Can I parallel connect batteries to a UPS not designed for extra batteries

Hi,

By chance I found two UPSes discarded in a rubbish bin. One of them, a
Powerware 5105, is a 500VA unit and works just fine (what luck!). The other,
an APC Smart-UPS 1000, is blown but the batteries are in fine shape.

I use the UPS at home and it is not connected to mission critical hardware.
As it stands, I have loaded the Powerware about 20% and have 30 minutes of
standby time with this load. The batteries rescued from the APC are exactly
the same size (electrically and physically) as the one used in the
Powerware.

Can I parallel connect the APC batteries to the Powerware UPS to get
extended standby time without having extra circuitry installed between the
batteries?

In article <(E-Mail Removed)>,
Larry Hatch <(E-Mail Removed)> wrote:

> Robert MacKinnon wrote:
> > Hi,
> >
> > By chance I found two UPSes discarded in a rubbish bin. One of them, a
> > Powerware 5105, is a 500VA unit and works just fine (what luck!). The other,
> > an APC Smart-UPS 1000, is blown but the batteries are in fine shape.
> >
> > I use the UPS at home and it is not connected to mission critical hardware.
> > As it stands, I have loaded the Powerware about 20% and have 30 minutes of
> > standby time with this load. The batteries rescued from the APC are exactly
> > the same size (electrically and physically) as the one used in the
> > Powerware.
> >
> > Can I parallel connect the APC batteries to the Powerware UPS to get
> > extended standby time without having extra circuitry installed between the
> > batteries?
> >
> >
> I am not an expert, but you might get a race condition between them.
> Meaning one lower battery will take from the other. But it should work.

Paralleling the batteries should *RUN* the critter fine, and extend your
runnable time, but don't bet on the beast being able to keep all the
batteries (however many that might end up being) properly topped off. I
highly doubt that the charge circuitry is set up to handle keeping a
proper charge on <insert some number greater than 1> batteries instead
the single that it was most likely designed around.

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Some UPS devices are in fact intended to charge multiple batteries, but this
is mostly a function of the higher end or professional types. Check the back of
your particular model and see if there is a large amperage DC plug there. If
so, use the limits that the manufacturer recommends. If not, then what you have
been told is true- they will certainly RUN from multiple parallel batteries and
greatly extend your running time, but they will in all likelihood be unable to
keep extra batteries charged.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

Don Bruder <(E-Mail Removed)> wrote:
> In article <(E-Mail Removed)>,
> Larry Hatch <(E-Mail Removed)> wrote:
>
>> Robert MacKinnon wrote:
>> > Hi,
>> > By chance I found two UPSes discarded in a rubbish bin. One of them, a
<snip>
>> > Can I parallel connect the APC batteries to the Powerware UPS to get
>> > extended standby time without having extra circuitry installed between the
>> > batteries?
>> >
>> >
<snip>
> Paralleling the batteries should *RUN* the critter fine, and extend your

Unless it melts due to lack of cooling.

> runnable time, but don't bet on the beast being able to keep all the
> batteries (however many that might end up being) properly topped off. I
> highly doubt that the charge circuitry is set up to handle keeping a
> proper charge on <insert some number greater than 1> batteries instead
> the single that it was most likely designed around.

If it's just a relatively simple constant current- constant voltage supply,
then it will, without any problem, it'll just take a lot longer to come up
to charged.
As batteries are charged over several hours, there probably won't be
any thermal issues on adding more.

If it's 'smart', then it may have a timer which cuts off charge, or
the software may be unhappy with the change.

--
http://inquisitor.i.am/ | private.php?do=newpm&u= | Ian Stirling.
---------------------------+-------------------------+--------------------------
"I am the Emperor, and I want dumplings." - Austrian Emperor, Ferdinand I.

In article <3f0714e5$(E-Mail Removed)>, (E-Mail Removed)
mentioned...
> Hi,
>
> By chance I found two UPSes discarded in a rubbish bin. One of them, a
> Powerware 5105, is a 500VA unit and works just fine (what luck!). The other,
> an APC Smart-UPS 1000, is blown but the batteries are in fine shape.
>
> I use the UPS at home and it is not connected to mission critical hardware.
> As it stands, I have loaded the Powerware about 20% and have 30 minutes of
> standby time with this load. The batteries rescued from the APC are exactly
> the same size (electrically and physically) as the one used in the
> Powerware.
>
> Can I parallel connect the APC batteries to the Powerware UPS to get
> extended standby time without having extra circuitry installed between the
> batteries?

You can parallel batteries if you use a rectifier diode between the
battery and the load. These very high current diodes are available at
RV stores, where they are used to parallel the battery to get more
'juice' in RVs and trailers. I believe they are Schottky diodes for
low voltage drop.

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Hmmm. The answers to my question are surprising in that I hadn't thought
about the charge cycle, just the discharge cycle. My concern would be that
one of the batteries with a higher terminal voltage would discharge into
another battery with lower terminal voltage. This would probably mean that
I'd have to have some sort of equalizing circuit that prevented this. A
diode as one poster pointed out would suffice however I think it would also
block the charging circuit.

> > runnable time, but don't bet on the beast being able to keep all the
> > batteries (however many that might end up being) properly topped off. I
> > highly doubt that the charge circuitry is set up to handle keeping a
> > proper charge on <insert some number greater than 1> batteries instead
> > the single that it was most likely designed around.
>
> If it's just a relatively simple constant current- constant voltage
supply,
> then it will, without any problem, it'll just take a lot longer to come up
> to charged.
> As batteries are charged over several hours, there probably won't be
> any thermal issues on adding more.

That's what I think also. I may end up getting a longer running time while
on batteries but the recovery time of the UPS would be correspondingly
extended. However, at some point in time, all cells would be charged to
their capacity.

>
> If it's 'smart', then it may have a timer which cuts off charge, or
> the software may be unhappy with the change.

The UPS is smart in that I can monitor the various aspects of its operation
from a controlling computer -- its terminal voltage, boost, buck,
temperature, frequency and so on. There must be enough intellegence in the
control circuitry to handle charging as well.