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December 17, 2010 at 7:07 pm #36768
Many off gridders choose 12V systems for a variety of reasons. Among the reasons is a perception this is safer than 120V inverter driven systems.
Unfortunately many of these systens are DIY and include short cuts taken by people who are not trained to work with electrical systems. One of the many short cuts is just twisting wires together and covering with a bit of tape. s a marine electricians I have seen actual fires as well as incipient fires in 12V circuits carrying less than 10 amps sometimes as little as 4 amps.
It is current not voltage that causes heat in a circuit. If the resistance of a connection is high enough it will heat up. A loose connection will heat up and left undisturbed will reach the ignition temperature of plastics and wood.
There are several products on the market to prove this statement. Cold heat is a soldering iron which can deliver 700F temperatures to the soldering tip and melt solder. The product is powered by a set of 1.5V AA batteries.
With the coming of winter in the northern hemisphere we also have longer periods of darness and interior lighting is used for longer periods. This is prime time for 12V circuits to develop excess heat in high resistance connections and cause fire in RV and camper applications. For safety sake, check your 12V circuits and all connections for signs of heat creation. check all terminal screws are tight and do not rely on simply twisting the wires together and covering it with a bit of tape. Such connections do not have the tight join between wire surfaces. AS the wires oxidize it increases resistance and eventually this will overheat. Dampness will accelerate the corrosion / oxidation so any damp location is more prone to developing problems.December 17, 2010 at 9:22 pm #41187
Very good advice
12 volt is more of a fire hazard than higher ac voltages
all my 12 volt conections are soldered even my crimp ring terminals are soldered as well.
I spent many years installing accesories into cars,trucks and boats and if it wasnt soldered it would be back one day coroded or burned out or causing some sort of wierd fault.
if you have any twist conections or crimp conections that now need to be redone you may now have to use an acid core solder as they are likely coroded beyond soldering with standard rosin core electrical soldersDecember 18, 2010 at 12:25 am #41188
Acid core solder has its own risks and problems. Unless you have experience with handling this it is not recommended for the typical DIYer. Presumably the original wiring was done correctly with a suitable service loop so you can cut back the corroded crimp and remake it. Sealing the cut ends with a dab of solder on the lug side of the crimp is fine but generally all standards now prohibit solder only connections.
These days newer technology is available so now its easier to get adhesive lined wshrink tubing waterproof crimp lugs. The come is various sizes and styles. The better automotive wholesale supply stores carry them under the application heading of waterproof trailer wiring devices. You are not likely to find them in the ordinary big box consumer stores. Go to an industrial wholesaler or if they do not sell to the public, find out where the nearest commercial user is located then go and buy what you need there. Be aware these do cost more but are worth while because of superior quality long life splicing. Experienced wiring guys can also improvise by using non insulated lugs and long bulk lenghts of adhesive lined shrink tubing.
If you are working in a vehicle that is often on the road and thus subject to vibration do not solder connections. Extensive testing has proven soldered connection of stranded wire causes a hard point that will fail as the copper strands fail due to work hardening at the flex point.December 18, 2010 at 12:28 am #41189
Given a choice of one shot fuses or circuit breakers chose breakers. Yes the fuses are cheaper but Murphy’s Law says the fuse you blow will be the one size you no longer have a spare for. IIf you accidentally trip a breaker you fix the problem then reset the breaker. Power restored and you do not have to scrabble around looking for wher you last remember storing the extra fuses.December 18, 2010 at 1:30 am #41190
A couple of years in service and many wires are already coroded right up the insulation ive seen this many times either replace the wire completely or use acid core.
its not such a big deal with houshold wires which seem to be less strands of thicker wires but in auto aplications the wires tend to be more strands of thiner wire to stand up to lots of flexing these wires will quickly become
unservicable due to corosion and you will need to replace or use an acid core
could also have something to do with the quality of the wire but i would expect many of us off griders to skimp on wire cost or recycle if we can.
also totally disagree with the automotive case they do become weaker at the joint thats a fact, but good taping or shrink wrap will aleviate that problem and you will have a joint that will outlast any crimp connection even a factory original.
main problem you have with a solder joint is flexing either side of the solder
good taping or shrink wrap to provide strain relief will aleviate that problem.December 21, 2010 at 7:56 am #41192
I find that crimp connections that fail are often made with inferior crimpers. I got a T&B crimper (the TBM45S is ideal for the usual wire sizes you use on an offgrid system, the TBM-8 is for *really big* wires).
I got a TBM45S and the crimps *never* come loose. They’re awesome.
(Yes they’re expensive. I bought mine from Specialized but you can get them for roughly half of that by looking around for construction people selling them in craigslist and ebay). However you wont make a faulty crimp again.December 21, 2010 at 8:27 pm #41197
Remember that all DC fuses and breakers must be manufactured and listed for DC service and listed for use in DC service. Arc flash is very different in DC than AC, since there’s never a return to zero voltage and current in DC. AC devices will catch fire, since they are not designed to open properly for use with DC.
Under NEC 2011, all DC breakers are also required to sense arc flash in the system and open immediately.
Don’t use automotive devices – unsafe and illegal in PV applications.
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