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Old 02-23-2014, 04:43 PM   #21
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Russ
I do not see a problem with MC4 connectors coming off the panel. 100 Watt panel voltages are usually in the 17 range, if you use a voltage calculator for DC and estimate 5 amps you can see you can get by with as small a wire as 14 gauge and still have a run of 100 feet. With the above numbers I have a drop of 1.28 volts. The solar controller will now drop that down further, my dual 6 volt are recommended at 15.3 volts, they are Interstate batteries. Because the panel produces more than the battery can handle most solar controllers are dissipating volts.

Now, once you get to the solar controller then you want to use heavier wire. But now the MC4 does not come into the mix and you can use a connector of your choosing. Again remember you want that controller as close as possible to the battery, a meter distance would be ideal.

I am not sure I like the "pinch" connector. The tool will not be found when needed is my experience.

By the way, I never heard of a MC4 connector until your post but when I looked it up I saw it was familiar, never knew the correct description.
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Old 02-23-2014, 09:06 PM   #22
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Originally Posted by fudge_brownie View Post
100 Watt panel voltages are usually in the 17 range, if you use a voltage calculator for DC and estimate 5 amps you can see you can get by with as small a wire as 14 gauge and still have a run of 100 feet. With the above numbers I have a drop of 1.28 volts.
That's almost 8% of panel's output being wasted as heat due to wire resistance... seems a lot to me, but if panels are cheaper than wire than it may be a good choice.

Also, the 17 volt value is for maximum power output in full sun. In realistic conditions, it seems like a volt or two could be the difference between reaching the desired battery charging voltage or not.

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The solar controller will now drop that down further, my dual 6 volt are recommended at 15.3 volts, they are Interstate batteries. Because the panel produces more than the battery can handle most solar controllers are dissipating volts.
There's a big difference here. No controller is just a resistor like a too-small wire, throwing away power - they would heat up like toasters under some conditions if they were.

Also, again that 17 volts is for maximum power transfer. At higher currents (and a big pair of RV batteries could take much more than 5 amps in the bulk charge stage) the panel output voltage will be lower and the controller may be just passing the panel output through directly.

The MC4 connectors look like a great way to series connect (daisy-chain) panels together, but of course that is not normally done on RVs. Once panels are to be paralleled, it would make more sense to me to use a MC4 termination box to transition to larger gauge wire for the combined current. Using the MC4 connectors for the output of each panel in moderate lengths to termination boxes or controller inputs seems like a good way to make weatherproof connections which can be disconnected.
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Old 02-23-2014, 09:35 PM   #23
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What happens when the battery becomes fully charged? I know it goes into a trickle charge or maintenance mode. What is happening to the 17 volts and 5 amps coming off the panel and into the solar charger?
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Old 02-23-2014, 10:03 PM   #24
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Brian
What happens when the battery becomes fully charged? I know it goes into a trickle charge or maintenance mode. What is happening to the 17 volts and 5 amps coming off the panel and into the solar charger?
A basic controller just shuts off, like a switch: all the voltage is lost, but no energy is dissipated - it isn't produced because the panel goes to an open-circuit condition (typically 20 volts and, of course, zero current). A PWM controller does the same thing, just more gradually by switching rapidly on and off and eventually reaching an all-off state. In trickle mode, the PWM controller is off most of the time. In this state, I agree that the loss due to wire resistance doesn't matter, because the panel has power capability to spare.


It's the operation when the battery is at a lower state of charge that I think matters here - that's when you want as much power as you can get, and neither a simple switch or a PWM is losing any voltage... they're just letting the panel go to a higher-current and lower-voltage point in their performance curve.

In this low-battery-voltage state an MPPT controller should do even better, creating more current at a lower voltage than the panel is putting out, although these controllers have their own inefficiencies.


In any charging condition, I think it help to keep in mind that the panel is not always putting out 100 watts (in our example), any more than the 230 hp engine in my van is always putting out 230 hp. The state of the load (battery voltage, internal resistance, wiring resistance, and controller action in this case) determines where on the performance curve the panel will operate; in my van, even at full throttle it can't make 230 hp at only 2000 rpm. If not connected to anything, the panel can't put of 5 amps (or any current at all) even in full sunlight, although it will produce as much as 20 volts; if connected to a dead short the panel can't put out 17 volts (or any voltage at all), but will put even more than 5 amps through that short if in full sun.

In a really quick search, it looks like Wholesale Solar has a decent page explaining the voltage-current relationship.


I realize this topic was supposed to be about how to connect the parts of a simple solar system, and lots of this detail isn't needed to answer that question. My point is just that resistance (in the wires, or in the connector) does hurt the system performance, even if the voltages you see quoted are higher than the battery needs.
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Old 02-24-2014, 04:52 AM   #25
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Russ
I do not see a problem with MC4 connectors coming off the panel. 100 Watt panel voltages are usually in the 17 range, if you use a voltage calculator for DC and estimate 5 amps you can see you can get by with as small a wire as 14 gauge and still have a run of 100 feet. With the above numbers I have a drop of 1.28 volts. The solar controller will now drop that down further, my dual 6 volt are recommended at 15.3 volts, they are Interstate batteries. Because the panel produces more than the battery can handle most solar controllers are dissipating volts.

Now, once you get to the solar controller then you want to use heavier wire. But now the MC4 does not come into the mix and you can use a connector of your choosing. Again remember you want that controller as close as possible to the battery, a meter distance would be ideal.

I am not sure I like the "pinch" connector. The tool will not be found when needed is my experience.

By the way, I never heard of a MC4 connector until your post but when I looked it up I saw it was familiar, never knew the correct description.
Paul,
There is no problem with the MC4. I just commented about the wire size limitation. Normally the 10 gauge wire handles the current with not too much loss when the controller is mounted near the battery. My tethers are 30' long, so I opted for bigger wire. If you were to mount the controller at the panels with 30' tethers it would be more important to up size the conductors to ensure your battery was getting full voltage. My controller is mounted next to the battery, so only 4' for pos and 4' for neg = 8' of wire in circuit. I used 4 gauge for that. I see 14.8v at times going into the battery, so I know the wire size is good. The Trimetric monitor is useful for monitoring what's going in and out of the battery.
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Old 02-24-2014, 06:28 PM   #26
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I understand now that using a standard 12v plug is not optimal for use with a solar panel and I should connect the panel to the battery using one of the other style of plug. Do you think Reace would install one of the suggested outlets? What's the procedure for this, do I buy the equipment and have it sent to the factory?

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Old 02-24-2014, 07:42 PM   #27
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I am having Reece install the plug as pictured on post #19, it is called a deck connector and found at marine hardware stores. I found a small chain of marine hardware stores in the Vancouver area and ordered from them and am having it shipped to Escape. Reece will drill the hole and install the connector but not do any of the wiring.

I am getting a little worried about the place I ordered from, it has been 10 days and no receipt showing up at Escape. (They have been notifying me when they receive items). Also nothing showing up on my credit card. I had to call in my order and upon completion of the order I asked for a confirmation number. The order taker said he would call me with the number. RED FLAG RED FLAG. Needless to say I do not have any way to follow up. We will give them some more time.
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Old 02-24-2014, 08:35 PM   #28
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We are using a 90 watt portable system purchased at last year's Casita gathering. I have it connected directly to the batteries using a pigtail with an inline fuse and a SAE connector.

This picture is this year in Quartzsite, you can see the panels.

We camped 4 nights in Quartzsite, and another 5 nights in Organ Pipe Cactus National Monument without needing our generator.

This included nightly use of the Dish receiver through our 1000 watt inverter, a 12 volt TV, LED lighting, water pump, and the propane heater.

In no case were we anywhere near over taxing the batteries, and the panels had no trouble recharging them during the sunny Arizona days. BTW we are still in AZ, near Sun City tonight, but with full hookups , heading back west tomorrow.

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Old 02-25-2014, 09:24 AM   #29
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[QUOTE=DeadEyeDan;44998]We are using a 90 watt portable system purchased at last year's Casita gathering. I have it connected directly to the batteries using a pigtail with an inline fuse and a SAE connector.

In no case were we anywhere near over taxing the batteries, and the panels had no trouble recharging them during the sunny Arizona days. [QUOTE]

Hey Deadeye--

That is exactly what I want to do. Just recharge the batteries easily and simply. What do you use for a controller and did you do anything to increase the wire thickness between controller and battery? I'd like to see a photo of your connections.

By the way, what's that strange geometric cube thing near the propane tanks?

Harris
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Old 02-25-2014, 10:44 AM   #30
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Hey Deadeye--

That is exactly what I want to do. Just recharge the batteries easily and simply. What do you use for a controller and did you do anything to increase the wire thickness between controller and battery? I'd like to see a photo of your connections.

By the way, what's that strange geometric cube thing near the propane tanks?

Harris
That solar package (the same one we have) comes complete with a regulator and charge controller built in, and the cable and several connectors that allow you to choose how you want to hook it up. That includes the SAE connector that can connect directly to the battery like I did.

I did not change the wire sizes or modify it. I did buy an extension cable so if I am camped under trees, I could move the panels further away and hopefully find direct sunlight. I am sure there is some voltage drop if I did that, but I have had excellent results just how it comes.

Since my batteries are in the front storage box, I dremeled a 1/2 circle in the lip of it to allow the lid to close and lock with the wire to the panels connected, and not pinch the wire.

It folds and stores nicely into a suitcase that is included. Plus if you sell your trailer and upsize, it isn't mounted to the trailer and you can keep it! (which we did when we sold the Casita and bought the Escape).

Here is the link to the package.

The guy came to the Casita gathering in Quartszite and offered a discount this year and last year when we bought it. Mention that and you might still get it.

Sorry I don't have a handy picture of my connection.

The cube thing is a Dish Network Tailgater satellite TV.
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