UT-511 power supply - Page 1
Forum section: electronics / testgear

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 12:23:46 am
content: I just received my UNI UT-511 today. I was impressed with the quality. For the money, I don't think it can be beat. My one complaint so far is the power requirement. It uses 8 C-cell batteries. This isn't a tool I'm going to get a lot of use out of and the idea of leaving batteries in it to leak bothers me. They sell a wall wart for it. The company I bought the meter from doesn't sell them. I thought I'd just make a power supply and tuck it inside the battery compartment. As I was reading the instruction manual, it says to only usetheirpower supply or batteries. My question is this, other than the manufacturer warning, are there any reasonable arguments fornotmaking my own power supply?

author: mariush
author_rank: Super Contributor
timestamp: April 04, 2014, 12:45:53 am
content: I think they want to make sure the device is floating.I would suggest using a small 9-12 vAC 15-20VA toroidal transformer and then further regulated to 9-12v depending on the transformer you choose, using a 7809/7812 or a 1117. It may even fit inside the battery compartment.The manual says for the adapter Output voltage DC 15V, MAX current 600mA but since the device has to work on 8x1.5v =12v, it will work with less than 15v.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 02:34:18 am
content: What does "floating" mean?

author: PedroDaGr8
author_rank: Super Contributor
timestamp: April 04, 2014, 02:39:41 am
content: Quote from: chipwitch on April 04, 2014, 02:34:18 amNot referenced to ground. It's a safety precaution with such high voltages involved.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 05:28:05 am
content: Ah... still acclimating to the European (non-American) lingo. I know it as isolated. Kept seeing "PE" in another thread and couldn't understand what that was... then someone spelled it out. Oh... I've never heard it called anything but ground, here. Y'all tawk funny yonder.

author: notsob
author_rank: Frequent Contributor
timestamp: April 04, 2014, 05:49:56 am
content: Before you make one, ask Franky for a price for one [iloveelectronics on the forum]

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 12:48:16 pm
content: Quote from: mariush on April 04, 2014, 12:45:53 amAre some DC wall warts' negative tied to PE? I thought they wereall"floating?"Why toroidal?

author: mariush
author_rank: Super Contributor
timestamp: April 04, 2014, 01:31:39 pm
content: Some have a capacitor between the secondary side and primary side, for EMI/noise reduction. Some cheapo power supplies don't have properly safety rated capacitor, just a plain ceramic one which could short closed.As that device works with high voltages, by accident it could be possible for high voltage to arc over to the primary side and your mains socket.I suggested toroidal because these usually have lower height (and just smaller overall), so it would be possible to put everything in a small box hidden inside the battery compartment of the unit. Saves space on the desk.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 02:18:13 pm
content: Quote from: mariush on April 04, 2014, 01:31:39 pmI was thinking of simply supplying the battery terminals with a filtered dc supply. In order for that high voltage to arc over to the mains, it would have to travel by way of the battery terminals, right? Which means that by accident, the potential exists for 1000 volts to be applied to your 12 volt battery supply? I don't see how anything on the supply side could possibly cause a malfunction within the meter itself resulting in 1000 volts being applied to the supply. Am I missing something?I was expecting some to have concerns over an inadequately filtered power supply causing damage to the meter or worse, creating a dangerous condition for the user.QuoteGot it, thanks!

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 04, 2014, 02:35:01 pm
content: FYI, the meter indicates that the batteries are depleted when the voltage gets down to 8.5V, at which time readings can no longer be considered reliable. At 8.6V, however, accuracy will be unaffected. Nice to see they left some headroom.

author: Monkeh
author_rank: Super Contributor
timestamp: April 04, 2014, 02:54:28 pm
content: Quote from: chipwitch on April 04, 2014, 02:18:13 pmOne of the battery terminals will be connected to the common input. Consider what this means if you apply a -1000VDC ground referenced signal to the meter with an external power supply connected to the battery terminals.In fact, consider that it generates 5kV internally, referenced to those battery terminals.