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Old 02-22-2017, 11:46 PM   #1
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How do I hook up a solar panel to my coach batteries?

I have two deep cycle 12 volt batteries for the coach & want to hook up a 40 watt panel. Just to keep the batteries charged up when the motor-home is stored with no source of outside power. Do I attached to (+) red on one battery then (-) black on the second battery so both batteries are being charged equally? Thanks for your help......Len
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Old 02-23-2017, 12:34 AM   #2
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If your panel doesn't have a built in charge controller, you'll need to buy one so you don't send too much voltage and so it can shut off when the batteries are charged. You can get one on amazon for $10-$20 that would be sufficient for a 40w panel.
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Old 02-23-2017, 03:40 AM   #3
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To answer your question on the battery connections, I'd suggest making the connection on the buss bar, to avoid having multiple wires at the battery connections. Then by default, the connection is spread correctly on the batteries (not that it matters much with little charge current).

If you have to go with attaching at the batteries, it's not a lot of current so really isn't going to matter that the + is on one battery, and the - is on the other battery. Do it where you can get good clean connections and the wires won't rub/fray.
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Old 02-23-2017, 06:32 AM   #4
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If your panel doesn't have a built in charge controller, you'll need to buy one so you don't send too much voltage and so it can shut off when the batteries are charged. You can get one on amazon for $10-$20 that would be sufficient for a 40w panel.
That's what I did --- I put a 40w on the roof of the storage building and ran the wires to the controller then into the chassis batteries.
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Old 02-23-2017, 07:11 AM   #5
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At 40 watts you don't need a controller. At most you will get 2-3 amps to the batteries. You, if the batteries are off(disconnected) will at most maintain not charge. At 100 watts I would add a controller. Red on one battery and black on the other would balance both batteries.

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Old 02-23-2017, 09:11 AM   #6
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At 40 watts you don't need a controller. At most you will get 2-3 amps to the batteries. You, if the batteries are off(disconnected) will at most maintain not charge. At 100 watts I would add a controller. Red on one battery and black on the other would balance both batteries.

LEN
Len has it right. And to go one step further, the panel will act like a drain when connected to the batteries directly without the sun. This is one of the reasons for the charge controller. If you want to do it right, get two panels about 235 watts a piece and hook them up in parallel to a charge controller and relax. I looked on my local Craigslist and found panels for $90. Otherwise, when you hook them up to the batteries, without the charge controller, you might do as much harm as good.

The most absurd work of a solar panel-discharging a battery |
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Old 02-23-2017, 09:20 AM   #7
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Len has it right. And to go one step further, the panel will act like a drain when connected to the batteries directly without the sun. This is one of the reasons for the charge controller. If you want to do it right, get two panels about 235 watts a piece and hook them up in parallel to a charge controller and relax. I looked on my local Craigslist and found panels for $90. Otherwise, when you hook them up to the batteries, without the charge controller, you might do as much harm as good.

The most absurd work of a solar panel-discharging a battery |
From your article,

Most of the solar panels produced today have a series diode to block the discharge of the battery.*

You would probably have look hard to find one that doesn't.

This is a non issue.
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Old 02-23-2017, 09:55 AM   #8
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From your article,

Most of the solar panels produced today have a series diode to block the discharge of the battery.*

You would probably have look hard to find one that doesn't.

This is a non issue.
"This is a non issue" because you know for a fact that the 40 watt inexpensive panels have diodes built into them? And your electronic credentials are? Sometimes reading information from people who don't have a clue about electronics can really be damaging to your coach.
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Old 02-23-2017, 10:12 AM   #9
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Don't know for a fact. Yes It is a non issue.


BLOCKING AND BYPASS DIODES

Many older books and articles recommend using blocking diodes to prevent reverse current flow back through the panel at night ("dark current"). Many others do not (including us, mostly). It actually depends on the situation, but as a general rule in 12 volt systems, you will lose more power from diode losses than you will from leakage back into the panel at night. The situation gets much worse at higher temperatures with crystalline panels. All regulators (charge controls) have built-in blocking circuits. About the only case where a blocking diode might be needed is with small thin-film panels, such as the Unisolar US-5 or Siemens ST5, where the panel is connected directly to the battery. Diode losses are much less in higher voltage systems, such as 48 volts.
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Old 02-23-2017, 01:39 PM   #10
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Don't know for a fact. Yes It is a non issue.


BLOCKING AND BYPASS DIODES

Many older books and articles recommend using blocking diodes to prevent reverse current flow back through the panel at night ("dark current"). Many others do not (including us, mostly). It actually depends on the situation, but as a general rule in 12 volt systems, you will lose more power from diode losses than you will from leakage back into the panel at night. The situation gets much worse at higher temperatures with crystalline panels. All regulators (charge controls) have built-in blocking circuits. About the only case where a blocking diode might be needed is with small thin-film panels, such as the Unisolar US-5 or Siemens ST5, where the panel is connected directly to the battery. Diode losses are much less in higher voltage systems, such as 48 volts.
When you plagiarize someone else's work you should at least give them credit. I believe you copied this website for your insight.

https://www.solar-electric.com/solar...cal-tips.html/

"About the only case where a blocking diode might be needed is with small thin-film panels, such as the Unisolar US-5 or Siemens ST5, where the panel is connected directly to the battery."

From your own quote.
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