# voltage drop calculator

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• Banned Posts: 17,615 ✭✭
Re: voltage drop calculator
mshen11 wrote: »
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

99 44/100% correct.

Your wording on the 'series is more efficient' is a bit shaky. Voltage drop is basically Vin / line resistance + load resistance. Line resistance increases with length and/or smaller wire size. Start with a higher Voltage = end with a higher Voltage. Losing 10% along the way is not as devastating with 60 Volts as with 6.

Wire sizing is indeed based mainly on current.

(Now wait for the engineers to jump in with all the fine details. )
• Banned Posts: 17,615 ✭✭
Re: voltage drop calculator
mshen11 wrote: »
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.

As Mike said, you always need higher than battery Voltage to charge the battery. EQ Voltage for a 12 V flooded cell can be 15.5 V. A bit higher Voltage to a given load is one thing. A much higher Voltage is another.

When you hook a "17 Volt" panel through a PWM to a 12 Volt battery, there is a drop in Voltage from the panel which becomes an increase in current. As the Voltage in the battery goes up (from charging) the two Voltages become closer, and the current goes down.

Too much difference: things heat up. Batteries boil. Fuses blow (hopefully).
• Posts: 6,290 admin
Re: voltage drop calculator

There are many calculators on one page of http://www.electrician2.com/
It apparently is an electricians online course, but the calculators seem good.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

there are many calculators out there if one wished to look, but the one here is quite accurate in its calculations and it does account for temperature too. although i did not design the exel program's layout the math is basically correct in it. i often get confused myself as to how it is arranged as per the guy that created the exel program as i'm not that knowledgeable with computers, but taking it a step at at time and writing each step down so one does not get confused is a good way of going about it if you are in doubt. the other guy wanted it to show multiple strings, but that should be done individually as each string is an independent circuit. usually the one with the longest length away from the cc will be the worst case and the one with the shortest length away the best case unless different wire gauges were used.
the scope of this thread is not to list all calculators encountered out there, but mainly to address the one that was co-created by me. to list all of them encountered will clutter and detract from the original. now if there's somebody out there that knows pc programing in exel and you believe you could improve its layout then contact me via pm.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

brock no longer carries the calculator and my thanks to him again. solar guppy (thank you) gave this zipped file as a solution;
• Solar Expert Posts: 9,274 ✭✭✭✭✭
Re: voltage drop calculator
niel wrote: »
brock no longer carries the calculator and my thanks to him again. solar guppy (thank you) gave this zipped file as a solution;

can the first post (with a bad link) be edited to have a working link in there too ?
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

I have updated the first post with the new link...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 192 ✭✭
Re: voltage drop calculator

Just wanted to let you know I just used it for the 4th time as I am upgrading my system. I'm on the right track with my wire sizes/lengths. All below 2%. Thanks for the calculator. It saved me money and eased my mind, too.

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

Updated first post with link to new location on Solar Guppy's server.

Thank you again S.G. for hosting the spreadsheet.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

i'll second my thanks as i had already sent the first by pm.:D
• Registered Users Posts: 14
voltage drop calculator

Hey All,

This calculator I found you just plug in the length and amps and it gives you numbers ! lol It runs in JAVA so no need to DL another program.

Thanks again for all the info
Bernie

http://www.stealth316.com/2-wire-resistance.htm
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

hi bernie and to all else as well,
i should point out here that the calculator this thread was created for was not one just grabbed someplace off of the net as it was created with formuli and data that i gave and another person with the spreadsheet layout had worked on. it is rough on its delivery as it beckons a bit of understanding in its use, but encompasses allot of info and aspects not always found on other calculators and with high accuracy. i am not saying another calculator won't do this and i'm not jealous of another calculator either, but i don't want this thread to wind up being a conglomerate of on the net calculators and i don't just say this to you bernie as it needs said to all. let's keep this one about the calculator i helped to create. others are free to create another thread or even to make references to another calculator here for comparative purposes. i hope this doesn't sound too harsh and i hope you all get that i want this thread for primarily this calculator.
• Solar Expert Posts: 175 ✭✭✭
Re: voltage drop calculator

Tried out V drop calculator niel and it comes out close to using the tables from my 1970 ARRL handbook. It is very close to real world on my 2 panel 160 watt RV system with Sunsaver 10 controller. The question I see is the gain in current through the controller. The amps out appear to be based on watts in = watts out which would be ok for a large array with mppt but doesn't seem that way with my real world measurements. I measure the same current into the controller as I get coming out. By the way with today's sun during the test the panels only produced 135 watts not the 160 expected so it wasn't a perfect solar day. The battery did reach full charge after starting at about 50% SOC.
I say about as I don't have a hydrometer with me so couldn't check SG.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

scrubjaysnest,
there are probably differences due to the fact i design for higher temps on the wires. they are most likely giving figures for 25 degrees c from the arrl. also, just because one has an mppt controller does not mean that one will not see lower figures at times, but i'm not there to say what may or may not be right with what you are seeing.
• Solar Expert Posts: 175 ✭✭✭
Re: voltage drop calculator

You are correct there, I saw a note that said wire type and temperature effects the ratings and to see the NEC tables to correct. The bottom line is my first system is doing as expected over all. I checked the battery voltage after setting over nite and with air temp of 61 degrees it showed 13.09VDC.
• Solar Expert Posts: 308 ✭✭
Re: voltage drop calculator

I found the link to this under one of your replies (well ALL of your replies) and thought I would give it a try...

Changed the values for 12 V array, 12 V battery, Used #4 wire for everything.. just not sure what the # of feet for string 1 would be ? I just plugged the cables that came with the panels into the combiner box with a 6" piece of #6 , - is that what you mean ?
So with that info plugged into the converter, I have a voltage drop of 0.355 from Array to Cont. and .396 from Array to Bat. Not bad, if I did it right

Thanks for the link, it is now saved on all my machines
2 - 255W + 4 - 285W PV - Tristar 45 MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
9 -220W PV - net meter - Enphase inverters and internet reporting system.
420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
Current project is drawing up plans for a below grade Hobbit / underground home.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: voltage drop calculator

skippy,
all interconnecting wires in a string need accounted for as well as the wire runs to the cc and batteries. say for instance you have 3 pvs in a series string for string 1 and they each have 2 36 inch #10 copper wire pigtails for connection. that would be 6 total at 3ft apiece for a total of 18ft at whatever v drop % that equates to. add to that the wire that connects from the ends of the pigtails in the string to go to the combiner even if it is only 6 inches. if it is 6in then that is 6in x 2 = 12in or 1ft at whatever v drop loss is for that section. when you encounter the combiner you must remember that it combines the amperage of all strings that go to it and thus changes the overall v drop % for that wire run to the cc.

as i've stated in other places when you have multiple strings, do not add all of the individual string v drop %s together. pick the longest or worst one and figure it from that. if that turns out to be an acceptable v drop % when added to the rest of the circuit to the cc and batteries then you know the other strings will also show to be good too all things being similar such as wire gauge, pv watts, etc. if the worst string turns out to be too high then that needs a better wire solution, be it the run to the combiner and/or making the other wires shorter/bigger thicknesses. if that's unfeasable in the string itself then changes need made with the other wire runs to compensate. also, if that worst string's v drop % is bad then the others are suspect as well and may need computed. it can seem complicated, but it's not. the description is what is hard to get across to those that aren't familiar with electricity or electronics.

i can't confirm or deny what you figured as i lack the full information needed to do so.
• Solar Expert Posts: 98 ✭✭✭✭
Re: voltage drop calculator

Thanks to everyone that made this calculator available. I've used it compare various configurations of wiring, panels, etc. and it's very adaptable for that purpose. I like to document and save the results and the protected cells don't allow documentation. So I suggest unprotecting row 1, column k and remaining columns and the rows below the notes.

Protecting the calculations is probably a good idea. I did remove the protection mainly to add my comments and of course checked the calculations. :-)
• Registered Users Posts: 3
System2 said:
Re: voltage drop calculator

"We are taught both in our schools but I'm willing to bet no one else is. "

Lost your bet!~ ;-) I was brought up in the UK, and now live in Canada, Both are officially Metric but because we have to deal with our good friends in the US we learn and use both. I remember a time when Britain was changing and I was working on a building project where all the wall studs were spaced imperial and all the drywall sheets metric... Loads of cutting on that job!