700m run to electric gate

[PaulD]

I've got a 700m run to an electric gate and been advised by the gate company they need 6 amps and to run a 6mm armoured 3 core cable.

 

Obviously cost of this cable length is £££, could I run 6mm for say 400m and then 2.5mm for the final 300m to reduce cost ?

 

Yes I know this is probably a question for an electrician but any advice would be welcome.

 

[TonyT]

You will probably need 25mm2 to allow for the volt drop..

[PeterW]

Ask them for the spec on the gates and ask if they do a battery backup version. I’ve seen this before and you basically run a 1A battery charger on the gates (or even solar) and then use the batteries for the grunt as they only need the power to open and close. 
 

Lots of farm gates have similar setups due to exactly this reason. 

[Ajn]

6A is a one HP motor. It must be a big gate. As has been stated the problem is voltage drop and the reguired start current if it is a 1hp motor.

25mm cable is goingto be very very expensive.

 

Thing is, if the gate company is any good they should be aware of all this.

 

 

 

[PaulD]

@PeterW ... great advice thank you .... yes I've seen solar solutions for remote farm gates ... that might be a consideration ... guess it depends how the figures stack up. What cable would be required for a 1 Amp trickle charge I wonder over 700m ?

[Radian]

Vdrop=I * R so from these tables

 

Resistance per metre of copper conductors at 20°C

Conductor cross-sectional area (mm²)	Resistance per metre run (m ohms / m)
2.5	7.41
4.0	4.61
6.0	3.08

 

for 2.5mm2 cable the round trip would present a resistance of 1.4*7.41 = 10.37 Ohms and a therefore a volt-drop of 6*10.37 = 62.24V

ditto 4.0mm2:  1.4*4.61 = 6.45 Ohms and a therefore a volt-drop of 6*10.37 = 38.72V

ditto 6.0mm2:  1.4*3.08 = 4.31 Ohms and a therefore a volt-drop of 6*4.31 = 25.87V

 

Starting current will probably be the issue. They seem to be happy with something in the region of 200V to get the motor started but you might be able to get them to tell you the minimum voltage.

 

You should be able to see that for a 1A charger on 2.5mm2 you'd get a volt drop of 10.37V which would be fine for a battery charger.

[JohnMo]

Solar powered?

[Ajn]

  On 27/02/2022 at 19:36, PaulD said:

1 Amp trickle charge

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You need a lot more information from them. e.g. is that 1A at 240v (10A at 24v) or 1A into the battery which requires a lot less.

 

Also where you run the cable has a lot to do with the load you can put on it i.e in the air, on a fence or underground. This is because the loss in the cable results in heat.

You would also need a local earth at the gate. Even if the supply is PME most distribution network operators (DNOs) do not allow the export of an earth.

[PeterW]

These are standard off the shelf items on every major manufacturers list - it’s rare for any of the motors now to be 230v, the majority are 24v and have transformers in the control boxes. And at 700m from source I am a bit surprised they have requested a mains supply. 
 

@PaulD how are you controlling the opening from the property ..? 700m is too far for CAT5, is this being done by GPRS ..?

[Temp]

  On 27/02/2022 at 19:47, JohnMo said:

Solar powered?

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+1

Google suggests there are several companies selling solar powered gate systems for farm entrances. 

[joe90]

I have a neighbour with solar powered gates and SIM card controlled.

[Radian]

  On 27/02/2022 at 20:22, joe90 said:

I have a neighbour with solar powered gates and SIM card controlled.

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Too bad 3G about to be switched off ?

LoRa is supposed to be workable to 10km (in ideal conditions) - that would be my preferred communication system.

Even if the motor is 240V it could be powered by a 24V inverter connected to a 24V LifePo4 battery + charge controller + 250Wp PV module. Probably costing less than the drum of SWA.

Edited February 27, 2022 by Radian

[Temp]

WiFi with directional aerials both ends should work. If not companies make dedicated point to point links for 1km, 3km etc. Think they would be around  £150.

 

I don't think ethernet over the mains will go that far but might be worth trying if you already had the kit.

 

[PaulD]

Thank you everyone for the comments and replies. I've decided to go off grid with a solar/battery powered gate and 4G intercom/camera. Thanks again !