voltage  - Page 1
Forum section: electronics / beginners

author: nus
author_rank: Contributor
timestamp: October 28, 2018, 01:58:17 am
content: Can i use -12v as ground to get +24v out of a -12 +12 ac to dc converter

author: nus
author_rank: Contributor
timestamp: October 28, 2018, 01:59:36 am
content: Muti meter says +24v but was wondering if that was just the difference between the two points

author: helius
author_rank: Super Contributor
timestamp: October 28, 2018, 02:02:13 am
content: You can do so if there are no other ground connections in the device or anything it attaches to.For instance, an attached device with a "capacitive dropper" line power supply is referenced to ground, and could create a short when connected to your device.

author: tkamiya
author_rank: Super Contributor
timestamp: October 28, 2018, 02:15:02 am
content: You have to make sure not a single part of your power supply is connected to ground either directly or indirectly.For example, if casing is connected to the ground prong of mains connection, and ground of your output is connected to the same level, you've just created a dead-short.Otherwise, you can.Your multi-meter says it is 24V because it's the difference. Voltage is just a difference - most of the time, difference from ground. But doesn't have to be that way.

author: nus
author_rank: Contributor
timestamp: October 28, 2018, 02:31:51 am
content: So no part of what im connecting it to is going to touch ground. However there is a virtual ground in between the -12v 12v regulators. Transformer is not center taped.Lm7812 and 7912.

author: nus
author_rank: Contributor
timestamp: October 28, 2018, 02:38:13 am
content: I know i could change the dc converter to get 24 v out of it but i dont have 24v reg.Was hoping to use -12v as ground to get 24v

author: tkamiya
author_rank: Super Contributor
timestamp: October 28, 2018, 02:41:05 am
content: You can. What you just called "virtual ground" cannot touch your load.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: October 28, 2018, 03:11:25 am
content: Ground is an arbitrary point. If you designate the -12 as ground then the original ground is +12 and the original +12 is now +24. You just have to be consistent. Ground is the reference for the other voltages. I have done just what you are suggesting when I needed a higher voltage. but you can't have it both ways at the same time.Sent from my SM-G900V using Tapatalk

author: bsfeechannel
author_rank: Super Contributor
timestamp: October 28, 2018, 03:26:50 am
content: Quote from: nus on October 28, 2018, 01:59:36 amThat's the very concept of voltage: a potential difference. Your multimeter will always indicate the voltage difference between two points.You can take one of the points as a reference and attribute 0 volts to it.In the picture below I show the output of your ACDC conv. Notice that the potential difference is the same in all three configurations. What changes is the 0V reference that I can arbitrarily choose.So you can merrily connect your ACDC conv like in the picture below: +12V to the positive terminal, -12V to the negative terminal of your load, and 0V not connected.However, there is a caveat. If for some whim of fate the conv and the load get connected by an alternate route, say, some ground provided by another cable connected to the conv and the load, or by a metallic shelf, or the chassis of a car, you're in for a disaster.How can you be certain that there won't be a problem? Before you connect and turn everything on, use your ohmmeter to test the terminals between the devices for continuity. Test terminal by terminal inverting the leads, because ohmmeters have polarity.If you're still not sure how to proceed, summon a friend that is acquainted with electricity. Everyone should have such a friend, by the way.

author: nus
author_rank: Contributor
timestamp: December 28, 2018, 07:37:50 pm
content: cheers thanks everyone