For the past, well, decade really, my mom has worked from home.
And about a year and half ago, she and my dad moved to the country, surrounded by farmland
roughly a two hour’s drive from Chicago.
Her most recent work setup includes a RAP, which essentially creates a dedicated, hardwired
VPN connection over the Internet, so as far as her computer and desk phone know, she’s
still at an office in Chicago.
She occasionally makes trips into the office, but for the most part works here.
Now in the past few months, for some reason the electric service at their house has gotten
a little unpredictable.
They’ve never been without power for more than a day, and usually less than 8 hours,
but in the last month there have been two power outages.
And they’ve happened during her working hours.
Which kinda sucks.
Actually, it really sucks, because depending on the circumstances of the day, she might
have to hop in the car and take a two hour drive to work at the drop of a hat.
So today, I’m gonna fix that for her.
Now before you suggest so, they do have a portable generator.
But the generator lives in a shed, and takes time to set up--plus, it’s cumbersome and
too heavy for my mom to move by herself.
And regardless, their generator produces a really dirty and noisy power output, which
some electronics really don’t like.
Since all of this equipment belongs to her company, she’s real leery on plugging any
of it into the generator.
And I don’t blame her.
We know from experience with the generator and a small uninterruptible power supply that...
well the UPS didn’t find the generator’s output safe enough and wouldn’t pass its
power through.
And it never worked correctly after that.
So what we’re gonna do is use a deep cycle lead acid battery as a temporary power source.
A pure sine wave inverter on the battery will produce a clean output that hopefully won’t
bother her setup.
And to recharge the battery, we’ll simply use an automatic car battery charger, as after
all a 12v lead acid battery is pretty much universal in how you charge it.
But, that doesn’t mean all lead acid batteries are the same--no they are not.
I’ll explain shortly.
I want to add here that this process was done with expediency in mind.
My mom elected to buy this inverter on Amazon and have it overnighted to her, and we would
just pick up a battery at Menards that day (I was due to visit them).
The inverter is great--no qualms there--but the battery is less than ideal.
This is a marine deep cycle battery.
As far as batteries go that you can just buy at a hardware store, this is the closest to
the best kind.
But it’s probably not going to last for too many charge cycles.
Here, let’s explain a bit about lead acid battery chemistry.
Hold up--if you’re a newcomer to the channel and are just looking for how to do this, go
ahead and skip to this time.
On this channel I like to explain a lot about how stuff works, and I totally understand
if that’s not why you’re here.
Lead-acid batteries are incredibly simple.
They are the oldest type of rechargeable battery, invented in 1859 by French physicist Gaston Plante’.
Their construction is quite basic--two plates, one lead and the other lead dioxide, are submerged
in a bath of sulfuric acid which serves as the electrolyte.
When it’s fully charged, the acidity of the electrolyte solution is very high, thus
there are a lot positively charged hydrogen ions floating around, as well as negatively
charged sulfate ions.
Now I won’t get into the chemistry specifics--I’ll save that for another video--but energy in
the battery comes mainly from the acid.
The sulfate ions will react with both the negative and positive plates to form lead
sulfate, and the hydrogen ions react in the positive plate with oxygen atoms to form water.
The more concentrated the acid is, the more charged the battery is.
Conversely, the more lead sulfate that appears on the plates,
the more discharged the battery becomes.
And this is where we get into the nitty gritty of battery types.
There are two basic categories of lead-acid battery; deep cycle, and SLI which stands
for Starting, Lighting, and Ignition.
Essentially an SLI battery is a car battery, and these are absofreakinlutely terrible at
being deep cycled.
If you just buy a car battery for backup power, you’ll be lucky if it lasts a dozen cycles
before it’s dead.
And that’s because of how they are designed and constructed.
Car batteries need to be able to produce an enormous surge of current for the starter motor.
To get more current, you need a large surface area on the plates of the battery.
And with limited room, this surface area is created by making the plates small, numerous,
and sort of like a sponge.
These spongy plates are great at producing tons of current, but they limit the battery's
ability to be discharged and recharged.
See as the battery discharges, the plates don’t just get coated with lead sulfate.
They become lead sulfate--just as a rusty piece of metal isn’t covered in rust--the
metal has turned to rust.
And lead sulfate isn’t a good conductor.
If you let a car battery get discharged too much, the spongy plates can sort of get clogged
with the lead sulfate.
The more this happens, the less current it can pass, and then it can’t be recharged
to reform the lead and lead oxide.
Another common occurrence is called shedding.
Again due to the spongy nature of the plates, the expansion and contraction as the lead
plate becomes lead sulfate and is turned back to lead through recharging can actually cause
bits of the plate to fall off, thus limiting not only current passing ability but also
capacity.
But normally, a car battery will stay almost completely charged all the time.
The starter will only run for a few seconds, then once the engine is running the alternator
will swiftly replenish that charge.
Ordinarily, the battery is hardly cycled at all, and very little lead sulfate forms anywhere
in the battery.
Thus, it’s typical for a car battery to last 5 years or more, but may only survive
a few episodes of leaving the headlights on.
Deep cycle batteries, on the other hand, have big, thick, solid plates.
With limited surface area, they can’t produce monstrous surge currents, but they can tolerate
much more lead sulfate building up without harming the battery.
They’re less susceptible to shedding due to the non-porous nature of their plates,
and in general are more specialized and a bit more expensive.
Due to their inability to create surge currents, they aren’t used as a car battery but instead
for things like golf carts, battery backup solutions, and some early electric cars used
them as their main source of propulsion power.
For this project, we’re using a compromise battery.
There is a subset of batteries called marine batteries, and within that subset there’s
a subsubset called marine deep cycle.
That’s what this is.
These batteries have thicker and stronger plates than an ordinary car battery, but they
can still provide a generous surge of current.
I chose this battery because it was A) Readily available and B)
cheap.
A whopping $89, however a $7 core charge was placed on top of that because I didn’t have
a used battery to return.
Speaking of, did you know that lead acid batteries are among the most recycled things in the world?
Everything in here can easily be recycled and purified, with only the paper separators
between plates being impossible to recover.
Because of that core charge, people are incentivised to not throw their batteries into landfill,
and battery manufacturers have a steady supply of used batteries to condense into their constituent
parts and make new batteries again.
It is almost certainly the case that this battery was once many other batteries, with
the materials having hopped from car to car and from boat to boat.
Look at that, society coming together to solve a problem and no one’s complaining about it.
Great job.
So first, we want to determine what our needs are.
And I was going on an estimate.
This setup uses a laptop in a docking station and two 20 inch monitors, but there is also
a power supply for the RAP, her phone, the Google WiFi router (though that could be turned
off if required), and the actual DSL modem, so while the computer and monitor are probably
the bulk of everything, there are a lot of small loads that might add up.
I basically just assumed 100 watts would be enough, and let’s roll with that.
Annoyingly this sort of battery usually isn’t labeled with a helpful figure like amp-hours
or watt hours.
Instead it has a stat called reserve capacity.
Now I simply picked the largest battery they had among this selection, and I didn’t yet
know what RC meant.
So after some googling, I learned that a battery’s reserve capacity is the time in minutes that
it can sustain a discharge rate of 25 amps before it drops to 10.5 volts,
which is pretty dead.
This battery’s reserve capacity is 170, so 25 amps over 170 minutes is about 70 amp
hours, and since this is a 12 volt battery, that means it has a capacity of about 850
watt hours.
This was good, as I had estimated her setup would use about 100 watts, and it should just
barely get her through an 8 hour day.
But, another fun feature of lead-acid battery chemistry, is that its capacity will go up
the slower you discharge it.
So while this battery may only be 850 watt hours with a 300 watt load, cutting that load
down to a third might boost the capacity into the kilowatt hour range.
If we’re real lucky, with a slow drain, we might get
1.1 or 1.2 kilowatt hours out of this thing.
So, we’ve got a battery.
But now we need a way to convert the 12V DC into the 120V AC that her stuff uses.
That’s what inverters are for!
These devices will boost the voltage and continually invert the phase up and down to create A/C
current from a DC source.
If you’re running electronics, you definitely want a pure sine wave inverter.
This will replicate the sine wave pattern as seen in true A/C power.
Cheaper inverters will simply throw spikes up and down, which many modern power supplies
can tolerate, but which probably isn’t great for everything.
In choosing an inverter, we went extraordinarily overboard.
I basically combed through reviews for my mom on Amazon, and while there was a much
cheaper inverter that would have done the trick, it had some lackluster reviews indicating
it might overheat, so we went with this enormous beast.
You never know, it might truly come in handy someday.
And we also need a way to charge this battery.
For that, we’ll use an automatic car battery charger that my parents already had.
This is a relatively slow charger, only putting out 6 amps, but that’s 72 watts and will
be enough to recharge this battery from empty in 16 hours or so.
If there were an extended power outage, the charger could be run from the generator overnight.
But having a slow charger is probably a good thing.
See, you do have to worry about hydrogen production when the battery is being charged.
Ordinarily very little hydrogen is produced,
in fact ideally close to none should be produced
and the bulk of hydrogen would come from a battery being overcharged, which this automatic
charger should prevent from occuring.
But, even if it were to overcharge the battery, the amount of hydrogen generated is directly
dependent on the amount of current being pushed into the battery.
I ran the numbers and determined that in order for hydrogen to reach dangerous levels in
this room with 6 amps of charge current, it would require about a month of overcharging.
So clearly, that’s not a concern.
However, I did alter course for safety--I was planning on situating the battery on a
small cart, but its partially enclosed top could trap hydrogen and potentially create
a small explosion risk.
So I went to work setting things up.
This battery has threaded studs to mount cables to in addition to standard lugs.
We’ll use the studs with the supplied cables from the inverter, but I did add a large fuse
for short-circuit protection.
The inverter could theoretically pull 125 amps continuously
(though the battery could not sustain that for very long)
so I looked for a fuse above that rating.
Now, I’m only adding this for protection from a short circuit.
The inverter has built-in protections of its own, but in case something metal should get
lodged behind the inverter, or some other stupid thing causes a dead short, those 600+
cranking amps need something to stop them.
But then, I added this little guy.
This is a battery level monitor and voltage indicator.
This is really neat, it can support different battery chemistries and voltages, but came
preconfigured for a 12v lead acid battery.
Now it’s showing that percentage based on the battery’s voltage reading.
This will give you a relatively good indication of charge, but it means that if there’s
a load on the battery, thus dropping its voltage, the reading also drops.
Additionally, whenever the battery is being charged, the reading will jump to 100%, as
the charger gives the battery a higher voltage when charging.
However, it will still serve as a useful indicator, as after its initial drop, that percentage
will steadily drop as it discharges.
Best of all, pressing the button turns on the backlight, and pressing it again will
change to an actual voltage reading.
The specs on this thing indicate that it draws 112 microamps when idle.
That’s practically negligible, and will perhaps cause the battery to lose 1% of charge
over a few months.
You’ll also notice that this is connected straight across the battery.
It would be wise to fuse this as well, however it’s fairly likely that there is a fuse
on its circuit board somewhere
(even if it’s just a resistor or something that’s not “supposed” to be a fuse)
and even if there wasn’t one, these thin wires would
quickly melt in a dead short scenario.
Thus, I’m not worried about it.
So now, this setup is pretty much done.
After putting on the charger long enough for it to switch to float charging mode, I lugged
the battery and inverter down to her workstation.
I also finally used a kill-a-watt to determine the actual draw of her workstation.
Hopefully it’s 100 watts or less.
Amazingly, everything here only draws around 52 to 55 watts!
It occasionally spikes to 70 watts, but even if we take that as a worst-case figure (plus
this will account for the 10 to 15% loss in the conversion from the inverter), this battery
will now easily pass 12 hours of backup time, and with an average of 4 and a half to 5 amps
being drawn from the battery, it may be even more.
This extra capacity also means the battery won’t be as deeply cycled in a day, which
will prolong its useful life.
To use this is really simple.
Everything is already plugged into a small uninterruptible power supply, but this is
really small and can only realistically provide 20 minutes of power,
maybe an hour if we got super lucky.
However, it means that in the event of a power failure, everything is seamless.
If the power goes out, everything in her setup will remain powered on.
To switch to the large backup supply, all you need to do is unplug the power cord of
the UPS from the wall, and plug it into one of the outlets on the inverter.
After you switch the inverter on, the UPS will say “hey, that power looks OK”, and
it switches back to what it thinks is normal AC power.
At this point, the entire setup is running solely from the large battery.
This should provide at least a full day’s work of backup power, and possibly 2 if the
slow drain boosts the battery’s capacity up to 1.2 kilowatt hours.
When the power comes back, just switch off the inverter.
The UPS will kick back into action briefly, but after plugging it into the wall, it will
be on true AC power again.
Then, just grab the car battery charger, hook it up, and after an overnight charge the battery
will be full again.
If there’s a prolonged power outage, the battery charger could theoretically become
an indirect power source for the inverter, using the battery itself as a large buffer
or ballast.
The dirty energy coming from the generator would be converted to DC power, and when the
inverter switches it back to AC, it will be clean as a whistle.
This charger might even be enough, as 6 amps works out to 72 watts.
However, it would be pretty close.
A larger battery charger might be desired for this purpose.
But using this with a generator isn’t really the point.
If that were the point, then a wiser investment is a generator with a built-in inverter, which
can safely power electronics.
Rather, the goal of this setup is to provide immediate, easy, and convenient backup power
that will last at least a day.
For most power outages, this battery will be all that’s needed to get my mom through it.
One last thing before I sign off--this brass lug on the inverter should be grounded.
Right now, when on battery power, none of this equipment has a connection to earth.
This isn’t necessarily an abhorrently dangerously scenario, but to be safe a ground lead should
be attached here.
We could attach a lead to the ground wire inside this electrical box, or we could use
an adapter like this.
Whichever you choose, make sure it actually has a good ground connection.
Thanks for watching, I hope you enjoyed the video!
Lead-acid battery technology may be wicked old, but it has some compelling applications
such as this.
But remember, this battery won’t last many cycles.
It doesn’t have to, as it will probably only get a discharge a few times a year if
that, but if you want to regularly charge and discharge a lead-acid battery for energy
storage, you want to choose a better battery.
Golf cart batteries, which are usually 6 volts and thus require a pair to be wired in series
to get 12V, are a good start.
The solar power community seems to favor Trojan batteries for longevity.
I’m planning on making some videos analyzing the costs and lifespan of deep cycle lead
acid batteries versus lithium ion for stationary energy storage, because the winner may be
less obvious than it seems.
But for now, thank you to everyone who supports this channel on Patreon, especially the fine
folks who have been scrolling up your screen.
With the amazing support of people just like you, I’ve been able to turn Technology Connections
from a weird hobby into my full-time job.
And there are big projects just around the corner.
If you’d like to pledge some support to the channel to help it grow, please check
out my Patreon page.
Thank you for your consideration, and I’ll see you next time!
♫ do do do do do do ♫
♫ a jazzy sax ♫
♫ some piano and drums chime in ♫