Best Solar Panels For The Buck

[Azul]

Originally Posted by foggysail

Azul-- My last order had the MC4 connectors on about 3' pigtales. I just got them a few weeks ago.

They just have a male and female MC4 on 90 mm of cable. They are going to add a MMF and MFF Y pigtail so that you can connect two panels in parallel to one cable without having to buy the pigtails which are $15. They may also have a pair of longer cables to add to the pigtails he wasn't sure (25 feet would be nice.) You need to add another set of MC4 to avoid having to cut off the supplied MC4 on the panel thus voiding the warranty. Hard to find MC4 cables larger than 10 AWG.

[willardj]

Originally Posted by Azul

They just have a male and female MC4 on 90 mm of cable. They are going to add a MMF and MFF Y pigtail so that you can connect two panels in parallel to one cable without having to buy the pigtails which are $15. They may also have a pair of longer cables to add to the pigtails he wasn't sure (25 feet would be nice.) You need to add another set of MC4 to avoid having to cut off the supplied MC4 on the panel thus voiding the warranty. Hard to find MC4 cables larger than 10 AWG.

Yea that's why when I ordered my panel I went ahead and picked up a set of MC4 ends to make my own extension's. Being I only needed 1-145w to run all my stuff and a 18' run of wire I wanted 8ga instead of the 12ga to keep the voltage drop to a min. And if I move up to 190w-230w panel to add a fridge I want have to change any wiring in my system. With the MC4's I ordered 8ga fit just fine. I ran 18' 8ga panel to cc and 5' 6ga cc to batts.

[Azul]

Originally Posted by willardj

Yea that's why when I ordered my panel I went ahead and picked up a set of MC4 ends to make my own extension's. Being I only needed 1-145w to run all my stuff and a 18' run of wire I wanted 8ga instead of the 12ga to keep the voltage drop to a min. And if I move up to 190w-230w panel to add a fridge I want have to change any wiring in my system. With the MC4's I ordered 8ga fit just fine. I ran 18' 8ga panel to cc and 5' 6ga cc to batts.

Should probably use 4 AWG between the controller and the battery and keep the run under 3 feet if you can. See HandyBob "Solving the RV battery charging puzzle."

[willardj]

Originally Posted by Azul

Should probably use 4 AWG between the controller and the battery and keep the run under 3 feet if you can. See HandyBob "Solving the RV battery charging puzzle."

I would have run #4 but want fit my cc. Max that I will have from my cc is 14.1v and 15a so #6 is fine. My voltage drop from cc to batt thru that #6 is only .5% so plenty gd and from my panel to cc is 1.1%. Handybob is running a tristar 45 and it will take #4 even a #2 wire. I found his site about a year ago has tons of good info.

[noelex 77]

Originally Posted by willardj

I would have run #4 but want fit my cc. Max that I will have from my cc is 14.1v and 15a so #6 is fine. My voltage drop from cc to batt thru that #6 is only .5% so plenty gd and from my panel to cc is 1.1%. Handybob is running a tristar 45 and it will take #4 even a #2 wire. I found his site about a year ago has tons of good info.

Are you sure of those calculations?
It would put your cc only 3 feet from the batteries for example.

[Pete7]

Originally Posted by noelex 77

The Vmp is published for a cell temperature of 25C. In practice the cell temperature will be about 40C. The negative temperature coefficient of Vmp means that Vmp drops by about 1.5v under real world operating conditions.

Surely that depends on location. In the UK my panels don't get hotter than luke warm even in direct mid day sun, certainly not 40'c which is why I think they are particularly suitable for higher latitudes. Okay they don't produce much during the winter but then we don't sail when there is snow and ice about.

Pete

[noelex 77]

Originally Posted by Pete7

Surely that depends on location. In the UK my panels don't get hotter than luke warm even in direct mid day sun, certainly not 40'c which is why I think they are particularly suitable for higher latitudes. Okay they don't produce much during the winter but then we don't sail when there is snow and ice about.

Pete

Yes the climate does have an effect, but at lower irradiance the Vmp will fall signicantly anyway. So in the UK the cells will be often be cooler because there is less light, but the voltage will also be lower.

If the panels are getting enough light to hit their max power and reach the Vmp on the spec sheet they will be getting reasonably hot even in a cool climate.

[willardj]

Originally Posted by noelex 77

Are you sure of those calculations?
It would put your cc only 3 feet from the batteries for example.

Yes I am at 5' cc to batts not 3. If I did move it to 3' it would only drop to .3% over .5% @ 5' with #6 and that is not worth moving my cc. this is the voltage calculator I use Voltage Drop Calculator - for single and 3 phase ac systems and dc systems In less you are talking about my batt voltage and cc ampage? In that case yes the same. I have sealed batts and cc set at 14.1 and have equalizer turned off and the max ampage of my cc is 15a.

[noelex 77]

Originally Posted by willardj

Yes I am at 5' cc to batts not 3. If I did move it to 3' it would only drop to .3% over .5% @ 5' with #6 and that is not worth moving my cc. this is the voltage calculator I use Voltage Drop Calculator - for single and 3 phase ac systems and dc systems In less you are talking about my batt voltage and cc ampage? In that case yes the same. I have sealed batts and cc set at 14.1 and have equalizer turned off and the max ampage of my cc is 15a.

You are forgetting there is a voltage drop in both the + and negative cables.

If the cc is 5 feet from the batteries and carrying 15A. The total wire length is 10 feet and the voltage drop is 0.096v with AWG 6 guage wire.
This is 0.8% if referenced to 12v.

[Azul]

Originally Posted by willardj

Yes I am at 5' cc to batts not 3. If I did move it to 3' it would only drop to .3% over .5% @ 5' with #6 and that is not worth moving my cc. this is the voltage calculator I use Voltage Drop Calculator - for single and 3 phase ac systems and dc systems In less you are talking about my batt voltage and cc ampage? In that case yes the same. I have sealed batts and cc set at 14.1 and have equalizer turned off and the max ampage of my cc is 15a.

Noelex, if his cc only bulk charges at 14.1 V would he not be better off to leave his equalization on? My cheapo charge controller equalizes at 14.8 for one hour but bulk charging is only 14.4V. If he has 5 feet of #6 cable his voltage at the batteries is probably even lower than 14.1 and I wonder if his batteries are significantly undercharged. What part of the algorithm actually determines how pumped up the batteries are before they go to float on these cheaper chargers?

[goboatingnow]

14.1V for sealed batteries is correct it errs on the side of caution. The problem here is the batteries not the charger. BTW this is the absorption cutoff point rather then anything to do with bulk

Dave

[willardj]

Originally Posted by noelex 77

You are forgetting there is a voltage drop in both the + and negative cables.

If the cc is 5 feet from the batteries and carrying 15A. The total wire length is 10 feet and the voltage drop is 0.096v with AWG 6 guage wire.
This is 0.8% if referenced to 12v.

Makes sense. Also the max the cc is rated for is 15a my panel will only give me about 10a. 145w/12v=12.08a max 145w/14.1v=10.2a max Then subtract the losses so probably 8a-10a. Best I have seen so far is 9.2a.

[goboatingnow]

Originally Posted by willardj

Makes sense. Also the max the cc is rated for is 15a my panel will only give me about 10a. 145w/12v=12.08a max 145w/14.1v=10.2a max Then subtract the losses so probably 8a-10a. Best I have seen so far is 9.2a.

Unless the mpp point is at 12 or 14 v you'll not get W/V output the output curve of a panel isn't linear. ( that's why mppt co trollers exist)

[willardj]

Originally Posted by goboatingnow

Unless the mpp point is at 12 or 14 v you'll not get W/V output the output curve of a panel isn't linear. ( that's why mppt co trollers exist)

I'm just going by what I have seen coming across my Trimetric 2025 monitor. Still don't know as much about the mppt's as I want but they do make a difference.

[noelex 77]

Originally Posted by Azul

Noelex, if his cc only bulk charges at 14.1 V would he not be better off to leave his equalization on? My cheapo charge controller equalizes at 14.8 for one hour but bulk charging is only 14.4V. If he has 5 feet of #6 cable his voltage at the batteries is probably even lower than 14.1 and I wonder if his batteries are significantly undercharged. What part of the algorithm actually determines how pumped up the batteries are before they go to float on these cheaper chargers?

14.1v is ok for gel, but too low for flooded batteries. 14.8 is a bit too high for a regular bulk/absorption set point.
The CC with totally adjustable voltage point are much better they enable you to select the ideal voltage.

The voltage drop from the panel to the CC won't have any effect on voltage set points or the voltage at the battery (it will just reduce output, particularly with a MPPT CC).
The voltage drop from the CC to the battery does effectively reduce the voltage set point, but the effect is not linear as the batteries become charged the current drops and so does the voltage drop. If the wiring is adequate the effect is minor.