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Keith
12-08-2013, 09:50 PM
So… I plan on making a few "battery boxes" in the coming months. Thought I'd start a thread to share my progress and get input.

First one I'm building will be to use for emergencies and to test out HAM and other 12V DC stuff at home without messing with the truck. My original motivation for building one of these was when I realized all HAM stuff runs on 12V DC and I think I'd rather buy a couple batteries than an almost as expensive AC to DC converter to run HAM radios at home.

Anyway, this first one is going to be built around 2 x 50 Amp Hour batteries. I got a screaming deal on these: http://www.batterystuff.com/batteries/mobility-scooter-wheelchair/UB12500-45977.html

I also picked up one of these: http://www.batterystuff.com/battery-products/g3500.html

That's all I can really afford for the month, but my eventual plans are to build a plywood box to house the 2 batteries. My plans for outputs are probably about 6 power pole outlets, 2 USB outlets, and one cig lighter output.

For power input I plan to permanently mount the above controller/charger and a solar controller. I'll likely end up plunking this down in the garage with it connected to a 60 watt solar panel. I have said 60 watt panel on my truck now but plan to upgrade it to a 100 watt in the Spring.

DaveInDenver
12-08-2013, 10:13 PM
KC0YRM and I found at Field Day 2012 that a generator is the way to go. Battery based emergency power is fine but short term, a day or so, but longer than that or significant operating time and you quickly deplete them. If you intend to continue operating you need to size the recharging capacity to be something like twice the operating use. IOW, if you are consuming 120W per hour (say roughly a 100W HF station operating 50% duty cycle during a contest) from the storage and you have 1200W-hr available you can go 10 hours. But you need to plan on using zero storage during the day light (if using solar) and rebuilding the reserve simultaneously, which means you need 240W during the summer when you have 12 hours of sunlight. In the winter if you get 6 hours of good sun you need more like 400W of solar to run deep into the night. Brian's 1000W generator was awesome...

rover67
12-08-2013, 10:54 PM
I have a TON of batteries you can have to get a huge amount of capacity. free.

Keith
12-08-2013, 11:03 PM
Dave, I plan to build a few of these. The one above will be for testing purposes mostly and will probably run a 2m radio in my garage. The next couple I plan to build around 2 x 100 amp hour batteries and I plan to hook them up to 2 x 100 watt solar panels.

A generator is too easy…

Marco, you got any that are AGM (gell cell)? For the ones in boxes I don't wanna have to deal with corrosion and venting. But might be interesting to see what we could come up with using a whole mess of old car batteries to make a franken-rig.

rover67
12-09-2013, 09:33 AM
They are sealed batteries that we use at work to power our mobile CT scanners. I grabbed 15 of them that were being replaced during PM. They are all about motorcycle sized batteries.

DaveInDenver
12-09-2013, 09:41 AM
There is a ratio of solar panel to capacity that's required to keep them fully charged. I run roughly 2x panel capacity to battery size because the panel will only produce full power with proper incident light which only happens if you track the sun and if it's above the horizon enough. In the winter I might get a couple of hours of full charging from my panel (which have historically just been roof mounted at home), which is a 24V panel to-boot. In the summer it's a lot better, the battery stays topped a lot better.

Those batteries Marco has are probably perfect being SLABs. If you need to condition them I can do that, although I doubt they do.

Generators get the same multiplier as mains powered stations, so I do guess it is too easy. OTOH it's sure a lot easier to run your house fridge during longer power outages...

Keith
12-09-2013, 09:47 AM
They are sealed batteries that we use at work to power our mobile CT scanners. I grabbed 15 of them that were being replaced during PM. They are all about motorcycle sized batteries.

Sweet! I'll stop by and take a look sometime soon… Any way to measure their capacity? Can we just attach a known load and see how quick they drop?

Maybe use one of these: http://www.powerwerx.com/digital-meters/dc-inline-watt-meter-power-analyzer-powerpoles.html

Keith
12-09-2013, 09:54 AM
Generators get the same multiplier as mains powered stations, so I do guess it is too easy. OTOH it's sure a lot easier to run your house fridge during longer power outages...

On some level I do want this around in case of a prolonged power outage, but it seems like that hardly ever happens in Colorado. Mostly I just wanna fool around with solar technology. If we did have a really long power outage, I could put everything we really needed from the fridge into my Edgestar and run it off the truck or off one of the 200 amp hour / 200 watt systems.

I will say it would have been really nice to have one of the 200-sized systems built up this summer to be able to drop it off to some of my friends up in Lyons who didn't have power for a few weeks.

DaveInDenver
12-09-2013, 10:09 AM
Think about capacity. 200A-hr at 12V is 2400W-hr. That is what is available from one regular household outlet. Sum up what you're running 24/7 and consider that you only get to charge during daylight. I run the Engel around the clock when we lose power, which consumes around 50W-hr when set to freeze. It runs pretty continuously. That along with a radio on receive is about 65W-hr and I will draw down my 100A-hr battery in about 15 to 18 hours. I put 240W-hr back into the system with my solar panel and can run continuously unless we get more than one day of continuous overcast.

Keith
12-09-2013, 11:44 AM
The math I did showed I could use it (The 200 watt and 200 amp-hour system) to run an Edgestar at 40 degrees farenheit for about 2 days. (It draws about 1200 watt-hours per day under normal conditions in the summer.) And that it would take about 12 hours of direct sunlight to fully recharge the batteries. So, assuming I can get 12 hours of sun every two days, I'm good.

Obviously, that would be cutting it close in the winter, but it's also not very hard to keep food cold in the winter. Most of the time, I will be using it to run my home network, desktop computer, and any HAM stuff I have in the house. That draws about 1,000 watt-hours per day. If we don't get a lot of sun for a couple days, I can always just plug in the battery charger at night.

I will also be building one of these for someone who wants to use it to run a fridge for camping trips where he won't always have the option of running stuff off his alternator. I figured that 200 amp-hours and 200 watts would be the minimum to guarantee that the system will keep his beer cold about 95% of the time.

Of course, all of this is pretty theoretical. We'll see what happens when the rubber meets the road.

DaveInDenver
12-09-2013, 01:06 PM
Yeah, panels may be better now. Mine's a Sharp 24V, 240W from 2011. I don't get close to 240W from it unless I get the incident light is perfect. I don't have a tracker or anything, on the old house it was just bolted on a south facing roof on the garage and here I just use a 2x4 frame and set it out in the backyard when I need it.

Since I had it flat mounted on the roof I was limited to the slope, which was pretty steep at 8-in-12, roughly 34 degrees and not too bad on tilt. The way I do it now, with the frame I put it at 40 degrees in the back yard.

Anyway, point is that for every 10 degrees of elevation or azimuth misalignment my panel output drops 5%. If I leave it set up directly due solar south all day I might get on average about 135 W-hr and get full output for about an hour or so total (which incidentally isn't noon but about 9~10AM and 2~3PM and above 80% efficiency for around 3 hours total. If go out and rotate it every hour or two it does better (this would be 1-axis rotation), about 165 W-hr, but my tilt is non-ideal really. I tore it all apart this fall and plan to make once that I can adjust the tilt and dispense with the cinder blocks and guessing.

I have not done year-round detailed measurements since I don't leave the panel set up all the time. But what I have done indicates to me that 75% is the best you can do and to get it you'd need to do 2-axis alignment and even then the 240W rating is during ideal temperature, too. In the summer my panel gets really hot during the day and efficiency drops a ton. The output rating is for 25*C and Sharp gives a temperature coefficient of -0.51%, which means for every degree over 25*C the panel output drops 0.51%. So if my panel gets to 40*C the output will have dropped 7.65%. That's not all that hot, 104*F, and in full sunlight during the summer the panel will get much hotter than that, 50 or 55*C isn't unusual. You can give up 10% or 15% efficiency there alone.

That the reason why with a fixed panel I was getting less than 50% capacity and why I suggested the 2x capacity. Just the amount of sun missing it took ~20% easily and then the heat zapped a bunch more. OTOH in the winter the temperature coefficient works to your favor and efficiency goes up as it gets cooler. Which is good because you start to loose a lot because the lower sun angle and more energy is absorbed and refracted by the atmosphere.

Also sizing the panel much larger allows the load to be comfortably accommodated simultaneous with charging at the same time in all weather. There are a lot of places to lose solar energy and panel capacity itself is really a small part of the equation.

Seldom Seen
12-09-2013, 07:29 PM
I crunched the numbers for a solar system, before springing for a honda generator, and came up with close to what Dave posted. I even re-ran them at 20 watt output (giving up ~1 S unit at the other end of the string) and concluded the generator was still more cost effected.

Couple of the "gotchya's" Dave didn't mention:
1) Ancillary equipment drain:

A) I'm running a RT-100 and need 3 amps* injected at the Bias Tee for a few seconds at beginning of each transmission to feed the tuner.

B) it's takes 12 watts/hr* to keep an iPad charged for logging and running PSK31 and 5 watts/hr* to keep an iPhone charged up so you can tether to the iPad for QRZ look ups and checking DX Sherlock for spots, E paths and MUF.

C) A small 12V low wattage CFL lantern for night ops.

D) FT meter, draws only a watt or so*

*All numbers are from memory but the point is they all add up and must be taken into account.

2) The BIG Gotchya: The price of the solar controller. You can't use the el-cheap-o Pulse Width Modulated Controllers as they put out way to much hash. You'll need to run a MPPT controller. When I was pricing them out a quality (read no Chinese knock offs) 200 watt MPPT controller was half the price of what I paid for the genny.

DaveInDenver
12-10-2013, 07:07 AM
My controller is a Morningstar Sunsaver MPPT 15 which is supposed to hit up to 97% efficient at getting energy from the panel to the battery. I've never personally measured it, though.

You can find MPPT controllers a little cheaper than this one, especially if you don't use 24V panels. I went with a 24V PV system for a couple of reasons. One is that if in the future I want to expand my system beyond 1 battery to use an inverter 24V makes sense, reduced DC current and allows a wider selection of heavy duty inverters.

Even if I just add more storage and stick with a 12V battery bus, running a 24V panel and MPPT controller you get a higher overall energy recovery since the controller is rarely running near its max duty cycle and current. The max panel power rating for the controller doubles at 24V to 400W over 12V panels. My single panel and 12V battery sits right in the middle of most of the rating curves for this controller, so it's never seriously taxed.

Plus, the Morningstar allows me to jump up to 36V panels if I wish in the event I want to build a true self-contained system independent of the grid.

nakman
12-10-2013, 02:16 PM
So what's the story then with the $8-$12 solar charge controllers you see on ebay? I get that they may not be the best for base station use, but what about trickle charging a little juice back into a backup car battery?

http://www.ebay.com/itm/30A-Solar-Charge-Controller-Solar-regulator-12V-24V-max-input-volt-60V-PWM-Mode-/141136355420 for example

DaveInDenver
12-10-2013, 03:33 PM
Remember these charts. They are representative of PV panel characteristic curves.

http://www.electronicproducts.com/images2/fapo_AltEn_Fairchild02_jun2011.gif http://www.electronicproducts.com/images2/fapo_AltEn_Fairchild03_jun2011.gif

The box you link looks like a simple battery buck charger. It takes an input, slices it into pulses (quantizes) to cut it down to a lower average voltage. It's taking whatever the panel is giving it and making it match the battery by switching from off to on for various lengths of time. In bright sunlight the panel is outputting say 27V it produces a relatively short duty cycle that averages 14ish volts. In lower light the panel might be at 15V or 20V. The duty cycle would increase to keep the average voltage where the charger wants it to be.

http://d32zx1or0t1x0y.cloudfront.net/2011/06/atmega168a_pwm_02_lrg.jpg

But looking at the panel curves at high voltages it's producing relatively low current. You need current to charge a battery. Not to mention that any time the voltage is above or below the knee on the curve your total power made is lower. So there is a small window where the panel is making its full /power/.

http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/content/content/62049/62049-fig-4.jpg

They feed the PV output into a non-inverting buck-boost converter that can produce more output current (or voltage) than the input. This is possible because it's converting power. So rather than just chopping a higher DC voltage down to a lower DC voltage they are attempting to get the full power from the panel to feed into the battery.

MPP is an algorithm that matches a solar cell's maximum power point to the battery. The controller attempts to keep the system operating right on the panel's I-V knee so that the most amount of power is extracted and fed into the charger for whatever the solar energy density (on the left) and module voltage (on the right) happen to fall.

The key here is that it's matching the system, so the panel, load, converters all working to find the MPP. The 'T' part is tracking, which means it uses various control principles to figure out the MPP. The Morningstar uses perturb-and-observe, if you remember your controls theory.

At some times the MPPT and buck converter would be close to equal, small windows of time. But over a whole day, particularly during the middle of the day when the panel output is above MPP voltage, but also for some time before and after as the sun rises/sets, the MPP the buck efficiency will lag a lot behind an MPPT converter. When the terminal voltage is above MPP the buck is throwing away a whole lot of power. The software in MPPT controllers can be sophisticated while a buck converter probably doesn't have a microprocessor at all.

rover67
12-10-2013, 03:59 PM
So what's the story then with the $8-$12 solar charge controllers you see on ebay? I get that they may not be the best for base station use, but what about trickle charging a little juice back into a backup car battery?

http://www.ebay.com/itm/30A-Solar-Charge-Controller-Solar-regulator-12V-24V-max-input-volt-60V-PWM-Mode-/141136355420 for example

Funny, that's the EXACT one I have on my truck with my 130watt panel charging my two group 31's.

Sounds like it may be time for an upgrade.

Thanks for the explanation Dave, makes a whole lot of sense.

DaveInDenver
12-10-2013, 04:44 PM
There is nothing wrong with a simple battery charger like that. Primarily they protect the battery from over voltage but just realize that they leave a whole lot of energy on the table. With a sophisticated charger you can use a smaller PV array to keep a larger battery fully charged and across deeper discharges. In a word it'll be more efficient.

nakman
12-10-2013, 07:55 PM
There is nothing wrong with a simple battery charger like that. Primarily they protect the battery from over voltage but just realize that they leave a whole lot of energy on the table. With a sophisticated charger you can use a smaller PV array to keep a larger battery fully charged and across deeper discharges. In a word it'll be more efficient.

Wow, thanks. So ok, you're saying a cheapo charge controller essentially leaves energy on the table, compared to a more expensive one. Is there any difference in the way it delivers that energy to the battery, that would affect one adversely? I guess what I'm getting at is, is it cheaper to just add a second panel to offset this, rather than pony up for a better charge controller? Yikes this feels like trying to overcome lack of wheeling skill with more horsepower.. :o

How much is a "good" charge controller anyway? Can you put up a link to a one? :beer:

Seldom Seen
12-10-2013, 09:03 PM
How much is a "good" charge controller anyway? Can you put up a link to a one? :beer:

Morning Star (http://www.morningstarcorp.com/en/home)

Out Back (http://www.outbackpower.com/)

Genasun (http://genasun.com/products-store/mppt-solar-charge-controllers/)

DaveInDenver
12-10-2013, 09:34 PM
Nice thing about nice ones like the Morningstars is that they sense load to balance charging against usage. They also can do equalization which is nice to keep batteries conditioned. Sometimes you don't get a good charge because your load take priority over charging while other times you have excess power during low usage that could be used to condition the battery. They can also remote temperature sense the panels which is one variable used in the MPPT algorithm to determine peak efficiency.

The risk for simple chargers is mainly if they don't do a good job and over/under charge your batteries. Going over voltage is bad, leads to sulfation and ruins the battery.

It's more likely that they starve them perpetually of current. If you remember time and current are the two variables in the battery charging equation. There are specific voltages and currents required to fully satisfy a battery during all phases of charging.

It's mainly during bulk charging that you will need to give the battery the current it wants and this is measured in percentage of capacity (C). So a C of 100A-hr might require constant current for 8 or 10 hours at 0.1*C at 2.35V per cell or 14.1V for a 12V type. If you dip below this you will starve the battery, resulting in insufficient chemistry reversal but exceed this current and you overheat the battery. Heat is a big enemy of batteries especially during charging. Usually once a battery hits stage 2 or 3, what is usually called maintenance or floating, the internal resistance begins to climb and they regulate their current themselves. It's when you are starting to charge a deeply discharged one that you have to be careful to give them neither too much or too little current.

None of this is to say that you /must/ spend a lot to get a high quality charge controller, but often you do get what you pay for.

nakman
12-10-2013, 10:11 PM
this is great info, thanks Dave & Brian in particular for jumping in here. Keith I suspect you don't mind the hijack here, as this is directly relevant to your project, yes?

So say you were presented with one of the new, low cost, turn-key solar charging solutions for RV's. Something like this one, a 200w deal: http://www.ebay.com/itm/Complete-Kit-200-WATT-2pcs-100-Watt-100W-Solar-Panel-12-Volt-24-Volt-RV-Boat-/261297690217

It comes with a pair of solar panels, cheapo charge controller, some plug & play wiring, and some brackets. Presume that you wouldn't ever be using this to try to breathe live back into an over-taxed battery, but instead it's just used for camping trips... where an AGM-type battery measuring 12.4 volts when running the fridge gets a little positive drip from this panel.. end goal being at the end of the hot day, it doesn't go much below 12.1, and if it can start tomorrow at 12.4 even better. Best case is your truck could camp indefinitely with hot sun and cold beer, worst case is you can last another day or two, compared to no solar.

How much better would you think results from using a "better" charge controller would be compared to the cheap one? Not asking you to quantify it, just gut feel- worth another $100?

DaveInDenver
12-11-2013, 06:54 AM
I'm no fan of cheap chargers on any level but I acknowledge in your hypothetical that a decent 3-step charger (I'd maybe go with a known brand, like Battery Tender or something) would make financial sense compared to a more expensive MPPT controller. If you already have a good charger at home then something inexpensive is probably fine used sparingly. Battery life is cumulative of every half charge, over charge and what-not.

I have an Iota DLS-45 with the IQ-4 option that I use to periodically condition my batteries. Lately I've been letting the AGM that I use with the panel float on it but I will run a conditioning cycle on the other batteries, especially the Optima, a few times a year.

http://www.iotaengineering.com/dls45.htm

Couldn't tell you about the panels in your eBay link. Since they wouldn't be out in the weather I'd be less concerned about their quality. With constant exposure to wind and snow and sun good panels will last longer. Less expensive panels typically use plate glass instead of tempered, which you recognize the safety issues there. They are also more likely to begin clouding over if the glass is cheap. OTOH being banged around in the back of a truck will probably break even good panels and replacing them will hurt more. I'd probably go with the cheaper panels myself, too. Build some sort of hinged case to protect them a little.

Seldom Seen
12-11-2013, 09:12 AM
Goal Zero will be at the Costco Road Show at the Aurora Costco Dec 13-22. Probably be able to pick up some Boulder 30 panels for cheap.

DaveInDenver
12-11-2013, 09:27 AM
Do you have one of those Brian? Goal Zero seems nice but on the high side for what you get.

rover67
12-11-2013, 09:45 AM
Do you have one of those Brian? Goal Zero seems nice but on the high side for what you get.

Agreed that it seems high...

I went with a Renogy 100w panel for the top of the 60 and have been very happy.

100w for 150 bucks free shipping. It fits under my Gamiviti rack so I can still use the rack.

http://www.ebay.com/itm/100W-Watts-100-Watt-Solar-Panel-Off-Grid-12-Volt-12V-RV-Boat-USA-Solar-Cells/281117901727?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D3325091786707950004%26pid%3D100011%26prg%3D1005%26rk%3D2%26rkt%3D5%26sd%3D300900335483%26

Seldom Seen
12-11-2013, 10:13 AM
Do you have one of those Brian? Goal Zero seems nice but on the high side for what you get.

No, but I'm planning on hitting the road show to see if I can score some Goal Zero panels at Costco prices.