My 2 year second battery, solar and Wit’send rear quarter panel project (1 Viewer)

[Qball]

I'm still learning about solar panels, but wouldn't the current output be affected more than voltage depending on how much light it was receiving? I would think that in poor lighting you could still have 16-18V but only be pushing an amp or two. It's watts that you want out of it, not voltage per se. Maybe I'm thinking about it wrong...
That's cool that the Renogy panels have lenses on them to make them less sensitive to the angle. My Goal Zero panel has no such thing.

Solar panel has a fix Amperage and changes the voltage based on power. The reason for that is the system can use higher voltage which reduced voltage drop during transmission over long distances. Wires on rooftop panels can be pretty long. This is the same reason EU and rest of the world uses 240v electrical system vs our 110.


Here is Renogy's technical specifications document:

http://www.renogy.com/template/files/Specifications/100-Watt-12-Volt-Monocrystalline-Solar-Panel-Specifications.pdf

In it there is the voltage vs amperage chart:

 

[george_tlc]

Charge controller should be near the battery since that is what the controller needs to sense/measure for charging purposes. The charge controller should also be at similar temperature as the battery (for temp compensation).

Long wire to solar panel and if your charge controller can do it and you have a couple of panels (or folding panels) you can set the panels in series and let the mppt of the charge controller convert the higher voltage down to the battery charging voltage.

cheers,
george.

 

[Qball]

I like those panels, and something to be aware of with any solar setup is the gauge of wire used and length.. Now I am not going to assume you haven't considered this but it popped in my mind when "long" wire was mentioned. Here is some great reading on the subject that might help, if you don't already know everything this guy puts in the article. In short he talks about where the charge controller should be in relation to the batteries and the panels, gauge of wire and length.

The RV BATTERY CHARGING PUZZLE

Written in 2004 and continuously updated since. Last extensively revised December, 2010. If you found this by having somebody send you to it, you may not realize it is only one part of an extensive…

handybobsolar.wordpress.com

Yup! I have 20 feet of 10AWG which is a little overkill for 1 or even 2 panels, it's connected directly to the Ctek charger so well short of standard house installations which usually have an array on a pair of 10AGW cables. High voltage is the key to minimize power loss and safety, slightly counter-intuitive.

 

[Qball]

Charge controller should be near the battery since that is what the controller needs to sense/measure for charging purposes. The charge controller should also be at similar temperature as the battery (for temp compensation).

Long wire to solar panel and if your charge controller can do it and you have a couple of panels (or folding panels) you can set the panels in series and let the mppt of the charge controller convert the higher voltage down to the battery charging voltage.

cheers,
george.

My Ctek is very close, probably less than 3 feet of wires and fuses.

Ctek comes with a temperature sensor which I strapped to the top of the battery.

Ctek has MPPT controller built in and will charge batteries at 14.4v or 14.7v if setup for AGM, recommend solar setup for Ctek is 150-300W.....I'm at only 100W so might get another panel.

Per Ctek manual:
Do not connect two solar panels in series. Max. input voltage 23V.

So parallel only, which is pretty easy with Y connectors.

 

[george_tlc]

^ all the trendy folk are using the victron mppt chargers so they can nerd out with the bluetooth telemetry

The victron can handle up to 75V at the input or 100V for one of the 'bigger' models.

Anyhow, parallel with your ctek is fine, just need heavier gauge from controller to panels if you want to save every millivolt

cheers,
george.

 

[mkZero]

Doing some reading, trying to learn. From the reading I've done, it looks as if the voltage is affected fairly little by of the amount incident light whereas the current changes much more drastically:

"An important feature of solar cells is that the voltage of the cell does not depend on its size, and remains fairly constant with changing light intensity. However, the current in a device is almost directly proportional to light intensity and size1. Figure 6 shows example I / V curves for a single cell as a function of light input"

Taken from here: Solar cells -- performance and use

 

[george_tlc]

^ The important measurement is power. So, yes, voltage isn't very important and you can have a panel with lots of voltage (open circuit) but that voltage drops like a rock when you draw a bit of current.

Measuring a panel's "voltage" means very little if you have no current draw...

If you take your curves above and multiple the voltage and current (the x/y axes) you get power and you'll see there is a peak (maximum power point) where the panel produces its maximum power. That is what an MPPT charge controller tries to do - draw current where the product of the voltage at that current and the current peaks (i.e. the maximum power point).

cheers,
george.

 

[mkZero]

Yeah, that was my point. Measuring voltage doesn't tell you much about your panel's output, you really need to be measuring current or, better yet, power. The OP should not assume he's getting good output (power) from his panel because he measured 15-18 volts, it could be putting out next to no power and still be at that voltage.
I think this graph is pretty good, it helped me understand better, along with the one I posted previously.

Cool stuff!

 

[george_tlc]

^ Yep, that's a typical V * I curve that illustrates the maximum power point (V * I = Power).

Agreed, measuring open circuit voltage tells you nothing much in terms of what power the panel can output. A panel in very cloudy conditions with minimal current load will show nice and high voltage...

cheers,
george.

 

[Qball]

^ all the trendy folk are using the victron mppt chargers so they can nerd out with the bluetooth telemetry

The victron can handle up to 75V at the input or 100V for one of the 'bigger' models.

Anyhow, parallel with your ctek is fine, just need heavier gauge from controller to panels if you want to save every millivolt

cheers,
george.

Thought about victron except it’s not a dual controller and rather big, much bigge than CTEK. The thing CTEK lacks is data, it only shows what’s going on with 3 LEDs and that’s it. I wish CTEK has even remotely close to the victron in terms of data.

 

[Shoredreamer]

I also recently redid my electrical setup and added solar. I suggest wiring in some ammeters, or easier, buy a clamp meter to measure dc current thru any circuit. You can’t rely on what specs are published and you’ll learn a ton. For example, I can see with the voltmeter and ammeter what charge stage the BCDC is in. I can measure how much my panel is giving the BCDC, how many solar amps the BCDC is putting into the batteries, and how many amps any accessory is pulling, etc. It’s rad!

I’ve got a similar setup as you that I’ve been running with great results. My ARB 50qt has been running nonstop 24/7 for 50 days now and haven’t had a hiccup. I decided to try solar because I don’t drive my truck daily but I drive it enough that plugging in a shore charger doesnt make sense. The solar keeps both batteries charged to 100% better than my 110v Battery Minder wall smart charger, when the truck is in the driveway.

Some compare and contrast:
-I have a 110 watt Merlin flexible panel mounted on my RTT
-panel running to my Redarc BCDC1225d, which charges my house (and also my start battery)
-I’m running 14’ of 10awg from panel to BCDC, then 2’ of 8awg from BCDC to the house battery
-House battery has an Blue Sea ammeter shunt to monitor +/- charge
-My ARB fridge has the ARB canvas and is boxed in with my drawers in the back, with all rear windows blacked out. Also, one advantage of having the RTT is it absorbs all the sun and heat instead of my Cruiser’s metal roof. I keep only beer and drinks inside, 1/4 full.
-Our environments are a little different between Sierra Foothills and Pacific Coast. It’s full on June Gloom here in Santa Cruz with highs in the 60s and sunshine for only 5-6 hrs a day vs. you in the 90s and 100s every day.

I’m curious how my setup would do in your environmental conditions.

 

[Qball]

Thanks, I need one of those ammeter pronto!!!

There is something wrong with my setup, I left everything off and let the solar charge the battery all day and it barely raised the voltage front 12.1 to 12.4. Pretty sure the solar is doing fine so it could be the battery or the Ctek. Ammeter should be able to tell me what’s going on.

 

[Qball]

Quick update:

Received a second 100w renogy flex panel today. Plugged both in and holy cow, what a difference. The battery went from 12.6 to 12.8 in just 1 hour!! In contrast to 1 panel I barely gain .3-.4 V all day! So it is possible that the Ctek MPPT charger runs more efficiently when there is more power.

I should receive my ammeter tomorrow so I will test out the charging amperage between 2 panels, the old and the new panel.

I saw some postings on internet regarding Ctek solar performance or lack of so hopefully I’ll find out tomorrow with my amp meter. I don’t like the fact that it’s not working well with just one panel or need 200W to work, hopefully it’s just a bad panel.

 

[george_tlc]

No, the mppt won't be 'more' efficient with a second panel, if anything it'll be less efficient (DC DC converter will be running harder).

I'd suspect your 1st panel has an issue or its wiring has an issue. I bet the 2nd panel alone would have done the job without the 1st.

100W should be near 7A output (with mppt conversion) from a nominal 100W panel. Assuming 100W/12.8V = 7.8A (assuming 100% efficiency etc) and of course BRIGHT sun. That would charge a mostly already charged battery within a few hours.

cheers,
george.

 

[Qball]

Sigh, I am really thinking this Ctek thing for solar is a bust. After the sun go down I measured again and battery is at 12.1 with the fridge on. Even at low light right before sunset the panels were still putting out 15v which should be about 140-150 watts still. And yet my battery lost voltage/capacity? this is very disappointing to say the least....down right lame in fact.

Now I’m at a cross road, do get the Victron solar charger and leave the Ctek for DC to DC charging or do I get the Redarc. Biggest problem is real estate on the rear quarter panel mount.

The last generation Victron bluesolar controller is a lot smaller than the current generation controller which happens to be twice as big. Might just order that and if it fits then call it a day. I love the idea of lots of data and it’s a lot less cost than Redarc, and a lot less rewiring.

 

[Shoredreamer]

I’ve got Redarc BCDC in stock here at Rhino Adventure Gear in Richmond. I can ship you one for a good price. I’m very impressed with mine and I’ve converted at least 4 other 80s now.

 

[Shoredreamer]

Victron is good stuff also and has all the Bluetooth, SOC info etc. You may run into further issues combining dual charging sources with a Victron MPPT and the CTEK thing. CTEK may see a charge on the house and do funky stuff. Rewiring to a BCDC should be quite easy and you will save real estate. @DanMedeiros is removing his victron/renogy setup and going to a BCDC soon as well.

 

[Qball]

I’ve got Redarc BCDC in stock here at Rhino Adventure Gear in Richmond. I can ship you one for a good price. I’m very impressed with mine and I’ve converted at least 4 other 80s now.

Thanks for the offer, PMed you about the price. Although I’m liking the idea of nerding out on data from Victron. Plus it’s pretty cheap and I did the mock up and I have just enough space to fit the last gen charger.

 

[Qball]

Victron is good stuff also and has all the Bluetooth, SOC info etc. You may run into further issues combining dual charging sources with a Victron MPPT and the CTEK thing. CTEK may see a charge on the house and do funky stuff. Rewiring to a BCDC should be quite easy and you will save real estate. @DanMedeiros is removing his victron/renogy setup and going to a BCDC soon as well.

I see what you did there, you are good....very good!

In theory Ctek shouldn’t have issues with separate solar charger but in theory Ctek should work well with solar also.

 

[george_tlc]

As someone mentioned, get a DC current clamp and actually measure the current flowing out of the panel(s) and out of the CTEK into the batteries. Without some current measurements you're guessing at actually output by just measuring voltage.

I assume your battery is in good condition...

cheers,
george.