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Old 03-26-2014, 1:56 PM
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Default Solar gel cell to power portable base station

Hi all,

I would like to get a gel cell and solar panel to keep it charged. Intended use would be long-term power source for a portable hf/vhf/uhf base station, such as FT-897 or maybe FT-817. I mention portable to point out that power requirements would be on the low side, but it will be my primary base station and used daily.

Can anyone point me to a good article that explains the concepts, equipment, and limitations involved with a setup like this? Google searches are returning plenty merchants that sell gel cells, and some articles that don't cover this. Maybe I'm not using the right search criteria.

Any suggestions for a good starting point for my research would be greatly appreciated!
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Old 03-26-2014, 2:17 PM
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Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_1 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8C148 Safari/6533.18.5)

Get a marine battery instead more amps and will last you longer.....
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Old 03-26-2014, 6:36 PM
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If you need a gel cell because they will be indoors with you and you are worried about off gassing and no ventilation then I would go with a optima they are pretty reliable. But if you can I would look at getting two 6 volt rv batteries. They can take the abuse that's what I use in my trailer. They should supply plenty of capacity especially if you have several cloudy days in a row and you want to be able to use the radio during that time and don't have another means of charging. I would also get a good solar controller. You wouldn't want the panels to cook your batteries.
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Old 03-26-2014, 9:07 PM
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Most of what you need to know can be found right here: Installing your own small, remote off-grid solar system by Jeffrey Yago, P.E., CEM

Now after that... unless you have little kids about (acid hazard), or plan on turning the batteries upside down on a regular basis, flooded lead-acid deep-cycle marine/RV batteries give you more bang for the buck than gel cells. One group 24, 27, or 29 size 12V battery will be plenty to drive your rig. KF7OQQ is right though, two 6V golf cart batteries can take a lot more abuse. However, they are less portable.

Typically a 100 watt radio pulls 20 or more amps when transmitting, and this is much larger than the solar charging system needs be, since it'll be charging continuously when the sun's shining but you'll only be transmitting intermittently. Therefore, wire the radio straight to the battery, not through the solar controller, and you can get by with a 5 amp controller ($30-ish) instead of a 30 amp controller ($150+).

If you have any questions after reading that article, ask away. I'm running my FT-450D off of a 45 watt solar system and a group 27 battery and it works great.
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Old 03-26-2014, 10:43 PM
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PrimeNumber - Great link and info -- That will keep me busy reading for a while, and I'm sure I'll have some more questions once I know a little more about this. Thanks for the tips!
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Old 03-27-2014, 10:55 AM
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while i know you were looking for articles, it appears this has been provided so here is a low profile product i am looking at for use myself...

i am looking at putting a 30 or 60 W sheet on the truck canopy to keep a standalone 12vdc battery charged to power my FT 2900.

Portable Remote Power - PowerFilm Solar

btw, forgot about using a marine bat, suggestion was much appreciated.

wa88it
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Old 03-30-2014, 11:59 PM
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Since my shack is in the basement with no ventilation, and the battery would be right next to my rig and my computer and 2 very curious cats, etc, etc, I would feel a lot better going with a gel cell, so I have pretty much made up mind about that part, but one other thing I was wondering about --

My rig will be about 75 -100 feet from where my solar panel will be located, and the only place to route wires would be right next to my antenna coax (the wires would actually be touching). Would it make sense to have have two gel cells -- one charging and on standby, and the other being used to power my rig? That way, I can put the cell being charged at the end of the house with the solar panel. When the voltage in the cell being used drops too low to power my rig, I would switch them.

BTW, decided on the FT-897d (100w). I would be using the rig for receiving on the average 1-2 hours per day, little to no TX. How long will a group 27 cell power the rig with this type of use? I certainly don't want to be carrying the cells back and forth every few days. If it comes to that, I guess I'll have to go the long wire route, but I don't want to. I'm already looking at 120 feet of coax for an HF antenna, another 100 feet for a vhf/uhf antenna. This craziness has to end at some point, right?

Also would using a cell until the voltage drops to unusable levels shorten the life of the battery?
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Old 03-31-2014, 7:54 AM
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Quote:
Originally Posted by Rastaman147 View Post
Since my shack is in the basement with no ventilation, and the battery would be right next to my rig and my computer and 2 very curious cats, etc, etc, I would feel a lot better going with a gel cell, so I have pretty much made up mind about that part, but one other thing I was wondering about --
Yes, that makes sense. The hazard from hydrogen gas is WAY overrated, but with your curious cats around, gel cells make sense. Either way, get some battery boxes to keep Mittens out of the wires. BTW, all of the pre-made ABS battery boxes I've found are either for 24's or 29's. If you get group 27 batteries you'll have to jump up to a 29 box, so there's no space savings there. (This is me kicking myself for getting 27's instead of 29's, thinking it'd be a little more compact.)

Quote:
My rig will be about 75 -100 feet from where my solar panel will be located, and the only place to route wires would be right next to my antenna coax (the wires would actually be touching). Would it make sense to have have two gel cells -- one charging and on standby, and the other being used to power my rig? That way, I can put the cell being charged at the end of the house with the solar panel. When the voltage in the cell being used drops too low to power my rig, I would switch them.
Hrmmm, two batteries, swapping them as needed is an idea.

Pro: No long feed line between the panels and the batteries. The voltage drop can be significant over 100 feet, and you'd need to go with 10, 8, maybe even 6 gauge wire, and that gets expensive fast. (Calculate twice, buy once.)

Con: How's your back feeling these days? Also, I know that I'd get lazy and end up over-discharding my batteries, but you may be more on top of things. Batteries do a lot better when they're kept topped off. Letting one sit around a few days at 70% won't kill it, but doing this chronically is not good for long-term battery health.

Quote:
BTW, decided on the FT-897d (100w). I would be using the rig for receiving on the average 1-2 hours per day, little to no TX. How long will a group 27 cell power the rig with this type of use? I certainly don't want to be carrying the cells back and forth every few days. If it comes to that, I guess I'll have to go the long wire route, but I don't want to. I'm already looking at 120 feet of coax for an HF antenna, another 100 feet for a vhf/uhf antenna. This craziness has to end at some point, right?

Also would using a cell until the voltage drops to unusable levels shorten the life of the battery?
Hmmm, My 450D (similar, close enough for a quick calculation) draws 1.5A when listening. A group 27 battery hold about 75 A-H, so that's 50 hours right there. BUT you don't want to draw the battery down by more than 50%, and more like on a daily basis 20% if you can help it. So just on that you're looking at 10 hours of listening. Again, don't deep discharge your batteries unless there's a good reason. They'll last quite a few cycles if you do this, 200-ish is the number I've heard, but they'll work much better and longer if you keep them topped off.

Bottom line, I'd just figure the voltage drop over the length feed line you're contemplating (use the amp spec from the panel, and keep the total voltage drop < 5%) and put in an appropriate-gauge cable and be done with it. Given the cost of gel cells, it's cheaper than buying two, swapping them every couple of days, and having to replace them every year or so because they're staying 30% run-down all of the time.
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Old 04-01-2014, 5:38 AM
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Quote:
Originally Posted by Rastaman147 View Post
BTW, decided on the FT-897d (100w). I would be using the rig for receiving on the average 1-2 hours per day, little to no TX.
First thing is to differentiate between GEL and AGM. AGM is what you want, as gel-cell's are commonly mistaken for them. Popular in the 70's, but not today, and especially not for solar since they need to be slow-charged on purpose so as not to develop voids in the electrolyte...

AGM is the modern replacement. Unless you totally abuse them, they are safe indoors since they don't vent hydrogen. Again, under normal charging conditions.

Let's say the 897 draws 1A on rx. You want two hours a day. That's 2ah daily. Easy.

1) You don't want to take a battery past 50% DOD or Depth Of Discharge especially if you are using it daily. So... that means you require at least a 4ah AGM. Let's make that 5ah since that is easier to find, like a Powersonic, UPG, B&B etc.

But what is 50% DOD for a small agm - how do you measure it? After 4 hours of no-charge and no-load, measure the battery terminals. Don't let it go below 12.2 volts. Under your 897's small load, I'd say don't let it drop below 12.0 volts as shown in the 897's voltage display. Note that the 897 voltage display may differ from a quality voltmeter, but unless you are using something like a Fluke 87V or better, the 897's voltmeter will be in the ballpark.

2) Small agm's like this can only handle 0.25 to 0.3C max charge current. That means the largest current you can hit it with is 1.5A. (0.3 * 5ah)

3) For solar, a small 20 to 30 watt panel will suffice, with charge controller. A "nominal 12v solar panel" usually has an ocv of anywhere from 17-21 volts or so. Let's say 18v. 20w / 18v = 1.1A. That would be fine. A slightly larger 30 watt panel would put out 1.6A. Just barely exceeding a 5ah max 0.3C charge current battery limitation. (C = the ah rating of the battery)

4) A suitable charge controller would be something like a small Morningstar Sunsaver SS-6-12V pwm. It has two choices for charge voltage, "sealed" and "flooded". Even though AGM's are sealed batteries, you want to select the "flooded" option, as this is the correct VOLTAGE for agm's. What Morningstar calls "sealed" is actually intended for GEL's, which need a lower voltage, and is not a chemistry we want for solar. Essentially, go by the proper voltage - in this case "flooded" is about 14.4v charge. Small agm's like 14.4, and some even 14.7 or so. Basically what I'm saying is to purposely remove the jumper so that you are feeding it the "flooded" voltage for your small agm to let it charge properly. The Morningstar will eventually drop to 13.8v float when the battery is full.

5) Make sure you have at least 2 hours of "solar insolation" per day to get the battery charged up properly from your use the day before. Visible daylight is not the same as solar insolation. Basically, we are talking about the typical hours between 10am and 2pm for the biggest benefit. Early morning and late afternoon hours have weak solar output typically. There are charts for this based on your location, but 2 hours should be doable nearly everywhere.

Place the battery and charge controller close to the solar panel! If you run 100 feet of cabling back to your battery from the panel, you'll suffer huge voltage drops and the battery won't charge properly - unless you run something like #00 wire, which would be ridiculous for your basic rx-only application.

Unless you are transmitting with heavy power draw, a small agm battery and small panel would work out fine - just do the math in the first few steps according to the battery size you need. Keep a small agm-specific charger on hand like a Battery-Minder or Battery Tender that has temperature compensation built in as you don't want to let a battery sit around half-charged for weeks on end. AGM's have very little self-discharge, so if you don't use it often, just charge it fully and then top it off every 1 or 2 months.

If you are transmitting, then you should consider the bigger dual-purpose AGM's like an Optima yellow or blue top, but for now, have fun with a small 5-7ah agm battery and 20-30 watt panel and a morningstar sunsaver controller.

Last edited by hertzian; 04-01-2014 at 6:00 AM..
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Old 04-01-2014, 11:14 PM
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I use a 100 amp hour gel cell battery and a couple of 24 volt 125 Watt solar panels. For charging I designed a comparator circuit to switch a relay on to charge the battery when it drops below 12 volts and turns off the panels at 14.5 volts. But I would suggest you get a real charge controller for best results.

Here's my setup last year at field day, the two solar panels are on the roof of my car.

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Old 04-01-2014, 11:43 PM
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Hertzian -- It must have taken you a while to post all that great info -- Really appreciate it, especially the specifics with the controller.

Based on what you and others have offered so far, it looks like I am going to have to totally re-think my original plans, though. Due to trees, the only place I can put my panel to get 2 hours of direct sunlight will require 66 feet of wire to reach my basement. From that point, it will take 50 feet of wire to reach my shack, total wire length wire will be 116 feet. No getting around that.

If I need to top off the battery every 2 -3 days for good results, I am not going to consider switching out 2 batteries. The battery will need to be permanently fixed.

Using #00 wire is definitely not a solution. If I can't do this with 12 gauge wire, I would use a battery charger, which kind of defeats the whole purpose of this exercise.

If locate the battery just inside my basement, It would be 66 feet from my panel to the battery on my basement floor, with 50 feet that point to my shack. Would this give me adequate results (as opposed to one single length of wire at 116 feet), or should I just move on to plan B?

For this situation, the numbers are not flexible, but for future projects, what do you call the formula to calculate the wire gauge needed for a particular distance and voltage? (PrimeNumber mentioned earlier that the voltage drop should be <5%) I'm sure there are calculators for this online, but it would help if I knew the right terminology for my search terms......

Thanks again!
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Old 04-02-2014, 12:17 AM
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Bellingham_Scanner - Cool pic! That's super hard-core -- With a little luck and a lot more experience, I can see myself doing stuff like this in the future... Awesome shack, too!

Question regarding your ST-2 -- I have the same antenna mounted just like yours at about the same height, and I think it works well - local police, EMS, and ham frequencies are crystal clear...... BUT....I have recently been using a homebrew (my first antenna project) flower pot UHF/VHF antenna situated on the floor of my attic, about 10 feet lower, and it seems to work just as well on all the frequencies except maybe 11m (and maybe even better for aircraft) as the ST-2.

The only difference might be in the higher frequencies -- With my ST-2, I can pick up the weather broadcast on 924MHz. Sometimes I pick up this freq using my flower-pot, but most of the time I don't. That's the only 900+ frequency I have ever picked up on either antenna, so I can't really test and compare, and I've actually just decided to take down the ST-2 and replace it with a Comet GP-1 antenna to give me better range with VHF/UHF.

Question is - How do you like your ST-2, and what are you able pull in with it that you can't get with your HAM antennas?

Related question - Is there any reason I wouldn't want to hook my scanner up to the GP-1 antenna?

Sorry to hijack my own thread, but based on your pics, you would be a the right person to ask about this.
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Old 04-02-2014, 7:35 AM
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Quote:
Originally Posted by Rastaman147 View Post
If locate the battery just inside my basement, It would be 66 feet from my panel to the battery on my basement floor, with 50 feet that point to my shack. Would this give me adequate results (as opposed to one single length of wire at 116 feet), or should I just move on to plan B?

For this situation, the numbers are not flexible, but for future projects, what do you call the formula to calculate the wire gauge needed for a particular distance and voltage? (PrimeNumber mentioned earlier that the voltage drop should be <5%) I'm sure there are calculators for this online, but it would help if I knew the right terminology for my search terms......

Thanks again!
The voltage drop over a length of wire is:
delta V = IR

You can get the current (I) from the solar module's specs. For example, this panel
Solartech 40 Watt 12 Volt Multicrystalline Solar Module
puts out 2.35 A at max power.

For delta V = 5%, that's 12V/20 = 0.6V. Turning the first equation around to solve for R leaves:

R =delta V / I = 0.6 V / 2.35 A = 0.255 Ohms

This is the maximum resistance you can stand for your application. Anything less is just good news.

From this table Resistance of Wire (Wire Resistance Calculator) we see that 100 feet of #12 wire has 0.1588 Ohms resistance. Looks like with 116 feet of #12 at 0.184 Ohms you'll be good to go.

About where to put the battery... If you're just listening, it won't matter much, you're only drawing about 1.5A. When you key the mic, the radio will draw about 20A. In that case you DEFINITELY want the battery near the radio.

(BTW, the wire gauge recommendation charts at solar-electric.com have a bug in them, don't go there for that info. The rest of the site is great though.)
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Old 04-02-2014, 8:51 AM
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Higher voltage lower current will have a smaller voltage drop in the wiring. Most charge controllers can run at a much higher voltage input range for charging 12 volt batteries.

Power is the important part, one 12 volt 10 amp panel is 120 watts, but two 30 volt 4 amp panels wired in series to produce 60 volts at 4 amps is also 120 watts and loss from a long wire run would be a lot less.

In large solar setups both grid tie and off grid 600 volt arrays are very common and they are slowly moving towards 1000 volt arrays, for that exact issue.

But as for the SC2, I find is good on VHF but a bit lacking on UHF. You really can not compare the SC2 and my Cushcraft vertical as the Cushcraft is HF 10m-40m.
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Old 04-02-2014, 10:42 AM
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Prime# & Bellingham_Scanner - Thank you both again for this very helpful info -- This forum is GREAT!

This is a fascinating hobby, and if I had the opportunity for do-over, I would go back 30 years and choose a degree in EE. I got started with this stuff way too late in life, and I really wish I had more experience but I guess it's better late than never. I'm really looking forward to the road ahead. Peace!
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Old 04-04-2014, 1:06 AM
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Quote:
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Due to trees, the only place I can put my panel to get 2 hours of direct sunlight will require 66 feet of wire to reach my basement. From that point, it will take 50 feet of wire to reach my shack, total wire length wire will be 116 feet.
Ok - I'm assuming you mean "1-way" or point-to-point distances, and not a "round trip" length measurement. Some online calculators may not specify and you could end up with the wrong size wire.

This chart is pretty handy from a good solar site - look at the 12v chart and if you can swing either #6 or #8, you just might get away with charging up to say a 10ah agm. (10 * .3C = 3a) (which by the way would be a 60 watt panel max) Be sure to see the forum too:

Voltage Loss Tables for AWG Wire

You may also want to look at the second edition of Michael Bryce WB8VGE's book on Emergency Power For Radio Communications - ARRL

I think your project can be done. You could go to a 24v panel (or two similar 12v panels in series) and run that into an mppt charge controller, but you might experience some HF noise from the internal switcher. I have no noise from my morningstar pwm CC's.

The simplest would be to just run #6 or #8 with a max or no more than 3amp current to a small agm, like 10-12ah. That would also give you a bit more "autonomy" as you'd have a bit more capacity to play with should you suffer a dark day or two.

If you see a true "gel", pass on that. Most lump gels and agm's together as "gel cell", but that is a moniker from the 70's when that was all there was. AGM is what you want.

Note - most don't know that true gels can only accept up to C/20 charge current, (at 14.1v max!) else they start to put voids in the gel and trash the battery. If you had a 5ah gel cell, that would mean a max charge of only 250 milliamps!! Not the same with small AGM's which can accept up to C/3 or therabouts max. Now you see why true gel's with solar is not a good match - it takes just too long to charge them *properly*.

And just so you know, AGM's come in various application specific categories - like SLI (Starting-Lights-Ignition), deep discharge, and dual purpose. If you can, avoid the "SLI" versions as they are really designed to just repeatedly use no more than about 5% of their total capacity on a regular basis starting a vehicle. Running deep discharges on SLI specific batteries will quickly degrade their capacity.

The little ups type ones are not always deep-discharge either, but are inexpensive enough to replace in this kind of hobby service.

Last edited by hertzian; 04-04-2014 at 1:23 AM..
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Old 04-04-2014, 1:38 AM
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More quick notes to make sure your project gets off the ground ...

To see your solar insolation based on your location, this chart is handy, although there are more exacting calculators out there. Use the "winter" or "low" hours to give yourself some headroom:

Solar Insolation - Sun Hours Per Day

These hours are what you use to calculate how much you can achieve each day. The most common mistake when doing solar is calculating your hours based on sunrise to sunset, when the early morning and late afternoon produce very little power.

Do not try and test a charge controller for functionality when there is no battery present. They don't work without a battery and many good controllers get returned because of this.

In addition, unless otherwise specified, attach the battery to the controller FIRST. Why? Because the controller needs the battery as a reference - if you attach the panel first with no battery, the controller might just shut down, or in some cases go no higher than float voltage as a safeguard for its internal circuitry.
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Old 04-05-2014, 12:02 AM
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Hertzian - Thanks again for the information. It is looking like I am going to need to do much more research before trying to tackle a project like this.

I had expected it to be challenge after having so much trouble finding a guide to doing this online intially, and you have definitely confirmed that there are a lot of variables that need to accounted for (and understood well).

You explain this stuff very well, and I can follow what you are saying, but it's becoming clear that I am going need to understand a lot more about how the battery, panel, controller, and wire all work together in a system before I attempt this.

My transceiver just arrived arrived today -- I'm playing with it now, and my flower-pot antenna (built about a year ago, with some advice from you, actually, I think) worked flawlessly with my HT, but unfortunately, I can't pick up much on my new rig, except for the weather broadcast. So I will need to get this figured out, and hopefully get my new antenna up and running in the next week or so. Then, I guess I will need to dig in and figure out this solar battery thing. 73!
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Old 04-05-2014, 2:15 AM
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My pleasure!

Doing the research first will save you a LOT of money up front. One of the most common mistakes in solar is doing a "deficit charge" scenario, where the solar power is woefully inadequate for proper charging and maintenance of the battery. The battery gets quickly abused, but the owner doesn't know it is sulfating and capacity gets smaller and smaller over time. Worse yet, some throw an additional battery or larger battery online, and it too takes a hit. It's the "too small a panel for too large a battery" syndrome.

Keep the research fun - you'll get it. Just don't do it backwards. Do it like this:

1) Calculate your power needs for a day. Use a multimeter to measure dc current, or if running things off an ac inverter, a "kill-a-watt" meter from P3 International is commonly used.

2) Based on #1, size your battery. This will be at a minimum TWICE your power needs as one does not want to take a battery below 50% DOD on a regular basis. For an agm battery, that is typically 12.2v in a 4-hour rested condition of no charge, no load. Of course you can do this under load, but consult the manufacturers charts for what 50% DOD is under the current you are pulling.

3) Calculate your panel and wiring infrastructure needs. Critical to being successful, is using "solar insolation" hours, and NOT sunrise-to-sunset hours.

4) Know up front that going solar with batteries will cost you about 10 times the money from the POCO, since after 4 years or so, batteries need replacing generally.

5) Don't go cheap or you'll pay for stuff twice sooner or later. Stick to name brands - Morningstar, Outback, Stecca, etc. Personally I run PSW or "pure sine wave" ac inverters instead of the cheaper MSW or modified square wave, and these can suck up current just idling doing nothing so turn them off when not in use.

6) At some point, the wiring infrastructure for 12v becomes ridiculous, say in a large cabin with remote panels, so going higher in voltage to at least 24v should be the order of the day. 12V is for RV's, field-day, tiny shacks and the like.

Last edited by hertzian; 04-05-2014 at 2:20 AM..
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