I have an application where I am using AC 110V timers and 24V DC motors.
I am using a power supply that converts 110VAC to 24VDC
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Overall I need a way to protect the 24VDC motors (this is "protected" by overvoltage and overcurrent by the power supply) AND the 110VAC timers. I can use 24VDC timers but then I the price goes way up.
What type of circuit/power supply, or anything can I use to protect both 24VDC and 110VAC elements?
Honestly, I am not using fuses either. I wonder if by using a fuse I can protect everything, except these are remote systems so I would have to travel to change the fuse...
overvoltage and overcurrent by the power supply) AND the 110VAC timers. I c an use 24VDC timers but then I the price goes way up.
24VDC and 110VAC elements?
protect everything, except these are remote systems so I would have to trav el to change the fuse...
One way of protecting 24V input from 110V AC is to put a resistor on series with any input to the 24V side that can see 110V AC, and clamp the 24V sid e of the resistor to the 0V and 24V with diodes. If the hot side of the inp ut goes above 24V, current flows through the diode into the 24V rail, clamp ing the input to 24.6V (which is usually okay) and it fit goes below 0V cur rent flows through the other diode from the 0V clamping the input at -0.7V.
You then have to chose a resistor which won't burn out when it is carrying the clamping current.
We used to use loads of 0.7W Phillips axial lead resistors for all sorts o f jobs.
Power dissipated in the resistor is V^2/R. At 110V, V^2 is 12,100, so an 18 k 0.7W resistor will survive continuous exposure to a 110V AC fault current (which is limited to 8.6mA so the cheapest little diode with a reverse rat ing of 25V can be used for the clamping).
In the UK we were more worried about 240V AC and used 100k 0.7W resistors f or the same job.
Simplest is to uses fuses, or if its remote use polyfuses aka thermistors, which self reset when powered down. You might also add a crowbar to the 24v line. But as said, its not clear where your overvoltage would come from.
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I love to cook with wine. Sometimes I even put it in the food.
Did you ever stop and think that maybe the 24V supply may also operate from a 120VAC source at some point? Since this is all being used in a single application, wouldn't a basic fuse and MOV's on the entrance of the 120VAC be the proper action?
Hell, you can buy power entrance modules with fuse, CMF and MOV clamps built in.
I don't think you would do well in the design reviews of consumer products for cost verses reliability, in the design.
Out_Of_Touch_with_reality Bill SLugman does it again.
On Thursday, 2 October 2014 12:35:56 UTC+10, Maynard A. Philbrook Jr. wrot e:
oth 24VDC and 110VAC elements?
can protect everything, except these are remote systems so I would have to travel to change the fuse...
ries with any input to the 24V side that can see 110V AC, and clamp the 24V side of the resistor to the 0V and 24V with diodes. If the hot side of the input goes above 24V, current flows through the diode into the 24V rail, c lamping the input to 24.6V (which is usually okay) and it fit goes below 0V current flows through the other diode from the 0V clamping the input at -0 .7V.
ing the clamping current.
ts of jobs.
n 18k 0.7W resistor will survive continuous exposure to a 110V AC fault cur rent (which is limited to 8.6mA so the cheapest little diode with a reverse rating of 25V can be used for the clamping).
rs for the same job.
So Jamie doesn't understand it. No surprises there.
What's that got to do with anything?
The OP didn't want to use fuses, because he'd have to go out to remote loca tions and change them.
But that was a solution that the OP had explicitly rejected.
The OP didn't seem to be describing a consumer product. I've not worked on "consumer products". The closest I ever got to that was a proposed replacem ent for the telex/TWX machine - Teletex - which actually worked in Germany and Sweden for a few years, before getting washed away by e-mail. For that product we had circuit protection specialists.
The 100k resistor plus clamping diodes is what was used - when we could get away with it - for industrial process control at Kent Instruments in Luton in the mid-1970's.
Clearly, I'm not in touch with your reality, for which I'm grateful.
Bill, I'm going to killfile Maynard A. Philpot (the "Ham", KA1LPA) because every time I read one of his posts my IQ goes down a point or two. It's a good thing that I have some to spare.
I suggest you do the same. Protecting your IQ doesn't hurt.
I don't see it quite that way. When writing manuals and the like, re-reading what you've written with an eye to the ways in which a half-wit could misinterpret it is part of the job. Jamie provides a similar service.
Reading what he writes isn't exactly a pleasure, but it does provide access to the half-witted point of view. Krw is no less half-witted, but doesn't usually react to technical posts.
And you really think you can change that? You think you can educate him? I can't believe you believe that. I think you just want to bait him so that you can try to make him look foolish in your eyes.
This is a game for you, isn't it? Get a life, Bill.
No. I'm doing it to sharpen up my expectations of how the less clever membe rs of the population will react to specific information. If I could improve him, I would, but I don't go further than pointing out when he's talking n onsense, and I doubt if he takes my opinion all that seriously.
I don't need to bait him to have him post stuff that looks foolish in my ey es - he does that without any help from me.
It amuses me from time to time, but the winnings aren't generous.
Good idea. I've been working on it for a while now, without too much succes s.
Perhaps. I might improve it out of existence, rather than "handling" it.
"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man." George Bernard Shaw, Man and Superman (1903) "Maxims for Revolutionists"
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