Dry vs Wet Cell Lead Acid Battery Charging

[Hasan A. Khan]

Hi all,

I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
price.  It was cheap because its batteries were near the end of their
life.  Replacing the batteries with the same kind of dry cell lead acid
is prohibitively expensive here.  I was thinking I would replace them
with ordinary wet cell automotive batteries because they are really
cheap.  These wet batteries are not the maintenance-free type and they
won't obviously fit in the casing.  I will have to keep them watered but
that's ok by me.

My concerns are: is there a charging cycle difference between the two
types of batteries?  Will the charger in the UPS work OK?  Any danger of
batteries getting burnt or exploding?  I did some search on Google and I
could only learn that UPS batteries are deep cycle while automotive
batteries are not.  Will that have any negative effect on the UPS?  Any
help is appreciated.

-Hasan.
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[Bob Blick-4]

Hasan A. Khan wrote:

> I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
> price.  It was cheap because its batteries were near the end of their
> life.  Replacing the batteries with the same kind of dry cell lead acid
> is prohibitively expensive here.  I was thinking I would replace them
> with ordinary wet cell automotive batteries because they are really
> cheap.  These wet batteries are not the maintenance-free type and they
> won't obviously fit in the casing.  I will have to keep them watered but
> that's ok by me.
>
> My concerns are: is there a charging cycle difference between the two
> types of batteries?  Will the charger in the UPS work OK?  Any danger of
> batteries getting burnt or exploding?  I did some search on Google and I
> could only learn that UPS batteries are deep cycle while automotive
> batteries are not.  Will that have any negative effect on the UPS?  Any
> help is appreciated.

Hi Hasan,

Sealed lead-acid batteries are more fussy than liquid electrolyte types.
So I think you should have no problem electrically using wet cells.
Automotive batteries can take fewer deep discharge cycles, but unless
you frequently run the UPS flat I see no problem with lifespan.

But please be aware that if you mount the batteries externally, unsafe
voltage will probably be on one or both of the terminals, 240 volts is
quite possibly connected to one terminal depending on where ground is
referenced.

Being "wet" cells the surface of the batteries may also have high
voltage that can cause accellerated corrosion to anything they are in
contact with. Putting them in battery boxes is a good idea. Or at least
"non flammable" picnic coolers or plastic storage tubs. :)

Cheerful regards,

Bob
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[Olin Lathrop]

Hasan A. Khan wrote:
> I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
> price.  It was cheap because its batteries were near the end of their
> life.  Replacing the batteries with the same kind of dry cell lead
> acid is prohibitively expensive here.

I also got a APC UPS for dirt cheap ($0) with a dead battery.  It turns out
APC has a battery swap program.  For a few 10s of $$ they sent me a new
battery and a prepaid UPS label to send back the old battery.  I don't
remember the battery specs and the exact price, but do remember thinking the
price was fair at the time.  That was a year or so ago, and the UPS has been
working fine and rode out a few power glitches since then just fine.

> I was thinking I would replace
> them with ordinary wet cell automotive batteries because they are
> really cheap.

In my case a car battery would have cost more.  The real problem with car
batteries though is that they are not intended to be deeply discharged.
They are optimized for high current delivery for a short time as apposed to
capacity and the ability to recover from deep discharge.


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[Kevin Jones-35]

>In my case a car battery would have cost more.  The real problem with car
>batteries though is that they are not intended to be deeply discharged.
>They are optimized for high current delivery for a short time as apposed to
>capacity and the ability to recover from deep discharge.

You would need to get a "Deep Cycle"  Wet Cell Lead Acid battery.
These are often referred to as "Marine" or "RV" batteries as well.
They are designed to be discharged down much further than auto
starting batteries without serious damage to the battery.

Regards,
Kevin Jones
   

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[Larry Bradley-2]

As well, you will get a LOT more running time when the power fails.
Conversely, it will take a lot longer to recharge them when the power comes
back on, since the charger is probably designed to put out current
appropriate for the existing batteries. But since (hopefully!) the time
between power failures is relatively long, this shouldn't matter.

Larry



Original Message:

You would need to get a "Deep Cycle" Wet Cell Lead Acid battery.
These are often referred to as "Marine" or "RV" batteries as well.
They are designed to be discharged down much further than auto
starting batteries without serious damage to the battery.

Regards,
Kevin Jones


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[Dwayne Reid]

At 01:14 PM 4/30/2009, Hasan A. Khan wrote:

>Hi all,
>
>I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
>price.  I was thinking I would replace them with ordinary wet cell
>automotive batteries because they are really
>cheap.

Couple of things:

1) Should work just fine in terms of charging.  Gel-cells are WAY
more fussy than flooded batteries about charge techniques.

2) Modern automotive batteries aren't designed for frequent
deep-discharge cycles.  They will tolerate some deep discharge
operation but not as often as RV or marine batteries.  That said: how
often do you expect the batteries to operate until they are dead?  If
that's not often, then no problem.  Occasional testing is definitely
NOT a problem.

3) Make sure the battery terminals can't be touched.  There is a
significant chance that the batteries are connected directly to the
incoming power line.  Plastic battery cases with lids would help
there, along with appropriate warning labels.  Keep in mind that you
are trying to protect people other than yourself from harm.

4) Try to get batteries with removable vent caps - both so that you
can keep the battery filled as well as for hydrometer
testing.  Purchase a battery hydrometer and learn how to read and
interpret it.  Mark the hydrometer reading on the battery when it is
new and fully-charged so that you have something to compare to in a
few years time.

Go for it!  I suspect that you will be quite happy with the results.

dwayne

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[Herbert Graf-5]

On Fri, 2009-05-01 at 00:14 +0500, Hasan A. Khan wrote:

> Hi all,
>
> I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
> price.  It was cheap because its batteries were near the end of their
> life.  Replacing the batteries with the same kind of dry cell lead acid
> is prohibitively expensive here.  I was thinking I would replace them
> with ordinary wet cell automotive batteries because they are really
> cheap.  These wet batteries are not the maintenance-free type and they
> won't obviously fit in the casing.  I will have to keep them watered but
> that's ok by me.

Frankly, it's been a while since I've seen a car battery that wasn't
maintenance free. Adding water? That's a long time ago.

You're main problem is regular automotive batteries are designed to
always be at the top of charge and deliver short bursts of many amps.
They are called "starting batteries" and are completely the wrong type
of battery to connect to a UPS.

What you need a "deep cycle" batteries. They are more expensive, but are
designed for the kind of load a UPS is.

> My concerns are: is there a charging cycle difference between the two
> types of batteries?  Will the charger in the UPS work OK?  Any danger of
> batteries getting burnt or exploding?  

Lead acid charge cycles are pretty much the same across the board,
pretty much any lead acid charger will work with a lead acid battery, as
long as the charged isn't designed for a LARGER battery then you plant
to use. Make sure you match the capacities of the replacement batteries.

> I did some search on Google and I
> could only learn that UPS batteries are deep cycle while automotive
> batteries are not.  Will that have any negative effect on the UPS?  Any
> help is appreciated.

Don't even bother using non deep cycle batteries. Just a few cycles and
their capacity will be so destroyed as to be almost unusable.

TTYL

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[Nate Duehr]

Herbert Graf wrote:

> On Fri, 2009-05-01 at 00:14 +0500, Hasan A. Khan wrote:
>> Hi all,
>>
>> I recently purchased a used APC SmartUPS 2200VA UPS at a dirt cheap
>> price.  It was cheap because its batteries were near the end of their
>> life.  Replacing the batteries with the same kind of dry cell lead acid
>> is prohibitively expensive here.  I was thinking I would replace them
>> with ordinary wet cell automotive batteries because they are really
>> cheap.  These wet batteries are not the maintenance-free type and they
>> won't obviously fit in the casing.  I will have to keep them watered but
>> that's ok by me.
>
> Frankly, it's been a while since I've seen a car battery that wasn't
> maintenance free. Adding water? That's a long time ago.

Actually if you look at most of them carefully the cheaper (non-AGM
style) "Maintenance Free" batteries, the little cell covers come right
off on top, and lo-and-behold, there's the good old fashioned battery --
same tech it always was.  The only difference is the seals have gotten
better, so less water evaporates.  I've found "maintenance free"
batteries that needed distilled water badly, came right back to life
when "maintained".   Go figure.

> What you need a "deep cycle" batteries. They are more expensive, but are
> designed for the kind of load a UPS is.

Like these...

http://www.cdstandbypower.com/product/battery/vrla/pdf/12_310.pdf

I got lucky and got four of these from a site that was required to
"decommission" them every couple of years, whether they needed to or
not.  Many critical big rack-mounted UPS systems are required to replace
their batteries on a schedule, no matter their condition.  These were fine.

Nate
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[Sean Breheny]

On Thu, Apr 30, 2009 at 11:38 PM, Nate Duehr <[hidden email]> wrote:
>
> Actually if you look at most of them carefully the cheaper (non-AGM
> style) "Maintenance Free" batteries, the little cell covers come right
> off on top, and lo-and-behold, there's the good old fashioned battery --
> same tech it always was.  The only difference is the seals have gotten
> better, so less water evaporates.  I've found "maintenance free"
> batteries that needed distilled water badly, came right back to life
> when "maintained".   Go figure.
>

Hmmm. Water doesn't leak out through evaporation or seepage - it is
lost when the battery is charged, which inevitably results in some
water being turned into H2 and O2. In a sealed lead acid battery,
there has to be some material to hold the electrolyte slightly "away"
from the plates so that the O2 can reach them to recombine (either a
gelled electrolyte or a glass mat - anything which will allow gaseous
diffusion between the plates and the airspace above them). This takes
some hydrogen from the acid and combines it with the O2 to make water
again (at the expense of slightly weakening the acid). The H2 can
diffuse right through the plastic case so it does not recombine. This
is still better than letting the battery dry out.

So, as far as I know, there is no such thing as a flooded lead acid
battery which does not need to have water added. I suppose that you
could prevent the user from adding water, but then a perfectly good
battery would be wasted.

The amount of water loss is greatly reduced if you do not overcharge
the battery, since most of the hydrolysis of water happens at the very
end of the charge. It could be that modern cars control the charge
voltage better so that there is significantly less hydrolysis.

Note that no lead acid battery can be completely sealed. The gel cells
and AGM batteries have little one-way valve vents which open when the
internal pressure reaches a certain point. They close again when the
pressure goes back down. This is needed as a safety mechanism as it is
normal for the pressure to rise inside the battery. You can even hear
these "squeal" a bit when a sealed lead acid battery is overcharged -
which is actually somewhat necessary to equalize the cells and reverse
sulfation of the plates.

Sean

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[alan.b.pearce]

>3) Make sure the battery terminals can't be touched.  There is a
>significant chance that the batteries are connected directly to
>the incoming power line.  Plastic battery cases with lids would
>help there, along with appropriate warning labels.  Keep in mind
>that you are trying to protect people other than yourself from harm.

And to protect yourself from harm while checking the batteries, go down to
your local auto wrecker and see if you can get enough of the little plastic
terminal covers that get put on the 'hot' battery terminal when they are in
a car. These will protect you from touching the terminals accidently, or
inadvertently shorting across a battery with something metal, while checking
the electrolyte.

The battery supplier may also be able to supply these as well, or supply
them from old batteries.

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[Lee Jones]

Most UPS manufacturers, APC included, ensure that the batteries
are not labeled with the voltage or amp-hour rating because they
want you to buy their battery packs.  If you measure the existing
batteries, you can compare dimensions & known values to catalog
data to figure out what third party batteries are exact matches.

> You would need to get a "Deep Cycle" Wet Cell Lead Acid battery.
> These are often referred to as "Marine" or "RV" batteries as well.

Most of the UPSes that I've worked on use multiple 7 to 12 amp-hour
batteries to form battery packs.

Most car batteries are 25-35 amp-hour.  Large truck batteries may
be have even higher amp-hour ratings.

If you make a battery pack from wet cell car batteries, what the
original UPS battery pack saw as a deep discharge (for a given
load for specific time) is a much less deep discharge of the car
batteries.  Most power outages (in the US) are only a minute or
two, so the UPS won't deeply discharge either a dry (sealed) or
a wet cell pack if the batteries are in decent condition.

                                                Lee Jones

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[Howard Winter]

On Fri, 1 May 2009 02:37:27 -0700, Lee Jones wrote:

> Most UPS manufacturers, APC included, ensure that the batteries
> are not labeled with the voltage or amp-hour rating because they
> want you to buy their battery packs.  If you measure the existing
> batteries, you can compare dimensions & known values to catalog
> data to figure out what third party batteries are exact matches.
>
> > You would need to get a "Deep Cycle" Wet Cell Lead Acid battery.
> > These are often referred to as "Marine" or "RV" batteries as well.
>
> Most of the UPSes that I've worked on use multiple 7 to 12 amp-hour
> batteries to form battery packs.

I've done some experimenting with UPSs and their batteries - the ones they supply aren't Deep Cycle, they're designed (and often labelled) "for standby use" which
means they expect to be kept topped-up, and not discharged very often.

By discharging a bank of UPS batteries until the UPS shuts down and recharging them immediately, once a day, I found that the time they'd run would start to
deteriorate after about ten or a dozen cycles.  Starting at about 4 hours' endurance, after a month it was down to about 2.5, and dropped by a few minutes each
day.  After three months it was less than an hour, and I stopped at that point.

> Most car batteries are 25-35 amp-hour.  Large truck batteries may
> be have even higher amp-hour ratings.

Indeed, but they're not designed for Deep Cycle either - they're designed to start the engine and then be immediately recharged.  Back in the good old days when
cars were fitted with ammeters, you could see when the battery was "full" because the ammeter read zero while the engine was running.  A single start takes only
about a quarter of an hour to recover, but if you have starting problems and almost flatten the battery, it would take three or four days' normal journeys before it
was "full".
 
> If you make a battery pack from wet cell car batteries, what the
> original UPS battery pack saw as a deep discharge (for a given
> load for specific time) is a much less deep discharge of the car
> batteries.  Most power outages (in the US) are only a minute or
> two, so the UPS won't deeply discharge either a dry (sealed) or
> a wet cell pack if the batteries are in decent condition.

Proper Deep Cycle batteries have much heavier plates than any other type, so they tend to be bigger and heavier for a given capacity - and also much more
expensive.  As you say, the bigger the battery capacity the better, because for a given amount of energy extracted it will be discharged less deeply.

As for how long a power cut lasts - the record here was 17 hours!  It has to be said that was the longest by far in the 25 years I've been living here - a tree came
down in a storm and took down the HV lines *and* blew the transformer (the next longest was 8 hours, then about 2.5).  You can't expect to use UPSs for this, so
that's when I broke out the generator.

Cheers,

Howard Winter
St.Albans, England


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[Byron Jeff]

On Thu, Apr 30, 2009 at 11:38:28PM -0400, Nate Duehr wrote:

> Herbert Graf wrote:
> > On Fri, 2009-05-01 at 00:14 +0500, Hasan A. Khan wrote:
> >> Hi all,
> > What you need a "deep cycle" batteries. They are more expensive, but are
> > designed for the kind of load a UPS is.
>
> Like these...
>
> http://www.cdstandbypower.com/product/battery/vrla/pdf/12_310.pdf
>
> I got lucky and got four of these from a site that was required to
> "decommission" them every couple of years, whether they needed to or
> not.  Many critical big rack-mounted UPS systems are required to replace
> their batteries on a schedule, no matter their condition.  These were fine.

Nate,

Can you define "fine"? I have access to used batteries of that exact model
and manufacturer. I'd like to use them for my electric car that I'm trying
to put together.

Have you done any controlled charging/deep discharge cycling as described
elsewhere in this thread? If so how did they hold up?

I'm probably going to pull the trigger on them anyway because I can get a
full double bank for less than $500. But it would be good to know how well
they function in a moderate to deep discharge cycle application.

BAJ
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[Jeff Findley-2]

"Herbert Graf" <[hidden email]> wrote in message
news:1241128232.6224.15.camel@not-the-one...
> Frankly, it's been a while since I've seen a car battery that wasn't
> maintenance free. Adding water? That's a long time ago.

Funny, the batteries in two of my three cars let you add water.  Also, in
the past, I've had a few "maintenance free" batteries where you could still
pry the tops off and add water.  Those were weird.

> Don't even bother using non deep cycle batteries. Just a few cycles and
> their capacity will be so destroyed as to be almost unusable.

Agreed.  Plus the deep cycle battery I've got at home (battery powered
backup sump pump) has screw on caps to add water.  It's about the size of a
car battery and wasn't terribly expensive (maybe $60 a few years ago).

Jeff
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[Herbert Graf-5]

On Fri, 2009-05-01 at 11:44 +0100, Howard Winter wrote:
> By discharging a bank of UPS batteries until the UPS shuts down and recharging them immediately, once a day, I found that the time they'd run would start to
> deteriorate after about ten or a dozen cycles.  Starting at about 4 hours' endurance, after a month it was down to about 2.5, and dropped by a few minutes each
> day.  After three months it was less than an hour, and I stopped at that point.

Wow, that's kinda surprising, thanks for running that experiment! I
thought the batteries in UPSs were deep cycle.

It's reassuring though to read that your results matched what I've read
in the past (that "starting" batteries are significantly effected
capacity wise after only 10 deep cycles, vs. the 100+ of real deep cycle
batteries).

TTYL

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[Nate Duehr]

On Fri, 1 May 2009 07:08:18 -0400, "Byron Jeff" <[hidden email]>
said:

> On Thu, Apr 30, 2009 at 11:38:28PM -0400, Nate Duehr wrote:
> > Herbert Graf wrote:
> > > On Fri, 2009-05-01 at 00:14 +0500, Hasan A. Khan wrote:
> > >> Hi all,
> > > What you need a "deep cycle" batteries. They are more expensive, but are
> > > designed for the kind of load a UPS is.
> >
> > Like these...
> >
> > http://www.cdstandbypower.com/product/battery/vrla/pdf/12_310.pdf
> >
> > I got lucky and got four of these from a site that was required to
> > "decommission" them every couple of years, whether they needed to or
> > not.  Many critical big rack-mounted UPS systems are required to replace
> > their batteries on a schedule, no matter their condition.  These were fine.
>
> Nate,
>
> Can you define "fine"? I have access to used batteries of that exact
> model
> and manufacturer. I'd like to use them for my electric car that I'm
> trying
> to put together.
>
> Have you done any controlled charging/deep discharge cycling as described
> elsewhere in this thread? If so how did they hold up?
>
> I'm probably going to pull the trigger on them anyway because I can get a
> full double bank for less than $500. But it would be good to know how
> well
> they function in a moderate to deep discharge cycle application.

Sorry, not yet.  They've been on one of those little "four cycle" 1A
lead-acid chargers that are commercially available for a few years, and
only get used during power outages.  

The "stuff" hooked to them is connected through a powerpole distribution
block that has a low voltage cutoff that is set for around 10VDC, and
it's never tripped.  (They power the ham shack.  Slowly moving to having
everything including the PC on 12VDC, but it's not a high priority for
me right now, since I'm not home enough to really enjoy the ham shack
right now... nor is the three year old tower project even started yet.
LOL!)

I probably *should* run some tests to see how long the four of them
would last and to make sure they're still matched, but haven't done it
yet.

A local group has also been using them for Field Day activities for as
long as I've had mine, and they're not reporting any loss of capacity
yet (three years).  They "abuse" them more than I do mine.  They use
them once a year, store them, charge them maybe twice a year...

They seem pretty "tough".  But no, I can't quantify that in any real
"engineering" way.  Sorry.  I was just using them as an example of a
very high capacity lead-acid supposedly *designed* for
UPS/high-current/deep-cycle duty, vs. say a standard car battery.

Another local friend loves his AGM "Yellow Top" Optima batteries since
they're supposed to be somewhere between "deep cycle" and "starting
battery", but I've had a "Red Top" fail in a rather concerning way in my
Jeep (it bulged badly while just using it for normal staring duties, and
the rest of the system checked out fine) and I won't use them anymore.
I was an outspoken fan of them too, right up until my starting battery
gained a couple of inches of height!  Not cool.  

(That leads to a completely unrelated story, but I love Sears.  I
started with a "4x4" battery, it failed early, paid a slight difference
in price on warranty to "upgrade" to the Red Top, and it bulged, and
they replaced it again, free of charge.  They've been great about
replacing batteries that are dying before their time.  With no
electrical problems, I suspect the high vibration environment of "real"
4X4 roads on a regular basis is the root-cause reason these batteries
are dying.)

Nate
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[Hasan A. Khan]

Thanks for everyone for their help!
My main concern was if the UPS's would work fine with wet cell batteries
and according to you guys, it will. So I am mostly happy.  The concern
about deep cycle issues is still there since the batteries will be
discharged to about 80% of full charge atleast twice a weak. Given that
the batteries are well taken care of otherwise, will they last two years
with that frequency of deep discharge?

Also I was not aware of the fact that 220V can appear on the battery
terminals.  I don't understand how that can happen.  I'd like to look at
some basic UPS circuits that will show it.  Any pointers welcome.  I
thought some sine/square wave is pumped into a step-up transformer with
input and output being isolated by the transformer.  So how does high
voltage appear at the battery terminals?

Thanks again.

-Hasan

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[Olin Lathrop]

Hasan A. Khan wrote:
> The concern
> about deep cycle issues is still there since the batteries will be
> discharged to about 80% of full charge atleast twice a weak. Given that
> the batteries are well taken care of otherwise, will they last two years
> with that frequency of deep discharge?

This has already been abundantly answered.  It seems the only issue is you
don't like the answer.


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[John Gardner-3]

Hasan -

Auto starter batteries in your app are unlikely to last more than a few months.
If that's what's available I suggest adding batteries in parallel to
increase the
A/H capacity. Starter batteries discharged below 15-20% capacity will have
short and unhappy lives.

Adding batteries in parallel is not a good solution - Meticulous,
ongoing attention
is necessary to connections - Short, heavy gauge, and clean...

Good luck.
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[Sean Breheny]

Hi Hasan,

I'm not sure I understand - when you say "discharged to about 80% of
full charge" do you mean
discharged from 100% (fully charged) to 80%, or do you mean from 100%
to 20%? For example, on a 10 amp-hour battery,
do you mean you are going to discharge out 8 amp-hours or 2 amp-hours?

If you mean only discharging 20% depth of discharge (from 100% to 80%
state of charge), then I think it is likely that an automotive battery
would last almost two years. If you mean discharged 80% depth of
discharge (100% to 20% state of charge) then no, they would not last
very long at all.

Maybe you explained this already and I missed it but why are you going
to have such discharges on your UPS twice per week?

As for the possibility of 220V on the battery terminals, I am not
familiar with typical UPS design, but it is entirely possible that, to
save money and weight, an auto-transformer or simple inductor was used
instead of a fully-isolated transformer.

Sean


On Sat, May 2, 2009 at 3:06 PM, Hasan A. Khan <[hidden email]> wrote:

> Thanks for everyone for their help!
> My main concern was if the UPS's would work fine with wet cell batteries
> and according to you guys, it will. So I am mostly happy.  The concern
> about deep cycle issues is still there since the batteries will be
> discharged to about 80% of full charge atleast twice a weak. Given that
> the batteries are well taken care of otherwise, will they last two years
> with that frequency of deep discharge?
>
> Also I was not aware of the fact that 220V can appear on the battery
> terminals.  I don't understand how that can happen.  I'd like to look at
> some basic UPS circuits that will show it.  Any pointers welcome.  I
> thought some sine/square wave is pumped into a step-up transformer with
> input and output being isolated by the transformer.  So how does high
> voltage appear at the battery terminals?
>
> Thanks again.
>
> -Hasan
>
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