Monday, 26 September 2016

When did you last check your wiring ?

One for my records but some may find it interesting .....

I blogged a few weeks back about my Smartgauge error codes and my concern I had not got the best performing battery bank in the way I had it connected. Halfie off NB Jubilee reminded me of something I'd seen before from the guy who invented the Smartgauge -Gibbo.  

My set up was worse that the one below in that:
  • I was putting feeds in and taking load out from different points on the three bank battery set up
  • I had wildly different lengths of interconnecting cables
  • My 'third' battery was remote and not installed in a way it would pass the BSC
  • I was getting E11 errors where the Smartgauge was activating the relay to connect the starter and leisure batteries together but still reading different voltages
    • this can only be if the relay is not working or
    • The cables on the two banks are so different there is voltage drop and the banks show different voltages....hence the error 
Back to best practice .....

From the Smartgauge web site... 

If we draw 100 amps from this battery bank we will effectively be drawing 25 amps from each battery. Or so we think.
In actual fact what we find is that more current is drawn from the bottom battery, with the current draw getting progressively less as we get towards the top of the diagram.
The effect is greater than would be expected.

Battery internal resistance = 0.02 Ohms
Interconnecting lead resistance = 0.0015 Ohms per link
Total load on batteries = 100 amps
The bottom battery provides 35.9 amps of this.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.
So the bottom battery provides over twice the current of the top battery.

So I decided to move out the starter and put it into a proper battery box  - plastic and lidded leaving the area free for my third leisure battery. In moving them about I then made up and crimped and heat shrinked new leads all the same size (length and girth  - AWG American wire gauge '2' or 35mm2 ) 

Method 2
All that has changed in this diagram is that the main feeds to the rest of the installation are now taken from diagonally opposite posts.
It is simple to achieve but the difference in the results are truly astounding for such a simple modification.
The connecting leads, in fact, everything else in the installation remains identical.
Also, it doesn't matter which lead (positive or negative) is moved, Whichever is easiest is the correct one to move.
The results of this modification, when compared to the original diagram are shown below. Only that one single connection has been moved.

After this simple modification, with the same 100 amp load....
The bottom battery provides 26.7 amps of this.
The next battery up provides 23.2 amps.
The next battery up provides 23.2 amps.
The top battery provides 26.7 amps.
This is quite clearly a massive improvement over the first method. The batteries are much closer to being correctly balanced. H
So this was the before with the starter at the top...

This is  now all three leisure batteries connected  - tidy and hopefully efficient. Once challenge is getting all the connections onto the battery terminals. I couldn't so I nipped over the Streethay and brought two terminal clamps (did you ever realise the pos and neg posts are a different girth?) 

The starter sits in its own box now by the side of the engine. it is still all connected to the split charging relay but with the advantage of much of the Samrtbank wiring and control box now living safely in a sectioned off part - quite tidy. 

Problem is when I got back to the boat today I still had an E11 code - I am thinking the relay may want its contacts cleaning - or the boat a good run - I will do the latter first !

Now the scary bit....I found this wear and damage on the main 12v pos feed off the batteries ...!!

On Waterlily we had electrical problems due to a wire shorting out in the engine hole, this could have given the same effect but much worse!!

I was able to trim back to decent cable section and remake the connection.

So I may have to remove the relay and check it but I am hoping a nice deep charge from an extended cruise will sort it all out !!