Shore and Solar Power Schematic

[MadMango]

Anyone care to give me a sanity check on this schematic? This is for a camping trailer I'm building. I want the ability to connect to shore power when it's available, and also run on solar when it's not. I also just realized that the polarities are swapped on the output of the charge controller.

"Art without engineering is dreaming; Engineering without art is calculating."

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[itsmoked]

I love that you call it "shore power".

I work in passenger rail service and and everything is either "Generator",
"Head End Power" (from the locomotive), or "Shore Power" if plugged into anything
coming from the ground. I believe that's the standard since I've never heard of
called anything else.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Amazon LCD Panel Meter


This meter shows volts down to 0.xx which is what you need to be able to see the real State-Of-Charge.

It's back lit so it draws 8mA, which is nothing to consider if this trailer is charged regularly.
If not, disconnect the backlight and it draws 3mA.

Personally, I'd skip two batteries as that's ALWAYS more problematic and will never "last twice as long" or live very long.

I'd use one of these:
Trojan AGM 140AH

Keith Cress
kcress -

http://www.flaminsystems.com

 

[stevenal]

Keith,

I believe the RVIA standard colors are black for +12V and white for -. At least that's how my camper is wired.

 

[itsmoked]

Ah, stevenal, I gladly differ to your suggestion. I was more to pointing out that he should
have different colors for the DC which helps a lot on repairs or future mods. On the other
hand those two particular colors, when mixed with AC wiring.... suck. I'd use about any other
colors.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

You can get inverters that also charge the batteries. Of course that requires purchasing the inverter but it gets rid of that whole clumsy battery charger, switch and duel power strip scheme. Look at RV or Marine or Solar sources for an inverter, not your local box store. People build solar systems all the time with a charge controller on the solar system and an inverter with generator backup also charging the batteries so the two can work together just fine.

The downside is that the inverter would have to be ON for shore power to charge the batteries. But, if the trailer is parked outside between uses then the solar panels should easily keep the battery charged with all loads off. If you store it inside off-season then I'd personally recommend you disconnect the battery and use a smart charger on it every month or so.

 

[waross]

I don't see why you switch between powering the 120 Volt power strip and the charger.
I would feed the power strip directly and plug the charger into the power strip.
Add a switch for the charger if you desire.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MadMango]

Thanks for the thoughts and brain crunching. I've tried to simplify this yesterday, before I saw Keith's mark-up. I think I'd rather have resettable breakers than have to hope to have a spare fuse around.

"Art without engineering is dreaming; Engineering without art is calculating."

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[itsmoked]

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

Has anything changed?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[itsmoked]

Well. It appears he added a fairly useless switch, kept a wrong sized breaker, changed another
breaker up to a size his batteries can't support, persisted with pluses and minuses where they
are nonsensical (AC power), and ditched a solar panel.

But other than that I see no changes.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MadMango]

I said I made it prior to recent comments.

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[stevenal]

The battery disconnect doesn't do what it says. Open the switch, and the battery remains connected to all the loads.

Keith,

There's not too much mixing of the circuits. The fridge is AC/DC, but the AC part is easily traced to where it plugs in. The converter is the other point. Romex is always AC.

 

[MadMango]

I apologize for posting the last schematic, I understand how useless it was. I do try to take everyone's advice, which is greatly appreciated in this endeavor.

Most of my "round trip" lengths are going to be less than 10ft, so according to the charts posted above on West Marine, it looks like I can get away with 12-14AWG wiring. This works out well, as my plan was just to use extension cords and lop the ends off to make connections.

RVers recommend a battery disconnect, which is what I had above. They say it is nice to disconnect the battery. I guess it's just as easy to just take a wire off a battery terminal.

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[ScottyUK]

Most of your wiring for the 12V system won't be sized on thermal capacity, it will be sized on acceptable volt-drop. I'd work on keeping volt-drop to no more than 5%, which on a 12V system means <600mV drop in the loop between source and load, including the return path. If you can keep it lower then so much the better.

The wiring where the heavy currents flow, e.g. in the loop feeding the inverter, should be separated from the other loads to prevent modulation of the lighting by the large loads. Are you sizing the wiring to the lighting and small loads such that it is protected by the 150A breaker? 10AWG isn't anywhere near big enough, at least not by my reckoning.

 

[LittleInch]

The 30A breaker looks to be in the wrong place. As soon as you plug in your invertor it would break. did you mean to put that on the low power side? Doesn't make sense to protect one battery outlet and not the other.

The 150A breaker is far too big and won't protect the wiring or invertor. You really should use proper sized bits not just because you have something to hand.

I would wire the big load (the invertor), direct from both batteries direct with large wires and maybe a 50A breaker and the other loads from the battery via a different circuit with a 30A breaker.

Why show a negative feed into the 12V dist bd when you then collect all the negative wires separately? Are you going to wire it that way or run a pair of wires from the board?

Getting there and at least it's simplified compared to initial design.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dgallup]

When I wired up a simple 1 solar panel electrical system in my cabin 5 or 6 years ago I initially thought about using 12 volt lighting. However, the cost of the large gauge wire and the lighting fixtures quickly led me to scrap that idea. It is simpler and cheaper to just use all standard 120 VAC wiring and fixtures. The only thing 12 volts is the solar panel, charge controller and batteries. A high quality inverter can be well over 80% efficient over most of the operating envelope.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[itsmoked]

Yes, it's looking much better Mango!

As Scotty and Little were mentioning for a 350W inverter all you need is a 30A breaker.
At 350W your batteries will last about just about an hour at 30A if you drain them clear down to
50% which is about where you should stop.

At 30A you CAN still use 10AWG to the inverter, if the distance is a few feet between the
batteries and the inverter. If it's much farther you should use 8AWG as the inverter is
simply multiplying the voltage given it, so as Scotty is saying, much drop makes a larger
difference in the inverter's output. In fact it's about a 10 times difference. For every
volt missing at the inverter's input the output will be 10 volts lower.

The breaker between the batteries is to prevent a shorted battery from involving both in
the event. An alternative that might be better would be two 30A breakers, one in each +
lead so you could isolate individual batteries in case one chokes. This would also allow
you to check the individual battery's health by turning each off individually and checking
the voltage on the meter. If for instance one battery reads 10.5V then you have a shorted
cell in it and it should not be hooked up or included in the pair and should be removed
from service immediately.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

So you're now buying an inverter and a battery charger? I'm going to ask again, why not use something like this?

http://www.theinverterstore.com/600-watt-pure-sine-inverter-charger.html

 

[LittleInch]

I'd still get a prepackaged ups. Has in built chargers, invertors, battery monitors etc. I think dgallup is right, run it all at 110v. Then all you need is an invertor from your solar panels. As soon as you plug in the shore power it takes over all the loads, charges the batteries automatically and nothing else needs changing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MadMango]

I am trying to use what I have on-hand. I understand that turn-key solutions are available and will serve me better, they are just not in my budget now.

Loads-
two 12w LED lights
two 6w fans
maybe a 95w fan

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?