are correct. Some clarification from your client will either verify you are headed in the right direction or that you are wasting your time. Sometimes, some extra effort is required to determine what a client needs and to help him understand that.
 
Just an comment,

out right speculation, a medical laser would sound the part for potentially requiring heating/function, then cooling/function, or a multi laser selective array, class II - IV?

again, just curious speculation
 
Still curious as to what a '20 amp' peltier unit is and to what heat pumping capacity it's suposed to work at too. :rolleyes:

Can it be powered off a '20 amp' battery of indeterminate/irrelevant voltage for an unspecified amount of time? o_O

What if I connect it to my 'infinite amp' zero volt power supply? Any issues there? :angelic:
 
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