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Old 04-14-2013, 04:42 AM   #1
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Size of Solar Panel?

Hi, I just installed some GREAT AGM batteries on my 2007 Tiffin Allegro Bus. I want to keep these batteries in top shape. I store my motorhome in a lot where I can't plug into electricity, so I'm looking into solar panels to keep batteries from draining. I'm not looking so much for the ability to actually charge the batteries from a discharged state, but only to maintain them in a charged state. I see that battery tender has a 15W panel with a built in controller, but I have no idea if that is enough. Again, I'm not looking for panels to provide enough juice for boondocking or similar.... just enough juice to keep the batteries from discharging while in storage. Thanks!!!
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Old 04-14-2013, 04:54 AM   #2
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How many batteries are we talking about?
1999 Trade Winds 7371 Cat 3126B w/current upgrades
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Old 04-14-2013, 05:10 AM   #3
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One of the advantages to AGM batteries is that they do not self discharge at the same rate as conventional deep cycle batteries so no damage if disconnected for long periods. This however is the key, no draw powering anything. This gets to the you need to monitor the batteries and the best choices to do that are a Vectron or Trimetric battery monitor. Either one can tell you the condition of you batteries and if you do not disconnect, leaving some loads on, what that current draw is. That will tell you what size panel(s) you will need. We have a large teardrop trailer with a 150AH Concord AGM and the 185W panel supplis all of our needs including maintaining the battery.
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Old 04-14-2013, 09:17 AM   #4
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Your Tiffin should have had a single 120W solar panel available as an option for that year. That panel would have been fine for maintaining your batteries if it was installed. If not you can go either of two ways. Get a panel and small charge controller and install it like the optional pannel Tiffin used to install, or go down into your two battery compartments and find the manual battery disconnects. They are large manual switches that you have to rotate a quarter turn to the right to completely isolate the house and engine batteries. When rotated, the green "ON" will show a red "OFF" legend on the switch. With the AGM's you should be fine for the winter as long as no one hooked any other pirate draw directly to the batteries. You can also disconnect the ground feed directly from the batteries, but the rotary shut-offs are a lot easier.
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Old 04-15-2013, 04:50 AM   #5
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We have a small 5W panel on our motorhome and leave our mh in storage several months at a time (Florida in the winter, Ontario in the summer) and even with that, I've never had a low battery when we took it out of storage. You're Bus probably has 2 chassis & 4 house so you probably need a bit more than us but I'm sure anything over 20W will be fine as long as you have good sun exposure.

If your batteries are full charged when you put it in storage and you do use the battery disconnects, you really don't need much to keep them topped off.
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Old 04-15-2013, 05:27 AM   #6
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thank you all for your replies... yes we have 4 house batteries. I will try the disconnect method using the rotary switches. I didn't realize they had a slower discharge rate... so hopefully this will work out.
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