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Sun Mar 30, 2008 9:38 pm

pros,cons of either? there is an electric one at Bi-Mart for $40 that seems like it would suit me,but would like to go solar in case we out in the boonies for a few days. would like to stay under $100 for a solar one. is it possible to get one (solar) that will be strong enough for my batteries (at the link below)?

http://www.gotbatteries.com/items.asp?params=batteries/SLA/1/Hawker/Enersys/SBS40/SL203/36L203S1

Mon Mar 31, 2008 3:59 pm

If you are planning on maintaining an already CHARGED battery, then a plug-in AC trickle charger will work fine. I would suggest one that puts out at least 2 amps and has true three-stage capabilities or you'll cook your battery. If you are going to use a solar panel as a trickle charger, you are going to need, again, a minimum of 2 amps or 24 watts to MAINTAIN your battery and be able to park that 24 watt panel out in full sun all day.

Camping in the boonies and charging a 38 AH battery is a whole different story. Since you do not want to discharge more than 50% of that 38 AH battery, you'll have to supply 19 AHs of power back to the battery with your solar panel. The aforementioned 24 watt panel would take a full 9+ hours of full sunlight on your 24 watt panel to recharge those 19 amp hours. Not a likely scenario unless you are camping at the Arctic Circle all summer.

A 40- 50 watt panel would be a better bet for that 38 AH battery. Used solar panels are getting cheaper to come by these days as more and more older ones are taken out of service. I just got two 53 watt panels for $150 each on Craigslist. Mono and polycrystaline solar panels suffer very little degradation over the years so used ones are nearly as good as new ones. Stay away from the "flexible" panels as well as thin-film panels. Flexibles are expensive and inefficient and thin film panels tend to be a little cheaper but also less efficient. Thin film panels do have the advantage of working better in lower light, however. Good if you live in a foggy place, I suppose.

If you do get a panel in the 40-50 watt range, you'll need a charge controller. Charge controllers are basically a voltage regulator for your solar panel. Solar panels create anywhere from 17-21 volts of power and you need a controller to monitor and feed your battery the proper voltage or, again, you'll cook your battery.

Those cheapo "dash chargers" are a waste of money. They produce very little power and often don't even come with a diode attached so they actually drain your battery a little when the sun goes down. Get a real solar panel, a controller and a decent battery and you can camp anywhere.

Jeff

87 Syncro Westy EJ22

Mon Mar 31, 2008 6:12 pm

Good answer, Jeff, but I would differ somewhat on a couple of your points, just from my own experience living powered by PV for awhile now.

For the hypothetical 38Ah Hawker (man, that's an expensive battery!), a 1A trickle charger would be fine for maintaining a fully-charged battery. That gives better than a C/40 rate, which is enough to hold voltage to 13.2, a normal float rate. I suspect with no load on the battery and full sun, C/40 would raise V even a bit higher. This isn't, for sure, enough to do any recharging, though.

That sizing for a camping panel to keep up with a 50% depth of discharge is great. A 50w panel will make about 3.2A; given a 5 hour average charging day, about normal across the southern tier states, you could get 16Ah, pretty close to the 19Ah used at 50% DOD. A 65w or 75w panel would be just right.

Stick to monocrystalline panels if you want to keep it as small as possible for stowing while traveling. Mono's also have the least degradation over time. But 20 year-old panels aren't nearly worn out, so used can be a great deal, in any type, although I would beware buying any used flexible panels. Hard to be sure how they have been handled and stored.

With a single 50-75w panel, for camping, I don't think you would really have to have a charge controller if you're using the battery daily. Just use a voltmeter and if you do manage to get charge up over 14.8, disconnect. Unless you have loads of charge time, that may never happen. But the same panel could be used for maintenance, and if so, only with a charge controller.

Mon Mar 31, 2008 6:49 pm

10¢--

Yeah, I was trying to keep the price, and thus watts, down on the panels. He only wanted to spend $100. Most people are pretty surprised at what the panels will cost.

That is a CRAZY expensive 38AH battery. Must be gub-a-ment issue... extra Mars Rover battery, perhaps? I put a 105 AH Diehard (RV) under my backseat for $89. Lots of folks just run WallyMart starter batteries and return them every year for fresh ones on the warranty. Whoops. Did I say that out loud?

Old panels work great. Mine are 12 years old and crank out 19 volts.

Agreed on the controller with a 50W panel but I like to "set and forget" so a controller in this case is more of a convenience than a necessity.

Any thoughts on MPPT controllers? A friend recommended a BZ Products 250W (smallest MPPT they have)---he uses one and like the company---small and easy to deal with if there are issues. I know its overkill for my 110W Westy setup but MPPT makes more sense---on paper anyway---than a PWM controller. $129 on eBay for the MPPT 250.

Jeff

Mon Mar 31, 2008 7:02 pm

I picked up a trunk full (a Meceredes 300CD trunk mind you, BIG) of VW solar panels. Most with cigarette lighter plugs, some with EDB.

I put three in array and keep it plugged in. My battery (single to date, double soon) stays topped off nicely. They sit in trio. So far, so good.

I made a bonehead move and left the lights on all day at work. Walking out, after dark, I could see the glow of the marker lights.

One bump, she started.

Mon Mar 31, 2008 7:21 pm

Jeff, I like "set and forget", but I was just considering cost, too. I would always use a controller, but I'm sure I have a couple laying around, so for me, no problem. But I mentioned that because using one isn't strictly necessary with such a small and intermittently-used system as a weekend camping battery.

I think MPPT is great, I won't spec a plain PWM for any PV system I design anymore, and urge my friends with existing systems to make the switch when their old CC's wear out. But these are all big enough that it's cost-effective to pay extra for MPPT; my benchmark is when the MPPT CC costs the same as a quarter of their existing PV capacity, then it's directly cost-effective. For one-panel systems, another panel would be cheaper. But for a campmobile, you have to have a place to stow more panels. So you make your choices.

Mon Mar 31, 2008 8:02 pm

well I picked up another Hawker battery from my auto electric repairman today. he even made me a nice cable to wire them in parallel,$20 for the battery and cable. got it all installed with my inverter (Cobra 800 watt) and a electric battery tender I picked up at Harbor Freight. (at link below)
priced around for a solar one,just to much money.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93258

total of $150 invested in 2 batteriers,tender,inverter and go westy aux. battery kit.

Mon Mar 31, 2008 8:18 pm

the battery tender I bought has a light that stays on all the time indicating "power". i'm wondering if this will draw power and if so how much? being it is designed to stay connected to the battery,I would't think it (the light) could draw that much.does anyone else have this product? it also hums like a bugger and gets pretty warm when plugged in for awhile.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93258

Tue Apr 01, 2008 3:25 am

Doesn't the light go out when the battery is fully charged?

Tue Apr 01, 2008 5:43 am

there is a light for "power" and one for "charged" so for the power light has been on since I hooked it up last night. still on this morning.