4AWG from the factory?

[Jsoboti]

Trying to work smarter not harder...

Picking up a new Hawk in December to be put on my 2014 F-350. Specced with a single 79Ah AGM battery and "pre-wired" for solar (no charge controller installed). I plan on adding a second 79Ah battery right away and eventually solar.

I'll be doing a lot of winter camping and I think I would like to install a DC-DC charger. (more amps= less truck idling time to top off batteries if needed??). I don't know if the 2014 F350 has a "smart alternator" or not.

My real question is... should I ask the installer, Mule Expedition Outfitters, to install 4AWG wiring on initial install instead of the smaller diameter normal wiring harness. So that I don't have double efforts in a month or so when I want to install the DC-DC charger and presumably need heavier gauge wire? If I don't install a DC-DC charger, will having 4AWG wiring from truck to camper increase the amps I see come across while driving anyway, perhaps receiving me of the necessity of the DC-DC charger?

 

[rando]

If you are installing a DC-DC charger, you don't need larger wiring. The DC-DC charger will boost the voltage, offsetting the voltage drop on the skinnier wiring.

With heavier gauge wiring you may not need the DC-DC, but have you priced a DC-DC vs ~50' of 4AWG wire? The DC-DC converter is not much more.....

 

[Jon R]

Call Mitch or the shop at Mule Outfitters and I'm sure they can tell you what they are willing to do on installation. I suspect they'll do whatever you want but may need to charge extra for the heavier wire or extra labor. I know from having asked that FWC at the factory isn't doing any changes beyond the offered configurations.

I assume the reason for the DC-DC charger is to raise the voltage delivered to the camper battery and allow a high level of current to be delivered even though the truck's "smart" alternator and the wiring to the camper are causing insufficient voltage at the camper battery for charging. If you have that situation, increasing the wire size may help some by reducing the loss in the wire but I suspect it won't be sufficient to compensate for the low alternator voltage. Maybe others have actual experience with this.

From what I've read all new trucks are being delivered with smart alternators as of a few years ago. I don't see why FWC still delivers a camper charging system that doesn't work effectively with the new trucks. The installer can put in a relay that hard switches the charging connection on when the truck is running rather than using an isolator, but that doesn't solve the inadequate alternator voltage problem. FWC's production has been high so maybe they are planning a change but haven't had time to develop and implement it. I'm crossing my fingers hoping FWC addresses that issue (and offers a lithium battery option) before my camper gets built in late Spring 2021. Otherwise I'll have to do a lot of modification to get the capability I want. I don't mind doing the work but I hate paying for wiring and components I just have to take out.

 

[Vic Harder]

+1 to what rando said. Just get the DC-DC charger. I would imagine that it is important to position the charger close to the camper battery to minimize charging losses between it and the battery though!

The DC-DC is also a "better" option than heavy wire if you are planning to go LiFePo4 later, and/or you are worried about smoking your alternator. With 2g wiring on my "dumb" alternator 2002 GMC truck and feeding 275AH of AGM batteries, I occasionally saw 90A when charging, but not for long because of the internal resistance of the AGM batteries. LiFePo4 batteries have much lower internal resistance, so I imagine (have not tried this yet) that they would suck down even more amps for longer... potentially burning out my alternator.

I am using a Victron Orion non-isolated charger. It delivers 30A to my 200AH Battleborn battery pack in a safe, predictable and controlled manner.

 

[Jsoboti]

Thanks for the replies.

Doing a quick search of the Victron Orion Instruction Manual, it looks like the lightest gauge wires the recommend is 5AWG from the truck battery to the unit itself. I think that I'm not interpreting something correctly.

You're saying I should be able to have them install the same wiring they do on every FWC install (12AWG right?), slap the DC-DC charger in and be totally good to go?

I'm new at this so I really appreciate the help!

 

[rando]

The Victron recommendation is unclear, it would makes sense for the output cable, but not for the input cable. I am pretty sure FWC uses 10 AWG wire, which is rated for (and should be fused for a maximum of) 60A, so you have plenty of margin there. One thing to note is that they typically install a 30A breaker, if you plan on using a 30A DC-DC charger, you may need to switch it out for a larger breaker.

 

[Jon R]

Just as an example, here is the manual for a line of Renogy DC-DC chargers. Page 14 of the manual has a chart with recommended wire gage versus wire run length and nominal charging current for the upstream and downstream runs. You should be able to interpolate for a 30 amp charger, or look for a similar chart in the manual for whatever charger you are buying.

https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf

 

[Vic Harder]

To add to what rando is saying (totally agree) I'd go with 40A breakers (one on each end of the wires... you want to protect the wire from a short happening). Why? Let's assume the Orion is trying to create 30A output at 13.0V to charge the batteries that are sitting at 12.4V (partially discharged). 30A going across 10g wire will suffer about a 12% voltage drop, or power loss. Combine with about 5% efficiency (didn't look that up) of the Orion itself, it is conceivable that the Orion will need 36A to generate 30A.

 

[Jon R]

The Victron recommendation is unclear, it would makes sense for the output cable, but not for the input cable. I am pretty sure FWC uses 10 AWG wire, which is rated for (and should be fused for a maximum of) 60A, so you have plenty of margin there. One thing to note is that they typically install a 30A breaker, if you plan on using a 30A DC-DC charger, you may need to switch it out for a larger breaker.

What kind of 10 awg wire is rated for 60 amps? Typical rating for 10awg is 30 amps, isn’t it?

 

[rando]

This is the ABYC (marine) spec, you are likely thinking of household wiring:

 

[Jsoboti]

After looking at several models' instruction manuals, it seems that for a >10ft run for a 30Amp system, 6-8AWG is recommended. Is it dangerous to use 10AWG or are you just forfeiting some efficiency, not running the risk of overheating, damage, fire, etc.?

 

[Vic Harder]

10' on which side, input or output? Either way, there is inherent inefficiency with running thinner wire. No risk with 10g as it can easily carry 30A, as rando noted above. On the output side, the inefficiency matters more, but likely not much. I would run the fattest wire that fits into the terminals on the device on the output side.

 

[rando]

It is not a safety issue - as mentioned previously 10AWG is rated up to 60A, so no issue there. You do want the wires on the output of the DC-DC to be short and/or fat so that the battery being charged is seeing close to the same voltage as the charger is providing.

Assuming a 15' round trip from the engine bay to the camper, you will have about a 6% voltage drop. This doesn't change the rate of charging, but means the alternator will need to provide 6% more power - not really noticeable in the grand scheme of things.

Assuming you are considering a Victron DC_DC, then the only possible issue I can see would be tuning the 'engine on detection parameters' to work with your alternator and the voltage drop in the wires. You may need to adjust these from the default.

After looking at several models' instruction manuals, it seems that for a >10ft run for a 30Amp system, 6-8AWG is recommended. Is it dangerous to use 10AWG or are you just forfeiting some efficiency, not running the risk of overheating, damage, fire, etc.?

 

[Zirdu]

When I purchased my new Grandby in 2017, it was through the FWC dealer in Salt Lake City. I asked them them to use bigger wire than the standard 10 AWG in wiring up the alternator to the camper. They basically refused, saying it was not necessary and that they were not set up for it. So, a few years later, I re-wired to 6 AWG myself, using an Anderson connector between truck and camper.

 

[wicked1]

I'd bet Mule is willing to use a larger diameter size (if this is the thread where the OP mentioned Mule was installing it).
I bought some equipment from them and was chatting w/ them, and they told me they often upgrade the 10awg to 6 or 4 for people, specifically when they install a DC/DC charger. (to support lithium or when switching the factory stuff to a new power system). And, per the DC/DC charger instructions. Both Victron and RedArc suggest using heavier gauge wire if you rtfm.

 

[Jon R]

Thanks Rando. Yes, I was assuming it was the same as household wiring.

 

[ntsqd]

For DC voltage I've never seen a static ampacity listed for any wire size. The length of the circuit is always a factor. Can not use AC ampacities, i.e. the National Electrical Code, for DC voltages.

I frequently refer to these ref pages when sizing DC conductors: https://www.ancorproducts.com/en/resources

 

[rando]

Isn't there one on the page you just linked to?
https://www.ancorproducts.com/en/resources/conductor-sizes

The key thing about sizing per length of conductor is that you have to assume an acceptable voltage drop. Most tables seem to assume 3%, which is an OK ball park estimate. But like most things, the devil is in the details - for some things 3% may be too much drop (like charging a lead acid battery), but for other things you will be fine with much more drop (a DC-DC charger, or 12v->5V USB charger).

There is a tendency for folks to quote these tables like it is some sort of hard and fast rule, without considering the details of the actual application.

 

[Jack]

Assuming you are considering a Victron DC_DC, then the only possible issue I can see would be tuning the 'engine on detection parameters' to work with your alternator and the voltage drop in the wires. You may need to adjust these from the default.

The run from the truck battery to the DC-DC in my 2015 Fleet on a Ford Ranger took all of 25 ft of 8 AWG (50 ft round trip).

With the factory 10 AWG, I had a lot of trouble with the Victron DC-DC starting to charge and then dropping out within a second or less. I wish I still had access to a DSO to see what was going on, but I suspected that the voltage drop was too much for the 30 A draw and the DC-DC was sensing engine-off and shutting off. After a delay of 10 or 20 seconds, this would repeat. I replaced the 10 AWG with 8 AWG, wired directly to the DC-DC (I had no idea where the negative side of the factory wiring went). This solved the problem.

I have visited Mule here in Portland a number of times and am very impressed with their operation. They like to run 4 AWG from the truck to the camper, but as rando and others have pointed out, it doesn't buy you anything. Both the Renogy and the Redarc DC-DC chargers require an engine running sense line so voltage drop is not an issue. The Victron also offers that option. Size your wire from the truck for the DC-DC. 10 AWG is fine for the Renogy and Redarc and I would (I did!) choose 8 AWG for the Victron.

 

[wicked1]

Redarc actually recommends 4 or 6awg, depending on the length of the run. Their install manual goes from 2 to 6, depending on the run. There's a little chart in it.
And, same as you, only w/ redarc, it did not like the 10awg factory wiring. Redarc and Mule both suggested I upgrade it, which I did, and problem solved.
redarc does have a engine sense line, but it is not "required" unless you have a smart alternator.
I don't have a smart alternator, but maybe connecting that line would have solved the issues I was having w/ voltage drop.. Not sure.. I just ran heavier wire.