Hi everyone,
Recently I acquired a broken down SOLA 1500 sinewave UPS which I was
able to repair. Since I already have a UPS for my PC I decided to use
it solely as an inverter. I replaced the internal 24v battery pack
with 2 external 65AH deep cycle marine batteries connected to the unit
with 2 80cm 300A high grade welding cables to minimise losses.
Problem is; when the unit is running under a light load, it
immediately sounds the "low battery" alarm. It can run for hours like
this, but the thing that makes me uncomfortable is when looking at the
battery voltage on my CRO, I can see very pronounced "dips" approx
every 9mS; alternating between 2 distinct "dips" of 4-5 volts and 2
volts with apparent high frequency harmonics. Either my batteries are
damaged, they were bought as new factory seconds with cosmetic
defects, or these types of batteries simply cannot supply the heavy
surges of power needed, fast enough. Under load, they steadily supply
around 24.6 volts which is probably why the UPS is complaining.
However, I do not like these dips in voltage since I can hear the unit
struggle when a large monitor is switched on, which does not happen
with the internal batteries. I doubt they are defective though, so I'd
like to build a capacitor and choke filter close to the UPS unit to
"support" the batteries. An LC filter would help, I suspect, however I
have never built one even remotely as powerful as this unit needs.
Could anyone please point me to a schematic or describe a simple
filter that would be cost-effective? How many turns of what gauge wire
would I need and would I be able to salvage the inductors found in
wrecked PC power supplies?
If you read through all this; thank you. I'd be grateful for your help
and post an update with any success or failure stories.
Recently I acquired a broken down SOLA 1500 sinewave UPS which I was
able to repair. Since I already have a UPS for my PC I decided to use
it solely as an inverter. I replaced the internal 24v battery pack
with 2 external 65AH deep cycle marine batteries connected to the unit
with 2 80cm 300A high grade welding cables to minimise losses.
Problem is; when the unit is running under a light load, it
immediately sounds the "low battery" alarm. It can run for hours like
this, but the thing that makes me uncomfortable is when looking at the
battery voltage on my CRO, I can see very pronounced "dips" approx
every 9mS; alternating between 2 distinct "dips" of 4-5 volts and 2
volts with apparent high frequency harmonics. Either my batteries are
damaged, they were bought as new factory seconds with cosmetic
defects, or these types of batteries simply cannot supply the heavy
surges of power needed, fast enough. Under load, they steadily supply
around 24.6 volts which is probably why the UPS is complaining.
However, I do not like these dips in voltage since I can hear the unit
struggle when a large monitor is switched on, which does not happen
with the internal batteries. I doubt they are defective though, so I'd
like to build a capacitor and choke filter close to the UPS unit to
"support" the batteries. An LC filter would help, I suspect, however I
have never built one even remotely as powerful as this unit needs.
Could anyone please point me to a schematic or describe a simple
filter that would be cost-effective? How many turns of what gauge wire
would I need and would I be able to salvage the inductors found in
wrecked PC power supplies?
If you read through all this; thank you. I'd be grateful for your help
and post an update with any success or failure stories.