Reducing Voltage Drop over distance

[Stese]

Hi all,

I'm really just after an understanding check here. For my project (Model Railway in the garden), to prevent me having to run 240v all around the garden, i'm planning on putting the 240v/220v to 12v transformers in a shed, keeping the dangerous stuff out of the weather.

I want to minimise the voltage drop over the distance, so i've been investigating what cables I have.

According to https://en.wikipedia.org/wiki/Voltage_drop the simplest way to reduce voltage drop is to increase the size of the conductor.

The standard wire I use is 7/0.2mm. I also have 16/0.2mm and some single core .5mm.

Its my understanding that simply increasing the number of strands of the same size, (for instance using the 16/0.2 rather than the 7/0.2) won't decrease the voltage drop, but using the single core .5mm will have a lower drop. I believe this is because the 0.2 has the same resistance for the same length regardless of the number of strands.

The 7/0.2mm and the single core .5mm have roughly the same diameter overall.

Am I correct in my thinking the the single core .5mm is superior in terms of voltage drop, or should I use the 16/0.2mm for 'best performance'?

N.b. I don't want to add additional circuitry to boost the voltage etc, as I'd prefer to keep it simple.

TIA,

Steve

 

[ramussons]

I believe this is because the 0.2 has the same resistance for the same length regardless of the number of strands.

No, your belief is wrong.

Each of the 0.2 has the same resistance for the same length. So, if you increase the number of strands, the overall resistance will drop proportionately.
A 16 strand wire will have Half the Resistance of a 8 strand for the same Length and strand size.

 

[WHONOES]

The best way to reduce the voltage drop is to use the thickest wire that you can something like 32/0.2 or 2 lengths of 16/0.2. As well as that, put in a second set of power supply wires from the same source halfway round you track layout. This would essentially be the same as the ring main in your house.

 

[Bluejets]

Hi all,

I'm really just after an understanding check here. For my project (Model Railway in the garden), to prevent me having to run 240v all around the garden, i'm planning on putting the 240v/220v to 12v transformers in a shed, keeping the dangerous stuff out of the weather.

I want to minimise the voltage drop over the distance, so i've been investigating what cables I have.

According to https://en.wikipedia.org/wiki/Voltage_drop the simplest way to reduce voltage drop is to increase the size of the conductor.

The standard wire I use is 7/0.2mm. I also have 16/0.2mm and some single core .5mm.

Its my understanding that simply increasing the number of strands of the same size, (for instance using the 16/0.2 rather than the 7/0.2) won't decrease the voltage drop, but using the single core .5mm will have a lower drop. I believe this is because the 0.2 has the same resistance for the same length regardless of the number of strands.

The 7/0.2mm and the single core .5mm have roughly the same diameter overall.

Am I correct in my thinking the the single core .5mm is superior in terms of voltage drop, or should I use the 16/0.2mm for 'best performance'?

N.b. I don't want to add additional circuitry to boost the voltage etc, as I'd prefer to keep it simple.

TIA,

Steve

The correct place to start is how much maximum current will be drawn and go from there.

 

[hevans1944]

The correct place to start is how much maximum current will be drawn and go from there.

...And how much voltage drop can your electric train engine tolerate under load? Current and voltage drop are related, and both should be considered.

In smaller (indoor) track layouts, it is not uncommon to have multiple electrical connections to the rails at fairly frequent intervals, often as short as a meter or so, because of intervening disconnects such as turnouts and stuff like that. Your garden railroad is probably going to be just a circle or oval of track, so multiple electrical connections may be unnecessary.

Perhaps you can run the train engine from a lead-acid car battery (or two) to determine current requirements. Then a simple Ohm's Law calculation will reveal the voltage drop you can expect. You could also "jury rig" some nichrome "cone heaters" to simulate the wire losses before purchasing expensive copper wire:



These are still available from sellers on eBay as "New Old Stock" or NOS, but they are probably considered fire hazards (they certainly are!) and unavailable off-the-shelf today. If you do decide to use them, be aware that nichrome wire has a large positive temperature coefficient of resistance... it's resistance increases as it gets hot. In it's original application at the turn of the 20th Century, these heaters operated at 120 VAC or (sometimes) at 240 VAC and became red-hot incandescent to become effective infrared radiant heaters. They did need ceramic, Edison-base, light sockets for this type of operation, but those are still available, mainly for outdoor use. At 12 or 24 VDC these should perhaps become slightly warm, but measure the voltage drop across one, as well as the current through one, to determine the "hot" resistance. Wait a few minutes for the nichrome temperature to stop increasing after applying power before taking any measurements. One, or a few of these in series/parallel combinations, should be enough to simulate your wire resistance to see what effect (if any) your wire resistance will have on train engine motor performance.

 

[WHONOES]

Should be able to calculate the volt drop from the wire's resistance. See link below for chart giving resistance per foot for various gauges. Then ohm's law comes into play.

http://www.devicecraft.com/ApplicationNotes/WireResistanceTable.pdf

 

[Bluejets]

..And how much voltage drop can your electric train engine tolerate under load? Current and voltage drop are related, and both should be considered.

Usual is 5%.....

 

[wingnut]

Hi all,

I'm really just after an understanding check here. For my project (Model Railway in the garden), to prevent me having to run 240v all around the garden, i'm planning on putting the 240v/220v to 12v transformers in a shed, keeping the dangerous stuff out of the weather.

I want to minimise the voltage drop over the distance, so i've been investigating what cables I have.

Steve

Or put a 240/220V to 14/15V transformer in the shed and it will lose a volt or two in transit to the shed.

 

[WHONOES]

You really do need to measure the maximum load in Amps presented by the trains at 12V. You will need to do it with all the trains that could be running at the same time. You can measure them one at a time pulling what ever load you expect. A cheap DMM would do the job. Then we can go from there.

 

[Bluejets]

Or put a 240/220V to 14/15V transformer in the shed and it will lose a volt or two in transit to the shed.

Possibly but that is entirely dependant on cable size and loading as Whones says and what we have been saying all along.

 

[wingnut]

Hi again Stese

I think you should run 220V to your shed. You are going to want to play with your trains at night, run power tools, entertain at night, maybe have wifi, boil a kettle etc. Its no biggie to buy 20mm PVC conduiting and twin-and-earth and run 220V to a shed and be as safe as anything. That is what I have done with my shed in the garden and never regretted having power for outside lights, inside lights in the shed, wifi, power tools etc.

 

[Bluejets]

Hi again Stese

I think you should run 220V to your shed. You are going to want to play with your trains at night, run power tools, entertain at night, maybe have wifi, boil a kettle etc. Its no biggie to buy 20mm PVC conduiting and twin-and-earth and run 220V to a shed and be as safe as anything. That is what I have done with my shed in the garden and never regretted having power for outside lights, inside lights in the shed, wifi, power tools etc.

Like that is going to solve the low voltage drop around the tracks how..??
Aside from that, it might be ok where you are, but many places, running mains cabling requires licencing of one kind or another.
Part of the licencing requires the knowledge that you apparently lack.

 

[wingnut]

Like that is going to solve the low voltage drop around the tracks how..??
Aside from that, it might be ok where you are, but many places, running mains cabling requires licencing of one kind or another.
Part of the licencing requires the knowledge that you apparently lack.

This is how we do it where I live. You climb the nearest pole with a pliers and a piece of wire you found lying next to the railroad track.

Stese is worried about the V drop to his shed. His trains have functioned perfectly well till now once he has 220 V.

 

[shrtrnd]

...And how much voltage drop can your electric train engine tolerate under load? Current and voltage drop are related, and both should be considered.

In smaller (indoor) track layouts, it is not uncommon to have multiple electrical connections to the rails at fairly frequent intervals, often as short as a meter or so, because of intervening disconnects such as turnouts and stuff like that. Your garden railroad is probably going to be just a circle or oval of track, so multiple electrical connections may be unnecessary.

Perhaps you can run the train engine from a lead-acid car battery (or two) to determine current requirements. Then a simple Ohm's Law calculation will reveal the voltage drop you can expect. You could also "jury rig" some nichrome "cone heaters" to simulate the wire losses before purchasing expensive copper wire:

View attachment 49164

These are still available from sellers on eBay as "New Old Stock" or NOS, but they are probably considered fire hazards (they certainly are!) and unavailable off-the-shelf today. If you do decide to use them, be aware that nichrome wire has a large positive temperature coefficient of resistance... it's resistance increases as it gets hot. In it's original application at the turn of the 20th Century, these heaters operated at 120 VAC or (sometimes) at 240 VAC and became red-hot incandescent to become effective infrared radiant heaters. They did need ceramic, Edison-base, light sockets for this type of operation, but those are still available, mainly for outdoor use. At 12 or 24 VDC these should perhaps become slightly warm, but measure the voltage drop across one, as well as the current through one, to determine the "hot" resistance. Wait a few minutes for the nichrome temperature to stop increasing after applying power before taking any measurements. One, or a few of these in series/parallel combinations, should be enough to simulate your wire resistance to see what effect (if any) your wire resistance will have on train engine motor performance.

 

[shrtrnd]

I want one of hevans1944's light bulb socket heaters. Never seen one before, haven't got a use for one, but want one.
(Tired of salvaging old toasters to get nichrome wire).
Thanks for the history lesson on those things.

 

[hevans1944]

I want one of hevans1944's light bulb socket heaters. Never seen one before, haven't got a use for one, but want one.
(Tired of salvaging old toasters to get nichrome wire).
Thanks for the history lesson on those things.

I think they are readily available on eBay at exorbitant prices. They might still be manufactured for all I know. Simple coiled nichrome wire (like you find in clothes dryers) wrapped around a tapered ceramic cone with molded grooves to support and separate individual turns around the cone. Pretty easy to make if you still like playing with clay, but the brass hardware might be problematical to find. Maybe salvage the base of a regular Edison-base light bulb?

If all you need is the coiled nichrome wire, that is readily available too, either coiled for use as a heating element or as straight wire. Visit your local appliance repair parts store.

Your local landfill might have an electric dryer you can salvage for some coiled nichrome wire. Use a battery-powered screwdriver/drill to remove the outside frame to gain access to the heating element(s). Wear disposable outer protective clothing with disposable nitrile gloves and a disposable dust mask. Obtain permission from the landfill operator before attempting any salvage.

Used (defunct) hair dryers are also a source of nichrome wire, some coiled, some flat ribbons like you find in toasters. My go-to source for everything thermal is Omega Engineering, although they can be somewhat pricey for hobby purposes. Here is a link to their straight (not coiled) spools of nichrome wire.

 

[hevans1944]

@Stese, in an earlier thread you mentioned an HO-gauge model railroad that would be used outdoors. Is HO the same gauge as your "Garden Railroad" which is the topic of this thread? Just askin'...

This is more like what I had in mind than an HO-gauge outdoor railroad.

 

[WHONOES]

HO gauge is 16.5mm between the rails.

 

[hevans1944]

HO gauge is 16.5mm between the rails.

Which is why I asked what gauge his "Garden Railroad" was. You don't need 4 AWG to energize HO-gauge track if the track is confined to your average backyard garden. "O" gauge (without the center "third rail" Lionel favored) is often used for Garden Railroads, but it is still rather small-ish to be carrying passengers, even small children. Small puppies, maybe, depending on the dog's temperament.