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4AWG from the factory?


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#41 Vic Harder

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Posted 25 March 2023 - 09:03 PM

This is a couple of years old - still feel the same way? I like Victron well enough, but I'm looking for more than 30A capacity in a DC-DC charger (looking at charging 270 AH of lithium battery as quickly as possible from a 400 Amp alternator). Any suggestions?
Thanks!

400A Alternator?  Cool.  Is that a dual alternator or marine alternator?  If you ok with really pushing the charging current (and potentially stressing the alternator) I believe (based on Battleborn's recommendations) that .5C is acceptable... so 135A in your case.  If it were me, I'd look at installing 1 AWG to limit the voltage loss to less than 10% (your wire would then dissipating 140W of power as heat at all times... something to keep in mind.. that heat has to go somewhere) and a remote battery switch and gauge so you can see the current and voltage going into the batteries.  When they got close to full charge, switch to DCDC or solar to allow the smarts in these systems to finish the charge process properly.

 

When I had 2 225AH 6V AGM batteries in my 2002 gas truck, I would see 90A over 2AWG wire when the batteries were low, but that quickly ramped down (within 30 minutes) to 40A or so.  Lithium would not ramp down in the same way because the internal resistance is much lower.  When I got to 95% SOC I'd turn off the direct connection and let my MPPT finish the charging process.   


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#42 ckent323

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Posted 26 March 2023 - 12:34 AM

Vic, et al,
 

Sizing wire for voltage drop so that the electronics function properly makes sense. Sizing wire for max current may be overly conservative and expensive. The Ohmic (Joule) heating of a wire has a time factor associated with it and it also depends not only on the material used for the wire (copper, aluminum, steel, etc) but on the wire construction as well (i.e. solid wire or stranded wire as well as the number of strands). Further, the resistance of the wire changes with temperature.

Often in automotive applications a wire may have a short term (transient) high current flow which drops quickly to a lower amount of current. This may only produce a minimal or acceptable amount of heating. This is part of the reason many battery jumper cables are made with only 6 gauge wire and they actually work without getting dangerously hot (generally one does not crank on a starter for more than 20 or 30 seconds - nor should one do so for longer than that before letting the starter and all the wires cool).
 

I recognize that every installation is different depending on the battery type(s) used as well as on the specific devices (ACR or Relay or connector, or etc) that are used and that it is probably easier to assume a worst case steady state current flow than to go through the calculations. I'm simply pointing out that doing so may result in unnecessarily oversizing the wire but at the same time there is no safety downside to doing that, only the cost and the inconvenience of dealing with larger gauge wire.
 

Standard automotive wire is rated for use between -40ºC to 80ºC (-40ºF to 176ºF) if PVC insulation is used or -40ºC to 125ºC (-40ºF to 257ºF) if crosslinked GXL, SXL or TXL insulation is used - Note that there are both hot and cold temperature limits. Depending on the location and use it may be perfectly acceptable for a wire to get hot to the touch and maybe as hot as 150ºF (66ºC) to 212ºF (100ºC) in regular use. I am not recommending anyone run wire that routinely gets that hot but as long as it it within the rated temperature range it should be safe.
 

The heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by

 

H = I^2Rt
 

this is called Joule heating (or Ohmic heating).

Here is a chart showing ampacity for various wire sizes (temperature in the column titles are the max temperatures for that particular type of wire insulation):


https://www.cityelec...acity Chart.pdf

 

EDIT 1: With apologies the chart at this link is for AC circuits I need to recover the link I found for the DC wire chart. In general, It is my understanding that wire gauge ampacity limits are determined by the maximum steady state current the wire can carry which produces a 30ºC temperature increase over ambient. As mentioned above there is a time factor associated with the heating so a short term higher current may not overheat the wire. I found a great site a year or two ago with the time dependent heating calculator for AC and DC wire and I posted that link to a comment to the WTW forum somewhere but I have not been able to find that link ror relocate the site so far.
 

EDIT 2: Here is a link to a calculator for constant current and temperature. There is another calculator like this that I have not yet relocated that includes a time (duration) of the current and resultant temperature rise.


https://www.omnicalc...cs/dc-wire-size

 

The version at this next link is specifically for 12 v wire.


https://www.omnicalc...s/12v-wire-size

 

Stranded DC wire resistance chart:


https://cpb-us-e1.wp...swc-1449hus.pdf

 

Stranded Ancor brand wire specifications table for 18 to 4/0 (000) Awg wires (gives resistance, no of strands, etc):


https://shop.pkys.co...roll_p_2418.htm

Edit 3:  Calculating Joule heating in a wire:
 

http://www.engineeri...–-joule-heating

 

Here is a short time (transient current) Joule heating calculator (for solid wire I think) - this is close what I have been searching for (need one for stranded wire):
 

https://www.nepsi.co...f-conductor.htm

 

For example: Assuming 13v and using 6 awg wire at an initial temperature of 70ºF and allowing a maximum wire temperature of 125ºF and assuming an 80A short term current run through it, it will take 157 seconds (about 2-1/2 minutes for the wire to heat up to 125ºF.  In 4 awg wire it would take 6.6 minutes.
 

Increasing the allowable maximum temperature to 150ºF to 6 awg wire would take 3.7 minutes and the 4 awg wire would take 9.4 minutes.
 

Dropping the current to 50 amps and allowing the wire to heat up to 150ºF 6 awg wire would heat up to that max temp in 9.5 minutes. At 30 amps it would take 26.4 minutes.
 

AGM Battery Bulk charging:

AGM charge current should be between 0.10 and 0.15 of the 20 hour rate AH rating. So a 100 AH battery should be charged at between 10 and 15 Amps. Using the short term current calculator (for solid wire) 6 awg wire can carry 20A for about an hour before heating up to 150ºF (4 awg 2.5 hours) and at 15A it takes about 1.5 hours for 6 awg and 4.5 hours for 4 awg to heat to 150ºF.
 

Assuming your 100 Ah battery is at 50% and bulk charging you need a bit less than 50 amps before the current flow drops off and the charging transitions to stage 2 (ref charging AGM or Lithium Ion batteries at the links below). At 15A per hour you would need about 3 hours of bulk charging time.  6 awg wire may get hot if your charger is flowing 15A instead of 10A. 4 awg wire should be OK.

Note: if you charge a battery with too high a charge voltage excessive current will flow into the battery, after reaching full charge, causing decomposition of water in the electrolyte and premature aging. At high rates of overcharge a battery will progressively heat up.

https://batteryunive...rging-lead-acid

LiFePO4 Charging:
It is my understanding that recharging LiFePo4 batteries is also best done with modest current (on the order of 1 amp per cell).

https://batteryunive...ing-lithium-ion

While there may be momentary inrush current transients in our charging systems, as best as I understand high current draw (more than 15 amps) in our campers should not be a common occurrence nor last more than a minute or so (assuming 100 Ah battery size - a 200 Ah battery size will roughly double the charging current).

Indeed, if we see high current flow (say more than 20 to 40 amps depending on battery size) and lasting more than 10 seconds or so (when not cranking the engine) I think we should be suspicious of a short or some other electrical problem that would cause high current flow. If anyone knows any of the above to be untrue please comment and explain.

 

 

Bottom line:  If you are running a 100Ah house battery and the one way distance from the charging source (assuming truck) is less than 25 feet and your charger allows a maximum current of 12A then a 6 awg wire is probably OK (do the calculations yourself or talk to an expert).  If you are using a house battery larger than 100Ah, have a longer distance or a higher charging current then you should use 4 awg or larger wire (again do the calculations or rely on an expert for appropriate wire sizing).

 

 

I hope his information is helpful

Craig


Edited by ckent323, 28 March 2023 - 02:05 AM.

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#43 Vic Harder

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Posted 26 March 2023 - 03:09 AM

Thanks Ckent!

 

Looking at that chart, does that mean that a 1AWG wire carrying 130A will get to 75*C?  


Edited by Vic Harder, 26 March 2023 - 03:11 AM.

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#44 Marvap

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Posted 27 March 2023 - 03:08 PM

Two 30 amp Orion 12/12-30 in parallel?

Good question, interesting idea, I'm not sure that they'd play well together - combined with the battery's internal management system it seems like a lot of controllers interacting primarily based on the voltage at the battery's terminals. Something to ask Victron about, I think.


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#45 Marvap

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Posted 27 March 2023 - 05:18 PM

400A Alternator?  Cool.  Is that a dual alternator or marine alternator?  If you ok with really pushing the charging current (and potentially stressing the alternator) I believe (based on Battleborn's recommendations) that .5C is acceptable... so 135A in your case.  If it were me, I'd look at installing 1 AWG to limit the voltage loss to less than 10% (your wire would then dissipating 140W of power as heat at all times... something to keep in mind.. that heat has to go somewhere) and a remote battery switch and gauge so you can see the current and voltage going into the batteries.  When they got close to full charge, switch to DCDC or solar to allow the smarts in these systems to finish the charge process properly.

 

When I had 2 225AH 6V AGM batteries in my 2002 gas truck, I would see 90A over 2AWG wire when the batteries were low, but that quickly ramped down (within 30 minutes) to 40A or so.  Lithium would not ramp down in the same way because the internal resistance is much lower.  When I got to 95% SOC I'd turn off the direct connection and let my MPPT finish the charging process.   

Thanks!
Some background: I'm doing a major camper upgrade from my 2005-era Tacoma/FWC Eagle to a 2023 F350/Flatbed Granby. As a side effect of various options, I'll end up with a dual alternator, dual battery system under the hood (gas engine). Ford says the alternator is 400 Amps, I'm not sure it that's each or total. The Granby house batteries are taken care of (FWC Lithium option), what I'm looking into is an auxiliary system located elsewhere in the vehicle to enable air conditioning without shore power (e.g., for pet safety while parked in the sun for a few hours). So, the battery (Battleborn 270 AH) will power the A/C (direct or via inverter, not sure yet), but in order to stay ahead of that kind of daily draw, I'll need to be able to supply a high rate of charge to that battery. My normal pattern involves a fair amount of daily driving, and I don't have anywhere to put extra solar panels anyway, so I'm looking for something more than 30A from the engine. Following Jon R's suggestion, I did a bit of checking and it seems that running Victrons in parallel is fine. 

Are you suggesting installing some switching to enable directly charging the battery from the alternator for the bulk of the charge? I think that might minimize my recharge time, but require that I pay more attention to how the system is operating than I think I can reliably deliver :-).
I appreciate your points about wire gauge from the engine - I'll look closely at that once I actually have the truck and can figure out the length of the cable run.


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#46 Marvap

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Posted 27 March 2023 - 05:20 PM

Good question, interesting idea, I'm not sure that they'd play well together - combined with the battery's internal management system it seems like a lot of controllers interacting primarily based on the voltage at the battery's terminals. Something to ask Victron about, I think.

Thanks for the suggestion, Jon R - I did a bit of checking and it seems that running Victrons in parallel is fine.


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#47 Jon R

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Posted 27 March 2023 - 10:11 PM

Thanks for the suggestion, Jon R - I did a bit of checking and it seems that running Victrons in parallel is fine.


The Orion web page and manual say it’s OK, and there was someone who posted here that runs two in parallel in a van. My Orion and my MPPT solar charger work fine simultaneously, and I’ve seen nearly 60 amps from the two of them a few times now.

Edited by Jon R, 27 March 2023 - 10:21 PM.

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#48 philos65

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Posted 29 March 2023 - 05:08 AM

I've installed the renogy 50 amp mppt/charger on my new rig (Scout Kenai on 2006 Ram 2500.  My project 80s era Keystone will be for sale shortly).  https://www.renogy.c...S-Datasheet.pdf

 

Note that the unit can take 50 amps from the alternator at 13.2-16 volts   It can take up to 660 watts from solar as well.  It is plug and play pretty much.  The Will Prowse video does an excellent job analyzing the renogy unit's performance and features. 

 

I'll have two 220 watt glass panels and one 175 watt flexible panel.  the lowest voltage among the three panels is 18 volts.  Combined amps from the panels is 35 amps. 35 x 18 =  630 watts in perfect conditions, which don't exist.  35 amps pushes the MC4 connectors, which at #10 AWG are rated for 30 amps.  But I doubt that'll be an issue, especially because I have circuit breakers or fuses everywhere needed to protect the system and conditions will never be perfect. 

 

I used high quality #4 copper wire from alternator to the mppt/charger, broken up with a 175 amp rated Anderson Power Pole Connector for when the camper is off the truck.  https://www.amazon.c.../dp/B082QW4TQM/

 

I've seen the alternator charge the the two 100 ah LiPoFe4 batteries through the Renogy unit push 435 watts.  I have a 2000 watt pure sine wave inverter that'll go in. 

 

When I run the CPAP with humidifier through a 12v plug, it draws about 60 watts.  The SEtpower 75 quart fridge/freezer draws about 65 watts when charging.  Starlink draws about that, down to 30 when it "idles" or whatever it does.   The diesel heater draws around 30 watts when running. 

 

I've used the system for a week with one battery, and one 175 watt panel and drove every day.  Once the temps get above freezing here in Laramie, I'll put on the two glass panels and hit the road.  Can't wait to test the beefier system.  As an aside, Scout campers comes with a Goal Zero Power Station which can be expanded using only proprietary parts.  The DIY solution is double the power for10% to 20% less money.   


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#49 Vic Harder

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Posted 29 March 2023 - 07:06 PM

That sounds like a very nice setup!


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