"Bob F" wrote in message news:rofsn3$ous$1...@dont-email.me...
I appreciate your thoughts. I definitely need to give this a lot of
research and thought. I may have to put together my own charge
controller to match up to the NiCd battery requirements.
This will be a slow project, but I will appreciate any additional
comments from anyone any time along the way.
How much AC power does your expected load need? If you don't hack a UPS
you'll need a DC power supply large enough to provide it plus enough extra
to recharge the batteries after an outage at the voltage appropriate to the
batteries and inverter. These voltage and current regulators might help by
expanding your choice of power supply to higher voltage switchers with
little or no output adjustment.
20A at 12V is only 240 Watts, which a desktop and peripherals can easily
exceed. The battery voltage has to be within the limits of the UPS or DC-AC
I changed to recycled business laptops with their own backup batteries after
measuring the high power demand of my desktops and monitors. When the grid
fails the laptops run on battery long enough to connect and power up my
large UPS, a free salvaged 900W APC1400 with 2 KWH of external marine
batteries, enough to run my (small) refrigerator and freezer overnight. The
batteries don't gas while charging (I checked) because both the APC and my
solar controllers are set to limit at the 13.6V float voltage instead of
using the faster charging method that raises the voltage to 14.4V
temporarily. Neither has a setting for NiCds, only Lead-acid or Lithium.
Like all the true-sine inverters I've looked at, the APC consumes
significant power internally, about as much as my freezer, so the UPS I run
constantly is a much smaller modified sine one that supports the antenna TV
distribution amp and the laptop that's set up to play and record TV, plus
one lamp and my power recliner. The laptops' external monitors, the audio
system and the power-hungry printer don't really need to be on a UPS if you
have an alternate AC source to manually switch to.
Before buying a UPS, confirm that it can handle extended run time on large
external batteries. The smaller, cheaper ones generally overheat if you try.
One of mine shuts itself off after 30 minutes.
You might look for an orphaned 12V or 14.4V NiCd power tool charger to
experiment with. Anderson Powerpole connectors are nice for battery systems
where either or both sides of a connection may be live.
Current shunts are safer than the internal current range on a meter.
The full scale voltage drop is 75mV so that shunt gives 1mV per Amp.