The blue terminal blocks on the Classics say 6 AWG (#6) wire. I just switched to #4 AWG (tight fit). According AWG and NEC, for power transmission #6 is good for 37 amps and #4 is good for 60 amps. The Classic 150 can output 90+ amps. Am I missing something here? Please advise.
Chris
What voltage are you running ?
I just plugged a few numbers in this calculator
12v , 90 amps, 6 feet, 3% loss and it shows 5 gauge wire.
http://www.freesunpower.com/wire_calc.php
Go higher in voltage and the wire size will come down. There are voltage drop calculators on the internet where you can design the whole wiring system.
Also look here
http://www.affordable-solar.com/solar-tools/wire-sizing-charts/
Also search around on the group here - this discussion has been done before .
Larry
In addition to what Larry mentioned,
The Ampacity Table is a good guide of what is Permissible for cables according to the NEC. Here is such a table:
http://www.cerrowire.com/ampacity-charts
In this table, you will see that THHN and similar COPPER cables have a Maximum Ampacity of 65 Amps for #6 AWG, and 85 Amps for #4 AWG -- use the 75 C column, as this is usually the maximum temperature permitted for most circuit breaker terminals, connectors, and terminal blocks, as are used on the Classic.
The above Ampacities are for only a maximum of three current-carrying conductors in a Raceway, conduit, etc. More than three conductors, up to six conductors, derate the above ratings to 80% (multiply by 0.8).
There are also deratings for Ambient temperatures above 30 degrees C.
NEC is generally considered to be very conservative regarding Ampacity of cables.
If you wish to use larger conductors than #4 on a Classic, you can use a short piece of number 6 or 4 AWG to a junction box, or perhaps, the enclosure that contains the breaker for the cables that connects the Classic to the battery. From the other side of this breaker, you can get as crazy with as largea cable as can be accommodated by that breaker's terminals.
For e-panels and similar "conduit & breaker boxes", the Free Air Ampacity will usually apply, which allows higher Ampacities, as these cables are not contained in a small space (like in conduit), and/or these cable runs are usually quite short, and so on.
Am notta Code Maven, but this is my read on things, FWIW, Vic
My system is a 24v (Outback Power VFX3524 + Mate 3). Roger that...thanks. I am using TEMCo #4 welding cable (lots of strands). Less than six feet for both POS and NEG. I run through a Baby Big Box and then down to the Blue Seas Systems 250A busbars. Just did the upgrade. But, I can already notice the improvement (power is up and heat is way down).
Hi again Chris,
Regarding the #4 Welding Cable. If you are using this for the battery connection from the Classic to the battery breaker, and from the battery breaker to the battery busbar, would say that this is not such a good idea. Fine-strand cable is not specified, generally, for these screw-compression type terminals.
The main reasons that it is best to NOT use fine strand cables on compression terminals, is that, first, fine strand cable is larger in diameter, and #4 b AWG fine cable will probably be a bit too large for the Classic terminal block. And, fine-strand cable cold-flows more than standard Building wire, like THHN (19 strands, generally), such that, there is a much greater chance that over a period of time (weeks/months) that the compression connection will become less tight, causing increased resistance. Higher R causes more local heating. Temperature cycling can cause further loosening, and more resistance, and so on. This is not a good situation, and could cause damage, poor performance, and perhaps local burning of insulation, terminals and/or busbars.
You may not have used this fine-strand cable for these connections, but just FYI, in case you did not know ...
Using fine cable in Lugs that are designed for it, and with Dies that are designed for those lugs is the proper way to use fine-strand cable.
FWIW, Vic
Yes, fine strand , but use ferules, or some solder to hold the strand bundle together (people argue about this).
Or do what most people do, mount the classics on the side of the disco, and run very short classic cable (less than a foot), so cable gauge is less critical. HOwever if like here youll lose a few tens of mV in the (blasted) carling breaker, and this will be as likely as not be greater than any cable loss.
I use swedge ferules as in pix.
red small double red larger , blue , double blue etc. then yellow to green that is for #3AWG
Loading pix screwed up the post .
Thanks! FYI - Had a stellar sunny day yesterday and my wiring and DC breakers in the Baby Big Box barely got warm at full power! So, the #4 AWG TEMCo welding cable is working. And working well.
Can I get a product link for those ferrules? Solderless? I can also "tin" the cable ends. I agree, with what you said about compression fittings on fine strand wire...good idea.
Thanks.
My Classic 150's 4 AWG wire got VERY warm whenever my Classic 150 outputs 70 Amps or more. So I changed all the wires to 2AWG, except for the -48V cable that connects the Classic to the -48V bus. That cable never passes more than a few Amps (only power that is consumed by the Classic itself). I left it at 4 AWG.
At this time of year, my Classic outputs 80+ Amps, and even 2 AWG wire gets warm.
The Classics don't actually support wire bigger than 4 AWG, so I used a wire stripper to cut just enough outer strands of the wire to fit the Classic wire terminals.
Running high power can challenge a system design. Originally I placed the two +48V 100 Amp breakers next to each other. I discovered that they would trip before hitting 100 Amps because of heat buildup. I've since spaced them apart enough so that air can naturally flow between them to fix this.
Chris
I think there will be the same current flow in +ve and -ve cables to Classic
You should be able to use short lengths of #4 to the DC distribution box, epanel, mndc etc
Then from there use larger cables such as #00 or #000 to the battery bank
dgd
If you have a DC-capable clamp meter, use it to measure the Amps running through the -48 lead on the Classic. E.g., when 80 Amps was passing through my Classic, the -48 lead showed only 4 Amps. Where is the rest of the current? It's flowing from the PV array -48 lead directly to my SW Plus Grid tie inverter. The 4 Amps is the PV power being consumed by the Classic itself.
Chris
Ok, I have not seen this before but then I have my PV array + and - wired into the Classic then the Classic Batt + and - 4gauge wired to Epanel. This means I see 70amps in both the + and - Batt wires to the Classic
In your config you have the PV- direct to Epanel?
I think I have seen this in some of the Midnite wiring diagrams but it never occured to me that this would mean only the Classic BATT+ connector would need to be a decent gauge cable with the BATT- possibly being much smaller 6 or 8 gauge. :o
dgd
POS + is the cable size to consider on this topic. ( the wiring schematic way ) I run 4 Gauge not fine strand. I have used temp scene guns to see hot spots .
VT
& the ferules are pre 80's .
We have many in Pico
Responding to dgd here ...
The copper between my battery bank and the inverter is 4/0 protected by 250A breaker. PV- is tied to the same place as Bat- and Classic-.
Actually you can't downsize the Classic -48 wire, even though it ordinarily carries only a few Amps. Here is why: There are fault conditions in which the Classic would need that wire to carry a current the equal of what either of the Classic 48+ wires ordinarily carry. In such a runaway fault situation, only one of the two Classic DC circuit breakers would be able to put a stop to that. If the Classic -48 wire was say a 10 AWG or 8 AWG, it could go incandescent without drawing enough current to trip the Classic +48 breakers.
Chris
So from what you are saying there is basically no advantage in wiring the PV- direct to the common
battery negative since its still necessary to have two same gauge cables, #4, to the Classic battery + and - connectors.
You may as well just wire the PV - and + to the PV inputs in the Classic.
Usually there will be a 500A Deltec shunt connected via 3/0, 4/0, 70mm2 or 90mm2
cable to the battery -ve. The other side of the shunt will be the common negative point for inverter connection and other devices such as charge controllers etc
The battery +ve 70mm2 cable uses one end of the 250A breaker as a +ve common connection point with the other end of the breaker connecting to the inverter +ve
Your original post interested me because you seemed to believe the 4A you measured in the -ve wire was indicating the power consumed by the Classic. That didn't look right to me as it would mean the Classic was consuming about 200 watts.
Or did I misunderstand what you really thought this 4A current flow was really showing?
dgd
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
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?
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 ...
Quote from: Westbranch on May 18, 2016, 04:00:25 PM
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
Quote from: cb487 on May 18, 2016, 10:33:26 AM
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
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
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