LINE Port LoopCurrent question
drgeoff:
A lot of words at http://www.sandman.com/loopcur.html. But what is genuinely useful and what is scaremongering?
SteveInWA:
I read that long article by Sandman, and it makes sense to me. Yes, he's selling hardware to mitigate or solve telco problems, but the advice is still sound. I didn't find any FUD or misleading information there at all.
I don't understand the comments stating it's extremely unlikely that a POTS telco could be at fault. Anything's possible.
The most definitive way to test this is to disconnect your premises (home, office, apartment, whatever) telphone wiring from the telco's service at their demarc box. Assuming that you don't own or have access to a telephone "butt set" or a telephone line 600 Ohm load tester, use an ordinary telephone, preferably an old fashioned "2500" model desk phone, or some other phone that you can remove the case and disconnect the line cord. Put a digital multimeter in series with the telephone line connections (inside the phone, disconnect one of the two wires leading to the modular line cord, then hook up the meter, one probe to the line cord side, and the other to the telephone. Leave the phone off hook. Set the meter to the highest current (amp) range. Plug the phone's modular plug into the modular jack on the telco demarc box. Read the current. It should NEVER be as high as 62mA; that would fry electronics. If it is significantly above 25mA, call the telco and demand that they look into it.
If it is within normal range, then you will need to troubleshoot the OBis. Their built-in voltage and current measurement feature may be bogus or fried on your units, but I have a 110, hardware version 2.8, and it properly reports normal voltage and current on my POTS line.
Mango:
drgeoff - thanks very much for the link. I bought their loop current regulator and it performs as advertised.
Obihai kindly replaced the OBi110 that was under warranty. I have installed the new OBi110 today behind the loop current regulator and it works perfectly. It's somewhat unfortunate that the OBi110 does not self-regulate loop current, but since the device was replaced for free I can't really complain.
Hopefully this puts an end to my premature hardware failures.
ProfTech:
That is all very interesting. My Obi is hardware 2.8. However there is a setting for the line port "CurrentLimitingEnable" that is UN Checked by default. The help screen says it will limit the loop current to 60 ma. Maybe the 2.8 hardware does a better job of handling excess current. My on hook line voltage reads 56 but the current only reads 29 ma with the box checked or unchecked. Doesn't change. Interesting find.
sailing:
I will venture a guess as to what is happening. We are talking about a dc current so we can easily apply Ohm's Law. (If is was an ac current, Ohm's law would still apply but it might complicate the explanation.) Ohm's Law is voltage=current x resistance. The voltage is the on hook reading with a voltmeter which is fixed. The current is dependent on the resistance. If you're close to the CO or if the wiring from the CO is larger then usual, the resistance will be lower. Hence you have too much current.
The original Ma Bell phones probably couldn't care less about currents that might be as high as 100mA. Electronic phones or adapters would be designed for a specific range. Currents over the expected range will cause clipping in the circuits, hence the distortion. Similar to overdriving audio amps.
Although this is a problem with today's electronics, the POTS and the Obi are not at fault. You just happen to be the lucky one that has to deal with a worst case situation.
Navigation
[0] Message Index
[#] Next page
[*] Previous page