Quick question...solar

[rbertalotto]

Bought 120w panel to be used remotely from my camper. Where do I put the charge controller for best efficiency? At the panel or close to the battery?

looking to run about 30 feet of cable....what gauge should I use?

 

thanks

[DesertMiner]

Put the controller as close to battery as possible. What type of controller...?

What do you hope to charge with only a single 120 watt panel?

10 ga solar wire would be fine for that distance. 

[oldjohnt]

  If I had my druthers I would locate the solar charge controller near the battery, but it will still work at either location with relatively small (subject to wire size, current, and distance) difference in efficiency. NOTE HOWEVER especially if they are lead acid, you don't want any electrical spark producing device in proximity (especially near top of battery) to hazardous potentially explosive gasses batteries can emit . Many of the small suitcase set out panels have the charge controller located with the panel. 

  As far as the wire gauge from solar panel to the solar charge controller, while it makes a difference if the panel was a so called 12 Volt or a 24 Volt, since it's only a 120 watt and you're only talking 30 feet, 10 Gauge will suffice although sure bigger cable means less line voltage drop.

Regarding charging your battery, a 120 Watt Panel, depending on the angle and intensity of the sun and condition and SOC of battery, might deliver 5 to 8 charging amps to your battery during peak sun periods which "may" (subject to actual load) be sufficient to replenish battery energy used for small electronics charging or LED lighting etc.

 While a PWM Solar Charge Controller, often used in low power low voltage applications, is cheaper, an MPPT can be more efficient plus allow for higher input voltages.  

 For more accurate answers you would need to know the panel voltage, wire length and current and use voltage drop calculators, but for a short sweet answer (although NOT perfect or exact) the above should suffice.

 

  John T

Edited October 22, 2019 by oldjohnt

[Lou Schneider]

On 10/21/2019 at 4:36 PM, oldjohnt said:

  If I had my druthers I would locate the solar charge controller near the battery, but it will still work at either location with relatively small (subject to wire size, current, and distance) difference in efficiency. 

I have to disagree with this, John.  Distance from the battery does matter for both converters and solar controllers unless you can adjust their voltage outputs and when they switch charging modes.

It only takes a few tenths of a volt in wire loss to make the controller / converter prematurely switch from boost to maintenance voltage.  30 ft. round trip of #10 wire between the controller and battery will lose 0.24 volts at 8 amps.  This won't have much of an effect on efficiency (the amount of power going into the battery) but it will make the controller drop to maintenance voltage prematurely, making the charging process take longer.

Edited October 23, 2019 by Lou Schneider

[oldjohnt]

16 hours ago, Lou Schneider said:

Distance from the battery does matter for both converters and solar controllers

  Lou, good post, thanks for your inputs, but actually I think for the most part YOU AND I ACTUALLY AGREE ON A LOT OF THIS !!!!! Yes, I  understand how a charge controllers output is based to a degree on battery voltage, so you don't want many variables (I x R Voltage Drop)  between the controller and battery.

  As far as your quote above,  I AGREE.  Although it will still  work EITHER way, if the charge controller is located nearer the panel or the battery, I still prefer it closer to the battery due to less wasted I Squared Heat Energy losses and less I x R Line Voltage Drop . One reason is if the panel is a so called 24 volt with a Vmp maybe 30+ volts there's LESS current FROM panel TO battery then there is FROM controller TO battery which is at a much lower charging voltage of say 14 volts. Since the line voltage drop = I x R and at 30 volts (given near same watts) there's less current, I would still prefer that long 30 ft run (panel to controller) be at the higher panel 30 volts versus the lower 14 volts (from controller to battery). So even if sure it works either way my preference would still be for the long 30 ft run to be at the higher voltage with the charge controller and its lower 14 volts to be close to the battery.

EXAMPLE:  30 Panel Vmp Volts at 120 Watts (Panel to Controller) would = 4 Amps,  while 14 charging volts at 120 Watts (Controller to Battery) would = 8.57 Amps    THATS WHY I STILL PREFER THE CONTROLER NEAR THE BATTERY

   Looks like we both agree  (given a 120 watt panel and a 30 foot run)  as you said     "This won't have much of an effect on efficiency"   I say DITTO  

   Looks like we both AGREE on your quote below also.

16 hours ago, Lou Schneider said:

Distance from the battery does matter for both converters and solar co

 Distance makes a difference on BOTH since the I x R Line Voltage Drop still applies  I AGREE WITH THE ABOVE

ANOTHER CONSIDERATION TO THINK ABOUT:  The Solar Charge Controller IS NOT 100% EFFICIENT it has heat losses so throw that in to even further complicate all this LOL

 Trouble is many of the small set out solar panels have the charge controller right at the panels so we don't have a choice unless we re configure which isn't hard or complicated.

 

 Thanks Lou, I enjoy and appreciate this techy sparky chat

 Best wishes n God Bless

 John T  

Edited October 24, 2019 by oldjohnt

[Sehc]

On 10/21/2019 at 5:40 PM, rbertalotto said:

Bought 120w panel to be used remotely from my camper. Where do I put the charge controller for best efficiency? At the panel or close to the battery?

looking to run about 30 feet of cable....what gauge should I use?

 

thanks

Not a complicated question. Not a complicated answer. The best efficiency dictates larger and/or shorter cables to reduce voltage drop as much as possible. At 30 feet, the controller should be at the battery end of the circuit. Then a reasonable cable size could be used. With a larger fuse at the battery positive post.  I used a Renogy panels and found ready made extension cables of 8AWG, red and black.  With such a small panel, PWM controller would be fine. MPPT would not make much difference, but would be subject to more failure than PWM controller.

[oldjohnt]

5 minutes ago, Sehc said:

The best efficiency dictates larger and/or shorter cables to reduce voltage drop as much as possible. At 30 feet, the controller should be at the battery end of the circuit

I HAVE TO AGREE 100% on that Lou. Bigger cables = less I x R Voltage Drop (sure 10 Gauge works fine yet 8 = less voltage drop) and controller at battery end is best. I'm running four panels at 1080 watts  up on the roof (only a 29 ft Class C) while my solar charge controller is relatively close to my three Renogy AGM batteries.

John T     Happy often dry Camper

[Randyretired]

I think the best thing to consider is, how much the 120 watt panel can charge a battery.  120 watts is just a little better than good battery maintenance.  It likely will take more solar to keep up with most RVers.  I have run into people who claim solar doesn't work after trying a small panel.  It is important to keep expectations reasonable.

[rbertalotto]

Just so we understand, my trailer has 420 watts on the roof. This 120 watt panel is to augment the rooftop panels and give the entire system a bit of a boost. 
 

after reading the above, I will place the charge controller at the batteries with the negative into the Bogart TriMetric shunt and the positive to the battery. In this way I understand I’ll be able to see total charge performance on the TriMetric monitor.

 

i will be using 24’ of number 8 wire from the panels for a total 48’ run.

 

thank you for all the assistance. Greatly appreciated

 

[rbertalotto]

BTW...this is the portable panel I purchased and received. Looks well made. The charge controller is attached to one of the panels. I will remove and relocate at my battery box.

https://www.ebay.com/itm/ECO-120W-12V-Mono-Portable-Folding-Solar-Panel-off-Grid-Kit-for-Camper-Boat-RV/362467394170?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Delivered was under $150.

[oldjohnt]

11 hours ago, rbertalotto said:

after reading the above, I will place the charge controller at the batteries with the negative into the Bogart TriMetric shunt and the positive to the battery. In this way I understand I’ll be able to see total charge performance on the TriMetric monitor.

 

i will be using 24’ of number 8 wire from the panels for a total 48’ run

Thanks for the feedback. Wise choice in placing the charge controller at the batteries and the use of 8 versus 10 Gauge wire will insure less voltage drop. Indeed ALL the negative leads (charging inputs and load outputs) wired to the shunt will provide valuable battery status information.

 Good job

John T   

Edited October 25, 2019 by oldjohnt

[rbertalotto]

So here is what I did today.......

Since the charge controller that cam with the portable panels is mounted to the back of the glass panels with some type of adhesive, I didn't want to remove it and risk breaking the panel.

I purchased a Generic solar controller that I feel is at least as good as the one on the panel and actually gives me more information.

I mounted it in my electrical cabinet which is connected to the batteries by 18" of #2 cable

From the high current, quick disconnect plug, I ran 8" of #10 wire to the controller and using another 10" of #10 wire to the shunt and the main battery cable. Short sections of this 10g wire should have negligible loss?

For now, I just ran the wire that came with the panel to another high current connector to just test it out. I ordered 25' of #8 welding cable that will be here on Sunday.

Everything works great! I can read the additional current from the portable panel on the trimetric. 

Its interesting that up here in the Boston area, at this time of year, the 420w of flat panels on the roof were only giving me an indicated  2 amps and the 120w panel aimed directly at the low sun (3pm) was showing 1 amp! 

Can't wait to try it out under real conditions in a couple months boondocking in New Mexico and Arizona

Read more here:

http://rvbprecision.com/

Edited October 25, 2019 by rbertalotto

[Darryl&Rita]

That's why people tilt their panels. When prices were higher for panels, tilting was a good way to make more power. Now, the price per watt has come down, so people will mount as many as will fit.

[rbertalotto]

With a 19' travel trailer, roof space is at a premium. I actually thought about doubling up the panels and making them fold out when stopped and folded in while traveling.....