What size battery cable are you running from the Classic?

[cb487]

Hi dgd,

I'm not sure I understand what you mean by there being an option to wire PV- directly to the battery.  PV-, Bat- and Classic-, by design need to be tied at the same point. Going through a shunt through any of those connections is OK, since a shunt is very close to being a wire.

Because of PV-, Bat- and Classic- tied are at the same point, and because of the way that the Classic works, any current on Classic- can only be Classic internal consumption. The Classic's job is to meter power from PV+ through to Bat+. Hypothetically, if you used a wire, resistor or diode in place of a Classic, all power would pass through this path. When my Classic has 4800 Watts of PV power presented to it, it is probably running at 90% efficiency. 4300 Watts makes it to the battery. The Classic is a DC to DC converter and there are always measurable switching and conversion losses. The only path for power in the Classic to go that doesn't go to the battery is through Classic-.

Chris

[grgdgreek]

Hello,
Just got done installing my new classics (2 *150) .
I love em!!
Is it me or are the terminals a wee bit ehhh... tight?

[Westbranch]

Well depends on what you mean by tight...  but YES forr $ ga they can be frustrating,  especially if using multi strand... Factory IIRC uses THHN ...

[Vic]

Well depends on what you mean by tight...  but YES forr $ ga they can be frustrating,  especially if using multi strand... Factory IIRC uses THHN ...

Really should not use Fine-Stranded cables on compression connectors.  19-strand is the most common cable as THHN / / / cables,  and that (as well as seven-strand) is what those connector for.   One could use Ferrules,  but  why?   Long runs,  with LARGE cable might need to be fine-strand,  and IMO,  those could easily use rated lugs,  and bolt down connections.

Have not found #4 19-strand THHN cable to be a real fit problem into the Classic's battery terminals.  One just needs to carefully prepare the stripped end,  so that all conductors are laid up properly.

Opinions,   Vic

[dgd]

I'm not sure I understand what you mean by there being an option to wire PV- directly to the battery.  PV-, Bat- and Classic-, by design need to be tied at the same point. 

There are two options with the PV-
the first is to have it connect into the PV- of the Classic,
the second is to connect it directly to the NEG common point on the shunt (where inverter and Classic
negs connect to)

You are using the second and the effect of this is that you only see 4A flowing in the cable between the Classic's BATT- terminal and the NEG common on the shunt.
I'm trying to understand what that current flow is telling us and if we can monitor and use that data over time and gain some information about the system performance.

As for using a much smaller gauge for the Classic's BATT- cable what about simply inserting a 5A breaker in it as a safety in case of failure elsewhere causing a larger current flow?

dgd

[cb487]

Hi dgd,

Inserting a circuit breaker on the Classic- line would address the fault conditions I was referring to. But the only situation I can think of where it would be advantageous to this would be if there is no room to route a 4 AWG wire. That's because putting a breaker on the Classic- line has the following disadvantages:

Cost. A DC breaker is significantly more expensive than upsizing a copper wire.
Efficiency: A circuit breaker consumes a lot more power than the wire it is assigned to protect.
Room: Now a circuit breaker slot has to be allocated.

Also, 5A is not big enough for a single Classic. At full power, a Classic can consume 9A @ 48V. So the exact current rating of a breaker there needs to be calculated precisely.

I have a question for you: the conduit holes on the sides and bottom of a Classic, do they line up with metric-sized electrical fittings?

Chris

[dgd]

Chris,

You are right thats its not worth the cost of a breaker or the bother or cabling to where it is mounted.

I am having some difficulty getting my head around these current flows and what is happening with the neg cable from the Classic to the neg bus (or shunt) when the neg from PV goes direct to the shunt.
I have a spare Classic /battery/PVs that I use mostly for software testing so I might just wire it up with PV- direct to shunt and monitor all the current flows  i.e using an acs758 in Classic BATT- to shunt and another in PV- cable to shunt, the normal WBjr/Deltec and collecting data over a few days and listing/graphing in Arduino web server.

There must be a simple explanation but it eludes me (probably a case of can't see the wood because of the trees!)

Anyway, thanks for giving the original thought to explore this, I am always interested in discovering new data sources that may increase my understanding of system performance and efficiency.

As for metric fittings in Classic's case holes, its been a while but the cable glands I use are metric and I found some that almost exactly fit those cutouts

dgd