Posted: 4/2/2011 3:15:52 PM EDT
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i've googled and come up with several different answers and equations so i thought i'd ask here, since ya'll know more about this kind of thing than i ever will: i rednecked a 750 watt inverter to a optima 12v (55 AH) battery w/ a solar panel to facilitate SHTF charging (shown below without the solar panel). how long can i reliably run a 400w load (lamp, cell charger, fireplace blower, etc) before it dies (assuming it's charged 100%)? on the other side of that, if it's completely dead how long will it take to charge it with a 15w solar panel (assuming 100% sun, angle, etc)? thanks. 
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Doing simple arithmetic
55 Amp Hour = 55 amps in 1 hour (usually less if you are going at 55 AMP) X 12 Volts = 660 Watt Hours Or you will be lucky to get 1 hour out of the combo at 400 watts As far as recharge 660 watt hour / 15 watts = 44 hours but it is more because it is not 100% EFFICIENT. |
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i've googled and come up with several different answers and equations so i thought i'd ask here, since ya'll know more about this kind of thing than i ever will: i rednecked a 750 watt inverter to a optima 12v (55 AH) battery w/ a solar panel to facilitate SHTF charging (shown below without the solar panel). how long can i reliably run a 400w load (lamp, cell charger, fireplace blower, etc) before it dies (assuming it's charged 100%)? on the other side of that, if it's completely dead how long will it take to charge it with a 15w solar panel (assuming 100% sun, angle, etc)? thanks. http://i211.photobucket.com/albums/bb175/aceleroy13/e1cd3d0c.jpg That's a great start Hooch and your question isn't 'dumb'. It's actually a very good question that will be informative to all here. 
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I'm assuming a usb cell phone charger only uses a couple of watts, correct? Also, anybody know how to hook two panels up together for faster charging? Posted Via AR15.Com Mobile Just hooking the panels together in parallel will give you double the charge current. |
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Quoted: Wouldn't it be more efficient to use a car charger for the cell right off the battery instead of through the inverter? Just curious. In fact, using a12 volt lamp and blower motor would help a bunch too I would think. the blower for the fireplace is 110, and the original idea was to have something relatively simple to operate (think wife) and semi-portable (hence the hand truck) to heat and light my house with in case of a power outage during the winter. the inverter (which actually has a usb plug on it) just makes it easier to plug in smaller everday things (lamp, hot plate, laptop, etc). i have no delusions about powering my house with this thing, i'm just trying to get an idea of its capabilities and limitations. i've let it run for a couple hours with a light and fan before, but never till it died. |
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I'm assuming a usb cell phone charger only uses a couple of watts, correct? Also, anybody know how to hook two panels up together for faster charging? Posted Via AR15.Com Mobile If the S has hit the fan so bad there is no electricity why would you assume cell phones would work? ETA I think a 110v blower on a fireplace or stove is like 1.7-2 amps. If I remember correctly the kits they sell are good for like 3 or 4 days on one battery. ( I dont remember the AH though) |
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Quoted: Quoted: I'm assuming a usb cell phone charger only uses a couple of watts, correct? Also, anybody know how to hook two panels up together for faster charging? Posted Via AR15.Com Mobile If the S has hit the fan so bad there is no electricity why would you assume cell phones would work? it's happened here before......  |
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I'm assuming a usb cell phone charger only uses a couple of watts, correct? Also, anybody know how to hook two panels up together for faster charging? Posted Via AR15.Com Mobile If the S has hit the fan so bad there is no electricity why would you assume cell phones would work? it's happened here before......
Car charger? ETA if you are talking hurricane or tropical storm outage the wind would blow a temp panel set up around and cloud cover would effect the transmission of sunlight producing less power. A nice little gennerator with some stored fuel would be perfect for a short tearm outages such as a storm etc |
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Quoted: Quoted: Quoted: Quoted: I'm assuming a usb cell phone charger only uses a couple of watts, correct? Also, anybody know how to hook two panels up together for faster charging? Posted Via AR15.Com Mobile If the S has hit the fan so bad there is no electricity why would you assume cell phones would work? it's happened here before...... Car charger? explanation is a few posts up ETA: this is a backup for the generator & battery charger |
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My reply on this FWIW-there are NO dumb questions concerning things "normal people shouldn't fuck with"-electricity,reloading, explaining to you wife the drunken night with her twin cousins, etc.. Like G.I. Joe says-"knowing is half the battle"...If you mess up with electricity-and @ 12v it may seem trivial, but at the amps you are working with (and potentially could) knowledge will keep you with both eyes and 10 fingers. I have some telco batts in the shop that have a short circuit amperage of (I think) 35kA....in other words-an accidental short will seriously change the 'what are we doing later' part of your day. There are some really smart folks on here that have BTDT with solar/battery/inverter setups and they should be along shortly  . I know just enough to wire it up and hopefully not set something on fire in a large acidic fireball. Be safe and do your homework. And for God's sake, take pics of your setup when you get it going so we can learn something also!! |
| first off, running a battery till its dead is a good way to kill a battery FAST. they are not designed to be drained completely. we will assume that your inverter has a low power shut off. so that in and of itself shouldnt be an issue. second, dump that over priced POS optima and get you a couple of good deep cycle batteries. 2, 220Ah 6v batteries would be your best bet. any golf cart shop will have them or there is always the interweb. you can still have them on the hand truck but you will have to mod it some. 3rd, run everything you can direct off the 12v. there is no inverter loss by doing that and all it takes is a couple of the 12v acc plug modules. your wife surely knows what plug goes in a 12v acc plug. kinda hard to screw that up. check your stove, it may have a plug for a 12v battery already installed. if so, no need for the inverter to run that. you can also get 12v LED lights. you could mount them, or build a couple of stand lights mounted to the "cart" for lighting a room. you could even build a couple of LED lights that run off there own batteries and charge then with there own solar charger when the power is out. you want to make this as simple as possible so keeping as much as you can 12v would do that. OH, and get better/bigger panels. 15w isnt much if your really pulling a load. 45w would be the min i would have even with that setup and would probably buy a small gen with 12v charging ports to assist on cloudy days. even one of the small 2 stroke ones would do the job. thats my .02, hope it helps or at least gives you some ideas. |
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Quoted: first off, running a battery till its dead is a good way to kill a battery FAST. they are not designed to be drained completely. we will assume that your inverter has a low power shut off. so that in and of itself shouldnt be an issue. second, dump that over priced POS optima and get you a couple of good deep cycle batteries. 2, 220Ah 6v batteries would be your best bet. any golf cart shop will have them or there is always the interweb. you can still have them on the hand truck but you will have to mod it some. 3rd, run everything you can direct off the 12v. there is no inverter loss by doing that and all it takes is a couple of the 12v acc plug modules. your wife surely knows what plug goes in a 12v acc plug. kinda hard to screw that up. check your stove, it may have a plug for a 12v battery already installed. if so, no need for the inverter to run that. you can also get 12v LED lights. you could mount them, or build a couple of stand lights mounted to the "cart" for lighting a room. you could even build a couple of LED lights that run off there own batteries and charge then with there own solar charger when the power is out. you want to make this as simple as possible so keeping as much as you can 12v would do that. OH, and get better/bigger panels. 15w isnt much if your really pulling a load. 45w would be the min i would have even with that setup and would probably buy a small gen with 12v charging ports to assist on cloudy days. even one of the small 2 stroke ones would do the job. thats my .02, hope it helps or at least gives you some ideas. it allegedly is a deep cycle. the stove blower is 110v AC w/ no 12v plug. already have a generator. |
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i rednecked a 750 watt inverter to a optima 12v (55 AH) battery w/ a solar panel to facilitate SHTF charging (shown below without the solar panel). how long can i reliably run a 400w load (lamp, cell charger, fireplace blower, etc) before it dies (assuming it's charged 100%)? the following post will give you some background on how to calculate the running time of a given load from a battery of given capacity: http://www.ar15.com/forums/topic.html?b=10&f=22&t=604477#10323268 to reinforce what that post details, the discharge curve of a lead-acid battery is not linear with respect to the load. this is a complicated way of stating that the battery capacity is different for different loads. let that sink in for a second. a light load (few amps) will result in the battery having a higher apparent capacity. a heavy load (many amps) will result in the battery having a lower apparent capacity. so, to know how long a load will run from a battery, you need to know the battery's capacity at that load. it's not always straightforward but you can approximate it. your load is 400W which at 12Vdc is about 33A. this is not crazy high but it does require at least 8 AWG wire from the battery to the inverter input. the battery capacity given by the vendor needs more than just one parameter; saying it's "55AH" alone, without telling the load that was attached, is of no use. however the automotive industry generally rates battery ampacity of this sort in terms of a 25A load, simulating leaving your headlights on. in the auto battery industry this is called "Reserve Capacity". so, your 33A load is somewhat, but not a lot, higher than the 25A spec. figure it drops the battery capacity from 55AH to about 50AH. in general you should not discharge below 50% of that for greatest battery life, but let's say for SHTF applications you can discharge to 25% remaining capacity. so you have 0.75 x 50AH, or 37.5AH to play with here. with the 37.5AH of capacity your 33A (400W) load will last about 37.5AH/33A = 1.1H. ar-jedi |
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on the other side of that, if it's completely dead how long will it take to charge it with a 15w solar panel (assuming 100% sun, angle, etc)? reversing what i did in the post above –– you need to put 37.5AH x 12V = 450WH back into the battery. there are also conversion and heating losses with the charging process, so multiply this by about 1.5, giving you 675WH of energy needed to restore the battery to fully charged condition. 675WH / 15W = 45 H at peak solar panel output. hence if 15W can be generated approximately 3 hours per day, it's about 15 days to recharge fully. ar-jedi |
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first off, running a battery till its dead is a good way to kill a battery FAST. they are not designed to be drained completely. we will assume that your inverter has a low power shut off. so that in and of itself shouldnt be an issue. second, dump that over priced POS optima and get you a couple of good deep cycle batteries. 2, 220Ah 6v batteries would be your best bet. any golf cart shop will have them or there is always the interweb. you can still have them on the hand truck but you will have to mod it some. 3rd, run everything you can direct off the 12v. there is no inverter loss by doing that and all it takes is a couple of the 12v acc plug modules. your wife surely knows what plug goes in a 12v acc plug. kinda hard to screw that up. check your stove, it may have a plug for a 12v battery already installed. if so, no need for the inverter to run that. you can also get 12v LED lights. you could mount them, or build a couple of stand lights mounted to the "cart" for lighting a room. you could even build a couple of LED lights that run off there own batteries and charge then with there own solar charger when the power is out. you want to make this as simple as possible so keeping as much as you can 12v would do that. OH, and get better/bigger panels. 15w isnt much if your really pulling a load. 45w would be the min i would have even with that setup and would probably buy a small gen with 12v charging ports to assist on cloudy days. even one of the small 2 stroke ones would do the job. thats my .02, hope it helps or at least gives you some ideas. it allegedly is a deep cycle. the stove blower is 110v AC w/ no 12v plug. already have a generator. optima's quality has gone down faster than a cheap date over the last few years. i have seen ones last less than a year and others that lasted 5. its a hit or miss game and it usually fails at the worst time. who makes your stove(what is the model as well)? a small gen like THIS would be easy to use and sips fuel for charging the batteries on days the sun just isnt doing the job with the panels. |
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Yes, golf cart 6 volt batteries. Available at Sam's [best place I know to get them and good ones] for about $70 with this "dollar collapse" "inflation" we're having. gotta link? how do i wire those for 12v? thanks. sams has them on the shelf with the rest of there batteries. i dont believe they have them listed on there website. |
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Yes, golf cart 6 volt batteries. Available at Sam's [best place I know to get them and good ones] for about $70 with this "dollar collapse" "inflation" we're having. gotta link? how do i wire those for 12v? thanks. wire them in series. + on one battery to the load. Negative on the same battery to the posative of the second battery. Negative of the second battery to the load. 12 v output. |
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Quoted: Quoted: Quoted: first off, running a battery till its dead is a good way to kill a battery FAST. they are not designed to be drained completely. we will assume that your inverter has a low power shut off. so that in and of itself shouldnt be an issue. second, dump that over priced POS optima and get you a couple of good deep cycle batteries. 2, 220Ah 6v batteries would be your best bet. any golf cart shop will have them or there is always the interweb. you can still have them on the hand truck but you will have to mod it some. 3rd, run everything you can direct off the 12v. there is no inverter loss by doing that and all it takes is a couple of the 12v acc plug modules. your wife surely knows what plug goes in a 12v acc plug. kinda hard to screw that up. check your stove, it may have a plug for a 12v battery already installed. if so, no need for the inverter to run that. you can also get 12v LED lights. you could mount them, or build a couple of stand lights mounted to the "cart" for lighting a room. you could even build a couple of LED lights that run off there own batteries and charge then with there own solar charger when the power is out. you want to make this as simple as possible so keeping as much as you can 12v would do that. OH, and get better/bigger panels. 15w isnt much if your really pulling a load. 45w would be the min i would have even with that setup and would probably buy a small gen with 12v charging ports to assist on cloudy days. even one of the small 2 stroke ones would do the job. thats my .02, hope it helps or at least gives you some ideas. it allegedly is a deep cycle. the stove blower is 110v AC w/ no 12v plug. already have a generator. optima's quality has gone down faster than a cheap date over the last few years. i have seen ones last less than a year and others that lasted 5. its a hit or miss game and it usually fails at the worst time. who makes your stove(what is the model as well)? a small gen like THIS would be easy to use and sips fuel for charging the batteries on days the sun just isnt doing the job with the panels. as previously posted, i already have a generator. link to blower |
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Quoted: Quoted: Quoted: Yes, golf cart 6 volt batteries. Available at Sam's [best place I know to get them and good ones] for about $70 with this "dollar collapse" "inflation" we're having. gotta link? how do i wire those for 12v? thanks. wire them in series. + on one battery to the load. Negative on the same battery to the posative of the second battery. Negative of the second battery to the load. 12 v output. exactly the type of simple explanation i needed. thank you. |
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Quoted: Quoted: i rednecked a 750 watt inverter to a optima 12v (55 AH) battery w/ a solar panel to facilitate SHTF charging (shown below without the solar panel). how long can i reliably run a 400w load (lamp, cell charger, fireplace blower, etc) before it dies (assuming it's charged 100%)? the following post will give you some background on how to calculate the running time of a given load from a battery of given capacity: http://www.ar15.com/forums/topic.html?b=10&f=22&t=604477#10323268 to reinforce what that post details, the discharge curve of a lead-acid battery is not linear with respect to the load. this is a complicated way of stating that the battery capacity is different for different loads. let that sink in for a second. a light load (few amps) will result in the battery having a higher apparent capacity. a heavy load (many amps) will result in the battery having a lower apparent capacity. so, to know how long a load will run from a battery, you need to know the battery's capacity at that load. it's not always straightforward but you can approximate it. your load is 400W which at 12Vdc is about 33A. this is not crazy high but it does require at least 8 AWG wire from the battery to the inverter input. the battery capacity given by the vendor needs more than just one parameter; saying it's "55AH" alone, without telling the load that was attached, is of no use. however the automotive industry generally rates battery ampacity of this sort in terms of a 25A load, simulating leaving your headlights on. in the auto battery industry this is called "Reserve Capacity". so, your 33A load is somewhat, but not a lot, higher than the 25A spec. figure it drops the battery capacity from 55AH to about 50AH. in general you should not discharge below 50% of that for greatest battery life, but let's say for SHTF applications you can discharge to 25% remaining capacity. so you have 0.75 x 50AH, or 37.5AH to play with here. with the 37.5AH of capacity your 33A (400W) load will last about 37.5AH/33A = 1.1H. ar-jedi thanks for the link. quite informative |
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As mentioned golf cart batteries are probably best bang for the buck. Two of them will provide 220-240 ah total capacity at 12V.
Your inverter is probably around 80% efficient- 85% at best. That needs to be factored in to run data. The 15 W panel is tiny, for even a 55 Ah battery your' putting out .8-1amp. It will keep it the system topped off and do some small tasks like charging electronics though. I think several manufacturers want a charge rate of at least 5% of bank capacity, which would be about 3 amps in your current setup. A rule of thumb I have heard used is that to ensure a healthy battery bank use one watt of solar production for every AH of (12V) battery capacity. |
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are golf cart batteries ok to be used indoors? if i have to roll this thing inside i'm not gonna kill myself am i? as long as they are only trickle charging they should be fine. if your really putting the amps into the battery when charging they can off gas. if you run them down, take them outside to charge but for day to day upkeep they should be fine inside. |
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are golf cart batteries ok to be used indoors? if i have to roll this thing inside i'm not gonna kill myself am i? Sure, just open a window when you're charging hard. Install the batteries close to where they can be vented. I use standard battery box covers in the cargo trailer [where we sleep] and have flex tubes to the wheel wells under the bunks. They sometimes set off the propane detector and we just allow more ventilation. Not much of an issue for a couple batteries.... |