55 replies to this topic

[Vic Harder]

With reference to the original thread link, at the top of this thread link, I chose this one for revival due to the brevity. I am looking for any advice/logistics/help for A-Z planning that can be offered. I have received a very helpful PM so far. Here are my particulars ...

ETA early April I for my Grandby Shell from FWC. It will have the std. single battery Shell setup with a fuse box & battery separator in the Shell (so I am told), w/alternator hook up, no other electronics, no solar anything. I will replace the std. existing battery with one LiFePo4 12V 100ah. My power needs will be 12V. I plan on two 100W flex panels on roof & one 100W portable for camp. I want to stay light.

My power needs: two F fans (with altered diy variable speed fan control), interior LED lighting, std. FWC propane heater fan, Engel or similar fridge, cell phone & tablet charging, rare occasion exterior rear flood lighting.
With hopefully the same ETA, I will own a 2018 F-150 with optional interior 110v/400w, AC plug in, outlet. With these variables, I would like to KISS for myself, but most importantly, keep my solar system healthy. Monitor for capacity coupled with real time in & out. I am trying to read & learn but not in my wheelhouse. I would welcome any thoughts or design on needed components, gauges. Starting from scratch.
Thanks - Mark ..... Can not wait for my traveling tent, (tent & backpack lifer) with benefits, to start adventures. My wife is ready to go too.

 

100AH LiFePo4 sounds like lots of (House) battery for the listed items that will draw power.

KISS would be to NOT count on the truck to charge the house battery.  That way you don't need to worry about upgrading the wires from the alternator to house batteries, or figuring out how to control the charge the house batteries are getting from the alternator.

That requires that you will get enough solar to charge the batteries.

Which means we need to know a bit more about your camping habits:

- where do you camp? Latitudes, amount of sunshine, shade from trees/mountains

- how many days at time are you camping?

- can you count on getting a good charge every day?

- if not, how many days between good charge opportunities?

 

This latter info is important because you only have about 90 useable AH.  Your draw will be around 30-50 AH a day, meaning you have only have enough AH for 3 days at best.  

 

Assuming you get to 50% SOC often, you will want to be able to get 50AH back in a day, using solar (or 120v if available) only.

 

Your 300W of available solar power translates to about 240W at best (80%) of actual output.  240W @ 14.6V (LiFePo4 recommended charging voltage) =  16.4A... this is how much current you want your solar controller to be able to put out.

 

50AH at 16.4A = 3 hours of charging at full/max power output.  Most days you will not get 3 hours of perfect sun at the perfect angle.  However, you are certainly in the ballpark for being able to recharge your house batteries daily.

 

A Victron 75/30 controller and BM712 battery monitor would be a great addition to this setup for charging and monitoring your batteries.

[Stokeme]

Vic, I appreciate your response as it seconds the notion, proposed to me, of losing the truck to house battery connection. With my novice solar logic, it does seem that if I am traveling most days, my truck will be out in the Sun, my roof panels should probably keep my battery topped up. I will initially give this a go.
It is when I am camping in the trees for a few days, or a week at a time, then regardless of the truck connection, I will have possible issues . Thank’s for the AH/day estimate. That is more than I assumed, but again, learning as I go. Do I need 400W? Two portable panels? What other tricks afield can you suggest? I think I could order 3 - 120W Solar cynergy flex panels for the roof & one portable flex 100W. What controller would I need, 100/30, or larger?
The Battery I Ordered is Bluetooth capable. I am assured with the app (I will trial) it will be possible to monitor all battery functions with my iPhone.

[Vic Harder]

"Travelling most days" - that's good info.  If your solar panels can't keep up, then it might be good to investigate some way to charge your batteries via the alternator.  I do this.

 

My AH estimate is likely too high.  I have 220AH on board, meaning approx the same as what you have, in USABLE AH.  My batteries never get below 80%, or 60% if I had your LiFePo4's.  

 

Solar panels on the roof are good, but you need to avoid shade from the vents.  I see they are 21.3" wide.  So three abreast they would be 63.6 and 46.6" deep.  If you don't have a roof vent and just the one fan, you might be able to get these to fit at the front of your camper.

 

https://www.solarblv...-solar-panel-3/

 

3 of those 120W panels will be good if you can make them fit, and mount them with a bit of space under them so they can air-cool.  You will want to wire them in series, although you could do parallel too if you wanted to stay with PWM.  Let's look at parallel first. Let's assume 3 on the roof and one more as a portable.  Here are the stats on those panels:

 

Max V = 22.8V

Max A = 6.65

 

Max // A = 4x6.65 = 26.6 at a max of 22.8V

 

The Trimetric SC2030 can handle 30A, and would be great controller to use (it can be adjusted to work with your LiFePo4 batteries).

http://www.bogarteng...ar-charger.html

 

The advantage of going parallel is super simple wiring for the portable, as it will simply add more current to the existing roof array, if and when you use it.  Also, shade on any one panel only affects that panel's output.  

 

The disadvantage is some potential power loss over the 12g internal wiring in the camper.  That said, PWM controller throw away any "extra" power anyway, so in practice it doesn't affect you that much.  And how does this affect you?  Well, LiFePo4 batteries want a max of 14.6v, meaning anything more than that is unusable.  Assuming about 4% power loss over your internal wiring, you will get a max of 22.8*.86 = 18.24V at the controller.  18.24 - 14.6 = 3.64V.  Meaning that at max current,  26.6A * 3.64V = 96.8W.  You could be "throwing" away up to 97W.  

 

OK, now wiring the roof in series, your max V = 3x22.8 = 68.4V  The max current is only 6.65A, so it would appear that the Victron 75/15 MPPT controller can handle this.  However, consider the output current calculations below.  I missed this when I spec'd my camper to use 75/15's!

 

The advantage of series wiring and using series with MPPT controller is that you are minimzing power losses over the wiring, and not "throwing" away any extra power because the controller will always try to optimize current and voltage to get the optimum power output to the batteries.  But be aware of the max current!  The MPPT controller will convert the power coming in to what you have told it the batteries need.  So, for example, lets say you do have max power going in...

 

68.4V * 6.65A = 454W.  (something is awry here, as this calc gets me more than the stated 120W output of the panels)... but assuming the numbers Cynergy lists are legit, we get 151W per panel...

 

If your batteries only want 14.6V, then 454/14.6 = 31.2A  That's way more than the rated 15A output of the Victron 75/15.  A unit with a 30A rated output would be needed.  I have gotten two over current shutdowns because of this phenomenon in my setup.

 

The disadvanage of this setup is that the portable unit can't be easily wired into the onboard MPPT controller.  That said, you could easily buy a packaged "portable" system that has its own controller and wire that in.  What I did was use a second Victron 75/15 for use with my 2x 120W flexible panels that I use for my portable setup.

 

I might have made some errors in my calcs or theory, but then Craig, NTSQ or Rando seem to notice these pretty quick. 

 

Oh, and temper all these results with the knowledge of what I call "rando's rule of thumb" - 80% is all you will ever get from your solar panels.

 

I hope this helps.

[rando]

Nice explanation Vic!  As you predicted we are here to add some addendum!

 

For the power calcs, you want to use V max power (20V) and I max power (6A) which is how they arrive at 120W.      

 

Also to be clear, even if you are going to put your panels in parallel, there is really no point in using a PWM controller like the SC2030 when there are cheaper and better MPPT controllers available that will get you more power out of your panels. 

 

I recently switched to this one:

http://shop.pkys.com...th-_p_7182.html

Which can handle 3 120W panels and has built in bluetooth and the capability of adding an LCD display.

[ckent323]

Vic and Mark,

 

Max V = 22.8V

Max A = 6.65

 

"Max // A = 4  x 6.65 A = 26.6 A at a max of 22.8 V "  

 

Check!

 

 

"LiFePo4 batteries want a max of 14.6v, meaning anything more than that is unusable.  Assuming about 4% power loss over your internal wiring, you will get a max of 22.8*.86 = 18.24V at the controller. "

 

22.8* .86 = 19.61 V

 

"18.24 - 14.6 = 3.64V.  Meaning that at max current,  26.6A * 3.64V = 96.8W.  You could be "throwing" away up to 97W."  

 

==>  I think there is an error

 

19.61 V - 14.6 V = 5.01 V.   

 

therefore at max current   26.5 A * 5.01 V = 132.77 W

 

 

"wiring the roof in series, your max V = 3 x 22.8 V= 68.4V  The max current is only 6.65A, so it would appear that the Victron 75/15 MPPT controller can handle this. "

 

Check!

 

"68.4V * 6.65A = 454W.  (something is awry here, as this calc gets me more than the stated 120W output of the panels)... but assuming the numbers Cynergy lists are legit, we get 151W per panel...

 

454 W calculated vs 3 * 120 W = 360 W    454 W / 3 = 151.33 W

 

Check!   

 

 

"If your batteries only want 14.6V, then 454/14.6 = 31.2A  That's way more than the rated 15A output of the Victron 75/15.  A unit with a 30A rated output would be needed."

 

452 W / 14.6 V = 31.1 A   

 

Check!

 

I am not seeing a 75/30 Solar charger on the VIcrtron website (discontinued perhaps?).  I think they also made a 75/50 but it is not on the website either.

 

https://www.victrone...rge-controllers

 

The Blue Solar models do not have bluetooth built in and requires a dongle to use a smart phone with it - the Smart Solar models have bluetooth built in.  Most models are available in either version.

 

For clarity for other reading Victron model number means:  # V / max current   (e.g. 75/10 means 75 V/15 A max current)

 

The choices I see on their website are 75/10, 75,15, 100/15, 100/20 (smart solar only), 100/30, 100/50, 150/35, 150/85 &150/100  (there are other models that handle 250  V.)  All of these are MPPT.

 

I think the best choice from Victron if the 75/30 is no longer available is the Smart Solar 100/30.

 

 

Regards,

 

Craig

Edited by ckent323, 06 March 2018 - 09:35 PM.

[Vic Harder]

Thanks guys!  

[Stokeme]

Vic, Craig, Rando ... replies much appreciated

 

1) Can you guys give me the electrical reasoning why one would choose series vs parallel panel configuration? I do want a portable panel for a flexible approach to the Sun. That would be a big plus for parallel as Vic states, it is just "plug & play". Also in parallel the panels are individual and unrelated to shade cover. "One shaded does not affect all". I read (on Amazon review) that the 100/50 controller, though pricey, is “ultra fast”. One reviewer says it “almost seems to pull energy from the clouds”. It seems it is also touted for varying Sun & cloud type conditions, thoughts? If I can pull more, the $ seems worth it to me. If this does not really help me, then a SmartSolar controller either 100/20 or 100/30, depending on # of panels, and whether it is series or parallel also matters. Thoughts?

2) Is it the increased voltage/amperage relationship that makes a series configuration better? In parallel, does limiting the voltage to 12v, a negative issue for charging LiFePo4 batteries? Does the controller increase the voltage to the 14.6v  needed for LiFePo4?

3) How do you handle the system in between trips with LiFePo4? Shut it down somehow?

4) My Battery has Bluetooth monitoring capability, do I also need Bluetooth controller? I think yes. I believe this does though save me from installing a battery monitor. They would offer different info, correct?

Thanks ahead - Mark ... Believe it or not this post was heavily redacted.

[Stokeme]

Sorry to add one more query, but, if the distance between my panels and the battery is, what 5 feet? ... will I really lose that much power in a parallel configuration? Would heavier gauge wiring help alleviate that issue ... Again, novice questions here ...

[Happyjax]

You math guys make my head hurt.....lol

[ckent323]

Mark,

 

1)  Series vs Parallel - read this:      https://www.renogy.c...s-and-parallel/

 

2) "12 V"  in solar systems is nominal.  Actual voltage goes up to something like 18 V in some panels.   24 V panels are similar the actual voltage runs as high as 32+ volts.  Controlling the voltage and current to your battery from the panels is why you need a Solar controller.  It accepts the input voltage (and current) within the controller range and outputs what your battery needs.  The better Solar controllers let you program the bulk, absorption and float voltages to match the needs of your specific battery type.

 

3) My camper has been outside so I just let the solar systen do its thing.  If inside or under a cover I would get a NOCO G7200  Battery tender/monitor (or equivalent). It plugs into normal 110/120 V outlet and then controls the voltage and current to the battery.  The NOCO G7200 has setting for Flooded Lead acid, AGM and Lithium batteries.

 

4)  I recommend having the bluetooth monitoring of both the Solar charger (so you can see what your panels are putting out and what is going to the battery bank) as well as bluetooth monitoring of the battery (if you have the VIctron BVM-702 or BVM-712 you can get both temperature info as well as state of charge of the battery.  With the Victron Bluetooth app you also get a history logging function and the programming of the parameters is easier with bluetooth.

 

Makes checking things much more convenient.

 

Hope that helps and I trust that Rando or Vic will review and provide correction for any mistakes in my comments or add info for anything I overlooked. 

 

;-)

 

Craig

Edited by ckent323, 07 March 2018 - 09:23 PM.