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W5OT

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Battery backup with solar
« on: April 16, 2020, 09:25:57 AM »

Not sure if this is the right forum, please move if it's not.

I'm thinking of adding a battery backup for my ham shack.  I'm thinking of using a West Mountain Radio Epic PWRgate.  That way I can use my regular power supply on commercial power......it will charge my backup battery (when the power supply is on).  When the supply is off, I'll have solar for battery charging.

So....for emergency communication when commercial power is not available.  How much wattage for solar would I need to keep the batteries charged if my current draw is about 2 amps during recieve only??  I usually leave the radio on 24/7 when I'm home.  So a continuous 2 amp draw during day and night is what i'm looking for without depleting my battery. (i realize that battery capacity is a factor here....give me an idea what i'm looking at here.)  Transmit with a 100 watt xcvr would be intermittent and only when necessary.

Also, can you run solar panels in series/parallel configurations like batteries??  IE....two 12 v batteries in parallel gets you twice the amps at 12 volts for twice the power capability where as two 12 volt batteries in series gets you twice the volts AND amps for 24 volts at twice the amps for 4 times the power?? (the Epic PWRgate has a max solar input V of 30 volts.)

Thanks for any advice.
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KD0REQ

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Re: Battery backup with solar
« Reply #1 on: April 16, 2020, 10:33:03 AM »

two batteries in series gives you twice the voltage and the same current as one battery. you only get one advantage in a row.  not to mention, double the voltage, 0 radio, twice the smoke as a normal failure.

if your quiescent current draw is 2 amps, to maintain charge, you need at least that much plus trickle charging current from the solar array. at the terminal of the PWRgate. now, if you were looking to maximize transmit time, you'd install more panels and waste the extra energy possible.
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W5OT

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Re: Battery backup with solar
« Reply #2 on: April 16, 2020, 10:59:04 AM »

You're right.  It's been a long times since my power class in electronics.  Two batteries in series only increases voltage, not amps.  Sorry.  I was thinking two 6V batteries in series to increase both voltage and amps.  But, since amp capacity only increases in parallel, I might as well go with 12V batteries.

« Last Edit: April 16, 2020, 11:01:20 AM by W5OT »
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AD0AR

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Re: Battery backup with solar
« Reply #3 on: April 16, 2020, 11:29:41 AM »

I use 6 12v AGM 95Ah batteries in parallel from Wal Mart.  I did find that I would lose transmit power as the batteries discharged.  Many people find this with their go boxes with lead acid batteries too. 
  You can effectively only use about half of their capacity as the voltage drops too much to be useful. 
  Well I found this nifty boost regulator online called the Fluxcap boost regulator.  It can compensate for the battery drop and boosts even a low battery to 14.7v when it is turned on. 
  MFJ and another company make small ones that are overly complicated and have a questionable track record.  This company has been making these boost regulators for almost 20 years and their base model is rated for 50 amps continuous power which is much better than the competition. 
https://www.hlabs.com/products/fluxpower/index_files/MobileApplicationofFluxCap.htm

I use a 100 amp version in my QTH emergency power setup.  It is fantastic with solar power too as the radio always gets 14.7vdc even with intermittent clouds across the solar panels as long as there is some power in the batteries.  It's RFI quiet on all ham bands too.  I dig it, it's simple and effective, and can even power those 12v solid state amps like the ALS-500, SGC SG-500, etc... to full power and then some... Awesome product!
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K5LXP

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Re: Battery backup with solar
« Reply #4 on: April 16, 2020, 11:57:33 AM »

Your load seems consistent and predictable, so that's easy to calculate.  The standard battery capacity to consider is enough for 3 cloudy days plus margin for near end of life capacity reduction.  The bigger variable to determine is what the panel output will be.

No one here can guess your panel requirement because insolation and panel specifics are different for everyone.  I suggest to visit the NREL site and get an estimate of net panel output based on your specific location and installation parameters.  From there you can decide what size panels to start off with. 

https://pvwatts.nrel.gov/

Mark K5LXP
Albuquerque, NM
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W1MOW

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Re: Battery backup with solar
« Reply #5 on: April 17, 2020, 08:03:24 AM »

Found this line when reviewing their specs:

Battery charge suspend button to eliminate current draw or charger noise for 30 minutes. Possible RFI may be emitted from MPPT charge controller.

I would think twice and ask more questions!

Gary P.E. W1MOW
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The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt - Bertram Russell (1935)

So not much has changed in almost 90 years!

KB8VUL

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Re: Battery backup with solar
« Reply #6 on: April 18, 2020, 06:31:35 AM »

Tried posting this once and it disappeared.. Gonna try again

As far as building battery plants and utilizing them. 
Solar is great, when there is sun light.  When there is no light it makes it rough.
My advice would be running a 12 volt system since that is what you will be using primarily.  Running other voltages like 24 or 48 would require a regulator that is only going to have a limited current carrying ability. 
I would advise you to have both solar, wind and a grid power charger maintainer connected.  Yes, it's not truly off grid, but unless you have some specific need to 100% of grid (like there is NO utility)  it sounds like you want a system for emergency use. 

Couple thing to keep in mind with a battery plant.
Batteries need to match.  They need to match in age, type and labeled capacity.
Proper wire size and fusing is a must.  A 30 amp Astron will crow bar if you short it.  A battery will just keep pushing current into the short.  ANd cause a fire.
Ventilation and physical protection is important.  Batteries off gas as they charge.  That gas can go boom.  Also, hacing batteries with their posts sticking up exposed for metalic stuff to fall on is a bad idea.  Cover them with a sheet of plexi-glass or thin plywood.  But do NOT put them in a non-vented box.
Consider an inverter that can be used to run some 110 volt load.  And keep the 12 volt leads short.  It's easier to run 110 volts across the room at 10 amps (extension cord) than it is to run 150 amps at 12 volts (0 gauge copper wire) and extension cords are vastly cheaper.
Remember that you will need to figure out your charging system to run all the loads and maintain the batteries as well.  But consider the fact that you are running IACS and not full draw 100% of the time.  Meaning that your HF radio will only draw 20 amps when you are talking on it.  When you are receiving, it's drawing considerable less power.  If you build for maintaining the batteries when receiving  and allowing them to take up the slack when you are talking the system will do fine for you.  And you will realize that you don't need as big a system.
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K6AER

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Re: Battery backup with solar
« Reply #7 on: June 30, 2020, 02:11:10 PM »

Your going about this from the wrong direction. Set you battery bank for 24 VDC. Regulate down to 14 VDC. The converter regulator will be about 90% efficiency.
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N8AUC

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Re: Battery backup with solar
« Reply #8 on: June 30, 2020, 07:26:58 PM »

First, how much power do you intend to transmit with? That is the starting point for everything.

What I do is this:

To run for 24 hours, estimate 1 amp hour of battery capacity for each watt of transmitter power.
So a 100 watt transmitter will need 100 amp hours of usable battery capacity. How much battery
you need to buy depends on what battery chemistry you choose, and how much capacity you
need. If you use lead-acid (like flooded cells, AGM, or Gel Cells), you need to consider the
maximum depth of discharge is only 50%. So a 100 amp hour lead acid battery will have about
50 amp hours of usable capacity. If you choose Lithium Iron Phosphate (LiFePO4), the maximum
depth of discharge is about 80%, so a 100 amp hour LiFePO4 battery will have about 80 amp
hours of usable capacity. Note that if you exceed the maximum depth of discharge for your
chosen battery chemistry, you will probably shorten the number of charge/discharge cycles
in the life of the battery (cycle life). If you discharge too far beyond the maximum depth of
discharge, your batteries may not recharge at all.

If you combine batteries to get more capacity, your batteries need to match in terms of
chemistry, age, and capacity. Also, do not use automotive starting batteries for applications
requiring constant load current. Only use batteries rated for deep cycle applications. This
will prevent the need for premature battery replacement.

Then to charge the battery using solar, I figure 1 watt of solar per amp hour of battery capacity
in order to fully recharge the battery during one day of sunlight. So 100 watts of solar should be
enough to charge up a 100 amp hour battery in one day.

If you go light on the solar capacity, it will not only restrict your operating time, but it will take
more than one day of sunlight to fully recharge your battery.

I'd avoid doing voltage conversion. Every time you do a voltage conversion, you will lose some
power in the conversion, as no conversion process is 100% efficient. If you want to run 12 volt
DC loads, stick with a 12 volt system.

Another point to keep in mind, is to make sure the charge controller you choose is compatible
with the battery chemistry you choose. Different battery chemistries have different charging
profiles.

Also note that not all solar panels are created equal. There are several different types, and they
perform differently. If you want the most efficient panels, choose a monocrystalline panel. But
they don't generate power in less than optimum solar exposure. A polycrystalline panel is less
expensive than monocrystalline, but they tend to be temperature sensitive. Their power output
decreases as the panel temperature increases, and they are a bit less efficient than monocrystalline
panels. Thin film, or amorphous panels are less than half as efficient as the previous two types.
But they are not temperature sensitive, and they will generate power in lower light conditions
than any of the other types. They are also less expensive. But you need almost twice the panel
surface area to generate the same amount of power as monocrystalline panels.

My portable power setup consists of 100 watts of amorphous solar panel, and a 10 amp PWM
charge controller which is not the best but mine is RF quiet, and it was inexpensive. That feeds
into my homebrew portable battery box which contains 42 amp hours of deep cycle AGM batteries.
The battery box weighs about 30 pounds, and is built into a small plastic tool box from Home
Depot. I used this setup again for Field Day last weekend. During the day, the solar panels
were constantly recharging my batteries as I used them. At night, the solar goes to zero, and
the batteries were enough to carry me through the night. When the sun came out the next
morning, the solar panels again started recharging my batteries as I used them. By the end
of Field Day, my batteries were just about fully recharged. When I operate Field Day, I use
CW at 20 watts RF output. My FT-857D pulls about 4 amps of current during transmit at
those settings. What I have done basically, is tailor my transmitter settings to match my
available electrical power. For a deep cycle AGM battery, your maximum load current should
not exceed C/10, where C is the amp hour rating of the battery. If you exceed this you will
see increasing voltage drop under load (due to the internal resistance of the battery), and
you will hasten the discharge of the battery.

When my AGM batteries reach their end of life, I intend to replace them with LiFePO4 batteries
for the reduced weight, increased cycle life, and greater allowable depth of discharge. LiFePO4
batteries also have a lower internal resistance than AGM, so I'll see less voltage drop with
increasing load current. This will enable me to run higher amounts of transmitter output power.
When I do that, I'll also have to replace my charge controller, because the one I have isn't
compatible with LiFePO4 batteries.

Of course your mileage may vary, but that is what I do. Hope this helps a bit in deciding
what you are going to do. I really enjoy using my portable power setup, and I hope you
enjoy whatever you choose.

73 de N8AUC
Eric
« Last Edit: June 30, 2020, 07:42:58 PM by N8AUC »
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K5LXP

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Re: Battery backup with solar
« Reply #9 on: July 01, 2020, 07:01:02 PM »

Good info in general but some details in question:

If you use lead-acid (like flooded cells, AGM, or Gel Cells), you need to consider the
maximum depth of discharge is only 50%.

So why are batteries spec'd by the manufacturer to 80% DOD?  Doesn't total Ah delivered over service life enter into the equation?

Quote
Then to charge the battery using solar, I figure 1 watt of solar per amp hour of battery capacity in order to fully recharge the battery during one day of sunlight. So 100 watts of solar should be enough to charge up a 100 amp hour battery in one day.

Optimistically that would only be about 50% of the watt hours required even at 100% panel output.  The sun isn't maximum for 12 hours a day.  (100Ah @ 12V = 1200Wh / 100W = 12 hours)  Even in sunny NM I can only count on about 70% peak panel output during the summer.  You also have to account for the time spent at absorption to complete the charge which won't be contributing much towards Ah.  That 1W/1Ah rule of thumb would be more like three or four days depending on location and season.

Quote
I'd avoid doing voltage conversion. Every time you do a voltage conversion, you will lose some power in the conversion,

True.  But what about devices like transceivers that aren't spec'd for, or operate erratically at voltages below about 11.75V?  You either have to add battery capacity or use some form of booster or converter.  Most are >90% efficient and if that conversion allows access to all the battery capacity the efficiency loss is offset by the net increase in available Ah and operating time.

Mark K5LXP
Albuquerque, NM
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N8AUC

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Re: Battery backup with solar
« Reply #10 on: July 02, 2020, 04:35:48 PM »

So why are batteries spec'd by the manufacturer to 80% DOD?  Doesn't total Ah delivered over service life enter into the equation?

Mark K5LXP
Albuquerque, NM

Good question, and I don't know the precise answer. I chalk it up to marketing.

But if you follow the money...long cycle life for you, isn't really what the manufacturer
wants, but they'll never say that. What they want, from a cash flow perspective, is for
you to buy batteries more often. They're in business to sell batteries, not to have yours
last a long time. Success in business is all about revenue and margin, and that requires
sales volume. One other thing...never trust or believe a battery sales person. Very few
of them have any clue what they're selling, or how it works. But they all know how to
cheerfully ring up a sale.

As for total Ah over service life, I've never seen that on a battery spec sheet. If you have,
I'd like to know where to find it, because that would be interesting to know. As you have
mentioned before, it is totally reasonable for the battery capacity to degrade as the battery
ages.

With my portable setup, I don't think I've ever seen this charge controller go into bulk
charge mode. The charge controller was in definitely in absorption mode when the direct
sun first hit the panels in the morning.  This is based on the output voltage coming
from the charge controller, and the amount of charging current the battery box was showing
on its bidirectional ammeter. By 1PM, the controller was in float mode, with it's output voltage
throttled back to about 13.8 volts, and the charging current a little below 1 amp. We kept
operating until 2PM local time, which is 1800Z. Once I got everything taken down and put
away, it took another hour of float charge in the house for the charging current to reach
zero, indicating a full charge on the batteries.

Also note, I'm using cheap rigid amorphous panels. Those don't need maximum solar
intensity to generate enough power to charge a battery, although like everything else,
more is usually better. Having used this setup for the last 3 Field Days, I've seen enough
output from these panels to charge batteries until about 45 minutes before local sunset.
I do make it a point to reposition my panels several times during the day to better face
the sun. By evening, they're pointing almost due west. Total daylight in northern Ohio
at the summer solstice is about 14 1/2 hours. Field Day around here usually sees sunrise
about 0630, and sunset around 2100 local time. The downside, is that the panel surface
area I need to generate 100 watts of solar is about double what I'd need if I had the
more efficient (and expensive) monocrystalline panels. A good 100 watt monocrystalline
panel from someone like Renogy is about half the size, and half the weight of my setup.
If the sky is cloudy, I still get enough output from the amorphous panels to charge the
battery, but not as much as if it's sunny. If the overcast is heavy, things get kind of tough,
although it will still float charge. A better MPPT charge controller would help too, because
my PWM controller is only about 75% efficient at best.

It's loads of fun to watch the whole setup work like it does. I get a big kick out of it.
I'm a bit excited to do the planned upgrades to my system though. But that has to wait
for available cash flow. Because I flat out refuse to incur indebtedness to pay for my toys.

73 de N8AUC
Eric
« Last Edit: July 02, 2020, 04:38:43 PM by N8AUC »
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K5LXP

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Re: Battery backup with solar
« Reply #11 on: July 03, 2020, 08:25:02 PM »

I chalk it up to marketing.

No, actually there's a technical basis for it.  The problem is that few understand that basis and simply propagate the idea then embellish it a bit with the dire consequence of "killing" the battery.  For any one and probably several reasons batteries will crap out and most will point to "50%" but in reality deep cycling is the least of the reasons.  Batteries are made to deep cycle.  But they're not made to be left half dead for months at a time, under charged, over charged, left to dry out and the myriad of subtle but cumulative damage they suffer that ultimately takes them out.

There is a slight bump in energy delivery efficiency somewhere between 40 and 60% DOD depending on the battery and load profile.  For folks living off grid with large expensive banks of batteries this slight gain can make a difference over years and thousands of cycles.  Hams, and most other users of deep cycle batteries (boats, RV's) don't have the controlled conditions of an off-grid solar system.  Frequency and depth of cycling is all over the map so trying to eek out some incremental (<10%) gain in efficiency by imposing an arbitrary discharge threshold is rearranging deck chairs on the titanic.  All you will do is inconvenience yourself by not running your stuff and do little to improve the service live of your batteries.

"Service life" - important distinction from "cycle life" which is what's on the data sheets.  Cycles don't run your stuff, amp hours do.  If you apply the Ah delivered over the depth of discharge times the number of cycles at that depth you get a hard number of energy delivered by the battery.  You don't see "service life" specified because there are too many unknown variables for manufacturers to provide a hard number but a good approximation can be gleaned by using the Ah rating of the battery at a given rate and the specified cycle life. 

Even at 80% DOD most deep cycle batteries can deliver hundreds of cycles.  If you work this out to one cycle per weekend (which would be a lot for ham radio) the battery would expire from age before you wore it out from deep cycling.  Even if you cycled it this deeply every single day (which isn't easy to do) it would take a couple of years to wear it out.  The thing a lot of folks don't see is that they anguish over "preserving" their batteries but all this usually accomplishes is they never get all the delivered Ah out of the battery it is capable of and end up junking it when it expires from age or cumulative damage with cycles left on the table.  The *most* cost effective battery is one you use up before it expires.  So in my view if you're not running your batteries hard and using them up, you're spending a lot more on batteries than you have to.

I agree, it's way cool to be up in the mountains or wherever and know that the stuff you're running is being powered by the sun.  I've been playing the portable/solar game a long time and it's nice when everything works to plan.  This year at Field Day I got a reality check when halfway through the afternoon it clouded up and my charge rate went way into deficit mode.  I didn't operate overnight though so it picked up the next morning where it left off.  But it does underscore that all the panel capacity you think is enough is scuttled with the first cloud that goes by.  Fun stuff though, solar and battery storage can be a interesting and challenging engineering exercise.

Mark K5LXP
Albuquerque, NM

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WA8NVW

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Re: Battery backup with solar
« Reply #12 on: July 04, 2020, 07:40:15 PM »

One adjustment when you are calculating reserve capacity for sunless days:  3 days will work in the Southwest, but if the site is between Portland OR and Seattle WA, or Cleveland OH to Buffalo NY you need to allow for 30 continuouis days of no sun to keep the cell voltage high enough that they can take a charge back to full capacity. BT,DT,GTTS.
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KD8SKM

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Re: Battery backup with solar
« Reply #13 on: August 30, 2020, 06:42:48 AM »

Greetings fellow HAM's

Lots of good information in the above posts - wanted to share my experience with Solar and LFP (Lithoum Iron Phosphate) batteries.

The chemistry has been around about 10 years now and was originally developed by A123 Sysyems which later went bankrupt and was bought by a Chinese company which I believe I have found since the mention "nano-phosphate".  Not all LFP batteries are created equal however their spec sheet states more than 2000 cycles at 100% depth of discharge and greater than 80% capacity remaining.  I will post a snapshot of the spec sheet below as I am sure some will not believe me....

I can tell you I have 8 years of history with this chemistry and the batteries are fantastic.  my 7.5 year old cabin pack is still slightly ABOVE its rated capacity and has been cycled thousands of times though not all are full cycles.  this would be a typical use case for an off grid system.  I expect these batteries will go more than 10 years as I have only lost 8 amp hours on a 600 amp hour pack in 7.5 years!  measured 607 recently.

We have been making and selling Solar Charge Controllers now for over 5 years - we went into business doing this because there are a lot of sub par products out there and a truly high performance, low RFI controller did not exist for a reasonable price.  see: https:// www.diysolarforu.com

All products are on sale 20% off thru September 15th, 2020.  Lots of HAM's world wide use our controllers with excellent results.

Remember too that a PWM controller is cheap and wastes a lot of power - see our competitive performance table on our main page.
if you want to use Deep Cycle / AGM / Lead Acid batteries with our products you can just keep in mind these have limitations in performance and as stated should not be discharged below 50% if you want long life.... in an emergency however this is ok to do.

As for Solar and Clouds - this is where an MPPT controller such as ours really shines... can be as high as 216% more power with MPPT as we have measured over a PWM controller in cloudy conditions.

Just wanted to chime in about these few important issues - stay safe everyone as we all get through COVID-19 HELL.

Cheers,

Rob
KD8SKM
DIY Solar for U
https://www.diysolarforu.com

From the LFP Battery spec sheet - note the cycle life rating and depth of discharge:
2.1
Nominal Capacity
20Ah
25±5℃,1C discharge 2.2
Internal Impedance
≤10mΩ
2.3
Nominal Voltage
3.2V
2.4
Weight
520±20g
2.5
Max
charge Voltage 3.65V
A
t CC mode
2.6
End
of charge Current 0.05C
At C
V mode
2.7
Cut
off discharge Voltage 2.00V
2.8
Standard Charge Method
1C CC/CV
25±5℃ 2.9
Max pulse Discharge Current
5C
Discharge Time: 10 seconds
2.10
Recommended discharge current
≤20A
2.11
Max continuous discharge current ≤60A
2.12
Cycle Life
2000cycles
At room temperature 25
℃℃; 1C
Continuous Discharge and 1C
continuous charge current;
≥80% SOC
(100% DOD)
25±5℃


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