Need Some Help Calculating Voltage Drop For A 220 Foot Run With Multiple Branches Off
I am trying to do the math as far as voltage drop. I am trying to control about 12 strikes all from the same relay (all will be locked or unlocked at the same time). The strikes are all on doors that are along a hallway that is about 220 feet long. The plan is to run one main wire down the hallway, and branch off by each door. Is an 18/2 wire a thick enough gauge for the main wire? I would have a 22/2 going for each branch?
I can use 12vdc or 24vac. Would one work better?
Thank you
The higher the voltage the less voltage drop. In order for me to calculate this I need to know the amperage rating of the strikes being used. I can almost guarantee you that 18/2 will not be enough for 12 strikes. A typical strike at 24VAC/VDC and 250mA with that distance would require 12awg wire. HES says anything lower than 21VAC/VDC is a low voltage condition which reduces the life of the strike and will also cause overheating and other issues.
24VAC/VDC @ 220 feet with a load of 250mA * 12 = 3 Amps using 12awg wire
Voltage drop: 2.10V
Voltage drop percentage: 8.75%
Voltage at the end: 21.9V
If I understand things right, you want a single relay to simultaneously trip strikes on 12 different doors along a 220 foot run? So the strikes are connected in parallel?
Before considering voltage drop, do you have current worked out?
Which strikes are you using? Which relay? Which power supply?
Give this a try. Fill in all of the data (it can be obtained from the specs on your locks and power supply) then just hit the calculate key. The resulting voltage will be displayed for you.
I would recommend an RB5 relay or as many as you need. They are flexible, durable and I believe they can take 5amps each.
So, if the runs are all parallel and spaced evenly by 20 feet (for arguments sake), the voltage drop is considerably less than a single loop.
The distance is offset partially by the drop off in current.
Assuming again that the first strike is at the relay (only because it makes the distances an even 20 ft.)
With 18AWG here are some vdrops at the different strikes.
 1800ma
 1650ma @ 20ft
 1500ma @ 40ft = 23.23V
 1350ma @ 60ft
 1200ma @ 80ft
 1050ma @ 100ft
 900ma @ 120ft = 22.62V
 750ma @ 140ft
 600ma @ 160ft
 450ma @ 180ft
 300ma @ 200ft
 150ma @ 220ft = 23.58V
Again, just showing the general effect, don't know what your actual distances between strikes are.
IMHO.
Don't forget to include 'inrush current' in your calculations. A strike is a motor after all. You will have to heavily suppress the relay and strike ends to avoid horrendous noise. This does not sound like something I would entertain.
This is much like calculating voltage drop for fire alarm notification circuits.
You need to understand the holding current of the strikes and the inrush current. Start by calculating the voltage drop of all devices from the relay to the door. You can use 12VDC or 24VAC for the calculations. If your starting voltage is 24v and your drop is 2 volts at the first strike, start with 22v and reduce by that strike. Each leg needs to be calculated.
My practical experience would say this isn't going to work due to holding current, inrush current.
There are programs that help calculate this.
So on the data sheet for this particular strike no inrush current is called out. It says only "current draw".
The inrush current for the Secoalarm strike is the same as the hold. It's DCsolenoid.
With that in mind, and with the addition of MOV diodes at every branch, can anyone say why they don't think the 18/2 solution will work?
I have completed the remaining vdrops on each branch below, notice how they are symmetrical values to the max. sag at 22.62 at the midway.
 1800ma
 1650ma @ 20ft = 23.58V
 1500ma @ 40ft = 23.23V
 1350ma @ 60ft = 22.97V
 1200ma @ 80ft = 22.77V
 1050ma @ 100ft = 22.66V
 900ma @ 120ft = 22.62V
 750ma @ 140ft = 22.66V
 600ma @ 160ft = 22.77V
 450ma @ 180ft = 22.97V
 300ma @ 200ft = 23.23V
 150ma @ 220ft = 23.58V
There's no way the voltage can go up even if you eliminate all devices after #6.
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