# How to test Ballast with DMM?



## jbfan (Jul 1, 2004)

you are not going to be able to test the ballast.
The meter does not have a high enough voltage range.
Replace the ballast and be done.


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## dmxtothemax (Oct 26, 2010)

You cannot test an electronic ballast with a digital multi meter !
You can however test a transformer type ballast.
And even thats not 100% accurate.

If you do try to test it, then the high voltage start pulses, which are many thousands
of volts, will destroy your meter quick smart!


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## Iconoclast62000 (Jun 9, 2014)

Thanks to JBfan for telling me it cannot be done.
Thanks to dmxtothemax for telling my why.

I replaced the ballast & light works fine now. It had failed to turn on most of the time but, occasionally, as I researched repair, tests, etc. It would turn on just fine. When on, no flicker & would stay on for days till I forget & turned switch off & then refused to come back on. Turing the switch on & off many times would not help. The fact that it could turn on (rarely) just fine made me unsure it was the ballast.


I’ll have to find other uses for my new DMM. <GRIN>


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## jschaben (Mar 31, 2010)

Iconoclast62000 said:


> I’ll have to find other uses for my new DMM. <GRIN>


I'm sure you will.
In the majority of cases in dealing with fluorescent lights, the economical way to diagnose is to change the bulbs first... if that doesn't do it, change the ballast. 
Kind of goes against my grain of wanting to definitively identify the problem before tossing parts at the thing but that is the reality of labor vs parts cost... You do want to make sure the tombstones are intact or any other obvious problems before you do either though.


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## bernie963 (Dec 18, 2010)

and don't forget a good ground. many fluorescent bulbs require the capacitance between the bulb and fixture to light the tube. I had a bad ground from when the house was built (20 years before i found the problem) a ground wire in the switch box was not under the wire nut when the house was built. as time went on the fixture became more temperamental as time went on. until replacing tubes and then a new fixture did not fix the problem..then i found the bad ground. all better now.

bernie


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## Iconoclast62000 (Jun 9, 2014)

John, 

Yes, that was my original plan. 1st change bulbs, 2nd change ballast. I had replaced the ballast easily in an older T-12 in that same room 10-12 years ago & I read about how much better T-8 fixtures were & looked into converting the fixture. Instead, I found a better looking T-8 fixture @ Home Depot & bought it & replaced the old fixture in 2010. So, when it recently failed to turn on, I checked bulbs, decided both bulbs would probably not fail at the same time but, I bought 2 new bulbs anyway...which did nothing. I had been told to check tombstones for cracks & they looked fine. I noted all the details re my presumed bad ballast & fixture:

Old Ballast: 4 blue & 4 red wires + B&W line wires
Keystone Cat# KTEB-2C72-1-TP /B
Electronic Ballast
Sound rated A, Class P, Type 1, Outdoor No PCBS
61E1
0.85A

Fixture: 2, T8 32W lamps
Lithonia Lighting
Artisen
4’ 10814 BZA Antique Bronze

Went in to Home Depot to buy a replacement ballast & the fun began. 

With 2 employees spending 20 minutes ‘helping me’ a ballast could not be found. All the ballasts were several inches longer & none had the same wires. (most had 2 blue & 1 red) The employees even opened a returned box of my same fixture which they still sell, to examine the ballast. They ended up suggesting an electric supply company or to contact Keystone for an exact replacement. (I know now how silly that advice was) 

I emailed Keystone, Lithonia lighting & 1000 bulbs.com for advice in how to find a replacement. No helpful replies. I was reluctant to pay 3x the typical ballast cost + shipping to get a replacement from Keystone. Especially if my problem turned out to not be the ballast. Even if it was, why buy the same brand that had failed in only 4 years? 

I then bought a non contact voltage detector, Sperry(VD6505), hoping it could tell me if the ballast was good or bad. With wall switch off, no voltage anywhere; line wires, R or B wires, ballast or end of fixture. With switch on, voltage everywhere! I had assumed I’d see voltage at the line wires & then no voltage exiting the ballast going to the tombstones which would prove the ballast bad. I checked my wall switches (3-way switches), checked the wire nuts & wiggled the 8 red & blue wires @ the tombstones. Everything seemed fine. Just for the hell of it, even w/o the ballast cover in place, I put in a bulb to re-verify that my light does not work. To my surprise it lit up! WTF?! Reassembled with both bulbs & worked fine! I guessed that moving those wires in the fixture or the switches ‘fixed’ it. 
Next day fixture again would not turn on! 

I was later advised that you cannot test a ballast with a non contact voltage tester, I need to use a multimeter & check for 120vac on the B&W ballast wires. So, I bought a DMM (Equus 3320) in order to follow the suggestion. I then learned here that I could not do such a test & would destroy my equipment!

I also had finally learned the truth about replacing ballasts, I could ignore the wires/colors on my old ballast & follow the wiring diagram on the replacement one (which Home Depot did have!) Yes, I’d need to splice wires together or make wire jumpers & find another mounting hole for the longer ballast. I also discovered my old ballast was a rapid start rather than an instant start, which may explain the difference in wires.

So, quite the leaning experience for me.

BTW, Bernie, I ran across a tip to use a metal file or sandpaper to get the paint off the ballast in a few places where it attaches to the fixture to make a better ground connection. I did just that. So, my new ballast has shiny bare metal touching at both ends instead of the factory black paint. 



Steve


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## Removeb4flight (May 12, 2013)

You can not test the output of the ballast with the muti- meter, but the black and white wires are the input. You can test there for 125 volts AC, but that just tells if the circuit is supplying the light with power.


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## Iconoclast62000 (Jun 9, 2014)

Dmclean701,

When someone (on another forum) had said: “...check for 120vac on the black and white ballast wires.” I bought the DMM & replied: “ How exactly should I proceed to do this test? Do you mean for me to use the ACV function & touch the probes to the B&W line wires while circuit breaker is on, live circuit, light switch on. So, I leave ballast connected to line wires with wire nuts & insert probes into the wire nuts? If so, won’t this just test that the line wires are 120VAC? Same thing I learned using my Neon Circuit tester. (While I didn’t learn the Voltage, the fact the neon bulb turned on proved I had power to the line wires & my trouble was elsewhere.)”

I never got a reply. I already knew that I had power @ the ceiling wires. I really doubted that all of the sudden my ceiling wires were no longer supplying 120V & supplying some other voltage causing the issue. I figured he knew some way to use the MM to test the output of the ballast. On this site, Jbfan (electrical contractor) set me straight!


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## bernie963 (Dec 18, 2010)

back to my post #6: my ground problem was not in the fixture, but in the ground pigtail inside the light switch box. the ground going to the fixture pulled out of the wire nut most likely when it was pushed back into the box during installation. 

the first ten years it worked fine (single tube in a closet). then slowly the connection of the grounds deteriorated. the tube would flicker and by flipping the switch several times it would "light". When dim if i touched the tube it would light, and stay lit.

i replaced tubes first, little change, then the fixture, no change either. replaced switch, no change. then i found the loose ground. reconnected and problem solved.

bernie


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## RoundedRooster (May 9, 2014)

If you don't know how to use a DMM or understand electrical/electronic theory, I wouldn't begin on a ballast. 

There is a way to test a ballast (magnetic or electronic), but you'd need resistors to simulate loading and filaments (unless cold cathode). You'd also need to build a resistive divider to measure the HV out, but your meter may not be fast enough to capture this. As the other's pointed out, if you connect directly across, you could destroy the meter, depending upon the level of internal protection. 

The ballast can deliver enough current where it could potentially harm you or possibly kill you. If you do not know what you're doing, just replace the ballast. Get the manufacturer off the ballast, call customer service and ask for a suitable replacement. Lithonia uses the main lighting electronic companies; Philips, Tridonic, GE, ULT, etc... You can also browse their online catalogs for your T8 Class P ballast. I'd recommend an electronic ballast with either rapid start or programmed start (fires filaments first then strikes the lamps). The catalogs have ballast dimensions and mounting specs to easily compare yours. I personally would not trust a home improvement center for their advice on what ballast to replace your old one with. I would trust a lighting electrical supplier.


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