Registered: Dec 2000
Location:
Posts: 2

i recently got a thincom modem as part of my christmas present and while everything seems to be working okay with it, i did have a question (if only to see if i'm being paranoid). after about 10 minutes of usage, it seems to generate a bit of heat. not a lot, but definitely noticable. since this is my first time with a module, can anyone tell me it this is normal? thanks for the help.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

It's normal. Mine does it, too. The Xircom SpringPort gets warm as well. Personally, I think of it as a subtle reminder to check the batteries!

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Registered: Dec 2000
Location:
Posts: 2

thanks for the reply. it's nice to know that i'm not really losing my mind after all...or maybe it's the other way around. regardless, you put this paranoid's mind at ease!

Registered: Sep 2000
Location:
Posts: 33

This has been an issue which has generated a bit of confusion on some customers' part -- so we would like to clarify:

There are two potential sources of heat (thermal dissipation) from a modem:

1. Heat generated from the digital portion (processing, etc.) of the modem. This heat is basically coming from battery energy.

2. Heat generated by the DAA (direct access arrangement), which is the circuitry which must interface with the telephone line. The energy producing this heat comes from your telephone company's CENTRAL OFFICE BATTERIES (or power supplies).

In general, heat listed in '2' above is generated by ALL telecommunications equipment which goes 'off-hook' on a telephone line. This is because the telephone ITU standard requires that any telephone, modem, answering machine, etc., essentially 'short' the phone line with a specified resistance curve to generate an 'off-hook' condition. This results in generated heat. The amount of heat generated varies depending on the resistance and other factors of your particular phone line.

So, all phone equipment generates heat listed in 2 above. It is generally not noticeable, though, because telephones and the like are rather large and the heat dissipates and spreads internally.

A typical heat generated by 2 above is P=IV (power = current * voltage) = P = 25mA * 10Volts = 250mW (1/4 watt). In a small package, such as Thinmodem, this heat is very noticeable.

Heat generated by #1 above varies depending on the processor/DSP and its corresponding efficiency. I large generalization, it takes 30-50 MIPS to perform modem functionality. For Thinmodem (which is extremely low power, btw), the consumption from the battery runs at approximately 45mA while on-line, transferring data, etc. Running at 3.3V, P=IV = 45mA*3.3 = 145mW. However, this power doesn't all translate directly to heat in the same manner as #2, which is basically a few components acting like a big resistor.

So, if you were to open up your Thinmodem (we don't suggest this, btw), and surf with it, you'll find that the DSP (digital signal processor) doing all of the thinking feels cool or room temperature to the touch, but a few components on the DAA (a transistor and resistor, specifically), will be rather warm. These latter parts are generating the heat you feel near the upper end of the back of the modem.

I should note that a *typical* portable modem consumes 120-150mA at 3.3V. This translates to 120mA*3.3 = ~400mW of processing heat generated.

-Card Access