Rectifier wiring

"Karl Townsend" skrev i en meddelelse news:4c2e0047$0$77568$ snipped-for-privacy@auth.newsreader.octanews.com...

*LOL*

That's a good one Karl :-)

If you don't get that mess cleaned up pronto, it IS a PITA.

Ever cleaned up a blown cap? Fluff and foil everywhere!

A neat use for bridge rectifiers is to put in battery powered devices so that the battery can go in either way .

Yes... if the device can tolerate a constant voltage drop of 1.2V (or greater).

Coincidentally, comp.robotics.misc has just been having a lively thread regarding these battery contacts that allow a battery to be inserted in either orientation, completely through the geometry of the contacts.

I was about to say something ironic/sarcastic, about how this has already been done with battery shape -- but was pleased to read that this system works with common existing cells. Great idea -- if it works.

"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.

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?

Karl

Yup. Each silicon diode gives 0.6V to 0.7V drop. Make sure the diode's current rating is sufficient.

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.

(...)

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

Actually, when I found out a major company had stolen my patented product and contacted them, I got a flat "so, sue us", followed by being hung up on. They have bigger lawyers than I, and they knew it going in. That was an expensive lesson.

Newb

Ouch!

--Winston

Exactly!

However, I can not shut off my inventor lobe, nor will they stop me from life in the prototype lane. I have concluded that the ticket is to get in and out of production (before being ripped off) to make enough to cover expenses and perhaps buy a few new tools ; )

The silver lining to this lesson is that if anyone ever accuses me of never having an original thought, I can prove otherwise.

Newb

(...)

That is a lot of hats to wear. One must be equally good evolving the idea, producing the product, publicizing it and handling the business end as well. The guy that can do all these things equally well is the guy that does them all equally poorly. :)

?The world in general doesn't know what to make of originality; it is startled out of its comfortable habits of thought, and its first reaction is one of anger.?

William Somerset Maugham

Hey, I *starred* in that play. :)

--Winston