New FWC's have 10awg wire internally, why have a thicker wire from truck?

[kmcintyre]

I was inquiring about running a 6awg wire from the truck battery to my (someday) new hawk flatbed and asked what they do at the factory.

They replied that the internal wiring inside the camper is 10awg; which they use from the truck battery to the camper.

If that's true, the only benefit I can see is that there might be a slight voltage drop from the truck battery to the camper but after that, it won't matter.

Calculations for a 15' run @ 6awg, 10amps is a .4V loss.
Calculations for a 15' run @ 10awg, 10amps is a .98V loss.

So, you lose about .5V using 10awg.

Since I don't know how they do the connections on a Flatbed (or how they do it now vs. my 2001) I imagine that the wire comes into the flatbed and into a fuse box where it splits off to the house battery and electrical components in the camper? If that's the case, you could upgrad the wiring to where the fuse box is and then upgrade the wiring to the battery.

I'm leaving off the DC-to-DC charger, etc. for ease in this discussion.


Kevin

 

[PaulT]

The primary benefit of the larger wiring from the truck to the batteries is that the voltage drop is less allowing the batteries to be charged more completely and in a shorter time. Voltage drop from the batteries to the lights or appliances that use 12 volt power is not as critical and 10 AWG is likely fine. The half volt difference between the two wire gauges can make a significant difference in charging the batteries.

Paul

 

[pvstoy]

Did you include both negative and positive wire runs in the loss? Times a one way wire run by 2.

I remember reading that charging straight from alternator wire loss makes a difference to the camper battery. Add a DC to DC charger then 10 gauge may not be a issue, but some have had problems with factory 10 gauge cycling on and off the DC to DC charger due to the loss in wire size and length.

 

[Beach]

Might affect the bulk charge on some batteries. If your battery requires 14+ volts(as many do for bulk charge) and your output from the alt is 14 or so volts, then you drop approx. 1 volt on the way to the battery, you will not get a proper charge.

 

[kmcintyre]

The primary benefit of the larger wiring from the truck to the batteries is that the voltage drop is less allowing the batteries to be charged more completely and in a shorter time. Voltage drop from the batteries to the lights or appliances that use 12 volt power is not as critical and 10 AWG is likely fine. The half volt difference between the two wire gauges can make a significant difference in charging the batteries.

Paul

The only thing is they run 10 awg from the truck battery to the camper and then the camper has all 10awg. Doesn't matter in this scenario other than making sure that you get less voltage drop from the truck to the camper (at least that's what I'm thinking).

 

[kmcintyre]

Might affect the bulk charge on some batteries. If your battery requires 14+ volts(as many do for bulk charge) and your output from the alt is 14 or so volts, then you drop approx. 1 volt on the way to the battery, you will not get a proper charge.

I wonder how many people have the standard 10awg wiring then...

 

[kmcintyre]

Did you include both negative and positive wire runs in the loss? Times a one way wire run by 2.

I remember reading that charging straight from alternator wire loss makes a difference to the camper battery. Add a DC to DC charger then 10 gauge may not be a issue, but some have had problems with factory 10 gauge cycling on and off the DC to DC charger due to the loss in wire size and length.

I have a DC-to-DC charger for my LifePO4's!

 

[Vic Harder]

Think of it this way: From the DC fuse box, the wiring FWC/ATC/Others use is NOT 10AWG, it is 14 or even smaller. But, to the distribution panel/fuse box, they all see the wisdom in using a fatter wire. And that is for a run 10' long or less from the camper battery to the dc fuse panel.

With smart alternators, and differing battery chemistries, we definitely want to minimize the voltage drop from the truck to the camper.

 

[Wallowa]

I have a DC-to-DC charger for my LifePO4's!

My Orion DC/DC was wired with 4awg...Tundra/Hawk [side dinette] battery box right front corner of Hawk floor tub...not sure if that was what you were asking about but you mentioned DC/DC.

 

[Jon R]

I wired mine with 6 awg Ancor marine wire from the truck battery to the Orion 12/12-30 and it works fine. The voltage drop at 30 amps is small enough that the Orion’s engine running verification test cycling is not triggered. My wire run is about as long as anyone would have for a truck camper installation. My truck is a crew cab long bed and the battery compartment with charger is at the very back of the camper.

 

[Wallowa]

I wired mine with 6 awg Ancor marine wire from the truck battery to the Orion 12/12-30 and it works fine. The voltage drop at 30 amps is small enough that the Orion’s engine running verification test cycling is not triggered. My wire run is about as long as anyone would have for a truck camper installation. My truck is a crew cab long bed and the battery compartment with charger is at the very back of the camper.

Jon,

I have seen, but can't find, a chart that lists voltage drop by distance vs wire gauge...do you have site for this?

Thanks,
Phil

 

[Vic Harder]

AC and DC Voltage Drop Calculator AS/NZS 3008 | jCalc.net

There are many out there... google is your friend!

 

[Jon R]

Sorry for not responding yesterday Phil. I went to Mt. St. Helens. The picture is from Johnston ridge. Why Mr. Johnston thought he’d be safe there i don’t get. Even in a vertical eruption that place is really exposed.

Ancor has data for their wire on their web site.

 

[Wallowa]

Sorry for not responding yesterday Phil. I went to Mt. St. Helens. The picture is from Johnston ridge. Why Mr. Johnston thought he’d be safe there i don’t get. Even in a vertical eruption that place is really exposed.

Ancor has data for their wire on their web site.

Great photo...I remember the chilling pictures of him "monitoring" the eruption from there and then being enveloped; I believe that was Mr. Johnston...sad indeed...

 

[rubberlegs]

I remember reading that charging straight from alternator wire loss makes a difference to the camper battery. Add a DC to DC charger then 10 gauge may not be a issue, but some have had problems with factory 10 gauge cycling on and off the DC to DC charger due to the loss in wire size and length.

Our truck was probably wired with 10 gauge. If I got a 30A sized DC-DC charger, then the voltage drop for 15' of truck wiring would be about 0.45V. I could improve that to 0.18V if I rewired the truck to 6 gauge. That's about a 0.3V difference. But there's still a voltage drop at 30 amps.

I'm exploring if it would work with the existing 10 guage truck wiring.

Can the DC-DC charger handle a half-volt input drop, say from 13.2 to 12.7, and work ok? Although there is loss in the line, would have full functionality? So I could procrastinate rewiring (or not bother if it works ok)?

Then again, maybe the 50A charger is the way to go... but we only use a 90W solar panel and don't think we need more than, say, 200W that I can ever imagine.

 

[TacomaAustin]

12.7 volts is the shut off threshold for my DC 2 DC charger. Also, 30 amps through 15 feet of #10 gauge, I'm guessing the voltage drop will be closer 9/10ths of a volt.

 

[rubberlegs]

Thanks for the reply, TacomaAustin. I just found out that the one I'm looking at also cuts off at 12.7V -- which answered my question. https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf

Also that manual says 8-10 gauge is ok for the 30A version, but you need 6 gauge for the 50A version. I got my voltage drop as follows -- does this look reasonable?

V = IR = (30A) * (0.9989 ohm/1000') * (15') = 0.45V

The 0.9989 value came from http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html

 

[Jon R]

Make sure you account for the total circuit length through the positive and return wires -not just one way. If your batteries are 15 feet apart you have 30 feet of wire.

 

[rubberlegs]

Ah, that would double it to TacomaAustin's 0.9V.

 

[pawleyk]

Just to answer the original question.. you don't JUST rewire from the truck, but internally to the batteries as well.

A dual 6v system in a fwc can see as much as 50amps of charging from your alternator when discharged, with correctly sized wire.

The rest of the wiring is fine, fuse block, solar etc. None of that is affected by this.