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Old 08-01-2012, 05:05 PM   #1
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Question uses and limitations of old solar panel system?

Hey folks,

In 2003 I installed a solar kit on my 1986 345 MH. Since I just turned 55 yesterday I cannot find my documents or remember for the life of me what it can and cannot do. When I googled the model # on the monitor, Siemens RV20, I found that it was not listed among current models and I'm having trouble finding info on it. I'm hoping one of you has a better memory and can help me answer the following questions:

1) What can a unit this size power and what can't it power? Does 20 mean 20 amps?
2) It's currently hooked up to the coach batteries which are dead. We disconnected them temporarily and at some point during the restoration we will replace them. But it turns out that the alternator is not working to recharge the engine battery right now. Can/should we hook up the solar to the engine battery?
3) Can we swap in gel batteries for the regular batteries we've been using to avoid having to worry about the things drying out? I understand this is a problem with solar kits, that they keep exercising the battery because they're constantly topping them up (desirable) so they dry out the battery (undesirable), and since I am lazy (undesirable), I often forget to check them and then I ruin the battery (undesirable).
4) Is it worth putting more panels on the roof for more solar power? What could they do now that they couldn't do in 2003? Are people using them for more stuff?

Plenty O Questions, I realize, any thoughts welcome.
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Old 08-01-2012, 07:43 PM   #2
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If it's the GP-RV20 kit (see here), it's 20 watts. It's basically battery maintenance only, or minor recharging duty. It's not going to recharge a dead battery or supply much power for any lights or appliances. It will run some LEDs.

I have gel batteries (Optimas) in mine. They're fine, but you have to watch the charger - if you have a single stage charger, it'll kill them quickly. Your current solar system probably isn't enough power to do that, but a larger system could be a problem.
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Old 08-01-2012, 08:22 PM   #3
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Hey Skater, thanks. I saw the GP-RV20 online but I wasn't sure it was the same one. I suspect we do just have a single stage charger. It fried the coach batteries but it had plenty of time to do that. So it sounds like I should not leave the charger connected to the batteries most of the time.

Here's the thing. I have a kill switch in the back and a kill switch between the engine battery and the coach batteries. With a solar kit like this, how are you supposed to manage it during periods when you're using it and periods when you're not using it? If you let it sit too long, you won't be able to charge it with the solar because it will be too low. But say it's all charged up. How long can you disconnect it from the solar before you need to reconnect it?

And if I have three new batteries, an engine battery and two coach batteries, is it a good idea to leave them all connected together so they all stay topped up from the solar? And, same question, , if it is, how long is it safe to do that before I fry them?
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Old 08-02-2012, 06:45 AM   #4
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Well, if it's charged when you start, the solar will keep it charged, even through some light-duty usage. I don't think the 20 watt panel is enough to fry batteries, but I could be wrong - someone who knows more about the system should comment on that. My understanding was that for small systems you don't really even need a controller at all.

The other thing about a 20 watt panel is that it's 20 watts max - full sun, new panel, etc. The panels produce less power over time, shade, clouds, etc. - these will all reduce the power it actually produces.

I guess if the system was putting too high a voltage in the battery, even at low current, for a long time, it probably could damage the battery. But keep in mind a battery won't last forever anyway - car batteries are generally good for 5 or 6 years, remember.

We have a ~200 watt solar system on our roof, so I've learned some, but it was installed on our camper by a previous owner, so I'm not an expert. We replaced all three batteries last year and upgraded the 120 volt/12 volt converter to a 3 stage model to keep that from overcharging the batteries (that was the converter I was referring to in my previous post). This spring we also replaced the solar controller that was in it (a simple one stage model) with a three-stage converter, so it shouldn't damage the batteries either at this point. But that just seems like overkill for your system, unless you're planning to add more panels.
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Old 08-02-2012, 07:21 AM   #5
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Quote:
Originally Posted by Jenniflow View Post
Here's the thing. I have a kill switch in the back and a kill switch between the engine battery and the coach batteries. With a solar kit like this, how are you supposed to manage it during periods when you're using it and periods when you're not using it? If you let it sit too long, you won't be able to charge it with the solar because it will be too low. But say it's all charged up. How long can you disconnect it from the solar before you need to reconnect it?
A properly-installed solar kit would have the solar panel directly connected to the house batteries, bypassing the kill switches. That way, you never disconnect the solar panel from the batteries. Solar by itself won't deplete the batteries, only charge them, so there's no reason to ever disconnect the solar panel.

My 50watt solar panel keeps my house batteries at 100% while the unit is in storage, day in, day out, even when it's parked for a month or more; though I'd never leave it in storage for a month or more if I had any choice in the matter. The only time it wouldn't keep the batteries topped off is if I parked where snow covers the panel, or if I put it in a cave where it gets no light at all.
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Old 08-02-2012, 10:14 AM   #6
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Many of the new solar panels do not include a blocking diode in the panel. The solar manufactures expect that you are using a charge controller which will have a blocking diode to protect from backfeed during the night.
By eliminating the diode in the panel, they are able to rate the panel at a slightly higher watt output.

If you have two battery banks and a smaller solar system, you are probably better to have two independent solar systems for the most efficient gain unless you are going big on the solar panels, and then you can use one system and a "battery separator, SurePower 1315-200" between the battery systems.

Generally speaking,(my experience) a 20W panel hooked to a GP 31 battery (or 2X T105 Trojans) would not require a charge controller as long as it has a blocking diode and you service the batteries at least once a year. ( best to do battery service spring and fall )

http://www.airforums.com/forums/f313...ml#post1109933

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Old 08-02-2012, 10:33 AM   #7
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Just wondering if people mean AGM batteries when they say Gel.
I use AGM's regularly and I live them for a pile of reasons. I have not had much success with Gel batteries. I know people who love Gel's but I am not one of them......
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Old 08-02-2012, 11:16 AM   #8
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Quote:
Originally Posted by Protagonist View Post
...
My 50watt solar panel keeps my house batteries at 100% while the unit is in storage, day in, day out, even when it's parked for a month or more; though I'd never leave it in storage for a month or more if I had any choice in the matter. The only time it wouldn't keep the batteries topped off is if I parked where snow covers the panel, or if I put it in a cave where it gets no light at all.
I have the same experience with the factory 53 watt panel on the Bambi with the 2 AGM (not gel) batteries. We keep the Bambi stored (mostly) under trees in our yard, and it will still maintain the charge fairly well. Recently, I noticed a decrease in output, so while inspecting and cleaning the top of the trailer, I discovered the same gray/black mildew that covered the roof, was also covering the solar panel. I carefully pressure washed the whole thing, and it's working like new.
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Old 08-02-2012, 12:14 PM   #9
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Quote:
wondering if people mean AGM batteries when they say Gel
A flooded lead acid battery (FLA) is a variable-voltage & constant-current charging scheme.

A true Gel battery is a constant-voltage & variable current scheme.

An AGM battery is usually a hybrid between the two with semi-gelled electrolyte and a limited variable-voltage charge profile. AGM's try to offer the best of both battery types while being built around surviving abuse long enough to get through, or nearly through, the warranty period.

I have 10-year warranty AGM/Gel batteries that are specified for no more than 0.20V variation float-only charging (with temperature compensation) but need a charger rated for 35% of the name-plate amperage capacity (38A) available to help circulate electrolyte. Those high currents only circulate for a few minutes as the cells recover quite rapidly bulk-charging.

One problem with Gels is applying normal charging voltage above a certain battery core temperature will create bubbles that leave scars and a forever decrease in capacity. The needed compensation curve increases float voltage for cold cells, passes through the suggested voltage at 70-80F and decreases it as temperature climbs above that. Just hard usage, charging & recharging, with warm ambient temperatures can put Gels (and long-life AGMs) into a hazard zone.
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Old 08-02-2012, 12:41 PM   #10
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My apologies. I said gel but really meant AGM above.
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Old 08-02-2012, 05:47 PM   #11
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Question

Very interesting. So even in storage under trees, the system will maintain a charge? That's really surprising! I will be storing it outside away from shore power so I will be relying on the the solar and the generator.

OK, so it sounds like a charger of my strength has minimal use except for topping up a healthy batter and the low power is not much of a hazard to the battery. When we replace the two coach batteries do they have to be the same type as the engine battery? We've already gotten a standard battery, I was thinking of getting what I guess is an AGM but I don't want to mismatch.

Just so I understand, what does a blocking diode do exactly? and how I could tell if I had one? Well, the panel is ten years old, so does that mean I have a blocking diode in the panel and not in the charger?
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Old 08-02-2012, 06:12 PM   #12
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Very interesting. So even in storage under trees, the system will maintain a charge? That's really surprising! I will be storing it outside away from shore power so I will be relying on the the solar and the generator.
Depends. Trees that provide a direct view of the sky during some part of the day will allow the solar panel to provide a charge during at least part of the day. Dense trees where the branches interlock with neigboring trees, blocking the sun from direct view all day, the solar panel will not come anywhere close to full output.

Quote:
OK, so it sounds like a charger of my strength has minimal use except for topping up a healthy batter and the low power is not much of a hazard to the battery. When we replace the two coach batteries do they have to be the same type as the engine battery? We've already gotten a standard battery, I was thinking of getting what I guess is an AGM but I don't want to mismatch.
Yes. Solar is only good for a trickle charge or a "float" charge. If the batteries are slightly discharged it will top them off, and if they're fully charged the solar panel will keep them that way. If you drain the batteries to the point that a meter shows less than 10v available, the solar panel will not charge the batteries at all, because there's not enough current to power the charge controller anymore.

House batteries probably should NOT be the same type as the engine starting battery. Starting batteries are rated in "cold cranking amps" which is a measure of how much amperage is available for a quick (about a minute) discharge to spin the starter motor, followed by an equally fast recharge from the alternator.

House batteries should be rated in "amp-hours" which is a measure of how long a battery will pump out energy in a long, slow discharge. A battery optimized for starting the engine will be crap for running your appliances, and vice versa.

House batteries come in three main types: wet cell (lead-acid with filler caps on top of each cell); AGM (Absorbed Glass Mat, where the acid is soaked into a fiberglass mat rather than a liquid); and Gel-Cell, where the acide is suspended in a gel. Any type will work as long as they have an amp-hour rating, but for safety and ease of maintenance most people prefer the AGM.

Therei s a fourth type that is sometimes unsed in boats, but which hasn't made the crossover to RVs just yet. MasterVolt makes a Lithium-Ion house battery that provides more amp-hours for its size than just about anything else, but they're helaciously expensive.

As long as you don't try to hook ALL of the batteries to the engine alternator, there should be no problem. Only the engine starting battery should charge from the alternator. House batteries should charge from (1) a charger hooked up to shore power; (2) a charger hooked up to a generator; (3) solar.

There is another option that might be attractive for boondockers, and that's wind power. West Marine sells a couple of wind-powered generators that can be mounted on a trailer as easily as on a boat, though you would want to disconnect it and store it inside when you're driving down the road.

Quote:
Just so I understand, what does a blocking diode do exactly? and how I could tell if I had one? Well, the panel is ten years old, so does that mean I have a blocking diode in the panel and not in the charger?
Blocking diodes act as a one-way street for direct-current wiring. Say you've got a solar panel set up to charge your batteries, and you hook up to a generator as well. Without the blocking diode, the generator, which puts out far more power than the solar panel, would try to back-feed current the wrong way along your solar panel wiring. With the blocking diode, however, current always flows from the solar panel to the batteries, never the other way around.
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Old 08-03-2012, 12:14 AM   #13
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Thumbs up We want to frame your post

Protagonist, my husband and I were so impressed with your post that we want to frame it. That was exceptionally lucid and complete and very helpful. Thanks so much. It really answered the most pressing questions that I had left and now I have to go to sleep because I ate too much.

Tomorrow is another day for buying batteries. But now I know a lot more than when I started this thread, thanks to you folks who are so generous with your time!
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