Where to place the Charge Controller?

Re: Where to place the Charge Controller?

The CC normally goes near to the inverter and batteries. Where monitoring and adjustments are easier Many integrated systems like Outback and Xantrex XW system are networked and there integration hardware puts the CC next to the Inverters

Re: Where to place the Charge Controller?

roks wrote: »

Thanks for the quick replies guys.

Is a PWM CC, so I'll keep it near the battery and run a long cable one size bigger than the max current of all panels combined.

hmm. what size would that be and how did you come to determine that size?

Re: Where to place the Charge Controller?

roks,
i can see it is not being done correctly, but it may be easier for you to give more info and i'll do it. first of all just what make and model pvs do you plan on here? in doing the calculations there are 2 things right off the bat that are wrong and they are 1> the pv voltage is for nominal operation voltage and not vmp and 2> the run lengths will be far too short to be of real value.
on point 1> a 35v vmp pv will be a nominal 24v pv as it coincides well with a 24v battery.
on point 2> a wire run is half the length of the entire wire length that would be entered on the calculator because there are 2 wires involved that go that distance. if the pvs are side by side the end pvs have much farther to go than what you indicate, but i may be wrong on that account as i have no picture of how the arrangement of the pvs will be in my head. i find it very difficult to believe you could send power from each of these pvs in such a short run of wire when in parallel to go to the combiner. the shortest you list is a 3ft length making the max run distance 1.5ft because the run involves 2 wires. maybe you are overlooking the fact there are 2 wires in the space between the pvs so if 2 junctions are 2 be say 3ft apart then the total wire length would be 3ft of + and 3ft of - for a total of 6ft of wire.
each string or in your case each paralleled pv should be looked at seperately as how it will look. i know i'm probably confusing you somewhat on this, but you can consider each pv as an individual circuit that is later paralleled and each circuit can operate independant of the others, however, each share wiring and that wiring is to be determined.
ok 3 things as you do not need to multiply this by 1.25 as this is being based strictly on realtime voltage drops and not fuse ratings.
just give me more details and we'll tweak it from there.

Re: Where to place the Charge Controller?

ok, what i see in the diagram is a daisy chain and that complicates things somewhat. what i thought you were going to do was run each pv's output straight to the combiner box. in a daisy chain the current from pv1 to pv2 gets added to the current when going from pv2 to pv3. this continues to add more current for each section of the daisy chain so unless you use thicker wires as you go down the line this can be a problem. the calculator does not do daisy chains on the pvs unless you account for the current increases down the line.
so before we go on here, is it your desire to use the daisy chain? if so you won't need the combiner. i would need the wire run distances between each set of pvs in that case.
the nominal voltage for a 35vmp pv is 24v and you will want to use 24v and the ipmax or imp for the current. so in the calculator it is a 24v pv voltage and 24v battery voltage.

Re: Where to place the Charge Controller?

i think it's looking better, but i still have difficulty believing that all 6 pvs are within 3.5ft of the combiner. i might believe this of 3or 4 pvs maximally, but not 6.
as you can see by the calculator the high currents going through the thicker wire has a greater voltage drop because of the distances involved. if you can't shorten the distance then thicker wire should be used for that run to bring those %s in line. i spec'ed a 3% figure, but others like outback spec even lower figures at 2%.
in the calculator you don't need all of the pvs added together as each is its own run circuit so to speak and they don't need all of their voltage drops added together then until they are shared in a common wiring (talking parallel pvs here). i did not design the calculator for xls., but i gave the pertinent info needed for the calcs as the calculator was a joint effort.

Re: Where to place the Charge Controller?

how much will that reduce the wire run to? also, you may add larger wires for the cc to battery and especially the battery to inverter as inverters can draw huge amounts of current creating large voltage drops, all of this in addition to your wire run shortening.

Re: Where to place the Charge Controller?

that 5ft of wire total will only save you about a quarter of a percent and i'll recommend that you run the next gauge of #4 as this drops the 70ft length of wire's voltage drop to 1.66% or about a percentage point lower than the #6. it may be more expensive wire, but you don't want to cheapen the system's ability by using too small of wire. remember that pv power is expensive and voltage drops cost you some expensive power and not once, but all of the time. it may also be good to go with larger wires if you plan to expand in the future.

most inverters specify what they deem best for wire, but if you keep the runs around 5ft or less (rough guess) you can go by the normalized capacity the nec uses for 120/240vac wiring and you need to know the max current the inverter will draw. longer runs can be a problem with the extra length adding more of a voltage drop so i guess you can just figure it out with the calculator using the battery voltage also as the pv voltage plugging in the current needs and the wire gauge and length to obtain a vd percentage. keep it under 2% if using 3% for the max on the rest of the system so that from generated power source to the load (in this case the inverter) is no more than a 5% vd.