Yes it's kind of interesting how this works. The simple answer is that with a resistor and capacitor, the resistor will always eat up some energy. With an inductor and capacitor, these both store energy and in theory do not dissipate any energy at all. Thus if one transfers to the other (and the cap energy can transfer to the inductor also in various cases) no energy is lost. As you know there are no perfect L and C so there will be a little energy lost, but not nearly as much as with a resistor with a cap or inductor.

You might note that in the definition for a resistor we have:
P=R*i^2=V^2/R

which means it dissipates energy. For an inductor or capacitor, we do not see this kind of formula, instead we see a formula that indicates the STORAGE of energy not the LOSS of energy.
Storage means it is saved for use later like filling a tank with water then using it later for something. Loss means we lose it which is like pouring water down the drain.

Indeed. However, some tests I did a few years back came in at around 40% overall, but that also included the losses from the solenoid cores and other losses such as the bits of circuitry that are active, such as the FET switch and external connection cables. So as I see it, while the transfer of energy from an inductor to a capacitor can be highly efficient, when one takes into account all the other losses in the overall process, the efficiency of taking battery energy and converting it to ‘pulse energy’ is about the same (and as bad) as an internal combustion engine. Do you think that’s fair comment?

 

the efficiency of taking battery energy and converting it to ‘pulse energy’ is about the same (and as bad) as an internal combustion engine. Do you think that’s fair comment?

It is not unusual to have efficiency 90 and more percents.
For example μModule LTM8040:
_____

 

It is not unusual to have efficiency 90 and more precents.
For example μModule LTM8040:
View attachment 332324___View attachment 332323__

Ok, I should qualify my statement to say, with the setup I’m using.

 

converting it to ‘pulse energy’ is about the same (and as bad) as an internal combustion engine.

Internal combustion car gasoline engines are typically about 20-40% efficient.
Your circuit should be well above 50% if properly designed.

Note that the inductor resistance can have a significant effect on efficiency, since its losses go up as the square of the current.
That's why switching supply use as high a switching frequency as feasible (where the switching losses become significant), to allow the use of a smaller inductance with lower series resistance.

 

I'm sure you are right but circuit efficiency was not the main focus or need in this case.

Having been told elsewhere that arriving at a custom Spice model for the stw12n170k5 was too difficult a job, another contact has developed one for me including its 'breakdown' behaviour, so I will be playing with that and post some outputs in due course. However, I'm sure I will still need to tweek some details of the other components for an even better match.

Even if in the end I will be using practical measurements for my numbers, a sim model can visualise things that the bench can't.

 

I'm sure you are right but circuit efficiency was not the main focus or need in this case.

Having been told elsewhere that arriving at a custom Spice model for the stw12n170k5 was too difficult a job, another contact has developed one for me including its 'breakdown' behaviour, so I will be playing with that and post some outputs in due course. However, I'm sure I will still need to tweek some details of the other components for an even better match.

Even if in the end I will be using practical measurements for my numbers, a sim model can visualise things that the bench can't.

And your contact has derived the voltage dependencies of the three capacitances. I can try to make it for Qspice if you are interested.

 

Indeed. However, some tests I did a few years back came in at around 40% overall, but that also included the losses from the solenoid cores and other losses such as the bits of circuitry that are active, such as the FET switch and external connection cables. So as I see it, while the transfer of energy from an inductor to a capacitor can be highly efficient, when one takes into account all the other losses in the overall process, the efficiency of taking battery energy and converting it to ‘pulse energy’ is about the same (and as bad) as an internal combustion engine. Do you think that’s fair comment?

Well, not really.

The top efficiency of an ICE is around 45 percent, while an electric motor can be 85 percent, and a switching power supply can be 90 percent or better. 90 percent vs 45 percent is a big difference. Of course it's a different technology but when you consider how hot an ICE gets it's no wonder.

When I worked in the industry, we did fairly complicated true sine converters and got to 90 percent with 1 percent distortion when we went to using MOSFETs vs Bipolars. That's a complicated circuit and yet the efficiency was quite good. We even got high using the newer Bipolars at the time.

Low ESR inductor and capacitors help to get the efficiency up there.

I am not sure what kind of tests you were doing, but when you do tests like this you have to log all of the data and explain the entire setup in detail, and even log the model numbers of the test equipment used to do the measuring. That's so that your tests and conclusions can be duplicated by a second party. You would have to explain all this to us in order to figure out why you got such a low efficiency. There must have been some extreme losses there. 40 percent is just plain terrible. You have to realize that if you had a 1000 watt output converter at 50 percent efficiency (higher than your measurement) it would require 2000 watts input. The thing would get as hot as an electric space heater that would be used to help heat a small room. Nobody in their right mind would purchase anything like that (unless they needed a power converter that could also heat their room ha ha).

If you can supply some details about your 40 percent tests maybe we can figure out what went wrong. Either that or you could just go on to follow some more modern design guidelines and be done with it. We've come a long way since the 1950's and 1960's.

 

I'm sure you are right but circuit efficiency was not the main focus or need in this case.
<snipped>

Well you seemed to be complaining about the efficiency so you got a lot of comments about that.
If not efficiency, then what IS most important here?

 

My aim is not to produce the highest efficiency but to know fairly accurately what the efficiency is. I have never complained about the efficiency but only sought to know how to determine it well enough.

 

My aim is not to produce the highest efficiency but to know fairly accurately what the efficiency is. I have never complained about the efficiency but only sought to know how to determine it well enough.

Then a simulation is the easiest way to determine that.
Since the MOSFET is used as a switch, the exact model will likely not have much effect on efficiency, as long as you select a model with a similar on-resistance and gate charge to the one you have.

 

Yes, but I will still be comparing bench measurements, using a previously described method, with the sim results but I am still trying to get the model to show pulses. Gate input fine but only 12V out so far. I am also unfamiliar with doing various ‘post measurements’ calculations inside Spice but all in good time. The transients first

 

I am still trying to get the model to show pulses.

Can you expand on that?
Where are you trying to see pulses?

 

Can you expand on that?
Where are you trying to see pulses?

I have them now but they are much higher than they should be. Real ones measure around 1600V.

 

If you want I will post the sim and model files.

 

If you want I will post the sim and model files.

Sure, if it's an LTspice .asc file.

 

If you want I will post the sim and model files.

JulesP
Have you set the inductance resistances?

 

Here are the two files. I have had to change the file extension of the .mdl file to .txt to upload it so it needs changing back.

There are various factors still not inserted, such as an accurate series resistance and inductance for the capacitor (tracks and ext. wiring), a IN4001 model for D1 (instead of 4007), series resistance (ext. cable and PCB tracks) and parallel capacitance for V2, V1 is a PSU so some values should be entered I guess, and possibly a few other tweaks.

The 53mF capacitor is actually comprised of 4 x 15mF joined in parallel and measured at 53mF.

 

JulesP
Have you set the inductance resistances?

I put in 14.5 Ohms for each.

 

I have them now but they are much higher than they should be. Real ones measure around 1600V.

There are two obvious errors in the schematic on post #93.

C1 has no connection to its top terminal.
D2 is shorted by a wire going right through it.

 

There are two obvious errors in the schematic on post #93.

C1 has no connection to its top terminal.
D2 is shorted by a wire going right through it.

If C1 was connected there would be no spikes shown. The voltage after the output diode would be at the cap voltage. If you connect the cap then the voltage after D2 rises to about 12V.
Re D2, yes well spotted. An overzealous wiring. But it won’t change the flyback voltage I imagine, but it might change the voltage the cap gets to as voltage can ‘leak’ back to the Drain - I guess.