Extra winding on UPS transformer for regulating voltage? - Page 1
Forum section: electronics / beginners

author: chaseadam
author_rank: Contributor
timestamp: April 02, 2016, 04:10:49 pm
content: I have a core type transformer (pictured) pulled from a 48v to 120v UPS with an unknown configuration. The "high" side of the transformer has 4 isolated windings, two on each side (ignoring the 48V side for this discussion). I connected one set of windings to the device and measured the other set of windings. The device winding voltages are 122v and 16v while the other windings (with a 60W load) measured 147v and 32v. When connected to the device, both 120v windings are connected directly in parallel, but the the two lower voltage windings are connected via a 30A fuse.I have two hypotheses which I have for this lower voltage winding and would like feedback (and possible explanation):1. Balancing the core transformer, but I believe the 120v parallel connected windings would balance without this extra winding.2. This is used as part of the automatic voltage regulator in the UPS.

author: chaseadam
author_rank: Contributor
timestamp: April 02, 2016, 04:21:11 pm
content: Looks like Dave may have already worked on one of these styles of autoformers. watching it now.

author: chaseadam
author_rank: Contributor
timestamp: April 02, 2016, 04:59:44 pm
content: It is the same topology as the UPS in Dave's teardown, but I am still unsure of what this extra winding does. The patents he refers to does not mention it either.

author: johansen
author_rank: Super Contributor
timestamp: April 02, 2016, 06:58:27 pm
content: your post is confusing.do you have, two 120volt windings and a 16 and a 32 volt winding?or do you have a 120volt winding, a 16 volt winding, a 147 volt winding and a 32 volt winding?are these windings all isolated or not?anyhow, my apc1500 connects the transformer differently during inverter or standby operation. when inverting the 110 v coil is the 120vac output, when in standby, the 120vac output is the output and the 114v and 145v tap is used to buck or boost the line voltage.

author: chaseadam
author_rank: Contributor
timestamp: April 04, 2016, 12:05:21 pm
content: Because it is a core-type transformer, there are two isolated winding "sets". Each set has three isolated windings. From what I can tell it has:48V for the battery side120v for the mains16v ? (but appears to be related to the 120v part of the device) (the 32v measurement was on the other side of the core transformer, but all the windings read higher voltages on that side for some reason, yes I had it loaded with a 60w bulb)All windings are completely isolated from one another (as opposed to a tapped autoformer). My guess is that when the mains gets too high or low, the UPS will switch the windings to connected them in series and create a single tap autoformer. Are there any other clever techniques of using this extra winding for the purpose of an AVR which I am not aware of?

author: johansen
author_rank: Super Contributor
timestamp: April 05, 2016, 09:37:29 pm
content: Its a reasonable assumption that the 16v coil is used to buck or boost the line voltage.Its possible when the unit is recharging the battery or in standby, the 32 volt coil is in series with the 120volt coil. when this happens, that 16 volt coil is now 12.6 volts, making it a more reasonable buck or boost voltage. (this would also explain the 30 amp fuse connecting them)far as i know some of these transformers recharge the battery by using the transformer as a boost inductor, shorting out the transformer to boost the voltage to get to nominal battery volts. obviously, due to losses and topology limitations, the transformer's ac rectified output has to be less than 10.8 volts per 12 volt battery.so to ensure that dead batteries will not be recharged at too fast a rate, as soon as ac power is available, there is an additional coil in series with the 120vac side.anyhow, yes you'll get a bit of a difference in voltage between one coil and the other, but not twice the voltage.