Amps and Volts and Watts ... Oh My!

I think my brain is fried. :/ I can calculate how much dopamine to put in a bag to keep the blood pressure of a 1200 gram baby at an acceptable level, but for some reason all of this electricity stuff is just not computing. Good thing I didn't want to be an engineer.

Anyway, I'm attempting to put together a small solar system just to run some lights and keep the laptop charged ... for now. I plan to expand it as finances permit. I currently own two 100 watt panels and a 2000 watt inverter. I know I need some sort of a regulator and a battery or two or six, but I'm plowing through all of the info online and just not making heads nor tails of it. My current budget is about $500, give or take. I totally understand that I will not get all of my power needs met at that price point, and I do have a generator. I just want to get the ball rolling and be able to use solar power for at least some of my plug ins.

Somebody tell me what to buy. Links would be cool. If you ever come through southwest TN, I'll pay you in brownies.

Ferne Reid wrote:I currently own two 100 watt panels and a 2000 watt inverter. I know I need some sort of a regulator and a battery or two or six, but I'm plowing through all of the info online and just not making heads nor tails of it. My current budget is about $500

Do your solar panels, or your inverter have a charge controller built into them?

Hi, Ferne. Its hard to go wrong with a couple golf car batteries. 90-100$ each at batteries plus or that wal store.
Duracell has a 230ah 6v battery that is the right price. The inverter is way plenty and you may find that a smaller inverter or an automotive charger for your laptop will be efficient.

Generally, not always but, larger inverters can have a high standby load of 15-40 watts even when not supplying power, so its usually best to turn it off when you are not using it.

200 watts of solar can do an impressive amount of work as far as general use lighting and communications/entertainment.

You will want anywhere from 2.5-6 days of storage depending on your weather and site.

At 12vdc, 230ah will provide 1400 watt-hours daily use off grid, to 2200 watt hours of storage for backup or occasional use.

This is 1400w for one hour or 1 watt for 1400 hours, or anywhere in between. It a rough figure as high amp loads deplete batteries differently than low amp draws.

Another thing to look at are the portable power packs, usually lithium, usually have usb ports and charge from 12v. They make biguns too.

A laptop 80w charging for an hour is 80 watt-hours, plus losses, so 90 to 100 w/hr to do the job or about 40 minutes to an hour of sun time if your main battery was full or near full.

There is a lot to this, but if you pick up at least a 100ah 12v sealed battery or better, you will likely see good usefulness. A 100ah battery is bordering on as small as you can go with your solar input unless there is site conditions or your controller that can limit amps from solar to battery instead of taking the whole 'bulk'

Joseph Lofthouse wrote:
Do your solar panels, or your inverter have a charge controller built into them?

No, they do not.

Frank, thank you for making sense! Your explanation helps a lot!

You will need a good charge controller to shut down the power when your batteries are full or the life of the batteries will be very short even with good deep cycle batteries. Zantrex makes one that I and several of my neighbors have used for years with no problems but there are many other brands.  If you think you may add more panels later buying a larger controller now wouldn't cost much more and you wouldn't have to replace it to upgrade.  A 40 amp controller would handle 480 Watts of panel (40 amps x 12 volts). The other thing that kills batteries fast is drawing the voltage to low. I have a freind who made her golf cart batteries last 13 years but she never took them below there rated voltage. Most inverters rated for 12 volts can operate down to about 10.5 volts so waiting for the inverter to shut off will shorten the life of your batteries dramatically.  Many charge controllers and some inverters have a built in digital volt meter or it can be added separately for only a few $. Keeping the voltage above 12 volts will add years to the life of your batteries. You should also check the water level several times each year and if low add only distilled water because minerals in tap water can cause problems over time. When setting up your system put the charge controller as close to the batteries as conveniently possible so voltage lost in the wire doesn't keep your batteries from being fully charged and use large enough wire to carry the power without much loss. 12 volt power needs wire much larger than 120 volt for the same amount of power (think of the amount of water from a hose with only 12 psi as opposed to the same hose with 120 pounds of pressure) . You can google tables that show what size wire to use for your voltage, watts or amps, and the distance of your run. To use the power your 2000 watt inverter is capable of producing the wires between it and the batteries must be huge with copper the size of a finger. Many people use large welding cable for this and to connect the batteries to each other. If you have other questions post them and I'll try to answer. I'm in Colorado but I think UPS could handle brownies and I would pay the shipping.

https://www.altestore.com/store/charge-controllers/solar-charge-controllers/pwm-solar-charge-controllers/morningstar-charge-controllers-pwm/morningstar-prostar-ps-30-30a-charge-controller-without-display-1224v-p789/

https://www.altestore.com/store/charge-controllers/solar-charge-controllers/pwm-solar-charge-controllers/xantrex-solar-charge-controllers-pwm/xantrex-c40-solar-charge-controller-40a-122448v-p2070/

https://www.altestore.com/store/charge-controllers/solar-charge-controllers/pwm-solar-charge-controllers/midnite-solar-charge-controllers-pwm/midnite-solar-brat-30a-pwm-charge-controller-p11775/

All of these controllers are likely good choices for 12v or 24v  battery systems and range from $80 to $180 if you wanted status displays, up to $140 without display.

The Zantrex C40 will work for 12v, 24v, and 48v batteries and it will allow a maximum (do not exceed) pv input of 125v!

The other two will allow 60v pv in.

The Midnite Brat is a spartan weathertight device with sophisticated load and lighting control features.

There are cheaper options, but these are robust.

If you have specifics from the inverter, panels and distance between equipment, and a few other details, i think your budget will allow for all the bits.

Thank you both! Finally, people who can talk about electrical stuff and still speak English!

It's late and I've had a long day, so I'm going to look at those links and shop for batteries tomorrow. I'll post what I'm thinking of buying here so you guys can take a look at it.

You could just use direct DC from panels to charge the laptop.

It uses about 19 volts DC, just add there between a voltage regulator.

Or if you read the laptop wallplug recharger, it most def has 19 volts output. But it drops a little, when it recharges.

As your panels provide 12 voltages, you can use this step-up module to adjust it to 19 voltages which is cheap, US $12 and it is 150 watts, usually laptop chargers are 60 watts (it reads also in bottom of your wallplug recharger of laptop).

No need for battery between or other electronics. This can make 19 volts out of 10 volts so the panels dont need to work even at maximum.

The bad point is, that you can reload your laptop only when there is enough sun.

(In the end there reads that it can handle 90 watts, but 150 watts when you change the cooling to more effective..)

http://www.ebay.com/itm/DC-DC-Adjustable-Step-up-CVCC-CCCV-LCD-Dual-Display-Power-Supply-Module-Shell-/182145022844?hash=item2a68b07b7c:g:bEYAAOSwV0RXuwQj

I would say you have assembled a good list of advice.
At 200 watts of solar please bite the bullet and get 2 6 volt golf cart batteries.  A single 12 volt will have to be a marine deep cycle which is nowhere near as robust as a true deep cycle. If that is all that's available get 2 still.  For charge controllers if the panels are within 20 ft of the battery the simple chargers (pwm types) recommended will do fine.  More expensive types (mppt )really shine when it's not a perfectly sunny day or the panels get further away. I would stick to the inverter for charging laptops and such.  Do be careful as you are running a modified sine wave inverter and they don't play nice with some chargers (mostly powertools). For laptops, cell phones, lights, flatscreens you are fine. If you incorporate the system into your daily life it will help offset the cost. It's a fun hobby and does not have to be crazy expensive.
Best regards, David

Thank you, Henri and David, for your input.

My inverter is a pure sine wave ... I did figure out the difference there LOL ... and I have the space to put the batteries right next to the inverter.

So if I'm looking at 6V golf cart batteries, I gather I need 2 of them to equal 12V? And going with Frank's suggestion to stick to a minimum of 100ah, is that 100 for each battery or for both batteries combined? I'm finding 12V golf cart batteries, too ... is that a better option?

Seriously, I'd rather intubate and hang an epi drip ... :/

My bad on the inverter good for you for not buying junk.  A golf cart battery will be 6 volts at 200 amps approx. A 12 volt will be 100 amps.  Same weight of battery same total power capacity. Crack open that case and the 6 volt will have 3 2 volt cells in it the 12 volt battery will have 6 but half the size. Your 2 6 volts will give you 12 volts and 200 amp hours . Clear as mud?  From those 2 batteries you will have a useable 1.2 kw of power since you want to use only half of your capacity to keep the batteries happy.  You could use as much as  1.68kw every now and then but you shorten their life span.  That works out to 50% and 70% discharge.  An easier way is try to keep the voltage above 12 as you use them.  Run something heavy for a minute the voltage will sink to 11.9 or 11.8 no problem but on a small load keep that voltage in the twelves.  I'm sure you've got this so go out and burn some amps!

I haven't used 12 volt golf cart batteries so can't speak from experience but my thought is that to make 12 volts 6 cells are needed.  Putting 3 cells in each of two 6 volt batteries would alow them to be built more durably than putting all 6 cells in one 12 volt battery. If someone has long term experience with 12 volt golf cart batteries I hope they will share it with us but until then I would go with the track record of the 6 volt. I know they can last for 10+ years if treated with care.

If your inverter is 12v, you will need 2x 6v golf car batteries. The result is 12v-230ish amp/hrs.
If your inverter is 24v, you would need 4x 6v golf car batteries.

At 12v, and two 6v batteries in series you will have about 1400 watt hours available in storage at 50% depth of discharge and 2200 watt hours at 80% depth of discharge. Thats alot of laptop and lighting time.

Your panels could be as far away as 40 feet on #10 wire. You will need larger wire to go further and stay below 2% loss.

Max continuous amp draw is around 175a at 11.5v, so 2/0 cable is a minimum for max output, 4/0 cable and a 250 amp fuse is better unless 2000w is the max surge and not max continuous or unless you are not going to go anywhere near peak power.

 Either way the battery, inverter, cables and power distribution are the core of the system and require special consideration. People sometimes focus on solar and controllers and pv wire, but its just a charger and you can get charge from many sources, grid, generator, car, wind, thermoelectric, crank-pedal-treadle, hydro, pv, etc...

Integration and build of your battery box and power center is important for ease and reliable use.

What inverter do you have and what are yhe specs for your panels?

At 200w pv, 4 hours of peak sunshine should put 600-800 watt/hours into your system...  that would be michigan average, you may get 6 peak average sun hours over a day at your location, maybe less.

That would be 5-6 laptop charges, or 10-12 hours running with a full laptop battery, or 6 hours of computing and 6 hours of lighting at 80w of led (4-6 x 8 watt led/60w equivalent each bulb)! Plenty of light!  May as well put your modem on it too and have uninteruptable solar power to your comms and entertainment.

For this type of use and solar input, your battery would be a 3 day battery, no sun/no conservation...4-6 days on a stretch of half-sun or less and conserving where needed. This would be maximum discharge and would be used as a reserve, the 4 to 6 days. Micro systems gan do big things. Plenty of villages around the world couldnonly dream of this level of easily maintainable power.

So much good stuff in here.  To be clear I did mean2x 6 volt golf cart batteries hooked up in series.  
Cheers, David

There are great 12v deep cycle batteries, here are two of my favorite sizes. These are flooded and require maintenance, but have long service life.

150ah, one battery, 12v simplicity.
http://www.trojanbattery.com/product/t-1275/

225ah, one battery 12v.
http://www.trojanbattery.com/product/t-1275/


If you want sealed AGM, Fullriver Battery has been great in our backup and offgrid installations. They make 250ah and smaller in a 6v or 12v configuration, larger if you like$$$.

http://www.fullriverbattery.com/product/batteries/DC210-12
About $500! Good battery, budget breaker though.

Dont forget one of these kits or equivalent.

http://www.invertersupply.com/index.php?main_page=product_info&products_id=2080&gclid=CIvLha21iNMCFUM9gQodTmgD9g

I can get a couple of these at the local Batteries Plus store. Seems like a decent price, plus they have another 10% off if I order online and pick up. Good choice?

https://www.batteriesplus.com/battery/rv/deep-cycle/6/sligc110

I think I'm gonna go with the Midnite Solar Brat controller.

Looks good and the brat is a great pwm controller.  Please invest is some well gauged cables 4/00 250 amp cables and either fuses or breakers to match for the battery interconnects and the inverter cables.

That battery is a great battery for small systems. Widely available, tough enough for reliable use and the price is right. This one has a few more amp-hours for $10 extra, per battery.

https://www.batteriesplus.com/battery/rv/deep-cycle/6/sligc115

I have a idea to consider for later addition, how about an electric garden tractor? cut your grass, pull trailer, plough veggie garden, grade or clear snow with a plow blade, and the 4 x12v 120ah batteries could supply power for your home / inverter or power tools when not being used in the garden, of course it could be charged by solar or generator, for more info see website:- electrictractor.net

i question why invert you power to ac?you lose so much energy,if you truly just need to charge laptops phones and run lighting,just stay dc.all come ready to charge that way,or need a cheap adapter to make it work.i know there is big money involved with most systems but we use a poor mans version of that. go to your auto parts dealer and get a solar trickle charger with built in battery minder[about 40 bucks]and a cigarette lighter for a car about 6 bucks and your ready to go a few tricks to effectiveness is use cat5 wire to run your lights and a simple rocker switch again from the auto store we have been doing this for over 20 years[ok my brother builds the leds for me,but we can sustain light for 26 days with out a charge,we have done this a few times to test it.and as a note make sure your solar charger has a 2.7 amp or higher charge rate. hope this helps

frank li wrote:A laptop 80w charging for an hour is 80 watt-hours, plus losses, so 90 to 100 w/hr to do the job or about 40 minutes to an hour of sun time if your main battery was full or near full.  

Hi Frank. You're a wealth of knowledge. I've always wondered if it is feasible to run a desktop computer and a laptop on solar or wind power. I want to be as remote as possible, while still being able to work on the internet. I'm thinking I may be able to find a WISP (Wireless Internet Service Provider) who can send me internet point-to-point 15+ miles from their location. That could include land with no power access.

I need to decide whether I should consider land that doesn't have electric or I would need to stick to a location that does if I still want to be able to work (which takes far more hours, bandwidth, and power than just using the internet casually).

I hope the original poster doesn't mind me jumping into their thread. If I started a new one, I don't know that Frank would see it to answer.

Jump away, Gail!

I have my batteries. Waiting on the other things to arrive.

Mongo brings up a good question ... why don't I just stick with DC for the lights and laptop? The short answer is that I eventually want to be able to produce enough solar power to keep some food cold, heat up the coffee, and run the mixer. I can't buy everything I need for that all at once, but I already have the inverter, so I might as well set it up now and then just add to the system as I'm able.

One more question ... well, no promises to stick to that LOL.

Would these cables be OK to go between the batteries? http://www.ebay.com/itm/PowerDrive-2-Gauge-Heavy-Duty-DC-to-AC-Power-Inverter-Installation-Kit-/301961167823?hash=item464e49c3cf:g:I1AAAOSw74FXPfb8  Batteries Plus had some cheap battery to battery cables, but they seemed rather flimsy so I didn't buy them.

Also, there are cables that came with the inverter to connect it to the batteries, but they don't have a fuse attached. Can I put a fuse on there somehow and not spend another $120 for another kit?

Well to do it legally and once I would use 4/00 cable for a 2000 inverter they are more expensive of course.  A fuse block to match or better yet a disconnect breaker box.  I build code compliant systems though so I have no choice. 2/00 cable and a 175 amp fuse should be OK in most situations.
https://www.amazon.com/gp/aw/d/B00UB42ZYO/ref=mp_s_a_1_22?ie=UTF8&qid=1491873834&sr=8-22&pi=AC_SX236_SY340_QL65&keywords=2+0+battery+cable
Best solution something like this:
https://www.amazon.com/gp/aw/d/B06XNNS2C5/ref=mp_s_a_1_1?ie=UTF8&qid=1491874081&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=175+dc+fuse+solar
Not getting any easier is it?
Best regards, David Baillie

Not getting any easier is it?

No, it isn't. And people do this voluntarily, all day, for a living? :O

The $316 breaker box puts me over my budget, but I can certainly do those cables and a fuse.

So when I finally have all the pieces parts, I just string it all together with the cables, positive to positive and negative to negative? Or could it not possibly be that simple?

Ferne Reid wrote:Jump away, Gail!

I have my batteries. Waiting on the other things to arrive.

Mongo brings up a good question ... why don't I just stick with DC for the lights and laptop? The short answer is that I eventually want to be able to produce enough solar power to keep some food cold, heat up the coffee, and run the mixer. I can't buy everything I need for that all at once, but I already have the inverter, so I might as well set it up now and then just add to the system as I'm able.

Gail have you ever stooped in a big truckstop and looked around?most every convenience you can want is available in dc.....ive even seen trucks with microwaves
oooops i mean
Frene

Ferne, here is an acceptable fuse block. The heavier one is $40, i like it. This one is minimal, and $20! Plus the cost of a fuse.

http://m.overtons.com/modperl/product/details.cgi?pdesc=Blue-Sea-ANL-Fuse-Block-300A-w/Cover&i=82376&utm_medium=cpc&utm_source=googlebase&s_kwcid=googlepla&cvsfa=2587&cvsfe=2&cvsfhu=3832333736&s_kwcid=adwords__&gclid=CIz0o93AnNMCFYe2wAodumwGGA


2/0 is your minimum cable and is good for 195 amps continuous in an industrial enclosure with 90°c insulation. In open air or a large cabinet where cable does not touch anything.... and 105°c insulation, possibly more. You should be on the safe side, fused at 175a and assume 90°c.

Fuse as close as possible ( 2"-6") to the positive battery terminal, even if your inverter has on board fuses. You are responsible for your system and it pays to install safety.

This is for comparison to budget. Look for crimped on ring terminals that match your studs...5/16" hole for the fuse. Not sure about batteries and inverter terminal stud sizes. Custom cables are inexpensive, have nice heavy terminals, crimped in a machine fixture, and heat shrink.

https://www.altestore.com/store/cables-wiring/battery-to-inverter-cables/battery-to-inverter-cables-20-awg-60-5ft-redblack-pair-p9964/

https://www.altestore.com/store/cables-wiring/battery-interconnect-cables/battery-interconnect-cable-20-awg-8-black-p9949/

We get ours built to spec at this place.
https://www.marysvillemarine.com/about.asp

But battery and fuse terminals will likely be 5/16" so if you can crimp on appropriate terminals to your inverter cables, you will only need battery interconnect(s) cable(s), a fuse, a short cable for battery to fuse and some ring terminals.

A good crimper and technique is required for reliability and safety of high current cables and terminal types must match wire type.  Flexible cables made of ultra fine wire need specific crimp terminals, and machine tool wire can be used with regular electrical supply store types. Not so flexible, but you can bend wire to shape and terminate between battery, fuse, inverter, etc., as long as you dont allow wire to put strain on connections. Then you can shop at a local store and not be left to thin, poorly crimped terminals available at most battery, autoparts, and farm stores... these can work but are not likely listed as safe for the home.

Dont fret over these, but see that all parts meet spec. 175a and low voltage capable.

Ferne Reid wrote:

Not getting any easier is it?

No, it isn't. And people do this voluntarily, all day, for a living? :O

The $316 breaker box puts me over my budget, but I can certainly do those cables and a fuse.

So when I finally have all the pieces parts, I just string it all together with the cables, positive to positive and negative to negative? Or could it not possibly be that simple?

Yes it's mostly that simple.  Lot of good wiring diagrams online. And yes everyday for a living... Some evenings I wish I was still swinging a hammer. Then I wake up and remember that it's really cool stuff.  In round two of your project please upgrade to the breaker box.  It's a good solid design pretty cheap and you can breaker your charge controller and any dc loads you put in from it.  When you order the inline fuse get 2 (life lesson there) Everything listed above you can recycle into the next stage if you push on.
Best regards, David

Gail Gardner wrote:

frank li wrote:A laptop 80w charging for an hour is 80 watt-hours, plus losses, so 90 to 100 w/hr to do the job or about 40 minutes to an hour of sun time if your main battery was full or near full.  

Hi Frank. You're a wealth of knowledge. I've always wondered if it is feasible to run a desktop computer and a laptop on solar or wind power. I want to be as remote as possible, while still being able to work on the internet. I'm thinking I may be able to find a WISP (Wireless Internet Service Provider) who can send me internet point-to-point 15+ miles from their location. That could include land with no power access.

I need to decide whether I should consider land that doesn't have electric or I would need to stick to a location that does if I still want to be able to work (which takes far more hours, bandwidth, and power than just using the internet casually).

I hope the original poster doesn't mind me jumping into their thread. If I started a new one, I don't know that Frank would see it to answer.

Office power can usually be done on a reasonable budget. The best way to find out is to place the whole office on a meter for power consumption.

As long as your total power is under 15 amps you can plug in whole blocks of appliances, room by room or all in one.

http://m.homedepot.com/p/P3-International-Kill-A-Watt-EZ-Meter-P4460/202196388

This will tell you how much power your system will require daily, weekly or yearly from a small sample or a longer one, longer is better... month? And you can make adjustments particulars to your need.

30$ is a good investment and these are just fun to plug stuff into and get real consumption figures, you will likely use it for shopping appliances, that new ultra efficient pc and monitor combo, which are coming in 24v these days, and that radio link modem...!

mongo silverwolf wrote:i question why invert you power to ac?you lose so much energy,if you truly just need to charge laptops phones and run lighting,just stay dc.all come ready to charge that way,or need a cheap adapter to make it work.i know there is big money involved with most systems but we use a poor mans version of that. go to your auto parts dealer and get a solar trickle charger with built in battery minder[about 40 bucks]and a cigarette lighter for a car about 6 bucks and your ready to go a few tricks to effectiveness is use cat5 wire to run your lights and a simple rocker switch again from the auto store we have been doing this for over 20 years[ok my brother builds the leds for me,but we can sustain light for 26 days with out a charge,we have done this a few times to test it.and as a note make sure your solar charger has a 2.7 amp or higher charge rate. hope this helps

Mongo, the fact is that it is more efficient electrically, to run dc to all devices... convienience and availability are an issue sometimes.

Rv, trucker and marine appliances are usually downsized and many times of quality inferior to appliances made for the home. Additionally, some people just want traditional plug in appliances bought at regular outlets.
the selection of ac appliances and devices is wide, quality available and brands familliar.

This and having inverted power ensures that visitors will not be left out of the power loop! Just lacks that off grid funkiness. Im not an inverter snob! We use dc power where it makes sense. Everybody has different requirements.

David Baillie wrote:Well to do it legally and once I would use 4/00 cable for a 2000 inverter they are more expensive of course.  A fuse block to match or better yet a disconnect breaker box.  I build code compliant systems though so I have no choice. 2/00 cable and a 175 amp fuse should be OK
Not getting any easier is it?
Best regards, David Baillie

The seperation between appliances used in and around the home /// and systems mounted to a building and connected to the building electrical has to be determined before getting all legal. There is a difference and most small projects can not stand the bugetary consideration as if they are a part of the building electrical, this is possibly a case in point.

frank li wrote:

David Baillie wrote:Well to do it legally and once I would use 4/00 cable for a 2000 inverter they are more expensive of course.  A fuse block to match or better yet a disconnect breaker box.  I build code compliant systems though so I have no choice. 2/00 cable and a 175 amp fuse should be OK
Not getting any easier is it?
Best regards, David Baillie

The seperation between appliances used in and around the home /// and systems mounted to a building and connected to the building electrical has to be determined before getting all legal. There is a difference and most small projects can not stand the bugetary consideration as if they are a part of the building electrical, this is possibly a case in point.

I won't disagree with you.  I'm always hesitant to recomend consumer grade gear though when I know if and when someone wants to build on it they will have to start all over.  Rereading the thread you've probably judged the end goal better.
Best regards, David