A simple multimeter question.

[JDCAVE]

I can’t figure this one out. I’m not an electrical rocket scientist by any means, but I have used multimeters from time to time and I’ve got 3 of them. Two lesser quality ones at home and one Blueseas one on the boat.

I have one of these running my outside DC lighting system at the house for 18 years and the lights go on and off as necessary.

Intermatic ML88T Malibu 88 Watt Low Voltage Transformer Timer Power-Pack

Currently it runs halogen lights which I am thinking of retrofitting over to brighter LEDs. So I put my multimeter on the terminals and get no reading. The lights are on but it just reads “0”. I go inside and try the meter out on D cells, AAAs, and also the output from my computer charger and get realistic voltages.

What am I missing here? Why don’t I get a reading in the vicinity of 12VDC?

Jim

 

[sbman]

I can't find anything on that particular device that says it outputs DC. Have you tried the AC setting on your multimeter?

 

[kchace]

Yup. A lot of those are AC powered. Try the AC range on your meter.

Ken

 

[psneeld]

Pretty sure it is a 120 to 12V transformer after I looked some up...but it was my first thought too.

 

[Shrew]

https://www.homedepot.com/p/Interma...VC4TICh3Y3gvIEAQYASABEgJub_D_BwE&gclsrc=aw.ds

Look at the plug.......120VAC

 

[psneeld]

Staight from the owners manual from the link in the OP.


"This Intermatic ML88T low voltage safety transformer is specifically designed to supply 12 volts to pool/spa lights and outdoor garden lights. The 24-Hour plug-in timer module included is a multi-event timer that turns your outdoor lights on or off at programmed daily settings. No driver or converter required! Two trippers, black plastic housing, and 2 feet of cord are included! No driver or converter required. It's a perfect low voltage solution for landscape lights, pool, spa lighting, garden and fountain lighting."

 

[High Wire]

Yep. Volts AC not DC.
Batteries are DC
Transformer output is AC.
Whatever you do, DO NOT try to measure Ohms on anything energized or you let the smoke out and it won't work anymore.

 

[sbman]

Yep. Volts AC not DC.
Batteries are DC
Transformer output is AC.
Whatever you do, DO NOT try to measure Ohms on anything energized or you let the smoke out and it won't work anymore.

Measuring ohms on an energized circuit should just blow the fuse in the multimeter

 

[psneeld]

Guy is measuring power output on a AC-DC transformer power supply, and the multimeter reads 0 despite powered lights being on.... but takes it inside and it works on batteries.....


Have I got the story wrong?

 

[sbman]

Guy is measuring power output on a AC-DC power supply, and it doesn't work.... but takes it inside and it works on batteries.....


Have I got the story wrong?

The documentation on this device does not say it is a power supply. It is a simple transformer that is 120V AC to 12V AC.

 

[psneeld]

You are right.... I did look too quickly and saw what I am used to 12V DC low voltage garden lights...but below is from the manual also


"OUTPUT TECHNICAL SPECIFICATIONS: 12V AC ~ 88W"

 

[Comodave]

You are right.... I did look too quickly and saw what I am used to 12V DC low voltage garden lights...but below is from the manual also


"OUTPUT TECHNICAL SPECIFICATIONS: 12V AC ~ 88W"

That would account for no voltage showing if the meter is set to DC.

 

[psneeld]

I know, see post #4....

 

[Ka_sea_ta]

Currently it runs halogen lights which I am thinking of retrofitting over to brighter LEDs. So I put my multimeter on the terminals and get no reading. The lights are on but it just reads “0”. I go inside and try the meter out on D cells, AAAs, and also the output from my computer charger and get realistic voltages.

What am I missing here? Why don’t I get a reading in the vicinity of 12VDC?

Jim

One word of caution what ever led's you choose to use, make sure they are 12v ac/dc compatible if you use dc led's they will have a very noticeable flicker

 

[Comodave]

One word of caution what ever led's you choose to use, make sure they are 12v ac/dc compatible if you use dc led's they will have a very noticeable flicker

Well you get a light show that way...

 

[JDCAVE]

Yes. Thanks. That’s what the neighbour said too. I tested it and got 11.5 VAC. I saw 12 volts on the label and just assumed it was DC.

Thanks for the advice on the LEDs. I won’t muck around with 12 VDC LEDs.

Learn something new every day.

 

[C lectric]

One word of caution what ever led's you choose to use, make sure they are 12v ac/dc compatible if you use dc led's they will have a very noticeable flicker

Huh? I use and have used for about 7-8 yrs. DC only LEDs. No flicker at all.
You do need to watch who you buy from even now.
Choose a decent supplier, try one led to see if you like the light. Mine were 2700 Kelvin.

Mine are not dimmable.
They can operate on 10 - 30vdc.

 

[sbman]

Huh? I use and have used for about 7-8 yrs. DC only LEDs. No flicker at all.
You do need to watch who you buy from even now.
Choose a decent supplier, try one led to see if you like the light. Mine were 2700 Kelvin.

Mine are not dimmable.
They can operate on 10 - 30vdc.

The OP has a 12V AC transformer. An LED wired for DC only will flicker at 60hz which could be unpleasant to the eye. There are LEDs with built in diodes that can accept AC or DC and that's the recommendation for this application.

 

[C lectric]

Forgot about the xfrmr.

 

[Barking Sands]

All LED's are DC. They are also diodes. If a single LED is fed the correct voltage but in AC it will chop off half the wave. Thats why it flickers. You can get around flicker by wiring multiple LEDs on a chip 180 out so at any given time one set will illuminate on either half of the wave.

 

[STB]

Hey Barking Sands,

I'm not sure one would want to solve the problem that way....it is a lot of diodes, 2x as many as are needed for the light output, and still a lot of ripple.

4 diodes configured as a bridging rectifier would have the same effect by flipping the negative wave up -- without needing 2x as many diodes.

Add a capacitor to charge and discharge smoothing the ripple, a resistor to bleed it down so no one gets zapped, and a zener diode for voltage regulation -- and there would be less flicker, more light, greater energy efficiency, and, depending upon the number of LEDs involved, a lower cost.

....and more sophisticated drivers exist...

 

[Barking Sands]

Yes...no doubt thats the better way for a better product. But there are some designs that are direct driven in a 180 out configuration with some tricks to reduce flicker.