Voltage Drop and Other Solar Musings/Solar Lunchbox

pittchristine

jkjenn:  Can you post a photo of the trolling motor connection?  TIA!

jkjenn

Here is one on my old propane cover with the cable plugged in and here it is on the new Outback style propane cover, closed. I don't have a photo of the three prong plug, but if you search for them on Amazon, you will see them.

ScottG

We had to skip camping Memorial Day weekend, but made it away last week for a full 8 days of dry camping. This was twice as long as any previous trip without hookups, so the ability to recharge with solar was critical.

The solar lunchbox setup was effective and convenient. I hooked everything up the first morning, and--with the controller safely under cover in the tub--left it all in place the entire week. The best sun on our site was in the morning, so the panels were awake and working long before we were!

The 25' cable allowed quite a bit of flexibility for positioning the panels. Even though it is a little undersized at only 12g, I could still get >17V from the panels in full sun. Monitoring the controller was as easy as opening the lid of the tub.

Of course, it didn't hurt that we had mostly sunny weather and decent exposure at our site. However, even on the one cloudy day there was enough light reflected off the adjacent lake to provide a little bit of charge.

Sharon_is_SAM

Scott, we replicated your system sans the lunch box.  We have an inexpensive charge controller from Renogy that tends to lose its grip on the wires - using 10 gauge.  We briefly tested it this AM and plan to dry camp in July in the Adirondaks.  If we have a very full battery - 98% - should we expect to see a limited current?  The sun was barely up which may have been a part of it.

ScottG

@SAM, in general I notice higher current associated with higher voltage (which is associated with brighter light). However, I admit I'm not very knowledgeable about how all those charge controller numbers are determined. It makes sense to me that the controller would back off the current once the battery is full--"smart chargers" do something like that--but I'm really not sure.

Studying up on charge controller circuitry is on my "to do" list--but not very high up!  :-)

Sharon_is_SAM

Thanks Scott.  We were in dim light, so I suspect that was at least part of it.  

ScottG

@SAM, I take back at least part of what I said above--photos don't lie, after all! These three images were taken in order within one minute of each other under what must have been variable shading. You can see how both the voltage and the current from the panels changes in a manner that is not necessarily proportional. The max output of these panels is ~18V and 5.5A.

With a simple PWM controller like this, the voltage going to the battery (not shown) is stepped down if needed, but the current is always the same as that coming from the panel.

Again, not claiming to understand it, just saying what it is!
 
(Voltage in this photo is >17V)

Sharon_is_SAM

Oh boy, more homework to do!  Yeah, I don't get that either.

jcfaber1

When evaluating your PV, you need to understand what phase of charging you're in.  Bulk, absorption or float.  If you're in any other stage than bulk, any extra charge will be wasted as the battery does not require any more.  The controller should show you what stage you are in.
John

sqrpeg

@ScottG - are you still happy with your DIY SJOOW extension cable(s)? I'm about to pull the trigger on ordering some 10/2 SJOOW for my remotely-deployable panel project. I like the idea of a single, flexible two-conductor wire instead of having to deal with separate POS and NEG wires.

Also, regarding the MC4 connectors, it looks like you used Renogy-brand MC4's throughout, which I will probably do as well since my Renogy panel already has two MC4s pre-attached. Are the Renogy MC4s handling repeated connects/disconnects well?

ScottG

Yep @sqrpeg, the SJOOW cable works great--very rugged and very flexible.

I did used Renogy MC4s. I've had no problems connecting and disconnecting, but with the new system I only do that once per trip, so they really haven't been subject to all that much use. After setting up the controller in the tub I leave it in place until I break camp.

sqrpeg

Thanks @ScottG!

I was curious about the Renogy connectors because different manufacturers have slightly different designs, with some apparently being easier to use/more reliable than others.

FYI to others - since "MC4" is not an actual standard, different brands aren't necessarily compatible with each other (sigh), and so there can be advantages to sticking with one manufacturer for a given project.

ScottG

Good point, @sqrpeg. I wasn't sure about the compatibility among brands and since I also had some pre-exisiting Renogy MC4s that's what I stuck with.