Hi folks and my apologies for taking so long to get something going in the thread but I’m working 7 days a week, trying to keep order delivery times down.
But in the last month or so, I have had a number of situations brought to my attention, where people have either purchased an “expert designed” dual battery kit or had a dual battery system installed by a “professional”, and have end up with a death trap.
While most of the gear I supply Land Rover owners, is in kit form, and therefore is designed to be a safe as possible, but since the introduction of the latest versions of my isolators, I am supplying a lot more isolators to people with other makes of vehicles, and quite a few of these people already have had systems fitted and either want to upgrade their isolator or are planning on fitting their own set up because I do not have a vehicle specific kit for them.
What is happening, when people are purchasing one of my isolators, to make sure they are getting the best isolator for what they want to achieve, I will often ask them about their current or intended setup. This is where I am hearing about the down and outright death traps being supplied or fitted by self proclaimed “experts”.
The problem comes from people, who have no idea what they are selling, but they are giving “professional” advice about how a dual battery setup should be equipped. Again, this is info from people who have no genuine auto electrical knowledge, particularly when it comes to auto electrical SAFETY requirements.
Almost every component used in any dual battery setup has operational characteristics that most people are unaware of, especially safety perimeters that MUST be factored in when designing a dual battery setup.
The most common error, and the most dangerous one, is the use of totally inappropriate sized fuses and circuit breakers.
Here is an example.
There is an individual who has a book out on requirements for setting up for RV use, which covers all manor of RV subjects, including electrical “advice”. In the advertising used to promote his book, he displays a diagram of a basic dual battery wiring setup.
In his diagram he uses 6B&S cable to run from the tow vehicle to the house battery in the caravan and this is a good choice.
He recommends the use of 50 amp Anderson Power Connectors to connect the cable between the tow vehicle and the caravan, and again, a good choice.
He shows fuses being used near the batteries at each end of the cable, which is the correct safety requirement for this type of auto electrical setup.
Then it all goes pear shaped because he recommends using 100 amp fuses at each end of the cable.
While there is a lot more to it, which I will cover in more detail in a later post, but surely commonsense ( not auto electrical knowledge ) would dictate that if you are using a 50 amp rated Anderson plug, then the maximum current rate of the circuit protection device for the same circuit should be no more than 50 amps, not 100 amps.
6B&S cabling is rated at a maximum continuos current of 105 amps BUT, this is in open air, which the cabling is not, when run through a vehicle.
A number of cable manufacturers have DERATING tables on their websites, making it pretty easy to work out safe maximum current capacities of deferent cable sizes, including 6B&S. The maximum safe continuos current for 6B&S should be based at around 80 amps.
While 50 amp Anderson plugs are called just that, 50 amp, but in the right circumstances, a 50 amp Anderson plus can safely carry a continuos current load of 95 amps. More on this later.
Here is where the real danger lays. Few people working in this industry have never bothered to look up the operating specs for the standard automotive fuses or circuit breakers, and this has lead to grossly higher current rated fuses and circuit breakers ( CB ) being commonly used where they should not be used.
First off, the current marked on an automotive fuse or CB is what that fuse or CB is designed to carry for at least 4 hours. But to be able to carry it’s marked rate for 4 hours, it needs to carry higher currents for shorter times.
On average, automotive fuses and CBs will carry 125% to 135% of their marked rate for around 30 minutes and much higher currents for shorter periods.
This means that the 6B&S cable in the diagram could carry 135 amps for 30 minutes without causing the fuse to go open circuit ( to blow ), which means, for 30 minutes, the cable could be carrying around a 75% high current than the cable can safely handle.
Now to the specs for a 50 amp Anderson plug. The maximum continuos safe current for a 50 amp Anderson plug is 95 amps, but this is at 25C, but with 6B&S cable connected to the Anderson plug and with the cable carrying it’s maximum safe current limit of 80 amps, the cable will be quite WARM at that current rate and will cause the Anderson plug to run at a higher temperature.
The cabling and plug are going to be closer to 50C, which brings the Anderson plug’s safe maximum current rate down to around 75 amps.
So with the maximum safe current for the 50 amp Anderson plug being around 75 amps and the 100 amp fuse not likely to go open circuit with currents under 135 amps, you risk having currents nearly double the safe maximum being carried through the Anderson plug for around 30 minutes.
NOTE, until recently, a well known Australian supplier of dual battery gear also recommended 100 amp fuses in similar setups????
When setting up a dual battery system using 6B&S cabling, the maximum current rating for in-line fuse or circuit breaker protection is 60 amps, not 100 amps. To improve the safety of my dual battery systems, I prefer 50 amp Auto Resetting Circuit Breakers, but I will cover this in a later post.
While I would not classify the misinformation in the diagram as amounting to being a death trap, it is exceedingly dangerous. In my next post I will show how companies, who are nothing more than Box Sellers, are putting people’s lives at risk by selling much more dangerous setups.
Bookmarks