Re: Need 5VDC 100mA to 12VDC 1A converter
From: dwight elvey (dkelvey_at_hotmail.com)
Date: 09/22/04
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Date: 21 Sep 2004 18:45:52 -0700
Hi Mike
I think you are missing one thing. It only takes
the 12V to actuate the solenoid. The voltage and
current can be quit a bit less to actually hold
it open once it is actuated. Look at setting up,
for experimenting, a large cap with a series resistor
to something like 20VDC. Place a 1 amp diode in series with
a low voltage supply that you'll use to hold the coil.
Experiment with different holding and charging voltages.
You may find that it is not all that impractical after
all.
Dwight
"Mike Turco" <miketurco@yahoo-nospam4me.com> wrote in message news:<%O93d.306920$sh.4430@fed1read06>...
> "Mike Turco" <miketurco@yahoo-nospam4me.com> wrote in message
> news:_jp1d.265316$sh.133675@fed1read06...
> >I have (almost) 100ma available in a circuit. I want to drive a 12V, 1A
> >solenoid that opens a lock. I'm thinking about using a DC/DC converter and
> >charging up an electrolytic cap. I'm just guessing here, because I haven't
> >done any such calculation for a long time, but it seems like I'd need quite
> >a cap to store enough energy.
> >
> > There are obviously some unanswered questions here, such as how long the
> > relay needs to be open, etc., which needs to be studied once I have a
> > working circuit. Also, swapping out the solenoid isn't an option.
> >
> > I'd appreciate any links to a cheap/simple DC/DC. Also, if anybody's
> > crossed this bridge before, I'm curious as to how you handled it.
> >
> > Thanks!
> >
> > Mike
> >
>
> Sorry for the late response. I took a few days off of work for the Jewish
> New Year. Happy New Year everyone. May everything you design, program and/or
> build work the first time.
>
> I've rec'd parts and have done some experimentation. The solenoid draws
> 800mA at 12V, 400mA at 6V, and doesn't work reliably at less than 6V. (That
> seems like a hell of a lot of current for a small, weak solenoid. Whatever.)
>
> No matter how you slice it, that solenoid requires 400mA to run, or damn
> close to it. Within the constraints of this project, using a cap simply
> won't work. Keeping the solenoid open long enough for somebody to open the
> door requires too big of a capacitor, and the recharge time of the cap is
> too long.
>
> For various reasons, I do not want to put batteries in the product.
>
> Hobby motors also draw a lot of current.
>
> Therefore, I am stuck with a wall wart. I'm not very happy about that, but
> there's no choice.
>
> In one post, somebody asked whether, in power failure, doors were left
> locked or unlocked. The answer is locked, but they can still be opened with
> a key.
>
> Thanks, everyone, for all your feedback.
>
> Mike
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