I recently got a SMX2200HV (230V) that now powers my office. The SMX series is advertised as a switch-mode unit that is basically a step-up from the SMT series (Features, extended runtime, efficiency).
These claims all match up very well for the smaller series up to 1500VA. However, the bigger models (SMX2200HV and SMX3000HV) seem to have a "poor" (i.e. significantly lower) efficiency in low-load scenarios according to the efficiency graph on the product website: https://www.apc.com/shop/uk/en/products/APC-Smart-UPS-X-2200VA-Rack-Tower-LCD-200-240V/P-SMX2200HV
For example, at 10% load the SMX2200HV has 85% efficiency. The SMX3000HV does a bit better, but I suspect they use the same circuit inside since at 200W load, both units exhibit 85% efficiency.
On the other hand, the smaller units have a much higher efficiency in low-load scenarios. For example, the SMX1500RMI2U has an efficiency of 92% (!) at 10% load - thats a 7% difference!
I would really be interested why that is, or if this is an error on the website.
The SMT and SMX units are designed on different platforms and as such have different efficiency curves. SMX units can be used with additional external battery packs so they have larger chargers. You are correct that at low loads, the efficiency will be reduced. Personally I like to size these units so they will have about a 40-60% load attached. This will give you room for expansion if needed, but also keep things running efficiently.
Hope this helps,
thanks for your reply. My main concern however was that compared to smaller models of the SMX series, the larger models of the same series still have low efficiency at the same load percentage (e.g. 10%, which is 120W for the SMX1500 and 200W for the SMX2200).
Correct. For best efficiency you would want to not oversize the UPS. That being said, none of these units is wildly inefficient, but obviously if you are talking about larger deployments (some customers have hundreds or even thousands of these units in use) it can certainly add up.
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