solar options

[chloe_s_ranch]

Last summer I had a 240 watt kit(from Solar Blvd.) Installed on our MH. It has two 120 watt panels feeding a 20 amp charge controller. I recently had the two stock 12 volt marine house batteries replaced with four Trojan T-105s since we almost always dry camp or boondock and wanted more amp hours to get us through the shoulder season when we run the heater more(and there is less sunlight.) We also hate running the generator because of the noise. I know a rough rule of thumb is about 1 watt of solar for each amp hour of battery capacity and I now have a 450 amp hour battery bank. So if I have more solar installed here are some options: A--Have another kit from Solar Blvd.installed with its own wiring and another 20 amp charge controller so both kits would work in parallel charging the batteries. They have a 300 watt kit for $500. Or B--get their 120 watt kit and have them swap out the 20 amp charge controller for a Blue Sky sb3000i 30 amp mppt charge controller for about $500 also. I know option B would require heavier gage wiring since all three panels would be wired together feeding a single controller. Or option C--get the 300 watt kit and pay a little more to swap out the 20 amp pwm charge controller for a 40 amp pwm charge controller and wire all four panels into it. Again needing heavier gauge wiring. It seems to me that option A(having two separate kits feeding two separate 20 amp pwm charge controllers) offers the most bang for the buck. What are your thoughts?

[pianotuna]

Hi chloe,

If you are using a pwm controller voltage drop doesn't matter, so long as the wire is "legal" for the number of amps of current.

example:

17 volt panel drops down to 14.8 volts by the pwm controller. That is about a 13% voltage drop. Quite a bit more than you would ever see from the #10 wire.

If you are using an MPPT controller, place the panels in series--just make sure that nothing on the roof can cause shading on any of the panels at any time.

OR

Replace the #10 wire, use MPPT and a parallel panel configuration.

If you won't be going over 480 watts of panels, then the 3048 Rogue is state of the art, and includes a temperature sensor. Temperature compensation is a "must do" in my opinion.

Blue Sky is.....some what out of date and charge for extra for the temperature sensor. They also do not have battery voltage sense wires.

chloe's ranch wrote:
Ed suggested using a second 10 guage wire between controller and batteries. Is that better than using a single heavier guage wire? Easier since one 10 guage wire is already in use? Two tens equals what guage single wire? The controller is about three feet from the batteries. Thanks again!

[NinerBikes]

10 gauge for 30 amps, or under, from the panel to the controller, will work. You'll want something like 6 or 8 gauge from the solar panel charge controller directly to the battery terminals, and as short a run as possible. The loses between the charge controller and the battery pack, after the volts and amps are controlled, is the critical wire diameter and lenght issus. Keep them short, and fat, to minimize losses in voltage and amps. Fat wire is low resistance wire.

[time2roll]

Don't use parallel wires. Get the right stuff.
NEC and RVIA frown on parallel.

[chloe_s_ranch]

Ed suggested using a second 10 guage wire between controller and batteries. Is that better than using a single heavier guage wire? Easier since one 10 guage wire is already in use? Two tens equals what guage single wire? The controller is about three feet from the batteries. Thanks again!

[westend]

It sounds like you will definitely be upgrading the amount of panel you have and connectivity is at question. If you use a combiner box on the roof, it will all be a lot easier, no matter which wiring schedule you choose. The combiner box can offer easy termination of parallel sources and can also be used for a series string.

Since I'm a miser about lost voltage and I already had a spool of 4 AWG , I used that from the combiner box to the controller. I only have one module, at present, but can easily add more, if needed. Like Niner says, initial tally of how much power used in a typical day (along with some headroom) is a good starting point.

At some point, you may want to think about multiple higher voltage modules. There's some cost and ease of use benefits with the bigger modules. The layout of your roof will dictate, sometimes, what you can fit. The higher voltage panels will also mean MPPT controller, only.
FWIW, I have a Morningstar controller and it is quite a sophisticated device for the price. It allows a user to tailor charge settings, duration, equalization, and is temp compensated. It also has a PC interface so data logging, graphs, etc. can be made and saved. Lots of geekiness.

Good luck with your upgrade.

[eb145]

chloe's ranch wrote:
Thanks again everyone for the help. Sounds like an adjustable controller might be a good idea. If I do go with option B(adding a third 120 watt panel to my current 240 watt system and using the Blue Sky 30 amp mppt controller) I have another question. Currently my two 120 watt panels are wired in parallel with 10 guage wire down a vent to the existing controller. Should I have the additional 120 watt panel run with a separate 10 guage wire down the vent and then spliced together with the current wire at the controller, and then 6 or 8 guage wire from controller to batteries?

A single 10 gauge wire can handle the 3 120 watt panels in parallel. Yes there will be some voltage drop, but that is usually not the critical voltage drop for your system. The controller (PWM or MPPT) will reduce the voltage even more as it does its work.

What is critical is the voltage drop from your controller to batteries - that is what can really slow down the charging. Short fat wire is needed from the controller to the battery to minimize voltage drop between them. What gauge wire is currently between your battery and controller? And how long is the wire run between them?

A great way to measure the voltage drop between controller and battery is to measure the voltage across the controller output and then across the battery posts when the solar panels are sending lots of amps into your batteries. The voltage at the battery terminals is what needs to be high to get the most amps into the batteries.

So while adding a 10 gauge wire from your new solar panel to your controller will help a little bit, it is more likely that adding that 10 gauge wire between your batteries and controller will provide you with more benefit. Note I said "adding" the wire between batteries and controller - you can add more wires between the two points or substitute thicker pure copper wires between them - whatever it takes to minimize voltage drop at the battery posts.

Ed

[BFL13]

With the MPPT you could put the three 120s in a series string and stay with #10/8 Assumes the controller can take over 66Voc

[NinerBikes]

double post

[NinerBikes]

With four T-105's, you have 450 Amp hours at 12v. 50% discharge means that you'd need to replace 225 amp hours, per day. Basic rule of thumb, on the weak side, is 1 watt of solar, or more, per amp hour of battery. In the winter, you will likely need more than 1 watt per amp hour.

Since you already have 2 120 watt panels, for 240 watts, and about 13 amps, I would add another 2 120 watt panels, if you have the room, at a minimum, which should bring you up to a max charge rate of 26 amps an hour. You are capable of using 250 amps a day, that's 11 hours of charging under ideal conditions to get it all back. In winter, 6 or 7 hours is tops. Each panels will generate about 6. to 6.5 amps, peak, so a 30 amp converter of some sort should handle all your needs, in the summer, not so much in the winter, more panels are needed due to lower sun angle and shorter days.

Something like this:

Charge controller

In my view, until you know what your daily consumption is in amp hours per day, it's pointless to buy more panels, one at a time, or two at a time.

Nail down how many amp hours per day you go through on the shortest day of the year, and take it from there for worst case scenario.

[chloe_s_ranch]

Thanks again everyone for the help. Sounds like an adjustable controller might be a good idea. If I do go with option B(adding a third 120 watt panel to my current 240 watt system and using the Blue Sky 30 amp mppt controller) I have another question. Currently my two 120 watt panels are wired in parallel with 10 guage wire down a vent to the existing controller. Should I have the additional 120 watt panel run with a separate 10 guage wire down the vent and then spliced together with the current wire at the controller, and then 6 or 8 guage wire from controller to batteries?

[NinerBikes]

BFL13 wrote:
"So, then if I set my adjustable Voltage Charge controller voltage to 15.0V, does that mean my T1275's will get an actual 14.8 volts from my solar panel? "

You need a voltage spread but not necessarily 0.2v. I got that 14.8 /14.6 from an earlier version of the Iota website.

It depends. I think the PD expert on here said it was just a tiny spread needed and a lot of the spread you see is voltage drop on the wires.

Solar controllers are even more fun where you have losses in and out and who knows which voltage the adjustable setting sets? I suggest a trial and error measurement and see what makes it come out right to 14.8 Of course that 14.8 is only for 77F and it should be higher when colder and lower when temp is higher.

It does have temp compensation, but a 150 amp/hr T-125 is not going to get hurt by .1V extra if set to 15.0 with only 6.6 amps max coming out of my 120w solar panel, under ideal conditions. It's relative. Battery capacity % to charge capacity %.

[BFL13]

"So, then if I set my adjustable Voltage Charge controller voltage to 15.0V, does that mean my T1275's will get an actual 14.8 volts from my solar panel? "

You need a voltage spread but not necessarily 0.2v. I got that 14.8 /14.6 from an earlier version of the Iota website.

It depends. I think the PD expert on here said it was just a tiny spread needed and a lot of the spread you see is voltage drop on the wires.

Solar controllers are even more fun where you have losses in and out and who knows which voltage the adjustable setting sets? I suggest a trial and error measurement and see what makes it come out right to 14.8 Of course that 14.8 is only for 77F and it should be higher when colder and lower when temp is higher.

[BoonHauler]

NinerBikes wrote:

BFL13 wrote:
AFAIK the Iota IQ4 goes to 14.8 but that's so the batteries can get to 14.6. Once the batteries reach 14.6, it stays there for 15 minutes and then drops to 14.2. Phooey on that!

I don't know any converter that will do it right in every way. That's why I still use the 13.8v Parallax 7355 as the converter for when on shore power (works great) and use separate chargers for the real battery charging stuff to proper high voltages for my 6s and Trojan 1275s.

For fast charging four 6s I use a 100amp charger that goes to 14.8 and stays there, or I can crank that voltage higher if it is cold out so it should be more like 15.1v Note that 100/440 is only a 22% charging rate and you could safely go higher to a 30% charging rate on the four 6s if you want.

Yes it is a way to get by in the fall/spring when solar is not as good as in summer, to just charge for an hour in the morning with charger and then go solar for the rest of it. Trick is to have :
- a serious charger and gen to run it
- gen hours that let you run it in the morning.

That may let you off the hook for getting more solar, so you end up with too much solar in the summer. I keep going back and forth on this, where I get too much solar for summer and sell some, then buy more for the spring and then wish I hadn't and sell that, then a sale on panels happens I can't resist so I buy more and end up with too much solar again! There is nobody who can help you if you get that affliction. 😞

So, then if I set my adjustable Voltage Charge controller voltage to 15.0V, does that mean my T1275's will get an actual 14.8 volts from my solar panel?

Is your solar charge controller temperature compensated? If not it should be.

As for charge set points I myself feel that higher is better. I have Crown 6 VDC 260 A/H batteries. Crowns literature said to charge to 14.5 and float at 13.5. I charged to that and had low SG.

I spoke with the technical staff at Crown and they came back saying that I could go as high as 15.1 on the bulk charge rate.

I now have my charger set at 14.9 Bulk and 13.8 float. The longer I float (now set at 4 hrs) the better it is.

Temperature compensation is a must in my book just as a good battery monitor is as well.

[time2roll]

BFL13 wrote:
I keep going back and forth on this, where I get too much solar for summer and sell some, then buy more for the spring and then wish I hadn't and sell that, then a sale on panels happens I can't resist so I buy more and end up with too much solar again! There is nobody who can help you if you get that affliction. 😞

Another reason to mount them fixed to the roof.