Need the solar/power pros to weigh in

[dreadlocks]

yes, you can feed it more wattage than it can output... actually thats better because you wont overload your converter.. it should be bigger than the output of the solar so its only running at like 80% output instead of 100% output.

 

[luthj]

Most panels have a blocking diode, so you can safely connect a higher voltage converter in parallel.

 

[Buddha.]

Any recommendations about where to get the panels? How about this one from Craigslist? Seems like a hell of a deal, watts/$ wise. I'd buy 2 if they'd work.

 

[dwh]

Most panels have a blocking diode, so you can safely connect a higher voltage converter in parallel.

Um...bypass diodes yes, but blocking diode? You might want to verify that...my 300w panel has 6 bypass diodes, 0 blocking.

 

[dwh]

Any recommendations about where to get the panels? How about this one from Craigslist? Seems like a hell of a deal, watts/$ wise. I'd buy 2 if they'd work.

Link?

 

[Buddha.]

Link?

Sorry, I guess a link would help. The one I was most interested about seems to have been taken down but there are others.
Am I just looking at cost per watt or is there something else I'm looking at? Maybe some have features?

Solar panel 245watt

Solar panel sale 245 watt panels for $100 each 80 left out of 500 selling fast

minneapolis.craigslist.org

500 W Solar Panels Mono-crystaline

Ten K Solar APEX PV Module APEX 500 New - Never installed Heavy duty commercial units Performance Specifications (with integrated electronics) Peak Power (PMAX): 500W Cell Type: Mono-Crystalline...

minneapolis.craigslist.org

Panasonic and Canadian Solar 235/230W Solar panels

Approximately 30 used but functional solar panels available. Approximately 10 years old. Professionally installed and uninstalled.

minneapolis.craigslist.org

 

[luthj]

cost/watt and total size is about the only major concerns. If you want to use a single panel with an MPPT controller, a higher Vmp would be nice (36V panel). Some panels are more efficient than others, and thus will be smaller/lighter for the same wattage. Note that panels loose some capacity as they age, so panels that are over 7-8 years old will be down 5% or so.

 

[Buddha.]

Most panels have a blocking diode, so you can safely connect a higher voltage converter in parallel.

Um...bypass diodes yes, but blocking diode? You might want to verify that...my 300w panel has 6 bypass diodes, 0 blocking.

So there's some concern that power could flow into the panels from the truck? Is there some kind of off the shelf diode I could buy to prevent that?
Would it be eaiser to just buy a separate solar charge controller to separate it from the other solar charge controller? Perfably a cheap PWM unit like this?

Amazon.com : EPEVER 30A PWM Solar Charge Controller 12/24/36/48V Dual USB Max 96V Input Solar Charge with Temperature Sensor Weatherproof LCD Display : Garden & Outdoor

Amazon.com : EPEVER 30A PWM Solar Charge Controller 12/24/36/48V Dual USB Max 96V Input Solar Charge with Temperature Sensor Weatherproof LCD Display : Garden & Outdoor

www.amazon.com

 

[luthj]

You want an MPPT controller if you are using a DC-DC greater than 18V.

You can just add a diode in series with the panel. see below for various options. Just double check the panels current and voltage doesn't exceed the diodes rating. Some panels have them, it just depends on the panel type. You can check the spec sheet, or sometimes just pop the cover off the junction box and have a look.

Amazon.com: ACOPOWER 15A 4 Pair in-Line Diode Connector Solar Panel Cable Connectors: Electronics

Amazon.com: ACOPOWER 15A 4 Pair in-Line Diode Connector Solar Panel Cable Connectors: Electronics

www.amazon.com

Amazon.com

 

[Photobug]

This looked like a convenient way to add a diode.

Amazon.com: Signstek Solar Panel Cable Connectors MC4 in-Line Diode Connector : Office Products

Amazon.com: Signstek Solar Panel Cable Connectors MC4 in-Line Diode Connector : Office Products

www.amazon.com

Amazon.com

 

[dwh]

Charge controllers have two primary purposes; prevent overcharging the battery and prevent backfeed through the solar panel.

The cells used in solar panels become little radiant heaters if you feed power to them. So at night you want to make sure you don't run your battery down using the solar as a heater.

Since the charge controller does that, most panels don't have blocking diodes. They have bypass diodes to bypass strings of cells, because shaded cells become heating elements, drawing power that could be going to the battery, and also possibly getting overheated and damaged.

 

[Buddha.]

Charge controllers have two primary purposes; prevent overcharging the battery and prevent backfeed through the solar panel.

The cells used in solar panels become little radiant heaters if you feed power to them. So at night you want to make sure you don't run your battery down using the solar as a heater.

Since the charge controller does that, most panels don't have blocking diodes. They have bypass diodes to bypass strings of cells, because shaded cells become heating elements, drawing power that could be going to the battery, and also possibly getting overheated and damaged.

Thanks for the clarification, the blocking vs bypass part was confusing me.

 

[dreadlocks]

dont a series of bypass diodes together just act as a blocking diode? Its still not going to let current flow back into the panel w/a series of bypass diodes.. the very last bypass diode is going block any return current to the panel.. the only reason for a blocking diode is if your putting panels in parallel w/no bypasses in place (ie, a bunch of <=50w panels not in series)

 

[luthj]

This is typically how they are wired internally.

 

[TantoTrailers]

Use your amp meter to find a known load. Say 10A. An incandescent light bulb works. Measure the current, then you can remove the meter from the circuit if you like. Apply the load and start timing it. Once you hit 11V or so, it's done. Now recharge immediately. You have time and amps, do the math.

I would just wait until you get the BMV installed. Set up as approximately 100 amp hours to start. Then you can use the bmv to perform the load test . Simply disconnect all charging and apply a load such as a fridge lights etc. and wait for the battery to reach approximately 11 volts under load or 10.8 volts unloaded. The Bmv can show total AH removed. Usung this number, adjust the BMVs programmed capacity.

Alright so I am back and ready to get this capacity test completed. With A LOT running I was able to get up to 9A draw. I will start the test tomorrow morning and monitor closely as I will be home. Took some snap shots of the charger and BVM prior to testing.

Charger plugged in for a few hours after my return:


immediately after unplugging the charger:


about an hour after unplugging:


my test load for tomorrow