Testing UPS with bench power supply - Page 1
Forum section: electronics / repair

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 17, 2019, 12:51:47 am
content: I have 3 UPSes I want to get back into working condition. Before I buy a set of batteries, I was wondering if it would be safe to hook up a bench power supply in place of the batteries. I have a Tekpower TP3005T. It's linear and isolated.

author: PKTKS
author_rank: Super Contributor
timestamp: October 17, 2019, 10:15:25 am
content: Probably NOT.vast majority os BENCH PSU are NOT!!! made to sink currentand vast majority UPS will try to make dead sure theBATs are sinking some current - to determine BAT load percent.Bad things may happenPaul

author: Jeroen3
author_rank: Super Contributor
timestamp: October 17, 2019, 11:34:37 am
content: If the supply can source enough current you can probably test battery only mode.Do not connect mains. As per reasons described above.

author: TheMG
author_rank: Frequent Contributor
timestamp: October 18, 2019, 02:30:15 am
content: Quote from: PKTKS on October 17, 2019, 10:15:25 amTrue, however...Quote from: PKTKS on October 17, 2019, 10:15:25 amMost likely not. I have yet to come across any bench power supply where this would be an issue. While feeding external voltage into the power supply will not cause it to sink any current (after all, it's not a programmable load!), it should also not cause any damage to the power supply (as long as the externally applied voltage does not exceed the maximum output capability of the power supply).It's really no different than, for example, hooking up a charged battery to the output of the bench power supply while the power supply's voltage control is set to zero (or any value lower than the battery's voltage).As for testing UPSs with one, I've done it a few times with no issues. Note that the inverter in many UPS draws a rather high peak current at a rate of 100 or 120Hz, which may exceed the current limiting of the bench PSU if the UPS itself does not have significant input capacitance. A nice beefy capacitor in parallel with it can help.

author: PKTKS
author_rank: Super Contributor
timestamp: October 18, 2019, 10:51:41 am
content: Quote from: TheMG on October 18, 2019, 02:30:15 amWild guess... any PSU should have a sampling network the mostpossible close at the load... otherwise regulation is crap.If the PSU was indeed designed to SINK (C and V - all quadrants)there should be safe...otherwise the LOAD income current or voltage will definitelygo wacko with the foreign values leading the FB loop unstable... not even a guess know what will happen...Last resource of using a DIODE to suppress sinking may workbut why not use any old battery? can't figure..Do the right thing. Put a battery there and do not risk your PSUunless you have 100% certain it is a 4 quadrant design.Paul

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 19, 2019, 03:07:54 am
content: Quote from: PKTKS on October 18, 2019, 10:51:41 amDon't have any old batteries that will take a charge. Even when the batteries were new, the UPS were questionable. However, I'm not sure if the batteries I had were any good in the first place. It once upon a time was a very good UPS.