Re: [OCLUG-Tech] Re: power usage
Stephen Gregory wrote:
I have retested the Tripplite UPS and an APC UPS. As far as I can tell
the Tripplite does consume 10+ watts at all times. Oddly when I
connect a low load, less than 1A, into the Tripplite the ammeter reads
a little lower then when nothing is connected. It could just be that
the Tripplite has a crummy power factor. I would need better equipment
to figure it out.
The APC UPS behaves as expected. It draws close to 2w. It does not
show the odd spikes of current draw either. The APC is an older basic
200VA model. I used to seem them under cash registers all the time at
the grocery stores.
--sg
I would surmise from this that the Tripplite uses a diode bridge
rectifier running from the transformer on the input side to create the
DC to charge the battery. This is far less efficient than using a
switch mode power supply to do the same task. The APC uses a switcher
IIRC. Tripplite has been around a lot longer, therefore it is probably
they are using the older technology (which was cheaper back then). You
can't turn off a transformer like you can a switcher.
Tripplite (Again IIRC) had a real affection for ferroresonant
transformers - very robust, but not extremely efficient. If run in
saturation, "ferros" add quite a bit of brownout holdover, greatly
helping the switchover delay while turning on the inverter in the event
of a mains failure. If your hear a persistent light buzz when the
Tripplite is running, it is probably stack vibration in the
transformer. If the buzz goes away when the system is running off the
inverter, that is another piece of circumstantial evidence.
Conclusions: The higher efficiency of the APC will have much lower long
term operating costs, but a predictable problematic potential waveform
"blip" during switchover to battery driver inverter. The Tripplite (if
I'm right) probably has a more consistent switchover without the
potential for wave collapse, but does so at a high efficiency penalty.
The way to determine this conclusively is to capture and observe AC
output with a storage scope, triggered on the zero crossing detect circuit.
For general PC usage, the APC will be fine. For sensitive equipment,
medical applications etc., the Tripplite would probably be better (but
not as good as a true UPS that always runs off the inverter). True
on-line UPS cost much more in both efficiency penalties and purchase
cost as the batteries and inverter circuit have to be stressed to handle
full time operation.
--
Bill