[NTLUG:Discuss] OT battery substitute

[Fred James]

agoats at compuserve.com wrote:
> First, let's understand batteries:
> AA sets the size and format and a nominal 1.5V charge based on a 
> carbon type cell. All other chemistries have different voltage and 
> current ratings even though they use the same size and format.
> Based on the chemistry of the battery, the current capability varies, 
> but is measured in mA/hr (milliamps per hour). This seems to range 
> from about 1200mA/hr to 2800mA/hr (or 1.2 to 2.8 Amps/hr). Current 
> draw is limited to the device and not the battery. A short causes the 
> battery to discharge completely, quickly, overheating the battery with 
> a possibility of catching fire or exploding. Voltage seems to vary 
> from about 1.2 Volts to 1.6 Volts based on the chemistry. NiCd, NiMH, 
> Li-ION, Carbon, Alkaline, Zinc and many other types of chemistries exist.
>
> Next, power supplies:
> The wall outlet is 120V AC and has to be converted to some voltage, 
> DC. This can be done with switching power supplies like the ones in 
> Computers and for most laptops. These are more efficient and generally 
> operate above 60Hz.
>
> The other type uses a transformer to drop the voltage down and other 
> circuits to set the DC voltage, it does typically have either a 60Hz 
> ripple or hum if single rectifier is used or doubled to 120 Hz if a 
> bridge rectifier is used. These depend on large value capacitors on 
> their output to reduce the amount of ripple or hum that exists at DC 
> levels.
> Current draw is limited to what the device pulls from the power supply 
> and no more. If the device is shorted, current draw is a maximum and 
> the power supply should have over current protection that shuts off 
> the power supply or trips a circuit breaker. If this fails, it will 
> either catch fire, explode the capacitor(s) in the power supply or 
> trip the house circuit breaker.
>
> EMI/RFI Chokes:
> These are typically ferrite based toroids that you wrap the cable 
> through so that AC or momentary surges are suppressed by interfering 
> (buck) or absorbing magnetic fields. If the choke is not designed for 
> the frequency you're trying to suppress, it won't work for you (it 
> will help with spikes, i.e., light switch current surges, lightening 
> strikes, etc but not your hum). A lot of the switching power supplies 
> operate at very high frequency and use ferrite chokes to block the 
> high frequency AC from your device.
>
> All that said.... you have a noisy AC power supply and need something 
> with less noise.  Higher current power is no issue unless the device 
> is bad.  Too high a voltage can be bad as it typically causes your 
> device to overheat trying to either regulate the power to a lower 
> voltage (has an internal voltage regulator) or by operating at the 
> higher voltage (Note that CPU's that operate at higher voltages are 
> faster AND require more cooling while the lower voltage CPU's which 
> are cooler and require less cooling; try comparing Pentium III vs. 
> Celeron, same frequency and class, but different Voltages).
>
> If you can, check the power supplies for the amount of "ripple" they 
> have at DC. The lower the ripple, the lower the noise.
>
> Most cheap "wall warts" are extremely noisy with high ripple, 
> frequently due to a cheap or too low value output capacitor (called a 
> "low frequency filter").
>
> If ultra low noise is required and you have to have an AC power 
> supply, a gimmick used is to run a power supply to a battery pack 
> (charging the battery pack) and the battery pack is used to drive the 
> device. There is a reason the battery is represented by multiple 
> polarized capacitors in series... it is a capacitor! Most of these 
> designs use lead acid batteries so you have to be careful about 
> instantaneous current draw and other such issues if you use some other 
> type, like maybe using a capacitor in parallel with the battery pack. 
> Based on the number of milli amps per hour and the charge equations 
> for capacitors, the battery is typically in the Farads, whereas the 
> typical capacitor is measured in micro Farads. Ripple is nearly 
> non-existent with these set ups.
>
> Alvin
>
>
>
> Fred James wrote:
>> OT battery substitute
>> This may seem contrary, but I have a couple of devices (land line 
>> phones) that require 4 AA batteries each and I want to substitute AC 
>> adapters for those batteries.
>>
>> Figuring 4 AA 1.5V DC batteries equals 6V DC, I tried a 6V AC to DC 
>> adapter and found two undesired effects
>>    (a) a light that is meant to blink when there is or has been a new 
>> or unanswered call, simply glowed steadily - as in all the time 
>> regardless of call activity
>>    (b) there was an annoying steady buzz in the receiver that 
>> continued throughout any and all calls - incoming and outgoing
>>
>> Now I think we can know that the device does not require a constant 
>> 6V DC because of course DC batteries do run down and while that is 
>> happening the devise continues to function properly.
>>    (a) I was told by a representative from a battery supplier that 
>> most 6V DC devices will continue to function well down to 5V DC
>>    (b) I had been running them on rechargeable batteries, which are 
>> rated at 1.2V DC each, or a total of 4.8V DC, without any issues
>>
>> My question may be moot because I have already ordered a pair of 5V 
>> DC adapters, but ...
>>
>> So to me, it seems possible that the 6V DC adapter is just too much 
>> power (volts or amps?), and I was wondering if there might be someway 
>> of mitigating the output from the adapter?
>>
>> By the way, I did measure the adapter and it shows a good 6.1V DC.
>> Thanks
>> Regards
>> Fred James
Alvin
Thank you for the explanation ... that does clear things up a bit ... 
let me ask a few questions to be sure, please?
(a) I spent <$5 on my "wall wart" so in fact I have a "noise" generator?
(b) there really isn't any "cheap" way to solve that?
(c) are there any 5 or 6 volt "wall warts" that aren't "noise" 
generators, and if so how can I tell, or at what price range should I be 
able to expect it to be "quiet"?
I persist in this adventure because I really would like to eliminate the 
batteries from the mix, and in searching for phones (for home use, with 
caller ID) they all seem to say "No AC required" ... short hand for you 
will need to supply 4 AA batteries for the caller ID feature to work.  
Could I be faulted for thinking that the batteries are a cheap way for 
the manufactures to get around the "noise" problem?
Thanks again
Regards
Fred James