Advice Wanted! Dual Battery/Solar Set Up

[kins18q]

Hey guys. My girlfriend and I are preparing a 2002 Suburban 4x4 Z71 for a year on the road to launch her adventure photography business full time.

Here she is on Instagram @katcarney

I am hoping to get some feedback on my proposed system, because I have no real experience with this...just reading thread after thread.

Power needs:

We would love to be able to power these things for 3-5 days without driving...
30L Indel B Fridge
Camera batteries
Laptop
2 Cell phones
6 tiny LED lights

Proposed System Based on EVLDAVE's kickass design
100w Flexible Solar panel mounted to top of rooftop box that can be tilted towards sun
30 Amp PWM Charge Controller
100 Amphour AGM battery
200 amp solenoid between the starting battery and the deep cycle battery to get charge from the alternator when driving and so I can jumpstart the starter with the deep cycle (if need be)
400w inverter???
Or Pure Sine inverter???

Questions:

Am I missing anything?
Do I need the pure Sine inverter?

Any help is greatly appreciated!

 

[Semi-Hex]

I can't answer all but you can do away with the inverter. There are 12v DC adapters that you can use for your laptops. The rest of your fear should be all 12v DC. This saves you from the headaches that are inverters. Link: http://www.amazon.com/BiXPower-Cigarette-Power-Adapter-Macbook/dp/B00823OLUM
A 10 amp controller works well with a 7amp max panel.

 

[Joe917]

The big draw is the fridge at 50 Watts, approx 4 amps @ 12 v so approx 50 amp hrs in 24 hrs @ 50% duty cycle.Throw in minimal laptop use and charging lets say consumption is 60 amp/hrs/day.
Charging from 100 Watts X 4 hrs(a fair expectation)= 400watts= 33 amp hrs.
with no driving you have 60amp/hrs out and 33 amp/hrs in.
Double your solar minimum and if possible go to 200 amp hrs battery.

A battery monitor is a vital part of the system, without it you are guessing at battery charge(voltage is of no use in a working system). I recommend Trimetric but there are others.
http://www.bogartengineering.com/products/trimetrics/

As for charge controller :http://www.amazon.com/Morningstar-S...ywords=morning+star+sun+controller+ss-20l-12v

I have also heard good things about Bogart's combined solar charger and monitor:
http://www.bogartengineering.com/products/solar-charger/

Lastly anyone doing their own solar would be well advised to set aside some time and read this:
https://handybobsolar.wordpress.com/

 

[kins18q]

I can't answer all but you can do away with the inverter. There are 12v DC adapters that you can use for your laptops. The rest of your fear should be all 12v DC. This saves you from the headaches that are inverters. Link: http://www.amazon.com/BiXPower-Cigarette-Power-Adapter-Macbook/dp/B00823OLUM
A 10 amp controller works well with a 7amp max panel.

Cool I like this idea. I assume I would need to rewire some 12v outlets to run off the deep cycle instead of the starting battery to do this? Am I right that we are talking about plugging everything into 12v outlets in the car?

 

[kins18q]

The big draw is the fridge at 50 Watts, approx 4 amps @ 12 v so approx 50 amp hrs in 24 hrs @ 50% duty cycle.Throw in minimal laptop use and charging lets say consumption is 60 amp/hrs/day.
Charging from 100 Watts X 4 hrs(a fair expectation)= 400watts= 33 amp hrs.
with no driving you have 60amp/hrs out and 33 amp/hrs in.
Double your solar minimum and if possible go to 200 amp hrs battery.

A battery monitor is a vital part of the system, without it you are guessing at battery charge(voltage is of no use in a working system). I recommend Trimetric but there are others.
http://www.bogartengineering.com/products/trimetrics/

As for charge controller :http://www.amazon.com/Morningstar-S...ywords=morning+star+sun+controller+ss-20l-12v

I have also heard good things about Bogart's combined solar charger and monitor:
http://www.bogartengineering.com/products/solar-charger/

Lastly anyone doing their own solar would be well advised to set aside some time and read this:
https://handybobsolar.wordpress.com/

Thank you for the response! So your calculations say we can do about 36 hours with no driving before we put the battery at less than 50% charge. This is no bueno, so maybe we will get a second panel. Or second battery, probably not both. I was just reminded that we have a mini solar thing that can take care of our phones...not that they use much at all.

I'm thinking add a panel for 4 lbs instead of a battery at 60lbs... what would you do?

 

[Joe917]

Educate yourself. Read: https://handybobsolar.wordpress.com/ then read it again.
I would add the solar.
50% is hard even on true deep cycle batteries less is better.
How will you know when you are approaching 50%? A battery monitor, and I cannot stress this enough A VOLTMETER IS NOT A BATTERY MONITOR!

 

[IdaSHO]

Yep, you are on the right track.

For extended stops like your 3-4 days, what ultimately dictates the system is the power consumption per day.


Once you know your consumption, you can calculate two things.... what size battery bank you need, and how much solar you need.


Ultimately you do not want to draw the deep cycle bank below 50% as mentioned.

And you need enough solar to replenish your consumption (ideally) every day. I baseline things using 6 hours of usable sunlight

Many seem to error on the side of too little solar, and see a daily overall loss. This is fine, if you keep your stops short and have the ability to charge the house bank on the road.

I like to error on the side of slightly too much solar, so there is no daily loss (or rarely), and no real requirement to ever start the vehicle. This allows you to park it in one spot for a day, a week, a few months, an never a worry about the batteries.



With that said, in general, for every 50 amps worth of daily usage, bare minimum for extended dry camp you need roughly 100 amp/hr of battery capacity, and roughly 200 watts of solar.

That will provide just enough battery bank to keep the bank healthy, and just enough solar to replenish every day, so long as you see a full 6 hours of good useable sun every day.


As always, your mileage may vary

 

[Vanaroo]

There are so many variables that it's hard to give a definitive answer (everything from the amount and angle of insolation, to how much you use your laptops, ambient temp where the fridge is, etc.). However, I have somewhat similar usage, so I can give you a real-world report on that.

I'm running two 100-watt panels in series. I have all my wiring sized for less than 2% total voltage drop over all the legs, and an MPPT controller (Sunsaver 15). I have an "oversized" battery bank (375 amp hours, AGM), but that's only because I planned for twice as much solar. (More on that in a minute.) I monitor with a Victron BMV-700 and a Smartgauge (I like data), plus the display for the Sunsaver. I do have a 1/0 cable to connect the start battery with the house bank, but rarely use it as the solar controller is much "smarter" (custom programmable for battery specs) and the alternator is stupid. The solar takes care of my needs 99% of the time.

My typical draw is around 30-45 amp hours per 24-hour day. This is running a Dometic 50 liter compressor refrigerator (cooler style body), charging my laptop (via 12 volt adapter), plus charging camera batteries, phone, Eneloops for headlamp, etc. My lighting is LED and I use a marine fan (less than .5 amp draw). So the fridge is the big draw, and it averages 25 amp hours or so a day (set at 31ºF). A bit more in hot weather, obviously.

I tend to camp in sunny places, but still, last winter I was in places where the sun "set" around 2 p.m. due to mountains. Given that my battery bank is so disproportionately large, I knew that the "normal" 50% draw down would be very difficult for me to re-charge. But as it happened, I have never gone below 85% in normal use (so that's around 60 amp hours). That would be a day or two of clouds or partial clouds. So my two 100 watt panels have been able to get my batteries back to 100% at least five days per week (this keeps them healthy).

Originally I had planned for 400 watts of rooftop solar, hence the 375 amp hour battery bank (plus I'm a night owl). But I had the two 100 watt "portable" panels so set them up as a trial. Somewhat to my surprise, it's been just about a year since I did that, and they have easily kept up with my usage. The one time I have issues is if I'm traveling for a few days. I'm not super keen to use the alternator (since it's "stupid"), and it's not that convenient to set out the panels in parking lots or in-transit type camp spots. For this reason I'm going to add some rooftop solar. But I won't be giving up the ground panels because I like camping in the shade with the panels in the sun - that has been a great bonus I didn't really think about.

At any rate, that gives you an idea what 200 watts will power. If that were all I had planned on I'd only have around 200 ah of battery. I may actually remove a battery! (Save weight.)

One note is that I don't have many "hidden" draws. No water pump, no furnace fan, no appliances to speak of. That's just the way I'm used to living (boats). So you may have more power usage, depending on how you like to live.

I do have a small (100 watt) inverter that plugs into a cigarette lighter socket. It's for the very few things I have that I don't charge with 12 volts. Namely one set of drill batteries, a Dremel battery charger, and a toothbrush. (Although my newer drill, a Ryobi, does have an optional 12-volt charger.) Everything else is 12-volt.

If you tend to stay in places with long stretches of cloudy weather, this might not work so well.

PS: The reason I ran the two panels in series was so that I could run smaller/longer wire on my ground panels. I have around 25' of 8AWG (plus the wire in the rig to the controller, plus wire from controller to batteries, and then battery jumpers). I wouldn't want the "umbilican" any shorter (or any heavier), so the series setup has worked well. I don't like to give away anything to voltage drop if I don't have to This does require an MPPT controller so it will be converted (by the controller) to the 13-14 volts the batteries want to see.

 

[Semi-Hex]

Cool I like this idea. I assume I would need to rewire some 12v outlets to run off the deep cycle instead of the starting battery to do this? Am I right that we are talking about plugging everything into 12v outlets in the car?

I would have a couple of independent 12v adapters in front and back of your rig that could be switched on (without your key). All of the other replies have been spot on here, you really can't over panel on the size of your car, you can undersize your wiring easily so do read Handybobsolar page. Bon chance!

 

[kins18q]

Another Question

Thanks for all the responses. We are going to try to keep everything 12v and avoid the inverter. And we have decided on 2 100w flexible panels to be mounted on the top of the roof box...With the box and bikes on the roof this is really our only option without mounting on hood. We are probably going to be pushing he capacity of the roof rack so the weight savings and ability to mount on the roof box make the flexy panels a no brainer. The roof box actually has deep channels running length wise so we should get airflow under the panels.

So a question (or two) about wiring!

What are the important distances between pieces of the solar/battery setup that should be as short as possible in order to keep from losing efficiency?

What type of wires do I need? Solar specific?

 

[Joe917]

Take care with the position of the roof mount panel and the roof rack. Any shade will kill panel voltage. If that is an issue rigid panels that you can move around camp are the "no brainer".
As for wiring, the charge controller to battery distance and gauge are most important. Wire type, marine grade is best but multi strand automotive copper is fine as long as you heat shrink all connectors.( you should do this for marine use too)
Length and gauge use :
http://www.calculator.net/voltage-drop-calculator.html
for voltage enter 14.4
for amps enter max panel amps
and DC and copper.
you really want no voltage drop between controller and battery.

 

[loonwheeler]

Length and gauge use :
http://www.calculator.net/voltage-drop-calculator.html
for voltage enter 14.4
for amps enter max panel amps
and DC and copper.
you really want no voltage drop between controller and battery.

I agree with Joe917 - try to maintain as little voltage drop as possible that is practical as well affordable. There are trade offs and considerations that should be taken into account. Is your charge controller output voltage programmable? What charge voltage is recommended by your battery manufacturer? It is best if you can take these considerations into account to determine what you need for your application.

 

[luthj]

Its important to keep the voltage drop between the controller and batteries at less than 1%. Choose wire accordingly.

I would suggest a second portable panel if you do not have room on the roof.

200W and 200AH would be a fairly safe bet. 100AH is going to be tight... At a minimum add more solar. Make sure your alternator to AUX battery charging wire is big enough to good charging rates. Ideally less than 2% voltage drop at 50 amps.

Consider adding extra insulation around your fridge, this can reduce run times noticeably.

The 200A isolator relay is overkill for your situation. A 50-120A unit would work just as well, and might be cheaper.

 

[rayra]

and keep the fridge shaded as much as practicable, while still allowing it to breath properly. blackout curtain in the window would do it.

And a bit on inverters, try to size them to your requirement / load. Even if it means you bring two - and you want two anyway for redundancy, 'two is one, one is none'. Akin to running a huge generator for a small draw, you lose a lot of efficiency / power / fuel / energy, if there's a big difference in sizing.

Consider a two or three panel roof array, which folds up on itself for vehicle movement. It wouldn't take much more space than a single panel. Better yet, with pinned hinges that let you detach a panel for ground or more optimum placement, and so when they are folded / stacked for movement, you have to top panel face up, in a functional position. It would not be at all difficult to make the hinging brackets.

Just a quick sketch. Easy to fashion brackets out of flat bar stock. Machine screws, nylock nuts, a washer as spacer between bracket and panel frame. You can make them fancier, use something like door hinges fitted so you can readily pull the hinge pins and release the panel. All sorts of wire loop latches or rubber hood latches could be used to bind the stack shut. Some peel and stick silicone rubber feet between the panels, in place before you size and attach the hinges, gets rid of rattle and wear.

Run the long axis of the panels with that of the vehicle, so the flanking panels lay out over the sides a bit. Or orient the other way so they lay out flat on the emptied roof. Add cabinet handles to the edges, use removable pins on the base panel mounting to and you can raise, angle or relocate the whole array.
Having all three panels on the roof is a twofer as well, as it shades a good portion of the vehicle, helping keep it cooler.

Use something like Anderson PowerPoles or other handy connectors in your wiring, and have a few longer runs as extensions for when you place the panels on the ground.

Also easy to add swing out legs onto the panel frames, make the leg lengths such that your panels stand near the optimum angle for your region.

 

[dwh]

What are the important distances between pieces of the solar/battery setup that should be as short as possible in order to keep from losing efficiency?

You get this from HandyBob? That's one place where he (kinda sorta) gets it wrong.

He advises that the wiring from the solar charge controller to the battery should be bigger than the wiring from the solar panel to the charge controller, and that the charge controller should be as close to the battery as possible. He's absolutely correct...IF you have an MPPT type charge controller (he does).

It's irrelevant if you have a PWM charge controller though. Oh, I see why he does it - it won't hurt anything to wire the PWM controller the same way you'd do an MPPT (won't really help though), and it keeps it simple (he doubtless answers tons of the same questions over and over and surely has a set of "pat" answers).

With a PWM controller just run the same wire size on both sides (solar side, battery side) since the amperage/voltage will be the same on both sides (a PWM is just a fast computer controlled on/off switch, not a voltage converter like an MPPT), and it doesn't matter if he charge controller is closer to the solar panel than the battery (it's just a switch - doesn't matter where you put it in the circuit).

Size the wire to handle the max amps that can be expected to be flowing: 200w x .80 (efficiency loss due to [solar Vmp/battery voltage] mismatch with PWM (MPPT eliminates that mismatch and gets the full 100% output from the solar) = 160w / 10.5v (worst case scenario - battery totally dead) = 15.2a. Call it 15a max on a bright cold day with a totally dead battery. Every other day, the amp flow will be less than that. So you need at least 14 gauge wire with a 15a fuse to protect the wire.

Voltage drop is (very) important when calculating wire size for your loads, but doesn't really matter for battery charging, so there's no need to oversize the wire to compensate for imaginary voltage drop that doesn't really exist (the voltage on the charging loop will be whatever the battery voltage is). If you used say #14 wire (thick enough to handle a 15a load) and you never take your battery below 50%, then the charging voltage won't ever be low enough to get the max output from the solar anyway. (Figure full charge is 12.8v and dead is 10.5v (these are the normal numbers for a "12v" battery). So 50% would be like 12.2v (with no load on the battery). 160w/12.2v=13.1a so you can see that with wire sized to handle 15a, you're *already* a bit oversized on the wire.


Not having oversized wire on the charging circuit might add a few minutes to the bulk charging stage, but it won't make any difference for that long slow absorb stage where the amps flowing is a lot lower (less amps flowing = less voltage drop) and takes hours. Spending the money on thicker copper in order to shave 10-15 minutes off a process that takes 6-8 hours is a waste of money in my opinion. Oh, it might be worth it if you were designing a large system for an off-grid house, but you'd run series panel strings and the higher voltages use thinner copper anyway.

What type of wires do I need? Solar specific?

No such thing as solar specific really. If the wire is outside, get something with good UV resistance. Inside...doesn't much matter. Any decent automotive/marine wire is fine.




[And just a note on the 50% rule. I personally ignore it. I buy cheap deep cycle batteries (but I buy good starting batteries) and replace the deep cycles every 1.5 - 2 years. That way, I can run them down to 0% and double my available daily power budget without having to double my battery bank size. It works out the same. I pay half as much for batteries, but twice as often. Or, I could abide by the 50% rule and pay twice as much for batteries, but half as often.

Over the years, the price works out the same, the daily power budget is the same - but I haul half the ballast around with me.]