Adding UPS functionality to an inverter - Page 1
Forum section: electronics / projects

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: May 12, 2017, 08:37:46 am
content: So I have a need for an inverter and a UPS and want to know if I could buy an inverter for now and add a UPS functionality to it later on. Or do I need two separate devices for my needs?

author: David Hess
author_rank: Super Contributor
timestamp: May 13, 2017, 09:50:02 am
content: A continuous duty inverter can be used in combination with a battery and DC power supply to make an online or double conversion UPS.

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2017, 02:14:46 pm
content: An on line UPS is composed of 3 main parts plus the battery:- The inverter- The battery charger- The static switchThe static switch has several important functions:1) to supply the consumer in the event of an inverter fault or at the end of the battery autonomy if the charger has failed2) to provide peaks current that exceed the max output current of the inverter3) to burn the consumer's fuses in the event of a short-circuit on one of the consumers

author: BrianHG
author_rank: Super Contributor
timestamp: May 13, 2017, 02:35:30 pm
content: Quote from: oldway on May 13, 2017, 02:14:46 pmCAUTION : You can only use a static switch if your inverter keeps phase/tracks your source AC source phase and the switch must be a guaranteed break-before-make contact without arcing. I once blew up all the mosfets in an inverter with a smaller relay switch though it was rated 240v, 15 amp contacts. I solved the situation with a huge oversized relay with wide contact openings.With the large relay, I got away without the phase matching of my AC primary, but, there's a blink in the lights during the switch-over.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 13, 2017, 03:10:14 pm
content: How big of a load are you planning to run? If it's a few hundred watts or more, you'll probably be best off finding a cheap used rackmount UPS. The ones that support external batteries (and even many that don't - enterprise stuff is very well built) are almost certainly going to be capable of running on battery continuously.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 13, 2017, 03:45:14 pm
content: Quote from: drummerdimitri on May 12, 2017, 08:37:46 amyou can buy a UPS and you'll have a very good inverter. as someone said, UPS is more than just an inverter. the drawback is only one, UPS is usually bulkier than inverter because it like to put the battery in the compartment and have a very big and heavy transformer.

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2017, 04:42:50 pm
content: Of course, the inverter must be in phase with mains voltage when switching, but that not enough: the voltage difference can't exceed a well specified value because in some cases, there is working in parallel during a short time of inverter and mains.Switching must be fast (less than 1/4 cycle) and is made by thyristors, at least in high power UPS.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: May 16, 2017, 08:41:12 am
content: Quote from: David Hess on May 13, 2017, 09:50:02 amWill that work with any type of battery? It should be set to 13.6V or so for Lead acid batteries and charge them once AC power is back on right?

author: MarkL
author_rank: Unknown
timestamp: May 16, 2017, 04:44:39 pm
content: I would look for an inverter that has UPS capability already built in (namely a charger and an AC transfer switch), instead of trying to add it later.I've had good experiences with various Samlex models. They're priced reasonably and are well made:http://www.samlexamerica.com/products/ProductsList.aspx?cid=S51My most recent installation used an EVO-2224 for a server farm. It has an impressive amount of flexibility in setting up operational options (trip voltages, hold-down times, battery chemistry, etc.), separate input/control for a generator set if needed, battery temperature charge compensation, event logging, and a remote control/monitoring panel.Some other manufacturers also worth looking at are xantrex.com and outbackpower.com.But no matter what you get, I'd highly recommend sticking with a pure sine inverter to keep your connected equipment happy.

author: David Hess
author_rank: Super Contributor
timestamp: May 16, 2017, 05:18:31 pm
content: Quote from: drummerdimitri on May 16, 2017, 08:41:12 amIt will work with any battery that can power the inverter and that will accept float charging. The problem is that some chargers will have problems properly charging the battery when a large load is present. In practice that limits you to batteries which allow float charging and no not require conditioning. An online UPS has this all built in and the charger is designed with the expectation of powering the inverter continuously while charging the battery.