[RE-wrenches] Battery Bank to Inverter Wiring

Jarmo.Venalainen at schneider-electric.com Jarmo.Venalainen at schneider-electric.com
Fri Jun 26 10:45:14 PDT 2015


Hi:

>From time to time over the years I've come across systems where the 
routing of DC cables between the batteries and the inverter has been the 
cause of  issues.

I'm not referring to wire thickness or quality of terminations.  For the 
purposes of this discussion, just assume that wire thickness and 
terminations are perfect.

What I am referring to is the routing of the positive and negative battery 
cables.  In particular, the loop area within the + and - cables as shown 
in the image below,


The problem I've seen in systems with a large loop in the setup is that 
the inverter does not provide good surge power and can even go into low 
voltage shutdown during large surges.

Recently this happened again and I wanted to get a better feel for it, so 
I did some math. 

For a cable length of about 12', the loop is an inductor which has a value 
of inductance of about 1 uH for side by side cables and as much as 6 uH 
for cables about 1 foot apart. 

This inductance is greatly multiplied by any ferrous metal in the loop and 
can easily be in the range of 10's to 100's of uH.  Examples being cables 
which run in steel conduits or along the steel frame of a motor home.

Inductance causes a voltage drop proportional to the rate at which the 
current is changing.  To get an idea of how large that rate can be for 
typical inverters, I did surge tests with a 5kW inverter and found that 
the rate of change of current can be as high as 100A per milli-second or 
100,000 Amps/second.

Given that, the voltage drop of the wire inductance is then , Vdrop = 
(rate of change of current) x (inductance), 

Vdrop for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V
Vdrop for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V
Vdrop for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V    clearly this is 
a problem.

Have any of the wrenches had systems with this issue?  If so, how often.


JARMO


 
_____________________________________________________________________________________ 


Jarmo Venalainen  |   Schneider Electric   |  Xantrex Brand  |   CANADA  | 
  Sales Application Engineer 
Phone: +604-422-2528  |   Tech Support: 800-670-0707  |   Mobile: 
+604-505-0291 
Email: jarmo.venalainen at schneider-electric.com  |   Site: www.Xantrex.com 
|   Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 








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