Solar Battery Charger

We have an '87 VW Westfalia Camper. I had previously installed a second battery in it to run the 'camper' stuff - radio, interior lighting, refrigerator and so on. This works well to make sure that the primary battery never gets discharged so that the starter won't work. The second battery gets charged from the alternator when the engine is running, but is disconnected (via a relay) from the primary circuit when the engine is stopped.

Here is someone else's take on how to do it. I didn't do it this way, I used the existing relay in the second battery compartment that cuts 12V power to the fridge when the engine isn't running. It's no big deal. Get a Bentley manual and follow the (torturous) wiring diagram. Or follow this advice.

Mostly, when we camp, we have access to grid power (110 VAC), so it's not a big deal. Under these circumstances, the second battery doesn't take much of a hit from simply lighting up the van, as we have an 11 watt fluorescent lamp which draws about an amp. Everything else - DVD player/TV, heater and so on gets hooked up to 110 volts. We carry a battery charger, so that even if the battery gets a little low, we can fix it.

But it's a bit limiting, not being able to 'dry' camp (no access to 110 VAC) for more than a day or two at a time without having to start and run the motor (not very good use of dinosaur juice) or drive somewhere else, just to charge the battery up. The alternative is to not use any power and lead a miserable existence - and that just doesn't cut it, for us.

Then there's my motorcycle. Where I park it, there's no access to 110 VAC, and every now and then, especially during the cooler months when it gets ridden less, I need to take the battery out and recharge it. This is a PITA, as it resets all the electronic gizmos like the clock and the trip meter. Wouldn't it be nice to trickle charge the motorcycle battery from a solar charger?

A word or two on 'Deep-Cycle' batteries

Yeah, I know, for the second battery I should have got a 'Deep-Cycle' battery. I will, some day. But, when I installed the second battery, the van was fairly new (to us) and we had no idea of the condition of the existing primary battery. So I simply bought a new battery of the correct type for the main battery, and replaced the existing battery, which was then used for the second battery. In hindsight, I would probably have done better to have got a 'Deep-Cycle' battery.

Why is this? Regular automotive batteries are designed to provide relatively huge amounts of current to 'get that motor runnin'. They don't respond kindly (ie, they shuffle off this mortal coil) if they are subjected to a 'deep' discharge pattern, meaning that they are repeatedly discharged to their capacity. 'Deep Cycle' batteries, on the other hand, are designed to provide smaller instantaneous current loads, but will also tolerate repeated discharge to 'flat'. However, they are expensive, and it's difficult to find a physical size that will fit into the limited space available without significant surgery.

Decision Points

I looked at the notion of independent charging a year or so ago, and with my limited knowledge at that time, figured that it wouldn't be much more expensive to get a Honda generator producing mega-amps of power for the same price as a very modest solar charging system. So, I shelved it.

My interest was 're-piqued' by a 'yet-another-time-to-charge-the-motorcycle-battery' moment recently, so I started digging, once again. Google is my friend, and I soon discovered that there were all sorts of vendors supplying what appeared to be really low-cost solutions - from back-pack to foldaway.

Then I was faced with the question of what exactly I needed. I reckoned that, given the ads I'd seen, I'd only need about 11 watts. Deities, here in So-Cal we get hours and hours of sun, and simply parked out there, that would be plenty to keep the battery charged.

But, I noted that some of the ads suggested that you need a thing called a 'charge controller' or 'regulator' if the power draw was over 20 watts or so (which translates, in a 12 VDC system, to a current of about 2 amps). This alerted my interest, and made me wonder what this was all about. I needed a guru.

Research

My Googling had led me to find that there were three possible purchase points in San Diego - Camping World, West Marine, and a small company called Discover Power. Camping World seemed like a total loss, as my experience there previously was that Customer Service and product knowledge was a joke. West Marine had previously provided some good stuff and the floor staff there seem to know what they are about. But Discover Power was featured in a web page by some Professor in Engineering from San Francisco who had assembled a seriously powerful rig at his home. So that's where I went first.

And encountered this amazing guy called Misha. Misha lives in the back-country. Twenty five years ago, he contacted the electricity company about getting connected to the grid via his neighbor's supply. He was quoted $56,000, with a monthly minimum bill of around $230. So, he started out and built a solar system, and hasn't paid a penny to SDG&E since then. What he doesn't know about solar energy is a whole lot less than I remember from my graduate studies in Biochemistry.

We worked through what the current requirement was - 1 amp (12 watts) for the light at 3 hours per night, 2 amps (24 watts) for say, an hour and a half for the DVD player, and then a little 'fudge factor' for conversion via the controller, led him to conclude that a 30 watt unit was what was required. At 5 hours per day of nearly guaranteed sunlight, this would be enough with a little but not a lot extra to meet the requirement.

By the time I'd added up all the costs of the solar array and the regulator, it came to about $240 + tax. Never mind the various connectors, wiring and security needs.

Can we economize by skipping the regulator? This question got answered by Misha when he explained that the solar panel actually produces about 16 VDC. This fact was verified by me when I tested the naked output with a voltmeter. It seems that if one has an even faintly seriously 'chunky' current output at this voltage, then one risks the chance that the battery will 'boil' and hydrogen will be your enemy.

The regulator adjusts the voltage applied to recharging by 'looking at' the 'back-voltage' that it sees from your battery. The fairly crude 'PWM' (pulse width modulation) unit that I purchased achieves this function. Much more efficient (and much more expensive) devices can sense voltage differences more, um, sensitively.

Armed with this knowledge and more, off I went to West Marine. I asked the Customer Service guy where the solar chargers were. He went into this 'between you and me' routine that they couldn't get solar panels from anywhere, and that, wherever you go, they're all from the same supplier'. I did, however, find an 11 watt unit, which was physically *huge* by comparison with the 30 watt unit that Misha had shown me. Allegedly, it's due to different technologies in producing the solar cells.

$240++ was still a bit of a big pill to swallow, so I decided to sleep on it, and consult with 'she who must be obeyed'. After all, how many batteries and how many gallons of gas can you buy for that amount?

So we discussed all the scenarios where this functionality might be useful. We decided that there were few, apart from a doomsday scenario, where it could be justified. Nonetheless, on a 'geek' basis, we decided to go ahead.

Purchase

I bought from Discover Power:

• PU30 30 watt solar panel
• SunGuard 4.5 amp PWM charge controller
• 6 feet of 10 gauge twin flat cable (although in fact, they gave me about 12 feet)

Here is a picture of the panel (it's really rectangular ... you're seeing parallax distortion in the photo):

Assembly

Here's a picture of the important bits:

Three screws allow you access to the solar panel's termination block (above the Discover Power label). The polarity is (not very clearly) marked. The controller is on the left. Although it's mounted as close as possible to the termination block. Its 'flying lead' cables weren't long enough to directly hook up to the termination block. Thus, I used a short length of the 10 gauge cable and connected it with 10 gauge automotive 'compression' connectors, and then wrapped it with electrical tape. It's a bit ugly, I would have preferred a screw type block and may well change this. The 'flying leads' from the controller to the connector were tied in a knot before being fed through an existing hole in the panel's frame, to provide some 'yank' resistance (as the flying leads are an integral part of the controller, and if they get pulled out, it's time for a new one!). The cables are simply kept tidy with electrical tape.

I searched for quite a while for some automotive connectors that would work for this application.  I wanted to be able to unhook the cable from the panel.  In the image below, you can see that I used domestic 110 VAC connectors. These are certainly 'man enough' for the job, but seem a bit out of place here since I'm not getting 110 VAC. Unless I find some 'appropriate' connectors, I will probably replace these with waterproof ones and have the leads emerging through the same edge that the regulator is mounted on.

Note also the use of 3/4" weather strip on the panel's edges. The idea was to cushion the panel against whatever it was resting on, and to lift it up so that neither the regulator nor the exiting cable were hitting hard bits. This idea was less than stellar, in practice, as the adhesive used for this particular weather strip had the awesome adhesive power of Post-It notes!

In the picture above, you can see why it needs to be raised a bit, because the controller is not flush with the underside of the frame. Why was I such a dork? Because, and although you can't see it, the depth of the solar units on the other side of the frame is about 1/4" or so. So, if I had drilled holes any lower, it would have been Goodbye Solar Panel. I'm glad I noticed that before starting to drill!

The last piece of the puzzle was to put a female 110 VAC plug on one end of the remaining wire and a pair of battery connectors on the other.

First Test

Checking continuity and polarity seemed to confirm that all was in order. There was, as expected, no continuity between the positive connector of the solar panel and the 'far' side of the controller. Putting the panel in front of a 100W incandescent light produced 16 V at the panel's termination block, but zip at the 'out' side of the controller. It was getting late by then, so the rest would have to wait until the sun came up.

Which it did the very next morning. Plonking the panel in the luggage rack above the cab of the camper, I again tested the voltage. Still zip! A quick trip to the MorningStar web site FAQ confirmed that this was, in fact, correct. Phew, that was a relief! Next job was to connect the thing to the battery and check the current. Yay! 1.4 amps with a few hazy and faint clouds twixt the sun and the panel. I'm guessing it wasn't more because the battery was pretty well charged up already, and the controller was just doing it's job.

First Use

Not really use, more a usability test. We camped overnight at Salton Sea. On arrival, we did all the usual 'arrival' stuff, which now includes putting the solar panel on the luggage rack and plugging it in. All of 30 seconds, I'd guess. The 10 gauge cable fits (just) between the top of the door and the door frame when the door is closed. I can't report that it worked, only that it didn't *not* work. We charged up our PocketPC/GPS combo, and 4 AA sized batteries, as well as running the light for a few hours. Truthfully, if I had been concerned about the state of charge of the second battery, I could simply have hooked up the battery charger as we had an electrical hookup at the site. But that wasn't the point, was it?

Modifications

The non-stick foam is replaced by a denser, more self-adhesive, foam from Home Depot. The 10 gauge cable has been replaced by 14 gauge, which seems perfectly adequate for the job and causes less distortion when jammed between the door and frame. Finally, the 110 VAC plug and socket has been replaced by a BMW motorcycle-style plug and socket (available from John Deere dealers, of all places!).

In the picture, you can observe how relatively unobtrusive the working system is. Shame that I couldn't get any white cable.

In this picture, the BMW-style plug and socket is featured. Not only is the socket integral with the panel, it's 'water-resistant'. In addition, there is no chance that by accident, someone is going to plug it into a 110 V supply.

In use

The real test will be when we stay at least 2 nights in one place, and then consciously use the battery for stuff the evening of the first night. If the battery gets back to full charge by the end of the next sunlight period, we'll be good to go. Plan A is a couple of nights in a fish camp in San Felipe, Baja California. Plan B is Bahia de Los Angeles. Watch this space...

San Felipe, B.C.

Hey folks, the results were mixed. We headed out for San Felipe Friday 17th March and wimped out at Playa Laura RV park, which has 110 VAC and piped water. But, we stuck to our mission, and on Friday night used only the auxiliary battery for our external display lights (low wattage 'stars'), the 11W fluorescent van internal light and the DVD player (in this case, the Dell laptop computer that my wife had brought along to do some work). I did some voltage testing earlier on Friday with the solar charger in place, and the juice was up there amongst the stars  -  about 13.7 volts - not surprising since the second battery had been charged en-route via the Westie's alternator.

Saturday turned out to be rainy, cloudy, and completely invidious to solar charging. In fact, we got only about an hour, late in the day, when there was any direct sunlight on the solar charger. Nonetheless, the voltage readings climbed slowly, inexorably, even when clouds intercepted the charger's view of the sun. But sadly, not enough to recharge the auxiliary battery to it's fully charged state. After running the laptop on 12V for about 20 minutes, the battery light went to yellow, as one might expect.

What to conclude?

Not too much.

I suspect that the 12V adapter for the laptop was drawing more than twice the current of our usual DVD player. And we got unlucky, with lots of clouds and rain in a place where the sun always shines.

But, in direct sunlight covering the whole panel, the charger gets about 13.7 V to the battery. I don't know what the internal resistance of the battery is, so the current being fed is unknown. Also, even in indirect sunlight, some amount of charging takes place.

At last, some proof.

This weekend, we went to Indian Flats campground, near Warner Springs. No hookups (no water!). Beautiful and quiet place up in the foothills. We did our usual stuff with lighting and watching a DVD. In the morning, the residual voltage on the second battery was about 12.45 volts. In about three hours of direct sunlight, the panel had the voltage back to 12.7 (after the surface charge was removed). Success! I think that I can now write with some certainty that this solar configuration is more than adequate for our needs. However, any kind of shadow, no matter how small, seems to cause charging to cease.

Onboard Battery Charger/Maintainer

By this time, most readers are beginning to think that I'm obsessed with keeping the auxiliary battery up to snuff, and they'd be right. I'd noticed that this battery's voltage was beginning to drop rather more than it should when not being used. Obvious first analysis was that the battery was past its sell-by date - after all, it had been discharged completely on several occasions, and after digging out the previous owners receipts, it transpired that it's nearly 4 years old.

However, before giving up on it, and thinking that even if a new battery were really needed, it would do no harm to install an onboard battery charger/maintainer from Kragen. This plugs into the 'spare' 110 VAC socket under the sink, and taps into the 12VDC power cables going to the refrigerator. So, every time we get connected to 'shore' power, this guy gets switched on. It's a 'smart' charger, so it switches itself off when the battery is charged up.

First use was at William Heise Park, Julian, CA, last weekend, where we were camped in shade (so we couldn't use the solar charger), and and it certainly seemed to function as specified.

By the way, we had the neighbors from hell there. When they arrived, they didn't turn off their diesel truck engine for about 20 minutes, claiming that the intercooler was hot and needed to cool down - b*llsh*t!, then left their a/c on overnight in weather that was perfect, right by our ears in the pop-top. Finally, to add insult to injury, when I started up the van to get out of there, their alarm system was so sensitively adjusted that just the sound of the van's engine starting set it off.

Replacement Auxiliary Battery

Even with the solar and onboard charger, I realize that this particular battery is history. It simply won't hold a charge. Yesterday, I spent about 4 hours trying to find a deep-cycle battery that will fit the space under the drivers seat. Well, ya know, there's not a single one (with half-decent capacity) that will fit. The 'height' dimension (a shade under 7 inches) eliminates offerings from every known manufacturer - even if the battery is mounted on it's side. This solution appeared to have some merit, but when I called Optima, they said that the top posts should absolutely not be cut off, as not only would it invalidate the warranty, but would cause structural weakness. So I got an Autolite (Exide) 41-84 regular auto battery from Kragen.

As I write, it's getting a 'top-off' charge via the solar panel :)

Hopefully, between the solar and the onboard charger, this battery will not suffer the deep discharges that I inflicted on it's predecessor. We'll keep you posted.

LED lighting

We got a '12V DC 30 LED light' from Harbor Freight (part # 93944-0VGA) that uses an amazingly small wattage (2.16) to produce a claimed 40 watt equivalent incandescent light output. I seriously considered using the 'stars' light transformer to allow it to run on 110 VAC, but at that wattage, the onboard charger will easily keep up with it.

Comments via Email

Blog

Jacque writes:

From: Jacques Pagé [mailto:jacpag@videotron.ca

Sent: Saturday, July 01, 2006 5:27 AM

To: Me

Subject: Solar Charger

Hi,

I had the same problem installing the deep discharge battery under the drivers seat. I selected this battery from Canadian Tire .

I think it is very similar to the Optima. This battery has the regular top posts AND two other screw type posts that are also on top. I cut off the screw type posts and put the battery in the compartment. I cut off the metal cover, making it just wide enough to cover the posts but narrow enough so that the seat can swivel. I then screwed the battery cover with its hinge, just an inch higher on the wall behind the driver’s seat. It was then high enough to cover the top posts. As for the rest of the battery surface and battery compartment opening, I covered it with carpet rendered stiff with a generous coat of contact adhesive. This setup looks good and works fine! Please note that my camper is NOT a Westy but a RIVIERA, which is very similar but has some differences, notably a 25 amps 12 volt transformer that supplies current when connected to an 120v ac source. This current charges the battery and powers all the accessories when parked.

Jacques,