yes that might be correct. I tried various cores. It was hard to find a configuration that allows startup at all.

Efficiency during normal operation is not too bad.

A very small $1 cooler is used, and the MOSFET heat dev. can be controlled well. The core of the inductor does not heat up reasonably.

For the TL494 SMPS, the cores heat up but only very slowly, it will take minutes until they get hot.

So the total loss in the cores is only 1W or something like this.

1. Exposing the cores to airflow
2. Using two cores in parallel

both helped to contain this isssue.

The cores are still not optimal, but there is no urgent need to change the circuit. I was mainly built for research, and I have experimented a lot with these two circuits + learned many things.

 

If the circuit is designed properly the inductances should not show any significant warming.

The pure inductance will not dissipate, it is just the resistance of the wire. Now those coils have pretty heavy gauge wire (for that precise reason).

As long as the cores do not go into saturation the current will just be what you want for your bulb and that sort of gauge wire should not even get warm with five or so amps going through it.

From what you describe, I'd estimate you are putting about 10W into warming the coils.

 

If the circuit is designed properly the inductances should not show any significant warming.

The pure inductance will not dissipate, it is just the resistance of the wire. Now those coils have pretty heavy gauge wire (for that precise reason).

As long as the cores do not go into saturation the current will just be what you want for your bulb and that sort of gauge wire should not even get warm with five or so amps going through it.

From what you describe, I'd estimate you are putting about 10W into warming the coils.

Maybe some day I should get more additional cores to experiment + more different types of magnet wire. The wire I have here is a bit thin.

The yellow cores I use for the TL494 are good but also have rather thin wire, many turns. I should get wire with about double diameter, and rewind them.

 

Ah , I did not realise you had rewound them.

I'm thinking of the sort of coils that are found in the onboard regulators of mother boards. They have relatively few turns but about 1mm thick wire. They are designed around the same sort of currents that you are want to use, so that should be a good starting point.

Mobo's are a good source of 60V high current nMOS devices with really low resistance.

 

Their inductance will be low since the delta voltage is only very small.
As well frequency is much higher very likely.

I would wonder if I get some 300 to 800uH from a motherboard.

If I use 60V input, and want 12V output, the delta voltage is 48 volts.

 

I've just pulled sturdy yellow toroidal out of the box, looks bigger than what comes of most mobos so I'm not sure what I recovered it from. I have written ~30uH on it, though not sure how I estimated that.

Inductance needed goes up with the voltage drop as you say but also comes down with increasing current.

Looking at the LM2596-15V and extrapolating to I max ~ 6A Vin=40 would seem to suggest ~100uH. Nominal 50kHz oscillator.


Where did you get the estimate range of 300-800 uH ? Seems a bit high.

 

I've just pulled sturdy yellow toroidal out of the box, looks bigger than what comes of most mobos so I'm not sure what I recovered it from. I have written ~30uH on it, though not sure how I estimated that.

Inductance needed goes up with the voltage drop as you say but also comes down with increasing current.

Looking at the LM2596-15V and extrapolating to I max ~ 6A Vin=40 would seem to suggest ~100uH. Nominal 50kHz oscillator.


Where did you get the estimate range of 300-800 uH ? Seems a bit high.

This is what I use for the TL494 circuit. And it seems reasonable. Frequency is also adjustable here.

The LM2576 regulator I built does not use LM2576 internal transistor for switching. External p-CH MOSFET is used.

Input is 60 Volts!

Inductor value is indeed unknown. I have experimented a lot with this circuit to increase efficiency.

Then I have also rebuilt this circuit on a smaller scale.
This time the core was rewound with thinner wire.
http://forum.cytron.com.my/viewtopic.php?f=30&t=11648#p20325

30 uH really can not be used for 60V input, 12V output.

For small dc/dc chips such as MCP1650, I use inductors like for instance 12uH. They work at much higher frequency, 500 KHz, and delta voltage is much lower, only a few volts.

 

It's the current x turns product that creates the magnetic field, you have loads of room with so few turns , what is the point of using thinner wire. This will just increase the resistance which is nothing but parasitic in this situation?

My PV output is around 30V at peak power so with a charging voltage of 13-14V I'm looking at a smaller drop. Also charging current in the range 10-15A so I may not be too far off if that coil is really 30uH. Though twice that value may be more comfortable.

 

Not entirely sure about that.

I have tried different number of turns.

A value in the 100s of uH range seems to be required.

Trying smaller numbers of turns, and the saturation was quite obvious to a point that input current was near output current, and very high heat developement.

I have tried at least 50 different configurations.

I have not seen your PV circuit neither a schematic or a photo, or information about the technology used.