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Questions regarding "So, you want to setup a good electrical system in your camper?"


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#41 Wallowa

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Posted 04 March 2021 - 02:43 AM

Yes...4 gauge wire is in the build....not certain which DC/DC is in the mix....whichever, KP has it "wired"... B) ...sorry could not help myself.

 

Vic and Jack thanks yet again...still fuzzy on the need for 40 volts [series] in my case if the Victron controller only 'needs' 5 V over battery 12V [Victron manual]...that the Victron controller modulates both the voltage and amperage to deliver the optimal watts into the battery is reassuring..

 

Also, from what I read the speed of charge is important on Li batteries longevity; I am assuming the Victron not only regulates for optimal watt input but speed of that input into the Li batteries...correct?

 

Phil


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#42 Wallowa

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Posted 04 March 2021 - 02:44 AM

Wallowa, my appt is April 19. 

 

 

Would appreciate a full report with details of the installation...thanks....

 

Phil


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#43 rando

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Posted 04 March 2021 - 03:10 AM

The short answer: if your panels are the same type/brand (or same wattage and very similar Vmax), connect in series up to what your MPPT controller can handle. I have four 100W 19Vmax panels - 76V - on my 100/30 Vic, which can handle up to 100V input. Some controllers are limited to 30V or 50V.

 

Your panel voltage will vary by about 2V to 4V depending on how much sun and how much current you are asking the panel to supply.

 

The higher voltage from two panels in series does not pull more current out of the panels - but the higher voltage (38V instead of 19V - it varies by a few volts) means that the voltage is always more than 5V above your battery voltage and the MPPT controller will always be adjusting the voltage (up and down) to get the most watts (current X voltage). The MPPT controller actually sets the output voltage of the panels to get the maximum watts.

 

You can see this with your AGM batteries. Charged and with almost no load, they should be about 12.6V. Now add load by turning on the overhead fan and the furnace (about 7A) and watch the battery voltage drop. The amount of current drawn out of the batteries changes the battery voltage. The MPPT, by controlling the current drawn out of the panels changes the panel voltage. What's different about solar panels is that the change is non linear. Lets say, for the same amount of sun, your two panels in series are producing 40V at 5A. That's 200W charging your battery at 14V X 14.29A. (The MPPT takes in whatever voltage and current the panels supply and outputs what is needed for the battery.) But if the MPPT finds (generally by trial and error with small changes) that if it lets 5.4A flow from your panel, the panel voltage will drop to 39V. 39V X 5.4A is 210.6W. Your MPPT just got you an additional 10.6W so your battery will now charge a bit faster at 14V and 15.04A. As the amount of energy from the sun coming into your panels changes, this sweet spot changes. Your MPPT is always hunting for it when the panel voltage is 5V more than what is needed to charge the battery or meet your load.

 

 

This is a good explanation, but it would be good to clarify on battery voltage + 5V point.  The requirement that the panel voltage be 5V above the battery voltage is somewhat artificially implemented by Victron and only applies at sunrise - once the MPPT is active it may track panel voltages below Vbattery + 5V.  The reason it is done this way is that there is almost no power available from a solar panel when the open circuit voltage is below 17V.  If the controller tries to load the panel down the voltage will immediately drop below the battery voltage and the MPP search will fail, wasting power.   Solar panels are current sources, not voltages sources (which is a hard thing to wrap your head around), and as a result the Voc will rise with very little illumination, and is almost constant, it is the current that increases with increasing sunlight:

benning_pv2_faq_question_14_a_en.jpeg

 

As a result, there is actually very little power to be gained by putting the panels in series from the Vbat + 5V limit.  There are two other advantages to series panels,  you can use smaller wires to the panels as the current is lower, and you can safely 'over panel' your controller - that is you can put more watts of solar panel than your controller is rated for based on the assumption that the panels will almost never put out their rated power in real world situations (unless you live at high altitude near the equator).   The disadvantage is that it makes it much harder to add a portable panel to your system,  and it is harder to mix different sized panels in series. 


Edited by rando, 04 March 2021 - 02:57 PM.

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#44 Wallowa

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Posted 04 March 2021 - 03:35 PM

Rando,

 

Thanks!  That explanation of voltage vs amp flow with illumination really helped me bring all this into focus.  I suspected that voltage was more or less a constant and that amps increased with solar input. 

 

I thought the Vbat +5V was not a voltage limiter but an optimal or minimal voltage target...

 

All things considered, with my system, 170/160W Zamps and changing to a Victron MPPT from the Zamp controller with BB 100AH....will the net watts into my batteries increase, stay the same or decrease by switching from parallel to series?  Do not want to chase my tail, but do want to grasp the parameters in play.

 

Thanks...Phil


Edited by Wallowa, 04 March 2021 - 03:36 PM.

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#45 rando

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Posted 04 March 2021 - 05:23 PM

Under most situations the net watt-hours will be essentially the same (to within a few %)  between series and parallel. 

 

If you plan on running a portable panel in addition to your roof mount panel and don't want to use a separate controller - then you need to wire in parallel. 

 

If your roof panels have different wattages then you should wire in parallel.   

 

If your panel wattage is higher than what your charge controller is rated for, then you should wire in series. 

 

If none of these apply then you can wire either way, but I would probably go with parallel - it is easier to understand and troubleshoot. 


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#46 Wallowa

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Posted 04 March 2021 - 06:02 PM

Rando,

 

#1 Differing size [W] panels:  Mine are 170 & 160W = 10W difference... a significant factor?

 

#2 Portable 80W Zamp that plugs into back of Hawk....only used once and with little success..no big deal to not have available.

 

#3 Installing Victron 100/30 which I assume is good for 3K Watts...my panels [series] 40V x 20A = 800W...good to go.

 

#4 But if as you say:  "Under most situations the net watt-hours will be essentially the same (to within a few %)  between series and parallel."; why go MPPT and in series if you really do not gain watts?  Or will the MPPT gain me watts independent of whether the panels are in series or parallel.

 

What am I missing?

 

Phil


Edited by Wallowa, 04 March 2021 - 06:04 PM.

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#47 rando

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Posted 04 March 2021 - 06:09 PM

#1 - not a big deal either way (5%).   It depends if the Imp or Vmp are closer to each other to figure out which way would work better.

#2 - if you go series you will not be able to use this without adding its own charge controller. 

#3 - not it is not good for 3000W, it is good for up to 30A at battery voltage, so around 400W (30A * 13V).

#4 - MPPT gets you more power than PWM regardless of series/parallel panels.   This has been explained many times.  There are reasons to go series as explained previously.  You have to decide which option works better for you. 


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#48 Wallowa

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Posted 04 March 2021 - 08:30 PM

#1 - not a big deal either way (5%).   It depends if the Imp or Vmp are closer to each other to figure out which way would work better.

#2 - if you go series you will not be able to use this without adding its own charge controller. 

#3 - not it is not good for 3000W, it is good for up to 30A at battery voltage, so around 400W (30A * 13V).

#4 - MPPT gets you more power than PWM regardless of series/parallel panels.   This has been explained many times.  There are reasons to go series as explained previously.  You have to decide which option works better for you. 

 

 

Thanks....appreciate the education.

 

Phil


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