DC wiring help
#1
10-08-15, 04:58 PM
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DC wiring help
I am wiring a mobile home from scratch and running both AC for outlets and DC for lights and fans. I've never installed DC before but have done some research. I'm confused about a few things. In the charts I have seen to determine wire size given amps being pulled on the circuit it shows 2 different answers based on a 3% voltage drop and a 10% voltage drop. Which should I be considering? I have been planning to use 12 volt batteries that are powered by solar panels. The mobile home is 27 feet long. One source tells me the total " run" of the circuit should be calculated distance from panel to light. Another source says it is the round trip run. Which is it? Does the run include the length of wire needed from solar array to panel as well? Most of the lights we are installing pull 3 or so amps each. We wouldn't have more than 6 running at a time which puts us close to 20 amps. The length from panel to the first light is about 15 feet. If we wire multiple lights in series that number would be closer to 25 feet. Should I consider this number the total run or 50 feet?
Furthermore, should I consider hooking the batteries up to make 24 volts? If so, what if my lights run on 12 volts? How would I step it down?
Thank you in advance for your help.
Furthermore, should I consider hooking the batteries up to make 24 volts? If so, what if my lights run on 12 volts? How would I step it down?
Thank you in advance for your help.
#2
10-08-15, 05:12 PM
Group Moderator
Stay with a 12v system.
I don't even use a wiring calculator when I do low voltage wiring. The minimum wiring size you should is #16.
You will be creating series strings of lighting where the lights are wired from one to another but the lights are actually wired in parallel.(+ to + and - to -).
Three 12v incandescent lights on one switch..... use #14.
Don't be afraid to use the next larger size. Always better to be larger than undersized.
I've change many motor home fixtures out to LED. For maximum lighting with the least power used..... consider doing the same. You can then downsize your wiring too.
Even those fluorescent strips they use are power mongers.
I don't even use a wiring calculator when I do low voltage wiring. The minimum wiring size you should is #16.
You will be creating series strings of lighting where the lights are wired from one to another but the lights are actually wired in parallel.(+ to + and - to -).
Three 12v incandescent lights on one switch..... use #14.
Don't be afraid to use the next larger size. Always better to be larger than undersized.
I've change many motor home fixtures out to LED. For maximum lighting with the least power used..... consider doing the same. You can then downsize your wiring too.
Even those fluorescent strips they use are power mongers.
#3
10-08-15, 05:29 PM
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Since I am wiring my AC with 12 gauge, it sounds like 12 gauge for the DC will be sufficient then?
#4
10-10-15, 06:31 AM
Use the round trip distance!
(Some voltage calculators, notably those that refer to "cable length", let you key in the one way distance and they automatically compute for the round trip distance, but check the fine print.)
A fifty foot length of 12 gauge copper conductor will handle about six amps at twelve volts AC or DC with 5% voltage drop which is okay all the way from the solar panels to the fan or light bulb. (Or 12 amps at 10% VD which you can get away with provided that there are no additional VDs or losses such as from solar panel voltage versus load variation on cloudy versus sunny days.)
Three percent VD is a rule of thumb when figuring from the source (e.g. pole tranformer) to the service panel or as a separate calculation from the service panel to the load (light bulb, etc.)
The arithmetic gets more voluminous when you have one feed from the solar panels (or pole traansformer) to the service panel and multiple branch circuits to the loads.
Wire sizing rules for 12 volts are very different compared with for 120 volts.
(Some voltage calculators, notably those that refer to "cable length", let you key in the one way distance and they automatically compute for the round trip distance, but check the fine print.)
A fifty foot length of 12 gauge copper conductor will handle about six amps at twelve volts AC or DC with 5% voltage drop which is okay all the way from the solar panels to the fan or light bulb. (Or 12 amps at 10% VD which you can get away with provided that there are no additional VDs or losses such as from solar panel voltage versus load variation on cloudy versus sunny days.)
Three percent VD is a rule of thumb when figuring from the source (e.g. pole tranformer) to the service panel or as a separate calculation from the service panel to the load (light bulb, etc.)
The arithmetic gets more voluminous when you have one feed from the solar panels (or pole traansformer) to the service panel and multiple branch circuits to the loads.
Wire sizing rules for 12 volts are very different compared with for 120 volts.
Last edited by AllanJ; 10-10-15 at 06:50 AM.
#6
10-10-15, 08:22 AM
Simple answer: Calculate voltage drop from solar panel to most distant light given the full amperage draw.
Example of voluminous answer: Calculate voltage drop from solar panel to control panel for full amperage. Calculate voltage drop from control panel to first light for full amperage. Calculate voltage drop from first light to second light for amperage minus that of first light. Calculate voltage drop from second light to third light minus that of first two lights. Etc. Add up the voltage drops to come up with what the last light will get.
The same number of volts are dropped when a given number of amperes flows through a given piece of wire regardless of the supply voltage. Losing 2 volts out of 12 volts is of course a more major concern compared with losing 2 volts out of 120 volts.
You would not connect two batteries in series to obtain 24 volts unless you wanted to build a 24 volt system, 24 volt solar panels (or 24 volt solar panel configurations), 24 volt solar control panel, and all. Twelve volt ligths can be used in a 24 volt system by configuring the lights in series pairs of identical bulbs. (Hot exposed terminal to one socket tip, jumper from that socket shell to second socket tip, second socket shell to other exposed terminal.)
Example of voluminous answer: Calculate voltage drop from solar panel to control panel for full amperage. Calculate voltage drop from control panel to first light for full amperage. Calculate voltage drop from first light to second light for amperage minus that of first light. Calculate voltage drop from second light to third light minus that of first two lights. Etc. Add up the voltage drops to come up with what the last light will get.
The same number of volts are dropped when a given number of amperes flows through a given piece of wire regardless of the supply voltage. Losing 2 volts out of 12 volts is of course a more major concern compared with losing 2 volts out of 120 volts.
You would not connect two batteries in series to obtain 24 volts unless you wanted to build a 24 volt system, 24 volt solar panels (or 24 volt solar panel configurations), 24 volt solar control panel, and all. Twelve volt ligths can be used in a 24 volt system by configuring the lights in series pairs of identical bulbs. (Hot exposed terminal to one socket tip, jumper from that socket shell to second socket tip, second socket shell to other exposed terminal.)
#7
10-10-15, 01:59 PM
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#8
10-11-15, 05:18 AM
Member
Any reason you need to go ac AND dc?
Stick with one only and there is less wire to run and fewer circuits and less complication. If you use an inverter to go all ac there will be losses at the inverter, but then ac travels longer distances with less loss then dc (it's one of the big reasons our North American power grid is ac instead of dc)
Stick with one only and there is less wire to run and fewer circuits and less complication. If you use an inverter to go all ac there will be losses at the inverter, but then ac travels longer distances with less loss then dc (it's one of the big reasons our North American power grid is ac instead of dc)
#9
10-14-15, 08:00 PM
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Thank you everyone for the help. My client wants to run both DC and AC so she can leave the DC on at night for the fans and turn the AC off since AC gives off more emfs.
