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DaJTCHA
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# Posted: 14 Jul 2012 10:24am - Edited by: DaJTCHA
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As you guys may already know, I've equipped my "rolling cabin" (ie a camper) at camp with a group 29M deep cycle battery that feeds a series of fluorescent and SBLED light fixtures and (2) modified WMart O2 fans...
After camping for 3.5 days in a row, using the fans most of that time either on the low or sometimes high settings and the lights intermittently...I reduced the reserve voltage on our battery from 12.86volts to about 12.36 (~70% state of charge). Currently I'm lugging the battery back and forth from home and charging it between trips, but I'd really like to keep it up at camp and recharging using a solar panel.
After that long winded intro, here's my ???:
I purchased this product from HFT:
HFT Briefcase Solar Panel
I realize that I need to purchase a charge controller as well, I'm getting there...but I'm wondering how well this unit can "top off" the battery during the day? Can someone do the calculations for me. I know everyone has an opinion based on their personal experience of how much sun they see, so let me relay what we have at our place: Sun comes up during the summer at 7-ish and hits a cleared (unobstructed) flat spot that I can pitch the panel to face the sun easily for at least 8 hours a day. It gets hot at our camp, so hot we leave for the valley and the spring fed streams from 11-5 to escape it all. Our property is located at the top of our mountain at 1600 ft. I would have the fans/lights turned off during most of the recharge periods.
How well do you think that this panel will recharge the battery during the day?
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VTweekender
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# Posted: 14 Jul 2012 11:31am - Edited by: VTweekender
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Well, it will be a trickle charge with that panel....in a 8 hour day of sunlight as you say, you will gain about 3 amps with it....you really won't need a charge controller with this small a charge if you are going to be present when charging, just go directly to the battery, it wouldn't be enough overcharge to really cause damage, which is what a controller does, but I still wouldnt leave it hooked up to the battery for days at a time and go home until next time without a controller on it..
Hard to do the math for you without specifics, but lets example, say your battery is a 200AH and you are using 20% a day in use. That would have you using 40 amps a day, with this panel it would take about 13 days to top it off after 1 days use.
What you pay for with those type panels is the super duper whiz bang new finangled "suitecase".....where you could just buy a 13 watt panel for about $20-25 to do the same thing......not saying you wasted money...you bought what you wanted....but in terms of turning dollars into value, it is wiser to buy a 80 watt panel for a few more bucks and mount it permanently, run the leads down to your battery and you would have a charge that would come closer daily to what you are using......still wouldn't need a controller with the 80 if you are there to monitor it with your meter, if the battery shows close to max just disconect..
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DaJTCHA
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# Posted: 14 Jul 2012 12:30pm
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I read somewhere a statement that the panel shouldn't be hooked up to the battery for charging while there was any load on the other end of things? I found that unusual because as I thought about some of the other trickle charger panels that are available for automotive use, the internal computer, clock and small amp draw appliances of a car are always pulling some sort of current while the solar panels are supplying their trickle charge to the battery? How would running two small fans off the battery while the panel charges it be that much different? Maybe I'm wrong, maybe the fans equal more draw than I'm guessing?
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razmichael
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# Posted: 14 Jul 2012 12:54pm
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The panel has an output of only 400 milli-amps so, as VT states, it is a trickle charger. If you are using up 30% of your battery in a few days, you should be able to get a better idea of average draw if you know your battery specs. Likely this is only provided in reserve capacity as I suspect this is a marine hybrid battery rather than a true deep cycle. If the panel warns against it being hooked up with a load it I would not do it. A couple of fans is much more of a draw than a clock and a few small LEDs on a dashboard. Think how long you can leave your car sitting without a problem (and the car battery will have even less amp-hrs or reserve capacity than your battery).
Unless you have a long time between trips to the camp and always have really good weather and do not use much power when up there you may find that this small panel will not meet your needs.
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DaJTCHA
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# Posted: 14 Jul 2012 01:08pm
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That's what I figured. I guess I'll take it back. I'm sure I would be much better served with getting a real panel and a charge controller to meet my needs. The fact that it folds into a briefcase is so darn convenient though and it makes storing it discretely and easily a plus as well. DARN IT!
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MtnDon
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# Posted: 14 Jul 2012 02:09pm
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As has been mentioned, 13 to 15 watts is only good for maintaining the charge on one or two fully charged lead acid batteries. I used to leave 30 watts permanently connected to the 4 golf cart batteries when we still had our RV.
The statement about not having a PV panel connected to a battery at the same time the battery power is being used is nonsense. Every off grid system that is PV based has the panels connected permanently. (via a charge controller of some kind)
Your 8 hours of sun is actually more like 5 hours of great sun unless you are moving the panel orientation during the day or you are very far south. I'm in northern NM and generally can count on 5 to 6 hours of good to great productivity on a good summer day. That falls in spring, fall and winter or when clouds occur. Our climate tends to produce the summer clouds during what would otherwise be the most productive PV time of day.
As the air temperature increases the output of any PV panel falls. That can be a considerable loss during peak temperatures. In winter the fewer hours of sunshine are countered a little by higher voltages in the cool/cold weather.
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DaJTCHA
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# Posted: 14 Jul 2012 03:09pm
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I believe it was in the absence of a charge controller that this was mentioned.
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