Joe,
1. Right, every time you convert from one type of power to another
you're only going to get 80 to 90% typ. Some devices claim up to 98%
eff, but that's only over a very specific operating range. Most
inverters are terribly inefficient for small loads. Some use 20 or 50
watts just idling! So coming right off the batteries will give you the
longest runtime in general.
2. A good charger stops when it's supposed to. A cheap-o charger
from wal-mart could cook the batteries. You need a good charger that
has several charging stages to take good care of the batteries. The
solar electric people like Outback and Xantrax make excellent ones, but
they're expensive. There are inexpensive units that do a good job too.
Just make sure that they back off the output when the batteries are
charged. Look for something called a "float" charge. Sometimes
chargers that have a "trickle" charge as the last charging stage will
cook a battery over time.
There are dc-to-dc converters (check mouser.com and digi-key.com)
that can take a wide range of input voltages and deliver a consistent
output voltage. These allow you to really discharge a battery and keep
your equipment running at a constant voltage. For instance, a dc-dc
converter could take 12 volts from a battery and deliver 48 v. Even as
the battery discharges to 9v or less, you could get 48 v. This however
is REALLY hard on the batteries, which are considered to be completely
discharged in the 10V range.
How it will behave will depend on the charger and the load. Most
good chargers have 3 or 4 charging "stages" and choose the correct
"stage" depending on how deeply discharged the batteries are. It goes
something like equalize-bulk charge-maintenance charge. I have a
feeling that with a small load like an AP, the charger would oscillate
from charge to maintenance charge over time as the batteries are
slightly discharged, then recharged, slightly discharged, recharged...
Or the maintenance charge might be enough that the batteries see no
discharging at all. It'll depend on the charger.
Here's one of my favorite links about batteries:
http://www.uuhome.de/william.darden/carfaq.htm
I've been studying up on it for quite a while now because I'm building
an off-the-grid home.
Jason
Joe Laura wrote:
As I understand it in order to be efficient you need to run right off the
batterys. Right? Would the battery charger stop charging precisly when
needed?
Superior Wireless
New Orleans,La.
www.superior1.com
----- Original Message -----
From: "Jason" <[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Monday, July 10, 2006 1:41 PM
Subject: Re: [WISPA] DC Inverter help
Gang,
I'm not a UPS expert, but if the batteries were deeply discharged,
wouldn't the extra load of the external batteries would make it hard on
the ups when it tries to bring them back up?
Maybe I misunderstood the question; but, if I needed 48VDC
uninterrupted, I'd string 4 deep cycle batteries together and connect a
good multi-stage battery charger. Then I'd run my 48 V devices right
from the batteries. If you don't need 120AC, then there's no need for a
UPS. If the UPS is already there and uses a 48V stack, then I'd tap
into that...
Jason
Gino A. Villarini wrote:
yes
Gino A. Villarini
[EMAIL PROTECTED]
Aeronet Wireless Broadband Corp.
tel 787.273.4143 fax 787.273.4145
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Mark Nash
Sent: Monday, July 10, 2006 1:14 PM
To: WISPA General List
Subject: Re: [WISPA] DC Inverter help
Gino, are you saying
a) that you've got external, non-APC batteries plugged into your UPS and
b) that your UPS/SNMP card recognizes the charge level?
Mark Nash
Network Engineer
UnwiredOnline.Net
350 Holly Street
Junction City, OR 97448
http://www.uwol.net
541-998-5555
541-998-5599 fax
----- Original Message -----
From: "Gino A. Villarini" <[EMAIL PROTECTED]>
To: "'WISPA General List'" <wireless@wispa.org>
Sent: Monday, July 10, 2006 9:02 AM
Subject: RE: [WISPA] DC Inverter help
We do it
Gino A. Villarini
[EMAIL PROTECTED]
Aeronet Wireless Broadband Corp.
tel 787.273.4143 fax 787.273.4145
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Mark Nash
Sent: Monday, July 10, 2006 11:14 AM
To: WISPA General List
Subject: Re: [WISPA] DC Inverter help
I'm curious if anyone has a) connected external batteries to an APC
UPS...
AND ... used the APC SNMP card to monitor the status of battery
consumption.
I currently use APC SU700NET UPSs in external 6"-deep boxes to
condition
power and provide battery backup. The SNMP card (AP9617) will e-mail
our
support if the site goes on battery power, giving us about 2.5 hours to
get
up the hill with a generator. When the batteries go below a threshold
of
charge left, it e-mails to let us know it's in a critically low charge
state.
So, if we put on extra batteries, does the UPS know this and does it
know
what kind of runtime it has left?
Mark Nash
Network Engineer
UnwiredOnline.Net
350 Holly Street
Junction City, OR 97448
http://www.uwol.net
541-998-5555
541-998-5599 fax
----- Original Message -----
From: "Mac Dearman" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "'WISPA General List'"
<wireless@wispa.org>
Sent: Sunday, July 09, 2006 8:15 PM
Subject: RE: [WISPA] DC Inverter help
Brian,
I guess I am an idiot because I hadn't thought of that! I don't have
any
(hardly) of my APC UPS's overloaded and it would probably be pretty
easy
to
do that. I bought some rack mount Compaq 3000Watt UPS's for the NOC
and
tied
4 Gel Cell 100lb batteries to each of those Compaq's. That has been
working
like a charm, but it scares the fire out of me to mess around them.
While
connecting them I managed to arc the wires and that produced a ball of
fire
that was bigger than I was! I later found out those 4 12VDC batteries
in
a
series (48VDC) produces more than enough DC voltage to knock your guts
out
while it blows the bottom of your feet off.
Sorry for that story - but it may keep some of us from "leaving here
early"
Mac
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On
Behalf Of Brian Webster
Sent: Sunday, July 09, 2006 10:00 PM
To: WISPA General List
Subject: RE: [WISPA] DC Inverter help
Mac,
Can you tap in to the battery lines on the UPS and add extra
external
batteries to extend the run time? This would give you the advantage of
conditioned power and automatic switch over of the UPS, and you would
still
have any other management features of the UPS still available to you.
Just
an idea to consider.
Thank You,
Brian Webster
-----Original Message-----
From: Mac Dearman [mailto:[EMAIL PROTECTED]
Sent: Sunday, July 09, 2006 10:35 PM
To: 'WISPA General List'
Subject: RE: [WISPA] DC Inverter help
Can anyone give me a lead as to what I am looking for? I believe this
http://tinyurl.com/lje7s is what I need, but I don't think I need
400Watts
as all I will be pulling at several new tower sites are a few RB532's
with
their radios. I think I ought to keep the RB532s powered at 48VDC as
they
will be in excess of 200' up a tower. My intentions are to put a
couple
Marine batteries in an enclosure for back up power and have the DC
inverter
to keep them charged and have a seamless transfer if a power outage
comes
along. I have been putting these big honking APC UPSs in all my
enclosures,
but am trying to get something that will last longer in times of
outages
Any help would surely be a appreciated.
Thanks folks,
Mac
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