Lossless voltage reduction using capacitors?

Thread Starter

Thane

Joined Apr 18, 2023
6
I'm attempting to convert 200v - 270v DC to 120v DC with the core goal to have as little loss as possible. I've been reading about voltage regulators but they all seem to have some loss however there are scientific articles about certain designs which are shown to have far less than average. As the articles are not new, I was hoping someone knew of a product or design I could buy/order. (2. ) Is there a product that could take the used or unused power from the conversion and store it into an array of capacitors that could somehow be used efficiently for the load and/or use the remainder elsewhere?
 

ElectricSpidey

Joined Dec 2, 2017
2,593
Not really.

The switch mode buck regulator is about the best it gets.

The trick isn't stashing produced power away for later, the trick is not producing waste power in the first place.
 

Papabravo

Joined Feb 24, 2006
20,378
I'm attempting to convert 200v - 270v DC to 120v DC with the core goal to have as little loss as possible. I've been reading about voltage regulators but they all seem to have some loss however there are scientific articles about certain designs which are shown to have far less than average. As the articles are not new, I was hoping someone knew of a product or design I could buy/order. (2. ) Is there a product that could take the used or unused power from the conversion and store it into an array of capacitors that could somehow be used efficiently for the load and/or use the remainder elsewhere?
Capacitors, by themselves, are useless when it comes to voltage reduction. In fact, the immutable rule of all DC-DC conversion schemes is that:

The output power will always be less than the input power. Sometimes it will a great deal less.
A carefully designed buck converter comes very close very close to being the best you can do.
 

DickCappels

Joined Aug 21, 2008
10,067
A switched capacitor approach may provide a viable solution if you don’t need regulation, for example a 2:1 voltage divider would be simple in concept, but you would probably have design it yourself or hire somebody to do it.

As per @ElectricSpidey I have found buck converters from around 200 volts to around 100 volts very easy to make and very efficient .
 

MisterBill2

Joined Jan 23, 2018
15,600
Probably a buck-mode switching regulator would be the best choice is my guess. But we are given no hint as to the required power required and that matters quite a bit.
 

Thread Starter

Thane

Joined Apr 18, 2023
6
The power draw would be generally about 800w - 1500w running a couple times per day times per day lasting 2 to 20 minutes. The 1500w would not run for longer than a couple minutes. 800w is probably the average draw. The input is from a traction battery and the voltage varies from 200 - 270. Thanks for the input. I apologize, i thought I had replied earlier but that must have been to another thread. Memory is fading fast these days, wow!
 
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MrAl

Joined Jun 17, 2014
10,590
I'm attempting to convert 200v - 270v DC to 120v DC with the core goal to have as little loss as possible. I've been reading about voltage regulators but they all seem to have some loss however there are scientific articles about certain designs which are shown to have far less than average. As the articles are not new, I was hoping someone knew of a product or design I could buy/order. (2. ) Is there a product that could take the used or unused power from the conversion and store it into an array of capacitors that could somehow be used efficiently for the load and/or use the remainder elsewhere?
Hi,

As others have said, a DC to DC switching converter is the go-to device for this kind of need.
In particular, the buck converter.

The buck converter stores energy in an inductor during the switch 'on' time, and releases some of it during the 'off' time.
This is what we call a true power converter. It is referred to as such because it can convert power from one voltage level to another and in theory with all ideal circuit elements, there is no loss in that conversion.
Unfortunately, there are usually no ideal components, and we have to use real life components which dissipate some energy as heat. This means the efficiency is not 100 percent but somewhat less than that. It can range from around 70 percent up to around 95 percent, but most will fall into the range of around 80 to 90 percent. This means you will lose some energy.
With an efficiency of 80 percent at 1000 watts you would lose about 200 watts. With an efficiency of 90 percent, you would lose about 100 watts. This is pretty much unavoidable.

Resonate converters seem to be making a comeback probably due to the increased demand for energy and high efficiency in almost everything these days. They work by switching during times when the transistor current naturally falls to zero and thus avoid some of the switching losses. They would be more complicated to build, however.

In the attached drawing you will see some waveforms for a buck converter. This one converts 120vdc down to about 50vdc. The waveforms shown are the inductor current (iL), the inductor energy (eL), and the capacitor energy (eC). The inductor current rises when the switch turns on, and falls when the switch turns off. The energy stored in the inductor increases when the switch is on, and decreases when the switch is off.
The scales in the drawing are not the same. Both eL and eC are scaled and offset in order to be able to compare with them with each other more easily. The scale factor for eL and eC is 1000 and they are both offset somewhat. Comparatively though, we can see that the energy in the inductor changes more than the energy in the capacitor and that is the main way we get true energy conversion.
 

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MisterBill2

Joined Jan 23, 2018
15,600
Resonant converters are a special case and I am not convinced that they are always the best choice for all applications. Both the input voltage range and the output, as well as the power level, will allow a choice of purchased models of regulators. So there will need to be some research to find the most efficient model.
What is the specific application? It may be that some specifications do not need to be kept so closely,, or some variable controlled more closely. More information will assist in getting better advice, with less guessing.
 

Thread Starter

Thane

Joined Apr 18, 2023
6
@MrAl Thanks, this is a kind of information I can easily digest. I searched Ebay for Resonant Converters and had a laugh at the complexity of this subject matter i'm attempting to digest when the first result was "anti-resonant converter" I just had to sit there and nod my head. Of course, an anti-resonant converter, why not. Thanks again, you've helped narrow it down some more and thanks again for the great explanation.

@Misterbi I'm wanting to run many different appliances from a hybrid traction battery which is being made into a specialized camping vehicle, as well as a tow hitch, water pump, welding machine, air compressor. Most importantly the pizza oven. :)
 

MisterBill2

Joined Jan 23, 2018
15,600
Some good news is that those types of appliance devices are not demanding of high purity power, nor precise regulation.
I suggest, however, in not shopping the random market place with unknown vendors peddling unknown products.
Electrical heating devices are not picky about the purity of their DC power, in particular.
I suggest examining the power supply products from companies that specialize in power supplies , as my guess is that aside from maximum efficiency there is also a need for a durable product that will not fail shortly after whatever warranty time passes. And adequate information about the supply will be important.
It does seem that for such a large variety of loads, more than one power converter may be useful, because a converter able to provide several hundred watts of power is not likely to be as efficient when powering a much smaller load.
 

BobTPH

Joined Jun 5, 2013
7,519
I would really worry about damaging a very expensive battery. A small generator would probably be more appropriate.

Do these appliances really all run on 120VDC?
 

MisterBill2

Joined Jan 23, 2018
15,600
I would really worry about damaging a very expensive battery. A small generator would probably be more appropriate.

Do these appliances really all run on 120VDC?
In a silent environment any engine driven generator is audible for a huge distance, at least to some folks. And every one of them consumes fuel that may not be conveniently replaced. An adequate array of solar cells to provide several hundred watthours of power daily is a "big deal", and may not have an adequate amount of sun-time in many wooded camping areas. And other than small systems, they are not readily portable. Of course, recharging any "traction battery"will require some sort of mains connection eventually.
With reasonable care and attention battery damage does not seem likely, but certainly battery discharge will happen. Thus my comments about charging.
 

AnalogKid

Joined Aug 1, 2013
10,558
High density DC/DC converters can do what you want. A couple of the latest gen units in parallel can be very efficient.

Is there a product that could take the used or unused power from the conversion and store it into an array of capacitors that could somehow be used efficiently for the load and/or use the remainder elsewhere?
No. The power loss in a conversion circuit is dissipated as heat. If the circuit is any good, there is not enough heat, or heat at a high enough temperature differential, to yield a usable amount of energy after it is converted back into electric current.

ak
 

Thread Starter

Thane

Joined Apr 18, 2023
6
Do these appliances really all run on 120VDC?
So far i've found out a microwave uses AC in its core process, as well as the motor that rotates the tray, but I could take it apart and weld my own simple inverter for a local AC supply. However, the more I research, the more it seems that since the voltage would still have to be regulated to a steady 120v, there may be no real power savings after all. The Toyota Prius creates many different levels of voltage within its own inverter ( ~5v to ~720v), next up is finding out if I can tap those while the car isn't moving.

@AnalogKid Wager a guess on how much energy would be saved with this DC-DC conversion over using a normal 12vdc -> 120vac power inverter?
 

AnalogKid

Joined Aug 1, 2013
10,558
So far i've found out a microwave uses AC in its core process, as well as the motor that rotates the tray, but I could take it apart and weld my own simple inverter for a local AC supply.
Probably not. A microwave oven can draw over 1200 W. There is nothing simple about a DC/AC converter at that power level.

ak
 

MisterBill2

Joined Jan 23, 2018
15,600
REally, a regulated switching mode power converter is about as efficient as you can get, because the method of regulation is to draw only enough power to provide the set output voltage. At least the better designed supplies do that. A Microwave oven uses a magnetron tube to produce the heating power and presently there is no cheap alternative. BUT there is at least one version that uses an inverter powered by the rectified mains voltage that may be adaptable to your battery voltage. (Panasonic "Inverter").
An interesting approach may be to use a variable voltage adjustable DC supply intended to be powered by rectified mains power, 220 volts. I have one such supply, although my model only delivers up to 50 volts at 50 amps. A different model was available that could deliver up to 100 volts at up to 25 amps. Not a cheap device, although I gat a great deal on mine because the previous owner could not make it work. I discovered the problem and and the way to make it work by reading the instruction manual.
A supply similar to that could be used to run many of the appliances that would be powered by DC .
 

MrAl

Joined Jun 17, 2014
10,590
So far i've found out a microwave uses AC in its core process, as well as the motor that rotates the tray, but I could take it apart and weld my own simple inverter for a local AC supply. However, the more I research, the more it seems that since the voltage would still have to be regulated to a steady 120v, there may be no real power savings after all. The Toyota Prius creates many different levels of voltage within its own inverter ( ~5v to ~720v), next up is finding out if I can tap those while the car isn't moving.

@AnalogKid Wager a guess on how much energy would be saved with this DC-DC conversion over using a normal 12vdc -> 120vac power inverter?
Hi again,

With 120v input and 120v output with nothing in between, the only energy wasted is in the wiring from input to output which would be small.
Anything else wastes some energy which would usually be much more than that.
The ratio of input to output or output to input plays a role in this. Converting from 12v to 120v would waste more energy than 48v to 120v for example, with the same basic design methodology. 96v to 120v would waste even less. They all waste something though, and you may find a better design for either of those.

12vdc to 120vac may not be such a bad idea due to the fact that there are a lot of products out there that do this already, and they put out a pure sine wave also. You just have to find one that has decent efficiency. Does it really matter that much if you only get 75 percent vs 90 percent, will it hurt that much, or can you upsize the battery. 1000 watts at 90 percent wastes about 100 watts, 1000 watts at 75 percent wastes about 250 watts. Will that 75 percent unit really be a huge problem or just a little problem. That's something to think about also.

Since you need AC output I guess then a pure sine converter is probably the best option. This will help to ensure appliances that need a decent sine wave do not develop problems if they were to get a square wave instead.

Oh and as to Bob's reply, yes you do have to make sure your battery has a max current rating that will not be exceeded and probably should be much higher than the usual load requires for better battery longevity.
 

MisterBill2

Joined Jan 23, 2018
15,600
note that 12 volts DC has not been a part of this thread. And certainly a heating appliance like a microwave oven can use power that is not a perfect sine wave. And while most of them provide a turntable with a motor, they do not require that to be usable.
The power source is a "traction battery" with a voltage that drops from 270 volts to 200 volts as it discharges. There is no mention of how it gets recharged, at least not yet.
It appears that the Panasonic brand "inverter" models of microwave oven us rectified mains power to feed an inverter, as the package does notinclude any mains frequency transformers. So a microwave oven operating on 200+ volts DC appears to be available.
 
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