not sure,but it could be around 1-1.5A i guess.

i was browsing around for some data abt this issue.and came across this article from silicon chip.
http://www.siliconchip.com.au/cms/A_103140/article.html
look at the last post.
i wonder is it really possible.say if my application draw 2AMPS then if i use a 12-0-12 2A transformer,it will solve my problem.
what do u guys think abt it.

 

Should work fine, just make sure you have the secondary of the transformer polarity connected so it bucks instead of booting the line voltage.

__________________
The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

of course i'll connect the output supply to the coil once i confirm the voltage.
(i have plenty of voltmeters,ready to spoil ;-))

but still iam little bit confused.
say if i connect the supply to one end and take out put from other end,result will be reduced voltage
and if i connect the input to center tap and take output from (any?) end,the result will be higher voltage.

so choosing the input line(end or center tap) decided whether to drop or increse the output?

 

AC line voltage has amplitude, and it has phase. From the center tap to one end of the secondary, the voltage will be in phase with the line voltage, and from the center tap to the other end, it will be out of phase. If you use one half of the secondary, you can either add 12V to or subtract 12V from the line voltage. If you use the entire secondary, you can either add or subtract 24V. You can't easily measure the phase of the output relative to the line, so you have to use trial and error to determine which connection increases the voltage and which decreases it.

__________________
Ron

 

This has turned into two threads, but I just want to check on something for the original question for a moment because I now have solenoid specifications (I think).

The coil is 12VDC, 28 ohms, 430mA (at 70F).
This works out to be about 5.2 watts.

I would like to use 24VDC.
I am thinking of using a 27 ohm series resistor.
A 30 ohm resistor is the other available choice, but there is a long cable distance so I opted to go with the lower value.
Any one solenoid would fire at the most for about 3 or 4 seconds twice per minute with the maxium ambient temperature in the enclosure of 150F. Would a 5 watt resistor work or do I need something larger?

There will also be a 1 amp series diode (to 'OR' the outputs of two different systems together) as well as a reverse protection diode to the common (also 1 amp to make them all the same).

Does all this seem correct?

Thanks,
Dale

 

A 5 watt resistor would be safe. You could probably go smaller. It would be easy for you to test on the bench, with a power supply, your resistor, a couple of clip leads, and your finger for a thermometer.

__________________
Ron

 

Ron,
5 watts is small enough for construction. I just wanted to make sure I didn't need something larger.

Do you think I could I put heat-shrink tubing (135C max working temperature) over the resistor or would it provide too much insulation for heat to dissipate?
Thanks,
Dale

 

thanks for the explanation audio guru.i got the solution.

@DSGarcia
as the resistor is the main part here.i think its better to place it in a small AL make enclosure(say 1.5*1.5*3inch lngth).this will protect the resistor and works as heat sink.

 

One caveat - if there is any possibility that the solenoid drive will get stuck ON, you need to consider that - although I your solenoid may also not be rated for continuous duty.

__________________
Ron

 

Steev, Thanks for the suggestion, but the heat shrink was to protect them electrically inside a junction box. I was going to bend one lead on each of the 12 resistors down along side the resistor to make it a radial part and have one long Euro-style terminal strip, but I decided to mount them axially going from one terminal strip to another so now the heat shrink would only be on the leads.

Ron, Good point. I will have a watchdog on the outputs so they will be shut off automatically if the I/O block looses communication with the controller.

Thanks,
Dale