 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : SMALL UPS...
  Page 2 of 5   |
|||||
| Author | Message | ||||
phil99 Guru  Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
To comply with that regulation I think you must use "Extra Low Voltage" which is up to 32VAC. Above that is "Low Voltage" and treated the same as mains voltage. Garden lighting systems usually use 24V to avoid the more stringent LV regulations. Long, long ago I was a sparkie and unless the definitions have changed since then this is how it goes for AC:- Extra Low Voltage is up to 32V. Low voltage is greater than 32V but not more than 250V. Medium voltage is greater than 250V but not more than 660V. High voltage is greater than 660V. These are Nominal voltages and can be exceeded by the same percentage that the supply voltage exceeds its nominal voltage. Eg. if the mains is 10% high the output of a 32V transformer can be up to 35.2V and still be ELV. DC has different definitions. Edited 2024-05-31 11:36 by phil99 |
||||
bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Phil, When I was doing my cabling course for my cabling license (and later Cat5 addition), it was Austel in those days. I am sure they told us that Low Voltage was upto 1500 Volts. I am not arguing about it and, of course I wasn’t learning to be a sparky but that is what they told us in the course(s). We thought at the time that it was pretty high for ‘low voltage’ but I suppose it is when compared to 66kV transmission lines. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
||||
TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6097 |
Then it depends on the installation. The upper limits may be lower if associated with LV. AS3000 refers to 25V AC in some situations. There is a whole book of rules for ELV. (I don't have it) Jim Edited 2024-05-31 13:01 by TassyJim VK7JH MMedit MMBasic Help |
||||
Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Yes, I thought that 50vAC was the maximum here classified as ELV, so that quote jives with my memory of the regulations. The telephone cables would be fine on that voltage, in fact, the old copper line "Ringing voltage" is somewhere in that ballpark from what I remember. Not sure how good the phone crimps and KRONE strip connectors would be a passing current though. In a phone circuit, it is next to nothing. Repurposing the existing infrastructure to power TV amps might exceed their capabilities. Something else to think about! Smoke makes things work. When the smoke gets out, it stops! |
||||
OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 926 |
Grogs, you may remember that the cabling is designed to handle ring current at 60vac as well as speech. I cant recall the exact current but it could make some noise.  0A47 |
||||
| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
It seems the regulations have changed in the last half century. Re phone cables, the two standard sizes were 0.4 sq.mm for Exchange lines and 0.2 sq.mm for Customer lines. Assuming these are 2 pair customer lines and you parallel the pairs you may be good for 4A. That should be more than enough at 48V. May even work at 24V. I base this on 10A cable being 1.0 sq.mm. A backwards 240/48V transformer at the load end should do the job. Even if there is quite a big voltage drop the amp will work down to 110V. |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Yes, that sounds like the business! This is how I am looking at doing it now, moving forward. My only question at this point if using the 48/230 transformer in reverse, is will the impedance of the 230v winding, be an issue with the switch-mode PSU when it tries to start? Most SMPSU's have a quite hefty inrush start-up current, and I wonder if a tranny in reverse will have enough grunt to get it to start? I might build a test rig on the bench, and try an amp on it. If it starts, fab. If it does not....well - back to the drawing board! Smoke makes things work. When the smoke gets out, it stops! |
||||
| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
As the amps have such a wide operating voltage it should be ok. For your test add some resistance to the 48V leg to simulate the phone line resistance. Looked up the wire tables. 0.2 sq.mm is rated at 2A with a resistance of 0.1Ω/m For a 50m run length = 100m x 0.1Ω = 10Ω per pair so 5Ω for 2 in parallel. |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4223 |
Grogster, I have no idea about the size of the network, and if the back channel is used as well (internet), or that it is only 1 direction. In case it is one direction and a relatively small network (20 houses or so) you may be able to beef the signal at the input (the antenna's, the head-end) and use passibe -20dB pickups (splitters) at each extension (input of the Televes)(*). These are passive, and will pass signal to the next regardless the Televes is powered or not. In case the network it is larger you can use a similar topology, but you need active splitters. I know these exist. The active splitters can be powered from a DC voltage that is added to the RF on the COAX. This is common technology in satellite connections (1-2GHz) but will also exist for TV signals. Another option could be to add a coax relay to the pass-through connection of the TeleVes. Power the COAX relay from same 230V (phone charger) that poweres the Televes. Once the Televes looses power, the COAX relay will switch to pass the input signal of the Televes to the output. The next houyse will get a slightly weaker signal, but it may solve the issue. Volhout (*) since the signal gets weaker due to cable losses and signal being routed to Televes units along the run, the first houses may need -20dB pickups, the later houses -10dB or -6dB or -3dB. Edited 2024-05-31 17:49 by Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4223 |
Something like this (make a small PCB, but make sure you design for 75ohm tracks, and use suitible connectors).  And this circuit:  Regards, Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Yes, that is another good idea - had not considered coax relays. Something else to think about. Lots of lovely ideas being thrown around here - thanks chums!  Smoke makes things work. When the smoke gets out, it stops! |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
UPDATE: At this point, I am planning to go down the path of a distributed LV AC via the old unused phone cables. Planning on using 30v AC, as I can get transformers for that voltage easy. The supply transformer will be able to push out up to 6A @ 30v AC, and this will go out via the phone cables to all the amps. At the amp locations, I will use standard transformers in reverse, to boost the LV back up to around 150v or so(or 230v), to power the amps. These transformers etc, will all be fully insulated for safety etc. The PSU transformer will be multi-fused, in that each of the outputs connected via phone pairs, will be fused - simple but effective. The next thing I will do, is get a couple of the transformers setup as a HV-LV-HV arrangement, and connect a test switchmode device to the final output, and see if it is able to start the SMPSU, cos if the setup CAN'T, then that's pretty much as far as that idea will go - unless someone comes up with a way to deal with the startup load of most SMPSU's.  Smoke makes things work. When the smoke gets out, it stops! |
||||
Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6783 |
Hmmm.... I hope my creaky maths brain is working. It might be a bit early for me yet. :) Consumption per device, say 20W to start up. That's 70mA at 230V but 670mA at 30V 22 AWG has a resistance of 16.46R per 1000ft. You might be lucky and have bigger pairs or you might be unlucky and have poor joints somewhere. If you said a distribution run was 500ft (i.e. 1000ft loop length - and it won't be in a straight line so you might easily double that for phone runs via junction boxes) that would give a loop volt drop of 16.46R * 0.666A = 11V. You get 30-11=19V at the load end. Running two pairs in parallel gives you half the volt drop, so 25.5V at the load. The transformer ratio is 7.666:1, so with 19V in you step up to 145.666V and with 25.5V in you get 195.5V. These are assuming max efficiency, which you won't get so the voltages will be a bit lower. It would be informative to short out a pair at each location then measure the loop resistances from your supply point with a suitable meter. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
I might arrange a purposeful short on a few unused pairs in the next few days. There is not really any realistic way to say how long each run is, as it is a something of a "Star off of star" wiring arrangement. You have the main trunk cables(50 or 100 pair) running around the village, but all sorts of other cables spliced into those as and when a house was finished and needed phone service. The sub-cables can be anything from 2-pair to 25-pair. All are grease-filled underground phone cables though, so they have stood up well against the moisture over the years. The point being, that a short on one pair to one location, probably will have no relevance in resistance, to another pair to another location, due to the star-from-star arrangement. Ultimately, even if I can only get 120vAC or so, those amps should work due to the wide input supply voltage range. As I say, I still need to bench-test the concept before I start doing anything at all, and that bench-testing will be the next step. Smoke makes things work. When the smoke gets out, it stops! |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4223 |
When they are phone lines, they are 600ohm. Do a time-domain-reflection tes, and you can see how long it takes for the reflection to show. Read u p on TDR. A simple square wave generator and oscilloscope and 600ohm resistor is all you need. Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
BENCH TESTING:  This is the very standard HV-LV-LV-HV transformer arrangement. (sometimes called HV-LV-HV) A happy 230vAC at the other end of the 100-meter link of speaker cable. (no load) Yes, I laid the entire roll out flat, I did not leave it all coiled-up on the roll, which would affect the results. Please ignore the direct 230v outlet to the clips of the "TX" transformer - this is NOT something anyone not competent with using live 230vAC should EVER use, but I have been using "Hot leads" like this for years, and due to my training, I know what I am doing. Note I still wrap the phase up in PVC tape. ...but I digress in the name of safety...  There is nothing special about this photo - it is basic transformer theory from the days of old and when we ALL learned about the benefits of AC power distribution.(vs DC) These transformers are single-phase 230vAC input, and 30vAC output @ 1 amp. The next thing to try, is seeing if a relatively modern switch-mode PSU of 15-20W, can start using the relatively high-impedance "New" 230v supply. I plan to use a Video Cassette Recorder as an experimental load, as it is about the same 15-20W load I am expecting at the far end for the TV amps, and therefore any "INRUSH" start-up current should be something of or about the same figure. Enough of this!  I'll keep the thread updated! Beer time now!  Smoke makes things work. When the smoke gets out, it stops! |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4223 |
Hi Grogster, A system like this would present a relatively high mains impedance for the Televes units. Especially including the long wiring runs. If you get "unexpected" results in your test, please understand that small (switchmode) power supplies as used in the Televes units have a low power factor. There is no power factor correction in these low power switchmode supplies (legally not required, so for cost reasons omitted). This could give a low efficiency with a high impedance mains source. So... they doe not behave as "load resistors". Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6783 |
I "liberated" a lovely mains test block from work when I retired, since I was the only person that used it. The RS version of the Cliff Quicktest QT1. The reversed transformer systems are useful for valve equipment now, as proper valve mains transformers are stupidly expensive. An incoming transformer giving 12V can handle two 6.3V heaters in series directly and also the reversed transformer to give an isolated 230V or 110-0-110. That gives roughly 155VDC or 325VDC for the HT rail. . Edited 2024-06-06 20:42 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Totally agree, and that is why I wanted to do at least a basic bench-test of the concept before I do anything on-site so to speak. As you say, the "RX" 230v for the amp, is going to be relatively high-impedance compared to connecting directly to the mains(which is relatively low impedance), and so I just want to see what happens on the bench first. The first test will be the VCR - if it starts and runs OK, I will then do some AC-clamp-meter current testing, followed by a TEMPORARY connection to one of the Televes amps that feeds the smallest number of units, then I can also put my digital TV and/or spectrum analyser on the output of the amp, and see if there is any dramatic change in output or signal level - QC check etc. All of this is just experimental at this point - nothing set in stone - don't worry! Smoke makes things work. When the smoke gets out, it stops! |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
UPDATE: Despite the relatively high-impedance of the "New" 230v out of the receiving transformer, the test VCR started up just fine with no issues, and it is a SMPSU based unit. Current in the 30vAC side of the link, is around 350-400mA, which sounds about right. I might try loading it up with more stuff, just to see how far I can push it! But this is encouraging, so the next step will be to connect this arrangement temporarily to a phone pair, and see if I can start one of the Televes amps on it. I have more testing-and-monitoring to do yet, but the initial test worked well, so that is a plus! I was kinda expecting the VCR PSU to not start due to the high-impedance of the "New" 230vAC. Most(if not all) SMPSU's have an initial inrush current that can be upwards of 20A or more, just for a fraction of a second while the PSU gets running. The low-impedance of the normal mains handles that without issue, but the high impedance of this kind of setup can often prevent SMPSU's from starting at all. Mains inverters had that as a common problem for YEARS, but it seems that the pure sine-wave inverters are much better at handling startup surges. But historically, many an inverter flatly refused to start anything with a SMPSU in it! Smoke makes things work. When the smoke gets out, it stops! |
||||
| Page 2 of 5 |
|||||
 Print this page |
