Solved ignition noise problem...thanks all!

[Sandy]

Good idea, but here is the problem, it's 2, yes, 2 thing in one. ;-) 

The diode does protect against reverse voltage, but it also keeps the
charge on the input filter caps if the voltage dips below what are in the
caps. Think of this, you turn on the key, the caps are sitting at 12V, you
crank the engine, your voltage drops due to the starter motors large draw.
Now the input filter which is at a higher potential then the battery now
can't discharge through the diode to help power your starter, it gets
applied to the input of the regulator. In pratice, I'm not sure how much it
will help, but in theory it is a good idea! Also make sure that on the
input you use a bi-directional TVS as who the hell knows what kind and
which polarity the spikes can be. Either way will work, but this costs only
about a volt in drop, and is not destructive if the battery is reversed.


Sandy

At 01:46 PM 5/16/98 -0700, you wrote:
>Is the 3 Amp diode in series for protection against reverse polarity 
>connection ?  If it is I have done this in another way - I have put a 
>diode in reverse direction in parallel with the whole circuit, then the 
>whole is connected to the battery through a high currect fuse.  Like 
>this if the circuit is connected wrongly the diode becomes a short 
>circuit and blows the fuse.  The fuse can also be made some 10A so that 
>it does not drop any signifigant voltage.
>Sorry if I went off track but I think the above is a good idea.
>Michael
>>
>>That is very similar to what I have, main power through a fuse, a TVS 
>to
>>ground, 3 Amp diode feeding an inductors and related filter caps.  I 
>think
>>the inductor does more then I think, but who knows, I have not tried it
>>without it. The diode in series is costly, but I think could be worth 
>it.
>>The Low Drop out Regs are nice, and they are not that hard to get from
>>Digi-Key. The best thing is they are drop in, and high temp to boot.
>>
>>Sandy
>>
>
>
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