electrical system and design

I just have a few questions regarding my electrical system design. Just so you know I have a 1992 Galant VR4. Here is what my system diagram looks like. Can you guys let me know if you think I need to change anything? My direct questions are this: 1. What size fuse should I use everywhere? I am not 100% sure what I should be using. 2. Is there anywhere else I should be putting a fuse? 3. Do you think its a good idea to put a capacitor into this system between the distribution block and battery? Or would a capacitor be useless? 4. Suppose I wanted to be able to use some of the electronics for a little bit after the car has been turned off, what would be the best method to maximize the amount of time I have? Large capacitor? Second battery? Thanks, Alan

What size cable are you running?  Your fuse should be sized according to the size of the power cable.  As far as operating with the engine off, the only way to extend that time is by using additional batteries.Support the12volt.com

Is that your only battery? If so, there is usually no fuse between the battery and starter motor. And an optima yellow isn't the best for cranking. Usually such systems use dual batteries. I would hence assume the normal cranking battery (wet cell) with the starter etc as not being shown on your diagram. And the yellow optima (or a better AGM battery) as you have shown it, but usually with an isolator between the 2 batteries. A capacitor would only be of use to lengthen the life of the AGM if it's a big "thumping" amp, which 600W isn't. (That's replacement life - not battery discharge time.) Normally fuses are placed at the start of each distribution segment (ie, after your distribution block). They are to protect the downstream distribution (cabling), and prevent loss of all loads going through your main "?? Amps" fuse. The ?? Amps main fuse is therefore sized to protect wire to the DistBlock, or the max current you expect to require (assuming that is smaller than the wire & DB rating). Without the abovementioned individual load fuses, the main fuse would have to be no larger than the lowest cable rating. As to Battery Isolators, I wouldn't worry about the solar being used to charge the main cranking battery. Hence no dual-ended voltage sensing isolator is required, and an ordinary UIBI (a relay controlled by the charge light) can be used. (With a fuse or breaker at each battery end.) PS (Zulu+10): Often inverters are kept quite separate to audio gear - eg inverters off the main ad audio off the secondary battery or vice-versa, but that assumes one does not discharge the main with the engine/isolator off. Good inverters (like SMPS amplifiers) should not inject noise onto the DC supply (which can still go thru the battery isolator, though the noise is usually attenuated the further it travels) and filters like chokes or caps may need to be added if it is a problem. And of course, keep any AC power leads adequately separated & shielded from audio signal and power leads, and sensors, PCs, etc. Many use dc-dc converters instead, though they can still inject noise (dc-dc converters are a dc-ac inverter with a rectified output - ie, dc-ac-dc).