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From: DoN. Nichols on 7 Jul 2010 00:41
On 2010-07-07, Karl Townsend <karltownsend.NOT(a)embarqmail.com> wrote:
>
> "DoN. Nichols" <dnichols(a)d-and-d.com> wrote in message
> news:slrni37h3q.4ds.dnichols(a)Katana.d-and-d.com...
>> On 2010-07-06, beecrofter <beecrofter(a)yahoo.com> wrote:
>>> A neat use for bridge rectifiers is to put in battery powered devices
>>> so that the battery can go in either way .
>>
>> Presuming that the device can accept the loss of two diode
>> forward drops from the battery to the load. (About 1.4V at reasonable
>> current levels and with silicon diodes.) Some things are close enough
>> to their minimum voltage threshold so this would not work well.
>>
>> If the battery and diode are followed by a regulator, you
>> probably are all right.
>>
>> Enjoy,
>> DoN.
>
> I'm curious. I use a 2:1 transformer, bridge rectifier and caps to power 80
> volt AMC drives. This comes out about 4 volts high but hasn't seemed to
> cause trouble. For a cheap volt drop could you just run the DC out through a
> couple more diodes on a bridge rectifier?

Yes -- but it might be cheaper to use individual diodes since
you would need several bridges to get 4V. Let's see -- somewhere
between 0.600 V and 0.700 V per diode, so 6.6 diode drops (3 + bridges)
and 5.7 diode drops (3 - bridges). I would put the extra diodes between
the output of the bridge and the first capacitor.

And that 4V high is pretty close to right on for 120 VAC input.
We start by dividing the 120 VAC by 2 for the transformer ratio, then
multiplying by the square root of 2 (1.414) and it comes out to 84.84 V
peak.

But any diode drop will soften the supply's stiffness somewhat,
because there is some variation in voltage drop with current. Not
nearly as much as with a resistor, but some.

Better is to add a small filament transformer in series with the
primary to adjust the voltage into the bridge to the right value. 80V /
1.414 requires 56.57 VAC into the bridge -- hmmm ... adjust for two
diode drops at 0.650 V per diode requires 57.87 VAC into the bridge, so
multiply by 2 for the transformer ratio and you get 115.75 VAC. If your
line voltage is really 120 VAC, you need to drop 4.24 VAC -- so a 6.3
VAC center tapped filament transformer would give you a choice of 3.15
VAC for half the winding, or 6.3 VAC for the full winding -- wired to
oppose the line voltage. The secondary of the filament transformer
needs to be rated to handle the worst case current into the main
transformer.

But really -- since line voltage varies with neighborhood load
-- or state wide load -- (and lots of air conditioning load where I am
today) you are as likely to get 115 VAC as 120 VAC -- and that would be
just about right for your transformer. Right now, a line voltage
monitor is telling me that I'm getting 115 VAC. It usually runs between
117 VAC and 120 VAC here.

So -- unless the drive says 80 V *MAX* -- don't sweat it. You
will be right on some of the time, and a bit high some of the time. But
your speed will be controlled by the output from the tach generator and
what the amplifier (drive) does with it, not the supply voltage, which
will simply set the limiting speed of the motor -- and it will almost
never actually run at that speed. Remember that the computer feeds an
analog voltage to the amplifier (drive) which tells it how fast to go,
and the amplifier compares that voltage to the voltage from the tach
generator to adjust what voltage goes to the motor's primary windings.
Your speed will be right as long as the amplifier (drive) does not break
down from the applied voltage. So -- look up what it can safely accept.
If it says that the absolute maximum voltage is 80 VDC -- then you want
to either lower the voltage a bit so at 120 VAC you will have no more
than 80V DC, or set up a regulator as part of the power supply to make
sure that the output voltage is never anything but 80 VDC. (This
requires the transformer to produce a bit more voltage so the regulator
can toss some away in the process of regulating -- say perhaps 100 VDC
before the regulator.

I hope that I haven't told you too much. :-)

Good Luck,
DoN.

--
Email: <dnichols(a)d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
From: Winston on 7 Jul 2010 01:50
On 7/6/2010 10:26 AM, William Sommerwerck wrote:

(...)

> "Giving away" inventions is not necessarily a good thing. The patent system
> actually encourages invention by increasing the likelihood an inventor will
> profit from his ideas.

I'm sorry to inform you that you are in violation of
my rights to those thoughts.

My lawyer discovered that any practitioner in the
field *could* have easily originated those thoughts
before you did; they are insufficiently
novel.

Additionally, with further work, I believe
we will be able to uncover historical instances
of each of those thoughts occurring as 'prior art'.

You are to cease expression of those thoughts or any
thought that could be considered derivative of them.

Either of those thoughts are now available for license
from me for a single - use fee of US $5.00.



See how this really works? :)

--Winston

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