# battery hr. rate

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Solar Expert Posts: 102 ✭✭
Hi guys, can you help me to understand what's an hr. rate on a deep cycle battery? I found a 12vdc AGM battery that is 100ah. with an 8 hr rate to 1.75 vpc @ 77 F and I'm tring to understand the difericence between the 12 vdc 100ah. @ 20 hr rate AGM... which of those two batteries will run longer under same current draw circunstance ?:Dcould you help?....

thanks again

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Re: battery hr. rate

Can you find the capacity chart vs rate for the two batteries in question?

Generally, for solar using our 3 day rule of thumb and 50% maximum depth of discharge--the 20 hour rate (the amount of current that would take a battery from 100% to 0% state of charge) most closely matches our recommendations.

As batteries are discharged faster, they are limited by internal resistance and ability for the chemical reactions to proceed at speed. Typically, this means that a battery with 100AH at the 20 hour rate may only have 80 AH at the 10 hour rate (and maybe 110 AH at a 100 hour rate).

Here is a "Concord AGM" Battery Spec. page (for their Sun Xtender line).

We look at the 100 AH @ 8 Hour Rate (100AH/8H=12.5 amps to discharge flat in 8 hours)... The 20 Hour rate is about 10% more capacity (real numbers 97AH@8HR is rated 108AH@24HR rate).

So--to determine which battery will better perform in your application, you need to figure out the Rate at which you will be both discharging and charging the battery (the discharge and charging rates may be different)...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: battery hr. rate

high draws for shorter time periods will diminish capacity. the 20 hr rate is standard and if that battery were to be made to discharge more in a shorter time period then it will lose some of its capacity. by that i would pick the battery that under a high and short discharge timeperiod still has a 100ah rating as the one at the 20hr rate will be derated under 100ah when at the 8hr rate. this is the peukert effect. http://en.wikipedia.org/wiki/Peukert%27s_law this has been brought up on the forum many times so feel free to search.
• Solar Expert Posts: 102 ✭✭
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Re: battery hr. rate

Hi guys, sorry for my hard head, but Niel said that he will pick the 100ah @ 8hr. rate because the 100ah. 20hr. rate it has be derated when is bring down to the 8hr. rate, it does make sense , on the other hand Mr. BB said that the 100ah. 20hr rate will have 10% more capacity, the current on my inverter is drawing 12.5 amps , it means that the 100ah 8hr. rate will perform better under the same circunstances?

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Re: battery hr. rate

HomerR.,

I was just trying to say that the slower you take energy out of the battery, the more "useful" energy you will get.

Likewise, the faster you charge a battery, the more "losses" there will be in charging it.

Each battery will have its own chart (like the one I linked too)...

In your case, the inverter is drawing 12.5 A, so:

100AH/12.5A = 8 Hour Rate

So, it is not that this is a good or bad battery--it is just that at the rate you are drawing (~8 hour rate), it will have ~100 Amp*Hour of capacity...

If your load was 1/2.5 as much (5 amps), then the battery will draw down at a rate of:

100 AH / 5 A = 20 Hour Rate

So, going and looking at the table/graph/chart, you would see that your "100 AH @ 8 Hour Rate" battery will have a "useful" energy content of "~110 AH @ 20 Hour Rate", so it would really last

110 AH / 5 A = ~22 Hours

Some batteries are designed for heavy loads and deeper discharging (such as a forklift battery) for long life under severe service, and others are not.

But, these improvements do come at a cost... A more expensive, heavier battery (physically larger cells) and, possibly, less efficient to charge and discharge (need more solar panels to make up for battery losses).

If you have a chance, follow Neil's link on the "Peukert effect"... What you will find is the "Peukert" number is an exponent... And its value will help define how well a particular battery will work under heavy loads (for storage batteries, roughly C/20 and lighter currents--20+ hour rate--currents are "light" and C/10 and larger currents are probably "heavy" loads.

So, either you get more batteries so that the average load is less than C/10 or C/20, or you get fewer batteries that can support C/10 or C/1 loads...

Sort of like comparing a car battery to a "D Cell" flashlight battery... At light loads, both will last perform very well... However, under heavy loads, the Car Battery can supply huge amounts of current... The Flashlight battery, not so much.

I am afraid I am confusing you. It is like AA batteries... there are the old carbon zinc, the alkaline, and then NiCAD/NiMH, and Lithium. At low level currents, the all work pretty well. At high level of currents you need the NiCAD/NiMH or Lithium (such as for digital cameras) because the other batteries are very poor at providing high current pulses required to run the camera. AA Alkaline may run a digital camera for 12 pictures, a AA NiHM may run it for 200-400 photos--but both batteries have roughly the same AH rating (at 20+ Hour Rate).

Do you have a data sheet/link to the battery you are looking at? And know

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 334 ✭✭
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Re: battery hr. rate

Let me see if I can simplify this as well, perhaps a combination of details will help illuminate...
First off are you indeed comparing two different batteries with battery A being rated at 100ah at the 8hr rate, and battery B rated 100ah at the 20hr rate? If that were the case it's very simple the one that is rated 100ah at the 8hr rate will have more capacity. The lower the hourly rate, the lower the capacity rating of any battery will be, so if you take battery B and compare it's 8hr rating it would be much lower than it's 20hr rating.
hope that helps.
• Solar Expert Posts: 102 ✭✭
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Re: battery hr. rate

Every day I'm learning something new on this forum and even lots of times gets confusing and a lots of people think that solar power will not pay back, just by keeping our brains thinking, it's the best pay back we can get for our money...

Thanks again to all of you.

H.R.
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: battery hr. rate

hr,
take a look at this chart for sunxtenders as it will show how higher drains on the same battery lower its capacity. take the ah figures in the columns and divide it by the hourly rates listed at the top for the current drawn. amps x hours = amp hours therefore ah/hrs=a
http://www.sunxtender.com/xtender_main.php
• Solar Expert Posts: 246 ✭✭
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Re: battery hr. rate

The way someone explained it to me,
A bit of a mechanical way to think about AH ratings, If you get in your car, fill the tank to the top, Then drive it hard/fast down a never ending straight road, It would run out of fuel after so many mile`s, (20ah)
If you get in the same car, with the same amount of fuel, but drove it gently/economically down the same road, you would do a lot more miles over a longer time (100ah)
same total fuel used (ah)
Big load = driving it fast

Have a good one
Tim
• Solar Expert Posts: 5,436 ✭✭✭✭
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Re: battery hr. rate
The way someone explained it to me,
A bit of a mechanical way to think about AH ratings, If you get in your car, fill the tank to the top, Then drive it hard/fast down a never ending straight road, It would run out of fuel after so many mile`s, (20ah)
If you get in the same car, with the same amount of fuel, but drove it gently/economically down the same road, you would do a lot more miles over a longer time (100ah)
same total fuel used (ah)
Big load = driving it fast

Have a good one
Tim

I think there is something wrong with your thinking on this.
In your former example, driving hard/fast would run any given battery down in X number of miles. Let's say for the sake of this argument the 20 ah battery would go 20 km.

Now if you drive carefully and slower,, (more energy efficiently) the same battery would deliver the same 20ah, but might for the sake of this argument let you travel 30km. The same energy used, but more net work done with it.

Now the difference between a battery 20ah rate at a 1 hour rate, and say a 20ah hour battery rated at a 20 hour rate, is (if I understand it right) is that a battery rated at the 20 hour rate will deliver lower amperage over a longer time. It is also possible that the 20 hour rated battery can't deliver 20 amps for 1 hour but could deliver 1 amp for 20 hours. The 1 hour rated battery might be able to deliver 20 amps for 1 hour, but perhaps not 1 amp for 20 hours. The basic difference between cranking and "deep cycle" batteries.

Tony
• Solar Expert Posts: 102 ✭✭
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Re: battery hr. rate

I'm trying to understand how icarus does to live off grid with only 4-105 trojans , and 200w of P.V. ? , I always wonder how many hrs. he run the generator to keep the battery bank above 12.3 volts?.....and running to how many hrs. after sun down ?

I have 800ah AGM battery bank @ 12v and is only good enough to run from 4:00 p.m. til 11:30pm a 32", 25" and my desk top comuter every sunny winters day, with 1300w of P.V @ no lower than 12.3 or 12.2 v, of course, as long is sunshine I can be on it all day but after 4:00 p.m. my hrs. are number.

I tried conservation but it is almost impossible with a 12 and 13 year old kids at home .

... it will get better , thanks again.;)
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: battery hr. rate

i would think the obvious answer would be he does away with most of all of those things and the time for them. he can confirm or deny it for his case or risk speaking of him in vain.:roll: i suppose the more people there are in a household that it would up the needs of the household too, but everybody conserves differently and it depends on how much one is willing to sacrifice.
• Solar Expert Posts: 5,436 ✭✭✭✭
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Re: battery hr. rate

Feel free to speak for me,,, probably better than I speak for myself!

We live pretty simply. On the other hand it is way more luxurious than it was in years past. There are just two of us, which really helps. The other big thing that helps is no TV. We almost never run a generator at night. I do a fair bit of power management during the day. For example I might kill the water pump after the sun goes down and the tank is full. We do most of our internet and computing during the day. (I am away for a month or so now, so I am on at all hours!)

We use net/net about 4-600 watt hours/day. The lighting is the biggest load by far. The numbers from the Trimetric get skewed somewhat because we draw most of our non- lighting loads at the same time the batteries are charging. The meter only reflects the net in /net out, not the cumulative of what is being drawn at the same time. It also gets a bit tricky to determine full charge because as the batteries get close to full and the charge controller dials down, we tend to run loads (charge lap tops , cordless tools etc) which drops the voltage a bit so that the controller never (seldom) goes to float, and the Trimetric may show 100% but seldom blinks "full". I sort of consider the batteries "full" when the Trimetric shows that we have put in as many ah as we have taken out over any given period.

Power management becomes an obsession both on the charging side and the loading side. As I have said so many times before, when you are building a system the loads WILL increase with time. For example, now that we have lots of power, I put the light bulb (incandescent to boot!) back in the fridge! I leave a 3 watt cfl burning in the mud room by the back door much of the time just because it is easier than turning it on and off.

Every choice is predicated on limited electrical draw. The propane gas stove draws no power. It has standing pilot lights on the top burners and in the oven. ( There are gas ranges that have spark type ignition that don't require pilots,, AND they don't draw much amperage when they spark,, wasn't available when I bought mine) I do kill the oven pilot if we are not going to use it for several days. I also kill the pilot to the water heater except when we are using hot water. The paddle fan on the ceiling is 12vdc so that it doesn't have inverter loses 24/7. We use a auto type stereo run on 12vdc that is way more efficient than a similar 120vac, without the inverter loss and the transformer losses converting the 120vac to 12vdc to run the stereo. Sounds just as good as well. The Ipod plays through it as well, and is charged through it with smaller losses. It is in all reality, a micro-system, but if we pay attention it is just about perfect.

Our biggest change in the last couple of years has been the addition of a 12 month water system. The submersible pump feeds a P-tank and then drains back to keep from freezing. It costs a few ah/day but pretty sweet to have hot and cold (very cold, in the winter the water comes from under the ice at ~33f! Sitting in the P-tank all day might raise it to 40f, great testamony for Paloma PH6 water heaters!) running water year round. In years gone by we would drain our gravity tank ~mid Oct. carry water in buckets out of the lake, until we could pump water again sometime in early May.

The reality, for us is the battery capacity is hardly an issue. The t-105s give us a 3 day reserve before we are at 80% soc. If no sun comes the third day, we fire up the TC-20 for a couple of hours. Our shortage is in panel capacity. (Not really, I am just lobbying to get a couple more,, Susan thinks we have enough).

We also have no electric washing machine or fridge. (If I had to do it over again I would buy a good energy star fridge instead of a Propane fridge however. Now I am stuck. If I want to run my propane on 120vdc it will cost me ~1.3kwh/day) I have done everything to reduce it's propane consumption as well, adding insulation to the outside of the cabinet, and a thermostatically controlled fan on the condenser to get rid of the heat faster. These changes cut the propane by an estimated 1/3, although it is difficult to really tell.

At night we judiciously use CFLs. We have learned over the years to light what we need well, and not light everything else. We have reading lamps at the comfy chairs, good lights in the kitchen and our office/workroom. We also have reading lamps over the bed and at the dining area/living room table. We use no 120vac heat generating appliances. Toaster is stove top, coffee pot is a Coleman MR Coffee that sits on the gas stove (way cool toy!) Coffee goes into thermal carafe with an additional cozy to keep it really hot all day. Our water use is quite small, (no flush toilets helps) Shower only, wood fired hot tub is our biggest luxury.

All in all we are very comfortable, but it is not a lifestyle that would work or most. The house is small, ~520 sq ft. Using a trick I learned from trappers cabins and native shelters, I built the house with low wall heights on the eves. At the back of the house the walls are only 6' tall coming up to a 6/12 pitched room. The front walls are only 7' tall, going up to a 10/12 to a peak that is offset from the center. The result is that teh vaulted ceiling height is high enough to have a paddle fan, plus it adds to the feeling of a large space but with out a lot of volume. Volume is one of the enemies for heating because taller walls mean more area exposed with less insulation than the roof. We didn't go too crazy with insulation however. We are only R-13 in the walls and R-21 in the roof. We do have R-20 under the floor, with a thermal break, 2 layers of foam board, one between the joists and on on top. At -40 cold floors are a pain. I know I am always spouting off about insulating the hell out of buildings, but this is not a normal house. Because it is so small and we heat with wood some heat loss is fine, or we would roast ourselves out most days. We have all our windows on the south side, with a window in the work room on the west side for afternoon light, and one in the bedroom on the east side for morning light. There is a north facing window over the sink, as well as a 1/2 light door on the north side mud room, and a full light glass door on the west side of the living room. The result is we never have to light a light, even on the darkest days until nearly sunset, and we get considerable solar gain. We keep that gain in by using insulated window quilts when it gets bitterly cold. The house has one big open main room that serves as both living room, dining room and kitchen. The woodstove is located near the centre on one wall so that the bulk of it's flue is in the house. Even thought the kitchen is at the back of the house, it gets enough natural light to not need lighting until after dark. Off to one side is a bedroom, off to the other side is our office/workroom/sewing/ junk room. It has a work bench/counter/desk build around three sides. (The fourth side is open to the main room, although it can be curtained off with a heavy wool curtain. (as can the bed room). The solar controls and batteries are in this room, in a sealed vented styrofoam box, sitting on a cart so that I can roll them out to service them. Off to the other side of the main room, behind the bedroom is the mud room with an exterior door. This room serves multiple duty. It is a place to come in and take the snow gear off, with hooks for coats, a tray to drain the boots into etc. Out side is a small covered entry to stomp off, hang skis or snowshoes on the wall etc. The water heater hangs on the wall, and at the far end is a small shower stall. (The water P-tank sits in a linen closet next to the shower).

We spent a bunch of time playing with ideas, and since we had lived in a similar size space before, we thought we could do it more efficiently. As it turns out, it worked out quite nicely. In many ways, it is more like a boat than a house in that there is very little wasted volume (or space). A trick to learn about small spaces is to use the area as many times as you can. For example our bed is a bit higher than most, (Originally to keep it off the cold floor in the old house) but under the bed is filled with drawers that pull out from three sides, and serve as our closets. There is a little "loft" over the mud room, that extends a bit over the bedroom as well, (without interfering with the "feel" on which we store all kinds of stuff we don't need very often. So in effect we are using the space three times. End table become storage lockers, bedside tables as well. Lots of deep shelfs over the desk/work bench.

Enough of this,, it makes me sound like I'm bragging,,, and I guess I am to some extent. We do use the genny for the power tools as needed. The gas is way cheaper than adding 10X the solar/battery capacity.

Tony

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Re: battery hr. rate
icarus wrote: »
(I am away for a month or so now, so I am on at all hours!)

-Bill "I'll bring the marshmallows" B.
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 144 ✭✭
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Re: battery hr. rate

p.s. do not for get the battery cell temperature. If it drops as well the capacity drops.

If you have a idea about the storage temp. in the winter use that to check the battery capacity. any higher temp. means more battery spare AH.

I have seen a nice setup the battery's in a store outside for ventilation and in the winter from the 800 AH 48 V there wash only around 200 AH so the generator wash running three times a day.:grr
• Solar Expert Posts: 5,436 ✭✭✭✭
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Re: battery hr. rate
BB. wrote: »

-Bill "I'll bring the marshmallows" B.

The house is open,, if you remove the farthest left shutter, the key is hanging on a nail behind it! You may have to shovel out a couple of feet of snow to get to the door!

Tony
• Solar Expert Posts: 102 ✭✭
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Re: battery hr. rate

WOW!!!

• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: battery hr. rate

"I leave a 3 watt cfl burning in the mud room by the back door much of the time just because it is easier than turning it on and off."

tony,
it sounds like you're well on your way to being spoiled.;):D wouldn't a cheap low power white led suffice better there if it's to be left on?
i guess you took the long explanation to what i said in that you do without or use it less. an example of how it's done is important if somebody wishes to achieve that kind of power consumption, but what is sacrificed can vary.
as to the frig, you will have to replace it one day and do you intend going to an energy star or another propane? if the answer is an energy star, then that's your reason for acquiring more pvs now in preparation for its energy needs.:cool:
ps maybe you could extend your computer time if you had one of those adapted exorcise machines to generate power. it could be a good re backup for when all else fails too. well anyhow, this is just kicking thoughts around with all of this.
pss that would bother me having to shovel the snow to your doorway for that's thousands of miles of snow between you and me
• Solar Expert Posts: 5,436 ✭✭✭✭
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Re: battery hr. rate

In our earliest 12vdc foray, we used some 12vdc led fixtures for night/entry/bedside lights. We still use a couple because the allow you to get into and out of the room without having to trigger the inverter. Of course they draw almost no power.

I don't expect to replace my any of my fridges anytime soon. We have a 1930's vintage Servel that still works as new, although we have retired it and use it for dry storage in the tool shed. My neighbour has a Dometic that has been burning continuously for 22 years. Gets shut off once a year to clean the burner. When the time comes to replace mine, perhaps we will have dilithium crystal powered fridges!

You don't need to shovel the snow,,, that's what skis/snowshoes/skidoos are for!

Tony