Question about Intermatic Malibu 121W Power Pack Transformer ML121RT

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Malibu transformer shuts down early

I have an ML121RT Malibu transformer with (3) 50 watt lights connected. The power source is timed. The lights come on o.k., but go off before they should. The timer tabs have been removed so it is essentially always on. I'm wondering if the transformer gets too hot and shuts down? I have another set which is a duplicate of this one and it works fine.

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I'm thinking that a better brand is in order. Mine shorted out and started a fire. Luckily we had just returned from vacation and put it out with a hose.

Posted on Sep 05, 2010

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Well, you're overloading the transformer by 30 watts. It's doing what it's supposed to do when overloaded...shut down. It's the _other_ (works fine) transformer that you should worry about possibly starting a fire, since it's not shutting down when overloaded.

Posted on Mar 10, 2009


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I have a malibu set of 8 lights about 80 foot of 12 gauge wire. They come on then after about an hour they shut off then come back on about 20 min later

Do you have photo-eye connected to the transformer?
Disconnect photoeye, or cover photoeye with black tape and see what effect it has.
Plug another light into same outlet and see if it has same problem.
Run temporary extension cord to transformer and see if problem is same.
When the lights are off, does the transformer make humming sound.
Intermatic/malibu timers have 5 year warranty if you have sales receipt.
Copy following link for troubleshoot resources, trippers, operation tips, etc.

Aug 15, 2012 | Malibu Intermatic Inc. ML121RT Low...

1 Answer

My 600 watt 12 volt transformer timer for out door lighting does not keep time properly. HOw do I get and install a new timer?

1) Amazon sells 600Watt power pack:

2) I bought new 300Watt Malibu power pack at Home Depot about 2 months ago.
Near the lighting section.
My new power pack has electronic time clock, so no more 'slow clock.'
I think Home Depot had 600Watt.
Lowes carries different brand.

3) Manuals for power packs at Malibu

4) Tips for buying and taking care of power pack:
-Match up wattage of bulbs with wattage of power pack
-15 each X 20 watt bulbs = 300 watts, so install 300Watt power pack
-Installing a 500W power pack on 300W of bulbs will burn out bulbs and power pack.
-Replace bulbs as soon as they burn out or other bulbs will burn out and power pack will burn out.
-When working on bulbs, unplug power pack or it may burn out.

5) How to install power pack.
Before unplugging old power pack, check which bulbs are not working.
Replace bulbs using phillips screwdriver.
Unplug power pack.
Notice how wires are connected to power pack, write down terminal connections.
Some power packs have three terminals ... extra terminal is for additional photoelectric eye.
Use pliers or screwdriver to disconnect wires.
New power pack has has same terminals.
Plug in power pack.
Read instruction manual before connecting wires.
Save instruction manual because a few years that manual won't be around as products change.

Dec 03, 2010 | Malibu Intermatic Inc. ML121RT Low...

1 Answer

Intermatic Inc. ML121RT Low Voltage 121-Watt Power Pack with Timer: I've had malibu lights for around 4 years,I have ...

If other lights are working the power pack is OK. Usually, as in your case, if changing the bulb doesn't work, check the connection where the light ties into the main run.

May 17, 2010 | Malibu Intermatic Inc. ML121RT Low...

1 Answer

Malibu 600 watt transformer timer not working. Can turn on and off w/ the switch but the timer isn't functioning.

The timer motor is probably bad. Unfortunately, Malibu transformers have very few user servicable parts :-( , and the timer motor isn't one of them. One cannot even access the internal connections. If you recently purchased the transformer, return it to the store. If the transformer is less than 5 years old, it's still under warranty. In that case visit the Malibu website for instuctions.

Oct 31, 2009 | Malibu Intermatic Inc. ML121RT Low...

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