Ron

How does one compute the gauge of wire to use because of the extra length of wire added.

I have a 10 amp charger with 2 banks. Leads are 5'. One of the leads goes to car with no problem, but I want to make the other lead longer so it will reach another vehicle which will require about another 15 ' of wire.

The question is what gauge of wire to I use when I splice. Figure voltage from charger at 5' to be 13.85 volts

Quadcammer

google broken?

Ron

Yes it is. Keen observation on your part.

IainM

Whatever you use will add resistance. However, at the end of charge you are down to a trickle therefore volt drop will be insignificant as it is product of resistance and current.

Just use same gauge the original 5' is, it'll be easier to splice and work just fine.

zechunique

The only problem is that the voltage drop added means that the applied voltage (at the battery) is lower than the charger wants it to be, so the charger will apply a higher voltage than it would otherwise to cause the same given charging current. I'm pretty sure it would still work okay, but wire's pretty cheap at 15' long, and the splicing shouldn't really be that tough.

What size is the original wire? For the sake of illustration I'll assume its #18...

If I assume it is #18 then at 5 feet and 10 amps charging current (that's 50 ampere-feet) a dc voltage drop is .64volts. If the charger is applying 13 volts to do that, its almost 5% drop.

If you lengthen to 15 feet (150 ampere-feet) then the voltage drop under the same circumstances is 1.92 volts, or 14.77%. That might have minor complications, I would think. Maybe...

If you bump the wire up one size to #16, at 150Aft you get VD=1.2
If you bump the wire up two sizes to #14, at 150Aft you get VD=.76
If you bump the wire up three sizes to #12, at 150Aft you ge VD=.48

If you go with #14, you get the closest identical performance, so that's what I'd recommend for a 15' length.

Just for the heck of it though, using #12 at 20 feet happens to be identical (VD=.64 at 200Aft). If the price difference of 40 feet of #12 over 30 feet of #14 isn't a deterrent, then its an even better modification. But going from #18 to #12 is a little clunky maybe...

Just my 2c. Not to argue with IainM. His perspective is just as solid as mine. Oh, and don't forget, this all assumes you are starting with #18. If you want help otherwise, just post the real size, or PM me.

Whatever you do, make sure you use stranded wire...

zechunique

BTW,
Here's what you get when you google broken.
Not sure how it applies to voltage drop though.

nine9six

Awesome reply! Must be an EE...

mgianzero

Yes, I agree. Great dialogue.

Ron ... thanks for asking the question and your persistence for an answer.

zechunique ... thanks for an awesome explanation!

Even if you just browse this website on occasion, there always seems to be some topic which leads to an insightful and very informative answer.

That's the spirit of Rennlist!

zechunique

Here, here!
(aka +993)

It is a rare pleasure to be able to contribute. I certainly will never repay what I have been given here.

Ron

Yes stranded wire and it is 14 gauge, that is for the charger which is dual pro two 10 amp banks charger made by pro charging systems.

Thanks for all the great information, Same thanks to all others who have helped me.

zechunique

No sweat. If the starting point is #14, then here are the revised equivalents:

For #14 AWG at 50Aft VD = .25V or 1.92%
For #12 AWG at 150Aft VD = .48V or 3.69%
For #10 AWG at 150Aft VD = .30V or 2.31%
For #8 AWG at 150Aft VD = .19V or 1.46%

For #8 AWG at 200Aft VD = .25V or 1.92%

So #10AWG gets you pretty close, but #8AWG at 20 feet is identical.

#8's are getting pretty big...

NC TRACKRAT

After reading all the above, my only question would be regarding the type of charger being used. If charging batteries that have gone flat, that's one thing but, if only wanting to maintain batteries, using a "smart" trickle charger is the way to go. I have Battery Tender Plus's, some of which I have added long leads with no apparent detriment to performance.

zechunique

I totally agree.

Voltage drop is directly related to current and length (that's why the term Ampere-Feet is used). It's the same, especially for DC applications, to have 1000 Feet with only one Amp as it is to have 1 foot at 1000 Amps. They are both 1000 Aft.

That said, "battery maintenance only" applications use very low current (as you said) and so the voltage drop is very small, often negligible.

For example,

If you have #14 wire supplied by a 12.1 VDC source, that is 5 feet long, with .5 Amps, the voltage drop is only .013V or .11%.

If you extend that to 15 feet long, the voltage drop swells to... drum roll please... .038V or .31%. Not quite so worrisome there I would think.

I imagine that the wire size for the leads on a trickle charger is more about mechanical strength toward product quality, and the use of readily available standardized supply materials than about voltage drop.

Hope I don't sound all lofty here. This stuff really isn't that mind bending or anything. I've just done it a few times...

pp000830

Here is some insights by cable length;
http://www.fastenal.com/web/products...0Cables%22%7C~