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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Archive for the ‘Retail system’ Category


60 watt solar system

Friday, November 21st, 2008

Hi Jeff:

Thanks for being available to answer questions:

I purchased a 60 watt solar system from Costco to keep my travel trailer batteries charged. The batteries are two 115 amp. The system appears to work for lights but when I use any electrical appliance it shuts down. My question for you is: Could the inverter that came with the system be a block to full delivery of the needed amps from the batteries.

Also, since the two 12 volt batteries are connected in series does this make the system a 24 volt? Is a possible solution then to disconnect the two batteries from each other and charge one at a time. Maybe I need a larger inverter?

I would appreciate your comments and recommendations.



No reflection on Costco, but most of these “retail” solar products are too light weight to provide any real backup power. I put these in the same category as those car emergency kits that include a toy hammer that could never break glass, a toy cutter that could never cut a seat belt, and a cheap flashlight.

The batteries are most likely wired in parallel for 12 volt operation, and they better be that way since all of the DC lights and appliances in travel trailers are usually 12 volts. The solar array size determines how fast the battery gets re-charged, not what loads the inverter can supply. Most likely the problem is your inverter is a “toy” and cannot handle any electrical load other than a few lights. For example, if you tried to power your microwave oven, it draws about 10 to 12 amps at 120 VAC. In order for any inverter to supply a 12 amp load @ 120 VAC output, it will require over 120 amps going into the inverter from the battery at 12 volts DC.

Your wire from the batteries to the inverter would need to be a #2 or larger cable, and I would have used a #2/0 cable to reduce the voltage drop if this wire is over 3 feet long. Also, as you see, your two batteries at 115 amp-hrs at 100% full means you have a total of 115 amp-hrs of capacity to get to them both to 50% discharged, which is as low as you should go to avoid battery damamge over time. This means operating your micro-wave oven, or equal size load for a total of 1 hour will drain your battery bank.

You need larger batteries, larger battery cables, a better quality inverter to handle any laods larger than a few lights, and about 3 more solar modules to keep the batteries charged.

Good luck!

Jeff Yago



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