Doubling Wire Run

[deadwood]

Blue sea is the marine standard. The only thing scarier than an electrical fire in a van is an electrical fire on a boat. They have all sorts of free resources and great tech tips written by Marine Electrical Engineers and you don't have to buy their products. I do because I see it as insurance as well. Pay once and have it work.


And the only thing scarier then an electrical fire in a van or on a boat is an electrical fire on an airplane. This is why in all three applications you take the best precautions you can. Build it right the first time.

 

[MarkK]

15481[/ATTACH] Scott7022 pid='327821' dateline='1504540608']Using the blue sea Calculator we see that 12 volts at 9 amps over 25 feet is ok with 12 gauge both for amps and 3% voltage drop No doubling required . So you answered your own question. Doubling isn't shown as isn't preferred method for reasons already pointed out. Doubling starts to happen with big length runs and/or huge amps. Rarely seen in our applications. Four Ought cable in my run was stupid big.

Smart and stupid are always relative to the subject matter. I didn't mean to offend, and if I did I apologize. My point was people assuming someones ability at a skill set. In this case wiring. So if you are coming directly off the battery and drawing 9 amps make sure you splice in a 10 or 15 amp fuse with 12 gauge or slightly larger wire as close to the battery as you can. Ideally within 9 inches.

It's all good Scott. I was confirming my skill level with electrical.

The run I am speaking of is from the panels to Charge Controller. Panels are sending 9 amps. The physical run is about 25' one way, and it seems that the measurement must be doubled for proper calculations. I already know I am losing about .7V along this physical run using 12awg wire. Inline fuses are at the panels, and at the batteries.

My panels came wired with 14awg to the cheap CC at the panel. That is about 4' of wire. Hope I'm not setting up a bottle neck here and am interested in re-wiring with heavier gauge and possibly using mc4's to connect as shoving 2 runs of heavier cable into the panel control box looks unlikely due to size.

In another thread I learned it will make more sense to get the CC closer to the batteries, which is what I will be doing by weeks end. The question now is whether to invest in 8 or 10 wire if the calculatoris supposed to have 25' or 50' entered for the run. Possibly this is where clarification is needed for me.

 

[John61CT]

Yes, controllers need to be at the bank.

#8 should be fine, #6 if less voltage drop desired. Get panel output voltage up and #10 is fine.

No harm in lighter-gauge at one end and heavier for the rest.

Just make sure to use good terminators and quality crimpers, or get a pro.

Also genuinedealz.com is fantastic.

 

[MarkK]

 Get panel output voltage up and #10 is fine.

No harm in lighter-gauge at one end and heavier for the rest.

Thanks John.

What do you mean by getting panel voltage up?

As to lighter and heavier. The lighter runs off the panels for a fee feet with 14 awg, if I go with 8 or 10 isn't very limiting on overall through put?

 

[ChetLazar]

In another thread I learned it will make more sense to get the CC closer to the batteries, which is what I will be doing by weeks end. The question now is whether to invest in 8 or 10 wire if the calculatoris supposed to have 25' or 50' entered for the run. Possibly this is where clarification is needed for me.

Are you are getting a new controller as the old one is glued on?  Is the new one MPPT?  If it is, connect the panels in series.  That cuts the current in half.  That cuts the voltage drop in half.  Without touching the wire it is in effect doubled.

 

[John61CT]

Have a close look at output from the Blue Sea app.

You'll see the gauge required for heat safety is **much** lighter than what you need to reduce voltage drops.

Plus a very short length like that will carry lots more amps than a long length.

In short, no problem.

Higher voltages don't require wiring as thick, so buying higher voltage panels saves cabling costs, and gives more headroom for MPPT to do its thing.

Also putting existing panels in series, long as you don't allow partial shading.

 

[ChetLazar]

Also putting existing panels in series, long as you don't allow partial shading.

Nominally 12 volt panels typically are wired in two 18 cell segments with bypass diodes to sidestep panel destroying hot spots caused by shading.  

Two panels in parallel, partial shade taking out one segment reduces power to half.  

Two panels in series, 4 segments in series, shading one segment reduces harvested power to three fourths.  The voltage is three fourths.  The bypass diode for the shaded segment carries the current.  The voltage at the MPPT controller goes from 40 to 30.  Loss of only 25% is much better than loss of half.

Series connection does not need an extra warning about partial shading over parallel connection.  The opposite is true.

 

[John61CT]

Post a new topic on the question (please!) and you'll get contention from some long-time very experienced members.

And not **all** panels have any such diodes.

 

[MarkK]

Are you are getting a new controller as the old one is glued on?  Is the new one MPPT?  If it is, connect the panels in series.  That cuts the current in half.  That cuts the voltage drop in half.  Without touching the wire it is in effect doubled.

I am getting the Victron mppt 75/15. Only concern for series is partial shading, but the rewire to series allowing me to stay with 12awg is tempting.

 

[ChetLazar]

Only concern for series is partial shading, 

They are portable panels.  Shading should be easily avoidable.

 

[MarkK]

They are portable panels.  Shading should be easily avoidable.

So if the CC receives say 35V but only 4A instead of 17.5V at 8A is it converting the extra Volts to amps at all stages, bulk, absorb, and float?

 

[ChetLazar]

So if the CC receives say 35V but only 4A instead of 17.5V at 8A is it converting the extra Volts to amps at all stages, bulk, absorb, and float?

Yes and no.  If the battery is full and the controller is just maintaining the float voltage it will not be pushing 8 amps into the battery.  You don't want it to do that.

However, in the prior thread jimindenver explained that the MPPT controller steps down the volts and steps up the amps no matter where the amps go.  If there is a load, a device, an appliance, a TV, a phone charger, a fridge, or computer, the available amps at 12 volts is more than the 4 amps at 35 volts.

The Eco-worthy 20a MPPT controller can be had from their site for $100, less on ebay. I have used them for 5 years, they are adjustable with a LED display. I have never had one fry. Would you get more power parallel vs series would be a interesting test.

As for does a MPPT controller continue to do it's thing after the bulk stage? That depends on what you mean by its thing. The MPPT program that controls the voltage in bulk mode stops functioning in absorb and float. It stops because there is no longer a need to control the voltage because the battery controlling both the voltage and acceptance rate. It also searches the array for the sweet spot that creates the most amps. The thing is the MPPT program is not what takes the excess volts and creates amps. The buck converter is. The power comes in from the panels as DC, is converted to AC and then back to DC again. It is what takes high voltage/low amps and allows it to come out low voltage/high amps to a PWM controller. There is no by pass of the buck converter to the PWM controller and you still get the benefit of the conversion.

I will have to see how many of the graphs and schematic was lost to Photobucket but yes I have proof. It started when I realized I could put a 15a load on a 230w panel with a MPPT controller in float and not have the batteries voltage drop. The panel was a high voltage panel with a Voc of 34 and was rated for under 9 amps Isc. Were the buck converter not still doing its thing the battery should have started dropping in voltage once the load passed 9 amps. I have seen my three panels on the roof of the trailer that are run in series for 105v and under 9 amps Isc produce 45 amps in absorb and float. Again without the buck converter I should see 9 amps and a lot of wasted voltage. Even running them in parallel would only produce 27a in absorb and float without the buck converter.

So if you are interested in starting a thread on the workings of a MPPT controller and are willing to accept it when proof is presented, then I am game. Should I not be able to bring up the graphs then I can have one of the controllers do a log and create a new graph. It is something I see from my system every day and I would not be able to do the things I do without it.

That said I agree that while a MPPT controller would get the most out of a single portable, a second portable would provide more additional power.

 

[John61CT]

> So if the CC receives say 35V but only 4A instead of 17.5V at 8A is it converting the extra Volts to amps at all stages, bulk, absorb, and float

Amps are just Watts divided by Volts, none of these get "converted".

Watts are really what counts, they measure actual power being delivered, volts are like "water pressure" and amps are a flowrate.

You could say amps are "worth more" at higher volts.

And if there is no other load, just charging a lead battery bank, then after the battery gets past 80% full, more and more solar power is "wasted" as the amps/watts accepted by the battery declines, until nearly zero, which means the bank is full.

On big boats, they heat up and/or freeze water to make use of that excess energy.

 

[ChetLazar]

MarkK is concerned that connecting his two portable panels in series will result in the batteries only getting 4 amps of charge rather than the 8 amps they could get if the panels are parallel connected.  Is that what you mean by "none of these get converted?"  Will MarkK only get 4 amps of battery charge but they will be better amps because they are "worth more at higher volts?"  

In the quoted post jimindenver describes the buck converter as making more amps from a high voltage/low amps input.  Is that incorrect?

 

[John61CT]

Series doubles the voltage (pressure) keeps amps the same.

Parallel keeps the same voltage, doubles the amps (flow rate).

Watts (power) stays the same in both cases.

MPPT gives a bit more power when volts are high, but can go either way. Ideal is a single high-voltage panel putting out the rated max watts.

PWM wastes high volts, need to keep them lower, stick to nominal 12V, if multiple panels must be paralleled.

 

[MarkK]

Amazing wire numbers when I use the circuit wizard given a series set up. The same 25' (50') run in 24V at 4.5A indicates a 14AWG wire is acceptable. When I run the numbers on a 12V circuit with 9A with the same run it wants me to use 8AWG wire. Looks like the series is getting the nod given I have 12AWG wire and the 14AWG used to tie the panels together can be left in place with the exception of swapping for series.

 

[Weight]

Will your charge controller handle the increased voltage from series connected panels?

 

[MarkK]

Will your charge controller handle the increased voltage from series connected panels?

I believe it will. Victron MPPT 75/15.

 

[MarkK]

BlueSolar Charge Controller MPPT 75/15
Battery voltage 12/24V Auto Select
Rated charge current 10A 15A 15A
Nominal PV power, 12V 1a,b) 220W
Nominal PV power, 24V 1a,b) 440W
Max. PV short circuit current 2) 20A
Automatic load disconnect Yes, maximum load 15A
Maximum PV open circuit voltage 100V

 

[John61CT]

The two key specs to not exceed are the 65Voc and 20A lsc.

3x 100w "12V" panels would be fine, a bit overpaneled, 250w total more conservative.