Using the same cables for charge controller and inverter.

[Retep]

Hello all and thank you for your help.

  On my friend's '85 house bus on which I am helping install solar, the inverter is a 16 foot run of 1/0 from the 12V battery bank.  Not changeable.  The Classic 150 will be mounted next to the inverter.  No other spot unless I put it in the engine/battery compartment.  She has on hand, a second run of 1/0 I was planning on pairing with the existing 16 foot run and have the paired wires (2 positive and 2 negative- not the same length runs) serve both the charge controller and the inverter.  Is there a problem with this idea?

Thank you-  Peter.

[dgd]

If the controller is beside the inverter then just connect it to the existing cabling to the inverter.
Use a breaker to the controller.
Since current tends to flow from battery to inverter and the other direction for controller then the existing 1/0 should be more than capable.
Also you could insert a shunt near the battery -ve connection and get the controller via WBjr to monitor battery SOC

Dgd

[Retep]

Thanks dgd.  I couldn't see anything wrong with using the same cable, but somewhere in my readings I had seen a warning against it, though I cannot find that post now.  Possibly too much solar forum reading leads to hallucination?

  She already has a Trimetric battery monitor I am installing with a 1000amp/100mv shunt.  Her starter supposedly pulls 1000 amps!

  We already have the extra 1/0 THHN to make a second run, so I'm imagining that pairing the cables, though they will be of a different length and path, and using the inverter's studs as my bus would be the optimum with what we have.  If I am wrong, please correct me.

  Thank you for your help-  Peter.

[TomW]

Thanks dgd.  I couldn't see anything wrong with using the same cable, but somewhere in my readings I had seen a warning against it, though I cannot find that post now.  Possibly too much solar forum reading leads to hallucination?

  She already has a Trimetric battery monitor I am installing with a 1000amp/100mv shunt.  Her starter supposedly pulls 1000 amps!

  We already have the extra 1/0 THHN to make a second run, so I'm imagining that pairing the cables, though they will be of a different length and path, and using the inverter's studs as my bus would be the optimum with what we have.  If I am wrong, please correct me.

  Thank you for your help-  Peter.

It is good to remember that just because you read it on the interweb thingy Does Not mean it is true.

I believe this method it is not ideal but should work OK.

Tom

[zoneblue]

Theres two issues there sag for the inverter, and battery charge voltage mismonitoring.

These sorts of things always boil down to "what is the voltage drop on the cable?"

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.3224&voltage=12&phase=dc&noofconductor=1&distance=16&distanceunit=feet&amperes=100&x=40&y=16

100amps is one third of a volt, 2.5%.   
50 amps will half that. 
200amps double etc.

[Retep]

Thanks all.

Zone blue- assuming 14.5 volts to charge the 12V 6 golf cart bank which is 16' away, if I limit it to 10%- 66A,
Voltage drop: 0.21
Voltage drop percentage: 1.45%
Voltage at the end: 14.29

with paired 1/0, assuming they carry equal loads, which they will not due to impossibility of matching length, age, tarnish, etc.
Voltage drop: 0.10
Voltage drop percentage: 0.69%
Voltage at the end: 14.4

The question as best as I can figure it, is will varying fits and starts of the inverter give the charge controller- Classic lite 150- fits of its own if the charge controller is connected at the inverter end of the cables instead of the battery end where possibly the batteries will cushion  the variances.

Thank you all so much-  Peter.

[zoneblue]

For charging what can happen if theres any drop on the battery cable, is that the charge controller thinks the battery is less charged than it is. One way around that for controllers with sense lines is run a seperate low guage wire to the battery. Classics dont have that however. The usual advice is use a decent cable between controller and battery. However lead acid is reasonable tolerant of overcharging so long as the batterys are maintained. As the charge current reduces so does the lost volatage and things will tend to come right near end of charge.

However you have double motivation of fix this properly. Dropping half a volt will cause the inverter to drop off line early, and struggle with peak loads.

>Also you could insert a shunt near the battery -ve connection and get the controller via WBjr to monitor battery SOC

If you use a WBJr near the battery it *should* be capable of tracking the actual terminal voltage, but youd need to check this with boB, if this functionality currently has been implemented.