# Need 5VDC 100mA to 12VDC 1A converter - Page 2

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Re: Need 5VDC 100mA to 12VDC 1A converter

quite
crossed

Is it possible to use a (hobby) R/C servo that pulls the lock?

--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)

Re: Need 5VDC 100mA to 12VDC 1A converter

No, I wish I could. Its a new board in an old product.

What I think would be really cool, and inexpensive, is a nitinol solenoid.

Mike

Re: Need 5VDC 100mA to 12VDC 1A converter

You realize that in common with most other solenoid-y type devices,
the current required to pull it open is much greater than the current
required to HOLD it open? You might only need 1A for a few dozen
milliseconds, then 100mA to hold it.

Re: Need 5VDC 100mA to 12VDC 1A converter

Can you document that? I've been poking around for solenoid data sheets all
morning. I also have a call into the manufacturer.

Re: Need 5VDC 100mA to 12VDC 1A converter

He speaks the truth, though I have no documentation
for you.  I fiddled around with solenoids more than
I'd care to admit, and the real trick is to get the
slug moving fast.  After that, it's all downhill,
current-wise.

Re: Need 5VDC 100mA to 12VDC 1A converter

The relay can withstand 24V for 9S. I think Vhold of 6v is still reasonable.
So there are two calculations:

1) Initial opening of the relay. Click -- can't take more than 100mS. Allow
for a DeltaV of 9V, calculates out to 9200uF

2) From there, a hold current of 150mA (on the safe side), 9V swing, hold
the lock open for 9 seconds.... gee, only 150,000uF.

What I can do is make the user wait before I open the hatch. The computer
will say, "OK, Open the hatch Cap'n", then there will be a few second pause
so that they can get their hand into place. Then I can engaged the solenoid.

I've calculated about as much as I can calculate here. Its time to hit the
bench and do some experimentation. I've been thinking ahead on this problem
so its going to take me a few days to get to the circuit. I'll post back.

By the way, re. the battery idea, I like it a lot. I can't go with it,
though, for a couple reasons. First, those little batteries with their
charging circuits appear to be quite a bit more expensive than caps. Also,
this thing is expected to last for years and battery changes really aren't
acceptable.

Mike

Re: Need 5VDC 100mA to 12VDC 1A converter

Maybe I just have crappy solenoids & should be using something else. My test
units pull 400mA after they've been energized.

I didn't create a big setup for measuring the initial surge. I imagine its
up there.

Given the need for a wall wart, based on my findings, I will probably end up
doing some redesign. But the current inventory needs to go first.

Any recommendations re. solenoids? My requirements are rather loose. Maybe
1/2 pound of force at 10mm. A 5V solenoid with a < 100mA hold current would
be great -- I could charge up a cap for the initial surge.

Re: Need 5VDC 100mA to 12VDC 1A converter

Hmm... let's see

1/2 pound * g * 10 mm = .250 kg * 10 m/s^2 * 0.01 m
= 0.025 Joule
=~ 0.021 A * 12 V * 1 s
= 0.1 A * 5 V * 0.25 s

[Note: your 'pound' may mean something different than I
assumed... non-imperial background here. ;-)]

So, at least in terms of pulse energy needed to *move* the pin, that
job shouldn't take the amount of energy discussed in here so far to
pull open.  Not by a factor of 50 or so.

Hold current would be a different issue, of course --- that will be
governed by wire resistance, not by mechanical considerations.

So yes, a better solenoid may still get you rid of this problem.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Need 5VDC 100mA to 12VDC 1A converter

It may be just how you worded it, but that isn't quite what you need to look
at.

Connect one of your solenoids to a variable PSU set to 12V, connect up a
current meter if the PSU doesn't measure current. Then crank the voltage
down and see how low you can get the current before the solenoid drops out.

--
Burn the land and boil the sea,
You can't take the sky from me.

Re: Need 5VDC 100mA to 12VDC 1A converter

It drops out, physically, around 330ma, ~5V, but that is below the point of
reliability. 6V, 400mA is the min.

Re: Need 5VDC 100mA to 12VDC 1A converter

Measure that with the solenoid doing its normal job.  Then at
least double the result for design purposes to ensure a reasonable
margin.

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
Available for consulting/temporary embedded and systems.
We've slightly trimmed the long signature. Click to see the full one.
Re: Need 5VDC 100mA to 12VDC 1A converter

Also make sure that the nominal solenoid current and voltages are
available at least for a few hundred milliseconds or for the worst
case mechanical travel time for the lock components. At cold
temperatures, the friction can be quite high and thus, decreasing the
acceleration and thus increasing the mechanical travel time.

The full magnetic flux should be available until the mechanism reaches
the stop. If the flux starts to fall before the stop is reached, it
might never reach the stop. If the lock is in some intermediate state
when people try to open the door, sooner or later some components of
the lock will be damaged.

If the system has been hacked to barely work in warm condition with a
well lubricated lock, in cold conditions or when the lock is dirty, it
may fail miserably.

Paul

Re: Need 5VDC 100mA to 12VDC 1A converter

All good points.

One concern of mine is that I am depending on gravity to close the lock
rather than a spring. Should things corrode, or get cold, that could be a
problem.

Holy Moses! coming up with a good latch design is difficult work!

Re: Need 5VDC 100mA to 12VDC 1A converter

Maybe you should consider a motor drive instead, as in hotel card key locks.

Re: Need 5VDC 100mA to 12VDC 1A converter

Ever been inside of one of those? Do they run on batteries or is there a
line goin' to 'em? I don't travel much, but I think the one's I've seen are
controlled by a central computer.

RS-422 + power perhaps?

I'd be curious to know what those motors use in terms of power.

Re: Need 5VDC 100mA to 12VDC 1A converter

From what I understand, these devices use a simple controller and a
battery pack. They don't use a lot of energy to do their job. The
locks just move a tumbler out of the way enough to allow you to open
the door. All the real work is done by the patron moving the door
handle.
The locks I have heard have a method where they don't actually tell
the door what the code is from central computer via wire. The locks
have a method that stores the current code and the next code for a
door. When they hand you a card key, it has your code number and the
"next" code number in it. When you insert your card, your current key
number should be the next one stored from the last customer, which it
moves to the current slot, it then stores the new "next" code from the
your card into its memory. The last "current" user got thrown in the
bitbucket , which is why the old card will now no longer work.
The computer then only has to give the next person a card with the
"next " number after you, and another new next number. Then your
card's "current" number gets thrown away, and you are locked out.
It just rotates through a codes.
The computer downstairs just has to handle the "current"/"next"
database.
If the batteries die in the lock, then they just start the system over
with a manager card I guess.

Not that this save you much but, you may want to look into latching
type solenoids. These will hold the solenoid down with permanant
magnets once you get the thing pulled in all the way, that way you
don't have to waste energy on holding the solenoid open. The control
of these can get more complicated, I had a nice one with two pairs of
coils, one to close, one to open and I could energize either with a
darlington transitor.
The problem with these in your scenario, of course, would be a failure
in open mode when the power fails. You need power to close them.

T.

Re: Need 5VDC 100mA to 12VDC 1A converter

This isn't universal. I've used video checkout in my room, and it has
warned me that after completing the process my key will no longer
work. I've tested it. It's true.

Re: Need 5VDC 100mA to 12VDC 1A converter
snipped-for-privacy@larwe.com (Lewin A.R.W. Edwards) wrote in message

True, as with most things in the world, you have your top of the line
BMWs and your low end Cheverolets.
The style of system I am describing is probably one of the "older"
electronic card versions out there. Generally used where you leave the
"key" on the nightstand on the way out the door.
T.

Re: Need 5VDC 100mA to 12VDC 1A converter

The "older" systems, huh? Nothin' like a little poke in the side to go with
breakfast ;-) As far as I'm concerned, electronic locks are new.

I like the tumbler/handle concept. I can't put it in this product because it
sounds like a lot of new drawings and re-tooling, but I'm going to poke
around with that when I get some time on the bench.

The lastcode/nextcode concept is interesting. It keeps you from having to
run all that wiring.

I remember once when I was on a business trip up north in San Francisco. I
was sitting on my bed going through some documents and all the sudden two
women unlocked my door with their cards and walked into the room! I know
this sounds like the beginning of a Penthouse Forum story, however, they
just wanted to know why I was in their room. I called the front desk, etc.
IIRC, they fixed the problem with the keys at the front desk before they
came out to the room.

Oh well.

This was, maybe, ten years ago. By the time the manager came, all the codes
had been re-programmed in the computer.

Mike

Re: Need 5VDC 100mA to 12VDC 1A converter
On my other suggestion, did you look at possibly using Latching solenoids?