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Failed on first attempt at off-grid. questions about voltage.

So I bought a 45W photovoltaic kit from Harbor Freight which comes with its own charge controller ($139 on sale), a used deep cycle battery with 135 amp-hours, and a 1.6 amp DC pump that moves over 300 gallons per hour. Yeah I know I should have done my calculations ahead of time but here they are, after the fact.

1.6 amp X 12V comes out to 20W per hour times 24 hours for (roughly) 480 watt-hours of consumption per day. At 45W the solar panels would need 11 hours of full illumination/full output per day to keep up with the pump's consumption, and I'm not getting that. So starting with a fully charged battery, it goes for about three days before the battery drops to the 11V cutoff where the charge controller kicks off flow to the pump.

Not a lethal problem, since I have back-up pumps running from the grid, but I'd need to add more solar panels to keep up with my pump's consumption. I can do that (if I can find space for them)--but here is a question that is more theoretical for those who know about electrical stuff.

My pump is rated to work from 5W-13W. If I connect the pump directly to the battery rather than to the charge controller with the 11V cutoff, the pump will continue to work as the battery discharges to a lower voltage, and at this lower voltage presumably the pump's draw will be lower as well. At some point, this lower rate of consumption will be equal to the feed coming off the photovoltaics, right? Would there be a problem with this? Is it hard on a 12V battery to keep it fluctuating at a lower voltage--say between 7-10V? Will operating at a lower voltage affect the pump's expected longevity?

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The numbers sound like they are not adding up. A simple test you can do to measure the real world power consumption and recharge rate would be to fully change the batteries with no pump connected. With a full charge, disconnect the solar panels and run the pump. Periodically check to see how much discharge you are getting over time. Once you have discharged down to the 50% point, switch the pump back over to grid power and do a charge test. This will at least give you some real world measurements as to how the equipment is operating and you can better proceed from there. You could alternatively also get a "Kill A Watt" meter to measure actual power consumption of your pump. Ive read around here rated power and actual usage can vary quite a bit. Hopefully that helps you out a bit on troubleshooting your problem.

You may not be saving anything but backyard aquaponics really doesnt save anyone anything. It is a hobby and as long as you are learning and having fun, its worth it isnt it? :P

I'm doing something less formal today. This morning the charge controller was reading 12.2 V (i.e., below the max) on the battery with no load and no sun. I turned the pump on and am leaving it on through the day. I'll turn it off this evening. If the solar panels are putting more watts into the system than the pump is drawing during that same interval, I should have a higher state of charge (measured by voltage with no load) at day's end, right?

And yeah, it's a hobby, and I'm having fun with it. These challenges are what make it a learning experience!

I have the same solar panels you have that I bought about 2 years ago, for the size they are very good. I have 5 deep cycle batteries bought from Wal-Mart and they are going on 6 yrs old. (yes I take care of them well). The issue you have is that the system doesn't give you 100%(45 watts) all the time, maybe like 75 or 80%, that is with any system. If you can watch your numbers going down on your controller then the load is way too much. Going by your controller you should never go below

12.0 on battery charge showing (being half) and when fully charged will show about 12.6-12.7 depending on battery age. The best way on this small of a system is fast fill, slow drain with many hours at night turned off by timer. You would fill once or twice an hour and let it slow drain for the rest of the time. I used a smaller pump (160gph) and set timer running on the on every hour and half hour during the morning from 8am to 8pm and then once at 11pm and 2 am. with 5 minutes to fill. This worked for me except sometimes with a lot of cloudy days. I have been off grid for 3 yrs. and can tell you that you will need more batteries and larger solar panels(PVDepot.com has some of the best prices on solar equipment) to do what your trying to  do. I do believe you have already put a good hurting on your battery life. All your numbers you have crunched are only good in a "perfect world" set up. I would figure about half of what you have gotten. You probably don't have your solar on a tracker so don't get full "sun" all those 11 hrs and that gives you less power too. The amp rating usage on the pump is probably on a level pump, not pulling out of bottom of fish tank, so will use more amps too. You will have to get more of power or change to "fast fill, slow drain" system with timer or continue to fail. Sorry, you have been to the school of hard knocks.

Ken, it sounds like you're moving a lot less water-- 5 minutes out of every 90 between 8 and 8, plus another 5 minutes at 11 and at 2--looks like a total of 55 minutes of pumping total for every 24 hour period at 160 g/hr--are you really getting away with pumping less than 150 gallons per day? How big is your AP system? How many and what kind of fish?

That's a huge difference from my target of having 300 gallons move per hour 24/7 (and this is still less than the recommended lower limit of one water change per hour). 



Jeffrey Ihara said:

Eh, I figured as much. The real world hardly ever conforms with the theoretically sensible. But aren't deep-cycle batteries made to be discharged to much lower voltages? 

So at 6V the pump would be drawing more current than at 12V? What if the pump's specifications say that 1.6 amps is the maximum? If there is a 1.6 amp max on the pump, wouldn't it just pump slower as the wattage went down with voltage of the battery?

It is from my understanding that only AC pumps will increase the amprage as you decrese the voltage.  This is because the motor will spin at a spacific speed because of the frequency.  DC motors are different.  A DC motor will draw less amps with less voltage.  If your DC pump was 100 watts at 12volts it would draw 8 amps.  If if was fed with 6 volts there would only be enuff power to push 4 amps through totaling 24 watts or 1/4 the watts

AC motors work compleatly different.  If you feed an AC motor with half the volts it will still try to spen at the speed witch it was desined.  It whould draw more amps and burn up.  

There are motors that do operate differently than this but for a rule of thumb if the moter does not have a drive of some sort it will opperate in these ways.



Jonathan Paul Grenard said:

 If your DC pump was 100 watts at 12volts it would draw 8 amps.  If if was fed with 6 volts there would only be enuff power to push 4 amps through totaling 24 watts or 1/4 the watts

Thanks. I was going to have to figure out the cause of nonlinearity between DC motor output decline and voltage--the relationship is only linear if you assume constant current, but it makes perfect sense that current will drop with the decline in power, and since you're multiplying current X power to get watts, it's going to be (roughly) a quadratic relationship between power and work. You saved me some time!

You're not kidding about expensive but then again we hope to be feeding ourselves and others from our systems for a long time.  It's difficult to put a value on good, fresh, clean food.  I bought solar in case of long term power outage.  If you're not concerned about that, you can build in short term backup a lot cheaper.  In fact, you may have enough now, for short term backup.

Jeffrey Ihara said:

This whole solar thing is a (kind of expensive) experiment anyways. I figure I would be saving a total of maybe $30 per year if I were to get the whole thing off grid(which I haven't), and it'll take more than a lifetime to have this recover the costs of the panels, batteries, pumps, and various accessories I'll be needing to buy in the meantime.

You're right, of course.  On best days, I get only 4-5 hours max sun.  I need more batteries too but don't know when or if I'll take that plunge.  

Ken Richardson said:

 All your numbers you have crunched are only good in a "perfect world" set up. I would figure about half of what you have gotten. You probably don't have your solar on a tracker so don't get full "sun" all those 11 hrs and that gives you less power too. 

Hey Jeffrey, now you see why people who do understand these things get so frustrated as our president continues to throw our tax money down this rabbit hole.

"and it'll take more than a lifetime to have this recover the costs of the panels, batteries, pumps, and various accessories I'll be needing to buy in the meantime."

Guess what, your panels will never last long enough to make a payback. They loose their punch long before payback is close to fruition not to mention all the battery costs or the huge pollution involved in manufacturing the lead acid batteries and the solar cells. Unless you NEED to be off grid you should use your system as a back up in case of grid failure. Solar power is still for the rich who do not care about "payback" but want to be cool and green. Water power, hydro, if you managed to buy land where you have a stream with at least a 50 foot drop that you can tap into is about the only scenario that actually works. Wind has it's own set of problems that I won't get into here, not to mention having to climb that 60 ft tower to maintain it. And you better get up to speed as a technician before attempting any of the above because if you have to hire people like me to maintain your system you are screwed even more. Ignorance is bliss, reality is a bitch. And politics is politics.

Sorry to be such a nay-sayer but someone has to be honest. Oh, and then there is the well documented issue of chemtrails that have reduced your solar energy by another 20% so you should add that factor to your calculations. The fun never ends.

Jeffrey Ihara said:

Sorry if I'm so clueless--I actually have a PhD in biology, but I have never tried to understand electricity until now.

 and it'll take more than a lifetime to have this recover the costs of the panels, batteries, pumps, and various accessories I'll be needing to buy in the meantime.

Evidently it doesn't take much to trigger a FoxNews-flavored tirade out of people these days. But I have no desire to derail the direction of this discussion thread and no intention of deep-sixing my experiment with solar technology.

I think people on this forum tend to be genuinely interested in pushing the limits towards sustainability, which is not within our reach now, but it's getting closer.

Jim Fisk said:

Hey Jeffrey, now you see why people who do understand these things get so frustrated as our president continues to throw our tax money down this rabbit hole.

"and it'll take more than a lifetime to have this recover the costs of the panels, batteries, pumps, and various accessories I'll be needing to buy in the meantime."

Guess what, your panels will never last long enough to make a payback. They loose their punch long before payback is close to fruition not to mention all the battery costs or the huge pollution involved in manufacturing the lead acid batteries and the solar cells. Unless you NEED to be off grid you should use your system as a back up in case of grid failure. Solar power is still for the rich who do not care about "payback" but want to be cool and green. Water power, hydro, if you managed to buy land where you have a stream with at least a 50 foot drop that you can tap into is about the only scenario that actually works. Wind has it's own set of problems that I won't get into here, not to mention having to climb that 60 ft tower to maintain it. And you better get up to speed as a technician before attempting any of the above because if you have to hire people like me to maintain your system you are screwed even more. Ignorance is bliss, reality is a bitch. And politics is politics.

Sorry to be such a nay-sayer but someone has to be honest. Oh, and then there is the well documented issue of chemtrails that have reduced your solar energy by another 20% so you should add that factor to your calculations. The fun never ends.

Jeffrey Ihara said:

Sorry if I'm so clueless--I actually have a PhD in biology, but I have never tried to understand electricity until now.

 and it'll take more than a lifetime to have this recover the costs of the panels, batteries, pumps, and various accessories I'll be needing to buy in the meantime.

Jeffrey, I am all for experimenting and hobby solar and wind and hydro. I too love it but I do not expect wind or solar to be money saving or offer a payback. I am however tired of the Clickbank scams  that promise 50% savings after spending only 200.00 due to a "Weird Trick" and building your own panels, etc. I am a Master Electrician in 2 states and have seen all the promises that the unaware fall victim to every day. If people go into these things with their eyes open (read knowledgeable) they won't be disappointed and can have a lot of fun with it, when you're a geek like me and probably you. But when I see people expecting a "payback" versus on-grid I know they are drinking the Koolade. I want to see private money fund the research and not our government picking winners and losers with our money.(read campaign finance payback) Odd how most go belly up AFTER they get billions from us and then give out huge bonuses (more than most of us see in a year) as they lock the doors. Aren't you getting tired of it?

Great as a hobby, great if you have no choice, great if you built a nice country home only to find out the electric co wants 15 or 20K to run the lines and hook you up. But to beat the price of our cheap grid in general. Don't hold your breath. Now if you want to talk small hydro, I'm all ears. A 1" pipe dropping 50 feet VERTICALLY not length, will produce all the power you will need for an efficiently run house. Why, because it runs full out 24/7. Not a sunny day here or a windy day there.

Sorry if that offends you. Not meant that way. I just don't like seeing people swindled.

And Fox News, you mean the people who at least tell half the truth as opposed to the rest that tell about 10%? Not a fan of any of them.
There is a great deal more to say on this solar thing like where to buy panels at wholesale, 6v verses 12v bats, how to get 6v bats cheap, etc. and I'll be part of that discussion any time as well. But let's keep it real.


Jeffrey Ihara said:

Evidently it doesn't take much to trigger a FoxNews-flavored tirade out of people these days. But I have no desire to derail the direction of this discussion thread and no intention of deep-sixing my experiment with solar technology.

I've made that blunder myself. I have a 15 w harbor freight solar panel, though, so the blunder is not quite as expensive. But still. The workaround I came up with was to ditch the big ass battery that the panel would never be able to charge fully, and drop my power needs.

So far, that means my panel runs one 2w air pump with a car inverter rated for 75 watts during daylight hours. ( I think I have the same charge controller as you do; its hooked up cause I don't know what I'm doing when it comes to anything electrical or solar. Its probably not needed, but hey.) The other pumps I have run on the grid and are on timers anyway, so not pumping 24/7 is no big deal. I have this air pump pumping water ( forced air method) to a single growbed so far, but it could run through the other 2 if I got off my hump and finagled it. I would really like to find a more powerful air pump first though, and see if the water flow is any different

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