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Old 17th Aug 2017, 10:16 pm   #41
emeritus
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Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
Default Re: How much ripple on DC mains?

I had always wondered about this: the catalogue does have a more detailed entry for an electric dentist's drill, but no mention of an electric mallet.

Your question prompted me to make an on-line search for "electric dental mallet" , which produced this page amongst others: scroll down to the last item, described as "A tiny electrically-driven jack-hammer helps dentists to pack amalgam fillings"..

http://www.uh.edu/engines/epi2299.htm

More detailed info here:

http://www.buzzworthytattoo.com/tatt...ric-tattooing/

Scroll down to "dental pluggers".
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Last edited by emeritus; 17th Aug 2017 at 10:40 pm.
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Old 18th Aug 2017, 9:17 pm   #42
dseymo1
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Join Date: Dec 2007
Location: Shropshire, UK.
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Default Re: How much ripple on DC mains?

Ah - thanks, that makes sense!
I must admit that I only noticed the 'dental' bit after posting.
I'm not sure that I'd be happy to have an electrcally-powered device in my mouth, particularly with the potential of back-EMF from those coils.
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Old 27th Aug 2017, 9:00 pm   #43
Bookman
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Default Re: How much ripple on DC mains?

This thread took me back to my old school days but in different ways. I thought to myself that DC transmission was either 2 wire or three wire and was always undertaken using compound wound motors; see https://electricalstudy.sarutech.com...ors/index.html

I remember the interest it had until those dreaded words "armature reaction" appeared. Whenever there were academic or similarly otherwise questions that could not be answered the reason given was always "armature reaction". What a stinker it was when you thought you were getting somewhere only to be confronted with those two dreaded words.
I would therefore proffer that given the ability to provide a mix of differing poles to offset any transients or otherwise not allowed for in any initial machine designs that system errors most probably caused by unknown armature reaction could be reviewed and over come.
Commutator syntax when used with DC machines should consider their use more as a rotating rectifier; nor is it specific to just a motor of generator. Similarly, there were AC motors that employed commutators such as the highly complex Schrage motor.

One needs also to bear in mind large complexes that would have their own DC supplies which back in the day would have employed Mercury Arc rectifiers which I note is discussed as a separate thread. These then gave way to high powered selenium rectifiers.
The mercury arc rectifiers that were located at BSC (Samuel Foxes) Stocksbridge were approximately 6 foot high and about 4 foot wide. They were connected as quadruple star (12 cathodes) and one large Anode. These were then paralleled to outgoing busbars. I remember that they were rated 500V but cannot remember the ampere rating but it would have been in the thousands.
There is therefore a major observation for consideration. If someone asks you if a DC motor can be used as a generator and vice versa you may wish to respond by saying" Well, I may need to check the armature reaction characteristics of the intended machine in relation to the intended load characteristics" and leave it at that.
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