Useing an 08M and SSR to dim a light?

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RogerTango

Senior Member
Well, I got my 4pc of Solid State Relays in. I have no problems at all using it to cut on or off a 40w incandescent bulb (high 2 and low 2). I would however, like to be able to dim the bulb to specified values.

Ive been trying PWM and PWMOUT and the best I can get is a flickering bulb.

My intent it to do a Christmas light show with varying degrees of brightness, and Ill be using Xmax lights instead of an incandescent bulb of course.

I am not sure if Im doing this right or not.

I know Im too late to get something working for this year, the target date is next Xmas, 2009. ;)

Help?

Thanks!
Andrew
 
A

Andrew Cowan

Senior Member
You could try using a digital pot. However, as one leg is usually tied to 0V, this may not be possible.

Have a look on Maxim.

A
 
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BeanieBots

Moderator
I doubt you'll be able to find a digital POT that can take mains across it. Most are only good for 5v, some go as far as 18v.
That circuit uses phase angle firing. Not possible with a zero crossing SSR.
If it's for Xmas lights, your best bet is to use low voltage DC and use PWM control via a FET. A lot safer too.
 
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RogerTango

Senior Member
Which FET would you suggest?

Ive got some experience using MOSFETs with DC sources, though Ive never done any PWM with it.

This thing is taking another wicket turn that I am working on understanding, please bear with me.

Thanks,
Andrew
 
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BeanieBots

Moderator
That would depend on what voltage and what current you want to run at.
Also, easier to use logic level FETs with PICAXE unless you have and/or know how to build a driver for them.
 
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RogerTango

Senior Member
Yes, a LL FET would be the prime choice.

I am seeking knowledge on this point: I use MOSFETs to switch DC loads presently, and you are suggesting to use an FET to switch AC loads. Correct?

Thanks-
Andrew
 
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BeanieBots

Moderator
FETs can only switch DC.
It's possible to make one switch AC by using a full-bridge rectifier but unless you give VA values, impossible to comment to any suitability.

I was suggesting to use a low voltage DC supply and PWM that but I'd still need to know voltage and current before I could advise further.
Personally, I'd use a IRF520 as that is already available on the PICAXE project board. It's good for 9A up to 100v.
Many Xmas lights are either 12v or 24v.

High voltage/current FETs require 'proper' drivers.
http://www.zetex.com/3.0/appnotes/apps/an18.pdf

The IRF520 can 'get away' with a lot less.
 
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hippy

hippy

Ex-Staff (retired)
Any mains lamp dimming is going to need synchronising to the mains itself, determining when the zero crossover point is.
 
R

RogerTango

Senior Member
BeanieBots said:
Many Xmas lights are either 12v or 24v.
Click to expand...
Im talking about the ones that have little filament bulbs and plug directly into 110v mains (USA). AFAIK, there 110v, but I dont know the science behind them!

I suspect I need to take a bulb out and see what the voltage is across the connectors, aye?

So, you say supply the bulbs with 12v or 24v DC?

Thanks-
Andrew
 
premelec

premelec

Senior Member
I have made PIC controlled xmas lights - two ways worked well for me - one was using a Velleman DC controlled dimmer and using filtered PWM to drive it [them - it was 4 channels] .

The second method was to use a D/A converter [8ch] controlled by a PICAXE 08M which then feeds an op amp comparator which drives an optoisolator into a triac... the trick here is using a 120 Hz sawtooth ramp on the input of the comparator which has the PICAXE D/A derived voltage on the other input so it fires the triac at a particular phase of the AC cycle.

I'm shortly converting to LED light strings which will have current controlled feedback from the D/A converter [DC supply to 8ch of LED lights] to regulate the light string current. The control element is a MOSFET driven from an op amp [LM324] with a series resistor from the drain of the MOSFET to V- that goes from 0 to .3 volts. Note this uses an isolated DC 160 volt supply [using one winding of a 120/240 volt transformer primary to isolate the DC from line]. Also I've found that some of the LED light strings have half one polarity and half the other so the string draws on both + & - AC cycle - I cut the strings at the half way joint and reconnected 'em so that one polarity drives the whole string for DC use...

Hope these comments are of help... I've tried a variety of stuff over the years... :)
 
W

westaust55

Moderator
RogerTango said:
Im talking about the ones that have little filament bulbs and plug directly into 110v mains (USA). AFAIK, there 110v, but I dont know the science behind them!

I suspect I need to take a bulb out and see what the voltage is across the connectors, aye?

So, you say supply the bulbs with 12v or 24v DC?

Thanks-
Andrew
Click to expand...


There are different arrangements of Xmas lights.

Some have a plugpack (wall wart) and drop the voltage to say 12 or 24V and all the lights are then in parallel. The type of Xmas lights that can also play tunes usually have these low voltage lights - which is much safer to handle.

Those that operate directly off the 110Vac or 240Vac often have all the lights in series. If one light fails then all the lights are out. Safety issues here as removing the failed lamp has 110 or 240Vac across the lamp holder. Even if some metal foil tinsel gets into the socket they can be dangerous.

I would recommend working with a set of low voltage lights. Simpler and safer.
 
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RogerTango

Senior Member
Thank you all!

This video is "sort of" something Id like to do:
http://www.youtube.com/watch?v=nD8_7c36yfw

Cant get much cheaper than this for simple ON and OFF states:
http://www.allelectronics.com/make-a-store/item/SRLY-19/1A-SOLID-STATE-RELAY-3-8VDC-CONTROL/-/1.html

Using a 08M, I will be trying to send serial data to a control box, each 08M has its own "serial number" that will only accept the ON and OFF state for that particular outlet.

Anyway, like I said, Im too late for this year, I hope to have something decent working by next year.

Still, its never too early to plan, and experiment! This is all a learning lesson for me!

Cheers,
Andrew
 
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BeanieBots

Moderator
Well, I didn't see ANY dimming going on during that video. It was all simple on/off control.
Damn good synch with the music. I'd suspect it used a synch track with the music. These are created manually.

SSR relays would be ideal for such a display but not for the sort which use wall-wart type power units.
Outdoor displays are more often than not, 24V AC types with a large 24v transformer powering the lights in parallel (for safety reasons). Again, controlling such lamps should be done post the transformer using a SSR.
 
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RogerTango

Senior Member
BeanieBots said:
Well, I didn't see ANY dimming going on during that video. It was all simple on/off control.
Damn good synch with the music. I'd suspect it used a synch track with the music. These are created manually.

SSR relays would be ideal for such a display but not for the sort which use wall-wart type power units.
Outdoor displays are more often than not, 24V AC types with a large 24v transformer powering the lights in parallel (for safety reasons). Again, controlling such lamps should be done post the transformer using a SSR.
Click to expand...
Your right sir, in that video it is all on and off.

However, a guy here in Roanoke has a show that does dimming:
http://starcitylights.com/Files/Videos/2008 Christmas Lights.htm
(You will need the Divx player for that)

I was initially interested in being able to also DIM, however... ON and OFF states are going to be 1000 times easier to incorporate!!

Cheers,
Andrew
 
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dennis

Member
Xmas lights in series

westaust55 said:
There are different arrangements of Xmas lights.



"Those that operate directly off the 110Vac or 240Vac often have all the lights in series. If one light fails then all the lights are out. Safety issues here as removing the failed lamp has 110 or 240Vac across the lamp holder. Even if some metal foil tinsel gets into the socket they can be dangerous."

I agree that the series type is potentially more dangerous but failure of a single bulb filament should not black out the whole chain because each bulb contains a shunt. This shunt is just a bit of wire covered with aluminium oxide wrapped across the pair of filament support wires. Normally this shunt only gets subjected to 2.5 volts and the oxide acts as an insulator but on filament burn out it the whole mains voltage of 110 or 220 V appears which is enough to break down the oxide and cause a permanent short.
Click to expand...
 
R

rWAVE

Member
Lights, Music, Christmas and Wind Turbines

Andrew,

This video is "sort of" something Id like to do:
http://www.youtube.com/watch?v=nD8_7c36yfw

For additional ideas, check out Holdman Christmas. The FAQ has some interesting info!

In addition to a spectacular display, the web site talks about why and how with a diy section. He uses Lights-O-Rama controllers and PC-based sequence software for music synchronization (also from LOR).

M E R R Y C H R I S T M A S

Richard
 
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sghioto

Senior Member
RogerTango
Andrew,

One simple way to control and dim the lights by Picaxe is to modify a store bought lamp dimmer. Below is a schematic of a low cost Leviton dimmer that I modified. It's rated 600 watts. The cover was easy to remove to install the photocell - LED assembly across the pot connections as shown. Now you can just PWM the LED as needed to control the lamp. This Leviton dimmer is as basic as it gets. Does not have any RF filtering or suppression as more expensive models. You could just build it I suppose. Leaving the pot in the circuit allows you to control the minimum brightness needed. Remember either way you're dealing with 120vac so be safe.

Steve G.
 

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