CWS-Bytemark's F150-F core looks like a good starter. It's skinny enough for a reasonably small mean length per turn, and it has a good, medium-sized area (0.591 cm^2). It's obviously a Mag Inc core, and you could cross-check the core data by going to their site and looking for a core with the same dimensions. What is helpful is that core sizes for ferrite toroids aren't too well standardized, unlike powder cores. For 40kHz, 1500 Gauss peak flux, you get 8-9 primary turns. Too bad they don't sell cut cores - I could use some...
Where did you get 1500 gauss? What would you use this core for, and if you wanted more power capability, what would you look for...smaller cross section? ...or since both I and N are proportionate to B would you want to decrease N to allow a higher current(I), or get a larger cross section that would require less N? B=(u*i*N)/(2*pi*r)...this is all helping, little by little.
You've never said how much power you're looking for... The core I mentioned will be limited by copper loss, not core loss, so the power capability will depend on the copper cross section you can pile on it. Mag Inc F material is pretty old stuff, so I picked 1500 Gauss as a nice conservative value to get enough turns so that I could spread them evenly around the core periphery without too much core loss. I pulled the value out of my ear from 20 years of experience with working with switchers of all sorts. I would think you could get at least 100W through the core without too many problems, as long as you size the wire properly. I would start with somewhere around 4 X 19 AWG for the primary. Pick 2 strands for each primary half. Remember that each primary is on only for 1/2 the time, so that the effective current density for each primary half is 1/2 the input current. Remember also the the amp you're feeding will not consume full RMS power, unless you are keen on having your ears bleed. If you want more power , you go for a larger cross-section core and fewer turns, with thicker wire or more parallel strands.
Contrary to standard cheapo commercial practice, you will want to put a small coupled choke between the rectifiers and the output capacitors to reduce the peak current in the rectifiers and switches. Your components will thank you, and your amp won't be bombarded with as much electromagnetic crap. The yellow/white powdered iron toroids will come in handy for this. The yellow/white signifies Micrometals type 26 powdered iron. You can find the specs for this stuff at micrometals.com.
Go ahead and try something fairly modest. You will want to make your mistakes with something small before you go for the gigawatt supply.
Contrary to standard cheapo commercial practice, you will want to put a small coupled choke between the rectifiers and the output capacitors to reduce the peak current in the rectifiers and switches. Your components will thank you, and your amp won't be bombarded with as much electromagnetic crap. The yellow/white powdered iron toroids will come in handy for this. The yellow/white signifies Micrometals type 26 powdered iron. You can find the specs for this stuff at micrometals.com.
Go ahead and try something fairly modest. You will want to make your mistakes with something small before you go for the gigawatt supply.
I was looking at, oh, say 400-500 watts. I know that this is getting into the range where a full bridge may be the best option, and I might just do that. I have been working on SMPS for a couple of months now, and feel fairly confident about everything but the actual transformer selection/turns thing.
So you're saying that 1500 gauss is a good number for B(optimal) in the F material, not the B(max)which is 4700 gauss, correct? With 1500 I get 3.4 turns at 35kHz with the F-193A-F(Ae=1.62cm) that I chose.(see initial post for core stats)now the Q is whether it will handle 40 amps or so
So you're saying that 1500 gauss is a good number for B(optimal) in the F material, not the B(max)which is 4700 gauss, correct? With 1500 I get 3.4 turns at 35kHz with the F-193A-F(Ae=1.62cm) that I chose.(see initial post for core stats)now the Q is whether it will handle 40 amps or so
First thing - always use integral turns with a transformer. Round up to 4 turns in your case. Are you really going to try to deliver 500W from a 12V source? That's switching 40A, which is not a trivial matter at all. If this is really your desire, you'd be better off going to a PQ or E-type core with foil windings. Wire certainly won't cut it. Snubbing leakage spikes will be a real problem as well.
tennisballq
I have tried building a fullbridge on a 12V input with bad results. The ON-resistance in 30V devices are not much better than 55V devices and if you connect two 30V devices in series the resistive losses become much higher than with two paralelled 55V devices in a push pull. Make some calculations before proceeding.
I have tried building a fullbridge on a 12V input with bad results. The ON-resistance in 30V devices are not much better than 55V devices and if you connect two 30V devices in series the resistive losses become much higher than with two paralelled 55V devices in a push pull. Make some calculations before proceeding.
This may be true, but if you are going for 40 amps primary current, you probably don't want to be dealing with a push-pull transformer with a foil primary. A full bridge at least has a single primary section. With any high power circuit of this sort, one will be dealing with paralleled devices. For a dissipation of 20W in the primary switches, you want 12.5 milliohms total resistance. Ths dissipation will be spread out between all the legs of the bridge, so it's not a lot of dissipation per device. 10 milliohm devices in a TO-220 package are pretty routine now, and not horribly expensive. Two paralleled switches will get you less than 10mohm total resistance, and three paralled devices will help to spread out the current to reduce the losses in the leads. You end up with 12 devices for a full bridge, which is not too bad considering the primary current.
I have set up the circuitboard for three devices parallelled for each transformer leg. I am using 75A, 55V mosfets with a 10m ohm typical resistance, 12m ohm max. It's printed for push pull, but I placed pads next to the transformer and mosfets so I could hardwire them with thick gauge, ad can wire it differently if I want.
Is it really not possible to wind my transformer traditionally? I have only seen a few high power(300-450W) commercial car amps opened up, but I didn't notice anything special or different about the toroid windings. I have also seen a few DIY designs claiming 350 Watts + by using wire strands to wind a toroid of about this size. Given, not everyone who publishes a design knows what they're doing, that's why I am asking. What advantage does the foil have over using several strands in parallel, flattened against the toroid?
Is it really not possible to wind my transformer traditionally? I have only seen a few high power(300-450W) commercial car amps opened up, but I didn't notice anything special or different about the toroid windings. I have also seen a few DIY designs claiming 350 Watts + by using wire strands to wind a toroid of about this size. Given, not everyone who publishes a design knows what they're doing, that's why I am asking. What advantage does the foil have over using several strands in parallel, flattened against the toroid?
Using full bridges at so low voltages has no benefits, it only increases costs, complexity and board/heatsink space required by the PSU
Car-audio manufacturers know this fact very well and never use full bridges on their amplifiers, just push-pull circuits. Biggest amplifiers tend to use two or more transformers
I've been repairing car-audio amps for several years now, and to the date I still have never seen a 12V full bridge PSU
Obviously, at increasing voltages full bridges start to have lots of benefits while push-pull starts to have disadvantages
Car-audio manufacturers know this fact very well and never use full bridges on their amplifiers, just push-pull circuits. Biggest amplifiers tend to use two or more transformers
I've been repairing car-audio amps for several years now, and to the date I still have never seen a 12V full bridge PSU
Obviously, at increasing voltages full bridges start to have lots of benefits while push-pull starts to have disadvantages
I've seen EE or EI transformers only in some old car-audio amps manufactured 5 or more years ago
Nowadays is very hard to find a car-audio amp not using toroidal transformer(s)
In the past I also wanted to know if foil primaries were used, but the EE/EI transformers I had chance to look carrefully at showed no signs of foil usage, just multiple thick wires in paralell for the primaries and single thick wire for the secondaries
I think that this kind of toroidal transformers with bifilar windings and small turn counts are cheaper to manufacture [in China, etc..] than EE/EI transformers and are much easier to fit inside the cases of car-audio amps. They may also show lower leakage inductance due to small turn counts and ratios and allow for thicker wires, but in consumer car-audio cost is actually the most powerful reason to use one or other kind of transformer
In the other hand, PC PSUs [also made in China, etc..] allways use EE/EI transformers [with a 40 turns primary and four secondaries, I'm sure they are cheaper to manufacture and board mount than toroidal ones, plus they have to provide >3KV isolation hard to obtain with toroids]
Nowadays is very hard to find a car-audio amp not using toroidal transformer(s)
In the past I also wanted to know if foil primaries were used, but the EE/EI transformers I had chance to look carrefully at showed no signs of foil usage, just multiple thick wires in paralell for the primaries and single thick wire for the secondaries
I think that this kind of toroidal transformers with bifilar windings and small turn counts are cheaper to manufacture [in China, etc..] than EE/EI transformers and are much easier to fit inside the cases of car-audio amps. They may also show lower leakage inductance due to small turn counts and ratios and allow for thicker wires, but in consumer car-audio cost is actually the most powerful reason to use one or other kind of transformer
In the other hand, PC PSUs [also made in China, etc..] allways use EE/EI transformers [with a 40 turns primary and four secondaries, I'm sure they are cheaper to manufacture and board mount than toroidal ones, plus they have to provide >3KV isolation hard to obtain with toroids]
Car audio amp manufacturers lie freely (or cleverly hide information) about their actual continuous RMS power capability, just like most of the audio industry these days. If you really want to deliver 400 continuous watts to a load with a 12V input, you will need to switch a little over 40 amperes. There is no way you can get an assemblage of magnet wire to handle this sort of current efficiently. Foil windings are used routinely in high current SMPS outputs. Imagine a a high current SMPS transformer turned around so that you are driving the secondary instead of the primary, and you have a similar situation to what is being discussed here. Personally, I think trying to get 400W continuous power into a car system is pretty crazy. I would compromise by building a 100W supply with large reservoir caps on the output to handle transient peaks, and leave it at that.
There are a lot of crappy 2x35Wrms@4 ohm, 4x50Wrms@4ohm, etc... car audio amplifiers, but nowadais it's not so hard to see 2x200 to 2x300Wrms@4 ohm car audio amplifiers bridgeable to obtain 600 to 1000Wrms@4 ohms, and I had to repair them sometimes
They tend to use two toroidal transformers and 12 to 16 switching MOSFETs rated at 55 to 60V and 50 to 80A in TO-220 casing. Switching frequencies are in the order of 40Khz and topology is allways push-pull
In push-pull topologies dissipation is divided evenly between each half of the primary so only half the magnet wire cross-section is required to match the target wire temperature rise
In the toroid transformers used in car audio amps, all wires are exposed directly to air flow since there is only one layer of windings, so heat exchange is much better than in EE/EI transformers
Lets assume we have a 1000Wrms bridged amplifier. There would be a theoretical maximum of 2000W peak instantaneous consumption [167A@12V] and a theoretical maximum of about 1500W average power consumption [125Arms@12V], altough real world average power consumption tends to be less than 500W at maximum volume before clipping due the high crest factor nature of music signals [42A@12V average, let's say 60Arms@12V]
In the worst case, these 125Arms will be split between each transformer so we have 62.5A/unit. These 62.5A flow alternately between each primary and each set of MOSFETs so we have 44Arms in each primary and each set of 3-4 MOSFETs.
Each primary winding tends to have less than 30cm [1ft] lenght so if we use 4mm^2 of total cross section of magnet wire we will have a total dissipation of 2.5Watts for each primary, easy to handle for 30cm of multiple small magnet wires exposed to the air
The MOSFETs used tend to have about .012ohms Rds-on [let's say 0.018 ohms when hot] so total conduction losses are 11W for 3 device sets or 9W for 4 device sets, pretty easy to handle I think...
Another example is that in one of my prototypes I'm using just five 1mm diameter wires for each primary [35Khz] to supply 72A continuous with reasonable temperature rise in the wire [50Arms into 4mm^2 of cross section and not more than 30cm/1ft length, 3W for each primary]
I've even tried 125A DC flowing through some meters of 6mm^2 wire and nothing burns, nothing explodes, the wire just raises its temperature to about 60ºC
No doubt that foil indings increase performance, but they are not required at all in order to make something cheap and working reliably
Never say 'it's not possible' just because you never have seen it working
They tend to use two toroidal transformers and 12 to 16 switching MOSFETs rated at 55 to 60V and 50 to 80A in TO-220 casing. Switching frequencies are in the order of 40Khz and topology is allways push-pull
In push-pull topologies dissipation is divided evenly between each half of the primary so only half the magnet wire cross-section is required to match the target wire temperature rise
In the toroid transformers used in car audio amps, all wires are exposed directly to air flow since there is only one layer of windings, so heat exchange is much better than in EE/EI transformers
Lets assume we have a 1000Wrms bridged amplifier. There would be a theoretical maximum of 2000W peak instantaneous consumption [167A@12V] and a theoretical maximum of about 1500W average power consumption [125Arms@12V], altough real world average power consumption tends to be less than 500W at maximum volume before clipping due the high crest factor nature of music signals [42A@12V average, let's say 60Arms@12V]
In the worst case, these 125Arms will be split between each transformer so we have 62.5A/unit. These 62.5A flow alternately between each primary and each set of MOSFETs so we have 44Arms in each primary and each set of 3-4 MOSFETs.
Each primary winding tends to have less than 30cm [1ft] lenght so if we use 4mm^2 of total cross section of magnet wire we will have a total dissipation of 2.5Watts for each primary, easy to handle for 30cm of multiple small magnet wires exposed to the air
The MOSFETs used tend to have about .012ohms Rds-on [let's say 0.018 ohms when hot] so total conduction losses are 11W for 3 device sets or 9W for 4 device sets, pretty easy to handle I think...
Another example is that in one of my prototypes I'm using just five 1mm diameter wires for each primary [35Khz] to supply 72A continuous with reasonable temperature rise in the wire [50Arms into 4mm^2 of cross section and not more than 30cm/1ft length, 3W for each primary]
I've even tried 125A DC flowing through some meters of 6mm^2 wire and nothing burns, nothing explodes, the wire just raises its temperature to about 60ºC
No doubt that foil indings increase performance, but they are not required at all in order to make something cheap and working reliably
Never say 'it's not possible' just because you never have seen it working
Well, it's intended to be an all purpose design, 160Wx2@4 ohms or 450W bridged @4. So really all I need the high power for is in case I decide to use it for a sub, in which case the power IS needed. I think I would be crazy to run mids and highs off of 400W too, though.
I also am aware of all the crap out there, however. One of my college professors explained it by saying that the manufacturers supply you with amps that may be capable of their rating, but then don't tell you about the power supply. So you might actually get a 300W capable amp, it's just being powered by +/-18V. Who knows.
I also have seen a lot of crappy advertizing. There was an Alpine 4 channel that I saw once in a large electronics store that was being advertized as 4x50RMS...@2 ohm. Garbage...even though Alpine does make some good stuff, just bad advertizing on the store's part.
So Eva, judging from your experiments, do you think I am good with 6-.8mm (20ga) wires for my primary(4 turns, ct, 4 turns)? Or should I add a few more? By the way...no color code this time, I coated this one myself with insulative varnish (the toroid). Better than a bare ferrite.
I also am aware of all the crap out there, however. One of my college professors explained it by saying that the manufacturers supply you with amps that may be capable of their rating, but then don't tell you about the power supply. So you might actually get a 300W capable amp, it's just being powered by +/-18V. Who knows.
I also have seen a lot of crappy advertizing. There was an Alpine 4 channel that I saw once in a large electronics store that was being advertized as 4x50RMS...@2 ohm. Garbage...even though Alpine does make some good stuff, just bad advertizing on the store's part.
So Eva, judging from your experiments, do you think I am good with 6-.8mm (20ga) wires for my primary(4 turns, ct, 4 turns)? Or should I add a few more? By the way...no color code this time, I coated this one myself with insulative varnish (the toroid). Better than a bare ferrite.
An externally hosted image should be here but it was not working when we last tested it.
tennisballg :
Assuming 3mm^2 cross section, 20cm winding lenght and 35Arms per winding you get 1.1mOhm and 1.4W per primary so you may even use less primary wires if this allows you to fit the secondary better
Try also to reduce Rds-on of the switching MOSFETs by using two groups of 3 or 4 devices in paralell, this will ensure low losses and low voltage drop on the power supply [heatsink requirements will be small]
Also, if the output voltage allows for it, use schottky diodes to reduce even more heatsink requirements
lumanauw :
Yes, I'm female but I'm not directly involved in car-audio, I actually dislike car-audio world and hate some of its people. [Also, I have no car neither a driving license]
It just happened that some years ago I found myself having some friends involved in car audio sales, enough electronics knowledge and a serious lack of money, so I figured out a way to make profit by repairing car-audio equipment
I have no EE studies, just 'computer science' half finished but somewhat forgotten. Anyway, internet and experimentation are great sources of knowledge [if you don't know how something works, try to measure it...]
Assuming 3mm^2 cross section, 20cm winding lenght and 35Arms per winding you get 1.1mOhm and 1.4W per primary so you may even use less primary wires if this allows you to fit the secondary better
Try also to reduce Rds-on of the switching MOSFETs by using two groups of 3 or 4 devices in paralell, this will ensure low losses and low voltage drop on the power supply [heatsink requirements will be small]
Also, if the output voltage allows for it, use schottky diodes to reduce even more heatsink requirements
lumanauw :
Yes, I'm female but I'm not directly involved in car-audio, I actually dislike car-audio world and hate some of its people. [Also, I have no car neither a driving license]
It just happened that some years ago I found myself having some friends involved in car audio sales, enough electronics knowledge and a serious lack of money, so I figured out a way to make profit by repairing car-audio equipment
I have no EE studies, just 'computer science' half finished but somewhat forgotten. Anyway, internet and experimentation are great sources of knowledge [if you don't know how something works, try to measure it...]
I think there may be some females posting here from time to time, look at this thread for example : http://www.diyaudio.com/forums/showthread.php?s=&threadid=28932&highlight=
Of course, I think It's a bad idea to go saying 'I'm female' all the time in such a sexist world and I hate those 'I have never seen a female here' comments. Sometimes I think I would have done better picking an ambiguous nickname or even a male one
So please, forget about my gender, I feel much more enjoyable talking about electronics only
Anyway, electrons doesn't have such a thing as gender
Of course, I think It's a bad idea to go saying 'I'm female' all the time in such a sexist world and I hate those 'I have never seen a female here' comments. Sometimes I think I would have done better picking an ambiguous nickname or even a male one
So please, forget about my gender, I feel much more enjoyable talking about electronics only
Anyway, electrons doesn't have such a thing as gender
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