Pairfone Intercomm Wiring Help Needed

[DavePEI]

I set up my 6V lantern batteries in parallel so they are hooked up positive to positive and negative to negative (or p to p to p and n to n to n with 3 batteries) and then I attach the positive lead on my multimeter to the positive and negative to negative. 

It confuses me that the ma doesn't double or triple when attaching additional batteries. It only goes from 36ma for one battery to 48ma for two in parallel to 54 for three in parallel. 

Look, Eric:

Read the instructions for your meter. You are NOT using it correctly. You can't have the meter on one of the ma ranges because if you did, the meter would be pinned to the right side.

With the leads across the batteries, you are set to measure voltage, and not current. Your dial needs to be set to the volts ranges (ranges vary according to meters, so this is why I say to read the directions for your meter.)

If this is so, what your are reading is actually voltage, and that indicates your batteries are not up to snuff for new batteries. All should measure 6.0 volts. I think it more likely you are seeing readings or 3.6, 4.8. and 5.4 volts.

To measure amps or current, you need to place the red lead on the battery post, and the other (black)  on the input wire to the load. The other load from the load goes to the negative on the battery. The meter does not go across either the battery or the load - it goes in series with it. Then switch the meter to the amperage or ma scale as per its instructions.

So none of your readings are valid. You really need to thoroughly read your meter's instructions. If you don't have them, there are any number of good tutorials on meters and basic electricity on the web...

Dave

[hatrick]

My multimeter has multiple functions and I am getting a correct 6V reading +/- .1V when I am testing for voltage when I test a single battery or when I test multiple batteries set up in parallel.  When I switch my multimeter to read ma is when I am getting the 36, 48 and 54 ma readings. 

[DavePEI]

My multimeter has multiple functions and I am getting a correct 6V reading +/- .1V when I am testing for voltage when I test a single battery or when I test multiple batteries set up in parallel.  When I switch my multimeter to read ma is when I am getting the 36, 48 and 54 ma readings.

Yes, but if you have the positive lead of the meter to the positive terminal of the battery and the negative lead of the meter to the negative terming of the battery as you said you did, you cannot read ma. The meter has to be in series with the load.

I suspect that one of your three batteries is low in voltage. Measure their voltage individually and not connected to each other. If one had a significantly lower voltage, discard that battery.

Remember voltage is measured in parallel with the battery.

Amperage is measured in series with the load.

Dave

[Scotophor]

If you are using good 6 volt batteries, and a load less than 100 mA, with the meter properly inserted into the circuit in series to take a current reading, then the number of batteries in parallel should have NO effect whatsoever on the current reading. Since you got 3 different current readings, you must have made some sort of mistake. Check the meter connection diagrams above again carefully - the "X in a circle" symbol represents the load. Since your intercom circuit is a bit more complicated, what you need to do to measure current is to disconnect one of the wires between your battery pack and one of the interphones' terminal #2, and insert your meter between those points.

With the meter connected like this, you should get zero current (or very close to it) with both interphones on-hook, a certain current reading with one phone off-hook (buzzer sounding), and another current reading with both phones off-hook (voice circuit). If your meter is digital, you will probably get a very erratic reading with the buzzer sounding; an analog (needle) meter is better for that purpose. The current for the buzzer will likely be much higher than the voice circuit current. Also, in case the phones have carbon mics, they will work best in an upright or near-upright position. If you neglected that factor before now, that might possibly explain the low volume problem you mentioned. If you have carbon mics and you moved the phones at all between taking different voice current measurements, you would get different readings too.

[hatrick]

My reading were just from the 6V batteries and not taken with the phones hooked up.  I wanted to just test the volts and ma of the power supply before attaching them to the unit.

It must have carbon mics since the mics didn't work at all when they were laying flat on the bench but started working when I stood them upright.

Eric

[DavePEI]

My reading were just from the 6V batteries and not taken with the phones hooked up.  I wanted to just test the volts and ma of the power supply before attaching them to the unit.

It must have carbon mics since the mics didn't work at all when they were laying flat on the bench but started working when I stood them upright.

Eric

There are NO ma with no load. That is why a battery will last for a very long time if not used - there is no current drain on it. Essentially amps/ma tell you how many electrons are flowing in the wire. None flow without a load. Essentially with no load, you have an infinite resistance between the positive and the negative on the battery so no current flows. Ma are a measure of current. Amps/ma can only be measured in between the battery and the load.

Likewise, as the hook switch disconnects the battery when not in use, you will get no current showing on the meter unless you lift one of the receivers or press the buzzer button. Then current will flow and the current can be measured.

The current rating published for a battery is only the MAXIMUM current which can be drawn from the battery in use without drawing down the battery.

On the other hand, volts tell you how hard those electrons are being pushed. Volts can only be measured across the battery or across the load. Only voltage can be measured without load.

Don't let the errant measurements you got confuse you. What you were seeing could only have been the effect of the meter protection circuit protecting the meter from the incorrect placement of the leads. If it had no protection, the meter would have gone up in a puff of smoke. Essentially measuring that way, you would have been placing a short circuit across the battery.

THE ONLY WAY TO MEASURE THE CURRENT IS TO MEASURE IT BETWEEN THE BATTERY AND THE LOAD. IN OTHER WORDS FROM THE BATTERY POSITIVE TERMINAL TO THE POSITIVE LOAD TERMINAL. You cannot measure current across the battery.

Dave

[G-Man]

 To reinforce what Dave and others have already stated, perhaps viewing these Youtube videos will help explain how to measure DC Volts and Amps.

http://www.youtube.com/watch?v=DmnsIBFx3UQ

https://www.youtube.com/watch?v=HWA9WqSEjg8

http://www.youtube.com/watch?v=rwHOHADRQ8g

[dsk]

I think I may have a workable solution.  I hooked up two 6V lantern batteries running in parallel so it is 6V and 48mA.  The buzzers are perfect and the receivers are working ok... could be a bit louder but it should suffice.  At least I am in the right voltage and miliamp ranges that are being recommended so hopefully no damage will be done.

Also, we do have w model 1917 field phones we use for WWI and a number of WWII British and EE8 phones.  The intercomms were supposed to be a cheap and easy solution for short range commo and they look pretty cool..

I guess this are good! The parallel of the 6 V batteries should not be needed, but if the ringers draws high current , it still may be needed.  The use of Field telephones should work better on long bad lines, the make and model will be of less importance. The newer the longer range, and better sound, but even an pre WW1 set should do the job.

Maybe a pair captured from the Germans might be of interest? http://tinyurl.com/nsj8h4p

Regarding the volts and amps thing.  When the current exceeds 50-60 milliamps the transmitter's carbon granulate may be burned. This is the reason for keeping the std local battery voltage at about 2 cells or 3 V. When the current has to go trough the receiver, and long lines, more voltage are needed to "press " the current trough the higher resistance. We get a voltage drop trough the system theoretically lost as heat, but this are so small that you can not feel it.

dsk

[Scotophor]

My reading were just from the 6V batteries and not taken with the phones hooked up.  I wanted to just test the volts and ma of the power supply before attaching them to the unit.

If you have a meter set to milliamps and connect it across a battery with nothing else in series with the meter, what you will be doing is one of the following:

   
• Blow a fuse in the meter!
• Damage or destroy the meter!
• Activate the meter's built-in overcurrent protection circuit (if it happens to have one).
• Measure the battery's maximum output current.

None of those will be useful in your present situation. Typically a 6V lantern battery should be able to output several AMPS (thousands of milliamps). Even a typical D cell can put out over an amp into a short circuit, which is essentially what an ammeter across the battery terminals is. NiCd rechargeable cells have especially low internal resistance and can put out several amps even from smaller cell sizes. High-drain NiCd cells used in RC racing can output dozens of amps!

What all of this alludes to, is that anyone using a meter with current measuring capacity needs to be very careful when taking current measurements, and especially when finished taking current measurements. ALWAYS be sure to switch the meter out of current mode when done taking a current measurement. Most meters require the use of a separate socket for at least one of the test probe leads when measuring current. It is MOST IMPORTANT to unplug the lead from this socket when not doing current measurement, to protect the meter or fuse (and possibly yourself) from damage, in case you later absent-mindedly grab the leads and put them across a power source (intending to take a voltage measurement) without first checking which mode the meter is set up for.

[dsk]

I'm wondering if we are talking about the same thing.
Since my English sometimes are a little more Norwegian than yours...
I have made a modification of the pic. posted earlier.
The picture shows how I would have put the amp meter.
The readings will wary with the sound level, usually highest at silence. It should not exceed 50 milli-Amps!
When ringing, it is another thin, it may be much greater, and the amp meter might need to change to another range metering up to at least 2 Amp.  The Voltage should be adjusted to keep the voice current up to 50 mA.   
This simple type of intercom has common voltage for voice and ringing and may get problems at high resistance lines. 

Now to the pure guessing: My guess are that 6V will do no harm, 12V may harm the transmitter.
If the battery was measured with amp-meter between battery poles either the battery are extremely bad, or the meter will be overloaded, and broken (fuse broken?). 

dsk

[poplar1]

Sometimes a picture helps:

http://www.ebay.com/itm/261443988954

[dsk]

Sometimes a picture helps:

http://www.ebay.com/itm/261443988954

This is my first time criticizing you, but this are a rather bad joke when we try to explain how to measure millamps trough a voice circuit.
The Voltmeter in your picture are an excellent tool measuring voltage over a single huge battery sell under load of a high amp load across the battery, but her it is just confusing. In another setting this joke would have been great fun.

Regards

dsk

[poplar1]

Sorry. I thought anything I said would detract from the message---which is: there is no way to measure amps with this Weston meter, and in fact it *is* designed to connect directly to the output of the battery, without a load in series. The point is that when you are connecting directly to the battery terminals, you are measuring Volts, and nothing else.

Sometimes a picture helps:

http://www.ebay.com/itm/261443988954

This is my first time criticizing you, but this are a rather bad joke when we try to explain how to measure millamps trough a voice circuit.
The Voltmeter in your picture are an excellent tool measuring voltage over a single huge battery sell under load of a high amp load across the battery, but her it is just confusing. In another setting this joke would have been great fun.

Regards

dsk

[dsk]

That makes Sense. I will absolutely give you right in that, the battery voltage at no load do not tell anything of its capacity of delivering current (or wattage).  Please excuse me for getting a little bit harm when you only dropped a picture I deemed to just be confusing.

dsk