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Old 10-17-2016, 01:06 AM   #41
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Originally Posted by rossfree View Post
Remember to use big cables when putting it together. Especially between the batteries and inverter. You will likely want to purchase a hydraulic crimper to make your own cables. I would use nothing less. Every cable end must be crimped solidly. You're looking at about twelve cables just between the batteries and also between the battery bank to the inverter. The cables from solar to the charge controller must be large enough to carry the current you expect to see. Likely four gage or thereabouts. And you have cables between the charge controller and batteries. And you should also have power disconnects between the batteries and the inverter and between the solar and charge controller. Lots of big wire cables. It adds up. Get a good hydraulic wire crimper that will do a bunch of different sizes of wire ends. Oh and a good pair of cable cutters.

The list of stuff goes on and on. My 480 watt system probably ran more like $2000 with all the stuff mentioned above. That's after getting my two 240 watt panels for $240 each. Keep your cable runs short and use BIG WIRE.

Solar rocks!

Ross
Try 4/0 AWG cables, not 4 AWG! I think you'll be losing way too much power with 4 AWG. I use 4/0 and 2/0 for all my battery and feed cables, with tinned closed-end lugs. My hydraulic crimper is OK on smaller cables up to about 2 or 1 AWG, but for the big 'uns I use a FTZ 94284 crimper that will make consistently good gas-tight circumferential crimps on lugs as large as 250 MCM, and a big Temco 24" cable cutter that can cleanly cut up to 750 MCM cables. Heck, if I could find 250 MCM cable and lugs for my emergency intertie cables from the house batteries to the starter, I would use them! My Delco 42MT starter can briefly draw up to 750 amps, so big is good.

If any skoolies are in SoCal, I'll be happy to help make cables for them. 4/0 is less than $4 a foot from eBay, and tinned 4/0 lugs are less than $2 at NAWS.

Yes, solar is good.

John
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Old 10-17-2016, 01:13 AM   #42
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Originally Posted by Iceni John View Post
I use a FTZ 94284 crimper that will make consistently good gas-tight circumferential crimps on lugs as large as 250 MCM, and a big Temco cable cutter to cleanly cut even the biggest cables.
I wonder if a tool rental place would have these, or something substantially similar, since I only intend to have to use them once....
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Old 10-17-2016, 09:00 AM   #43
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Keep your panties on John. Re-read my post. I said 4 gage between his solar panels and charge controller. If he runs two panels in series to each charge controller as suggested he will have a maximum current of maybe 13.5 amps at 48 volts in perfect conditions. If he keeps his distance between the solar panels and charge controller reasonably short he will be well below 1% loss.

On my 480 watt system I'm using 6 gage to the charge controller (cc), 4 gage from the cc to the inverter and 1/0 from the inverter to the battery bank. It works swimmingly (that's an engineering term)! If you're using 4/0 for everything, God bless you!

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Old 10-17-2016, 09:17 AM   #44
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I hear you on the crimper. You think one-time use (like I did) but you're building a custom bus conversion, likely over many months. Mistakes happen. Ideas change. Things get moved around. I pulled out my crimpers several times before things settled. They're $60 on Amazon. It's Chinese made but got the job done. Cable cutters are about $20. They have rounded cutting blades. Flat bladed cutters just don't work on big cables.

When you're making the short fat cables that connect your batteries terminal to terminal you have to use care that the cable connectors are planar before you crimp them. Mine were so short I also curved the cable a bit, as it would be in actual service, before crimping the end. Once they are crimped (the really short cables) they are not nearly so flexible.

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Old 10-18-2016, 06:34 PM   #45
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If running two charge controllers with two 305w 24v panels running to each charger, eventually into a 12v battery bank, do I ABSOLUTELY need MPPT chargers? Getting real pricey there ... the Morningstar Tristar 45 amp PWM's are $166 a piece shipped on Amazon while the MPPT variants are $420 each ... getting expensive. If not, what can I do to maximize my charge with the PWM's?
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Old 10-18-2016, 11:41 PM   #46
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I purchased a Tracer 4210rn MPPT charge controller off of Aliexpress and have been very pleased with it's performance. Right now they're going for around $225. While reviews say that they aren't as fast to respond to cloud cover as the Morningstars, for hundreds of dollars less I can deal with it

I would absolutely not go with PWM for any solar system over 200w. There's just too much wasted energy. A PWM controller is a real bottleneck in what could otherwise be a very efficient system.
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Old 10-18-2016, 11:48 PM   #47
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To use a pwm controller effeciently your solar panel output voltage should be a few volts higher than your battery bank voltage. For a 12 volt battery bank you would want 16 - 18 volts from your panels. PWM will lower the voltage to an acceptable charge voltage, say around 14.8 volts and send roughly the same current from the panels out to the batteries.

In your case the voltage from two panels will be close to 48 volts. A pwm controller would throw away those volts above the charge voltage.

For example if we use some simple numbers like a 50 volt solar system supplying 10 amps of current. 50 volts x 10 amps = 500 watts available from your system to charge your batteries.

Now let's say your charge voltage is 15 volts. Your pwm controller would drop the 50 volts to 15 volts and send 10 amps to your batteries. 15 volts x 10 amps = 150 watts!!! 350 watts never make it to your batteries!!!

An MPPT charge controller can be thought of as a dc to dc converter. It lowers the voltage from 50 to 15 volts (using the simple numbers above) while raising the current proportionately, sending approximately 33 amps to your batteries!

15 volts x 33 amps = 495 watts!!!

There are always losses through wire, controller inefficiency, etc. but MPPT controllers generally have good reputations for being more efficient especially when large voltage differences are in play between the solar system and battery bank.

I know this stuff is hard to digest in the beginning but hang in there and you'll pick it up. For a system of your size you are looking at two MPPT charge controllers.

Regards,

Ross
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Old 11-09-2016, 11:55 PM   #48
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Solar blueprint

Hi all, Google "rv solar wiring diagram". You get a page with at least a hundred pics of diagrams of different systems. Click on any pic and you will get a link to the site the diagram comes from. Pretty cool. Lots of ideas! Definitely going solar on my bus as I don't want ever have to find / pay for a hookup. And nothing quite beats a good dose of overkill.
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