# 12 Volt lighting AC or DC



## johnr9q (Apr 30, 2010)

I am installing outdoor lighting and also a pump for a fountain. I bought the lights and 200 watt transformer from home depot (Malibu) and bought a 12 volt water pump online. I wanted to remotely control the pump and lights seperately so bought a 12 volt remote control from Logisys online and a couple 30 amp relays from Radio Shack. I need the relays cause the remote control only puts out 6 amps and that isn't enough. I hooked everything up and it didn't work. The system does work if I hook the lights and pump directly to the transformer, but when I add the remote control/relays, nothing works. I used my volt meter to check the output of the transformer and when I set my volt meter on DC voltage I get no reading on the meter but the lights and pump are on. I was wondering if the output of the transformer could be 12 volt AC instead of DC and that is why I get nothing on my meter and my remote, which is designed for DC, is not working. The instructions for the transformer and the owners manuel don't say DC or AC. I have never heard of 12 volt AC but, then again, there are alot of things I have never heard of. Thanks, John R


----------



## AllanJ (Nov 24, 2007)

What comes directly out of a 120 to 12 volt step down transformer is roughly 12 volts AC. The actual voltage measured may vary depending on the load.

For model trains, computers, and various other uses the AC may be rectified (into DC) using other components in the transformer assembly.

Incandescent lights work equally well on AC or DC. For most other equipment including relays, motors, pumps, compact fluorescents, and electronics, you need to follow the wiring instructions Connecting AC where DC is needed *or vice versa* can damage equipment.

Use only the AC range on a voltmeter to measure AC.

DC relay fed with AC: The coil (input; control) may present too great a resistance (impedance) and the coil does not activate the switching (output; load).

AC relay fed with DC: The coil may present too little resistance and may burn out.

If you have never connected a relay before, note that power must be connected to the "output", treating the "output" as a switch. Subcircuit 1: Power hot to switch or remote to relay input to common (or neutral). Subcircuit 2: Power hot to relay output (contacts) to load to common.

For the transformer, the low voltage stuff is connected only to the output (secondary) terminals and the 120 volt power is connected only to the input (primary) terminals. One of the two terminals on the transformer secondary may still be referred to as a neutral and it is not connected to the 120 volt neutral.

OT: Another place where you do not connect the neutrals together is with a GFCI, between the line (input; feed) side and the load (output, protected) side.


----------



## kbsparky (Sep 11, 2008)

A simple bridge rectifier will turn your AC into DC.


----------



## johnr9q (Apr 30, 2010)

I got a response from Malibu (they make the landscape lighting and transformer) They said the transformer is 12 Volt DC. I don't understand why my voltmeter showed 0 when I had it set on DC volts. I tried a couple of times and also tried my volt meter on my car battery and it showed 12.7 volts.


----------



## Yoyizit (Jul 11, 2008)

johnr9q said:


> They said the transformer is 12 Volt DC.


Unlikely. 
Running an incand. lamp on DC causes notching of the filament and so shorter life.


----------



## troubleseeker (Sep 25, 2006)

Yoyizit said:


> Unlikely.
> Running an incand. lamp on DC causes notching of the filament and so shorter life.


There are incadescent lamps made for dc voltage, such as landscape lighting and for the marine industry.

Low voltage landscape lighting is mostly 12VAC, but there are low voltage DC systems. 
It may be you are underpowered, as low voltage systems are very sensitive to voltage drop on long runs.

I don't quite follow the part about the relays, so I'll leave that for some one more familiar.


----------



## Yoyizit (Jul 11, 2008)

johnr9q said:


> when I set my volt meter on DC voltage I get no reading on the meter but the lights and pump are on.





johnr9q said:


> I don't understand why my voltmeter showed 0 when I had it set on DC volts. I tried a couple of times and also tried my volt meter on my car battery and it showed 12.7 volts.


IMO this 'power supply' is almost certainly putting out AC. For the rest of it the OP needs to post a schematic. There's many ways this arrangement of relays can't work and only one way it can work.


----------



## johnr9q (Apr 30, 2010)

Yoyizit said:


> Unlikely.
> Running an incand. lamp on DC causes notching of the filament and so shorter life.


I have an RV that has incandescent as well as fluorescent lighting that runs on 12 volt DC and with most RV's, automotive and marine lighting this is the case. Unfortunately the transformer is at my daughters house which is 80 miles away so I won't be able to put my voltmeter on it again for awhile.


----------



## frenchelectrican (Apr 12, 2006)

johnr9q said:


> I got a response from Malibu (they make the landscape lighting and transformer) They said the transformer is 12 Volt DC. I don't understand why my voltmeter showed 0 when I had it set on DC volts. I tried a couple of times and also tried my volt meter on my car battery and it showed 12.7 volts.


I have dealt with this type of landscape luminaire and it is not 12 V *DC* at all it is straght AC.

get your voltmeter set on AC then it will show the correct voltage.

Merci,Marc


----------



## AllanJ (Nov 24, 2007)

RV 12 volt circuits are not either AC/DC in terms of what the lamps actually get, depending on battery versus land line power.

When an RV is plugged in to an AC outlet, there will be a rectifier somewhere in the 12 volt side of the line, either in the transformer unit or in/near the connection box in the RV where the external 12 volt power is fed in. (There may also be some 120 volt AC receptacles that may be fed directly by the land line feed when the RV is at a campsite, or by a 12 volt DC to 120 volt AC converter aka inverter when the RV is on the road.)

Transformers do not work on DC. The rectifier will therefore never be on the 120 volt primary side.


----------



## kbsparky (Sep 11, 2008)

The Mailbu rep does not know what he is talking about. Those timer/transformers have AC output. Use a bridge rectifier and a nice sized capacitor and make your own DC output. 

I did exactly that on a job where they wanted blue LED's lining some plate glass panels in an outdoor railing. Worked like a charm.


----------



## AllanJ (Nov 24, 2007)

Do they make bridge rectifier modules with input terminals and output terminals and with everything including filter capacitors hidden inside and with wattage/voltage stamped on a nameplate?

Or do you have to go to Radio Shack and buy a soldering gun and need electronic engineering experience?


----------



## Yoyizit (Jul 11, 2008)

AllanJ said:


> Do they make bridge rectifier modules with input terminals and output terminals and with everything including filter capacitors hidden inside and with wattage/voltage stamped on a nameplate?


Sizing a filter cap is pretty involved. 
Bridges will have the amps and PIV and maybe the thermal resistance listed so you can properly size a heat sink for it.


----------



## johnr9q (Apr 30, 2010)

I found on the label of the transformer that the transformer output is definately 12 VAC and also the pump requires 12 VAC so that is the reason why I wasn't getting a reading on my volt meter and probably the reason why the remote control won't work (the remote control won't work on my car battery now so I may have burnt it up?). The relays http://www.radioshack.com/product/index.jsp?productId=3020762 and the remote control http://www.logisyscomputer.com/viewsku.asp?SKUID=RM04&DID=REMOTE both require 12 VDC so I was wondering if I could use a small rectifier just large enough to operate the remote control and the control side of the relay with 12 VDC power. For the schematic for the relay see the schematic under SPST in the following: http://www.therangerstation.com/tech_library/relays.html Could I operate the coil side of the relay with this rectified 12 VDC (terminals 85 and 86) and the higher current side of the relay (terminals 30 and 85) could pass 12 VAC power directly from the 12VAC transformer? I'm an amature at this so any help I appreciate.


----------



## Yoyizit (Jul 11, 2008)

johnr9q said:


> (the remote control won't work on my car battery now so I may have burnt it up?).
> *Probably. And if the DC relays have transient suppression diodes inside they are probably clobbered.
> *


The DC value of full wave rectified AC is about equal to the AC RMS value [12 vac], but the relay will probably buzz on unfiltered DC. 
If you filter it with a capacitor the DC value will rise, so then you need a dropping resistor whose value depends on the coil current.

Paper calc's will get you close but you will still need to cut and try.


----------



## kennzz05 (Nov 11, 2008)

damn wouldnt it just be easier to control the high voltage to activate the transformer?? 
4 words, (clap on,clap off) that is all...


----------



## johnr9q (Apr 30, 2010)

kennzz05 said:


> damn wouldnt it just be easier to control the high voltage to activate the transformer??
> 4 words, (clap on,clap off) that is all...


Ken: The only problem is I want to have 2 channels, one for the lights and one for the pump.


----------



## johnr9q (Apr 30, 2010)

Yoyizit said:


> The DC value of full wave rectified AC is about equal to the AC RMS value [12 vac], but the relay will probably buzz on unfiltered DC.
> If you filter it with a capacitor the DC value will rise, so then you need a dropping resistor whose value depends on the coil current.
> 
> Paper calc's will get you close but you will still need to cut and try.


Yoyizit: I have no idea what you are talking about.


----------



## Yoyizit (Jul 11, 2008)

johnr9q said:


> Yoyizit: I have no idea what you are talking about.


That's why stuff burned out. You are in over your head.

The 200 w 'former puts out 12vac which is probably compatible with your pump and lights, because they work with it. Evidently the pump and lights draw less than 200w/12v = 17A.

The remote you pick can be powered either on 120vac or 12vac, or on DC if you get a wall 'former that takes in 120vac and puts out a compatible DC voltage. I don't recommend the wall 'former route.

Then, the remote can control the 120vac side of the 200 w 'former or the 12vac side, depending on what remote you get. Some remotes can only control DC.

Price out a few candidates - they'll probably be some clear winners.

Remotes that run on DC should be cheaper because they don't need an internal supply to convert 120vac into usable voltages. The hidden cost of ownership pops up when the buyer realizes the problems with supplying DC to the thing.


----------



## kennzz05 (Nov 11, 2008)

johnr9q said:


> Ken: The only problem is I want to have 2 channels, one for the lights and one for the pump.


 
purchase a second transformer so lights and pump are seperate


----------

