Plastic Classic Forum

Hello Everyone,

It's been a while since I've been to the site. I wanted to see if I could get some input on placement of electrical system. Does the length of the positive cable run from the battery to the ACR, switch, and engine cause any sort of voltage drop? My plan is to put one house battery in each settee, and then run the positive and negative cables aft to where the starter battery, switch, and ACR will be located, underneath the first step and the engine compartment. Is that possible without any detrimental loss in voltage?

Thanks,

Regards,

Jeff

It is possible if you size the cable properly. Use a standard voltage drop table with the length of your run (positive and negative) and the total amperage of your panel.

Try this Circuit wizard out and you can then size your cable properly. Be sure to use 3% for panel loads.

http://beta.circuitwizard.bluesea.com/#

The overall, round-trip length of the wire is directly related to voltage drop, but fortunately you can get around potential voltage loss by increasing the size of the cable accordingly.

You're not talking about exceedingly long runs, but they are longer than normal and you will need to adjust your cable size for voltage drop. Battery cable is expensive and heavy, so it pays to keep your batteries as close to the engine room as practicable, given all the considerations you have to factor in.

Here's a simple visual wire sizing chart to help you determine your needs. Use the 3% chart for battery cables.

This is the on-line wire size calculator I use. It is very simple tool and very easy to use. I thank the guy who plugged the formula's into Excel to create it every time I use it.

http://boatstuff.awardspace.com/awgcalc.html

Thank you for your response's, I'll assume that the typical expected loss is 3%. I'm not sure what amperage I should account for in the formula to determine wire size. I would think that the starting bank would push more short term amps than the house battery would ever see, is that correct? If so than I should use that as the standard for both runs to be safe. What is the max draw I could expect when starting an Atomic 4, if I'm thinking along the right line, that would be the key to the correct cable size.

Thanks,

Jeff

I am semi-guessing here but I think the A4 starter draws about 100-150 amps while cranking. With that assumption in mind I put a 200 amp fuse inline with the starting battery and it has not blown to date.

Big wires are expensive and unwieldy. I would not use anything bigger than you need. Your house battery wiring can be sized for the maximum expected load plus a safety margin which I assume will be a lot less than the starting battery draw.

Thanks Britton.