transformer repeated blow out

[vMike]

I thought someone in this group may be able to help me. I have an automatic
sprinkler system with a 120 v transformer. It puts out 26.5 volts dc / 1500
milliamp. The sprinkler box is outdoors as intended. I have replaced the
transformer 3 times the manufacters original replacement parts. They last
about 2 to 3 months before blowing out. Any ideas on what might case this?
Thanks
Mike

 

[default]

On Sun, 9 Jul 2006 12:57:51 -0400, "vMike"
<MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

I thought someone in this group may be able to help me. I have an automatic
sprinkler system with a 120 v transformer. It puts out 26.5 volts dc / 1500
milliamp. The sprinkler box is outdoors as intended. I have replaced the
transformer 3 times the manufacters original replacement parts. They last
about 2 to 3 months before blowing out. Any ideas on what might case this?
Thanks
Mike

Have you dissected one to see how it fails?

I take it the transformer is outside. Two things spring to mind heat
- in the hot sun? Lightning damage? Lightning (surges not direct
strikes) won't usually hurt a transformer but can be hell on the
rectifier diodes that this one has. They will often enough short out
with a nearby lightening strike. (inside or out)

Two things to try would be a simple plug in surge arrestor (mounted so
you can see the metal oxide varistor if possible - they sometimes self
destruct themselves while protecting equipment) - blow apart or burn
up. A fuse in the line to the protector is a good idea when using
surge protectors.

Another thing to try is to ground the wiring to the solenoid valves
particularly if the wire runs are long. Only ground one side, or
probably a better idea to ground the negative side of the transformer
if it powers the valves as well as the electronics . . . I had a
situation where I'd run a long extension to my battery charger and put
the charger inside the engine compartment to protect it from rain.
Lightening would eat a set of diodes right away - third set of
progressively higher voltage rated diodes and I grounded the negative
lead - no more problems.

Other possibilities is reduce the load by timing so that only one
valve is on at a time - assuming it allows multiple valves to be on,
or roll your own power supply with a big hefty transformer and diodes.

Check the valves themselves if the transformer powers them, one may
have a partially shorted coil - still work but eat transformers -
likewise the low voltage wiring to the valve may be compromised along
the way - only blows when on and a car drives up the drive or you step
in a certain part of the lawn, for instance.

With some inexpensive wall-wart transformers - the transformer serves
as a fuse - bestowing fire protection on the equipment it powers by
blowing up instead - it is a regulatory thing - manufacturer only has
to get a UL (or whatever certifying organization) transformer and not
have to pay to keep the equipment itself certified.

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[vMike]

"default" <none@nobody.net> wrote in message
news:n0h2b21mlsa4eh297c1gqh7r4145ur4uu8@4ax.com...

On Sun, 9 Jul 2006 12:57:51 -0400, "vMike"
MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

I thought someone in this group may be able to help me. I have an
automatic
sprinkler system with a 120 v transformer. It puts out 26.5 volts dc /
1500
milliamp. The sprinkler box is outdoors as intended. I have replaced the
transformer 3 times the manufacters original replacement parts. They last
about 2 to 3 months before blowing out. Any ideas on what might case this?
Thanks
Mike


Have you dissected one to see how it fails?

I take it the transformer is outside. Two things spring to mind heat
- in the hot sun? Lightning damage? Lightning (surges not direct
strikes) won't usually hurt a transformer but can be hell on the
rectifier diodes that this one has. They will often enough short out
with a nearby lightening strike. (inside or out)

Thanks for the ideas. I will have to investigate further. Also, I was

wondering, is there any harm in replacing a 26.6vac 1500mA Transformer with
a 25.2vac 2.0Amp one. The second is more readily available and cheaper.
Mike

 

[vMike]

"vMike" <MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote in message
news:wjdsg.6377$IF2.3656@bignews7.bellsouth.net...

"default" <none@nobody.net> wrote in message
news:n0h2b21mlsa4eh297c1gqh7r4145ur4uu8@4ax.com...
On Sun, 9 Jul 2006 12:57:51 -0400, "vMike"
MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

I thought someone in this group may be able to help me. I have an
automatic
sprinkler system with a 120 v transformer. It puts out 26.5 volts dc /
1500
milliamp. The sprinkler box is outdoors as intended. I have replaced the
transformer 3 times the manufacters original replacement parts. They
last
about 2 to 3 months before blowing out. Any ideas on what might case
this?
Thanks
Mike


Have you dissected one to see how it fails?

I take it the transformer is outside. Two things spring to mind heat
- in the hot sun? Lightning damage? Lightning (surges not direct
strikes) won't usually hurt a transformer but can be hell on the
rectifier diodes that this one has. They will often enough short out
with a nearby lightening strike. (inside or out)

Thanks for the ideas. I will have to investigate further. Also, I was
wondering, is there any harm in replacing a 26.6vac 1500mA Transformer
with a 25.2vac 2.0Amp one. The second is more readily available and
cheaper.
Mike

I forgot to mention that is says 27.7vac at no load , 25.2 with load and it

says current with load 760mA max current with no load 140mA max

 

[jasen]

On 2006-07-09, vMike <MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

Thanks for the ideas. I will have to investigate further. Also, I was
wondering, is there any harm in replacing a 26.6vac 1500mA Transformer with
a 25.2vac 2.0Amp one. The second is more readily available and cheaper.

should be OK. a 1500mA fuse may save it from the same ate as the old one.

Bye.
Jasen

 

[default]

On Sun, 9 Jul 2006 16:38:16 -0400, "vMike"
<MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

Thanks for the ideas. I will have to investigate further. Also, I was
wondering, is there any harm in replacing a 26.6vac 1500mA Transformer
with a 25.2vac 2.0Amp one. The second is more readily available and
cheaper.
Mike

I forgot to mention that is says 27.7vac at no load , 25.2 with load and it
says current with load 760mA max current with no load 140mA max

In your original post you mentioned that this was a DC transformer and
subsequent posts it is AC . . . the right flavor there - really
matters.

The lawn timers I'm familiar with, do use a nominal 24 VAC to power
the valves - less expensive to manufacturer. I have a "Rain Bird"
that I use to water garden plots - sits inside the house with a plug
in wall wart style transformer - has two outputs 24.5 VAC to power the
valves, and 9 VAC to power the electronics. And it is susceptible to
lightening. Replaced under warranty once and they let me keep the old
one - diodes in the low voltage supply were fried in mine.

I had a hospital grade surge protector/GFI protector and used it to
replace that receptacle - so far it has been years without a problem.
It is standard practice to specify transformers under a loaded
condition - so if it doesn't state otherwise - assume they mean loaded
output. I would guess that they use 24 VAC valves so anything
reasonably close should work - I wouldn't hesitate to use the 25 VAC/
2 amp transformer. And add a fuse, that might save you some money. If
it is a wall wart style, you can put an "in line" fuse holder in one
leg of the power wires from the transformer and fuse it at or lower
than the maximum output - like Jamie said 1500/1-1/2 amp would be
good.

I don't understand the idea of specifying a "no load" current at 140
milliamp max. That isn't done - as a rule no load means no (Zero
milliamps) load. A switching power supply - may specify a minimum
load as well as a maximum. But no load 140 with max after it makes no
sense . . . something wrong there.

There's a lot of leeway in transformer tolerance - the power line is
usually specified at plus or minus 10%, and the transformer can have
another 5% . They can add or subtract - you may have a high line
condition and a borderline transformer causing it to burn out. Power
companies may raise the voltage during summer to compensate for the
air conditioning loads dragging down voltage.

Using a 25 - 27 VAC transformer to power 24 VAC valves is common since
they use relatively thin (cheap) wire out to the valving as a rule.
Some voltage is dropped warming up the wire.

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[vMike]

"default" <none@nobody.net> wrote in message
news:f7f4b2lmqumnf8jhhffuacabhbi2a6mts8@4ax.com...

On Sun, 9 Jul 2006 16:38:16 -0400, "vMike"
MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

Thanks for the ideas. I will have to investigate further. Also, I was
wondering, is there any harm in replacing a 26.6vac 1500mA Transformer
with a 25.2vac 2.0Amp one. The second is more readily available and
cheaper.
Mike

I forgot to mention that is says 27.7vac at no load , 25.2 with load and
it
says current with load 760mA max current with no load 140mA max


In your original post you mentioned that this was a DC transformer and
subsequent posts it is AC . . . the right flavor there - really
matters.

The lawn timers I'm familiar with, do use a nominal 24 VAC to power
the valves - less expensive to manufacturer. I have a "Rain Bird"
that I use to water garden plots - sits inside the house with a plug
in wall wart style transformer - has two outputs 24.5 VAC to power the
valves, and 9 VAC to power the electronics. And it is susceptible to
lightening. Replaced under warranty once and they let me keep the old
one - diodes in the low voltage supply were fried in mine.

Yes I should have said AC. Anyway, I got a new rainbird transformer today

just to be sure. I put it in and turned on zone 7. After running about 8
minutes the zone shut off (before it was supposes to) and repeated pressing
of the manual button would not turn on any zone. I check the voltage and it
had dropped to about 15 volts. I turned the circuit off came back after
about 30 minutes and started it up. This time I started on zone 1. It ran
fine through all zones this time and the every time I measured the voltage
it was at the proper voltage. I am a bit baffled. Would a voltage drop be
cause by the line voltage dropping or more likely overheating because the
zone has some kind of short.

 

[default]

On Mon, 10 Jul 2006 20:48:16 -0400, "vMike"
<MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

Yes I should have said AC. Anyway, I got a new rainbird transformer today
just to be sure. I put it in and turned on zone 7. After running about 8
minutes the zone shut off (before it was supposes to) and repeated pressing
of the manual button would not turn on any zone. I check the voltage and it
had dropped to about 15 volts. I turned the circuit off came back after
about 30 minutes and started it up. This time I started on zone 1. It ran
fine through all zones this time and the every time I measured the voltage
it was at the proper voltage. I am a bit baffled. Would a voltage drop be
cause by the line voltage dropping or more likely overheating because the
zone has some kind of short.

Sounds like there might be an intermittent short there somewhere if
the 25 VAC transformer was putting out 15. That is well outside of
tolerance.

Or you really have the same type Rainbird transformer that I do: one
25 volt winding and one 9 volt winding - measure the wrong pair of
wires and you get 25 minus 9 or about 15 . . . That would also
explain the fact that you gave two maximum current ratings - each
winding is rated for a different current.

One assumes the power to the system was there - or you might have
noticed dim lights or other problems.

You pick zone seven and zone seven gives a problem - implies that you
suspect something there.

Two ways solenoid valves can fail: intermittent short that occurs
when hot, for instance - that's sort of rare when the valve coils are
potted in epoxy like they generally are for sprinkler systems

If an AC solenoid valve fails to pull in the solenoid - it can burn
out. The reason is that it depends on a certain amount of impedance
to function properly. Impedance is the AC resistance to current flow.
With the solenoid plunger pulled in, the inductance is higher, current
demand is less, less load on the power transformer.

Either short or stuck plunger should cause a noticeable temperature
increase in the valve coils. One way to tell you've got a problem -
feel it.

And since it is low voltage wiring - there's no strict safety
guidelines for installation - so perhaps the installation has a
problem?

My Rain Bird has the transformer specified at point eight amps on the
24 volt output and point one five on the 9 volt output - and there's a
3/4 amp fast blow fuse on the 24 volt output. - the fuse only
protects the transformer from shorted valve solenoids - not from
wiring mistakes from the transformer to the controller - and they
include a spare - so they must expect them to blow.

I'm thinking they get a lot of wiring errors since the wires are color
coded and the wire terminals are labeled for correct color and painted
with the correct color.

If you haven't got a fuse on your's, it would make sense to add one.

What is your level of competence? Any chance you're wiring the
transformer wrong?

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[vMike]

I'm thinking they get a lot of wiring errors since the wires are color
coded and the wire terminals are labeled for correct color and painted
with the correct color.

If you haven't got a fuse on your's, it would make sense to add one.

What is your level of competence? Any chance you're wiring the
transformer wrong?

The transformer only has two output wires (2 yellow). It also has a separate

volt battery which I think runs the clock and saves the settings. I
recently purchased the house (as is). The system is at least 10 years old
but the control box is brand new so they must have been having problems and
tried to solve it by replacing the box. I have found numerous wiring
problems in the house, (3 way switches wired wrong, outdoor circuits piggy
backed off of air-conditioning suggesting a non professional tweak jog) but
the sprinkler system installation looks professional. So I suspect something
in the line might be causing this. (or zone 7 because I noticed once before
it shut off early) I guess the next step is to power the controller from
another circuit temporarily and see if it continues to be a problem.

One other thought, the transformer has a metal pipe thread on the line side.
It is connected to the plastic conduit before the controller. Should it be
connected to a metal conduit to provide a heat sink?

 

[default]

On Mon, 10 Jul 2006 23:31:27 -0400, "vMike"
<MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:

The transformer only has two output wires (2 yellow). It also has a separate
volt battery which I think runs the clock and saves the settings. I
recently purchased the house (as is). The system is at least 10 years old
but the control box is brand new so they must have been having problems and
tried to solve it by replacing the box. I have found numerous wiring
problems in the house, (3 way switches wired wrong, outdoor circuits piggy
backed off of air-conditioning suggesting a non professional tweak jog) but
the sprinkler system installation looks professional. So I suspect something
in the line might be causing this. (or zone 7 because I noticed once before
it shut off early) I guess the next step is to power the controller from
another circuit temporarily and see if it continues to be a problem.

Or perhaps just disconnect zone seven if you can do without it (move
that valve it to a higher number) or temporarily take it out to see if
the problems follow the zone.

The valve for zone seven in the same location with the others?

Outside and AC circuits does sound hinky. That would be illegal in a
lot of places - outside circuits should have ground fault protection.

Is the house wiring good except for the amateur parts? Not so old it
has two wire gutta percha insulation or wires run through ceramic
sleeves in the walls, or wire runs following old gaslight pipes?

My wife's house is like that - I tell her to keep the insurance paid
up, and swear off hair driers, flat irons, toasters, and space heaters
.. . . rewiring that house would be a bear, bringing it to code a
nightmare.

One other thought, the transformer has a metal pipe thread on the line side.
It is connected to the plastic conduit before the controller. Should it be
connected to a metal conduit to provide a heat sink?

Interesting - I seriously doubt that they get much, if any, heat sink

through a steel conduit with a threaded connection - but what's the
chances that they want a ground at the transformer for lightening
protection?

Wires laying on the ground are able to pick up big transients with
nearby lightening discharges. I was camping my way cross country with
a motorcycle and rigged 30 feet of speaker wire to a tiny lamp so I
could put it in my tent for reading. I was stringing it up to the
tent as a storm approached and got knocked on my ass from a strike
that was four miles away.


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[vMike]

"default" <none@nobody.net> wrote in message
news:8me7b2t32rpi9l40615puvbp2kf9o4to4d@4ax.com...

On Mon, 10 Jul 2006 23:31:27 -0400, "vMike"
MicZhaYel.GeoZrgeY@noYandZ.geZwaYrrenZ.com> wrote:


The transformer only has two output wires (2 yellow). It also has a
separate
volt battery which I think runs the clock and saves the settings. I
recently purchased the house (as is). The system is at least 10 years
old
but the control box is brand new so they must have been having problems
and
tried to solve it by replacing the box. I have found numerous wiring
problems in the house, (3 way switches wired wrong, outdoor circuits
piggy
backed off of air-conditioning suggesting a non professional tweak jog)
but
the sprinkler system installation looks professional. So I suspect
something
in the line might be causing this. (or zone 7 because I noticed once
before
it shut off early) I guess the next step is to power the controller from
another circuit temporarily and see if it continues to be a problem.

Or perhaps just disconnect zone seven if you can do without it (move
that valve it to a higher number) or temporarily take it out to see if
the problems follow the zone.

The valve for zone seven in the same location with the others?

Outside and AC circuits does sound hinky. That would be illegal in a
lot of places - outside circuits should have ground fault protection.

Is the house wiring good except for the amateur parts? Not so old it
has two wire gutta percha insulation or wires run through ceramic
sleeves in the walls, or wire runs following old gaslight pipes?

My wife's house is like that - I tell her to keep the insurance paid
up, and swear off hair driers, flat irons, toasters, and space heaters
. . . rewiring that house would be a bear, bringing it to code a
nightmare.

No, it is newer than that. I once lived in a house like that. Fuses all over

the place too. I eventually rewired the whole house. That was fun, ha.
Anyway, thanks for your suggestions. I am just hoping the wiring in the
ground isn't bad somewhere. I don't know how I would be able to fix that.
Unfortunately, the valves are all around, instead of a manifold. Thanks
again.
Mike