6v vs 12v

[Lou Schneider]

Quote

(Thermal runaway is no joke)

At 12 volts the voltage vs. current loss of anything over a meter or two in length becomes the controlling factor on how much current you can pull through a wire, well before thermal heating is a concern.

 

[Chris1992]

Sorry if I was over reacting but larger cable is a bit out of my knowledge I only know what I know from smaller cables and under sizing 

[Yarome]

Thermal runaway is extremely rare and can really only occur in a 6v deep cycle battery when battery temperatures are "artificially" elevated and/or charge levels are set too high over an extended period. Generally speaking.. these days the safety valves are designed to rupture and do a rapid off-gas. Your batteries will "cook-off" before thermal runaway can occur or they explode. Not saying that it "can't" happen. Stick them in a poorly ventilated cargo bay in direct, intense, sunlight then run them through an equalization cycle. 

Even the AGM's you're looking at. It's not "entirely" true that AGM's don't off-gas... "period". They are also equipped with safety pressure relief valves. Prior to reaching "critial" internal pressure those valves WILL burst and off-gas.

[Chris1992]

Sorry should of specified not thermal runaway of the batteries i mean the cables melting which I now realise it would only be a problem on serously under sized cable

There are always safety valves fitted to them there would have to be or battery becomes bomb if over charged or discharged in rapid time 

[Kirk W]

4 hours ago, Chris1992 said:

There are always safety valves fitted to them there would have to be or battery becomes bomb if over charged or discharged in rapid time 

There are a number of different options for that. Most RV battery cables have a fusible link in them to prevent disaster from a direct short. It is designed to melt, should current ever be excessive. There are also resettable circuit breakers that can be used. 

[oldjohnt]

  When sizing 12 volt battery and charger and inverter cables:

 1) Sure bigger is better and closer (battery to charger or inverter etc) is better as it reduces line voltage drop, but I couple that with price, ease of wiring, reality, over kill and common engineering sense.  Its straight forward to compute the max load current and then knowing the cable length line voltage drop can be computed.

2) The very MINIMUM I would size the cables is so they have an ampacity of at least 125% of the "maximum continuous load". IE if the load were no more then say 24 amps Id use 30 amp minimum rated conductors.

3) Knowing the current and cable length and the wire gauge computed above, NEXT COMPUTE THE LINE VOLTAGE DROP. If its excessive then simply upgrade the conductor size until voltage drop is acceptable.

4) Of course, you must provide proper overcurrent and short circuit protection for the wiring at or near the energy source based on the calculations above.

5) Next I would add Convenience and Safety On/Off switching at appropriate and convenient locations.

 I wired much of my system so had the fine gauge stranded copper cables (like flexible welding cables) made up at the local Interstate Battery shop BUT THEY HAD NO FUSIBLE LINKS, so as mentioned above I installed circuit breakers to provide the necessary and proper overcurrent and short circuit protection. Once all was installed I used a bit of that anti corrosion protective spray to help reduce oxidation and contamination and occasionally check tightness.

Even more critical with flooded lead acid versus AGM, provide adequate venting of potentially explosive gasses and avoid any sparks or spark producing devices near the batteries ESPECIALLY near their top !!!!!!!!!!!!   

 As an attorney if I were advising the manufacturers I would err on the side of overkill and oversizing conductors (remember bigger is better) and then have a "catch all" statement WIRE PER THE NEC. 

BUY LOTS OF COPPER its good for the economy lol

PS one obvious advantage of a single 12 versus 6 volt batteries in series is less connections, but I suggest the use of true deep cycle (like golf cart) batteries versus  quasi so called RV/Marine  combination Starting and Trolling Motor batteries like sold at Walmart etc. 

John T  Live from Avon Park Florida (kind of a cold snap now)

  

[Sehc]

2/0 is 68 sq mm. It is rated for 330 amps. That is the meltdown safety. Voltage drop is a different issue. My inverter is labeled for 200 amps. The most I have seen is 110 amps. At 3 foot one-way wire distance from battery bank, I have less than 1% voltage drop using 2/0 awg x 200 amp. I chose 300 amp fuses at the battery terminal for the protection of the cable. A fuse is another resistance in the circuit. It is there to protect the wire. A larger fuse, within the safety of the wire rating, will have the least voltage drop added to the circuit. I use marine battery switches rated at 500 amp.

[Chris1992]

Thanks for all the help from everyone 

As I stated be for the chances of me going as high as 300 amp is really low almost tiny but I have oversized everything including the inverter to try and prolong life expectancy i don't really want anything at its limmit 

[ALLOY]

Not sure if it has been mentioned but  total length of wire ( - and + ) is used when figuring DC wire size.

If one uses an online wire calculator check if the calculator is for one or both sides.

 

 

[Chris1992]

Thank you very much J-T but was already aware of that fact I can see how some would forget to take into account the whole circuit I will be using at most 3m total 

[oldjohnt]

2 hours ago, Sehc said:

2/0 is 68 sq mm. It is rated for 330 amps. That is the meltdown safety. Voltage drop is a different issue

Sehc, I agree and you raise a good point. "Meltdown safety" is indeed a different issue then "voltage drop". Some time back I advised gents NOT to plug their 30 amp RV power cords into a 50 to 30 amp dogbone adapter (plugged into a 50 amp RV pedestal outlet) that didn't have (maybe they do ??? if so great) some sort of a fusible link or other 30 amp (the rating of 30 amp RV cords so as to avoid insulation meltdown) overcurrent protection because certain resistive or intermittent types of fault although NOT severe enough to trip the 50 amp pedestal breaker COULD STILL MELT THE INSULATION  (what you refer to as "Meltdown Safety"). If that were the case an exposed no longer insulated RV cord often laying in water or gravel or run over by bikes or golf carts etc where your barefoot grandchild was playing COULD CAUSE ELECTROCUTION and/or start a fire in certain situations and enclosures. Of course as many posted the risk was small and/or they had used such for years and never had a problem. AS ALWAYS I SUPPORT A PERSONS FREE CHOICE AND THEIR RIGHT TO ASSUME OR AVOID ANY RISKS WHATSOEVER 

Of course the risk is in the RV cord FROM the dogbone adapter TO the RV panel main breaker since circuits downstream of an AFTER the  30 amp breaker are properly protected HOWEVER that rubber cord laying in water or sharp gravel or under rugs or ran over by golf carts etc is where the electrical or fire hazard can be !!!!!!!!!!!!!!

FYI Sehc I just happened to run across an article by Mike Sokol of the NoShockZone website that agrees with the good point you raised and have copied and pasted a portion of it for you. His response in its entirety can be found at:        http://rvtravel.com/rv-electricity-overloaded-wires/

 

"While I can quote code chapter and verse from the code book all day long about current ratings, and even produce my own videos showing an intentional overload, that may not be enough to convince some of you. But as I like to say, seeing is believing. So here are two recent pictures sent to me that demonstrate EXACTLY what can happen if you make a wire carry more current than it’s rated for.

Current overload can be caused by things like additive neutral currents from a bootleg 240-volt outlet, or using a dog-bone adapter to step from a 50-amp pedestal outlet to a 16-gauge extension cord, or simply by plugging too many portable space heaters onto a circuit. However it happens, overloaded wiring is really dangerous since the insulation itself can burn and catch anything around it on fire. 

To review amperage capacity, a 10-gauge wire is only rated to carry 30 amperes of current. So if you ask it to pass 50 amps, then it will begin to overheat. Now this will take more than just a few minutes to reach the level of burning insulation you see above, but it could easily happen within a few hours of this level of overload.

So the takeaway is NEVER put more current through a wire than it’s rated for.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here"

 

GOOD CATCH SEHC   You are correct,    Meltdown safety is indeed a different issue then voltage drop.

Take care, best wishes and God Bless

John T

 

[Chris1992]

I know it may be a silly question but Is it ever a head ache or confusing using 120v and 240v I'm from the UK btw

[Kirk W]

6 hours ago, Chris1992 said:

I know it may be a silly question but Is it ever a head ache or confusing using 120v and 240v I'm from the UK

I don't know that it is silly as most of us here never have to deal with that issue because if we go far enough to have the voltage change we don't take the RV. What travel I have done to countries with different voltages the only thing I had to deal with was appliances and there are little converters for that. Do you have a US made RV?

[Lou Schneider]

On 1/3/2018 at 10:53 AM, Chris1992 said:

I know it may be a silly question but Is it ever a head ache or confusing using 120v and 240v I'm from the UK btw

Not really.  120 volts is our basic building block, like 240 volts is to you.   The only time we use 240 volts is when the power requirement is too much for a 120 volt circuit, then we use different plugs and sockets so there's no risk of an average user intermixing the two.

We get 240 volts by combining two opposing phase 120 volt circuits, so the two hot leads have 240 volts between them, unlike in the UK where 240 volts is fed down a single hot wire.  Each hot lead also delivers 120 volts to ground.  This means our 120 volt circuits use a single circuit breaker while 240 volt circuits use paired circuit breakers, one for each hot leg.  This also gives an easy way to differentiate between the two voltages.

What would be confusing is if we had both 120 or 240 volts available from single hot leg circuits.

[Chris1992]

The fact that you have different plugs makes sense never been to the US so never seen the system an no I don't have a US rv using one of them monsters over here would be a task and a half 

[Yarome]

On 1/1/2018 at 12:04 PM, Chris1992 said:

There are always safety valves fitted to them there would have to be or battery becomes bomb

Very true. AGM recombiners are quite efficient, but many are unaware they are also equipped with safety valves. Typically somewhere in the 1.5-3psi range. Since the recombiners are still active, even then it's a "very" minimal amount of off-gassing before they "catch-up"... unless you're really talking about a catostrophic battery failure.

[Chris1992]

42 minutes ago, Yarome said:

 unless you're really talking about a catostrophic battery failure.

Had a ford Mondeo (fusion) come into the work shop with steam coming from under the bonnet (hood) opened it up to find the alternator was pumping out a constant 16v and had blown the valve clean off the battery not AGM but still impressive made a hell of a mess of the engine bay but in nearly all cases it never gets that far 

[oldjohnt]

18 hours ago, Chris1992 said:

I know it may be a silly question but Is it ever a head ache or confusing using 120v and 240v I'm from the UK btw

Chris, NOPE its NOT a silly question. I've never been to the UK but are aware you use a lot of 220/240 VAC where we commonly use 120 VAC for small and medium sized electrical devices. Actually, if 240 volts (versus 120) is used for the same load the current is only half so there may be less (subject to conductor resistance) wasted I Squared R energy loss in the feeder conductors. Our typical 120/240 VAC single phase three wire service uses a transformer LV Secondary that's 240 VAC line to line BUT we tap that transformers winding in the middle (Neutral) so its only half or 120 VAC from EITHER line L1 or L2 to the center tap. Then we use both legs of 120 VAC in the home PLUS we have 240 VAC available for larger like HVAC, Clothes Dryers and Hot water heaters etc. As  mentioned above particular plug and outlet configurations are used to match the line and loads appropriately to avoid accidents and confusion. For the most part our RV's use 120 VAC versus 240 while the larger 50 amp rigs simply utilize BOTH legs of 120 VAC.

 

Come over the pond and visit us, take an RV tour of our National Parks, Americas greatest idea..............

 

John T

[Chris1992]

7 minutes ago, oldjohnt said:

you use a lot of 220/240 VAC where we commonly use 120 VAC for small and medium sized electrical devices. 

Its cool to know how you have 2 seprate live lines to make up the 240v is that still single phase? It's always interesting how different country's have different methods, We use 230 +/- 10v in all house hold applications except bathroom shavers 

We use 110v for work sites due to strict  safety regulations 

And use 480v for industrial instalments  

 

As for coming to America I will do at some point when I get a passport and a upgraded  driver licence due to the fact that your RVs are huge 

[oldjohnt]

3 hours ago, Chris1992 said:

Its cool to know how you have 2 seprate live lines to make up the 240v is that still single phase?

YES still SINGLE PHASE Chris, the technical jargon for residential home service is 120/240 Volt Single Phase Three Wire. The "three" wires are L1, L2 and Neutral (center tap of 240 volt transformer). Where used the Bare/Green is the "Safety Equipment GroundING Conductor" normally bonded to Neutral in the main service entrance panel in cases of non floating systems.  Its primary purpose is to provide a dedicated low resistance return current path ONLY FOR FAULT CURTRENT, NEVER normal return current, that's the job of the Neutral.  Its 240 L1 to L2  but half that or 120 L1 OR L2 to Neutral.

YES some (not me) have huge RV's but you could handle it, come on over

Nuff said before I "cornfuse" you further lol

John T

[Chris1992]

Not confusing at all mate its good to learn now I sort of understand why our 240v equipment is not directly compatible with yours 

what waight class RV are we talking here? 

[oldjohnt]

3 minutes ago, Chris1992 said:

Not confusing at all mate its good to learn now I sort of understand why our 240v equipment is not directly compatible with yours 

what waight class RV are we talking here? 

Chris, I'm just a "small fry" as compared to the behemoths many others here operate. I have a 29 Ft Class C cabover van style motorhome, 13,000+ lbs., reason being we are quite mobile and do a lot of Natl Forest and Natl Park (some with length restrictions) and BLM camping and dry boondock camping and on narrow steep tight mountain roads out west our smaller rig is just easier to maneuver and park, yet still just big enough to live in months on end. 

John T

[Chris1992]

Thanks for the reply

that is your small At 13000lbs way over my limit atm limited to 7000lbs so need to up my licence to a class 2 but it's on my list at some point although I don't really know how the licencing laws transfer 

[Yarome]

1 hour ago, Chris1992 said:

....I don't really know how the licencing laws transfer 

You wouldn't need a class 2 to drive in the U.S.. Short term UK visitors can drive under the same laws as a U.S. citizen on their category B licenses, however, many states also require you to have a valid IDP (International Drivers Permit) as well. That would need to be obtained prior to entering the U.S..

IDP's are more of a paperwork deal and only requires a valid license and a fee (beware of online IDP service providers. Many are scams and charge exhorbitant fees.)  No test is required. It's basically just a standardized document to show your are a valid license holder in your own country instead of some local officer in "whatever" state trying to read your foreign issued license and determine if it is real or not. 

So yeah... you could drive Johns rig with what you already got. 

To note: Your IDP is also valid in any number of different countries.

[Chris1992]

You have all been very useful and that is very useful info to know I will remember that for when I have the money and have the passport but most importantly have the time to visit the US  i will most likely get a IDP from the post ofice and i will have to get some recommendations from you all closer to that time for now I'm still seeing the UK