<VV> Battery charger as signal generator

[Frank DuVal]

Mr Lew Rishel wrote:

>> ----------------------------------------------
>> Smitty Says:  Dang Lew, what he said was and I quote.  I ran a continuety 
>>test between the positive terminal and ground and got no reading.  Now 
>>that it has been deciphered, lay an answer on him.  gggg
>>
>>OK, Smitty, I can understand that, i think.  The normal ohms reading 
>>across the tach unit would be high,  above  6 K at the power post (to 
>>ground), and above 20 Meg at the signal input. If the reading is indeed 
>>open, the tach is defective, obviously. However, Smitty, he did say 'the 
>>sending unit'  and that confused me, because the sending unit for the tach 
>>is the distributor, unless things have changed recently. Have they ??
>>    
>>

Recently things have changed on modern cars, but the Corvair still uses 
the distributor to electrically drive the tach. Modern cars use crank or 
cam position sensors.

>Now, I have the proper signal generator to provide signal to the tach, so I 
>can calibrate it correctly. Forget this nonsense about 60 Hz, etc. Half-wave 
>means the tops of the sine waves are lopped off, this does not change the 
>frequency. Anybody want argue this ??
>
>  
>

No argument for a half wave (single diode) charger. But, most I have 
worked on have a full wave rectifier (two diodes with center tapped 
transformer) which adds the bottom rectified half to the top rectified 
half of the sine wave, giving 120 Hz output.

BTW, even in a working tach circuit, there could be infinite (or very 
high) resistance from the tach input to ground if there is a capacitor 
to couple the signal in.

Frank DuVal