Re: Need GE MOV data

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

Putting fuses in line with MOVs defeats the whole purpose of them. If 
MOVs are hit with a surge too big to clamp, they are designed to fail 
short and take out the supply completely. Using an overcurrent device 
is good but it should be in line with the supply to the equipment, 
and rated such that it blows when the MOVs fail short.

I was once working on a job and when I switched it on there was a 
loud explosion and the breaker tripped. It turned out that I had 
wired the equipment's control power (meant to be 230V) between two 
hots of the 400V 3 phase supply by mistake. I blame the new European 
wiring colours :-< Anyway, there was an MOV inside the line filter in 
the equipment and this failed short, blowing the breakers and saving 
the equipment from destruction. The MOV exploded violently enough to 
blow a hole in the metal case of the filter, but the remains of it 
still managed to short out the supply. Once we replaced the filter 
and connected the equi pment to the proper supply voltage, it worked fine.

You can guess what would have happened if the MOV had been fused: the 
fuse would have popped and the equipment would have fried.

Steve Conner
http://www.scopeboy.com/


Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: Sparktron01@xxxxxxxxxxx

Gary

Watch the MOV's. They have a nasty habit of failing shorted.
I was testing some brand new electronics assemblies early
in my career. The assembly had GE V130LA20A
(130Vrms 200Vpk, 20J) across incoming AC line. Plugged
unit in, turn Control Power on ..... KKAAAAABOOOOM!!!!!

I thought the world had ended (and I had bought some
electronics :^C ) It was loud enough that I was surrounded
by co-workers in about 10 secs. Turned out the MOV's
were _soldered_ into crimp conne ctors, then tightened
down in a screw barrier teminal block. Soldering MOV's is
a NO-NO unless you heat sink them. You will shift the zener
knee voltage LOWER, and they will blow-up! OBTW, after
replacing with a new MOV _mechanically_crimped_ into
stak-ons and rewiring terminal strip, everything was OK and
no damage to sub-assembly was done (except for the black
smudge spot on the aluminum bracket ... :^D )

If you do use a MOV, put an OCD (fuse, CB) in line with them to
limit the "magic smoke release" when they do fail.

John A.: This tale of excitement also colloborates your
USN comments. The MOV when is let go threw a
plasma fireball the size of a tangerine!! I wasn't
hurt; my pants, that's a different matter ;^)

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA




-------------- Original message ----------------------
From: "Tesla list"
> Original poster: "Lau, Gary"
>
> I'm looking to add some MOV protection to my Variac/control box. I
> found a handful of MOV devices, but I can't seem to locate any data
> sheets on the web. The devices are marked with the GE logo, "V150
> LAX1002". Does anyone have a reference or cross-reference book to
> indicate what I have? I'm hoping that the V150 indicates that it will
> be fine at 150Vrms, on the 140V side of my Variac.
>
> Thanks in advance,
> Gary Lau
> MA, USA
>
>