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msachen
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# Posted: 10 Jul 2013 03:44pm
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Hey,
I've read through most of the posts and I'm more confused now than when I started. I stand in awe of the science that is being discussed on this site. I am not worthy! But here goes:
I'm moving to a place that is one of the wettest places in the US. Solar is a poor option, but we need power to charge cell phones, operate power tools, use powered speakers, satellite modem and router, and misc ac appliances. The refrigerator and cooktop are propane.
We'd like to have a Honda generator and a battery bank. The generator would run 4-6 hours per day during high energy usage and recharge the batteries, which would be used on a more limited basis in the evening. The question is sizing and matching the system for economics and efficiency.
I'd prefer a design that was overpowered for now, but had headroom for increased consumption in the future. If I started with a 2Kw generator, what would be a charge controller that would work now, but be ok if we added an additional 2Kw generator in the future? What battery bank would give me the balance I need now, but be upgradable with future expansion? Would I need a separate inverter, or is there a way to do without?
Basically, I need the help of people that know what they're doing, because I don't...yet. If there is a better place to post this, please let me know.
Thank you for your time.
Mike
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GomerPile
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# Posted: 10 Jul 2013 03:57pm
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You need to divide your loads into 2 groups. 1) are things you expect to be generator only devices, and 2) are things you expect to use 24/7.
I would guess that any AC appliances are generator only devices and lights, cell phone chargers, satelite modem, etc need to be always available.
The AC only stuff, just run from the generator with an extension cord. If you find yourself needing more power, buy a companion generator to bring your capacity up to 4000 watts from 2000. This gives you a redundant 2000 watts of power (one generator fails, you have a backup).
If you don't plan to use any solar panels at all you can charge batteries with a 30-60 amp microprocessor controlled battery charger available at Wal-mart, sears, Amazon, and elsewhere. Plug the charger into the generator so that it keeps your battery bank topped off.
If you want to add a solar panel, you can get 20-40 amp charge controllers for about $100. Look at the Morningstar Solar or the Xantrex Cxx series (I use a C40).
Connect a small inverter to the battery bank to run you "always available" stuff. You might also want to think about running 12V wires to power car power plugs and LED lights directly.
To give you a point of reference, I live off grid and power DSL modem, LED lights, hot water heater, fans, well pump from a bank of two 12v batteries. I use about 10-15 amp hours each day and charge with 140 watts of solar panels.
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msachen
Member
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# Posted: 10 Jul 2013 06:44pm
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Thanks.
So I have the 2Kw generator with an extension cord to a power strip for appliances and 'only when the generator is on' stuff. I then connect a 60 amp MPPT from the generator to the batteries to keep them charged. Then I connect an inverter to the battery bank for the 'always on' stuff.
Cool.
Now if I add a companion generator to double my power, will my 60 amp MPPT still match? What 12v batteries would you recommend? Inverter recommendations?
I don't mind spending money on quality components, but I'd hate to waste money on stuff that was inappropriate if I doubled up on the generators.
Thanks,
Mike
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GomerPile
Member
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# Posted: 10 Jul 2013 07:29pm
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No you would NOT use an MPPT charger....those are for solar panels and are waaay more expensive than a battery charger you would buy from sears or Walmart. Since you have AC power, you use it to power a plain old car battery charger (a nice modern microprocessor controlled unit...80 bucks or so). This charger will not care how many generators are running.
As for batteries, I use 2 deep cycle marine batteries. BUT I am not normal and use very little power. A cheap deep cycle battery from Walmart will get you going, but you may have better luck using a battery designed for PV applications. I have no experience with this type of battery, so I can't advise you on that.
Later on, if you want solar panels THEN buy the MPPT charger and hook it up.
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msachen
Member
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# Posted: 10 Jul 2013 07:35pm
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Thanks. Very helpful. I was thinking there was a way to do this with a charger / inverter combo.
Mike
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Truecabin
Member
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# Posted: 11 Jul 2013 02:13pm - Edited by: Truecabin
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Quoting: msachen I was thinking there was a way to do this with a charger / inverter combo.
yes there are combos and dont buy junk, good inverter chargers cost more than $1000 look at magnum energy for example there are others too http://www.amazon.com/dp/B004I7GEMO this one charges at 100amps
if you want to charge batteries with a generator a small charger like 15 or 25A is wasting gas every gallon is $4 that could pay for a big charger after 10 gallons wasted you could have spent $40 on a bigger charger
a 2kw generator can charge big amps get the biggest you can like 40A absolute minimum but 60, 80A is better a 2kW could charge at 100+ amps but that is an expensive charger
every gallon saved is $4 and you can apply it to your charger or inverter/charger. faster charging saves your generator too and is quieter.
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ICC
Member
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# Posted: 11 Jul 2013 06:15pm - Edited by: ICC
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Size the battery charger to the batteries. Too big cab be as bad as too small. Wet calls are more forgiving tham AGM or gel call when it comes to overcharge current.
Sizing example: , let's say the total amp-hour capacity of the batteries is 440 amp-hrs @ 12 VDC, The Capacity is C.
Then we use the formula C/10 , 440 / 10 = 44 amps.
C/10 is the ideal charge rate for lead acid wet cell batteries. It will get the charge up as fast as possible, minimal gasoline use, and generally not harm the batteries. A lower rate will be fine but is less efficient; more gasoline.
For anything off grid the place to start is sizing the battery bank.
I like the Iota brand of chargers. They automatically switch from bulk to absorb to float and can also equalize on a time schedule. They have a wide array of models and same amp size chargers can be stacked if you increase the battery bank size. Be aware that adding new batteries to older ones has a downside. The new ones act like the old ones when you have the old ones a year or more old.
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msachen
Member
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# Posted: 11 Jul 2013 09:06pm
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OK, so with chargers, it's better to be over than under. But spot on is better yet.
If the battery is 12v 210 Ah, and the bank is 24v 840 Ah, the C/10 formula applies to the bank, right? So, in this case, 840/10=84. Would it be preferable to charge with an 80 or 100 amp charger? Is a little under worse than a lot over?
You guys are great! Thanks,
Mike
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ICC
Member
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# Posted: 11 Jul 2013 11:56pm - Edited by: ICC
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Quoting: msachen If the battery is 12v 210 Ah, and the bank is 24v 840 Ah, the C/10 formula applies to the bank, right? So, in this case, 840/10=84. Would it be preferable to charge with an 80 or 100 amp charger? Is a little under worse than a lot over?
If the battery bank is 24 VDC with 840 amp hour capacity I would choose the 100 amp charger over the 80, but the 80 would do the job well. The caveat would be to somehow be able to monitir the battery temperature as the higher rate could cause the battery temp to rise above 125 F which will shorten battery life.
The other question is whether or not the generator can supply the required power for the battery charger in question.
Quoting: msachen If the battery is 12v 210 Ah, and the bank is 24v 840 Ah
So there are, or will be, a total of 8 of those 12 volt 210 amp hour batteries? Many people believe batteries should not be connected more than two rows deep (in parallel), some say three parallel maximum. Ideally there would be no parallel batteries only series.
If you need the total amp hour capacity that gives you might be better off changing to 6 volt batteries, 4 in series for 24 VDC. Maybe two sets of those in parallel?
12 volt batteries rarely have the thick lead plates like a good deep cycle 6 volt battery does. The 12 v may carry a deep cycle nname, but are often made with thinner plates. Something to think about and check into.
And all that applies to what are known as flooded cell lead acid batteries. AGM and gel may have different needs. Gels in particular are sensitive to over charge and over discharge rates.
As for what size battery bank should be assembled, you are the one who can decide what the needs will be. It may take some time but take the time to accurately assess the potential needs. Then add 10 to 30% for future growth for the things you thought you would never want or need. Better to have too much battery than too little, within reason.
As hinted at above, try to keep to a single series string if at all possible. When parallel hookups are necessary it is advantageous to use a stout buss bar system. Each series string is indeoendently connected to copper buss bars large enough to take the highest amperage the system could have imposed on it (usually the maximum amps for the inverter.
Further note; a top quality inverter / charger may be the best thing. When connected to a generator the inverter / charger will pass the genny power thru the inverter directly to the cabin or house. No need to run separate genny or inverter circuits.
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