Solar Panel Configuration and PWM Controller Question

The_Dreamer · September 2014

Hello. This is my first post to this forum. I suspect it will be the first of many as I have a number of questions regarding the proper configuration of my RV solar auxiliary power system. I appreciate any help that those with more knowledge and experience of this subject can offer me.

I am a full-time RVer, living in a converted school bus going on four years. I am doing an upgrade and redesign of my existing solar auxiliary battery system. Following is a listing of the components I have at present.

I have four identical solar panels, 140 watts each. Their specs are as follows:

Voc 20.6V
Vop 17.3V
Short circuit current (Isc) 9.63A
Working current (Iop) 8.1A

I have a Morningstar Tristar 60 Amp PWM controller.
I have two Concorde Sun Xtender AGM batteries (153 AH each).
I have a Go Power 3000 HD inverter.
I have the 30 Amp switch from Go Power to feed power from the inverter back into my 30 Amp World Friendship Power Converter Panel. (Comes standard with many Coachmen RVs.)
I have the Trimetric 2030 RV Battery Bank Monitor.

My first question relates to the proper way to wire my solar panels to feed into my Morningstar TS-60 PWM controller. The controller is designed for 12, 24, and 48 volt battery banks. Mine is configured for 12 volts. From what I can gather, the TS-60 accepts an input voltage as high as 125 volts, and to stay within recommended limits of NEC regulations a continuous current of 48 amps should not be exceeded. My panels wired either serially, or in parallel will not exceed either of these maximums.

I would like to understand better how the PWM controller works. I have read that if I choose to wire my solar panels in parallel my voltage would remain constant at 17.3 volts while my amps would quadruple to approx. 32 amps. From what I have read (I am a DIYer, not a trained electrician), this high current and low voltage would create tremendous reactance in my solar cable, and the resistance would result in a significant voltage drop. What I have read suggests to keep voltage high and current low to mitigate voltage drop-off. (I have 6 AWG cable and have a run of approx. 40 feet from the panels to controller.)

If I wire in serial I would probably be receiving 70-80 volts and 8 amps at the controller on a sunny day. There is a jumper in the controller to select the proper voltage for the battery bank, and I have it set for 12 volts. Would the controller pass the 70-80 volts directly along to the battery, and would this be too high of a charging voltage for a large 12 volt AGM battery?

I have considered the possibility of writing the solar panels half serial and half parallel to produce 35-40 volts and 16 amps coming into the controller. Is there an advantage to this?

I guess what I am struggling to understand is what is a good charging voltage and amperage for my 12 volt battery bank, and how does the charge controller handle it. I have read that the charge controller does not actually change the voltage, but merely tapers off excess current. Is this correct?

I posted this question on another forum and one member said they have the TS-45 controller and four 125 watt panels wired in serial and it works fine. Another user said that I definitely needed to wire in parallel since I will be charging a 12 volt battery bank. Who is correct? I don’t want to cook any of the expensive components, so any assistance is appreciated.

Thanks in advance!

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

PWM type charge controllers can NOT make use of extra voltage, it is just wasted, so the panels must be wired in parallel, If you combine them near the panels, you can minimize any voltage drop by sizing your wires running from the combiner box to the Charge Controller (CC) for the expected maximum voltage and current.

Here's a link to an article on Charge Controllers. Ignore the loss of power with PWM CC, I can explain why if you like but 20-60% is unrealistic.

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Thanks. What would be considered "extra voltage" on a 12 volt battery system like mine?

I will check out the link.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The_Dreamer wrote: »

I have a Go Power 3000 HD inverter.

This is a huge inverter for a 12v 300ah system! and likely not a good choice for a small system, it claims to use less than 2.5 amps idling or 25+watts, running it is 82-87% efficient, also as a modified sine wave inverter if it's running motorize things they will run less efficient and hotter due to the dirty current. Also at full load you will need some monster cables to connect this to your battery bank, even if you have very short run 4/0 would be minimum.

The_Dreamer wrote: »

(I have 6 AWG cable and have a run of approx. 40 feet from the panels to controller.)

If combined at the panels I think 6 gauge will be about a 6% loss, to get under a 3% loss you would need to go to a 2 gauge cable! Any way to shorten this run? I'm assuming a 40 foot one way?

The_Dreamer wrote: »

If I wire in serial I would probably be receiving 70-80 volts and 8 amps at the controller on a sunny day. There is a jumper in the controller to select the proper voltage for the battery bank, and I have it set for 12 volts. Would the controller pass the 70-80 volts directly along to the battery, and would this be too high of a charging voltage for a large 12 volt AGM battery?

The charge controller limits the volt to the batteries to the proper charging voltage, but a PWM CC can not utilize the extra voltage so it would be wasted. It would be the same as hooking up a single panel close to the charge controller, if the CC can handle the extra voltage.

The_Dreamer wrote: »

I guess what I am struggling to understand is what is a good charging voltage and amperage for my 12 volt battery bank, and how does the charge controller handle it. I have read that the charge controller does not actually change the voltage, but merely tapers off excess current. Is this correct?

The charge controller handle the charging, basically by rapidly switching on and off to maintain the proper voltage. The battery will naturally accept less current as it reaches full charge.

The_Dreamer wrote: »

I posted this question on another forum and one member said they have the TS-45 controller and four 125 watt panels wired in serial and it works fine. Another user said that I definitely needed to wire in parallel since I will be charging a 12 volt battery bank. Who is correct? I don’t want to cook any of the expensive components, so any assistance is appreciated.

Morningstar makes a MPPT type charge controller with a similar name. MPPT type controller can utilize the extra power and down convert to charge the battery.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The_Dreamer wrote: »

Thanks. What would be considered "extra voltage" on a 12 volt battery system like mine?

The batteries will want to 'see' up to just shy of 15 volts after all losses. If your panels produce 17.3 volts what ever is needed to above the losses in wire and Charge Controller would be considered 'extra'.

BTW- be sure to set your charge controller for AGM batteries! Do NOT EQUALIZE! this may out gas and ruin your AGM batteries!

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Hello Photowhit,

I wish I had read the explanation of the different capabilities of charge controllers at the link you provided BEFORE I purchased my TS-60. I would definitely have opted for the MPPT model so I could keep my voltage high and amps low in my solar panel cable runs. It looks like I have two viable options. I can get an MPPT controller as voltage drop would be excessive if I wired my panels parallel and ran the distance needed, and the cable would have to be so massive as to be impractical, OR I can relocate my panels (possibly to the roof of my bus) where cable length could be reduced 75% to approximately 10 feet, and keep my current equipment. I would then wire the panels in parallel as you suggested, and with 6 AWG wiring the voltage drop should not be too significant.

I am definitely leaning to this latter option. So, I am off to design a 4 panel roof mount system for my bus.

Thanks!

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

While I don't like the added charging claims, MPPT CCs have great utility in this situation. If you think about switching, They are rated on their output amperage, something we often see people confused about...

Another option is to dump the inverter, and run a 24v system, at 24volts you would be under a 2% loss on 6 gauge.

What do you need the high wattage for? at 3000 watts and 87% efficiency, you would draw something like, 3000/12=250, 250*1.14=285amps... likely shut down your inverter on low voltage before it ran anything!

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Photowhit wrote: »

This is a huge inverter for a 12v 300ah system! and likely not a good choice for a small system, it claims to use less than 2.5 amps idling or 25+watts, running it is 82-87% efficient, also as a modified sine wave inverter if it's running motorize things they will run less efficient and hotter due to the dirty current. Also at full load you will need some monster cables to connect this to your battery bank, even if you have very short run 4/0 would be minimum. If combined at the panels I think 6 gauge will be about a 6% loss, to get under a 3% loss you would need to go to a 2 gauge cable! Any way to shorten this run? I'm assuming a 40 foot one way?

I do plan on adding at least one more 153 AH battery to my bank. The reason I chose the Go Power 3000 is that I want to tie back into my RV's power box so that I can utilize all the receptacles and appliances that are already wired into it. I didn't want to run extension cords throughout my bus to power individual appliances. The Go Power 3000 is about the smallest inverter that I came across that is reported to be able to tie into a 30 amp RV breaker box (using a transfer switch). I read the account of another individual who had used this particular inverter for a similar application, and he gave it high marks, and reported that he had no problems running sensitive electronics with it.

Having said that, I don't actually anticipate running a full 30 amp load on the system when powered by battery. I rarely do even when I am attached to shore power, and that is with my rooftop AC unit running. I don't plan to run air conditioning when running off of battery. I have also optimized my rig for power efficiency. All my lighting is LED. The only electric appliances I will have running at all times will be a freezer (very high efficiency 1 amp model) and my Dometic refrigerator that is rated at 2.7 amps. I will be running a laptop computer and occasionally a printer, and a fan. With the amps used by the Go Power inverter, I am looking at less than 10 ah draw on average, and likely closer to 8 amps. I do anticipate some spikes, however, when I use the microwave (13 amps) or toaster. I want to monitor things for a while with my Trimetric power monitor before I decide to add more batteries, but I do anticipate adding one more. This would give me 459 AH in my battery bank, and with thrifty power usage I believe I can get by on less than 200 AH per day. I will know for sure once I start monitoring.

What are your thoughts on the ability of my 560 watt solar array to keep this battery bank charged? Will it be adequate? I am in Georgia, between 32 and 33 degrees north latitude.

I do admit that I don't like the fact that the Go Power converter draws so much amperage even when idling, but it was a lot less power draw (and money) than a pure sine wave inverter of a similar rating.

Thanks

Plowman · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Another option you could consider is placing your charge controller and inverter closer to the panels and running a line from the inverter to your bus. That's what I do. I have my panels mounted on a cargo trailer with the CC, batteries, and inverter inside, and I run an extension cord to my RV about 100' away. My current draw is pretty light, so voltage loss even over that distance is minimal because it's 120VAC.

BB. · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The reality is that going off grid / battery power -- You really need to look at conservation first--That is the best investment for your money.

A 3kWatt inverter running full tilt will drain your present battery bank in an hour or less (and could kill the battery bank too).

A 560 Watt solar array mounted flat to your roof of an RV in Georgia: using PV Watts, in Macon GA:

Month    Solar Radiation
(kWh/m 2/day)
1      2.51     
2      3.60     
3      4.67     
4      5.68     
5      6.19     
6      6.05     
7      6.10     
8      5.56     
9      4.54     
10      4.17     
11      3.13     
12      2.42     
Year      4.56

Using 4.56 hours of sun average per year (December at 2.42 hours of sun is pretty poor):

4.56 hours of sun * 560 Wat array * 0.52 AC off grid system eff = 1,328 WH = 1.3 kWH per day

A 3kW inverter running at full power sill use that up in less than 30 minutes per day.

Now--That "10 AH" draw (or 8 amps)... Assuming you intended 10 amp draw--Was that 10 amps at 12 VDC:

10 amps * 12 volts = 120 Watt draw

or at 120 VAC:

10 amps * 120 VAC = 1,200 Watt draw

Big difference here... When were many people get tripped up. Amps and Amp*Hours are "partial" units of energy--Need to know voltage.

Watts and Watt*Hours are a complete unit, it tells us everything about the basic energy requirements of a power system. And that is why we tend to use Watts and Watt*Hours when design a system--Lets us "forget" about voltage for a while as we juggle the numbers and requirements around.

Once we get basic agreement--Then we can break it down to Amps and Volts for the various pieces of the system (the 120 VAC and 12/24/48 VDC parts of the system).

-Bill

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The_Dreamer wrote: »

Having said that, I don't actually anticipate running a full 30 amp load on the system when powered by battery. I rarely do even when I am attached to shore power, and that is with my rooftop AC unit running. I don't plan to run air conditioning when running off of battery. I have also optimized my rig for power efficiency. All my lighting is LED. The only electric appliances I will have running at all times will be a freezer (very high efficiency 1 amp model) and my Dometic refrigerator that is rated at 2.7 amps. I will be running a laptop computer and occasionally a printer, and a fan. With the amps used by the Go Power inverter, I am looking at less than 10 ah draw on average, and likely closer to 8 amps. I do anticipate some spikes, however, when I use the microwave (13 amps) or toaster. I want to monitor things for a while with my Trimetric power monitor before I decide to add more batteries, but I do anticipate adding one more. This would give me 459 AH in my battery bank, and with thrifty power usage I believe I can get by on less than 200 AH per day. I will know for sure once I start monitoring.

I suspect your confusing amp and amps...lol. Amps are a measure of current. So a 1 amp draw at 120 volts will be a 12 amps draw x 1.15 (inverter use) or a 14 amp 12 volt draw. Many of the calculations revolve around watts = amps x volts. Add in hours for draw over time. Batteries are rated at 153 ah (amp hours at a draw of no more than 1/20th of the bank capacity)

The_Dreamer wrote: »

What are your thoughts on the ability of my 560 watt solar array to keep this battery bank charged? Will it be adequate? I am in Georgia, between 32 and 33 degrees north latitude.

I think it will be a challenge on when you have over cast days. It's likely you fried draws around 1kwh during a day, particularly in the heat. I'm from North Florida so if your in the foot hills of the Appalachian Mtns you might have cooler temps. Your total usable wattage on sunny days is likely around 5hoursx560watts/2 or about 1.4 kwh so with a freezer as well as a fridge and additional loads, I suspect it's doubtful the system will be able to keep up with your needs.

For what it's worth, you don't need to be able to produce 30 amps at 120 volts to tie into your panel, I have a 1800 watt inverter that runs my home and it's hooked into a 100 amp subpanel, but fused at the inverter for it's abilities. An Exeltech 1100 watt inverter is made to be hard wired and likely would run all but your microwave (could easily find a smaller microwave) for about $600. It's a pure sine inverter and designed to be hardwired.

If your inverter is a new returnable purchase, and you want to have a system that will stand a better chance against your loads, you might consider going to 24 volts add 2 batteries in series and parallel, and look to add 5-800 watts of panels. You might still want a generator for multiple cloudy days. The Exeltech comes in a 24 volt version.

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Thanks Bill. I do have my panels mounted at an angle with the sun. They have been ground based, but I will shortly be relocating them to the roof of my bus where they will also track with the sun. I am working on the rooftop mount design now. This is also going to give me much shorter cable runs. I estimate about ten feet from panels to charge controller.

I very much agree with you about power conservation being the place to start. That is why I changed all my RV lighting to LED which draws about 1/10th the power of incandescent bulbs for the same lumens. I also acquired a high efficiency freezer which I keep in a trailer I pull behind my rig. It is rated at 1 amp (it is 110 volt), and that is when it is running. During the winter, of course, being in an non-insulated trailer, the freezer runs very little. Even during the summer it runs only about 1/4 of the time as it is very well insulated.

For cooking I mainly use propane. Though when connected to shore power I frequently use the microwave, and occasionally a toaster or panini grill.
For heat I use small ceramic electric heaters when I am on grid, but when I am off grid I have a cast iron woodstove that I use for heat.

My main power consumption when boondocking is from my refrigerator (2.7 amps at 110 volts), my freezer (1.0 amps at 110 volts), laptop computer (I have no idea what its power usage is), and lights at night. I can do without the microwave and toaster if needed, as I can cook anything with propane. I do have a grain mill that may get run 40 minutes a week. By the way, the label on the motor for the grain mill says "90 watt, 115 volts, 50 hz, 1.4 amp," or "90 watt, 115 volts, 60 hz, 1.5 amp." I don't see how they came up with their figures using the formula you provided. If watts equals amps times volts then a 115 volts motor at 1.4 amps should be 161 watts, not 90 watts. This is enough to make a layman like me scratch his head in perplexity.

Anyway, aside from running my potable water pump perhaps 5-10 minutes a day, and charging up some batteries for various battery powered devices, that is the majority of my electrical consumption when boondocking. I would like to run all of this off of my 4-140 watt solar panels and 2-3 Sun Xtender batteries (153 ah each). Perhaps I am going about it wrong trying to tie an inverter into the RV's main power box. If there is a better, more efficient way to do this than using the Go Power 3000 inverter and a transfer switch, I am all ears and eager to be instructed.

By the way, I am in South Central Georgia about 40 miles south of Macon and about 100 miles north of the Florida line.

Thanks.

P.S. Using a smaller inverter like the Exeltech is an idea I need to look into, especially if it draws less power when idling. My system is set-up for 12 volt, however, as the World Friendship Power Converter box that runs all the AC and DC, and also charges the batteries when hooked to shore power, only works with a 12 volt battery bank.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Well heck, my grain mill uses 1000watts! What brand is yours? I use a Ktec Kitchen Mill. Not sure about the wattage discrepancy, perhaps a power factor, or running vs starting... Bill will likely know. So long as there are no additional loads, you could use your existing wiring. Use a Kil-A-Watt meter between and check, would take a bit of rigging.

The refrigerator isn't a thermo electric type that uses 2.7 amps continuously? A clamp meter might give you more information on what the actual power usage from the batteries is, it's likely to be a good bit higher running on a MSW inverter if it's a compressor type.

Things that heat and cool are the hardest to run in off grid homes. That said Forman grills are much like your Panini press and they cook very efficiently. There are less powerful microwaves, but I used a microwave in my cabin system which started at just under 1000watts(array).

I came back to mention that adding new batteries to old is normally not suggested, if they are less than 6 months old you should be okay, but suggest making sure the old are fully charged before adding any new batteries.

Was a photographer for the Warner Robbins Daily Sun(?) for a minute back in the early 80's... dang I'm old...

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I have the Country Living Grain Mill with the motor. It is made to either be operated by hand, or run by a motor. It is a very nice unit. Looks like it will last for generations. I like grinding my own grain for breads. I also grind up peas and lentils for soup bases and gravies and have even added bean flour to some bread recipes.

I worked at the Houston Medical Center in Warner Robins for 14 years. I left there in 1999. Warner Robins is about a 25 minute ride from my location. I guess your moniker of Photowhit indicates you have not lost your interest in photography since you worked for the Daily Sun?

I cannot really say whether the refrigerator is thermo electric, or whether it draws a continuous amperage. It is a pretty common Dometic model, made for RV's. This one came out of a Coachmen motorhome. It is designed to run on propane or electric, but I don't have it hooked up for propane.

I had heard that about not adding old batteries to new ones, and not to mix different manufacturers, or different capacity batteries. I suppose the reason for not mixing old and new batteries with one another is that their capacity and recharge rates change over time. This seems to be more of an issue when hooking batteries in serial than in parallel. On another website I found the following information. I suspect there are some who would disagree with the conclusions.
---
Connecting two battery banks of different amp-hour capacity together in series is a bad idea. The problem is that the battery charging controls will operate based on the average battery voltage and the two batteries will have very different voltages because their capacities are different. The 100 AH battery will become fully charged long before the larger one. The combined voltage will rise, but by the time the controller turns off the charging sources, the 100 AH battery will be overcharged. Meanwhile, the 200 AH battery will not get fully charged. When the bank is being discharged, the 100 AH battery will go flat and its voltage will fall well before the 200 AH battery. The inverter will eventually cut out but not before the 100 AH battery is excessively drained.

Connecting two banks with different capacities in parallel is technically fine since the batteries will be operating at the same voltage. Charge and discharge current will be shared, based on capacity. It is best if the batteries are of the same type and age. For example, avoid combining a sealed (gel or absorbed glass mat) battery with a flooded (conventional) battery because they have different charging setpoints. Broadly speaking, you can parallel batteries without problems, and the charge controller will look after them. Just make sure you give them plenty of charge. If the system tends to operate at less than a full state of charge, adding new batteries to old will probably just result in the old ones pulling the new ones down and everything getting sulphated.

Hugh Piggott • Scoraig Wind Electric
---
I am hoping this is true since I am going to be hooking my two Sun Xtender AGM batteries together in parallel and one is older than the other. To my knowledge, the older battery is charging up well. I had it hooked to a BatteryMinder for the past year to keep it in optimal condition. AGM batteries have a reputation for lasting up to twice the lifespan of a standard flooded lead acid battery, so I am thinking they do not degrade as quickly. It is hard to replace a $400 battery ($470 with shipping). I could never get my money back out of it since it is now considered "used."

So, is this guy completely wrong, and should I be worried? Since the batteries are hooked in parallel, won't they equalize with one another rather than one overcharging and the other undercharging as they would if they were wired serially?

Cariboocoot · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Not completely wrong, but not well explained.

The problem is how much difference there is in the two paralleled battery capacities. The greater the difference the greater the problem. As they move further apart in Amp hours the charging Amps becomes either too high for one or too low for the other, neither a desirable state.

So using a string of 232 Amp hour 6 Volt FLA's in parallel with a string of 225 Amp hour 6 Volt FLA's both new will probably not show any appreciable difficulty over their average lifespan. Connect a string of 220 Amp hour 6 Volt FLA's in parallel with a string of 395 Amp hour 6 Volt FLA's and kiss one set, the other, or even both goodbye before you've got your money's worth from them.

In short, the greater the difference, and kind of difference, between any batteries you are using the greater the potential for problems. This includes "identical spec" batteries which may differ by age (even when new) or manufacturer. We try for getting the best out of systems around here and whereas different batteries may not be a catastrophe (unless you try to charge GEL's and Trojan levels) it is also not ideal.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I think in your situation, apparently well maintained, I'd go ahead and do it... others here, use a year as the cut off point. In practice they will be different and likely the new will age with the old, if you could expect 5 years out of a new battery I would expect the new to expire when the old does. If that makes any sense...

I can't be sure of the name of the paper, but I know it was a Parker paper. I left with in 6 weeks of being hired since they refused to cover the local county fair since they didn't advertise with the paper. If you don't put news in the paper... it's just paper! The managing Editor left at the same time over the same incident, though part of his reason is they call my part time photog into the publisher to get chewed out for taking photos, that were published.

BB. · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The equation for power = volts * amps is a simplification -- Usually used for DC power.

The actual equation is a vector math of Voltage * Current -- Or:

Power = Voltage * Current * Cosine (phase angle) between Volts and Amps.

The Cosine can vary from -1 to 0 to +1 -- +1 is a "perfect load" (cosine 90 degrees = +1.0). A filament lamp, a resistance heater, etc. are example of PF=1.0 (Power Factor) loads.

Motors tend to range from 0.6 to 0.8 PF -- Although, it is possible to have better (closer to 1.0) or worse (less than 0.6) Power Factor. A pure inductor has near 0 PF.

A Kill-a-Watt type meter will give you Volts, Amps, Watts (V*I*PF) and VA (V*A).

Watts is "power" and tells us how much energy is being used. But VA *(volts*Amps) is useful because if the Volts and Amps are out of phase (poor power factor), you have more Amperes needed to get the same "work".

Think of a rope tied to the front of a car. If you stand in front of the car and pull--All your force goes into pulling the car forwards (PF=1.0).

If you stand 60 degrees to the side, then only (Cos 60 degrees=0.5) 1/2 of your FORCE goes into pulling the car forward. The rest is pulling the car to the side (no useful work).

In the second case, the rope has to be 2x stronger to get the car moving forward vs standing in front of the car.

It does get complex very quickly... And we try to help you design and build a reliable and safe power system that will run your loads.

Running a refrigerator and/or freezer is a real quick way to get from a small to a medium or large off grid power system.

From your numbers, if we assume 50% duty cycle for your fridge+freezer and PF near 1.0:

refrigerator (2.7 amps at 110 volts), my freezer (1.0 amps at 110 volts)

2.7 amps * 110 Volts * 0.5 duty cycle * 24 hours per day = 3,564 Watt*Hours per day (does not sound right--very high)
1.0 amps * 110 Volts * 0.5 duty cycle * 24 hours per day = 1,320 Watt*Hours per day (not bad)

A laptop can use from 100-600+ Watt*Hours per day if used heavily.

Your system would be doing well to give you 1,300 to 1,600 WH per day--The above loads will quickly swamp the daily production of your solar array (and may strain the battery bank too).

The Kill-a-Watt type meter will help you a lot to understand your power needs.

Too many guesses about your loads right now... But running fridge+freezer from a smallish off grid power system is very difficult to do.

-Bill

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Gosh Bill, that's an awesome explanation of power factors! You mods don't hear it enough, but thank you!

vtmaps · September 2014

Re: Solar Panel Configuration and PWM Controller Question

The_Dreamer wrote: »

I cannot really say whether the refrigerator is thermo electric, or whether it draws a continuous amperage. It is a pretty common Dometic model, made for RV's. This one came out of a Coachmen motorhome. It is designed to run on propane or electric, but I don't have it hooked up for propane.

That fridge is an 'absorption' fridge. That is a problem and the fridge should either be run on propane or replaced. When absorption fridges are run on electric power they are very very inefficient.

The_Dreamer wrote: »

Since the batteries are hooked in parallel, won't they equalize with one another rather than one overcharging and the other undercharging as they would if they were wired serially?

No. Parallel batteries are inherently unstable... even if they are identical model and age.
short discussion here: http://www.wind-sun.com/ForumVB/showthread.php?14674

--vtMaps

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

Thanks Bill for the great explanation. I feel like I am back in school. I always enjoy learning something, putting another wrinkle on the brain. I appreciate your time in sharing this information with me. It sounds like I need to get somewhat leaner on my power consumption so that I can keep my solar panel array and battery systems relatively modest. Unfortunately, replacing my refrigerator, a 2007 Dometic model DM2852, is out of the range of possibility. The reason is that it is built in, literally. It was brought in through the back door of my bus while the bus was in the early stages of renovation. Since then walls, beds, and other obstructions have been added. The refrigerator will only come out by literally tearing it apart, but since it is a fully functioning fridge valued at more than $1,000 I am loathe to remove it in this way, and I would have a similar problem trying to get a new refrigerator into its place. I did not plan on refrigerator replacement when I laid out the floorplan. Oops!

Since my freezer, a mid size chest type, is comparatively efficient, and its temperature can be easily controlled to serve as a freezer or refrigerator, if push comes to shove I will just use the Dometic for indoor shelf space (a handy pantry perhaps), and keep everything that needs chilling in the freezer. I think this would bring my power usage in line with my panel capabilities. I also can put the laptop away and use my Kindle Fire tablet. The thing can go a week on a charge, so it has to be super power efficient, and a low power bluetooth keyboard works just fine with it.

There is always something that can be chopped when it comes to power consumption.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I use to use a basic kindle to check my email in my cabin, since it used cell phone connection, though slow it gave me a connection. I was too cheap to pay for a land line to have internet ($65+ a month) I think there is a post or 2 on the forum, from when I was snowed in for 3 days. While very limited, slow processor/browser, forget most graphics, and slow, it was a connection with the outside world, and no additional fee. I don't know if they still do this with the newer models.

The_Dreamer · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I have also had the paperwhite Kindle that you mentioned. They do come with "experimental" (aka buggy) Internet access. I found it worked okay, though it had its limitations (small screen size, black and white only, limited graphics), but with a decent wi-fi connection it was fairly responsive. The Kindle Fire 8.9 HD is loads better. It does use more power than the paperwhite Kindles, but its power consumption is miniscule compared to a laptop computer. One telltale sign of the better power efficiency of the tablet versus a laptop is that it has no fans to vent heat, while my laptop has two of them. Without fans the Kindle Fire Tablet doesn't get hot either. The Kindle Fire 8.9 is advertised to run 10 hours on its small battery. My laptop battery is 8 times the size and is advertised to run only 3.5 hours on battery. That makes the Kindle Fire 8.9 twenty-two times more energy efficient than my ASUS ROG G750JM-DS71 laptop. Admittedly, the laptop is a power hog, being marketed as a gaming laptop and having a 17.3 inch screen. I am not a gamer, but I do appreciate the graphics performance.

If I had to curtail electric usage, the Kindle Fire tablet would be a whole lot better than no computer at all.

Photowhit · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I never tried over wifi, only the cell service. Maybe it was slow cell service that helped make it creep along.

Plowman · September 2014

Re: Solar Panel Configuration and PWM Controller Question

I use an Acer netbook as my main computer, draws ~25W when charging and in use, battery only lasts 3-4 hrs when unplugged. It's getting old, thinking about replacing it with an Asus Transformer (combo tablet-netbook). As far as I can tell the Transformer draws 10W, they say battery life is 11 hours, with a 2 week standby life. It's charged from a USB cable, so it can be easily charged from a 12V source.

For internet I use my Windows phone as a hotspot. I previously used an Android phone physically tethered, but that was a PITA, hotspot is much better. Speed is slow due to my phone plan (2.5 GB at 4G, unlimited at 2G). At 4G it's plenty fast, but I immediately burn through the 4G data and spend most of the month at 2G, which is pretty slow. But for $55/mo I can't complain.

BB. · September 2014

Re: Solar Panel Configuration and PWM Controller Question

For several versions of Android phones, I have used FoxFi as a hot spot ($8-$15 one time charge--I have had for a few years now and a few upgrades (all free).

http://foxfi.com/
http://pdanet.co/

Not all android phones will work with FoxFi as a hot spot.

And, many phone companies with "limited" data plans now have to offer WIFI hot spotting "for free" (as I understand)--The Cell company sells you X GBytes of data per month, the are not supposed to be able to charge you extra for tethering/wifi hotspot.

-Bill

Solar Panel Configuration and PWM Controller Question

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