Sizing a battery and solar panel system for a car

erw1988 · Nov 3, 2012

First of all, this is a real cool forum and I look forward to learning and interacting here. Second, my wife and I decided to start our adventure out, dwelling in an '88 Nissan Stanza station wagon. We'll be taking it from Texas, through a couple spots in the West (Grand Canyon, Sequoia Nat'l Park, and maybe Lake Tahoe) and then end up in the Pacific Northwest -- Portland, Seattle or Bellingham. Everything is pretty well figured out, except we're debating on whether we should get an auxiliary battery and solar panel. This would be the best way to go for us and we don't have a heavy electrical load, but I need a source of power so I can work while we're on the road. And also, late night Netflix viewing. Right now, we have the following items and we only really need a power source to charge them, except one thing: <ul><li>Two laptops, with 90 watt chargers</li><li>Two cell phones, which I figure are 15 watts a piece when charging</li><li>Digital camera, which I figure is 15 watts when charging</li><li>A Virgin Mobile hotspot modem, and though I can't find how many watts it is, it can't be anymore than the cell phone or camera</li></ul>Everything, except the hotspot modem, will basically be used for charging or top-ups. The laptops won't be on house power for any longer than 2 hours a day each, max. The cell phones charge in about an hour, so maybe 2 hours a day there. The digital camera may be charged for an hour a day. The hotspot modem can work off it's battery for 3 hours, and I'm unsure how long it takes to charge it. Gonna go ahead and say that the modem will be on house power for about 6 hours a day. Now, the solar panel will be used for when we're not connected at a camp site or at a friends house. It's hard to say how frequent that'll be. But I want to be able to go as long as we need to without having to hook up anywhere. With all of those variables in mind, I'm trying to figure what a good battery would be to use and how big of a solar panel we'd need, and it seems like all the calculators are telling me that I would need, at least, a 300watt panel and a battery rated for 200aHs. That doesn't seem right, so I'm coming here to ask: does that seem right to you? Thanks for any help. <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle">

VanLifeCrisis · Nov 3, 2012

I think that is more power than you will need to power those devices but I'm sure the experts will chime in.   That is actually larger than i was planning for my cargo van.   Im curious if you can fit a 300 watts panel on a stanza wagon.. dimensions seem to run 79" X 39" or there abouts Tho bob who runs this site advocates buying as much as you can afford, i think size is a specific concern for you..

erw1988 · Nov 3, 2012

Did you end up buying a solar panel system, or are you still on the fence about it? Yeah, size and weight are concerns. We'll probably have a rocket box on the roof, so that'll dramatically reduce roof space. If we can't get a solar panel small enough, we might mount it on the hood or just do away with it at all.

VanLifeCrisis · Nov 3, 2012

I've pretty much figured out what im buying, i am just waiting for the funds <img src="/images/boards/smilies/smile.gif" alt="" align="absmiddle" border="0" />  Its not my first step in my van conversion, but i needed to figure out where and how stuff has to be done so i can make space for things i need  (like where the batteries will be stored and vented, where the inverter and charge controller will go) and plan my savings accordingly.   I wont be full timing for another year minimum, but solar seems like necessity to me and free power is a no brainer. You can definitely get some amount of panels on there, it just might have to be smaller.  They even make flexible panels that can be stowed.. On this page here, bob himself seems to have 225 ah batteries, but only 185 watts of panels, you probably don't need 300 watt panel.  the 135watt panel you see there is 59.1in x 26.3in

bee · Nov 3, 2012

Are yo u going to be driving a lot? Then I would think your primary charge source should be the vehicle alternator for your second battery.  You would use a continuous duty relay to disconnect "house" battery when the engine is off.  I personally like the smart kind like a surepower 100amp, but dumb works as well. 200ah is probably more then you need for those loads.  200ah would be two 6v golf cart batteries linked in series for 12v.  Standard 6v golf cart batteries are usually the best deal in amp hour per dollar and they are durable so I wouldn't rule them out right away.  You should check there dimensions and see if you have a good place for them.  Otherwise look at 12v deep cycle batteries and try to figure out what would fit.  Wet cell batteries should be vented so take that into consideration as well. A very rough general rule is 1 watt of solar per ah of battery. Another "free alternative" If you are just taking an extended vacation then I would suggest a jump starter pack from walmart.  Mine died in a month, but it charges via cigarette lighter.  Then you just return it when it breaks.  Sometimes you can get them with an inverter built in.  This only works if you are driving a lot though.

erw1988 · Nov 3, 2012

My hope is that we won't drive a lot. We'll have a bicycle with us, so when we park, we'll use that for transportation -- going to the farmer's market or just hitting the back roads or something. The less we drive, the less gas we need and the more monetary resources we can save. My initial plan is to build/buy a box for the battery and put it in front of the passenger seat. That would have the battery, inverter and controller, so I was planning on getting AGM so I didn't have to vent.

wrcsixeight · Nov 4, 2012

You are underestimating the draw of the laptops, and I am not 100% sure about the draw of common smart phones when charging, but I believe you are vastly overestimating their current consumption. The laptops when running vary the current draw a lot depending on the task, but when they are using a bunch of computing power and charging a dead battery  they will use close to the full 90 watts.  Two of them drawing this wattage is a strain on any but the largest battery banks If somebody knows the amp draw of an iphone or similar with a dead battery, I would be interested to know. I have a dumbphone and the max I see it pull with a dead battery is a short lived 0.3 amps ~ 4 watts, and quickly tapers to between 0.1 and 0.2 amps. Car adapters for your laptops will save considerable energy over using an inverter to power the original laptop power brick.  Of course a big enough tinverter inverter wired directly to the battery can power both laptops and other things as well, the  DC to DC 'car adapters' just use less battery power to charge and run 19.5 volt laptops from 12 volt batteries.  Eveyr laptop has a car adapter.  Most laptops have several aftermarket car adapters available as well.  I bought a PWR + brand for my Dell for 22$ from Amazon.  Universal  laptop car adapters are usually good only to 80 watts. Many people see a hundred watt solar panel and do the math as if 100 watts during all daylight hours is the expected normal charging rate.  You will likely only see 85 watts from a 100 watt panel, 2 hours before and after solar noon, on a sunny day, with the panel aimed at the sun. You should be searching for the largest panel which can fit the area you intend to store it, if inside the vehicle.  If it is to be mounted to the roof, find the biggest  one which best fits the roofline. It is hard to have too much solar.   If this is a 24volt or higher nominally rated panel, an MPPT charge controller is necessary.  If is is a 12 volt nominally rated panel a cheaper PWM charge controller can be used.  If there is no chance the solar panel you get will be able to overcharge the battery, then you can get away with just connecting the solar panel  directly to the battery when you need it, and making sure to disconnect it at night, or before the voltage exceeds 14.5 in the sun. While shopping for the minimum size panel you think you will be able to get away with might seem wise now. Hindsite will will often prove this intention to be naive. Definitely take advantage of alternator amps when you are driving.  Upgrading the original charging is advisable when another battery is tacked onto it. In your case, a large  Marine battery under the hood with a low voltage disconnect to the auxiliary accessories might be the easiest method. During the day hook the solar panel right to the battery to recharge your devices and the main battery, then disconnect it come night time. A PWM charge controller is worth the expense and effort to wire it.  Worrying about overcharging is not fun.  An AGM battery in the  passenger footwell is not a great idea.  Accidents happen. A loose AGM battery is a deadly piece of schrapnel in a rollover.  Attaching it securely there would be a challenge If that is the only place for an additional battery, then stuff the biggest marine battery under the hood as you can and power the accessories through a low voltage disconnect so you can still start the engine.  Carry a jumper pack, and rig up a way to charge it when driving.  2 male ciggy plugs on a wire works very slowly.  Better is 10 awg  wire from main battery to alligator clips, or to male ciggy plug, but the plug must be live.  Some jumper packs have switches turning the ciggy plug off.

blars · Nov 4, 2012

There are smaller and lighter solar pannels available, if you are willing to pay the up-front cost (more $/watt).  AMsolar is one place that sells them.

peacetara · Nov 5, 2012

Get 12V car adapters for  your laptop(s).  That will help a LOT with battery draw.  You can search the internet with google or bing or whatever: the type of laptop you have and 'car charger' to find.  For me it's "Macbook car charger" I found one on ebay for $30, and I'm very happy with it! As for solar on the car... If you have roof racks, you could mount a panel up there I imagine.  Bob wrote a blog post about mounting to a roof rack (I was the model.. LOL).  But might be sure your roof rack can handle the weight/etc. I dunno if that would be an issue on a car?  Or you can do the rolly/flexible kind (they have foldable and rollable). You can't ever have too much solar panel I don't think! With Love, Tara

erw1988 · Nov 5, 2012

Thanks for the suggestions, y'all! I guess my concern with getting cigarette lighters is how soon it'll kill my car battery, since we'll have two phones (one smart, one dumb) and two laptops to charge. In addition, we'll have that wireless modem. I'm also just thinking about getting a Breeze fan from Fantastic Fan. wrc: would the AGM battery be an issue if I housed it in a battery box?

wrcsixeight · Nov 5, 2012

Wiring all ciggy plug receptacles to the second auxiliary battery should be a priority, but acquiring new receptacles means not having to tear the dashboard apart. AGM batteries are certainly safer than flooded inside the passenger compartment, but technically should still be vented to the exterior.  They can offgass if overcharged. If you manage to secure the battery in your intended location all should be fine. My concern would be a 60 pound piece of schrapnel sliding around on the rug stressing the wiring, or getting airborn in an accident.   Fully Recharging the auxiliary battery and how often you can manage to do so will directly correspond to its longevity and overall performance

peacetara · Nov 5, 2012

wrcsixeight: An iPhone can pull 1 amps max.  iPads can pull 2 amps max.  Obviously the closer it gets to fully charged the less it draws. erw1988: I agree with everything wrcsixeight said. Well, you will eventually run your battery down, and eventually you will ruin your battery if you don't charge it.  But regardless, the the car adaptors for your laptop, it will pull a LOT less from the battery (house battery or car battery). Electricity isn't "free"  it has to come from somewhere right... So you have something feeding your battery (input), you have your battery as a 'buffer', and you have your output, or draw (your laptops, cell phone, lights, microwave, tv, whatever). Overall your input needs to equal or exceed your output.  The buffer is just there to buy you some time, in case your input is not always around. input:    Solar, your car engine, a generator, wind power, a 110 outlet from 'the grid', etc.     * Solar tends to be your best bet, because it's the nicest to batteries, super cheap to operate (the sun does it for you!) and very very reliable, the warranties on these things are generally in the 20 year time-range.     * Alternators in your car are generally built to keep your batter alive enough to start an engine, but not really built to recharge it from low state to fully charged.  This is why it's generally frowned upon to plug in all your stuff when the engine is off.  It "works" but your battery will end up hating you eventually.     * Generators, etc.  they all do ok.     * You can't really have too much.. but you can put too much into your battery/buffer all at once, so you want something to regulate this.. a 'charger'  the cheapest ones work generally ok, the fancy ones let you be super precise and treat your batteries like gold (which at their cost, they kinda are!). Buffer/Battery:     * wet cell batteries (the ones for your car) have the potential to release bad evil things for your health.  They *generally* only do this when they are being rapidly charged, i.e. when they are working really really hard.  Bob the forum owner had 2 I think under his bed for many years, no issues.  Myself, I have 1 of these behind my passenger seat.  I don't do rapid input(charging), so I'm not very worried about it.  You can vent these batteries outside, or mount them outside somehow if worried.    * AGM Batteries don't have this problem, which is why everyone recommends them.    * Regardless, like wrcsixeight said, batteries should be stuck somewhere they won't cause problems if they decide to wander about, especially in an accident.  Anything big and heavy like that should be tied down securely.    * You can't have too much battery/buffer. The more you have the longer you can go away from inputs (even solar won't always work..... storms/clouds/etc).    * You generally don't want to drain your battery below 50% , which in 12V battery speak is somewhere around 12.2 volts.  Draining below 50% regularly will decrease how long your battery will last. Output/Draw:    * You want to minimize this as much as possible, and still do what you need to do.  The best way is to keep all of your output at the same voltage as your batteries, hence 12V car adapters for your laptops/cell phones/etc. and why they sell 12V fridges, heaters, ice makers, etc.    * 110V AC inverters that give you a plug like in your house are not very efficient the cheaper they are the less efficient they are.  They work if you need them, tho.    * You can always have too much of this <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"> Myself: I have a laptop, a cell phone, a MIFI device, LED light and I have 1 100ah cheapy walmart battery, and 200W of Solar panel. I work 9 or 10 hrs a day on my laptop, and use my Mifi device to access the internet the whole time.  I run the light for maybe an 1hr a day.  I have various other electronic things like a fan, that don't see a lot of use. I can go about 2 days if I'm conservative before my battery is 50% drained.  If I'm totally not careful (leave everything plugged in, don't turn things off, etc) I can go about 1 day before I reach 50% drain.  Generally speaking it doesn't matter at all that my buffer is so tiny, because my input is more than my output. I'll eventually add more battery, but I'm not in any big hurry. So with 2 laptops (that pull more than I do @ 60W) for less than 1/2 as long as I do, then a very rough guess is you would use about the same amount of electricity I do.  If you had the same setup as me, you would probably do ok.  The only thing I'd really change about my setup is more battery/buffer.  Total price for everything I did brand new would be about $600 or $650, but I didn't buy most of what I have new. Hope this helps! With Love, Tara

erw1988 · Nov 5, 2012

Thank y'all both for the information. It's invaluable. So, pivoting off your advice and what I've read on the Internet, I've come up with a plan: This plan sees me building a battery box in front of the passanger side seat, where the battery will be housed and strongly secured. I'm going to build 6 DC sockets into the box and rig them through the controller. I've tallied up our electrical needs, and it comes out to roughly needing a battery or batteries with, at least, a 215Ah capacity. However, that's overestimating usage. Realistically, we could probably get away with a 200Ah battery, or even a little less. I'm going to go ahead and go with 200Ah for the time being and just concentrate on conserving power. It helped that y'all pointed me toward DC, too, since all the electronics we have can be run through DC sockets. This'll all be serviced by a 154watt thin film solar panel. I read that thin film CIGS panels perform better than regular solar panels in cloudy conditions, making it better for the Pacific Northwest. But a question from this: if I run my stuff all through DC sockets, that negates the need for an inverter right? Since the point of that is to make DC into AC?

wrcsixeight · Nov 5, 2012

Define running your ciggy plug receptacles through the controller? Are you attempting to monitor how much electricity you are using from the battery?  I have all my ciggy plugs running right to a fuse panel or buss studs over thicker wire than they need. Unless you come across a device that is not able to run off DC power, then you do not need the inverter.  They are pretty cheap though, I wouldn't rule one out.  you could always add one.  Low wattage ones could plug into the ciggy plug receptacles, but Directly to the battery terminals is better, and necessary for high draw items.

angeli · Nov 5, 2012

Tara, I missed that blog post, thanks for the heads up! Tell me about your Mifi device.  Mobile hot spot?  Do you like yours and what are you using, etc.... If you've already commented about that, would you post a link? Trying just now to think about how to configure the power array of Josephine Van.   I've got two panels on my pop up camper.  The camper has problems I can't fix, so it will be sold, but I'm taking the panels off.  However, I didn't put them on, and have no idea what size they are.  They are working, and there is an attached charge controller, an inverter, and two deep cycle batteries that are all hooked up now, and will end up moving to the van. I have an older MacBook, which doesn't draw too much and a 12V adapter for it.  I don't work on the computer more than 2 to 3 hours a day max, unless I'm writing, then I can go to @8. I'm sort of embarrassed that I don't know more about what I have, but the camper was used, and the solar stuff already installed. Does anyone know how to tell the wattage of a solar panel if you didn't install it?  I may have to take it down and just see if I can find any kind of ID number on it.  It really looks like the 45W cheapie variety, but who knows.  Thanks for any ideas.

erw1988 · Nov 6, 2012

wrc: I was going off this guy's example, with the DC sockets going into the charge controller, which I guess it goes through the fuse box: <a href="http://www.sixgorillas.com/2012/06/blackout-buster-part-2/">http://www.sixgorillas.com/2012/06/blackout-buster-part-2/</a>

wrcsixeight · Nov 6, 2012

I think he was trying to take power right from the solar panel's charge controller for the outlets. Which does not really make much sense. Many people think solar panels directly power items.  While this is possible,  Solar panels are better thought of as battery chargers, and wired accordingly. I would not be running any wires to the charge controller but the fused wire from the battery, and the wires from the solar array, in accordance with the directions. Running load wires right to the charge controller might damage the charge controller if a load produces a surge from a relay or capacitor or some type of electrical failure of the load, or its wiring. On a separate circuit, have a multi circuit fuse block wired to the battery (+) stud which distributes power to Ciggy plug sockets.  A buss bar on the (-) studs allow many smaller wires to be fed there.  You don't have to use all the circuits on the fuse block, but it is nice for later expansion.  It is very nice for safety and keeping things organized.

With this device you run one wire from battery (+) to the center stud,  then have 6 separate fused circuits.  <a href="http://www.amazon.com/Bussmann-BP-15600-06-20-Quick-Connect/dp/B001BXKLNQ/ref=cm_cr_pr_sims_t">http://www.amazon.com/Bussmann-BP-15600-06-20-Quick-Connect/dp/B001BXKLNQ/ref=cm_cr_pr_sims_t </a>Then have a (-) buss bar next to the fuse block, and this makes wiring everything simple.

<a href="http://www.amazon.com/Chassis-Engin...d=1352182771&sr=1-2&keywords=buss+bar">http://www.amazon.com/Chassis-Engin...d=1352182771&sr=1-2&keywords=buss+bar</a> The battery is a big filter which reduces electrical noise.  Many DC charging devices make electrical noise.  Solar charge controllers do not meet the limits listed by the FCC on radio noise output.  It is better to have the battery between the charge controller and devices pulling energy from the batteries. Monitoring and counting how much current is flowing into and from the batteries requires another piece of equipment.  Some solar charge controllers will display how much current they are producing, but not be able to count the amp/ hours removed from the battery(s) If you want a Battery monitor which will give you an amp hour from full figure as well as a battery percentage remaining, you are looking at about an additional 200$ in equipment. Voltage is only accurate at determining state of charge on a rested battery, one which has not seen charging sources or discharging loads for several hours. A digital voltmeter display is handy to have, because with a lot of use you can notice trends and tendencies and make rough estimates as to how much remains in the battery.  If you want accuracy  as to State of charge within 10%, then all the current must be run through a Shunt and measured by a device like a Trimetric. <a href="http://www.bogartengineering.com/products/trimetric">http://www.bogartengineering.com/products/trimetric</a>

peacetara · Nov 6, 2012

Angeli: I just use whatever Verizon gave me, I just made sure it had an external antenna port, not that I have an external antenna, but I wanted the ability to get one, when I'm feeling rich. erw1988:  The wiring hookup should be Solar Panel wired directly to the Solar Charge Controller.  The Solar Charge Controller will connect to the battery. You will have a 12V ciggy plug connected to the battery.  Most 12V ciggy plugs have a fuse built into the end of them.  but you probably want a fuse inline anyways.  You also might want more than 1 ciggy plug.  You would be better off having each ciggy plug wired to the battery thru a fuse, or like wrcsixeight said, using a breakout box/bar/etc.  you don't *HAVE* to have one, if you need to save money, but it's a good idea to at least PLAN for that eventually <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"> At the very least, get a 25A Fuse, you can go to any electrical supply house (and probably most hardware stores, RV stores, boat stores) and collect an inline 25A fuse.  It will be connected between the battery and the ciggy plug(s). If you look at <a href="http://tara.birl.org/2012/09/28/solar-electricity-in-my-new-house/">my blog post (http://tara.birl.org/2012/09/28/solar-electricity-in-my-new-house/)</a>, it shows a very very very simple diagram for a solar setup. which should help you make sense of how everything hooks up <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"> With Love, Tara

Pikachu711 · Nov 6, 2012

I found a great picture of a wiring diagram for a RV Solar Panel system. Here's the link: <a href="http://midsummerenergy.co.uk/solar-...gDiagrams/CircuitDiagramSolarChargeController">http://midsummerenergy.co.uk/solar-...gDiagrams/CircuitDiagramSolarChargeController</a> Peacetara is correct that all you have to add add a few 12-volt lighter plugs at strategic places. Once that's done you have your solar setup. The only differerent thing you need to do that isn't mentioned on the wiring diagram is that you should ground your 12-volt batteries to the metal of the vehicle. Aside from that, that's the basics of wiring a solar panel system in your vehicle.

cedric · Nov 14, 2012

can someone please recommend wire sizes for this type of setup. I know it depends on length of run so lets say we are in a car. The battery box has controller and fuse box mounted on the side of the box. Ciggy sockets are near or on the box also 6-10ft from solar to controller 1.5 ft from controller to the battery 1.5 ft from  battery to fuse box 1.5-2ft from fuse box to ciggy sockets

Sizing a battery and solar panel system for a car

Help Support Van Living Forum:

Member

Well-known member

Member

Well-known member

Well-known member

Member

Well-known member

Well-known member

Well-known member

Member

Well-known member

Well-known member

Member

Well-known member

Well-known member

Member

Well-known member

Well-known member

Well-known member

Well-known member

Similar threads

Join the conversation!

Join today and get all the highlights of this community direct to your inbox. It's FREE!