How many times could a 66ah Battery Charge a Smartphone?

RoofTopPigeon · February 2016

How many times could a 66ah Battery Charge a Smartphone; before it would need recharged... However for this project I will be using a 15-watt solar panel with a built-in 12 volt charge Controller if that helps. When the Solar Panel is not connected how many times could a 66ah battery charge the average smart-phone off of a standard car charger before needing charged again? I am doing this project for a way to charge my phone during power outages

westbranch · February 2016

to start off there is only 1/2 of the capacity available if you want the battery to have a reasonable life expectancy.. so 33 ah.
then the sun has a reasonable amount of 4 -5 hrs of good charging per day, on a yearly average so 5 x 33 = 165 Ah....

So now you need to tell us the power consumption of the battery charge on an hourly or instantaneous amount ie A or Ahr..

RoofTopPigeon · February 2016

I will be using this to charge my phone off of; I am not sure how much they pull at a time. How many charges of a smartphone can you get from 66ah (or) 33ah like you mention? this is going to be a simple one battery system of course

http://www.bestbuy.com/site/tough-tested-pro-car-charger-for-mini-usb-devices/1306405513.p?id=mp1306405513&skuId=1306405513

BB. · February 2016

Some quick guesses/estimates:

Samsung S5 cell phone battery 2,800 mAmp*Hours
Call it 8 hours of life under moderately heavy use.

Watt*Hours. Should be batt voltage * AH rating. (3.85 volt cell*2.8 AH= 10.78 WH capacity per 100% use)
66 AH * 12 volts * 0.50 max Lead Acid discharge * 0.85 batt charger eff * 1/10.78 WH = 31 full charging cycles

Guess/rough estimate.

The maximum rate of charge for a Samsung S5 phone is ~1.75 amps @ 5.0 volts. With minimum charger and USB cable, have seen charging current below 0.3 amps (and a warning on phone about slow charging).

1.75 amps * 5 volts = 8.75 Watts

So, you can charge 1-2 phones with a 15 watt panel in full noon time sun. If you have the proper panel => cell phone charge controller setup.

If you do the "long way" around (panel->charger->lead acid battery->12 volt - usb charger -> cell phone), the entire energy per day from a 15 watt panel would look like (worst case numbers--charge lead acid during day, charge cell phone at night):

15 watts * 0.61 typical DC system eff * 0.85 usb charger eff * 4.0 hours of sun (relatively sunny area ~9 months of the year minimum) = 31.11 Watt*Hours per minimum 4 hours of sun per day
31.11 WH per 4 hour day / 10.78 WH per full charge = 2.9 full charge cycles per average spring/fall day

Recommend ~5% to 13% rate of charge for a lead acid battery. 5% for seasonal/weekend use. 10%+ for daily off grid use:

33 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 31 Watt panel minimum
33 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 62 Watt panel nominal
33 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 81 Watt panel "cost effective" maximum

-Bill

RoofTopPigeon · February 2016

WestBranch and BB; if it helps;

I will be using this panel with a built-in controller: Battery Tender 15 watt solar panel; along with a Optima Bluetop 66ah Deep cycle marine battery and a car charger. I was Trying NOT to mention brand names I don't know how strict this forum is about that because I just Joined tonight.

I will be using this to charge my phone off of; I am not sure how much they pull at a time. How many charges of a smartphone can you get from 66ah (or) 33ah like you mention? this is going to be a simple one battery system of course

http://www.bestbuy.com/site/tough-tested-pro-car-charger-for-mini-usb-devices/1306405513.p?id=mp1306405513&skuId=1306405513

BB. · February 2016

Asking about specific brands/models is fine here... Of course, we have a bunch of people that try to spam the forum--And most of the time I can tell when somebody is trying to game the forum.

My guess (using my cell phone as an example) would give you approximately 31 full charges from a 66 AH 12 volt battery (discharged to 50%).

And a 15 Watt panel will give you ~2.9 charges per day @ 4 hours of sun:

http://solarelectricityhandbook.com/solar-irradiance.html

Flint
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 47° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.86	3.53	4.20	4.61	4.86	5.15
Jul	Aug	Sep	Oct	Nov	Dec
5.31	4.89	4.61	3.68	2.59	2.53

The above list is average daily sun by month (long term average).

Depending on the phone (size, usage, etc.)--Your numbers will vary. Some links for you to read (with these tools, you can answer the questions for your exact phone/hardware setup).

USB Volt/Current meters:

Multifucntion DC/AC Clamp DMM (digital multi meter):

http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

The math for converting from mAH to Watt*Hours:

xyz mAH * charging voltage * 1/1,000 mAH per AH = Watt*Hours
1,000 mAH * 5.00 volts * 1/1,000 = 5 Watt*Hours

A nice (not cheap) Hydrometer (for flooded cell batteries--Not useful for Sealed/AGM/GEL type batteries)

http://www.solar-electric.com/midnite-solar-battery-hydrometer.html

Some nice USB chargers:

http://www.amazon.com/Car-Charger-PowerIQ-Technology-Motorola/dp/B00SSMRB9A (4 port @ 12 volt battery)
http://www.amazon.com/Charger-Aukey-charger-Smallest-Powerful/dp/B015WIGKY4/ref=sr_1_1?s=wireless&ie=UTF8&qid=1455170768&sr=1-1&keywords=anker+usb+12+volt+2+port (2 port @ 12 volt -- Good to 24 volts--May be able to connect directly to your 15 watt panel without the 66 AH 12 volt battery)

-Bill

RoofTopPigeon · February 2016

I'm going to assume the high mah that your cell phone battery is the less charges you will get. am I correct here? That you will NOT get as many charges for a 3900mah phone as you would for a phone with a 1900 mah battery? JUST for referance BB can I ask the Mah of your phone battery?

BB. · February 2016

My phone is a 2,800 mAH (or 2.8 AH) @ 3.85 volts.

Yes, the mAH (or AH) capacity of the battery is like the gallons of your gas tank. The larger the number, the more storage.

So, while a larger battery will last longer on your phone (some phones have standard and extra capacity batteries available)--The fewer number of charges from your 12 volt battery you will get.

But, as you can see, a cell phone is a surprisingly power efficient device. And, for example, my cell phone would charge ~31x (from near dead phone battery to full). Note that most people do not discharge there phone to dead--But to 50% or 30% of capacity before recharging (and charging when handy--perhaps at 90% of battery capacity, or only refilling the 10% needed to bring to 100% charge).

There are lots of variables--And getting a USB volt/amp (or volt/amp/aAH) meter will give you a lot more accurate information.

And, a USB Volt/Amp meter is very handy... You will be surprised that some chargers do not give full charging current (a smart phone will charge at 1.5 amps or more, older/smaller phones may charge at less than 1.0 amps). Also, some USB cables do not carry full current, or your USB cable/connector goes bad (USB cables+connectors are not, in general, very rugged--A meter to test your cable/charging source is really nice--I have had both USB chargers and USB cables fail--And I thought it was the USB tablet that was going bad until I got the USB meter).

Solar power systems--A great excuse to get more tools.

-Bill

RoofTopPigeon · February 2016

BB. said:

My phone is a 2,800 mAH (or 2.8 AH) @ 3.85 volts.

For example, my cell phone would charge ~31x (from near dead phone battery to full). Note that most people do not discharge there phone to dead--But to 50% or 30% of capacity before recharging.

-Bill

Thanks so much for all the help; you have been very helpful. I try not to let my phone get below 40% anyway;

as I've been doing some research and it seems the Lithium-Ion batteries in phones these days prefer to go up to 80% then down to 40% an back up to 80% again.

As they are a whole different beast from lead-acid batteries....

Since all phones are different Bill and you said you would get about 31 charges with your phone;

"I will cut my losses" and assume 25 charges for most phones and taking cloudier days into account to be safe.

would this be a good way of thinking?

And again thank you so much. By the way my name is Frank.

BB. · February 2016

It depends on what you want to do... Earlier I suggested that you want a 5% to 13% rate of charge for the lead acid battery... So, technically, at a minimum you would want to either put 30 Watts of solar panels on a 66 AH @ 12 volt battery or drop back to a 33 AH (or smaller) battery for at least 5% rate of charge.

Also, what is it that you want to do? Charge a bunch of different phones in one day, or have some emergency power for a couple phones that would last for days/weeks at a time?

The 15 Watt panel on a nominally sunny day would only charge your phone 0-100% ~3 times a day. Or say 30% to 80% (50% of capacity) almost 5-6 times (using my phone numbers).

We try for a balanced system... I.e., maybe 2 days of stored energy and 50% maximum discharge. Your present system has an "excess" of storage and/or a "deficit" of solar panels. I.e., you can charge 30 phones in one day, but it would take 5-10+ days for the single 15 Watt solar panel to recharge the lead acid battery bank back to full.

And to consider in emergency situations--Many times cell towers may only have hours (or no) battery backup--So having enough power to recharge 2-3 phones 10 days without sun may not be that useful (charged phones, no cell service--Or power is restored in a couple days). For example:

33 AH of lead acid battery discharge * 1/0.830 Amps (Battery Tender 15 watt panel) * 1.20 "charge eff" * 1/4.0 hours of sun = 12 days to "recharge" after charging all of those phones

Using the USB Volt/Amp/mAH meter to measure your actual charging usage will help you better size the system to your needs.

If you need to charge "30 phones" per day--You need more solar panel power.

If you need to charge ~3-6 phones per day--Then you have a much larger Lead Acid battery than you need (larger lead acid batteries need 5% minimum rate of charge).

If you are looking for emergency backup power--Standard flooded cell Lead Acid Batteries are not really ideal--They do not last very long in "float service".

Once you have your loads better defined--Then we can help better define a system for you. Or, if your 66 AH battery is relatively "cheap"--Just plan on getting a new battery every ~2 years (small UPS systems for computers replace batteries after 1-2 years anyway). And probably get a second 15 Watt panel so you have the power, when needed, to keep stuff working through the emergency.

-Bill

RoofTopPigeon · February 2016

The 15 watt panel and 3 Times a day is fine this is an occasional use system for power outages so between outages I'm sure it'll have plenty charging time. And even though there are. 3 Of us in the house it's highly unlikely all our phones will need charging at the same time. I could always go the route of having more then one battery and switching out while the other rest and charges I have a spare panel I can put the low battery on I will be using an AGM batt. As I am in a cold climate if I watch voltage levels it should last me 10 years or so

BB. · February 2016

AGM batteries are more sensitive to over charging. Make sure your absorb and float voltages are set correctly.

Not sure you will see 10 years--But a good AGM may last you 5-7 years.

Have fun Frank!
-Bill

RoofTopPigeon · February 2016

Bill the 15 watt battery tender panel I am using has a built in charge controller and its float voltage is 13.4 To 13.8 so I think I'm good there I will also have a volt meter mounted on the battery so I can watch that at all times. That way I'll know if the controller ever gives out. I picked up a volt meter from tender that I can permately attach with a ring harness. So I'm good. Thanks again Bill

zoneblue · February 2016

Me i would get these, And call it good.

http://www.ebay.com/itm/Foldable-5V-14W-Solar-Sunpower-Panel-Charger-for-Mobile-Phones-Tablet-Samsung-S5-/231330975024

http://www.dx.com/p/xiaomi-genuine-16000mah-dual-usb-mobile-li-ion-power-bank-w-4-led-indicators-silver-white-363631

But as bill said defining your loads is 90% of the battle in this business.

RoofTopPigeon · February 2016

zoneblue said:

Me i would get these, And call it good.

http://www.ebay.com/itm/Foldable-5V-14W-Solar-Sunpower-Panel-Charger-for-Mobile-Phones-Tablet-Samsung-S5-/231330975024

http://www.dx.com/p/xiaomi-genuine-16000mah-dual-usb-mobile-li-ion-power-bank-w-4-led-indicators-silver-white-363631

But as bill said defining your loads is 90% of the battle in this business.

Maybe so zoneblue; but not Near as much fun as putting it together yourself.

zoneblue · February 2016

Well.... if thats what were talking about... then how about a pair of GC2s, 3 x 100W panels and a midnite brat? Youll definately have some fun with that, and learn a thing or two.

RoofTopPigeon · June 2016

I have a sunny balcony; at my apartment.

and I want to be able to charge my cell phone

in power outages.

The Solar Panel is made by Battery tender and has a built-in charge controller;

so that it won't over charge. Except: for the actual phone charger

(and) the battery all other products are made by Del-tran Battery Tender.

My Question:

At 75 amp hours; how many times can the D31M battery

charge my phone before I have to give it a break and let it charge some more

Cell phone battery is: 2460-mah if it helps!!!

if I don't want; to let the battery go under 50% so it will last me a long time?

RoofTopPigeon · June 2016

BB. said:

My guess (using my cell phone as an example) would give you approximately 31 full charges from a 66 AH 12 volt battery (discharged to 50%).

And a 15 Watt panel will give you ~2.9 charges per day @ 4 hours of sun:
-Bill

I am sorry to bring this up again; but I am a novice Bill; Can you give me a chart of

200 ah = charges per day

100 ah = charges per day.

75 ah = charges per day.

My phone is 2460-mah; if it helps!

From my Research:

a 75 ah battery; will give me about 12 to 15 charges (down to 50%); in a power outage

if my phone is 2460-mah; Am I right here?

Because If i'm not mistaking I think 1-ah is 1,000-mah right?

I just want assurance that my math is correct; being a novice and all.

BB. · June 2016

OK... Here is how it works (these are rough estimates):

2.46 Amp*Hours * 3.85 Cell phone Battery voltage = 9.471 Watt*Hours total capacity for battery

Your phone may limit the operating range for the battery to 20-80% state of charge (60% of rated capacity) for longer battery life (just guessing). So, the actual capacity used would be:

9.471 WH * 0.60 derated capacity = 5.68 Watt*Hours "usable" battery capacity

And you asked several different capacity batteries--I assume are they are all 12 volt lead acid batteries at room temperature. And that you will use 100% to 50% state of charge or ~50% of battery capacity. I will also assume there is ~80% efficiency to recharge the cell phone battery (big guess):

200 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 169 charging cycles
100 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 84.5 charging cycles
75 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 63 charging cycles

The way to read the above equations in short segments:

200 AH * 12 volts = 2,400 Watt*Hours in your battery bank
2,400 WH * 0.50 = 1,200 Watt*Horus of "usable capacity" (if you deep cycle too deeply, battery life will be drastically reduced)
1,200 Watt*Hours from the battery * 0.80 efficiency for 12 volt converter and cell phone battery charging = 960 WH available for cell battery charging
960 Watt*Hours available / 5.68 WH cell phone cycling capacity = 169 Cell Phone Charging Cycles

You have not asked about how to charge your 12 volt battery--That is not a trivial question either.

-Bill

RoofTopPigeon · June 2016

BB. said:

OK... Here is how it works (these are rough estimates):
200 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 169 charging cycles
100 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 84.5 charging cycles
75 AH * 12 volt Battery * 0.50 capacity * 0.80 charge eff * 1/5.68 Watt*Hours of cell phone capacity = 63 charging cycles
You have not asked about how to charge your 12 volt battery--That is not a trivial question either.

-Bill

My Solar Panel it's self; has a Built-in charge controller to save me some money right there; if you see the tiny box on the bottom of it; I posted a picture of the panel; in an earlier post; that will be keeping the battery topped off. That panel can do a battery up to 200-ah. maximum. Per./ It's owner's manual.

Since most of out power outages don't last more than a week; an 75-ah 12 volt should be enough I suppose; as I said I am a novice in solar!

BB. · June 2016

Flooded Cell deep cycle storage batteries should have a 5% minimum rate of charge:

15 Watts * 0.77 panel+controller deratings * 1/14.5 charging voltage * 1/0.05 rate of charge = 15.8 Amp*Hour @ 12 volt battery maximum

You really cannot use just a 15 Watt panel to "charge" a >16 AH @ 12 volt battery bank. At 1% rate of charge--That would just keep a battery floating:

15 Watts * 0.77 panel+controller deratings * 1/14.5 charging voltage * 1/0.01 rate of charge = 80 Amp*Hour @ 12 volt battery float

Floating a battery is not charging--So, a 15 Watt panel on a ~80 AH batter bank--All of the solar panel is going towards just keeping the battery from self discharging--There would not be any "useful" energy (from the solar panel) available to charge your cell phone(s) unless you use an AC battery charger (mains/genset) to recharge the battery bank after an outage.

-Bill.

RoofTopPigeon · June 2016

I think your on a different page here Bill; I apologize; I am only using one battery NOT a Bank and it is an AGM battery; more specifically an Optima D31M Blue Top. if it helps; it happens to be 75-ah

BB. · June 2016

Frank,

Understand--Still, a 15 Watt panel will be, mostly, just keeping up with the self discharge of the 75 AH battery. Lead Acid Batteries all start with pretty low self discharge, but as the cycle (and age), self discharge current rises.

The battery you are using/looking at is an AGM type... Which typically have very low discharge current--So it is possible that you might have better charging performance with the 15 Watt panel than a similar 75AH flooded cell deep cycle battery.

http://www.optimabatteries.com/en-us/shop/bluetop/bluetop-group-31-dual-purpose-deep-cycle-and-starting/

-Bill

RoofTopPigeon · June 2016

BB. said:

Frank,

The battery you are using/looking at is an AGM type... Which typically have very low discharge current.

http://www.optimabatteries.com/en-us/shop/bluetop/bluetop-group-31-dual-purpose-deep-cycle-and-starting/

-Bill

I figured using it in this fashion; an AGM would be of benefit to me Bill; am I on the right track?

Secondly; Is AGM the best technology for my type of use as of today?

BB. · June 2016

Frank,

My observations...

For an "effective" off grid system... Either you need more/larger solar panels (5% to 10% rate of charge, not 1%) and/or a smaller (AH) battery bank.
AGM are very nice lead acid batteries (clean, no adding water, no spill, support high discharge/surge current into loads, lower self discharge--6 months between charging vs ~1 month for flooded cell lead acid). AGMs are expensive (perhaps ~2x the price of flooded cell), cannot measure specific gravity, do not last as long as equivalent flooded cell batteries (perhaps several years shorter life in application).
If this is an emergency backup system--Look for Telecom "float service batteries" (will last years in float charge, but only 10's to 100's of cycles). If this is a daily use system, then the AGM battery you have is fine.
If you want the "Best Technology" battery--A LiFePO4 (iron based Lithium Ion) battery is probably your best battery. As long or longer life in float service vs AGM. Much ligher weight (vehicle, moving sysetm around), higher surge/charging current support, slower self discharge, no issue with storing between 20% to 80% state of charge (AGM/Lead Acid store >75% State of Charge or they will have early death). Down side is high cost (2x AGM price?), you may need a Battery Management System (electronics to prevent under/over charging, equalization of cell charge).

Note, I am not "complaining" about your choices (perhaps the ratio of small solar panel to large battery bank is a "complaint" about an "unbalanced" design that leaves me wondering about what it is you want to use the system for)--But just making observations about your available choices.

If you want to "learn" about solar and how to manage charging, loads, etc... A flooded cell lead acid battery is very nice (rugged, fairly forgiving) and you can check specific gravity of your cells--Accurate method of estimating state of charge. AGM batteries are sealed--And you can only guess at their state of charge via voltage measurements.

You have not talked about tools... A battery monitor is nice--But not cheap and probably not cost effective for a small system like this one. A hydrometer--But only makes sense for flooded cell systems. And a DC Current Clamp DMM (digital multi meter) for debugging/understanding your system.

Some other tools that may be of use (now or in the future) (just suggested links to read--Not specific hardware/websites):

USB volt/current/power meter (measure your phone's charging current, some have AH/WH capability)
Kill-a-Watt 120 VAC Watt*Hour meter (for measuring you 120 VAC plug-in loads--conservation/AC inverter usage)
DC Amp*Hour/Watt*Hour meter (for smaller DC loads on your system)

-Bill

RoofTopPigeon · June 2016

BB. said:
Frank,

My observations...
If this is an emergency backup system--Look for Telecom "float service batteries" (will last years in float charge, but only 10's to 100's of cycles). If this is a daily use system, then the AGM battery you have is fine.
-Bill

This is for power outages; so at least; I can charge my phone in a power outage; Since we have 3 phones; with similar battery capacity's; I just wanted to make sure the 75 ah in that Optima that I am looking at is enough to charge 3 phones without going under 50%. That is my main concern is 75-ah enough?

This is what I did in an attempt to figure out what half of 75-ah was.

Here is the Math I did:

1-ah is equal to 1,000-mah (I googled that info)

Then proceeded as follows:

so 75-ah is 75,000-mah

75,500 divided in half is 37500

Then I divided that 37500 by 2460-mah (the mah of my phone)

and I finally came up with about

15.24 phone charges; with a 2460-mah phone battery. BEFORE I hit 50 % of the 12-volt 75-ah battery

I know this Math is a little different; But Did I figure this correctly???

I know you said the phone may limit operating range and NOT use the whole mah though Bill !!!

THAT'S WHY YOU; Came up with 63 instead of 15 I believe. RIght???

200 AH * 12 volt Battery * 0.50 capacity = 169 charging cycles100 AH * 12 volt Battery * 0.50 capacity = 84.5 charging cycles75 AH * 12 volt Battery * 0.50 capacity = 63 charging cycles

BB. · June 2016

No Frank, there is a "problem with the math".

Amps is a rate--But it only partially describes how much electricty is being used. You also need to know the voltage too.

Sort like using water to wash a wall... You can take a gallon of water and toss it at the wall.. (1 gallon per minute). Or use a hose (1 gallon per minute, but 50 PSI spray on wall), or a pressure washer with a 5 HP motor (1 gallon per minute with 2,000 PSI--Enough energy to peal paint and even cut concrete/stucco).

Amps is just the "flow" and Volts is the "pressure". So if we take flow * pressure we get "power".

1 amp = a "rate" (just the flow)
1 amp * 2 hour = 2 Amp*Hours (a total flow--But no "pressure" information)
1 amp * 5 volts = 5 Watts (a rate of energy usage or called "power")
1 amp * 5 volts * 2 hours = 10 Watt*Hours (the total energy usage)

For "normal humans", there is a confusion here... We talk about miles, and miles per hour. The "hour" is confusing when we talk about Amps (or Watts) and Amp*Hour & Watt*Hours. Note the the first is "per" hour vs the second which is "times" Hour (hour is in divisor vs on top).

Amps ~ Watts ~ Miles per hour (rate)
Amps*Hours ~ Watt*Hours ~ Miles driven (amount)

When we toss around amps and amp*hours--We are assuming that all the voltage(s) are the same... I.e., you have a 12 volt battery bank and a 1 amp light, 10 Amp Radio, 100 Amp starter. All at 12 volts.

When you have an AC inverter on a DC battery bank... You have 12 volts input and 120 volts output... Now when we talk about 10 amps--We have to ask what voltage (where in the system you are measuring the current or amps)... 10 amps*12volts=120 Watts; vs 10amps*120Volts=1,200 Watts -- Or 10x the amount of power.

When you have different voltages--You are now comparing apples and oranges.

So--Your cell phone battery is 3.85 Volts--Your car battery is 12.0 volts -- or over 3x the voltage. You are correct 1,000 mAH = 1.0 AH... But neglecting the voltage. 1,000 mAH has at 12 volts has ~3x amount of energy vs 1,000 mAH@3.85 volts:

12 volts/3.85 volts = 3.12x (exactly) ~ 3 times (approximately)

There are also conversion losses to worry about... Batteries have losses (lead acid batteries average 80% efficiency, AGM ~ 90% efficiency, AC inverter ~85% eff, chargers ~ 80-90% eff, solar panels are ~81% effective vs marketing numbers), etc... In solar power, it is not unusual to have 50% "losses" (difference between "ideal" and "real life" math).

Even the Amp*Hours of small battery packs are sometimes "lied about" by marketeers--Many will talk about 2x batteries of 1,000 mAH = 2,000 mAH capacity... however the batteries are ~3 volts but connected in series... The two batteries have 1,000 mAh capacity at 6 volts... Not 2,000 mAH at 6 volts. (confusion is a USB battery emergency charger has 2x ~3 volt batteries, but USB is 5 volts--And only 5 volts is available to the end users. A 2,000 mAH @ 3 volts is not what they are selling to the customer --- They are (usually) saying 2,000 mAH with 5 volt output--Which is a lie.

And notice that they are using mAH ratings, not Amp ratings... Who would pay $50 for a 2 AH battery pack--Everyone wants the 2,000 mAH battery pack--Right?

End of Rant.

The "math" matters, and the Amps vs Watts vs Amp*Hour vs Watt*Hours (vs Miles vs Miles per hour) is confusing. Even after 4 years of engineering school and decades of work--I still sometimes made the Amps per Hour and Watts per hour mistake (even on my early posts on this forum). For our purposes--Amps per Hour and Watts per Hour are incorrect/nonsense units.

-Bill "long answer to short question" B.

RoofTopPigeon · June 2016

Remove this post moderators.

RoofTopPigeon · June 2016

RoofTopPigeon said:

If you refer back to my post with the pictures in it;
Since; I DO NOT have an DC to AC inverter in my system and
Just a Car charger; and we're talking DC to DC;
and My system may be a little higher efficiency right Bill?

BB. · June 2016

I know--And that is part of my concern. 15 Watt (18 volt Vmp nominal) solar panel charging a 75 AH @ 12 volt battery is not not enough to do much more than float the 12 volt battery (long term storage). If you actively cycle the 12 volt battery, it will not return to full charge quickly enough--And will have a shorter life.

I could also add that alligator clips are make very poor connections... For you use, a few watts, they are probably OK for connecting to your phone/usb charger. However, I would not recommend them for "permanent" connection to your solar panel--They are too likely to fail (poor connections) and let your battery slowly self discharge and die. Bolted connections (with some sort of anti-corrosive paste) is highly recommended.

If you still want very small solar panel vs battery capacity--Then a LiFePO4 battery would be better.

More or less--Your entire "emergency" cell phone charger load is based on your AGM battery capacity and very little on your solar panel's ability to supply charging current. I guess this is a choice--If you live close to the poles (with little winter sun), or have weeks of bad weather (no sun)--Then large capacity battery bank can be worth while... But, Lead Acid Battery chemistry (including AGM), is not really the best one for long slow discharges--In general, Lead Acid is good for (and designed for) 1-3 days of storage--Then fully recharged. If you really want weeks of "no sun" battery support for cell phones, again the LiFePO4 (or other non-Lead Acid) chemistries are better suited.

I will also add--What happens to the Cell coverage if you have a regional power outage... The cell towers/repeaters may have a 4 hour battery reserve--But beyond that--I have not seen many (any in my cities) that have a genset+fuel supply that can supply even a few days of backup power.

Unless you life in an area (forested, ice storms, etc.) that make your local power unreliable compared to the rest of the region (i.e., cell repeaters still have power while you do not)--A large battery backed cell phone charging system may not make much sense.

Other questions--Do you actively use your cell phone (work, web browsing, wifi hot spot)? That may draw a phone down in 8 hours or less--So three charges a day... If just, mostly, for emergency phone calls, I can set mine to ultra low power (mostly "dumb cell phone" mode) and get upwards of 2 weeks of battery life on a single charge.

DC to DC converters have losses too (a bit more efficient than a typical AC inverter). Something around 80-95% efficient themselves (AC inverters are probably around 80-90% efficient).

In general, the small USB/DC2DC converters/Devices are designed for battery use--And are generally more energy efficient than their 120 VAC counterparts. But it is not a huge difference.

-Bill

RoofTopPigeon · June 2016

for any permanent connection

I use ring terminal's certainly for the solar panel Bill !!!

How many times could a 66ah Battery Charge a Smartphone?

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How many times could a 66ah Battery Charge a Smartphone?

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FlintAverage Solar Insolation figures

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Average Solar Insolation figures