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Old 08-10-2014, 12:46 AM   #1
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Battery cable sizes

I am in the process of installing a Trimetric 2030 monitor,and in the process discovered that my 2014 25 FB with factory 1000W inverter has cables to the inverter size 4AWG and battery cables size 6AWG. Wondering if this is going to be a problem down the road when I put in the planned 300W solar?Should I change all the leads now to a heavier cable?



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Old 08-10-2014, 01:00 AM   #2
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Download the free app from BlueSea.com and calculate the proper cable sizes.


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Old 08-10-2014, 01:47 AM   #3
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I recommend 4/0 on all battery, inverter, gen connections! Anything less would be uncivilized... lol
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Old 08-10-2014, 01:58 AM   #4
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Originally Posted by vinstream View Post
I recommend 4/0 on all battery, inverter, gen connections! Anything less would be uncivilized... lol
So why can Airstream get away with 6AWG?



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Old 08-10-2014, 02:09 AM   #5
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I am not sure why they do many of the things they do... That said, I also put battery, inverter and gen as close as I can to each other! I do not understand why Airstream puts batteries in the tung area (in the cold) and then run many feet of undersized cable back to the center of the trailer. I would put the batteries (very heavy) as close to the axles as possible and limit my large cable runs. 6AWG if you look at the charts below the size recommended for both the inverter manufactures, gen manufactures and standard wiring charts that area all over the internet. My guess is cost?!
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Old 08-10-2014, 10:44 AM   #6
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Thinking about it last night, and I guess the other possible reason is as I have the inverter option that only runs about 3 or 4 outlets,and no microwave plus the fact that all the lights are now LED , maybe they figure that 6AWG is all they need for the battery if they have 4AWG on the inverter ..



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Old 08-10-2014, 11:37 AM   #7
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Originally Posted by gmeikle View Post
I am in the process of installing a Trimetric 2030 monitor,and in the process discovered that my 2014 25 FB with factory 1000W inverter has cables to the inverter size 4AWG and battery cables size 6AWG. Wondering if this is going to be a problem down the road when I put in the planned 300W solar?Should I change all the leads now to a heavier cable?

George
I did that same Tri Metric change on my 2014 FC 20' I also changed to a pair of 6 volt golf cart batteries and a PD 4645 converter/charger. I have 200 watts of panels on my roof, with a Blue Sky MPPT charge controller. I have the factory 1000 watt inverter, as well as a smaller "donkey" inverter which has a much lower idle current than the original.

All the original cables in my 20' are completely adequate for the loads and locations (my cables mostly terminate under the front bed, and the inverter is there). The #10 pre wire solar wires are fine for the 200 watts of solar I have installed. The #4 for the inverter works just fine. The original battery wires from the converter/charger handle the charge current and the loads from the trailer with no problems. My solar wires connect to the front under bed buss and from there charge the batteries through the original cables. There is no sound engineering reason that the solar charge wires must go directly to the batteries, assuming the battery to buss cable is as large or larger than the solar charge wires.

There seems to be a certain "bigger is better" or even mandatory myth with battery cables. Quite frankly, the loads in most trailers today, those with LED lighting especially, are quite low. Even charge currents are modest after the initial charge is delivered with today's three stage chargers. The inverter load on factory inverter units is handled with separate inverter cables and they are properly sized.

I do understand voltage drop in wire, and how it can affect charge performance, especially with solar systems. Long runs of too small wire with a large panel capacity will cause the system to not produce the charge current it should. But reasonable runs, MPPT controllers (which do some compensation for voltage drop) and panel capacity in the 200 watt range do not require huge panel to controller cables, nor special oversized runs to the batteries. All terminals must be properly made, and be corrosion free and tight, of course.

Yes, I may get some flack for the above statements. But good engineering is not oversizing everything. That will almost always work, but is not necessary nor economical.
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Old 08-10-2014, 02:42 PM   #8
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Thanks for that Idroba. I was slowly coming to that conclusion. The SC2030 that I have to install along with the TM2030 will handle all the needs I have. I have heard that as long as you stay in the 200 Watt area that the #10 wires will do the job. I don't run any coffee makers or microwaves. Basically want to keep my batteries charged while out for 3 or 4 days at a time and be able to run minor electronics.
The solar wires will like your setup go through the SC2030 to the proper bus before going to the battery.
And I realized when I thought about it that the LED lighting isn't going to be too taxing on the system. We're your battery leads smaller than your inverter leads also?


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Old 08-10-2014, 03:35 PM   #9
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And I realized when I thought about it that the LED lighting isn't going to be too taxing on the system. We're your battery leads smaller than your inverter leads also?


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I think, but did not go out to check just now, that they are both the same size, #4.
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Old 08-10-2014, 03:51 PM   #10
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Interesting that Airstream uses 4AWG for inverter cables on the 1000 watt WFCO unit, you Magnum specifies 1/0 for any runs over 5' for their 1000 watt inverter.

I upgrade cable sizes on every solar installation that I do, The sizing is dependent on the load, length and purpose of the wiring.

I have used up to double 4/0 on long inverter runs for motor homes over 10' as specified by Magnum and NEC.


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Old 08-10-2014, 05:42 PM   #11
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Just checked the installation guide and #4 AWG is correct. Thanks for all your input. I guess I'll let well enough alone.


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Old 08-18-2014, 10:24 PM   #12
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voltage drop

Idroba, using your 200 watt setup how much amperage to you see going into your batteries, watching the monitor, vs. the amperage coming out of the solar charge controller? This would show voltage drop due to the factory solar wiring size.
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Old 08-21-2014, 10:34 PM   #13
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Idroba, using your 200 watt setup how much amperage to you see going into your batteries, watching the monitor, vs. the amperage coming out of the solar charge controller? This would show voltage drop due to the factory solar wiring size.
There are too many variables to find any meaningful data that way. The 200 watts my panels are rated at are done under specified standard conditions which are not duplicated in the field. For example, the sun angle vs the panel. Mine are of course flat mounted on the trailer roof, so I expect less output than specified. The state of battery charge is also to be considered, the closer you get to fully charged, the lower the charge current from the panels.

That said, I have seen a 11.5 amp charge going into my batteries, when they are down in the 75 to 80% range on the Tri Metric. Since the charge voltage is around 13.6 volts, the panels are producing 11.5 x 13.6 = 156 watts which is not too bad for flat mounted panels. My more typical charge current is in the 9 to 10 amp range, but then since the Tri Metric measures net amps, if the refrigerator is on or anything else, some could be going directly from the panels to those uses too. I have not done an exhaustive study with batteries low enough to take all the power from the panels, and on a sunny day and with nothing else running.

I have been doing solar for a long time (first system in 1995). At that time a 60 watt panel cost me $400+. Now I can buy a 100 watt panel for $140. In the old days we were very concerned about getting every watt from the panels to the batteries, because panels were so damn expensive. Today we have far less expensive panels, and much better charge controllers (MPPT types) so a little power loss in wiring is not as critical as it was. I am not saying it is unimportant, but a 3 or 4% loss in wiring vs a 2% is not something I get too concerned about.

I have just been kept out of my home for 8 days due to wildfire danger (I was lucky, no structures were lost). I lived in my 20' FC for that time, sharing it for 4 nights with displaced neighbors. The Forest Service campspot was shaded much of the day, so my 200 watts of solar panels did not get fully exposed to the sun any time. Yet, the Tri Metric showed that the minimum low charge on my two 6 volt golf cart type batteries was 75%, and each day I got back up to 85 to 90% charge. We used lights, charged computers, ran the Fantastic Vents sometimes all night. My 200 watt system worked very well, especially considering it was shaded about 80% of the day.

It is my opinion that with some moderation in use of your 12 volt systems that solar in the range of 200 watts will work for many people. If you have to run your television all day while boon docking, have the inverter on 24/7 to run the hair dryer now and then, and charge the cell phones with wall warts, and still have incandescent lighting, no, it will not be enough.

Hope that helps a little with my experiences.
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