555 relay current reducer

bitrex · 2016-01-02T15:10:49+00:00

I haven't built or simulated this yet but it seems like it should work hmmm not sure... -- ----Android NewsGroup Reader----

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John Larkin 10 years ago

I said, literally "It will guarantee that most relays hold closed", which is certainly true.

No, it's not. I guarantee that most (ie, >50%) of relays will stay closed at 50% of rated coil current. Which means that, for a given relay, this circuit will very likely work.

I said "most" relays, not "all."

You're nitpicking to be a PITA. Any competant engineer will check the specs for the relay at hand and make sure this circuit will work. Most of the time, it will.

The catch diode forward drop must be considered, of course. And the actual duty cycle of the oscillator, which won't be exactly 50%.

John Larkin Highland Technology, Inc lunatic fringe electronics

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John Larkin 10 years ago

That snort is getting worse and worse. Have you seen a doctor yet?

John Larkin Highland Technology, Inc lunatic fringe electronics

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M Philbrook 10 years ago

I see a salesman on the rise! jamie

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krw 10 years ago

Or you can use feedback to guarantee pick/hold.

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M Philbrook 10 years ago

And then you have this!

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Jim Thompson 10 years ago

Yep. That's the way to do it. ...Jim Thompson

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

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John Larkin 10 years ago

1995! Was that before digital logic was discovered?

John Larkin Highland Technology, Inc lunatic fringe electronics

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bitrex 10 years ago

Yes, needs a diode in series with it, oops

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bitrex 10 years ago

Diode in reverse-series or whatever, rather

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M Philbrook 10 years ago

I think long hair was just starting to be phased out!

Jamie

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dagmargoodboat 10 years ago

But it uses a 4:1 current ratio. John's being criticized for 2:1. (IRL, i(drop-out) is closer to i(pull-in)/10.)

Cheers, James Arthur

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dagmargoodboat 10 years ago

Yes. I almost had it with a 74HC74 one-shot + osc??, but have other things pressing.

Osc. duty sets the PWM. One-shot sets the pull-in interval...

.--------+----. | | | .------. .--o---. [R2] [C2] | PR | | PR | | | Vdd >--|D Q|-- --|D Q|----' === | | | | >--------|> | ---|> | | Q*|----. | Q*|----. | CLR | | | CLR | | '--o---' [R1] '--o---' [R3] | | | | '--------+ '--------+ | | [C1] [C3] | | === === Needs some gluing.

4:1 power is a darn good start, but 3-4:1 current is even better, 'natch.

They should build that into car relays. In normal running my car's got a bunch of coils cooking. Think of the carbon...

Cheers, James Arthur

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mike 10 years ago

Don't suppose anybody's considered a latching relay? Hold current approaches zero.

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John Fields 10 years ago

Indeed, and what's going to happen next is that - even though he hoisted himself on his own pitard - Larkin will fight tooth and nail to try to change the subject, make it seem like you're the one at fault for mentioning his gaffe, an on and on and on. Larkin is a very dedicated, practicing narcissist, you see, and will go to extraordinary lengths to keep from having to admit to error. John Fields

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tabbypurr 10 years ago

o

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it was easy enough to understand

NT

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Jim Thompson 10 years ago

Data suggests that relays are typically between 3:1 and 5:1. I'm sure that fuel injectors are heavily characterized. ...Jim Thompson

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John Larkin 10 years ago

Gaffe? What I said was literally true.

But if you want to misinterpret it:

Find a DC electromagnetic relay that has specified pickup/dropout voltages, and has dropout voltage above half of rated voltage.

Post a link to the data sheet.

Post that link for us.

John Larkin Highland Technology, Inc lunatic fringe electronics

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John Larkin 10 years ago

AC-coil relays are preferred in tough industrial apps, like shipboard, because they automagically reduce their own coil current when the armature seats. So they are more reliable than DC relays.

John Larkin Highland Technology, Inc lunatic fringe electronics

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Lasse Langwadt Christensen 10 years ago

and it dumps a lot of the energy in the Zener

modern direct injection injector drivers use a more elaborate design not only uses a boosted voltage for the opening but also switch between slow decay for the hold period and fast decay for the turn off

-Lasse

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John Fields 10 years ago

Wow!... That's a blast from the past in that Larkin's unwavering opinion is that latching relays have infinite gain. John Fields

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555 relay current reducer

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