# voltage drop calculator

## Comments

• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

bumping this up so it's not buried too far.
• Posts: 6,290 admin
Re: voltage drop calculator

THANKS!

I don't post too often, but the voltage calculatror is COOL! I am in the process of getting some more telco batts, and if I want to trade in some bad ones, it will only cost me lunch! This guy is going to basically trade me weight and type for like, so as long as they are VRLA batts, I can buy him lunch and get more batts. I wish I could get an inverter larger than 48 volts!

Skip
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

i'm glad you like the calculator and i do hope it is helpful to you. although it is setup for pv input this actually is any power source be it solar, wind, or even batteries. simply the program takes the resistance of the wire at xx temperature and multiplies that by the current passing through the wire to arrive at the voltage dropped. even small drops with large currents can present sizable losses in watts. those watts cost too much to waste even though copper wires are expensive. i believe the nec says a 5% loss from source to load. we generally have gone by 3% to be a good goal for the power source to the controller, but outback recommends 2%. that percentage is the voltage drop divided by the system voltage. that means that all of the wires in a system need to be evaluated. as an example, what good would having a 1% drop be from the pvs to the controller if you have a 10% drop from the batteries to the inverter?
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

ATTENTION ALL:

NOTE- I am recommending in the voltage drop calculator a change to the default temperature for calculation purposes. The default is 50 degrees C and NEC recommendations for this use are minimally 60 degrees C. I'm basing this on Whiles' article on the matter. http://www.sandia.gov/pv/docs/PDF/CodeCorner83.pdf

i know i capitalized this time. i thought it better to do it right this time. you may wish to use even higher temps under some circumstances as the article points out, but very hot areas of the country may wish to go even higher to be on the safe side of the calculations.
let's face it folks, you can use an accurate dvm or dmm (meter) and measure this rather than calculate it. measure the voltage from the pvs(source voltage) and then measure, under the same conditions and ideally at the same time, at the destination point (be it at the controller, disconnect, batteries, or whatever the other reference point is to be). the difference between the source and destination voltages is the voltage drop. to get the percentage, just take the voltage drop and divide it by the source voltage measured. calculations are great, but in reality fuses, switches, connectors, etc. can pose more resistance, or resistance that is unaccounted for by straight calculations, making actual measurements invaluable.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

bumping this up again. it seems i did get this to sticky after all so now i don't have to keep bumping it. yea
• Solar Expert Posts: 5,183 ✭✭✭✭
Re: voltage drop calculator

Hi Niel, I was trying to use the calculator and find a small problem.. I am 12 v only and need to change the 24 v to 12 v but no can do... any possibility of adding this facility?

Cheers
Eric

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

there should be a slider at the bottom to allow going to the right and allow you to change that area. if there's no slider you may get away with changing the screen resolution so as to expose it. i always had some troubles with excel as i'm not an excel expert by any means and one of those quarks was saving changes. don't save the changes as it goofed mine up in the past, but then again i could've done something wrong to cause it. if you still have troubles and would like me to calculate something for you then either pm me or give me an email with all of the needed info.

update:
westbranch,
if you made it over here to the new forum could you tell me if that solved your problem with the calculator?
• Solar Expert Posts: 5,433 ✭✭✭✭
Re: voltage drop calculator

Niel,

Take heart. The us system is a tax on our education system. The meteric system is so much better and the chance of arithmatic errors are dramaticly reduced. As a previous post suggests, how many engineers have to do the translation back and forth, each time inducing the possibility of errors. Wasn't there a Mars mission that crashed unceremoniously into the planet due to just such an error? How 'bout the Canadian flight that ran out of fuel in Gimli Mb due to us/gal. can/gal, kgs/lbs, litre/pounds! K.I.S.S

Those of us who straddle the Canadian/US become fluent in both. 20f nice day, -40? Who cares! 120km/hour, nice, 120 mph, big fine! \$1.25/litre gas, expensive, \$3.20/gal,,,seems cheap!

Now if consider the colour of our harbour, while you are shopping for a litre of milk at the shopping centre!

Icarus
• Solar Expert Posts: 9,274 ✭✭✭✭✭
Re: voltage drop calculator
icarus wrote: »
Niel,

Take heart. The us system is a tax on our education system. The meteric system is so much better and the chance of arithmatic errors are dramaticly reduced.

Icarus

How does "metric" measure volts ??
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Super Moderators, Administrators Posts: 31,680 admin
Re: voltage drop calculator

Actually, the "British" unit system inch/foot/yard/etc. has some very good reasons why it has remained popular.

You can, for example, divide 1 yard evenly by 2,3,4,6,9, and 12 into whole inch units... Let alone the fractional inch units (of 1/2, 1/4, 1/8, & 1/16). Even 1 foot can be divided by 2,3,4, and 6 into even 1" increments.

Try dividing 1 meter by 3 (evenly). 33.333333 centimeters anyone?

Not to say that one system is better than another, but there were reasons various units of measurements were chosen.

I remember the metrification of wine--Naw, 1 liter of wine will give you more than a quart for the same price--much of what I see out there is now 0.75 liters--or less than a quart for the same or higher price (not an expert here--rarely drink alcohol).

Years ago, when mechanical gas pumps were still used in the US--a few stations kept the old pumps and calibrated them in liters (to get over \$.999 per gallon limit on the pump). Interestingly, the price on the sign in \$/gallon did not convert correctly to the pump price in \$/liter (guess which way it was off and who got sued by weights and measures).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,433 ✭✭✭✭
Re: voltage drop calculator

Millimeters work quite well,,,on down to nanometers. Fractions of inches????
Meters ultimately divide just as well. Canadian carpenters still use inch tapes, 2x4 studs, 4'x8' plywood etc. (The young guys can build in inches but if you ask them how long thier boat is, they will tell you 4 meters.

The errors come in the world in between.

Icarus

PS. I don't think that a volt is an english or metric measurement, like Calories or BTU's, it measures something tangable (I think!)

PPS regarding my previous post(s),,,,,,I am a terrible speller.
• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
Re: voltage drop calculator

I was bi-educated. :roll: I learned both the metric and English system while growing up in Europe, and I learned both architectural (fractions) and engineering (decimals) versions of the English system in college. While I’m more culturally comfortable with the English system, I prefer the metric system.

I like that the original definition of a meter was one ten-millionth of the distance from the North Pole to the Equator along the prime meridian through Paris, France, where the original silver meter standard is on display. And, I like that a centimeter is 1/100 of a meter, that a cubic centimeter of distilled water at 4 C weighs one gram, that 1,000 cc is a liter, and that the mass of a liter of water is one kilogram.

Speaking of which, I like dealing with kilograms (mass) rather than with pounds (force) and slugs (English mass) when considering mechanics and dynamics, as pounds on Earth don't matter in space (remember the lost Mars Climate Orbiter?). I don’t like dealing with Imperial gallons (five U.S. quarts) vs. U.S. gallons (four quarts), and I've never liked that bigger wire sizes are described with smaller numbers.

And, speaking of alcohol, it may well be that dividing the Imperial gallon may have given rise to the business of the “fifth”. A fifth of an Imperial gallon is a U.S. quart, but a fifth of liquor ended up as a fifth of a U.S gallon – and still called a “fifth”. And it’s that latter fifth that’s very close to a 750 ml bottle of wine.

I also like the metric system of temperature (Kelvin and Centigrade) vs. the English system (Rankine, Fahrenheit). To me, there just something logical a scale that’s based on water melting at zero C and boiling at 100 C (at sea level, of course) instead of 32 F and 212 F, respectively.

I suppose we’re comfortable with that to which we are accustomed. But, I like the order of the metric system, and I can do without rods (16.5 feet), chains (66 feet, 4 rods), furlongs (660 feet, 1/8 mile), fathoms (6 feet), leagues (~3 miles, or the distance a person can walk in one hour).

But, enough’s enough, and I’m off to watch a show on my 1,168.4 mm, er, 46 inch TV.

Regards to all,
Jim / crewzer
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

icarus,
as far as translating goes you can do it, but it is you that must be carefull translating and not i. the metric system does not reduce math errors as our math is base 10 like yours.
bb,
you don't need to drink alcohol to see liters as my soda pop is in a 2 litre bottle. we gain slightly over having to buy a half gallon, but they still charge us like it's 4 liters of soda pop so what's the difference?:(
ps-radio wavelengths are measured in the usa in meters.
• Super Moderators, Administrators Posts: 31,680 admin
Re: voltage drop calculator

Not claiming that one is "better than the other"... Just saying there were reasons why the different systems evolved into their current form.

Packaging--it is all over the map.

The story I heard for the "5th" (US story--don't know if it was true--what I was told ~45 years ago when I asked) was that the "high taxes" on hard booze did not start until 1 US Quart or larger amount.

Tried to find the history of the "fifth of alcohol" and I got a whole bunch of links to fifth grade drinking problems--a sign of our times?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
Re: voltage drop calculator

I don't actually know the origin of the "fifth"... a quick Google search turned up definitions, but not the origin of the unit of measure.

On of my favorite combinations of the two systems is how tires are labeled. For example, a 265/75R14 tire has a cross section dimension of 265 millimeters, a sidewall height-to-cross section aspect ratio of 70%, is of Radial construction, and mounts on a 14-inch rim.

AArrrgggghhhhh......!!!!!!!!!!!!!!!!
• Solar Expert Posts: 5,433 ✭✭✭✭
Re: voltage drop calculator

My point about the "translation" is the danger comes in when you have to work in more than one system. Each time you translate the chance for errors increases, Mars probe living proof. As to being better, I live in feet and inches, but the nice thing about metric is that it (moslty) relates to something in real space. I don't suggest one is better, but the problem is when you try to mix the systems.

I think the idea of metric time has some merit, 100 minute hours, 10 hour days, 10 day weeks, 10 month years,,,,Hmm, what about leap year?
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

"I think the idea of metric time has some merit, 100 minute hours, 10 hour days, 10 day weeks, 10 month years,,,,Hmm, what about leap year?"

now time you can't mess with as those are natural divisions set up by the earth's rotations. it would make employers rejoice in making workers work their 8hr days though. ugh!
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

the question was not mine as it is from icarus and i had it in quotes. my answer is there though. not everything should be on a base 10 system or as some call it, metric.
• Posts: 6,290 admin
Re: voltage drop calculator
niel wrote: »
"I think the idea of metric time has some merit, 100 minute hours, 10 hour days, 10 day weeks, 10 month years,,,,Hmm, what about leap year?"

now time you can't mess with as those are natural divisions set up by the earth's rotations. it would make employers rejoice in making workers work their 8hr days though. ugh!

Hey, I LOVE IT...
I wrote a paper about it 40 years ago in college. What if all this was worked backwards, including pie (3.14159), so that all this stuff was in fact base ten.

Keep in mind, the thing we call 59 seconds or whatever is just man's concept - what if it was wrong?

I need a beer to go on.......keep up the good work.

Solar Ready Bill.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

after concidering this for awhile i concluded that it may be possible to convert it to base 10, but people don't have a concept of time now and to make this change would tend to create chaos with many not ever grasping the new standards.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

i'm posting a reminder to not save the changes made on the calculator when exiting as it could corrupt future calculations.
• Registered Users Posts: 10
Re: voltage drop calculator

So the reason why the panel volts is locked in increments of 60v is because that seems to be the optimal voltage for panel strings correct? Bah nevermind I am not paying much attention.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

you can put what it is you want for pv voltage, but that is usually in 6v increments like 12v, 18v, 24v, 48v and so on depending on the pvs used and how many, if any, are in series. same thing for battery voltages except that goes in 12v increments. it isn't locked that i'm aware of as you just click on the appropriate box and put what you want there.
• Posts: 6,290 admin
Re: voltage drop calculator

Hello,

Footnote 9 says:
When entering wire length use two way length. How long is each wire from the panel to the combiner box both ways? Same for all other wire runs.

So with 10 feet of wire, as measured off the spool, from the panel to the combiner, do I enter 10 feet, or 20 feet?

-TM
• Super Moderators, Administrators Posts: 31,680 admin
Re: voltage drop calculator

20 feet... The "round trip" length the electricity must travel.

A fair number of voltage drop calculators will multiply the run length by 2x to account for the round trip length--hence the confusion.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 185 ✭✭✭✭✭
Re: voltage drop calculator

w/ long wires... is there current drops? how do you calculate current drops?
• Solar Expert Posts: 9,274 ✭✭✭✭✭
Re: voltage drop calculator

Current remains the same in a series circuit. Voltage drops (dissapated as heat) via resistance, either intentional (a shunt resistor) or accidental wire loss.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 185 ✭✭✭✭✭
Re: voltage drop calculator

i think its all coming together.. can you correct me if im wrong...

current remains the same in series. you add voltage. and the MPPT takes care of the 'step down' by converting the extra voltage to current.

the reason why series is more efficient is because you have less wires, therefore less voltage drops (assuming wire size is the same in both series and parallel setups)

wire sizing is based on current, not voltage
• Solar Expert Posts: 185 ✭✭✭✭✭
Re: voltage drop calculator

something doesnt add up or you are oversimplifying.what happens:

a 12V PWM charger takes in a 12V panel that generates 17V?
if charger input == charger output then things would fry. but i think it doesnt in this case.
• Solar Expert Posts: 9,274 ✭✭✭✭✭
Re: voltage drop calculator

17V panel -> Charge controller -> Battery @ 14V

There are a couple volts lost in any charge controller, and you need to charge a 12V battery with 15V sometimes, so 17v is the power setpoint for many panels
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

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