From: David Van Horn <david.vanhorn@backcountryaccess.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Fri, 6 Aug 2021 11:27:57 -0700
Subject: Re: [EE] Latching relay ratings
Thread-Topic: [EE] Latching relay ratings
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It's not about the magnetics, but whether or not the contacts can actually =
break the current.
DC, especially with an inductive load, is very hard to turn off.  Wide sepa=
ration and beefy contacts are required.

________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Sean B=
reheny <shb7@cornell.edu>
Sent: Thursday, August 5, 2021 6:26 PM
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Subject: Re: [EE] Latching relay ratings

*EXTERNAL EMAIL*


Well, Bob was thinking that maybe AC wouldn't be able to exert an opposing
field for long enough to break contact but thinking some more about it, for
most relays, even large-ish ones, a millisecond is long enough to make the
contacts separate so I would think that if DC were enough to cause a
problem then AC of the same magnitude would at least make the contacts
chatter.

On Thu, Aug 5, 2021, 4:50 PM Denny Esterline <desterline@gmail.com wrote:

> It also seems reasonable to assume that any current level the relay is
> rated for will not lead to adverse behavior of the latching mechanism,
>
> -Denny
>
> On Thu, Aug 5, 2021 at 12:15 PM Sean Breheny <shb7@cornell.edu> wrote:
>
> > Correct - unless we're talking thousands of amps, I don't think it will
> > influence the latching mechanism.
> >
> > On Thu, Aug 5, 2021, 11:51 AM Bob Blick <bobblick@outlook.com wrote:
> >
> > > I gather from the discussion that nobody thinks electromagnetism from=
 a
> > > strong DC current through the relay will influence the relay's latchi=
ng
> > > response?
> > > Thanks, Bob
> > >
> > > ________________________________________
> > > From: Bob Blick
> > > Sent: Wednesday, August 4, 2021 3:32 PM
> > > To: Microcontroller discussion list - Public.
> > > Subject: [EE] Latching relay ratings
> > >
> > > I'm helping a friend out with his camper's auxiliary 12 volt power, a=
nd
> > > I'd like to set up an automatic low battery disconnect. His solar
> > > controller has a low battery voltage dry contact output but it's rate=
d
> > for
> > > only 0.5A. I know I could just connect a 40 Amp automotive relay to
> that,
> > > but then there'd be a constant 120 milliamp drain until the battery
> > > disconnected. So I am thinking of using a high current latching relay
> and
> > > some logic. But all the affordable latching relays, such as this 120
> Amp
> > > Omron G9TB-K1ATW-E DC12  are rated for AC only. I'm assuming it's
> because
> > > high DC current could cause the relay to unlatch due to
> electromagnetism,
> > > and running 12VDC at 30 Amps through the 277VAC 120A contacts isn't
> > really
> > > going to be a problem. Or am I wrong?
> > >
> > > Bob
> > >
> > > --
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