Question about Intermatic Malibu 121W Power Pack Transformer ML121RT

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ML 121 RT doesn't power all lights on the system

I have a ML121 RT transformer running a total of 92 watts.I just added 21 more watts bringing the total to 113 watts. I accidentally crossed two bare wires and now 5 of the 10 lights on the system no longer work. I checked for voltage on the leg containing the 5 lights with a multimeter and found no power. What's the matter?

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Go back to where the lights are working, Then inspect the cable leaving that point. You must have a bad spot somewhere after that point killing the voltage.

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Posted on Jun 27, 2009


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1 Answer

Does Malibu still make a model number ML500TW timer transformer

Intermatic/ Malibu series lights are available 44 watt, 88 watt, 100 watt, 121 watt, 200 watt, 300 watt, 600 watt, 900 watt.

None of the other brands sells 500 watt either.
Kichler sells 300 and 600 and 900Watts
Paradise does not have 500 watt
Malibu brand does not carry 500 watt
Portfolio does not carry 500 watt

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Where can I order some replacement ML Power Pack trippers for a ML600TW and ML 300RTW timer?

1) Copy following link for ML series trippers, troubleshoot, 5-year warranty info, and tips to keep power pack running longer.

2) Add comment if more help is needed. Jan 2013.

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Jan 18, 2013 | Intermatic Inc. ML121RT Malibu Low Voltage...

1 Answer

My Malibu ML 300 RTW has stopped working, but I can hear the timer. No lights come on, though.

Sounds like the transformer died which isn't uncommon. One cause is overloading the circuit (too many lights) figure out the total wattage by adding the bulb watttage usually 11 by the amount of lights you have. I would buy a transformer with around 200 Watts higher than you need to allow for expansion and the transformer wont have to "work" as hard.

Aug 28, 2011 | Intermatic Malibu 300W Power Pack...

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I have a ML121RT Low Voltage 121-Watt Power Pack with Timer hooked up with three 20 watt lights attached - going north. I want to add one more 20w llight going south. Can I attach an additional wire to...

Try it... should work
However minimum load for ML121 is 80% load rating.. so 80 watts is ok for 100 watt transformer... 60 watts is low and can cause early failure of transformer.

If you need further help, I’m available over the phone at

Jul 14, 2011 | Malibu Intermatic Inc. ML121RT Low...

1 Answer

Power into unit ok power comming out of unit is very dim.

If you have a volt meter, check the voltage, I believe it is supposed to be 12 volts.
Are your bulbs the proper voltage rating, that is 12 volts.
Do you have enough bulbs connected to the transformer, connected load should be close to 121 watts when you add up all your bulb wattages.
Don't confuse volts with watts. The transformer reduces voltage to 12 volts, but the wattage of the transformer is 121 watts. Each bulb must be 12 volts but wattage (brightness) can vary depending on the fixture from maybe 7 watts to over 50 watts.

Dec 01, 2010 | Intermatic Malibu 121W Power Pack...

1 Answer

Can you hook up two 12 gauge cables to the power pack of the ML 300 RTW transformer. Power cable would run in different directions. Thank you Joe

Hello yes you can the Important thing to remember here is not to exceed the wattage that the transformer puts out.

Add up the wattage of each bulb that you are running and ensure that you do not exceed 300 watts.

for example a 300 watt transformer could drive
a. 10 - 30 watt bulbs
b. 20 - 15 watt bulbs
c 75 - 4 watt bulbs

Its also ok to mix bulb wattage for example I use 10 watt bulbs in the fixtures in the front of the house but also power 4 20watt spotlights from the same transformer.

Hope that helps

Feb 26, 2010 | Malibu ML300RTW - Low Voltage Power Pack...

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