Battery charging questions - Page 4 - Fiberglass RV


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Old 11-10-2013, 06:31 PM   #43
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Byron will know for certain but I'm guessing 4 gauge conductors are complete and utter overkill IF the solar controller is placed in close proximity to the battery box. I believe Byron and I both have the controller on the panel to expedite charging vehicle battery without the cost of an additional controller. I'm using 25' of 12awg SJ cable simply because that's what I had at hand.

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Old 11-10-2013, 07:14 PM   #44
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I wouldn't leave the gen unattended in plain sight in any state. I have seen generator theft warnings posted in California state parks, and Oregon along the Columbia river. Thieves know no boundaries. Even coolers go missing! Woopie! Free beer!
Sorry, I was poking at you. I have noticed that the notices are generally in state parks. Along the Columbia or Oregon Coast anything is possible, extremely crowded, places I avoid except in the winter.
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Old 11-10-2013, 09:19 PM   #45
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If I were to hinge 2 hundred watt panels together, and fashion a stand for portable use it could be stowed for traveling on top of the rear mattress along with all the lawn chairs and barbecue stand.
Or you could do as I do with my scamp side bath and make a foam cover for it and the stand I made for it and store it with bungees on the front wall of the bathroom so its totally out of the way and the front bunks can still be put up or down. If you have a front bath perhaps you could store it on the flat wall in the bathroom.
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Old 11-10-2013, 11:39 PM   #46
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Or you could do as I do with my scamp side bath and make a foam cover for it and the stand I made for it and store it with bungees on the front wall of the bathroom so its totally out of the way and the front bunks can still be put up or down. If you have a front bath perhaps you could store it on the flat wall in the bathroom.
Carol,
That's a nice setup you have. Very tidy. In my trailer with side dinette the bath is in the front, but no space for the panel in there. I have in the past traveled with the side dinette table in the up position, but could put it in the bed mode and put the panel on top of the cushions and secure with bungees hooked to eyelets mounted to the fiberglass seat boxes near the wall. Thanks for the picture.
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Old 11-11-2013, 12:00 AM   #47
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Byron will know for certain but I'm guessing 4 gauge conductors are complete and utter overkill IF the solar controller is placed in close proximity to the battery box. I believe Byron and I both have the controller on the panel to expedite charging vehicle battery without the cost of an additional controller. I'm using 25' of 12awg SJ cable simply because that's what I had at hand.

jack
Jack,
I just threw the 4 ga. comment out there. I have not figured the voltage drop yet, as I don't know how much capacity to buy. I will go overkill on the panel rating and probably on the wire size just to preserve voltage and power. The panels only start at about 17 to 18 volts, and you need 15.5 volts at times, so there is not too much voltage reserve for losses in wire, switches, fuses, connections, etc. Also for flexibility in placement I would like to have a long tether to get the panels out in the sun. Maybe 30-40 feet. That length will add some resistance if I don't go big. I don't know if I will just buy a portable folding premade setup with the controller mounted to the panel, or make one up and have the controller mounted in the front closet near the battery. The MTTP controllers are a little fatter, and won't likely fit in the folded panel cavity, so would need to go in the trailer if used.
Russ
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Old 11-11-2013, 12:35 AM   #48
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I have an 80watt tether to graze rig similar to Byron's altho I sometimes bungee it to the front rock guard if the dogs are having a heavy macramé day with their tie out ropes. Depends on the season and angle of the sun also. If the sun track is high and no shade the rock guard mount makes sense. When the sun is low, I move the panel around to avoid shadows on the cells. I also have a pigtail made up of half a jumper cable lugged to a two pole flat connector that's the complement of the one exiting the cord on the panel. Gives me some solar charging for my truck battery in fall and winter. Now that I'm retired and don't drive 400mi. a week, sitting around feeding the vampire loads takes a good starter battery down pretty fast. I don't worry about conflict with the converter. It's on a breaker but the "switch" is when I pull the plug on the electricity tree and move to an offgrid site. I don't have a genset. I'm hoping I can get an honest 24 amphours of recharging daily in high summer as I recently installed a 12DVC/120VAC Norcold fridge and would like to make 48 hours offgrid before dropping to 50% battery SOC. We'll see.

jack
Jack,
My jeep tow vehicle has enough vampire loads to kill the battery in 2 weeks if not driven. I installed a knife disconnect to eliminate that. I have to remember to use it though! I have a relay to switch on the trailer charge wire from the Jeep, so the solar panel wouldn't be able to charge the tug and trailer at the same time unless the relay was triggered and the knife switch was closed.
Is your new fridge all electric or can it use propane too? My Dometic fridge is a 10 year old 120v or propane version. No 12v. It really gets cold and works perfectly even in the desert. I understand 10 years is probably near the end, so am collecting info on possible replacements for that sad day when it bites the dust.
Russ
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Old 11-11-2013, 01:27 AM   #49
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I've decided to hold off on the solar portable 40W panel and hope for the price to drop and technology to advance.
Meantime, I'm experimenting with Coke and Mentos.
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Old 11-11-2013, 06:38 AM   #50
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Meantime, I'm experimenting with Coke and Mentos.
Lol. Makes an awsome mess. The kids loved it.
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Old 11-11-2013, 08:57 AM   #51
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Byron will know for certain but I'm guessing 4 gauge conductors are complete and utter overkill IF the solar controller is placed in close proximity to the battery box. I believe Byron and I both have the controller on the panel to expedite charging vehicle battery without the cost of an additional controller. I'm using 25' of 12awg SJ cable simply because that's what I had at hand.

jack
I'm sorry I missed this earlier.
Like Jack I have the controller mounted on the panel so that I can charge other batteries, like my ham radio battery, or the tow if needed. I believe I'm using about 25' of 10 awg that's what I had on hand for the ham radio. The difference between 10 and 12 awg at worst would be it could take a bit longer to recharge with 12 awg than 10 awg, but not much. I believe it would take some pretty careful measurements to tell the difference.
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Old 11-11-2013, 07:36 PM   #52
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Byron,
From what I have read voltage drop can be a significant factor in these 12 volt systems. As long as you end up with enough voltage at the batteries all is well. The more panels you have the amperage increases and wire size needs to increase. At least that's my limited understanding of how it works. If I put together a two 100w panel system it would produce about 10.5 amps at full sunlight. Then if I were to need a 30' tether, I should be able to figure the voltage drop using Mr. Ohm's law and resistance of wire size charts. EE's please chime in if I am off base. The 200w system is probably overkill for a one battery system, but I may go to 2 batteries in the future if needed. The system will probably cost as much as a Honda 2000i, but will be even quieter and use no gas.
Russ
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Old 11-11-2013, 09:33 PM   #53
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If I may expand on some of your observations. First, I believe the panels put out considerable more that you realize, the usual voltage on a 75 watt panel is up to 18 volts. Since the controller is dropping the voltage between the solar panel and the battery from 18 volts to 13.4 the gauge of wire is not critical. I run over 100 feet using 14 gauge and I am positive the controller is still reducing the volts. If you run the resistance calculations you do not loose enough to make a difference.

The controller should be mounted as close to the battery as possible and the gauge wire here may need your attention. However, the inexpensive controllers only have 16 gauge on the output side so it may not make sense to go with anything larger.
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Old 11-11-2013, 09:52 PM   #54
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Byron,
From what I have read voltage drop can be a significant factor in these 12 volt systems. As long as you end up with enough voltage at the batteries all is well. The more panels you have the amperage increases and wire size needs to increase. At least that's my limited understanding of how it works. If I put together a two 100w panel system it would produce about 10.5 amps at full sunlight. Then if I were to need a 30' tether, I should be able to figure the voltage drop using Mr. Ohm's law and resistance of wire size charts. EE's please chime in if I am off base. The 200w system is probably overkill for a one battery system, but I may go to 2 batteries in the future if needed. The system will probably cost as much as a Honda 2000i, but will be even quieter and use no gas.
Russ
Voltage drop depends on current. The farther away from being fully charged the greater the difference between the charge voltage and the battery voltage the grater the current the greater the voltage drop in the wire. The closer to fully charged the battery the less voltage differential between the charging source and the battery voltage the less current required the less voltage drop in the wire. This continues until the voltage drop in the wire is so small it's not significant.

The idea that voltage drops are significant in 12 volt systems in not necessarily true, it all depends on what the current is. The more important is the heat generated in too small a wire for the current particularly in battery charging situations. Therefore it's best to select a wire size based the charts for current carrying capabilities vs wire gauge. Select a wire sized for the maximum current expected to flow in the wire.

Using a wire size much larger is simply a wast of resources, both in copper and cost for insignificant gain.

A 200 watt system is way over kill for most of our trailers and batteries. You'll get a much faster recharge, but that's it. After 2 or 3 days with running the furnace in the mornings it takes about 4 hours to fully recharge my battery with a 65 Watt system. With a 200 Watt system it would take probably somewhere between 2 to 3 hours. Hardly worth the additional cost.

I do keep two batteries charged.
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Old 11-11-2013, 11:19 PM   #55
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Byron,
Are your 2 batteries always connected as in 2 x 12v in parallel or 2 x 6v in series? If you are using both batteries and charging both I would say 4 hours is pretty acceptable charging time with a 65 w panel. Two batteries I would think would take twice as long to recharge as one. I wonder if one battery that was more deeply discharged would in theory accept a higher charging current than 2 slightly discharged batteries, and therefore recharge faster? Does your on panel controller feature voltage sense for reading actual voltage at the batteries? You would have another 2 small wires run along with your 10ga. current carrying wires. Sorry for all the questions, just interested in what others are using. Thanks for your comments.
Russ
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Old 11-11-2013, 11:30 PM   #56
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Byron,
Are your 2 batteries always connected as in 2 x 12v in parallel or 2 x 6v in series? If you are using both batteries and charging both I would say 4 hours is pretty acceptable charging time with a 65 w panel. Two batteries I would think would take twice as long to recharge as one. I wonder if one battery that was more deeply discharged would in theory accept a higher charging current than 2 slightly discharged batteries, and therefore recharge faster? Does your on panel controller feature voltage sense for reading actual voltage at the batteries? You would have another 2 small wires run along with your 10ga. current carrying wires. Sorry for all the questions, just interested in what others are using. Thanks for your comments.
Russ
My two batteries are separate most of the time one is on the trailer the other in the back of my truck. Used for two different purposes.
It would make no difference two, three or more batteries with the same about of total discharge. If I had several batteries and used the same amount of current as I do with, the charge time would be the same as one battery.

If two batteries were discharged to the same level I don't think the charge time would be double. The charge current is NOT linear and changes as the battery or batteries are charged. More current is used at the beginning of the charge cycle than at the end of charge cycle. Without doing more research I can't predict how much different it would be. However it would the same as if the same about of current had been used by a single battery.
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