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I need a 7v 1.2A DC power source Answered

I have a Brother label maker that i requires 6 1.5v AAA batteries. I don't want to fill it full of batteries but instead use a DC power supply. It requires 7V 1.2A DC, and I'm not sure how to get this. I have a variable power DC supply and some wallwarts but none of them fit the specs. I tried hooking up 7V from my power supply but no dice. How do i make sure it gets 1.2A? Anyone have some knowledge they'd like to pass on? Thanks

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ry25920 (author)2008-02-11

wall mart bricks? transformers?

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guyfrom7up (author)ry259202008-02-11

7 volts is a wierd voltage for walwarts.

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guyfrom7up (author)Korey2008-02-12

It also has a plug for a walwasrt, but I can't see from the datasheet what voltage the walwart has to be

wait... 6 x 1.5 = 9 volts not 7 volts, where did you get 7 volts from?

the walwart is probably a 9 volt.

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Korey (author)guyfrom7up2008-02-12

It says 7v right on the spec sheet..That is weird, must be a typo!

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trialex (author)Korey2008-02-12

Nup - 7V is probably exactly what it needs. It needs 6 x AA batteries because AA batteries will sag in voltage over time - so if you only used 5, it would be OK when they were fresh, but if they drop to 1.25V, the gadget would stop working. Look around for a "multi" voltage power pack - they ofen have a 7.5V option. This would propbably be fine for your application - the gadget probably has a small regulator in it.You will need to find the right size plug of course, and make sure you get the polarity right - most balled plugs are tip positive, but check to make sure.

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littlechef37 (author)2008-02-12

Go to Dollar store, Dollarama, Buck or two........ And buy a thirty pack of of AAA's ....Buy two..... Or you could phone wherever you got it from they might have adapters there. Or look it up on the internet......Build an adjustable power supply..... And someone said something about 6x1.5 not adding up two 9 volts.. I am not totally sure about it but I would guess that some of the components would reduce the voltage and give some more amps. I have seen this in many devices. (someone correct me if I am wrong)

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guyfrom7up (author)2008-02-10

make one from a radioshack transformer and a regulator.
maybe this:
http://www.radioshack.com/product/index.jsp?productId=2102700&cp=2032058.2032230.2032277&allCount=24&fbn=Type%2FTransformers&f=PAD%2FProduct+Type%2FTransformers&fbc=1&parentPage=family
and hook up a lm317 regulator? It can handle up to 1.5 amps, but you may have to heat sink it.

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VIRON (author)guyfrom7up2008-02-11

Agreed the LM317 is what to use, but power it with a 12V DC wallwart that can handle 1.5A or more. The basic LM317 circuit has a pot that adjusts the voltage. If you don't have a heat sink then the regulator automatically lowers it's voltage to protect itself if it gets hot.

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Korey (author)VIRON2008-02-11

I have a 20VDC variable power supply, am I not able to just use it? I just don't know how to make sure it gets 1.2A. Maybe im not understanding something here

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tech-king (author)Korey2008-02-11

check the back of the charger. if its rated to at least 1.4 amps, go ahead and use it. otherwise, find another one.

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guyfrom7up (author)tech-king2008-02-11

yeah, do what tech-king says off topic: tech-king: where did you learn about electronics? self taught with books or did you take some course?

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matseng (author)guyfrom7up2008-02-12

I would take anything tech-king says with a grain of salt....

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tech-king (author)matseng2008-02-12

part of our be nice policy is to give

constructive

criticism. instead of saying my advice is bad/wrong and the clicking post, explain why its wrong. as a human, i can be wrong sometimes.

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guyfrom7up (author)tech-king2008-02-12

ok, just to clear confusion, the diode would emit heat. I just spent half an hour trying to get everything straight about zener diodes from various books and tech-king. For this application: 1) attach a resistor to the anode of the diode 2)attach the other side of the resistor to power in 3) attach the cathode to ground 4)attach the load between the resistor and diode for power and the other end to ground. 5) the max current takenj up by the device is determined by the resistor attached o the diode. 6) The wattage of the diode depends on the value of the resistor 7) The wattage of the resistor depends on it's resistance everyone clear now!?!

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Korey (author)guyfrom7up2008-02-12

Thankyou! Ill giver a try

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tech-king (author)guyfrom7up2008-02-12

sorta like this? and yeah, it does emit heat

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guyfrom7up (author)tech-king2008-02-12

exactly (no need for a vout though) do you just make those drawings for instructables or for a class or what?

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tech-king (author)guyfrom7up2008-02-12

its from a book. i showed you this image a long time ago.

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tech-king (author)guyfrom7up2008-02-12

mainly self taught. i have the greatest book on electronics at home.

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guyfrom7up (author)tech-king2008-02-12

my favorite electronic books is practical electronics for inventors

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NachoMahma (author)Korey2008-02-12

. The amp rating of the power supply is the max current it can put out. How much current is determined by the load. If you have a high resistance/impedance load, the current will be low; low resistance, high current (up to the capability of the supply).

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Goodhart (author)Korey2008-02-11

Maybe a quicky course on Volts, Amps, etc will help; Try reading this explanation....first.

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Korey (author)Goodhart2008-02-11

I already had one of those....===>2 years in electronics engineering at college, haha kind of embarassing!

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Goodhart (author)Korey2008-02-11
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Korey (author)Goodhart2008-02-11

Dont worry about it.. It's my fault for not knowing something that one would think is so simple. Brain fart i guess you could call it

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tech-king (author)2008-02-12

1) i deleted my previous comment because i doubted its validity 2) zener diodes probably do create heat, but i doubt is would be as much as a vreg 3) a lm317 would probably be fine for a label maker. however, devices like digital cameras and laptops may need a more precise regulation. 4)amperage should not be a problem 5) you will need to heat sink a vreg (lm317)

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matseng (author)2008-02-12

Say what? Will a zener not heat up? Where do you think that all the excess power gets dumped thru? Zeners are seldom used to handle loads of this magnitude. And a zener usualy have a tolerance of 5% or thereabouts. So they are just as imprecise as a standard fixed voltage regulator.

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tech-king (author)matseng2008-02-12

1) a zener diode gets no hotter than a wire placed across the power leads. the excess energy goes to the ground wire. and maybe your zener diodes are 5%. i have seen 1% at my supplier. 2)and depending on what type of Vreg you use, they can be very precise. an lm317 is not even a fixed regulator. 3) whatever heat a zener diode generates is minimal to the point of being insignificant. especially compared to a Vreg.

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gmoon (author)tech-king2008-02-12

You need to reexamine your assumptions on this one. Especially:

a zener diode gets no hotter than a wire placed across the power leads. the excess energy goes to the ground wire.

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tech-king (author)gmoon2008-02-12

however, i am sure a zener diode will be more precise than a lm317.

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tech-king (author)gmoon2008-02-12

i'm checking the figures and........ there is no mention of heat output in my book. so its quite possible a zener produces heat. i assumed that, seeing as it merely shunted power, it would not heat up too much. its definitely possible im wrong on this one.

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