Solar Battery Charger

[Lin]

I was at Costco today.  They are selling a pair of solar battery chargers for about $30.  They put out 1.8 amps at 15-25 volts.  How would this work to maintain two or three house batteries.  We get lots of sunlight.  Could the two be paralleled to increase amperage or put in series to maintain 24v start batteries?

[Runcutter]

Lin, thanks for the topic.  Can I add to the question ....  How could it/they (or another solar charger) be set up to maintain the charge on a pair of 8D's, wired in parallel on a 12-volt coach?  Is there any issue with overcharging, or do solar chargers include some kind of controller?  When I was young, fueling and cleaning buses, I well remember the smell of cooking/overcharging batteries - one of those smells you never forget.  With a lot of business travel, the 4107 sits in the storage lot for extended periods.  I want to keep the batteries charged up, but sure don't want to cook them.

Thanks.

Arthur

[Chaz]

I'm VERY interested in this too. Hopefully Jerry or someone with some understanding of this can help us.

  Chaz

[Dreamscape]

Me Too! We have lots of sunshine here in Abilene Texas!

[luvrbus]

You never want to hook solar to your batteries without a good controller,I don't know if the Costco brand have a built in controller or not but I have 1 85 watt panel on my bus to keep the batteries charged with a controller the solar will fry batteries without one and they are expensive from a 100 bucks upwards            good luck

[Lin]

Actually there is a mistake in my posting.  It is not 1.8 amps, it is 1.8 watts and 125 Mah.  They claim that one does not need a controller for less than 15 watts.  It would seem that the charge is so small that it could not hurt anything.  They are calling it a battery maintainer.  I was wondering if it is powerful enough to do any good.  Here is the link:

http://www.sunforceproducts.com/english/details.asp?id=65

[Jeremy]

You never want to hook solar to your batteries without a good controller,I don't know if the Costco brand have a built in controller or not but I have 1 85 watt panel on my bus to keep the batteries charged with a controller the solar will fry batteries without one and they are expensive from a 100 bucks upwards            good luck

It really isn't true to say 'solar will fry batteries' with the kind of solar panels and batteries we are talking about here - in fact I'm not even sure those small dashboard panels (eBay is full of them by the way) would keep anything but the smallest lead acid battery topped up.

Also, it's worth distinguishing between a solar panel 'charge controller' and an 'intelligent battery charger' - the charge controller is there to extract the best out of the solar panel by electronically modifying the variable output of the panel to a smooth voltage - ie. under-voltages are stepped up and over-voltages are stepped down, with the current going down or up accordingly. The charge controller does not monitor the state of charge of the battery and adjust the charge current as required, which is what you need to do to prevent batteries 'frying'. It is true that the charge controller will prevent those occasional 'over-voltage' outputs being sent to the battery, but that does not mean that it won't be overcharged - in fact it will probably happen more quickly as ultimately more power is being sent to the battery.

None of the above is meant to suggest that solar charging isn't a very good idea by the way.

Jeremy

[Lin]

Jeremy,

Am I right in saying then that these small chargers may be okay to keep a regular car battery topped-off but not be adequate to keep my house batteries topped?  Is the small charge that they produce capable of causing any damage?  I am not looking for a charger here--merely a forget-about-it method to keep fully charged batteries at peak.

[Jeremy]

Jeremy,

Am I right in saying then that these small chargers may be okay to keep a regular car battery topped-off but not be adequate to keep my house batteries topped?  Is the small charge that they produce capable of causing any damage?  I am not looking for a charger here--merely a forget-about-it method to keep fully charged batteries at peak.

The quick answer is that I don't really know as it is not something I have done myself (yet). It is a length-of-string question anyway - 'theoritically' 1.8 watts  would be ample as 'theoritically' a battery of any size should be able to sit for a very long time without losing any charge in the first place - but in real life batteries do lose voltage, especially if they are still connected to the vehicle whilst sat, with the possibility of phantom loads also discharging the battery. Other factors (cold temperatures etc) also have an influence, so it's impossible to say whether 1.8 watts (or even multiples thereof) would keep the battery charged in you case - but I wouldn't hold your breath. There is certainly no chance that it could damage your battery though, so by all means have a go.

There may be someone on here who can give a better answer based on their own experience - failing that, there are plenty of 'proper' solar panel systems on the market designed specifically for keeping batteries charged - they are very common on boats for instance, which often don't get used for long periods of time. It might be worth speaking to a supplier of such systems to see what kind of panel size / power output they recommend for a typical battery installation.

Jeremy

[luvrbus]

Jeremy, if you read Lin 1st post that is what I replied too. I have a controller that regulates the charge going to batteries even has a temperature probe,this the second one I bought because the first  one would allow the batteries to over charge and AGM batteries are not a pretty sight when they are over charged.    good luck

[Lin]

Clifford,

Does that mean that even with a 1.8 watt panel one would need a controller?  It certainly would not be worth it for this little charger.  I have a 195 watt panel that has broken glass.  I was thinking of trying to seal that one with some clear Krylon-type stuff and seeing if I could use it.  If that worked, I guess a controller may be worth it.  The funny thing is that I would not be able to use the panel in the summer since this particular Sanyo model is said to develop problems in desert heat.  Anyway, that is a whole different issue.

[luvrbus]

Lin, like you said you don't need one for anything under 15 watts per Northern Az Sun and Wind also, for 30 bucks for 2 I would try them if I did not have my system  

good luck

[boogiethecat]

My only experience with a small solar panel like these is on my tractor... I put a 2 watt panel permanently on the battery about 5 years ago, and as of the moment I did it I quit needing to fetch a set of jumper cables every stinking time I wanted to start it. The battery has been in fine shape since, going on 6 years now.  No controller, just the panel and lots of sun. Just a normal automotive battery, maintanance free style.
I'm sure the same sort of effect will be had on a house bank with a small array such as this.
Cheers

[Sojourner]

About using 150 milliamps (1.8 watts) at 12+ volt solar panel.

From a fully discharged condition with a 1 Ampere charger as it would require roughly 1.5 times the battery's capacity

The solar panel is .15 (150 milliamp) amps at 12v equal 1.8 watts at full sun light.

About the need if controller…it calls trickles charge at 150 milliamps at the self-discharge rate. So there no need of a controller.

About how much charge is 150 milliamp to a large 8D-12v battery at 255 ampere (it not CCA).

1.5 x 255 = 382.5 hours at a rate of 1 ampere charging this is greater than self-discharge rate.

The trickle charge of 150 milliamps or .15 amps is 7 times less than 1 ampere.

So it would take almost 7 times longer….382.5 x 7 = 2677.5 hours to charge a dead to full state of charge.

However, remember a 150 milliamp is only at the self-discharge rate which mean it you can never charge a battery but to maintain it.

The bottom line is you can maintain popular size car battery with 12+ volts at 150 milliamp solar panel. So for 8-D battery's self-discharge rate is double of car battery. You will need 2 solar panel for each 8-D battery just to maintain of its state of charge.

Take 7 of these 150 milliamp solar panels to make 1 ampere charger with a controller.

Keep in mind….None of all solar panel works to full capacity unless it get full maximum solar sun beam in direct alignment So count the dim days of partial or no power.

Now the question is....Will the battery be ready after the long idle storage period is depend on the state of charge at the time you start the idle time and how many sunny days per idle period.

FWIW

Sojourn for Christ, Gerald

[bobadame]

I use a Harbor Freight solar charger/maintainer to keep a couple of 6 volt golf cart batteries charged. The batteries are connected in series in a Big Joe forklift. Been working fine for about 3 years now. The cell puts out 120 mA. I would think you could connect a few in paralell to maintain a couple of 8d's. I buy these on sale for under $15.00.