ups

[vk2kaw]

Hi Folks
I have a small 300w ups that runs on 12v
and was wondering if someone could tell me how to start it without the
mains connected to use as a converter 12v to mains (240v in Aus)
Thanks Alan

 

What are you trying to power with it ? UPS's don't provide much power
for long before the batteries die - especially little ones.

vk2kaw wrote:

Hi Folks
I have a small 300w ups that runs on 12v
and was wondering if someone could tell me how to start it without
the
mains connected to use as a converter 12v to mains (240v in Aus)
Thanks Alan

 

[vk2kaw]

yes the internal battery is to small but I wanted to run in in my truck
The ups is 12v on the input but will not start on 12v I was hoping to
use it to power the laptop and charger for the controls

 

[John Popelish]

vk2kaw wrote:

yes the internal battery is to small but I wanted to run in in my truck
The ups is 12v on the input but will not start on 12v I was hoping to
use it to power the laptop and charger for the controls

About a year ago, I did a bit of reverse engineering on a small UPS
and here is what I think I remember about how it worked:

The input line is connected to the output by a relay that is powered
by the incoming AC. The inverter transformer secondary was connected
to the output continuously. As long as the relay is on, it has a
contact that keeps the inverter controls shut down. Since the relay
connects the input AC to the output and the transformer high side is
continuously connected to the output, the input AC feeds backwards
through the transformer, charging the battery through the fet switch
body diodes. The inverter controls are not powered directly from the
battery, but from DC rectified from the transformer low side by
another set of diodes, whether because the high side is connected to
AC or because the inverter is running.

Once the input AC disappears, the relay drops out, first disconnecting
the input line from the output and then telling the controls that the
inverter is needed (break before make). The inverter controls have to
get the inverter going before a small storage cap across the control
supply bus fades out.

When input AC is restored, the relay first tells the inverter logic to
turn the inverter off, and then connects the input AC to the output.

If your unit is something like the one I opened, you might be able to
jump the battery to inverter logic (look for those two small diodes
from the low voltage side of the transformer that connect to logic
chip power pins or a low voltage regulator) through the on off switch,
so that it will run the inverter from a cold start.

Remember that you are dealing with very lethal voltages once the
inverter case is opened.

--
John Popelish

 

[jsmith]

The inverter requires a start up pulse and can often be achieved by adding a
push button switch that momentarily connects the 12VDC to the base of one of
the inverter power transistors through an appropriate resistor.

"Gary J. Tait" <classicsat@yahoo.com> wrote in message
news:j80lv09r1rlqmh2o33b39a6algt3vrrbn5@4ax.com...

On 27 Jan 2005 16:24:42 -0800, "vk2kaw" <alanwh@iinet.net.au> wrote:

Hi Folks
I have a small 300w ups that runs on 12v
and was wondering if someone could tell me how to start it without the
mains connected to use as a converter 12v to mains (240v in Aus)
Thanks Alan

why not get an inverter? They aren't that expensive now.