Tens Machine

Hello all, I have been using a Tens Machine for many years and still use one which must be 25 years old, the up to date models are better and have more options. The reason for this question is that the original Tens had a fault, I remember I was in a hotel I switched the Tens on the

four pads were placed on my lower back, as I switched it on I was knocked to my knees to the floor, and was left with four red type shock burns on my back, it automatically switched on at 10 the maximum. The power from these machines is amazing using three AAA batteries and the batteries last a very long time,the original Tens can be left on all night the new ones switch off after half an hour, this only happened once so that's why I still use it. My question is how can three AAA batteries have that power and last a long time in use. I've used the search on the forum with no results.

Bob

What is a Tens Machine ?

Transcutaneous electrical nerve stimulation machine;

Russell

Google tens machine there are a lot of different circuit diagrams
around for these things.

Look at this and it will give an indication of how these things work.

https://www.learningelectronics.net/circuits/transcutaneous-electrical-nerve_03.html

John

The answer is that while the instantaneous power can be high the average power is low as a result of the pulses being short.

Russell

They are useful for blocking pain signals, often used by pregnant women for pain relief. Obviously they are useful for pain relief by men as well.

Mike

Used primarily for pain relief, but also used in BDSM and other erotic games.

Although the voltages are reasonably high, tens to a hundred or so volts, the currents and duty cycles are low. Thus power ls low and AAA batteries are perfectly adequate.

Andrew

Do you remember these?

Hard to think of a way in which a TENS machine could cause a severe shock and even mild burns.

Burns require a high current to flow in the victim and a TENS unit doesn't allow that. A battery of small dry-cells power a low-voltage, low-current oscillator that pulses a step-up transformer to create mild electric tingle. (The tingle suppresses other pain by providing a counter-irritant. How well they work depends on the type of pain; anything between good and makes it worse. Well worth trying, but not a guaranteed miracle cure. )

The normal peak voltage is probably between 100 and 200V, but the amount of energy in each pulse is limited by the maximum current of the battery, the drive transistor, and the size of the transformer - all small.

Possibly a combination:

• Unit fitted with high capacity rechargeable or alkaline cells rather than dry cells with high internal resistances. (Allowing the battery to deliver much more current.)
• Condensation reduced the value of a resistor causing the oscillator to vibrate at higher than normal frequency. (Each pulse contains normal energy, but there are a lot more of them per second.)
• The higher than normal frequency happened to be resonant with the transformer causing exceptionally high voltage on the pads.

Although such a malfunction might deliver a surprising extra shock, especially to a damp victim, I'm still surprised a TENS unit caused visible damage. They aren't Widow Makers!

Condensation might explain why the unit is working normally now. Drying out would return the oscillator to it's correct operating range.

If condensation was the cause, the effect was downright unlucky because damp circuit boards are unlikely to work at all!

Dave

If the Tens pads are on my back for 24 hrs or more a visible and skin change in texture occurs, this is why I think up to date Tens have a max of 30 minutes. At the time of that full power shock I wished I took a photo of it as the marks were viable for a week or so. I use the Tens on 4, the most I can stand is 7, no way can I take 10. They are recommended for use with arthritis and strains, but not a cure just pain relief. In my opinion they are cheap to buy and no need for Paracetamol or any over the counter pain relief.

Bob

Just got a TENS machine myself and I must say it is quite effective in blocking the back ache/sciatica I'm having at the moment.

The unit I have can be switched between 10-60 minutes in duration, with a default of 20.

There are about 20 programmed settings which can be varied in their intensity, but I find about 70% power output to be good for me.

I too experienced a couple enormous shocks the other day and thought that was due to me trying one of the other programmes, but it actually turned out to be that the gel pads weren't fully plugged in, so I'm assuming the unit must have generated a voltage sufficient to jump the gap.

Martin.

Yes, I had one

When mine old one gave up after many years I purchased one from Lloyds chemist and glad to say it was not that expensive it does as you say have more options

H

That's a smaller version of the "Trembler coil" used in the ignition of the Ford Model T motor car.

Russell

I've used TENS for phantom limb pain and once when one pad was slightly dry it did leave a small burn.

I also found that the effect was considerably more powerful if one of the pads became unplugged or fell off, no burns though.

I bought it when I had killer sciatica last year, and it made my evenings much more bearable (sitting down was when the pain was worst). Martin's one sounds similar - I tried all the different settings at first but settled on the basic one at about 2/3 power and restarted the thing whenever it timed out - just having it running was more important than the level, and using maximum power definitely falls into the more... adventurous category of use as mentioned by Andrew.