Ananda Alumni: Mercury relay question [RE-wrenches]

[Allan Sindelar]

Mick,
Todd is correct on the role of the diode.

I have not heard of exploding mercury contactors - not to question Darryl's
experience, but in APT applications I have never seen a failure. We have
collected quite a few MDI contactors when we add a decent MPPT charge
controller, and reused some in other applications.

I have ordered mercury contactors from MDI (Mercury Displacement Industries,
the manufacturer used by Ananda/APT/Pulse) a couple of times over the years.
It's very hard to find an open coil relay with a coil voltage higher than
24V DC; also arcing becomes increasingly problematic at higher DC voltages.
The MDI units are available in 35, 60, and 100 Amps DC, 1-, 2-, and 3-pole,
and a variety of coil voltages. I don't know of another way to get a 60A
relay with a 48V DC coil. All available products can be ordered from their
website.

Incidentally, I recently blew an "ice-cube" relay switching a Shurflo 9300
pump running array-direct at around 33 volts DC. That's only a few amps, and
I misjudged the arcing potential. I replaced it (under our own labor
warranty) with a 30A DPST open-coil relay; much more robust. 

Allan at PosEnergy

-----Original Message-----
From: Darryl Thayer [mailto:daryl_solar at yahoo.com] 

Hi 
I would recomend a solid state relay, I have known of
mercury relays of the old type exploding under short
circuit condtions.  Besides the RV is a short  lived
product and the result is the mercury in the
environment.  I ususally just go to my local graninger
store for my solid state relays.  
Darryl
  
--- "Todd Cory, Mt. Shasta Energy Services"
> 
> A diode across a coil is usually a suppressor for
> the spike that occurs 
> from the collapsing magnetic field when a coil is
> deenergized.
> 
> Mick Abraham wrote:
> 
> >Hi, 
> >
> >My client's RV needs a "low voltage disconnect" for
> the 12 volt 
> >circuits...and we also want a remote control for
> "manual off" so a 
> >normal C-40 type control won't work. 
> >
> >I may build a control with a mercury displacement
> contactor for the 
> >switching, and the Morningstar Relay Driver for the
> deciding. 
> >
> >As installed in the Ananda Powercenter, these
> mercury relays have some 
> >cryptic components on the coil terminals and I
> wonder if I need those in 
> >my application? It looks like there's a diode in
> series with the coil 
> >control voltage, and a second diode wired reverse
> bias across the coil. 
> >
> >What are those widgets for? Do I need them?
> >
> >Mick Abraham, Proprietor
> >www.abrahamsolar.com
> >


[Non-text portions of this message have been removed]


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