Voltage drop between panels and Charge Controller

[1l243]

I purchased a 400 watt Grape Solar kit for my RV. Per the manufacture I up-graded to 500 watts by adding a extra panel. the kit includes 5 x 100 watt panels. A 40amp PWM Charge Controller. My system will include a 2000w pure sine wave inverter and a 340ah lead acid battery bank

I will be mounting the panels on the roof they will be wired in Parallel. According to the manufacturer the Charge Controller has to be mounted within 5 feet from the batteries. This can be done but it does create a longer run from the panels to the Charge Controller. The distance between panels and Charge Controller will be approximately 35 feet. I am using 10ga awg wire. Will voltage drop be a problem?

If I put in the right panel parameters a low voltage calculator shows voltage drop at 35 feet of 1.96v a voltage drop percentage of 10.88% and a end result 16.04v

Any Thoughts

 

[snoobler]

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[TKB4]

To answer your question it would work but that is a large percentage drop . Usually 2-3% or so is considered good but as long as it falls into the acceptable voltage input range of the charge controller it could work. Remember too that you are probably entering the VOC panel info into the calculator and it is likely that the voltage will be lower most of the time.

Let me ask what I feel is a pertinent question.
Why are you connecting the panels in parallel ?
What is the input voltage range of the charge controller?
Is there one pv input or 2 ? (unlikely to be more than 2)
Often the charge controller can take a much higher voltage input than its charging voltage and if this is the case then you could put some in series and if 2 pv inputs you could use the odd number as in not even number of panels efficiently.

 

[snoobler]

To answer your question it would work but that is a large percentage drop . Usually 2-3% or so is considered good but as long as it falls into the acceptable voltage input range of the charge controller it could work. Remember too that you are probably entering the VOC panel info into the calculator and it is likely that the voltage will be lower most of the time.

Let me ask what I feel is a pertinent question.
Why are you connecting the panels in parallel ?
What is the input voltage range of the charge controller?
Is there one pv input or 2 ? (unlikely to be more than 2)
Often the charge controller can take a much higher voltage input than its charging voltage and if this is the case then you could put some in series and if 2 pv inputs you could use the odd number as in not even number of panels efficiently.

He stated he has a 40A PWM controller thus necessitating that all panels be in parallel.

 

[MichaelK]

For a 340Ah battery, I think that even 500W is a little on the low side, especially if it will be feeding a 2000W inverter. 1l243, will you be mounting your panels flat on the RV roof, or will they be pointed towards the sun? If flat, I'd not expect more than 75% output from the panels, so what you actually need would be (340Ah X .125C X 13V)/0.75capacity = 736W of panels.

What I would do is throw away the PMW controller, get an MPPT controller, and 3 more panels. You could then wire the 800W in a 2S4P configuration. Laying flat, I'd expect them to put out about 45amps. Wiring two panels in series for 36V would help reduce voltage drop. With even just 1 more panel, you could have 600W in a 2S3P configuration, putting out about 35A.

 

[1l243]

For a 340Ah battery, I think that even 500W is a little on the low side, especially if it will be feeding a 2000W inverter. 1l243, will you be mounting your panels flat on the RV roof, or will they be pointed towards the sun? If flat, I'd not expect more than 75% output from the panels, so what you actually need would be (340Ah X .125C X 13V)/0.75capacity = 736W of panels.

What I would do is throw away the PMW controller, get an MPPT, controller, and 3 more panels. You could then wire the 800W in a 2S4P configuration. Laying flat, I'd expect them to put out about 45amps. Wiring two panels in series for 36V would help reduce voltage drop. With even just 1 more panel, you could have 600W in a 2S3P configuration, putting out about 35A.

I'm afraid I have to work with what I have. I will not drill one hole or cut one wire til I figure it out

 

[1l243]

The panels will be mounted flat on the RV roof. Tilting may be possible if I'm in one place long enough but not likely. Direction depending on site location.

 

[TKB4]

Just different MPPT controller would help a lot and get the right model and you could get 2 strings one with 3S and one 2S and get more power out of them too.
I would try to mount hinged on one side so when asked could release and push up one side. These 2 things along with selective asking could increase the useable output 35% or more.

 

[1l243]

That is interesting but you have to remember I am a Newb. I bought this panel as a Kit which was a mistake I think I am learning this is the KIT don't change it! If I was keep all my parameters the same except change to a MPPT charge controller and lets assume one string, which would allow me to wire panels in series how would that affect my distance volt drop situation?

 

[TKB4]

One string in series would keep the current the same as a single panel and simply increase the voltage and the loss would be much less. A wire can only carry a certain number of amps and efficiency drops quicker with increasing amps . A wire can also carry only so much voltage mainly determined by the type of insulation but most wiring is rated for very high amperage usually 600 amps or so which u will not surpass. Here is a table you can put in size wire 2 conductors length and see what you get If you enter 10awg wire 2 conductor 150v and 50 feet the drop is 1 volt and about .67% voltage drop or efficiency loss. compare that to 30v at 50amps and you will see a tremendous difference of 16.65% loss in efficiency. The problem is your charge controller may not allow 150v input or all 5 panels to be put in series and you could put 4 panels in 2 in series and 2 groups of 2 in parallel 2P2S then you would have a panel unused. 2 separate pv inputs could take 2 different voltages without losing much efficiency.

 

[mikefitz]

Assuming you want to get the best results from your system without getting a new solar controller then ideally the solar controller should be near the batteries. You have a slight error with the calculations, with five 100 watt panels the maximum current with a PWM controller will be panel max current x 5. With a typical 100 watt panel the current will be around 5.5 amps maximum giving 27.5 amps through the controller and to the battery. In practice, depending where in the world you are located, its unlikely the current will exceed 20 amps most of the time.
Thus the volt drop in your calculations will be around half. Also depending on the battery state of charge and the solar conditions the current will be lower.
The solar controller only has the voltage available at its terminals to decide on the battery state of charge and adjust the charging parameters as necessary, so any significant difference between the actual battery volts and that seen by the controller will compromise the charging process. Things will still function with a long cable run, but ideally install the controller near the battery with suitable cables. You will be limited by the connection points on the controller, perhaps 6ga, so go with this.
If you need to monitor battery state and charge status there are useful battery monitors available at low cost or just add a voltmeter and perhaps amp meter to the system .
A point to watch with some of the low cost PWM controllers, is that their control process is sometimes poor, leading to continually charging at full volts. Checking with a meter will be useful.
Consider at some time upgrading to a MPPT controller, besides converting all of the panel power to useful charging ( 10% to 30% more than a PWM), the setup and charge processes are much better.

Mike

 

[mikefitz]

lets assume one string, which would allow me to wire panels in series how would that affect my distance volt drop situation?

Five panels in one string may be too much for some MPPT controllers. The open circuit voltage of your 100 watt panels will be around 22 volts, five in series would be 110 volts. Some popular MPPT solar controller have a maximum voltage input of 100 volts, you would need a unit with a 150 volt maximum input.
With the panels in series the current will be 5.5 amps maximum into the controller, it wont effect the current between the controller and battery, if fact with a MPPT controller rather than a PWM, the current will be higher. In ideal conditions the system could deliver 40 amps ( in theory) compared to the 27 amps of the PWM system.

You should still mount the MPPT controllers near the batteries with heavy gauge cable. As with the PWM controller the unit need to know the actual battety volts. ( some controllers have a extra signal wire to monitor battarey volts). Most solar controllers have the capability for remote display and the excellent Victron smart range gives significant information of solar conditions and battery status via the app, so installing the unit without easy visual access is no problem.

Mike

 

[MichaelK]

A wire can also carry only so much voltage mainly determined by the type of insulation but most wiring is rated for very high amperage usually 600 amps or so which u will not surpass.

I think you need to be more careful with your terminology here! I think what you are trying to say is wiring is rated for high voltage (ie: 600V), not high amperage. You need to be careful when expressing limits to new people. Nobody here is likely ever to even see wiring that could handle 600amps.

 

[TKB4]

I think you need to be more careful with your terminology here! I think what you are trying to say is wiring is rated for high voltage (ie: 600V), not high amperage. You need to be careful when expressing limits to new people. Nobody here is likely ever to even see wiring that could handle 600amps.

My mistake I was interrupted and came back to it and lost my train of thought it was all about voltage. The amperage was previously covered .

 

[TKB4]

My mistake I was interrupted and came back to it and lost my train of thought it was all about voltage. The amperage was previously covered .

I would edit original but I am not allowed to do so.

 

[DixieMtCR]

I think you need to be more careful with your terminology here! I think what you are trying to say is wiring is rated for high voltage (ie: 600V), not high amperage. You need to be careful when expressing limits to new people. Nobody here is likely ever to even see wiring that could handle 600amps.

Good Catch!

 

[DixieMtCR]

So, where I live, 18mi NW of Portland Oregon, Sun is a premium. 1450ft elevation and it snowed off and on today. And then because I live in the woods on 5 acres of of land, and area where the sun shines, when it is out, is a premium. I have one place to position my panels. 100ft straight out from my front door. I will need to have the charge controller (MPPT), the batteries, and the inverter 100ft from the panel array, in my garage next to the load center. I plan on using #6 copper for the run. I am hoping the drop will not be significant. As I have been reading this thread here, the GRID power has gone out twice, for just a few minutes, but it does this all the time. Not uncommon to be out for days though. Need solar for basics. Lights in the house would be nice.

 

[Bill Taylor]

You know it really is a shame that the folks who sell this stuff don't offer design assistance for tech support. People have to get online to a DIY forum to find out how to hook stuff up? Maybe I'm getting old, but I remember when people behind the counter used to help you out with that sort of thing.

 

[HRTKD]

You know it really is a shame that the folks who sell this stuff don't offer design assistance for tech support. People have to get online to a DIY forum to find out how to hook stuff up? Maybe I'm getting old, but I remember when people behind the counter used to help you out with that sort of thing.

BayMarineSupply.com, where I bought some of my components does offer design help, but for a fee.

 

[williamsk913]

The voltage coming from the panels will always be more than that from controller to battery. With same size wires on both ends you will lose less if you make the wire that is lower voltage shorter, so make the wire from controller to battery shorter if you can rather than the distance from panels. You can move it closer to panels but will likely need to consider upgrading size of wire that runs from scc to battery bank.