19 replies to this topic

[Cpt Davenport]

With my Hawk delivery going down in just 10 more weeks, I'm asking FWC if they can upsize the wire when they do the installation. They make it sound like it is not something the do regularly. I asked if they could run 6awg. They said they'll see if they can do 8awg. 

 

1. Has anyone had 6awg or larger ran by FWC in Sac?

2. Would 8awg work for my DC/DC charger and 100ah lithium "good enough" to get by?

 

[m5040]

6awg is good for 50 amps up to 15' in length.  I believe when you list your batteries ah, that is amp hour, which is a general spec to compare to other batteries and that your battery can put out 100 amps for an hour (but in reality it may not be able to actually do that).  What in your camper would take such a massive amount of power?

[ckent323]

Most wire sizing tables and calculators rate the wire for the max steady state current it can handle without overheating and causing damage.  However, most charging scenarios involve high current flow for only a short period of time, maybe 10's seconds to a couple of minutes.

 

if you consider Joule heating and the damage threshold of the wire then for a given starting temperature and a max allowable wire temperature along with a given current load a time can be calculated during which the wire can handle higher current.

 

For example; Assuming a 28 C (82 F) starting temp and a max allowable temp of 80 C (176 F) 6 ga is good up to 70 amps for about 5 minutes before it gets hot enough to damage the wire. It is good up to about 11 minutes with a steady 50 A current flow.

 

Even though Jumper cables may carry 150 amps or more for a short period of time they are often made of 6 ga or 4 ga wire for this reason.

 

So the best question is what is the max current flow produced and over what duration.  Knowing that one can appropriately size the wire without running heavy cable.

 

That written another factor is voltage drop which depends on wire size and wire length.  A wire needs to be sized large enough so that the voltage drop does not create a problem for the battery being charged.

 

For Lead acid batteries need the bulk and absorption voltages typically vary between 14.0 and 14.8 V, and the float can vary between 13.2 and 13.8 V.

 

For LiFePO4 bulk/absorption voltages between 14.2 and 14.6 Volt will work! Lower is possible too, down to about 14.0 Volt, with the help of some absorb time. According to literature the BMS for most LiFePO4 batteries will allow around 14.8 - 15.0 Volt before disconnecting the battery.

 

For a 20 foot one way distance 6 ga wire will result in about a 0.4 V drop. If your source voltage is 15 V then the charge voltage will be 14.6 V.

 

I think voltage drop dictates the minimum wire size for most charging applications and 6 ga seems to be the appropriate minimum size.

 

https://grealpha.com...c/voltage-drop/

 

I see that the Redarc BCDC1250D puts out 50 A at a max of 15.3 V. So you need wire large enough to handle 50 A steady state (min 4 ga but that is the limiting current so the wire will run hot. Therefore, I would use 2 ga).

 

The Redarc BCDC1225D puts out 25 A at a max of at a max of 15.3 V. So you would need at least 4 ga.

 

Victron has 18, 20, and 30 Amp continuous output DC-DC chargers (Orion) that put out up to 15 V.  I think 4 ga is the minimum wire size appropriate for these too.

 

All these wire size minimums are based on the Joule Heating calculator or the wire size calculator (see links).

 

Ref:

https://www.nepsi.co...kkvYx6v_5_dDLp0

 

 

 

I hope this is helpful.


Craig

Edited by ckent323, 25 May 2022 - 04:11 AM.

[Cpt Davenport]

Thanks for laying it out Craig. Sounds like if I put in the Victron 12/12-30 I will need WAY bigger wire. So my next question is this.

 

Has anyone had continued success with a standard factory 10 wire and ACR setup and just swapping in a lithium battery?

 

It sounds like the biggest problem is this wont allow the alternator to bring the battery up to 100% SOS. I feel that most of the time the solar should top off what every the alternator could not accomplish.

[veryactivelife]

This has come up before in various FWC discussion groups and it has been reported that the factory wiring will not keep a Victron Orion charging successfully. It's always a lot further from truck battery to charger than you think. I ran 4 AWG wire and am happy for it.

 

I've never heard of anyone being successful at getting the factory to deviate from their obsolete wiring.

 

Dean

Edited by veryactivelife, 25 May 2022 - 07:29 PM.

[bajaphile]

Has anyone had continued success with a standard factory 10 wire and ACR setup and just swapping in a lithium battery?

 

 

Answer for me is NO. I tried using 10 AWG on my 2001 F350 Crew Cab, which turned into about a 25 ft wire run from the truck battery. The ACR would click on and off every time my electric fridge would turn on. I at first the ACR was faulty or something, even though I had installed it on several other vehicles and never had an issue. That being said, I had always used cut up 4AWG jumper cables. I then got a Victron 12/12-30 DC-DC charger and once again started having issues due to voltage drops. 

Finally just bought some big long jumper cables and wired up some large Anderson connectors, put on some heavy duty conduit and ran the wire back all the way to the Victron and everything started working as they should.

 

I plan on getting some high quality marine grade tinned copper wire at some point, but the jumper cables are working for now. 

[bsharp007]

The answer for me is also no and it isn't just the wire size, I have a 'smart' alternator that limits the amps going to the camper batteries. My Hawk is 2 months old and the first thing I installed was 330 watts of solar on the roof, 2 100 ah litium batteries, a battery monitor and a solar controller.  I can connect via bluetooth with the battery monitor while driving and noticed there is a DRAIN of 10-15 amps going FROM my camper batteries into the truck battery at times.  I have disconnected my ACR from the alternator and just use the solar while driving and I seem to get to camp fully charged.   Don't need the charging from the alternator.

[Cpt Davenport]

The answer for me is also no and it isn't just the wire size, I have a 'smart' alternator that limits the amps going to the camper batteries. My Hawk is 2 months old and the first thing I installed was 330 watts of solar on the roof, 2 100 ah litium batteries, a battery monitor and a solar controller.  I can connect via bluetooth with the battery monitor while driving and noticed there is a DRAIN of 10-15 amps going FROM my camper batteries into the truck battery at times.  I have disconnected my ACR from the alternator and just use the solar while driving and I seem to get to camp fully charged.   Don't need the charging from the alternator.

Great idea! I think I will disconnect the alternator, swap out the SLA for my lithium and see what happens! Negative amps is a bad thing for sure. When I pull the camper off I can upgrade my wire and will instal the DC/DC charger.

[ckent323]

Cpt Davenport,

 

Does your truck have a "smart" alternator?  If it does then a DC-DC charger may be a good choice. 

 

If not then a DC-DC charger is probably not the right choice and a ML-ACR would probably be more appropriate.  

[Cpt Davenport]

Cpt Davenport,

 

Does your truck have a "smart" alternator?  If it does then a DC-DC charger may be a good choice. 

 

If not then a DC-DC charger is probably not the right choice and a ML-ACR would probably be more appropriate.  

I'm not sure if I have a smart alternator. As I research online it looks like I need to test voltage while running to be sure. I was hoping to get an answer for my 2017 Silverado or an RPO code, but nothing.  If anyone has a yes or no for my year make model  that would be great.