Electrical Primer for DIY LED lights

Introduction

As DIY LED is such a great way to get a super efficient cheap grow light it is becoming popular but it requires a certain level of knowledge about electricity to do it safely. This is to make sure you are safe when doing DIY electrical work. (Note: I am not from the US so I will stick to core electrical concepts and stay away from specific local regulations, If a professional from the US wishes to add specifics to this thread please do so) Please remember I do this in my own time and will update and reply to this thread when I can.

Voltage

Voltage is the difference in electric potential between two points. This is the electrical “pressure” that causes current to flow in a circuit. It is measured in Volts, symbol V



Safe voltage levels (Safety extra low voltage)

Voltage levels that below which are considered probably non-lethal (May still hurt) to touch are less than 50V AC and less than 120V DC. Note: I would not recommend touching anything above 24V AC or DC for your safety. You can touch a 9V battery to your tongue and feel the tingling effect of the current flowing through it and thats only 9V REMEMBER ELECTRICITY CAN KILL YOU, BE SAFE



DC voltage (Direct Current)

Has a fixed positive side and negative side the negative is considered 0 Volts and the postive is measuerd against 0 eg 24 Volts DC. The current will only flow in one direction



AC Voltage (Alternating Current)

The volatge will vary between positive and negative following a sine wave usually at 50 or 60 Hz (cycles per second). The voltage measured will be the RMS voltage and the current will change direction with the sine wave hence Alternating Current.

Three phase or multi-phase voltages

I will not cover these unless asked as they are not generally used here except in industrial situations. (may be different in 110V countries)

How to test for voltage

I highly recommend getting a decent Multi-meter and learning how to use it as it could save your life, REMEMBER ELECTRICITY CAN KILL YOU, BE SAFE. A good multi-meter should be marked Class III or Class IV meaning safe to test for high voltage and no they are not expensive, just don't but the cheap one at the local auto store. To test for voltage use your Multi-meters Voltage range, Important: Your multi-meters leads must be in the correct holes. The black lead should be black Common hole. The red lead should be in the hole marked V. If this is wrong and you leads are in the wrong spot then the best thing that will happen is the fuse in your meter will blow, the worst is it will blow up in your face! Important: Be sure to select the correct voltage type AC or DC on your meter, if you test for the wrong type of voltage it will not indicate voltage! REMEMBER ELECTRICITY CAN KILL YOU, BE SAFE

There is usually no need to make disconnections to check voltage. To test connect the meter in parallel (more on this later) and make sure the black common lead is connected to the reference point. For AC this will be the Neutral always test for AC voltage to Neutral. To test for DC voltage always test to the 0V or negative.


To be safe use the prove test prove method to check for voltage.
Check you tester works on a known voltage source of the same type (AC or DC)
Test for voltage if none is detected
Check your meter is still working on the known voltage source of the same type (AC or DC)
This will prove your meter is working and also acts as a good check to make sure your meter is set for the correct voltage.

Safety notes

Ensure all the items and cabling you are using are rated for the voltage you are using, Do not use speaker cable, phone cables etc for power wiring.

Current

Current (Symbol I) is the flow of an electric charge. It is measeaured in Amperes, Symbol A abreviated to amps



To measure current in a circuit your meter needs to be connected in series with the load and you meter switched to the A range. Make sure your black lead is in the common terminal and the red lead is in the A terminal. Do not use the mA setting and terminal on a meter as this is usually fused at around 400 mA not enough for checking LED mA drive current and is generally used for industiral control testing of signals between 4-20 mA.

Current and cable size.

Your cable should be sized according to the amount of curent that is expected to flow through them.



Circuit protection.

Your fuse or circuit breaker should be sized at the maximum current capacity of the cable to protect the cable from overloading. If you have used a cable capable of 10 A but only ever expect to draw 1 A in normal use it is a good idea to lower the the rating of circuit protection to say 2 Amps

More to come when I get time.

Thanks very much for that. Good write up bud. Many LED newbs like myself will benefit from this thread.

Power
Power is measured in watts symbol w, It is the amount of “work” done by the electricity.
Power calculation
Power = Current x Voltage (P=IV) from this we can get I = P/V (current = Power/Voltage) and V=P/I (Voltage = Power/Current)

Efficiency
Efficiency is measured in percentage, example 80% efficiency means for every 100 w used in power you get 80w of actual work and the remaining 20 watts is generally wasted in heat.

Power measurement
You are billed by your power company for the amount of power you use over time measured in kilowatt hours (Kw/h) one kilowatt hour is 1000w of power used for one hour or for eg 100W used for 10 hours.

diggs99 said:

Thanks very much for that. Good write up bud. Many LED newbs like myself will benefit from this thread.

Click to expand...

No problem just trying to make sure people understand what they are getting into and can do so safely

Series circuits
In series circuits lights are "daisy chained" together with the LED drivers positive running to the positive of the first light, out on the negative to the positive of the next light and so on until it returns to the negative of the driver.

Series circuits are used with constant current drivers.
the current through every light will be the same regardless of what lights you have in the circuit. The voltage that the driver puts out will be divided between each light eg for 48V strips with 4 in series the driver will output 192 V but each strip will drop 48V across it to equal 192V (This is assuming all the strips in the circuit are the same, If you wish to vary the strips then this gets more complicated but I will keep it simple for now)
If the driver is a 500 mA driver then the combined lights output will be 192V X 0.5A = 96w

Parallel circuits
In a parallel circuit all the positives and all the negatives are connected together. The voltage that the LED driver puts out is applied to all the LED's but the current is split between them

Parallel circuits are used with constant Voltage drivers.
If all the lights are the same then the current will be divide equally between them. Eg with 3 x 48 volt strips that draw 1A the total current draw will be 3A for a total power of 3 x 48 = 144w

Thanks for taking the time to wright this up and share!