View Full Version : I need some elec help

01-08-2012, 05:33 PM
I have several sets of small candy canes. Each set has 10 canes and each cane has 5 mini lamps in them. I want to seperate them so I can control them individually. How do I figure out what resistance I need to add to the cut down string of 5 lamps to keep them from blowing out as soon as I power them up?

01-08-2012, 05:58 PM
Without having your system, it is hard to say.

Do you know what the voltage is driving 5 mini lamps? Take that voltage and divide by 5.
then you need to know how much current the 5-string draws.

Finally, you need to know the power supply you are going to use for the individual lamps. Now we can start calculating the resistance values and their power rating for individual operation.

How will you control each lamp?

The mini lamps I use are of the 2.5V @170ma variety - taken from a 50 or 100 lamp string.
I've heard of the 3.5V variety also, but don't know their current rating.

01-08-2012, 07:15 PM
Have you considered converting them to rope light? Incan rope light can be cut to very short lenghts (12", 18") depending on where you get it. Might make your task a little easier...........

01-08-2012, 07:31 PM
Re-reading your post, I could have misunderstood your question. Are your 10 canes tied together such that there is only one plug for all 10 canes? This then suggests that your mini-lights are 2.5V variety, so 50 per set, a common occurance.

Once you cut them such that you have 10 canes, each with 5 mini-lights, you would need at least a 12V supply (2.5V X 5 = 12.5V). In this case you may not need a resistor. You don't want to re-connect each cane to 120AC via a power resistor, but either use a 12VDC, or a 12VAC power supply. You should not exceed 200ma of current through a lamp or you will shorted the lamp life.

What do you plan to drive each with?

01-08-2012, 07:51 PM
I want to run them with a Ren64 and ssr's with each 5 light cane on a seperate channel. I checked the cord and the entire 50 lamp set is rated at 20.4 watts and .17amps.

01-08-2012, 08:16 PM
Yes, it is possible.
Each cane can be cut separately, as I mentioned before, and the voltage must be limited to 12.5V with the current limited to .17amps, for each cane.

Do you know if a Renard has a 12Volt system?
When you say "SSR", does that imply 120VAC only?

01-08-2012, 08:30 PM
I'm new to all of this and do not have the Renard or the solid state relays yet but I believe I can run 12 volts ac to each channel on the SSR and the Renard will just switch them on and off. If this is correct then this sounds like the best option. I have 3 sets or 30 canes so I should be able to power them all with one 12 vac 1 amp transformer?

01-08-2012, 08:44 PM
If you run your SSRs at 12VAC you need to replace the 180 ohm resistors with 22 ohm resistors. Read this thread (http://doityourselfchristmas.com/forums/showthread.php?145-SSR-TRIAC-Gate-Resistor-values) for more info


01-08-2012, 09:00 PM
If you run your SSRs at 12VAC you need to replace the 180 ohm resistors with 22 ohm resistors. Read this thread (http://doityourselfchristmas.com/forums/showthread.php?145-SSR-TRIAC-Gate-Resistor-values) for more info


Wow! That's some really old, really useful info! Thank's!

01-08-2012, 09:41 PM
No, not 1 amp.

Recall that each cane uses .17amps fully ON and you have 30 canes.
You also don't run a transformer at maximum current as it will heat up too much.
I would run a transformer at 75% of its maximum rating. Just a safety factor. You may choose something else.

So, .17amps X 30 canes X 1.25safety factor = 6.4amp transformer at 12VAC. 6.3 amp may be available. e.g MOUSER 553-VPS12-6300.

If you can assure that not all canes will be fully lit for long then you can relax the transformer current rating proportionally.

01-08-2012, 09:50 PM
Thank You all for the help. Lots of good info. Now I just have to get my boards built so I can play.