Cable square area, compared to fuse or diode square area
Tony Bev said
02:31 PM Nov 27, 2018
Can someone explain, in layman speak, so that I can understand it, please
We are informed that 12VDC cable should be a minimum of six square millimetres area, and that larger square area is better, for less voltage loss
A normal 12 volt 30 amp blade fuse has a much lower, (never measured it), square area than six millimetres Normally a fuse is close to the batteries, so would incoming/outgoing power, be affected?
A diode of 12/15/20 amps has a wire with a diameter of 1.2 to 1.3 mm, (1.13 to 1.327 square mm) In a normal situation, the diodes are at/near the solar panels. How does this affect the power from the solar panels?
Is the power drop of the fuse/diode negligible, due to the short length?
Edit to say that it is not my intention to start any flame wars, also when I am absolutely sure, that I know the answer, I do not ask the question
-- Edited by Tony Bev on Tuesday 27th of November 2018 02:39:49 PM
Warren-Pat_01 said
05:13 PM Nov 27, 2018
An interesting question, Tony!
I think your 2nd to last statement (Is the power drop of the fuse/diode negligible, due to the short length) is correct & having the fuse close to the battery is mandatory. Telecommunications exchanges' batteries where the load could be over 200A, always had the fuses (generally HRC type) close to the batteries.
I think of it was a unit - "battery, fuse & feed" to the load via cables or busbars. I couldn't guess what a "6sqmm fuse" would be rated at and it certainly wouldn't protect the cable + equipment hanging of it.
Your diodes on the solar panel fall into the same system - the heavy 6mm feed back to the battery(ies) prevent further voltage loss.
My thoughts only - left most of that stuff behind 12.5 years ago now.
Jaahn said
07:01 PM Nov 27, 2018
Hi Tony
Yes an interesting question. All these items introduce a small loss due to the resistance. But the diode wires are short so the loss is low. A higher rated diode has thicker wires so the loss is less. But another necessary loss that is needed for a necessary reason.
The fuse is interesting because the fusible part is thin and has a high resistance and runs so hot it will melt at the rated current, so it does have a measurable loss across it. But that is a price you just have to pay for safety. Be sensible with these items.
If I might compare it to something else, say a muffler on a motor car. Sure they cause a back pressure and resistance losses. Better off without one The young blokes think so, but everyone else accepts them as a necessary loss. Just the same idea.
Jaahn
Tony Bev said
07:31 PM Nov 27, 2018
Thanks for your input, Warren and Jahhn It was appreciated
It does make it a little clearer to me now
I probably tripped over this answer twice, while researching it, but it got lost (to me) in the technical jargon I was reading
Short length of thin (fuse/diode) cable/wire, gives minimal and acceptable loss, but long length of too thin cable/wire, gives enough loss, that we now do not have enough power, to charge battery/run appliances
Aus-Kiwi said
08:18 PM Nov 27, 2018
In some cases the cable used over the length is too large for the protection, connections Often links are fitted ? The issue with 12v over distance ! Its much the same with domestic 240 at times too .
oldtrack123 said
02:04 AM Nov 28, 2018
Tony Bev wrote:
Can someone explain, in layman speak, so that I can understand it, please
[1]We are informed that 12VDC cable should be a minimum of six square millimetres area, and that larger square area is better, for less voltage loss
[2]A normal 12 volt 30 amp blade fuse has a much lower, (never measured it), square area than six millimetres Normally a fuse is close to the batteries, so would incoming/outgoing power, be affected?
[3]A diode of 12/15/20 amps has a wire with a diameter of 1.2 to 1.3 mm, (1.13 to 1.327 square mm) In a normal situation, the diodes are at/near the solar panels. How does this affect the power from the solar panels?
[4]Is the power drop of the fuse/diode negligible, due to the short length?
Edit to say that it is not my intention to start any flame wars, also when I am absolutely sure, that I know the answer, I do not ask the question
-- Edited by Tony Bev on Tuesday 27th of November 2018 02:39:49 PM
Hi Tony
A little more to chew on.
[1] To minimise voltage drop in any cable to acceptable levels for the particular application , a number of factors have to be consider :
[a] max current through the cable.
the total length of cable[ both pos & neg],
From that ,the required cable size to limit the voltage drop to acceptable limits can be calculated
In some cases such as AS3001 "Transportable Structures "a minimum cable cross sectional area & number of strands may be specified. This is more for mechanical reasons cable movement [flexing in normal use] just as with extension leads.
[2] A thermal fuse or thermal circuit breaker must generate some heat in them to operate,
If you look at most 12V blade fuses you will see there is a small section of reduced section in the middle of the fuse That is the section calibrated to blow. It does limit the voltage drop across the fuse quite a bit compared to the small 12V glass fuses .
The length of reduced section when blowing must be long enough gap for the arc to self extinguish .That is a critical condition for all thermal fuses [the higher the voltage the longer the reduced section must be]
The fusing function is not dependent on where it is located in the circuit . It's location should always be as close as possible to the starting point of the positive line it is protecting. & should never have a higher rating than the current rating of the cable it is protecting. Also note All fuses are not the same , they can be fast blow or ,slow blow. even with the small 12V glass fuses depending on what protection is required & the actual load type .
[3]Others have answered the diode question very well so I do not need to comment on that ,except to say the actual size ,cross sectional area ,of the pigtail must be of sufficient current carrying capacity to suit the diode rating .It also serves as a heat transfer for the actual diode junction.
[4] The voltage drop is dependent on the following factor :
The actual current " Amps"
Cross sectional area of the actual conductor .
The total length of the conductor both pos & neg ,or with AC ,Active & neutral
The actual conductor material. [for normal wiring ,usually copper ,but can be aluminium.[with a higher voltage drop for the same current & conductor cross sectional area]
It should not start a flame war unless some who does not understand tries to tell you different,
Just one other comment on fuses
They are not all the same even though they may have the same current & voltage rating , the actual operational requirements will determine the fuse type required but that is not really relevant to the 12V wiring in a van.,
-- Edited by oldtrack123 on Wednesday 28th of November 2018 02:11:34 AM
Tony Bev said
02:43 AM Nov 28, 2018
Thanks for that explanation, Oldtrack123 (Ralph)
It was appreciated
Peter_n_Margaret said
09:56 AM Nov 28, 2018
The formulae for calculating voltage drop in copper cables is .
VOTLAGE DROP = [cable length (in metres) X current (in amps) X 0.0164] divided by cable cross-section in mm.sq.
Cheers,
Peter
Aus-Kiwi said
12:40 PM Nov 28, 2018
Why most domestic house pre meter fuses are incased in sand . Silica . 12v prefer breaker any day .
PeterD said
12:42 PM Nov 28, 2018
Tony Bev wrote:
Normally a fuse is close to the batteries, so would incoming/outgoing power, be affected?
snip
Is the power drop of the fuse/diode negligible, due to the short length?
In any circuit where the conductor varies in size the the voltage drop in volts per millimeter will be related to the size and resistance of the conductor. In radio equipment rooms we needed to run long leads between devices. Often the length of cable means it has to be a large one to limit the voltage drop to an allowable value. The large cable size will not fit the terminals on the battery charger or the device being supplied. In these cases a short piece of smaller wire is used between the heavy one and the terminal. If this piece of wire is short enough then there is only a very small voltage drop along its length and this will not affect the service by a significant amount.
In the case of fuses they are built material of higher resistance. This allows the fuses to build up enough heat to be blown is a short length. It does not matter where the fuse is placed in the circuit, it's effect on voltage drop will be the same. (The importance of a fuse being near a battery is purely to limit the possibility of a short occurring between the fuse and the battery.)
This dissertation was given to demonstrate the answer to your last question in the piece I quoted from your question. You can see how much voltage drop there is across the fuse from the following tables. You can use these fuses to measure the current flowing them. Just use a good digital volt meter, connect the leads to the little pads on the top of the fuse. Cross reference the voltage reading to the table and you can get a reasonably accurate reading of the current flowing through the fuse.
Why most domestic house pre meter fuses are incased in sand . Silica . 12v prefer breaker any day .
Yes . the actual location of the fuse & the possible MAX short circuit current does determine the fuse type ,especially with the higher voltages Ac & especially DC
The type of fuse you refer is technically known as a HRC fuse "High Rupturing capacity". The mineral filling helps quench the arc that is formed when the fuse blows.
The first few months [1945 ]of my apprenticeship was served in a powerhouse @ a dry dock .It supplied shore power either 110V or 220V DC to ships in for repair, The main generator fuses ,200A ,on the main switch board were big long open wire fuses holders
Quite a sight & sound show when one of those blew due to a short circuit in the ship to shore cable,
-- Edited by oldtrack123 on Wednesday 28th of November 2018 03:16:34 PM
T1 Terry said
03:46 PM Nov 28, 2018
With a diode, the junction inside the diode causes more voltage drop that the short piece in and out of the diode. If the circuit doesn't need them than the whole cable run will more efficient without them, but as has been mentioned if they are necessary then it is just one of the losses we have to put up with and add into the calculation. Small conductor size does not stop current flow as such, but the resistance does create heat and that uses up both amps and volts that can not be regained so lost from the total electrical supplied into the cable.
This heat generation is most obvious where blade fuses are used, it is not uncommon to see a fuse rated at greater than 20 amps with the plastic bit actually melted and often the blades welded into the fuse holder. The small piece of actual fusible material is not the cause but rather the poor design causing a high resistance joint between the fuse blades and the fuse holder.
T1 Terry
Tony Bev said
05:13 PM Nov 29, 2018
Peter_n_Margaret wrote:
The formulae for calculating voltage drop in copper cables is . VOTLAGE DROP = [cable length (in metres) X current (in amps) X 0.0164] divided by cable cross-section in mm.sq.
Cheers, Peter
Thanks for that Peter, your input was appreciated
I had read your formula in a different thread, (I think), but at that time, I had not got my (layman) head, around the fact that the main contributor to voltage drop, was the length of the wire
Using your formula, the diode (approximately 30 mm after trimming the ends)
Length 0.03 metres X current (14 amp in good weather) X 0.0164 is less than 7 millivolt (0.00688 volt), and not worth worrying about The normal 30 amp blade fuse, would have an even smaller voltage drop
I now rest easy, as my original idea of placing two diodes in parallel, was to give a greater square area for the current to flow I now feel, from a layman point of view, that having one diode (capable of carrying the current), is better than two smaller diodes
My gut feeling, is that it is possible for two smaller diodes not to be synchronised, and eventually to have interruptions from the solar panel, when one, and then the second diode, shuts down This shutting down of the diodes, (using my own observations), shuts the solar panel down, which in turn allows the diodes to once again turn themselves on, until their maximum amps are reached Also I feel that having two diodes side by side, and one fails in the closed position, it would be the same as having no diode in the circuit
Hopefully I have made sense by saying the above
Tony Bev said
05:17 PM Nov 29, 2018
PeterD wrote:
Tony Bev wrote:
Normally a fuse is close to the batteries, so would incoming/outgoing power, be affected?
snip
Is the power drop of the fuse/diode negligible, due to the short length?
In any circuit where the conductor varies in size the the voltage drop in volts per millimeter will be related to the size and resistance of the conductor. In radio equipment rooms we needed to run long leads between devices. Often the length of cable means it has to be a large one to limit the voltage drop to an allowable value. The large cable size will not fit the terminals on the battery charger or the device being supplied. In these cases a short piece of smaller wire is used between the heavy one and the terminal. If this piece of wire is short enough then there is only a very small voltage drop along its length and this will not affect the service by a significant amount.
In the case of fuses they are built material of higher resistance. This allows the fuses to build up enough heat to be blown is a short length. It does not matter where the fuse is placed in the circuit, it's effect on voltage drop will be the same. (The importance of a fuse being near a battery is purely to limit the possibility of a short occurring between the fuse and the battery.)
This dissertation was given to demonstrate the answer to your last question in the piece I quoted from your question. You can see how much voltage drop there is across the fuse from the following tables. You can use these fuses to measure the current flowing them. Just use a good digital volt meter, connect the leads to the little pads on the top of the fuse. Cross reference the voltage reading to the table and you can get a reasonably accurate reading of the current flowing through the fuse.
Thanks for your input Peter, it was appreciated
Sorry that I did not reply to, Peter n Margaret (Peter), earlier
As I now understand what his formula means
Tony Bev said
05:21 PM Nov 29, 2018
T1 Terry wrote:
With a diode, the junction inside the diode causes more voltage drop that the short piece in and out of the diode. If the circuit doesn't need them than the whole cable run will more efficient without them, but as has been mentioned if they are necessary then it is just one of the losses we have to put up with and add into the calculation. Small conductor size does not stop current flow as such, but the resistance does create heat and that uses up both amps and volts that can not be regained so lost from the total electrical supplied into the cable. This heat generation is most obvious where blade fuses are used, it is not uncommon to see a fuse rated at greater than 20 amps with the plastic bit actually melted and often the blades welded into the fuse holder. The small piece of actual fusible material is not the cause but rather the poor design causing a high resistance joint between the fuse blades and the fuse holder.
T1 Terry
Thanks for your input Terry
Once again, I can only say, sorry that I did not immediately reply to, Peter n Margaret (Peter), as his formula said it all, after I had finally got my head around it
oldtrack123 said
07:39 PM Nov 30, 2018
This link may help members to understand that a fuse does not blow " @ it's rated current.
The speed of blowing is dependent on the actual excess current & fuse type.The same applies to thermal circuit breakers
All have a overload to blow time curve. That does vary with actual type ie if standard ,fast blow or slow blow
-- Edited by oldtrack123 on Friday 30th of November 2018 11:24:55 PM
Tony Bev said
11:05 PM Nov 30, 2018
Very interesting, Ralph
It just goes to show, that I never knew, what I did not know, so thanks for that
Jaahn said
08:58 AM Dec 1, 2018
Tony Bev wrote:
Very interesting, Ralph
It just goes to show, that I never knew, what I did not know, so thanks for that
Hi Tony
To quote a now famous persons speech "There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Precisely
Jaahn
oldtrack123 said
11:54 AM Dec 1, 2018
Jaahn wrote:
Tony Bev wrote:
Very interesting, Ralph
It just goes to show, that I never knew, what I did not know, so thanks for that
Hi Tony To quote a now famous persons speech "There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Precisely
Jaahn
Tony Bev said
02:30 PM Dec 1, 2018
oldtrack123 wrote:
Jaahn wrote:
Tony Bev wrote:
Very interesting, Ralph
It just goes to show, that I never knew, what I did not know, so thanks for that
Hi Tony To quote a now famous persons speech "There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Precisely
Jaahn
I just had to laugh, when I saw the (clap gif) and then realised why it was there
I can assure everyone, that I had no intention of trying to be funny, with my reply
It is good to see, that no matter how serious we can get on this forum, our sense of humour can still shine through
Hopefully no offence was given, as certainly none was taken, by me
Izabarack said
04:16 PM Dec 4, 2018
Tony Bev wrote:
We are informed that 12VDC cable should be a minimum of six square millimetres area, and that larger square area is better, for less voltage loss
A normal 12 volt 30 amp blade fuse has a much lower, (never measured it), square area than six millimetres
Remember too, that advice about 12 DC cable is mostly predicated on the assumption that people will be using high purity copper cable and are concerned to ensure the voltage drop across the cable run is small. In designing a fuse, the material selected for fusible section is chosen with a focus on the temperature at which the material will melt or fuse. The rating of the fuse is determined by how much current is required to raise the temperature of the fuse material to melting point, given the cross sectional area of the fuse. Most fuses do not reach red hot, for example, just before they fuse. Nichrome wire such as used in a toaster, has a high resistance, compared to copper, and maintains its integrity while glowing hot enough to toast the bread. Pure lead melts around the 300 Degree C mark but solder of about 60/40 ratio melts closer to 185 Degrees C. Tungsten wire in a vacuum gets hot enough to emit visible light, without melting.
In the larger picture of things, heavy copper wiring is advised to minimise the voltage drop across the cable run and fuse wire is selected for its properties in regard being suitable for protecting the system against damaging current levels. The voltage drop across a fuse is tolerated because we want fuses for protection and as long as the fuse material is a very short length in relation to the whole cable run, better in than out.
Iza
T1 Terry said
11:49 AM Dec 6, 2018
Great answer Iza. Something to be very careful of is misleading advertising regarding cable size. 6 B&S cable is a min of 13.5mm sq, yet we had one supplier try to pass off 10mm sq conductor cable as 6 B&S. There are quite a few sellers peddling cable that is a mix of aluminium and copper, for the same voltage drop per mtr the cable would need to be a much larger cross sectional area if the conductor wasn't high grade copper.
T1 Terry
oldtrack123 said
07:21 PM Dec 6, 2018
T1 Terry wrote:
Great answer Iza. Something to be very careful of is misleading advertising regarding cable size. 6 B&S cable is a min of 13.5mm sq, yet we had one supplier try to pass off 10mm sq conductor cable as 6 B&S. There are quite a few sellers peddling cable that is a mix of aluminium and copper, for the same voltage drop per mtr the cable would need to be a much larger cross sectional area if the conductor wasn't high grade copper.
T1 Terry
I think the real problem is terminology rather than being deliberately misleading.
Especially if buying from an auto supplier. The thing to remember that auto cable size is based on outside dia & that can be highly variable[in simple words if you ask for 13mm cable you will get cable which is 13mm outside dia & a variable actual copper dia
If you go to an Electrical supplier & ask for 6B&s you will get 6B&S with a copper cross section area of 13.3mm , or simply ask them for 13mm sq cable
Aus-Kiwi said
11:25 AM Dec 25, 2018
Or get real tech and ask for 16x1.35 etc . Amount of strands then the size on mm of each ., We as lineworkers have to go by cable strength for gully jumps etc
Can someone explain, in layman speak, so that I can understand it, please
We are informed that 12VDC cable should be a minimum of six square millimetres area, and that larger square area is better, for less voltage loss
A normal 12 volt 30 amp blade fuse has a much lower, (never measured it), square area than six millimetres
Normally a fuse is close to the batteries, so would incoming/outgoing power, be affected?
A diode of 12/15/20 amps has a wire with a diameter of 1.2 to 1.3 mm, (1.13 to 1.327 square mm)
In a normal situation, the diodes are at/near the solar panels.
How does this affect the power from the solar panels?
Is the power drop of the fuse/diode negligible, due to the short length?
Edit to say that it is not my intention to start any flame wars, also when I am absolutely sure, that I know the answer, I do not ask the question
-- Edited by Tony Bev on Tuesday 27th of November 2018 02:39:49 PM
I think your 2nd to last statement (Is the power drop of the fuse/diode negligible, due to the short length) is correct & having the fuse close to the battery is mandatory. Telecommunications exchanges' batteries where the load could be over 200A, always had the fuses (generally HRC type) close to the batteries.
I think of it was a unit - "battery, fuse & feed" to the load via cables or busbars. I couldn't guess what a "6sqmm fuse" would be rated at and it certainly wouldn't protect the cable + equipment hanging of it.
Your diodes on the solar panel fall into the same system - the heavy 6mm feed back to the battery(ies) prevent further voltage loss.
My thoughts only - left most of that stuff behind 12.5 years ago now.
Hi Tony
Yes an interesting question. All these items introduce a small loss due to the resistance. But the diode wires are short so the loss is low. A higher rated diode has thicker wires so the loss is less. But another necessary loss that is needed for a necessary reason.
The fuse is interesting because the fusible part is thin and has a high resistance and runs so hot it will melt at the rated current, so it does have a measurable loss across it.
But that is a price you just have to pay for safety. Be sensible with these items.
If I might compare it to something else, say a muffler on a motor car. Sure they cause a back pressure and resistance losses. Better off without one
The young blokes think so, but everyone else accepts them as a necessary loss. Just the same idea.
Jaahn
Thanks for your input, Warren and Jahhn
I probably tripped over this answer twice, while researching it, but it got lost (to me) in the technical jargon I was reading 
It was appreciated
It does make it a little clearer to me now
Short length of thin (fuse/diode) cable/wire, gives minimal and acceptable loss, but long length of too thin cable/wire, gives enough loss, that we now do not have enough power, to charge battery/run appliances
Hi Tony
A little more to chew on.
[1] To minimise voltage drop in any cable to acceptable levels for the particular application , a number of factors have to be consider :
[a] max current through the cable.
the total length of cable[ both pos & neg],
From that ,the required cable size to limit the voltage drop to acceptable limits can be calculated
In some cases such as AS3001 "Transportable Structures "a minimum cable cross sectional area & number of strands may be specified. This is more for mechanical reasons cable movement [flexing in normal use] just as with extension leads.
[2] A thermal fuse or thermal circuit breaker must generate some heat in them to operate,
If you look at most 12V blade fuses you will see there is a small section of reduced section in the middle of the fuse That is the section calibrated to blow. It does limit the voltage drop across the fuse quite a bit compared to the small 12V glass fuses .
The length of reduced section when blowing must be long enough gap for the arc to self extinguish .That is a critical condition for all thermal fuses [the higher the voltage the longer the reduced section must be]
The fusing function is not dependent on where it is located in the circuit . It's location should always be as close as possible to the starting point of the positive line it is protecting. & should never have a higher rating than the current rating of the cable it is protecting. Also note All fuses are not the same , they can be fast blow or ,slow blow. even with the small 12V glass fuses depending on what protection is required & the actual load type .
[3]Others have answered the diode question very well so I do not need to comment on that ,except to say the actual size ,cross sectional area ,of the pigtail must be of sufficient current carrying capacity to suit the diode rating .It also serves as a heat transfer for the actual diode junction.
[4] The voltage drop is dependent on the following factor :
The actual current " Amps"
Cross sectional area of the actual conductor .
The total length of the conductor both pos & neg ,or with AC ,Active & neutral
The actual conductor material. [for normal wiring ,usually copper ,but can be aluminium.[with a higher voltage drop for the same current & conductor cross sectional area]
It should not start a flame war unless some who does not understand tries to tell you different,
Just one other comment on fuses
They are not all the same even though they may have the same current & voltage rating , the actual operational requirements will determine the fuse type required but that is not really relevant to the 12V wiring in a van.,
-- Edited by oldtrack123 on Wednesday 28th of November 2018 02:11:34 AM
It was appreciated
VOTLAGE DROP = [cable length (in metres) X current (in amps) X 0.0164] divided by cable cross-section in mm.sq.
Cheers,
Peter
In any circuit where the conductor varies in size the the voltage drop in volts per millimeter will be related to the size and resistance of the conductor. In radio equipment rooms we needed to run long leads between devices. Often the length of cable means it has to be a large one to limit the voltage drop to an allowable value. The large cable size will not fit the terminals on the battery charger or the device being supplied. In these cases a short piece of smaller wire is used between the heavy one and the terminal. If this piece of wire is short enough then there is only a very small voltage drop along its length and this will not affect the service by a significant amount.
In the case of fuses they are built material of higher resistance. This allows the fuses to build up enough heat to be blown is a short length. It does not matter where the fuse is placed in the circuit, it's effect on voltage drop will be the same. (The importance of a fuse being near a battery is purely to limit the possibility of a short occurring between the fuse and the battery.)
This dissertation was given to demonstrate the answer to your last question in the piece I quoted from your question. You can see how much voltage drop there is across the fuse from the following tables. You can use these fuses to measure the current flowing them. Just use a good digital volt meter, connect the leads to the little pads on the top of the fuse. Cross reference the voltage reading to the table and you can get a reasonably accurate reading of the current flowing through the fuse.
Yes . the actual location of the fuse & the possible MAX short circuit current does determine the fuse type ,especially with the higher voltages Ac & especially DC
The type of fuse you refer is technically known as a HRC fuse "High Rupturing capacity". The mineral filling helps quench the arc that is formed when the fuse blows.
The first few months [1945 ]of my apprenticeship was served in a powerhouse @ a dry dock .It supplied shore power either 110V or 220V DC to ships in for repair, The main generator fuses ,200A ,on the main switch board were big long open wire fuses holders
Quite a sight & sound show when one of those blew due to a short circuit in the ship to shore cable,
-- Edited by oldtrack123 on Wednesday 28th of November 2018 03:16:34 PM
This heat generation is most obvious where blade fuses are used, it is not uncommon to see a fuse rated at greater than 20 amps with the plastic bit actually melted and often the blades welded into the fuse holder. The small piece of actual fusible material is not the cause but rather the poor design causing a high resistance joint between the fuse blades and the fuse holder.
T1 Terry
Thanks for that Peter, your input was appreciated
I had read your formula in a different thread, (I think), but at that time, I had not got my (layman) head, around the fact that the main contributor to voltage drop, was the length of the wire
Using your formula, the diode (approximately 30 mm after trimming the ends)
Length 0.03 metres X current (14 amp in good weather) X 0.0164 is less than 7 millivolt (0.00688 volt), and not worth worrying about
The normal 30 amp blade fuse, would have an even smaller voltage drop
I now rest easy, as my original idea of placing two diodes in parallel, was to give a greater square area for the current to flow
I now feel, from a layman point of view, that having one diode (capable of carrying the current), is better than two smaller diodes
My gut feeling, is that it is possible for two smaller diodes not to be synchronised, and eventually to have interruptions from the solar panel, when one, and then the second diode, shuts down
This shutting down of the diodes, (using my own observations), shuts the solar panel down, which in turn allows the diodes to once again turn themselves on, until their maximum amps are reached
Also I feel that having two diodes side by side, and one fails in the closed position, it would be the same as having no diode in the circuit
Hopefully I have made sense by saying the above
Thanks for your input Peter, it was appreciated
Sorry that I did not reply to, Peter n Margaret (Peter), earlier
As I now understand what his formula means
Thanks for your input Terry
Once again, I can only say, sorry that I did not immediately reply to, Peter n Margaret (Peter), as his formula said it all, after I had finally got my head around it
This link may help members to understand that a fuse does not blow " @ it's rated current.
The speed of blowing is dependent on the actual excess current & fuse type.The same applies to thermal circuit breakers
All have a overload to blow time curve. That does vary with actual type ie if standard ,fast blow or slow blow
https://www.google.com.au/search?q=Time+current+curve+to+blowr+typical+12V+auto+fuses&tbm=isch&source=iu&ictx=1&fir=k7B4W7UtuGznqM%253A%252C8unE8TdxA1UDPM%252C_&usg=AI4_-kRS4_5Ng7ZP0NZAvApPN-f5v0adDA&sa=X&ved=2ahUKEwjp7-322fveAhXKEnAKHdN2DX0Q9QEwAHoECAAQBA#imgrc=k7B4W7UtuGznqM:
-- Edited by oldtrack123 on Friday 30th of November 2018 11:24:55 PM
It just goes to show, that I never knew, what I did not know, so thanks for that
Hi Tony
To quote a now famous persons speech "There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Precisely
Jaahn
I just had to laugh, when I saw the
(clap gif) 
and then realised why it was there 
I can assure everyone, that I had no intention of trying to be funny, with my reply
It is good to see, that no matter how serious we can get on this forum, our sense of humour can still shine through
Hopefully no offence was given, as certainly none was taken, by me
Remember too, that advice about 12 DC cable is mostly predicated on the assumption that people will be using high purity copper cable and are concerned to ensure the voltage drop across the cable run is small. In designing a fuse, the material selected for fusible section is chosen with a focus on the temperature at which the material will melt or fuse. The rating of the fuse is determined by how much current is required to raise the temperature of the fuse material to melting point, given the cross sectional area of the fuse. Most fuses do not reach red hot, for example, just before they fuse. Nichrome wire such as used in a toaster, has a high resistance, compared to copper, and maintains its integrity while glowing hot enough to toast the bread. Pure lead melts around the 300 Degree C mark but solder of about 60/40 ratio melts closer to 185 Degrees C. Tungsten wire in a vacuum gets hot enough to emit visible light, without melting.
In the larger picture of things, heavy copper wiring is advised to minimise the voltage drop across the cable run and fuse wire is selected for its properties in regard being suitable for protecting the system against damaging current levels. The voltage drop across a fuse is tolerated because we want fuses for protection and as long as the fuse material is a very short length in relation to the whole cable run, better in than out.
Iza
T1 Terry
I think the real problem is terminology rather than being deliberately misleading.
Especially if buying from an auto supplier. The thing to remember that auto cable size is based on outside dia & that can be highly variable[in simple words if you ask for 13mm cable you will get cable which is 13mm outside dia & a variable actual copper dia
If you go to an Electrical supplier & ask for 6B&s you will get 6B&S with a copper cross section area of 13.3mm , or simply ask them for 13mm sq cable