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Kevin
Kevin, Licensed Electrician
Category: Electrical
Satisfied Customers: 1041
Experience:  27 years as a Licensed Electrical Contractor in Illinois, 5 year college Electrical Instructor, Former Electrical Inspector, Diploma in Digital Electronics, Former Illinois Licensed Home Inspector
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Converting 120V AC fluorescent tubes to 12V DC LED tubes

Resolved Question:

I have two fluorescent light fixtures in my kitchen that each take two 8W 120V T5 tubes. I recently replaced all of the tubes with LED tubes. The LED tubes that I found have the same T5 base and use 2.4W to get the same amount of light output. However, they are designed for a 12V DC input.


 


I installed the LED tubes into the fixtures without making any modifications to the fixtures. They just worked. However, a few days later, one of the light fixtures stopped working. I verified that the LED tubes were still fully functional by putting both tubes in the working fixture. After some investigation, I suspect the ballast in the fixture is to blame.. but I have not yet confirmed this assumption (don't have access to the old fluorescent bulbs or an ohmmeter).


 


Now, I'm curious what the best approach to take is to ensure that these LED tubes are properly installed. Why does one fixture seem to work without any issues? Can I depend on the fluorescent ballast delivering the right amount of current? Should I remove the ballast and step-down the 120V input to 12V? What do I need to do/buy? Thanks for your help!

Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.

Hello.....my name is XXXXX XXXXX X will be happy to assist you with your electrical question. My goal is to exceed your expectations on Just Answer!

 

1) Just to confirm, you mention that the LED tubes are rated as 12 VDC? 12 VDC as in a 12 volt battery or are they 12 VAC as in Alternating Current and not Direct Current? ?

Customer: replied 1 year ago.

They are rated for 12V DC. I believe they are meant to be used inside of an RV/camper.


 


I purchased them because they were of the right fit. I didn't check before buying that the current in the fixtures would supply the correct current. I'd like to proceed with using them but would like to know how to properly make the bulbs compatible with the fixtures.


 


Thanks.

Expert:  Kevin replied 1 year ago.

1) Jerry..... the only way to convert your existing 120 volt Alternating Current supply voltage to use the 12 VDC LED's is with the use of a DC rectifier. I am surprised that the 120 volts AC did not immediately blow out or shatter the 12 VDC rated LED tubes?

 

2) AC and DC circuits do not mix well and if using one to convert to another type of power source, either a DC rectifier is required to convert from AC to DC or an Inverter is required to convert from DC to AC.

 

A plug-in DC type of transformer is also a form of a DC rectifier where it converts 120 volts AC to 12 volts DC (similar to a cell phone charger). If using one of these, you would need to purchase such a device with the exact supply current. This would also result in another issue since these types of transformers are plugged into a receptacle. Your ceiling box most likely does not have a receptacle. Even if it did, it would not look appropriate for aesthetic reasons.

 

3) A DC rectifier can be used to change the output 120 AC volts to 12 VDC but that would be somewhat of a costly solution. The DC rectifier would step-down the voltage to 12 volts and would simultaneously convert it to Direct Current on the output. I would not recommend using the 12VDC tubes, as you have already discovered, they don't work well with a 120 volt AC power source. You would require a DC rectifier to convert the voltage and step it down. This type of solution using 12VDC LED tubes is not economically feasible. Even if using a DC rectifier, these are typically a larger type of equipment and you would need to connect the rectifier to the 120 volt AC branch circuit in the ceiling. The DC rectifier would need to be located in the immediate vicinity such as on top of the cabinets or the countertop.

 

4) You can purchase 120 volt AC rated LED's from a local electrical supply that will work correctly in your application, thus no need to purchase a rectifier and/or re-design a circuit and do modifications. If converting from the traditional T12 or T8 or T5 to LED fluorescents, the ballast will need to be changed. 120VAC rated LED tubes are the most efficient as compared to even traditional T12, T8 or T5 fluorescent tubes. The only drawback is that 120VAC tubes are more costly.

 

5) The ballast is not the issue. The mixing of two different types of power inputs is the issue.

 



Hope this helps.........If you have any additional questions, let me know and I'll be glad to answer them for you.

 

Otherwise, don't forget to rate me before you log Off.

The next time you have an electrical question, you can also request for me at:http://www.justanswer.com/home-improvement/expert-your-electrician
..........Thanks..............Kevin!



Customer: replied 1 year ago.

Hi, thanks for your response. I'll probably look into buying tubes rated for 120V AC.


 


I'm still curious as to why one light fixture continues to work with the LED tubes installed? Is the fluorescent ballast changing the voltage and enabling the tubes to work? I suspect if I remove the ballast, I will destroy the LED tubes.

Expert:  Kevin replied 1 year ago.

1) I'm curious of that as well. A few years ago, I deployed an emergency lighting Solar Panel system in my home. At the time I was using 12 VDC CFL type of bulbs directly feeding off of a 12VDC Deep Cycle battery. A few months later, I converted my basement lighting system to 120 volts via a 12VDC to a 120VAC inverter. On one of the light fixtures, I forgot to remove the 12VDC CFL and replace it with a 120VAC CFL. It immediately blew out the 12VDC CFL light bulb.

 

I recommend to de-install the 12VDC tubes. If it shatters, it could present a possible safety issue.

 

2) A ballast is basically a limiting current transformer. A ballast limits the amount of current used in fluorescent T12, T8, or T5 lighting. The ballast is not changing the voltage, it is limiting the amount of current applied to the lighting load.

Kevin, Licensed Electrician
Category: Electrical
Satisfied Customers: 1041
Experience: 27 years as a Licensed Electrical Contractor in Illinois, 5 year college Electrical Instructor, Former Electrical Inspector, Diploma in Digital Electronics, Former Illinois Licensed Home Inspector
Kevin and other Electrical Specialists are ready to help you
Expert:  Kevin replied 1 year ago.

Thank you for the excellent rating as well as the bonus............much appreciated!

 

Take care and have a great evening................Thanks..............Kevin!

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