sundance-communications.com/forum Forums General General Telephone & Systems Information loop current

If that's the way you want to do it Michael, go for it. Like I said previously, it can be done with resistors.

Using the same Ohm's law, wouldn't that lower the T/R voltage considerably?

65 ma is way too high. Watts X amps = Volts So If his ma loop current is high his voltage is also high. It's a proportional inverse relationship to a certain extent.

If im wrong please correct me. I have used the combination of correct resistors but Sandman's unit works like a charm every time. It even gets rid of the Caller Id chirp. I bet the customer is right near the Central Office.

I have 75ma around here pretty common. It's doesn't effect your idle voltage and off hook voltage is about normal also. I know this is another post, but I'll try to briefly do this again. The LEC's used to used reg's to boost loop current to distant locations, they found it is far cheaper to boost loop current for everyone and let us worry about any problems that occur. So 75ma close to the CO translates to them being able to push voice over copper about 10 miles, where as prior to raising the current you had to add regs after about 4 miles if there is no carrier involved. I installed tons of 2a and 5a regs, they are no longer used at all.

dexman is right if you use the resistor method then put a 600 ohm on each side of line this will lower current and volume the Sandman devices are worth saving the hassle

The biggest problem I have seen is these key systems don't have alot of tolerance built into them.

The addition of a resistor or resistors will decrease the voltage between the tip and the ring when the phone is off the hook. However it will not measurably affect the voltage when the phone is on hook. The on-hook voltage should always be right around 48 Volts DC, which is the battery voltage in the phone company's central office.

That is one spec I'd like to see. I called Mike Sandman and spoke to him (very smart man), but I can't get anyone to show me that spec. There is an old graph I found in the ANSI standard which I interpret to read 23 low 45 high. But there is also a part of the graph that can be interpreted to read 125ma and I'm almost sure that is what the LEC is going by. I sent the graph and all supporting documents to Qwest and a few months later I asked them to send proof that 75ma was with-in limits. I got back the copies of the same documents I sent and I mean the same, my notes still in the margin! So like I said, I tried and tried to get someone, anyone to give me the supporting documents and have yet to receive them. OK just search "loop current" for the rest of the story.

well I hope you didn't use my name

have had some good conversations with mike over the years .

so he couldn't give you the spec ?

I just read it on his site and took it as fact , when I find high current Ive never called the telco about it just put on the regulators .

evan if we could get the telco to turn it down I would be concerned it might go up at a later date and start causing problems again

The voltage drop across any resistor is always proportional to the amount of its resistance. Here is a circuit diagram I borrowed from Wikipedia. Now in this figure, R1 is the total resistance from the central office to the phone set on the ring conductor, R2 is the resistance of the phone set, and R3 is the resistance from the phone set back to the central office on the tip conductor.

If you increase R1, then v1 will increase while v2 and v3 will decrease. If you increase R1 and R2 equally, then v1 and v3 will increase equally while v2 will decrease.



Now when the phone is on hook, R2 is extremely high and so v2 is practically equal to v4, the battery voltage. When the phone goes off hook, R2 is generally around 200 ohms, so v2 drops quite a bit, generally to around 5 or 6 volts.

If the sum of R1 + R3 is too low, then both v2 and current will be too high, meaning the telephone set is getting too much power.