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Old 10-03-2011, 08:50 AM   #1
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Solar controllers - how smart are they?

I'm working on upgrading the converter in the trailer, but I'm wondering about whether I need to worry about the solar controller too.

We have three Siemens 70 or 75 watt panels mounted on the roof of the camper. Due to their age, they're probably 60-65 watts now. There is a solar charge controller mounted under the arm of the couch. I'll have to take a closer look at it tonight to get the make and model number for it.

I'm replacing the converter because I don't want it overcharging the new AGM batteries. Do I need to worry about the solar charger too? Or have they always been multi-stage?

I'm guessing the controller is approximately 15 years old, installed when the trailer was new, and I remember reading that it checks once a minute to see what mode it should be in (there are LEDs on it indicating what it's doing).

Thanks in advance!
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Old 10-03-2011, 10:51 AM   #2
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I would change the controller to an MPPT controller. They are more expensive but there are some that are not that high in cost. Maybe the Morningstar SunSaver 15 Amp MPPT Solar Charge Controller From the Arizona Wind And Sun Website "The AGM battery has an extremely low internal electrical resistance. This, combined with faster acid migration, allows the Concorde AGM batteries to deliver and absorb higher rates of amperage than any other sealed batteries during discharging and charging. In addition, AGM technology batteries can be charged at normal flooded lead-acid regulated charging voltages, therefore, it is not necessary to recalibrate charging systems or purchase special chargers. Concorde AGM batteries can be bulk charged at high rates without damage - up to 10 times as fast as most gelled cells, and 4 times as fast as flooded batteries."
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Old 10-03-2011, 11:07 AM   #3
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Solar charge controller technology has changed a lot in the past 10 years. I would consider a new charge controller. I personally like the Xantrex C35 or C40 series. They are relatively inexpensive and always do the job.
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Old 10-03-2011, 11:20 AM   #4
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Only very recently have solar charge controllers been getting any reasonable smarts from what I can tell. Your old one is likely just a voltage driven gate. PWM and MPPT technologies have been around a while but small systems really haven't put much real need for multiple stage battery charging.

While the AGM internal resistance and high current features sound really nifty, when it comes to most RV uses, it is irrelevant. The only time most RVers get into a high current mode is when running a microwave off an inverter or something equivalent.

RV solar systems just don't have the oomph to produce much charge current because there is only so much area on an RV to collect the sun.

The key issue from what I see is storage maintenance. It is only recently I have seen any solar charge controllers feature consideration for sulfation inhibition and float charge tempering (to avoid plate corrosion and electrolyte loss). (it intrigues me that this issue, while a major failure cause for RV batteries, is also not a big item in converters, either)

It is also just recently that I am seeing MPPT charge controllers that will handle higher input voltages, such as putting your three panels in series. That leverages the MPPT idea for slightly improved system efficiencies.

The Morningstar linked is an example of the newer ones out there but its 200 watt rating is rather marginal for your 3 panels. Note that NAWS doesn't say anything about storage maintenance issues for this controller.
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Old 10-03-2011, 02:05 PM   #5
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Thanks for the replies so far. If I can summarize them (and please correct me if I misunderstood):

1. You do not expect the solar system to cause a problem with overcharging the batteries, simply because it really doesn't produce that much current in the first place.

2. However, a new controller might not be a bad investment anyway. It looks like the new ones demand a temperature sensor that I'm pretty sure mine doesn't have, giving weight to the theory that mine is just a voltage sensing model.

On the AGM batteries: my main purpose for going AGM is that I don't have to worry about them as much. I quickly destroyed one wet-cell deep cycle that I bought new by not keeping up with it, and I never checked the level in the deep cycle battery in the trailer we bought in June until yesterday (don't ask what the level was...). I just know it's not something I'm going to do regularly, so I want the maintenance free-aspect of AGMs.

But I don't want the solar system to kill them on me, either.
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Old 10-04-2011, 11:14 AM   #6
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re: "my main purpose for going AGM is that I don't have to worry about them as much. I quickly destroyed one wet-cell deep cycle that I bought new by not keeping up with it"

An AGM will not solve a neglect problem. If anything, AGM and other sealed batteries are more sensitive to charging abuse than wet cells.

That is why it is important to use equipment that features storage maintenance as well as charging smarts. Storage maintenance means doing something to inhibit sulfation and techniques to maintain a full charge without gassing or plate corrosion.

With the right equipment, even wet cells don't need much attention. Plug in the RV when home, check water levels every 6-12 months just to make sure and that should be about it.
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Old 10-04-2011, 12:52 PM   #7
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Rogue Power Technologies - Affordable, Renewable, Accessible Energy The Rogue which I have on the Tradewind does have an equilization mode and also has a temp probe included. This is the second gereration of controller. I have a zantrez c40 and a morning star 15 mppt controller . I prefer the Rogue.
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Old 10-04-2011, 01:41 PM   #8
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Quote:
Originally Posted by bryanl View Post
re: "my main purpose for going AGM is that I don't have to worry about them as much. I quickly destroyed one wet-cell deep cycle that I bought new by not keeping up with it"

That is why it is important to use equipment that features storage maintenance as well as charging smarts. Storage maintenance means doing something to inhibit sulfation and techniques to maintain a full charge without gassing or plate corrosion.
No kidding. Hence why I started this thread.
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