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looking for help on 7-13 V AC to 12V DC fixed converter with 7 amp

looking for help on 7-13 V AC to 12V DC fixed converter with 7 amp

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  #1  
Old 08-03-15, 09:57 AM
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looking for help on 7-13 V AC to 12V DC fixed converter with 7 amp

We have a simple device to convert 1.25 to 20V AC into 2.5 to 27v DC , it is regulated and working with LT1083. and can take about 7Amp , now we would like to make this with next specifications , 1st as small as possible , 2nd , input AC 7 - 13V AC converting to 12V DC , no regulation , no filtering , but pure the AC input converting to 12V DC , In attachment the pictures and parts , we really need to down size this to about 40mm x 40mm max or even smaller. these are the components now ,
KF301-2P x2
10A10 rectifier diode x4
1N4007 diode x2
3MM LED Blue x1
4700UF/50V x1
470UF/50V x1
10UF/50V x1
5.1K resistor 0.25W x1
100 ohm resistor 2W x1
3296-10K variable resistor x1
7A resettable fuse x1
LT1083 regulator x1
Board size: 74mmx46mm;
Heasink w45mmxh50mmxt15mm

I really hope soms body can offer us a nice solution to have this device very small. Name:  31961.jpg
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  #2  
Old 08-03-15, 10:02 AM
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I won't presume to do your engineering for you but if you really want a DC supply with no filtering and no regulation then you can eliminate all those bulky components. All you need is a small diode bridge rectifier. Problem solved.
 
  #3  
Old 08-03-15, 10:32 AM
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hi guy , this we already tried with many rectifiers , the problem is that the AC input is 7 to max 12V AC constant changing in this range and when you rectify 12V half wave than we end up with about 7V DC and that is 5V to short..... this device cranck up the Voltage to a stable 12V DC ( but can be adjusted from 2.5 to 27V DC output and that we don't need ) a stable 12V DC is more than good. So we start from this device as it works real fine , but need to make it much smaller, it can't be any big problem for people who know a little bit of electronics to find a way to get this done. We are thinking npw to get the diodes soldered together with the capacitor over the + and - , and then make a tiny small pcb board where all the other smaller parts can put on , then put all in a small plastic casing and fill it with epoxy , only the LT1083 will stick out to fit the heatsink , and the screw to adjust the voltage as it now is.
 
  #4  
Old 08-03-15, 11:11 AM
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Hi wim,
You are very optimistic, but provide some more information and I will see what your limits are.

What is the source of your 7 to 13 VAC?
Is it from two wires from a transformer or three wires from a center tapped transformer?
What is the current capacity of that AC input?

If you have only 2 leads, no center tap, then you lose 2 diode drops going through a bridge rectifier, 2 x 0.7 volts is a 1.4v drop.

If you have a center tapped transformer you could use a full wave rectifier and lose only one diode drop.

What is your load, you mention 7 amps capability for the LT1083 but you don't say how much current you need?

Will that load be a constant load or will it vary from some low level to some high level?

For reference, if you attach a 12 VAC input to a bridge rectifier (with a filter capacitor) with only a tiny load you will get about 15.5 volts for an output, but as you draw more current that voltage will decrease. Without a regulator the output voltage will change as the load changes.

Peak output of a bridge rectifier is 1.414 x 12 VAC minus 2 diode drops.

There are many problems with what you are hoping to get out of this. With more information I can point some out.

Bud
 
  #5  
Old 08-03-15, 11:49 AM
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to bud

dear bud , you seem to know what you are talking about , can i have your e-mail so i can send you all the info about this. The power is coming from the ac regulator ( power the ac headlights ) of a scooter. We have tried many options but the last device we have is working very well , i would like to send you all our info and i think you can see what we are talking about , i am not very qualified in the technics about this all , but as so far i found a solution ( let say a half one , lol ) as it is to big.
My e-mail address is , [email addy deleted for safety]
best regards
wim
 

Last edited by ray2047; 08-03-15 at 12:56 PM. Reason: Remove email addy
  #6  
Old 08-03-15, 11:52 AM
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dear bud , you seem to know what you are talking about , can i have your e-mail so i can send you all the info about this. The power is coming from the ac regulator ( power the ac headlights ) of a scooter. We have tried many options but the last device we have is working very well , i would like to send you all our info and i think you can see what we are talking about , i am not very qualified in the technics about this all , but as so far i found a solution ( let say a half one , lol ) as it is to big.
My e-mail address is , [email addy deleted for safety]
best regards
wim
 

Last edited by ray2047; 08-03-15 at 12:57 PM. Reason: Remove email addy.
  #7  
Old 08-03-15, 12:04 PM
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hi bud , what i was forgotten to say , the load is constant 35 watt. we can also have a device working with 55 watt ( depends on the type ) and at 12V DC constant. The AC is regulated ( input of the device ) from 7 to 12V AC. we can take about 10Amps out of the AC wires coming from the regulator , as this is fit for about 120 watt of use.
 
  #8  
Old 08-03-15, 01:54 PM
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Sorry, the only help I can provide is whatever we can discuss here on the forum.
Let's see what we have so far.
35 watts at a constant 12 volts would be a 2.9 amp load.
55 watts at a constant 12 volts would be a 4.6 amp load.

But, without a regulator, you will not have a constant 12 volts. Your meter might read 12, but with just a capacitor the voltage will fall after every half cycle based upon the RC constant of the capacitor and load. This is referred to as 120 cycle ripple. Whether your design can tolerate this ripple or not I do not know.

But, the components selected for 35 watts to give you an effective 12 volts (not a pure 12 volts) will provide a lower voltage with a 55 watt load. And the variable resistor shown in your component list will not work without the regulator.

Your 4 - 10 amp diodes are available in one package called a bridge rectifier. As Guy48 said, you can use just a bridge rectifier and a capacitor, but it will not meet all of your variables and objectives. If this were going to be produced in the several hundred thousand quantities then you could have a custom chip designed which could include everything you have stated with a best possible size determined by the necessary capacitors and total heat requirements. But the cost is not within your grasp.

I've tried to illustrate that what you want is beyond your capability to even specify for someone else to design.

Bud
 
  #9  
Old 08-03-15, 09:04 PM
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we really need to down size this to about 40mm x 40mm max or even smaller.
You're putting this on a scooter ? Why does it need to be so small ?
 
  #10  
Old 08-03-15, 09:35 PM
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Hi PJmax , because the space on scooters is limited. and we need to install two of them on some models. And yes we are putting this on a scooter as it will be used for a whole different reason ( not hifi ) but can't say to much about this. For 2 years we have asked and send inquiries to al kind of manufacturers of regulators / rectifiers and untill now , no results , what we would like to realize is told us 1000 times , " this is not possible and will never be possible " and yepaaaaaa we have done it. it works , so now we need to downsize it so it can be used all over the world. Maybe a dream maybe hard reality , and with the help of some people who are well know in the field of electronics we can pull of this little thing.
 
  #11  
Old 08-03-15, 09:38 PM
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It would probably be more cost effective to modify the alternator on the scooter to be regulated.

These are gasoline powered scooters ?
 
  #12  
Old 08-03-15, 09:55 PM
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this was one of the options we have looked for , but as there are so many different models , and it takes a well educated person to modify the stator , this option was fast put on the side. Also the more recent scooters have injection system with cdi and with to much changing the initial made parts this can go wrong very fast. Also for warranty purpose it is impossible to go change the original parts of the scooters. Now the device as i show here , cost about 5 dollar , so the cost effectif ratio will be in the favor of the device, not the modifying of the stator.
 
  #13  
Old 08-04-15, 12:32 AM
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To reduce the size you will need to find most or all of your design on one chip. I googled "one chip power supplies with a few variables like low ac input and high current output and seemed to be getting close. Here is a link that about half way through they mention they can custom design to meet someones needs. Their R-78xx-0.5 switching regulator is listed up to one amp.

If you talk to people like this they will already know the limits and may already have a product available.
The Power Supply

Other chip manufacturers like National Semiconductor or Texas Instruments will have catalogs to look through.

A thought, since finding something already in production would be less expensive than developing your own integrated circuit, do some reading/searching for converting wind turbine ac power to a regulated 12v dc. There are many small turbines out there and people who want to store that power using 12v batteries, so maybe they already have something.

Otherwise search single chip ac to dc low voltage high current power supplies, in a variety of search combinations. Even though my company, years ago, could make their own integrated circuits the vast majority of our product needs were filled by other manufacturers. Why reinvent the wheel.

Bud
 
  #14  
Old 08-04-15, 01:13 AM
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Hi bud , as i say before we are now 2 years of searching a good solution , and all we hear is , this is not possible , but we have this device now who do the trick , only it is to big and have to much extra's as we not need that. I am not reinventing the wheel , i want to make it only smaller for the job , the wind turbine and solar depertement only come up with expensive and totally different way of getting the 12V DC , we are laready talking to some companies who are manufacturing rectiefiers regulators and maybe the light is going to shine over there.
 
  #15  
Old 08-04-15, 08:21 AM
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I'm not an engineer but from what's been revealed I would have to side with the companies you've contacted. If you desire a clean regulated DC output at several amps you will have to use a semiconductor to regulate. The heatsink size needed to dissipate the heat so the mounted device will survive is not a variable and is going to largely set your final size.

Now IF you had control of the product this is intended for and could MOUNT TO IT in order to take advantage of its surface area this could lead to a huge reduction in size.
 
  #16  
Old 08-10-15, 03:15 AM
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For the moment we are looking to find some one who can re arrange the layout , on both sides ofthe pcb board , so all fits in a much smaller place , maybe need to chage the 4 diodes into one bridge rectifier as the GBJ2510. We are sure with an other layout all can fit in a enclosure of 40 x 45mm. all help is welcome for making this solution , best regards
wim
 
  #17  
Old 08-10-15, 03:19 AM
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the schematics of the pcb board

The picture is the schematic of th pcb board with all its components
 
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