Pairfone Intercomm Wiring Help Needed

[hatrick]

Thanks for all the help with this.  We do have a set of WWI field phones that we use to go from our bunker to the rear command.  I wanted to use these as a simple and inexpensive way to add commo to our front line.

I'll pick up a 6V lantern battery and see if that works. When I use a 4 AA pack the buzzer works pretty well and has decent volume (it would be better if it was a bit louder) but the main issue is that you can't hear anything through either of the receivers when you try to talk - or at best it is so faint it renders the set useless for talking. The 12V, albeit over-powered makes the buzzers very loud and the receivers work properly and you can talk over them normally. 

I've cleaned all of the contacts and the buzzer contacts already. I'll try tapping the units flat on the bench in case there is a carbon clumping issue.  If the 6V lantern battery doesn't work, I guess I can try a 9V battery pack (6 AA's or 6 D's) as an alternative that is at least a bit less then the 12V.

Just for my own knowledge, does having the higher voltage damage the units simply by running current through them or is the damage only done when you actually use the buzzer or when you go to use them??

Thanks,
Eric

[dsk]

Its not the voltage who kills the transmitter, it is the current. Do not apply more voltage than whats giving you a current of 50 milliamps. The ringing current may be much greater.

dsk

[G-Man]

 While in essence I agree with Dave regarding the use of excessive battery voltage, I am also mindful that these were not quality instruments even when they were new.

As I previously mentioned it appears that some of the brass strips have been overheated as if someone had made improper connections that may have caused internal damage that results in their present imperfect operation.

That said, at this point what is there to lose? I suggest continuing to use the higher battery voltage until they are no longer operable. Then, as Dave has previously suggested*, acquire either WWI or WWII field telephones to replace them.

(*correction- popular1)

[Mr. Bones]

I was planning on using 16 gauge military field phone wire for all three lines which I think will be fine.

It should, indeed. It will carry clear signal for quite the long distance. Gradually diminishing signals for even greater distances. Personal experience.

I am using them for WWI/WWII reenacting to run from our underground bunker to our front line trench.

Very cool! I'm all about Historical Reenactment, and Preservation. Do some of all that, as well as with Warbirds, Historical Military Vehicles, Mil Radio Gear.
IF you can't get the Pairphones to behave...
    I suggest getting a requisite number of TA-312 Field Phones. They're military, have olive drab cases, bags, etc., are even more historically accurate. 99.5+% of the viewing public will not know the difference. They're generally pretty available, affordable, reliable, relatively indestructible, weatherproof, and have a wet range of ~14 miles, wet conditions, to ~22 miles, dry. I'm guessing that this probably covers the scope of your reenactments.

If I can't fix them and get them running on a lower voltage, would having them hooked up to a higher voltage damage them if we were only using them 4-6 times in a weekend and only for 20-45 seconds at a time or is the damage done just by running current through them and not just when in use?

Short answer, yes. While it may work, for a short while, I can by no means recommend it. There should only be full power running through them when one station, or the other uses the PTT button, but...
     Mathematically, 12v would  be the same as sending 240v through your household 120v outlets and lights, or 480v through your electric range, or dryer. 24v, double that. Most probably, not a good long-term solution. BTW, Industrial Electrician, here. If it works, it works, but who can say for how long?

     I'm guessing, and hoping, that there is a far simpler solution to your problem with these Pairphones. There are many, ('most' here on the forum) that are far more enlightened than I, and are likely to come up with it. Until then, Endeavour to Persevere!

Good Luck, Eric!

[hatrick]

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..

[Mr. Bones]

Great,

     I hope it will work like a charm! I loves the easy fixes, I does, I'll warrant yer! BTW, the TA-312s were introduced in the '50's, and remain in use today, even in the US Armed Forces. There's a reason for that, given their technological age. They work, when nothing else does, or will.

    Mind you, though, Hide your Field Wire. Both we, and the 'Enemy' were fully aware of finding these commo wires; follow them to Command Posts, Listening Posts, Forward Artillery Observers, Observation Posts, etc. That, we did. Wish I had all the telephones. That'd be something, at least.

Best regards!

Best regards!

[Scotophor]

Glad to see that you got them working adequately.

We do have a set of WWI field phones that we use to go from our bunker to the rear command.  I wanted to use these as a simple and inexpensive way to add commo to our front line.

For a slightly more realistic approach, you could have the field 'phones in the forward field (trench to bunker) and the intercoms in the rear (bunker to command HQ). If your re-enactment area is a semi-permanent setup, you'll need to rewire it. If it isn't, well, you need to run wire every time you have an event, don't you?

[hatrick]

I wanted to thank everyone for all the help.  I still wish I better understood the Volt to Amp relationship but I guess that is something to keep working on.

Since there have been a lot of discussion on what phones to use and where... we are using our original WWI or WWII (depending on the event we are doing) filed phones to go back to the command bunker because they can plug into their switchboard and then transfer out.  The Paifone's were for the 150-200' from our living bunker to our front line.  I am keeping my eyes open for an older/wooden set of European intercomms but these should work for now.

Thanks,
Eric

[DavePEI]

I still wish I better understood the Volt to Amp relationship but I guess that is something to keep working on.

Hi Eric:

I hope this will give you a better understanding on how battery types relate to amperage.

Here is a chart I found for typical batteries. Note: It may not accurately reflect the output of the batteries you were using.

All of those below (AAA, AA, C, D, #6) produce 1 1/2 volts.

Battery Type  Capacity (ma/h) Typical Drain (ma)
AAA cell            1000                 10
AA cell              2000                 50
C cell                 6000                100
D cell                 12000              200
#6 dry cell         ---                   1500

6 volt lantern    11000               300


If you look at the chart above, size of the battery in no way effects the voltage rating. An AAA cell generates the same voltage as a D cell, 1 1/2 volts. The difference is the current rating is higher in the larger cells (as compared to other cells using the same chemistry.)

#6 dry cells were also 1 1/2 volts, but allowed larger current drain.

If you overload a cell amperage wise - you will generate heating of the battery and its voltage will drop. The lower the battery amperage rating, the more the voltage will drop.

Therefore. the larger batteries can support a higher current draw for a longer time than a smaller one can. Your AA battery may only be producing a fraction of a volt when a large amount of current is drawn from it. A D cell with the same current may still produce 1 1/2 volts.

4 AA cells in series will only produce 6 volts (no load), and still give a typical drain of 50 ma, but with a high current load may drop to 0 volts.

A 6 volt lantern battery will of course produce 6 volts, BUT can give a typical drain of 300 ma.

Therefore for a higher current application, the 6 volt lantern battery is the better choice, as it can support the drain for a very long time without the battery voltage dropping.

While none of these figures are exact, and will vary according to the ratings for your exact cells, I hope it will help you understand how an under rated battery will drop in voltage when too high a current is drawn from then.

So, put a high current on too small a cell, and it may no longer generate its rated voltage. Go to a larger battery, but stay within the rated voltage range..

Dave

[hatrick]

Dave,

That certainly helps out a bunch.  What I find interesting is that when I hook 6V lantern batteries in parallel to get a higher ma output while keeping the same 6V it does not multiply the ma output say 2X, 3X, 4X for how many batteries I hook together.  One 6V lantern battery was about 36ma but two together in parallel was only 48ma and when I hooked 4 together it was only 54ma.  I think I may look into a better 6V option that is rechargeable.  I'm sure there is some small brick style battery backup battery that would be better (and rechargeable). 

One final question on volts and amps... since when I hook up my multimeter I am trying to stay under 50ma output, what does that translate to in amps per hour?? I'm not sure how to make that calculation.

Thanks,
Eric

[DavePEI]

Dave,

That certainly helps out a bunch.  What I find interesting is that when I hook 6V lantern batteries in parallel to get a higher ma output while keeping the same 6V it does not multiply the ma output say 2X, 3X, 4X for how many batteries I hook together.  One 6V lantern battery was about 36ma but two together in parallel was only 48ma and when I hooked 4 together it was only 54ma.  I think I may look into a better 6V option that is rechargeable.  I'm sure there is some small brick style battery backup battery that would be better (and rechargeable). 

One final question on volts and amps... since when I hook up my multimeter I am trying to stay under 50ma output, what does that translate to in amps per hour?? I'm not sure how to make that calculation.

Thanks,
Eric

Ok, I will try to field that one. The 54 ma you are measuring is the total current drawn by the device, not the batteries. The batteries have to be able to supply at least that amount. If they can't, the voltage will drop below the rated voltage.

Amp/hour is the number of amps it can provide in an hour. Don't worry about the life of the 6 volt batteries. They should last a very long time.

Dave

[hatrick]

The 48ma and 54ma readings I am taking are directly from the 6V lantern batteries when I have them either 2 or 3 in parallel. I guess I need to figure out what the actual draw is of the Pairfones to get the best battery for them. Any advice on how to figure out what then need and not just what my battery packs are supplying??

Thanks,
Eric

[DavePEI]

The 48ma and 54ma readings I am taking are directly from the 6V lantern batteries when I have them either 2 or 3 in parallel. I guess I need to figure out what the actual draw is of the Pairfones to get the best battery for them. Any advice on how to figure out what then need and not just what my battery packs are supplying??

Thanks,
Eric

Quick question. Where are you placing the leads from the meter when you try to measure the current? For current, they should be in series with the load, and not across the load.

Dave

[hatrick]

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. 

I am assuming that more ma will make the mic/receiver stronger sounding which is why I am thinking I should get a 6V battery like the ones used for emergency lights or alarms but I don't have any idea what ah to get.  I am thinking at least a 6V 20ah or maybe a 6V 30ah battery.

Eric

[G-Man]

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. 

I am assuming that more ma will make the mic/receiver stronger sounding which is why I am thinking I should get a 6V battery like the ones used for emergency lights or alarms but I don't have any idea what ah to get.  I am thinking at least a 6V 20ah or maybe a 6V 30ah battery.

Eric

When you have your multimeter set to the amps position and you connect your leads across the batteries instead of in series with the load, you are most likely going to blow and internal fuse or burn-out the meter entirely.

Plus, increasing the current above 20-30ma through the transmitter and receiver is exactly what you do not want to do.