# Calculating voltages in circuits

Discussion in 'General Electronics Chat' started by steveparrott, Feb 14, 2006.

1. ### steveparrott Thread Starter Active Member

Feb 14, 2006
36
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I'm trying to nail down predictive voltage equations for three types of circuits used in low voltage outdoor lighting. I'm using this info for an article to be published in landscaping magazines.

They are :

1. The daisy chain method (lighting fixtures spliced at intervals along a single wire with one end connected to the power supply),

2. The daisy loop method (lighting fixtures spliced at intervals along a single wire with both ends connected to the power supply),

3. The t-loop method (lighting fixtures spliced at intervals along a single wire with both ends connected to a wire running to the power supply)

Knowing the output voltage of the transformer (12V), the resistance/ft of the wire, the distances of the wire runs between splice points and the wattages of each fixture  I'm trying to determine the voltage at each fixture lamp.

Please understand that I'm not doing this for profit, so don't think I'm trying to get something for nothing. My invitation is for someone who sees this as a fun challenge and as a way to help improve how landscape lighting installers wire their projects.

Also, if someone could get these equations rights and put them into an excel worksheet, I'd be willing to pay for that.

Thanks.

2. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
I suspect that no one (including me) understands your terminology (daisy chain, daisy loop, t-loop). These are not terms we use in electronics.
Another problem is that lamp resistance varies as a function of voltage, because of the temperature coefficient of the filament, so exact predictions will be impossible (for me, anyway).
Can you post some sketches of the topologies?

3. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,403
1,227
Steve,

RonH is correct.

My interpetation of what you said is attached.

4. ### Spoggles Well-Known Member

Dec 2, 2005
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Sounds to me a lot like class A, B and "T" tapping as in fire alarm and security system wiring.

http://www.systemsensor.com/voltdrop/index.html

There is an explanation and caculator at the above link.

"T" tapping is something to be avoided in supervised wiring , but I suppose it would be somewhat like a "branch" circuit in the electrical world.

Spoggles

5. ### steveparrott Thread Starter Active Member

Feb 14, 2006
36
0
Thanks, you're correct with the daisy and daisy loop. For the t-loop, image a pearl necklass (with five pearls), then image a wire run connected to the necklass string at any point.

By the way, I've created a calculator for what's called the hub or spider-splice method (wire run from transformer to a splice point  from the splice point are a number of fixture connected with equadistant wires. http://www.cast-lighting.com/volt-calc.html