Re: Battery question

On Wed, 08 Oct 2008 09:54:33 GMT, John Doe <jdoe@xxxxxxxxxxxxxxxxxx>
wrote:
Bruce L. Bergman wrote:
clare at snyder dot ontario dot

Get a pair of 7 or 8 ah AGM batteries commonly used in alarm
systems, emergency lighting systems, computer UPS, and other
rechargeable devices. Should cost about 25-30 each - possibly as
much as 35 depending where you buy them. Put the pigtail from the
old battery on and GO!

Note that the batteries made for UPS Systems have special codes
added to the standard model numbers, with a higher discharge rate,
and a corresponding higher price cause they cost more to make. And
they have different terminals (usually bolted lugs instead of QC
Tabs) that can pass the higher current levels.

My Internet Office 500 uninterruptible power supply UPS battery by
Tripp-Lite does not have bolted lugs, it has tabs that the
connectors slide onto. But I'm wondering how a sturdier connector
would be an issue anyway.

The 500W to 1000W size is at the upper end of how much current you
can send reliably through a .250 Tab Quick Connect fitting.

My Tripp-Lite Smart-UPS 2200W unit has four 12V 17AH high-rate
batteries - two 24V battery banks in series-parallel, bolted posts
with ring terminals, each battery bank fused at 100A and feeding into
the unit through 100A Anderson Powerpole slide connectors.

And I'm about ready to replace them AGAIN, but this time with four
low maintenance type deep-cycle batteries (90AH or 105AH) that will
cost about the same as the special batteries but give roughly 4X to 6X
the run time.

Your standard 7AH batteries have a 20A fuse and will see a 6A -
10A max load for an hour or two - the same size batteries in a
UPS might see 40A to 60A load, but only for three to ten minutes.

About the only other place this would be useful is driving an
electric starter for a small (under 10 HP) gasoline engine, where
the battery size and weight is an issue.

Why is being able to source more current a problem?
The motor will draw only the current it needs and the fuse will
work, whether the battery can source 20 amps or 1000 amps.

The batteries being able to source more current than the load needs
is not a problem at all, it's smart design and/or overkill. In the
case of the Power Toy that the OP wants to repower, those batteries
should last longer with the same treatment.

But the opposite can be a HUGE problem, when the load needs more
current than the batteries can provide /something/ isn't going to work
as designed. And THAT is the reason I brought up the warning in the
first place.

The buyer can easily decide simply based on comparing prices.

If you buy batteries for a UPS or other high-draw application based
on price alone (and buy the wrong batteries) you are setting yourself
up for a very painful and expensive fall. Saving $10 on batteries in
a critical application is dangerously false thinking.

A small UPS needs to reliably source a full 40A to 60A battery bank
draw continuously for ten minutes or so before the voltage starts to
fall off indicating a dead battery. The UPS is expecting high-rate
batteries with a predictable discharge voltage curve.

If you put in cheaper regular gel-cell batteries built for a 10A max
discharge rate, the voltage will start to drop almost immediately
because of the higher internal resistance, and when the battery
reaches total discharge instead of a slow and steady voltage drop the
output voltage will crash like a rock.

The UPS is expecting 30 seconds of remaining run time to issue
shutdown commands to the attached computer before the batteries run
critically dry. If the power fails only 5 or 10 seconds after the
low-voltage point (before the shutdown process can complete) you can
hose the computer, and corrupt all the program data from whatever
software and database applications that were running.

If the lost or scrambled records are the main bookkeeping database
with all the Accounts Receivable, or customer service queue for your
company, expect months of reconstructing them - if you are still in
business in three months...

And that's the real message here.

--<< Bruce >>--

.

Relevant Pages

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    ... A UPS 'floats the voltage to keep the batteries charged. ... not high enough the batteries will die and not hold a charge. ...
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  • Re: APC UPS
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  • Re: How much current safe for 30m extension?
    ... >>cost a bundle so I thought it would be possible to run a power cable ... >>underground to the big UPS we have in our computer room. ... Last time we had a major failure of the batteries and rectifier it cost ... The spare conduit is already in place underground, ...
    (sci.electronics.equipment)
  • Re: How much current safe for 30m extension?
    ... >>cost a bundle so I thought it would be possible to run a power cable ... >>underground to the big UPS we have in our computer room. ... Last time we had a major failure of the batteries and rectifier it cost ... The spare conduit is already in place underground, ...
    (sci.electronics.components)
  • Re: ups makes
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    (comp.sys.hp.mpe)
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