lighting problem

Status
Not open for further replies.
Bobhook149

Bobhook149

Senior Member
At my father in laws house there is a specific light where the bulb kept blowing frequently. The fixture was changed to a low voltage 12v fixture and now after a 2 month period the transformer has gone bad. Today i just pulled out my multimeter and voltage rings up okay, polarity is okay and so is ground. Do you think voltage is fluctuating??? The light keep dimming any time the dryer or range is on.??? Any ideas?

Thanks

Bob
 
I agree, but would a loose neutral cause a transformer to go bad??? Or would it just blow the bulb?Maybe coincidence i don't know???
 
Bobhook149 said:
I agree, but would a loose neutral cause a transformer to go bad??? Or would it just blow the bulb?Maybe coincidence i don't know???
Click to expand...

It could be voltage drop on the service. The dryer and range are 2 of the heaviest loads in a house, so would cause the most VD. That could drop the voltage enough to damage the transformer.


At my father in laws house there is a specific light where the bulb kept blowing frequently. The fixture was changed to a low voltage 12v fixture and now after a 2 month period the transformer has gone bad. Today i just pulled out my multimeter and voltage rings up okay, polarity is okay and so is ground. Do you think voltage is fluctuating??? The light keep dimming any time the dryer or range is on.??? Any ideas?
Click to expand...

Did you check the voltage with the dryer or range on?
Where exactly is the fixture located? There could be a non-electrical reason. When incandescent lamps burn out frequently, I always see if there is a lot of vibration at that location - under a kids bedroom, for example. (Although I doubt that would affect a transformer)
 
JohnJ0906 said:
It could be voltage drop on the service. The dryer and range are 2 of the heaviest loads in a house, so would cause the most VD. That could drop the voltage enough to damage the transformer.




Did you check the voltage with the dryer or range on?
Where exactly is the fixture located? There could be a non-electrical reason. When incandescent lamps burn out frequently, I always see if there is a lot of vibration at that location - under a kids bedroom, for example. (Although I doubt that would affect a transformer)
Click to expand...


VD was a thought but would that kill an incandescent bulb... lower voltage is longer life.... right? I could see it blowing a fuse in a transformer as voltage drops.

The light is in the kitchen, above there is not alot of things going on kids have all moved out so the upstairs is basically not used.

It is on a multi-wire branch circuit both on different legs.
 
Bobhook149 said:
VD was a thought but would that kill an incandescent bulb... lower voltage is longer life.... right?
Click to expand...
Yes, but if there is a neutral problem, the voltage could be higher on that phase other times of day.

It is on a multi-wire branch circuit both on different legs.
Click to expand...
In that case, it could be a neutral issue on the MWBC. You need to compare opposing voltages.
 
In that case, it could be a neutral issue on the MWBC. You need to compare opposing voltages.[/QUOTE]

What do you mean?
 
Iwire,

Thanks, I know that..

What do you mean?[/quote] was part of Bobhook149 reply. My reply was below that. I clicked "quote" but for some reason that wasn't part of the quote. I was trying to explain to him what Larry meant from comparing opposing voltages.
 
Last edited:
Lights dim all over the house when the dryer or range is on... but this is the only circuit that seem to have a problem and its just the light as far as i know. My father in law told me the incandescent would blow frequently. No idea how long they actually had it on a day. Never got around to looking into it till this friday the fixture had been changed to a low voltage 12v. worked for a 2 month period and now the transformer is bad. Voltage is okay now 123v . But maybe it is fluctuating. maybe just a crappy fixture. Can't trust what the customer says.... even if he is your father in law:D
 
Bobhook149 said:
Lights dim all over the house when the dryer or range is on... but this is the only circuit that seem to have a problem and its just the light as far as i know. My father in law told me the incandescent would blow frequently. No idea how long they actually had it on a day. Never got around to looking into it till this friday the fixture had been changed to a low voltage 12v. worked for a 2 month period and now the transformer is bad. Voltage is okay now 123v . But maybe it is fluctuating. maybe just a crappy fixture. Can't trust what the customer says.... even if he is your father in law:D
Click to expand...



Well its a bad connection sounds like its in the service neutral like iwire and others have said .

But think of this just because you measure 123 volts or 120 volts on your meter thats just voltage think of this if a battery is low lets say a 9 volt batt it will indicate almost full voltage but when you put a load on that little batt it dies real fast same kinda issue you may have 123 volts but not a good connection of your load for current to feed it thats a real problem .


So its going to find that voltage on any other leg or equipment meaning high voltage thur other leg.
Put your meter on that circuit and start your dryer tell us what happens then pull the meter and tighten up your wires coming in .

Its the main neutral
 
Last edited:
Had some tools on me today, opened the panel up. Neutrals are doubled up ... insulation under screws.. just a mess. Fixed that problem. Made sure the service neutral was tight in the main panel. Hopefully that was the problem.. all other connections are tight. I put my voltage tester on the main lugs coming into the panel and read 243v L to L When the dryer was put on it went to 239v and then the range it went down to 237v and stayed there. Is this normal or still an indication of a loose neutral? I have not checked the neutral passed the main panel yet.

Thanks

Bob
 
091226-1431 EST

Bobhook149:

First, someone mentioned low voltage to a transformer might damage the transformer. That is total nonsense. The only way it could be a problem is with some peculiar load that required an increasing current as the load voltage was lowered was the load. A motor on the output of a transformer might fall in this category, but that is not the case here and there would be other factors to consider.

A tungsten filament lamp as a load falls some where a constant current load and a constant resistance load. Following are current vs voltage values for a 100 W 120 V bulb in volts and amps.

20 0.297
40 0.440
60 0.556
80 0.664
100 0.755
120 0.833
140 0.904
At 120 V the resistance is 144 ohms. If a constant resistance of 144 ohms was the load, then at 20 V the current would be 0.138 A instead of 0.297 .

The voltage drop line to line for the large 240 V loads that you mentioned is only 100*6/243 = 2.5%. That is reasonable and maybe quite good.

A well balanced lighting load on your center tapped transformer and a poor neutral from the transformer should have caused come lights to brighten, and others to dim when a large 120 load was applied.

From your description of the termination of neutrals in the main panel it is likely that a 120 V circuit with the light that was burning out shared a neutral with a 120 load from the opposite phase, and the opposite phase had a 120 V load that was large relative to the lamp or transformer, and that caused excessive voltage on the lamp or transformer.

Transformers do not care about under voltage, but not very much over-voltage can burn them out. When you get transformer input voltage above the nominal rating the magnetizing current grows rapidly.

Hopefully getting rid of the neutral terminations where the screw was on the insulation has solved the problem.

Also, note that a standard tungsten filament lamp's life increases as the applied voltage is reduced.

.
 
Thanks for the reply,

The transformer on the low voltage 12v light indicated that it was internally fused at .55a on the load side. I think that means if the voltage was under the factories request that the amperage flow would increase and maybe blew the fuse.

Am i correct is saying this?

Also, i'm not quite following how the load on one phase is causing higher voltage on the other phase??


Once again thanks for the help
 
Last edited:
091226-1645 EST

Bobhook145:

If excessive voltage was applied to the transformer, then the results might be:

1. The secondary fuse blows because the increased voltage caused the lamp to use a higher load current. A short duration excess voltage could be the reason because the thermal time constant of the fuse is short. Truly the fuse should be on the outside so it can be replaced.

Disconnect the secondary from the lamp and with no power applied to the primary measure the secondary resistance. It should be low, probably less than 1 ohm.

If the fuse blew or the secondary winding failed, then the secondary resistance viewed from the terminals should be very high.

2. If the primary voltage was high enough and/or at a moderately high voltage for long enough, then the primary would show an open (high resistance). Also a burned out transformer might smell and show evidence of overheating.

3. If 2 occurs, then most likely 1 would occur.

.
 
Bobhook149 said:
What do you mean?
Click to expand...
What I mean is you need to measure the voltage between each line and the neutral. They should just about match at all times, within a volt or two.

When the neutral is an issue, the voltage between, say, L1 and N may rise while that between L2 and N drops, but L1 to L2 remains normal.

You have 120v problems, not 240v problems. A bit of L1-L2 sag is normal with 240v loads. You may need to check L1-N vs L2-N where the MWBC splits if there's no unusual readings at the panel.

That's what I mean. ;)
 
gar said:
091226-1645 EST

Bobhook145:

If excessive voltage was applied to the transformer, then the results might be:

1. The secondary fuse blows because the increased voltage caused the lamp to use a higher load current. A short duration excess voltage could be the reason because the thermal time constant of the fuse is short. Truly the fuse should be on the outside so it can be replaced.

Disconnect the secondary from the lamp and with no power applied to the primary measure the secondary resistance. It should be low, probably less than 1 ohm.

If the fuse blew or the secondary winding failed, then the secondary resistance viewed from the terminals should be very high.

2. If the primary voltage was high enough and/or at a moderately high voltage for long enough, then the primary would show an open (high resistance). Also a burned out transformer might smell and show evidence of overheating.

3. If 2 occurs, then most likely 1 would occur.

.
Click to expand...


Wouldn't low voltage cause the current to rise?
 
Status
Not open for further replies.
Top