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 > Anyone with 12v Air Conditioning Experience?

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stevenal

Newport, OR, USA

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Posted: 08/30/21 01:33pm Link  |  Quote  |  Print  |  Notify Moderator

Kaytag1,


I never purchased the standard, but from https://archive.org/stream/ansi-rvia-lv-........0and%20Recreational%20Vechicles_djvu.txt #8 stranded is good for 40A. But if the wires are part of the inverter, they should be covered by its listing, and RVIA would not apply.


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Kayteg1

California > Nevada

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Posted: 08/30/21 01:50pm Link  |  Quote  |  Print  |  Notify Moderator

Still how can 400 amp unit be supplied by wires rated for 40 amps?
Meaning between RVIA and Chinese codes used for inverter, the true will lay somewhere between.
In my inverter application, I used the small cable to paralel 2nd battery, when main inverter connection is #2 wire. Just becouse I had it on the shelf and I know that voltage drop on inverters can be crucial.
Still would I build big solar system, not likely I would put 100 lb of cables to connect it to battery.





HMS Beagle

Napa, California

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Posted: 08/30/21 03:50pm Link  |  Quote  |  Print  |  Notify Moderator

I think the Chinese codes are suspect. 8 ga AWG wire has 0.62 ohms/1000 ft. if of good quality. 18" of wire therefore has only 0.0009 ohms which doesn't sound like much. At 400A that is still only 0.37V drop which also doesn't sound like much. But it will dissipate 149 watts which sounds like one hellava lot! In fact it will do that for only a very short few seconds before the insulation melts and it is red hot. Wires are often sized for voltage drop, as apparently here, but there are also ampacity specs based on insulation temperature ratings, and #8 is typically 80 amps unless a very special high temp insulation - but never 400 amps!

So based on voltage drop of 3% - a typical metric for battery powered systems, #8 is fine because the run is so short, but based on ampacity you need at least 3/0, which is independent of run length.


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pianotuna

Regina, SK, Canada

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Posted: 08/30/21 04:17pm Link  |  Quote  |  Print  |  Notify Moderator

HMS nicely said. Thanks.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

pianotuna

Regina, SK, Canada

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Posted: 08/30/21 04:23pm Link  |  Quote  |  Print  |  Notify Moderator

Kayteg1 wrote:


Still would I build big solar system, not likely I would put 100 lb of cables to connect it to battery.


One would go MPPT with a 100 volt or larger input voltage.

I've often advocated for the charge controller to be as close as humanly possible to the battery bank.

I aim at less than 1% voltage drop, but I agree #8 wire is ummmmm a fuse at 400 amps.

HMS Beagle

Napa, California

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Posted: 08/30/21 07:17pm Link  |  Quote  |  Print  |  Notify Moderator

Also why my boat was wired 24V for everything that possibly could be. I probably saved 300 lbs in wire just from that.

* This post was edited 08/30/21 07:28pm by HMS Beagle *

Kayteg1

California > Nevada

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Posted: 08/30/21 10:44pm Link  |  Quote  |  Print  |  Notify Moderator

I had 24V coach in the past.
Don't know if wire weight saving on 16 tons vehicle was crucial, but keeping 3 different voltage wiring systems in working order sure could be confusing.

HMS Beagle

Napa, California

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Posted: 08/31/21 09:32am Link  |  Quote  |  Print  |  Notify Moderator

Not sure I'd build a camper with a 24V system. On the boat there are many high current devices (AC, watermaker, 3 winches, windlass, inverter) so a lot of big cable. With 24V you get half the current and can withstand twice the voltage drop, so the difference in cable size is quite large.

adamis

Northern California

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Posted: 08/31/21 09:46am Link  |  Quote  |  Print  |  Notify Moderator

HMS Beagle wrote:

Not sure I'd build a camper with a 24V system. On the boat there are many high current devices (AC, watermaker, 3 winches, windlass, inverter) so a lot of big cable. With 24V you get half the current and can withstand twice the voltage drop, so the difference in cable size is quite large.


I'm curious HMS Beagle where you keep your boat up in the North Bay? My folks have a 47' Gulfstar Sail Master in Sausilito that they stay on 50% of the time. When I was in college at San Jose State I used to drive up there on a regular basis to visit. I'm now in Gilroy so I can't get up there that often but still try to visit on occasion. My dad is an active sailor (was a Merchant Marine for 30 years before retiring and buying the sailboat) and loves taking his boat out. He's also been sailing in the Master Mariners Regatta. Guessing you might be involved in some of the same circle of people as my Dad.


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Siletzspey

Shedd, OR

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Posted: 08/31/21 10:06am Link  |  Quote  |  Print  |  Notify Moderator

stevenal wrote:

Have you checked the RVIA electrical codes?


I took a pass at trying to understand the relevant industry "codes / standards" and wire gauge x amperage tables, and my debrief WITH LINKS TO THOSE CODES is here.

http://www.barbless.com/share/lifepo4/TJG-Wire-Fuse-Sizing.pdf

Many codes that are stereotyped as "housing" codes do cover low voltage DC systems, and in fact are what the boating and RV standards build off of! IMHO the boating industry with its ABYC standard is the most comprehensive, mature and utilized standard for low voltage DC systems, not only for boats, but for RVs. The RVIA standard is sparse in comparison, and I've seen multiple comments that utilization of the RVIA standard is voluntary and sparse.

IMHO the biggest misunderstandings on various forums are: 1) confusing VOLTAGE DROP tables with THERMAL CURRENT-LIMIT tables and 2) arguing that you only fuse to protect the wire, which means all RVs with 10AWG DC wiring rated at 105C should be fused at 60A.

I'm not an expert, but I am putting my work WITH CITATIONS out for critical inspection and feedback.

--tg

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