Cheap Solar Charge Controller

[PNjunction]

Take a look at this article by MainSail. Although it is targeted towards marine, lots of good info of how not be ripped off. Ie, a LOT of fly by night panels for your application tout "SunPower" cells, but are of the trash variety.

https://marinehowto.com/installing-a-solbian-semi-flexible-solar-panel/

So, not cheap. Cheap and solar just don't go together for long-term applications. Good reading even if you aren't marine.

If interested peruse the other articles. Especially the LifeP04 stuff. I more of less emulated his findings 10 years ago right along with him on my own.

[Mike90250]

So your saying don't use the trailer plug ground wire. BUT do the house batteries need to be grounded? What happens if they're not?

That's not what I said. I said don't use the hitch. ( the ball the trailer hooks to ) it's dirty and greasy and makes poor contact. If your connector has a ground cable, you are already OK. Early connectors saved a wire, and it works OK for lights but not charging

[sdold]

So it's it better to get 180W at 5A (series) or 90W at 10A (parallel)?

Do you have a 12V battery? If you do, and if you wire the panels in series, the current is still 5A, so 5A x 12V = 60W harvested and delivered to the battery. If you connect them in parallel, the current doubles, so you'd get 10A x 12V = 120W. If you used a small MPPT controller and the ambient temps are not too hot, you might see close to 180 watts with the panels in series.

The panel's power specification is only valid when the panel is operating at its max power point, which is the combination of voltage and current that yields the most power. In lab conditions it's Vmp x Imp (shown on the nameplate), and those numbers are probably close to 5A and 18V. When you use a PWM controller, the panel is connected to the battery in an on/off manner with the on time varying depending on how depleted the battery is. During the on time, the panel is connected to the battery and is brought down to whatever the battery voltage is, about 12-13V. Since the panel's current is about 5A, the power produced is 5A x 12V = 60W.

What the MPPT charger does is allow the panel to operate at a higher voltage. It will convert the 18V and 5A of the panel to 12V and 7.5A at the battery. You get more current to the battery than you are getting from the panel. It's not magic, it's about the same power in = power out. Below is an app screen shot from an MPPT controller in a small solar power system I recently installed for a ham radio repeater, showing the same power in and out, but with much higher charge amps than the panel can provide alone. Not saying you should run out an buy an MPPT charge controller, because putting your panels in parallel would be OK for a small system. But it's nice to know how the PWM and MPPT compare.


victron.png

[Carv]

That would work if your battery is 24V, or if it's 12V with an MPPT charge controller. If it's a 12V battery with a PWM controller like the Prostar you'd want to wire them in parallel to get twice the current of a single panel.

So it's it better to get 180W at 5A (series) or 90W at 10A (parallel)?

[Carv]

Don't rely on the trailer hitch to carry the power return. Add a wire of matching gauge (of the + cable) to carry the - power.

So your saying don't use the trailer plug ground wire. BUT do the house batteries need to be grounded? What happens if they're not?

[Mike90250]

Don't rely on the trailer hitch to carry the power return. Add a wire of matching gauge (of the + cable) to carry the - power.

[sdold]

Will be running:1) 2 Renogy 100W 12v semi-flexiable panels in series on a 25 ft 10AWG non fused umbilical that I can just plug in.

That would work if your battery is 24V, or if it's 12V with an MPPT charge controller. If it's a 12V battery with a PWM controller like the Prostar you'd want to wire them in parallel to get twice the current of a single panel.

[Carv]

I've picked up a few things in the last couple days here's the update:

Will be running:
1) 2 Renogy 100W 12v semi-flexiable panels in series on a 25 ft 10AWG non fused umbilical that I can just plug in.
-Panels test out at 4.4A and 20.4W each while on flat ground...see specs below.

2) Morningstar Prostar PS-15 with the LCD screen.

3) Xantrex Prowatt SW600, pure sine wave 548W continuous and 1,200W peak. It has LCD monitor screen and uses 3W to 5W when no draw is present.
-Don't believe it has a "sleep mode" anybody know if it does?

4) 3.0 cuft insiginia double door mini fridge with freezer. Ran a kill-A-Watt on it and start up is 64W and runs about 46W once settled down. On a 8 hour test it used 0.20 Khw or 200 watts.


Panel specs:
IMG_20200901_195537342.jpg




Biggest issue so far is figuring out Wire sizing & fuse sizing on the "house batteries" from the alternator?

It's about a 23 to 25 foot run.
I got a Cole Hersee 200A 12V Continuous Solenoid (24213) that is ignition triggered so there is no back feed/draw when the car is not running.
Alternator is rated at 136A but will have secondary hook up and be drawing for original vehicle dual batteries at the same time. Based on this actual "people" I've discussed this with have told me that the depending on the state of charge the house batteries Amp draw will spike on start up and lower very quickly as the batteries start to charge.


Based on this I got a 150A re-settable marine style fuse right off the batteries and I got "battery cable" EPDM covered stranded 4 AWG for the 23ft run. Based on wire gauge/amp charts this should cover me at a 30 foot run up to 100A with a 10% drop. Since IF there would be a high amp pull it'd be very short, figured (and was told) the 4 AWG will cover me. Figure normal Amp draw should be around 15A - 30A as that's what my battery chargers throw at the batteries.

Anybody see any issues with this size wiring and fusing?

And do the house batteries need to be grounded or can I just run the positive lead from the alternator?




Thanks

[secessus]

Thank you Sun Eagle.
Is there a formula that will dictate or limit how many amps the rear/house/coach batteries will pull?

Lots of variables here, but some crude rules of thumb {insert caveats here} follow for deeply-discharged lead chemistries: flooded batts pull ~C/5 (battery capacity / 5, so 20A per 100Ah of capacity)
average-grade AGM at the same DoD will typically pull C/3 (33A per 100Ah of capacity). Higher-quality AGM will typically pull harder, like C/2.5 or more. Lifeline in particular can pull eye-watering amounts of current at first, like 5C (500A per 100Ah of capacity!).

[SunEagle]

Based on this the panel is closer to 3.5A, so a 10A would suffice.

Thanks

Remember you may want to add more panel wattage so you should go to at least 15A CC. There are a number of cheap 30A PWM type that you can find which are not much more money then a 15A unit.

[Carv]

Technically yes. The output from a panel is less then the stated value which is based on the wattage divided by the Vmp not the battery voltage so I expect the panel will output less then 16.67a. The 100% output value is usually the Imp rating.

A quality CC can handle a little more than then it's amp rating but usually they state how many watts you can connect to the input.

Based on this the panel is closer to 3.5A, so a 10A would suffice.

Thanks

[SunEagle]

If I did a 200W flexiable panel, what about running a Morningstar Prostar PS-15?

200W /12 = 16.67A, would that Prostar 15A handle it?

Technically yes. The output from a panel is less then the stated value which is based on the wattage divided by the Vmp not the battery voltage so I expect the panel will output less then 16.67a. The 100% output value is usually the Imp rating.

A quality CC can handle a little more than then it's amp rating but usually they state how many watts you can connect to the input.

[SunEagle]

Thank you Sun Eagle.

Is there a formula that will dictate or limit how many amps the rear/house/coach batteries will pull?

Wire size will not dictate how much draw the batteries will pull, it will only heat up if undersized for the draw load, if under sized, correct?

Surprisingly there really isn't a formula concerning the amps coming from an alternator to the coach batteries.

Wire size does not dictate how many amps the batteries will pull which is why you go as big as what can be delivered and then fuse appropriately. If you go too small the wires can heat up and in worst case burn up. unless there is a fuse that will open at or below the wire amp rating.

[Carv]

If I did a 200W flexiable panel, what about running a Morningstar Prostar PS-15?

200W /12 = 16.67A, would that Prostar 15A handle it?

[Carv]

Thank you Sun Eagle.

Is there a formula that will dictate or limit how many amps the rear/house/coach batteries will pull?

Wire size will not dictate how much draw the batteries will pull, it will only heat up if undersized for the draw load, if under sized, correct?