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Old 05-23-2024, 09:29 PM   #1
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Simulating nighttime for solar panel test

Without modifying my rooftop 100 watt solar panel wiring to my two Group 27 AGM house batteries, I’d like to test the staying power of my house batteries listed above in my 2018 Sunseeker. It’s parked in our driveway all year when we’re not on the road.

This present setup seems to support running our Dometic fridge running from propane perfectly during the daytime. According to the factory Convenience Center panel, it holds over 13 volts steadily. I’ve checked this reading with a digital meter, and it’s close enough for accuracy.

I’d like to pretend we’re dry camping after the sun goes down. I’m thinking of completely covering the solar panel to simulate nighttime conditions, thereby providing NO light at all to the panel. We use iPads instead of real books. There’d be no need for television. Assuming weather temperatures don’t need supplemental heat or fans, we have small solar motion activated floor lights, in case we need to use the bathroom throughout the night.

By “faking nighttime” with the covering during the daytime, I could repeatedly check in on the voltage reading several times over the hours that would be nighttime. I’d even like to test it to a maximum of 12 hours.

Wanda ya think? This seems better than getting up several times at night while I test the batteries. Should work right?
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Old 05-23-2024, 09:38 PM   #2
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Your solar charge controller may (should) have a setting to turn it off. No need to cover anything.
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Old 05-23-2024, 09:39 PM   #3
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Why do you need to test the staying power of the batteries?
Your refrigerator is running on propane and the igniter uses a very small amount of battery power. When you open the refrigerator and the lights go on inside the fridge, you're also using a very small amount of electricity.
It sounds like you're set up to boondock with motion activated lights, ipads and no demands on the batteries other than things like propane detectors.

There's no reason you can't run your test, but it seems like a lot of unnecessary work. The way you camp, 2 AGM batteries are going to last you a long time.
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Old 05-23-2024, 09:53 PM   #4
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What about using a shunt like the Victron that will graph your battery voltage? Not a bad idea to have a shunt if you plan to boondock anyway.
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Old 05-24-2024, 01:25 AM   #5
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Originally Posted by Reverse_snowbird View Post
Why do you need to test the staying power of the batteries?
Your refrigerator is running on propane and the igniter uses a very small amount of battery power. When you open the refrigerator and the lights go on inside the fridge, you're also using a very small amount of electricity.
It sounds like you're set up to boondock with motion activated lights, ipads and no demands on the batteries other than things like propane detectors.

There's no reason you can't run your test, but it seems like a lot of unnecessary work. The way you camp, 2 AGM batteries are going to last you a long time.
I appreciate all that you’ve stated. It only takes a minute to imitate nighttime. However, the AGM batteries are at least 7 years old, and we’ve always camped with shore power, and the batteries have subsequently never failed us. I’ve never tested their “staying power” for dry camping. We may try that this year, but I figured it’s best to know before we go.
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Old 05-24-2024, 04:53 AM   #6
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Originally Posted by DJ252 View Post
Your solar charge controller may (should) have a setting to turn it off. No need to cover anything.
My SCC don't have such a setting. Which ones do and why other than the rare reason such as the OP's?
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Old 05-24-2024, 05:25 AM   #7
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Unfortunately you are going to have to mess with the wiring or cover the panels

Most small RV installations don’t have a solar disconnect
If you want to add a disconnect you can do so

Otherwise learn where the solar controller is and how it is wired …… it’s easy to disconnect
do it real early in morning as the panel won’t be producing a lot of power
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Old 05-24-2024, 06:05 AM   #8
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My SCC don't have such a setting. Which ones do and why other than the rare reason such as the OP's?
The GoPower PWM 30 that came in my camper, had a switch in the settings menu to turn it off.

Any time you need to do work down stream of the panels, or upstream of the SCC, a solar disconnect switch would be handy. Covering one panel may not be much of a pain but covering an array, is a lot harder than flipping a switch, or changing a setting.
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Old 05-24-2024, 06:53 AM   #9
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Covering the panel is a good idea. One problem with faking the night time for the test is that you will be missing the day time charge. In your normal cycle you have a day time charge followed by a night time discharge. Covering the panel will take away the recharge for the day and give you two night time discharges.
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Old 05-24-2024, 06:59 AM   #10
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Originally Posted by DJ252 View Post
Your solar charge controller may (should) have a setting to turn it off. No need to cover anything.
Here’s my controller. I do not see a button to turn off.
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Old 05-24-2024, 07:06 AM   #11
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Here’s my controller. I do not see a button to turn off.
Mine didn't have a physical switch, it was a settings choice in the menu. Look in your manual, or at least the settings menu.

Maybe look up a "how to" on Youtube.
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Old 05-24-2024, 07:13 AM   #12
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Originally Posted by TacomaJoe View Post
Covering the panel is a good idea. One problem with faking the night time for the test is that you will be missing the day time charge. In your normal cycle you have a day time charge followed by a night time discharge. Covering the panel will take away the recharge for the day and give you two night time discharges.
TacomaJoe…..

Having the motorhome in our driveway, I would have the rig plugged in on night one. This would provide a strong charge to the batteries through the onboard converter. In the morning of day two, I would cover my single 100 watt panel (easy peasy). Throughout the day with the fridge running, and virtually nothing else (simulating our nighttime conditions) I can check the readout of the house batteries every hour or so, over the course of the day. This allows me to see what the voltage will/may drop to for a period of up to 12 hours.

My purpose is to see their minimum voltage to support the dry camping test as described in my original post, before we actually try it for one night. The following day, the generator or the solar panel could be back up and running to recharge.

If at anytime I found the voltage were to drop below 12 volts, I could stop the test, simply by plugging back into shore power, and letting the converter recharge the house batteries.
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Old 05-24-2024, 07:14 AM   #13
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Simplest solution would be to add a shunt
Then you can watch the performance and if battery appears to not hold charge it may be time to replace it

If you are not a power hungry user a cheap shunt from Amazon May fit your requirements

As noted above … leave panels connected and when batteries can no longer provide enough power for overnight / bad solar days time to look at replacing battery

If they lasted several years and suited your camping style replace them with same size and style

If you want a bit more power upgrade to lithium, not hard to do and prices are low now

Packing up today to go home
been camping 5 nights on Solar and lithium… never had to turn on the converter

Have not needed converter since Solar install
which includs a trip Florida to Toledo and return
using 12v fridge and furnace
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Old 05-24-2024, 07:39 AM   #14
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Originally Posted by Aussieguy View Post
Simplest solution would be to add a shunt
Then you can watch the performance and if battery appears to not hold charge it may be time to replace it

If you are not a power hungry user a cheap shunt from Amazon May fit your requirements

As noted above … leave panels connected and when batteries can no longer provide enough power for overnight / bad solar days time to look at replacing battery

If they lasted several years and suited your camping style replace them with same size and style

If you want a bit more power upgrade to lithium, not hard to do and prices are low now

Packing up today to go home
been camping 5 nights on Solar and lithium… never had to turn on the converter

Have not needed converter since Solar install
which includs a trip Florida to Toledo and return
using 12v fridge and furnace
Thanks for your input, however I’d like to test the theory of our present equipment with the factory installed 100 watt solar panel on the Zamp Controller as simply as possible, without spending any money. Aside from that, purchasing and installing a shunt might be a whole other story for me as a DIY guy.

Shouldn’t completely covering the 100 watt solar panel stop any charge to the batteries for pure testing?
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Old 05-24-2024, 07:47 AM   #15
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Not sure why this is taking 15 responses. Solar panel won't charge with covered. Or simply disconnect from the batteries.

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Old 05-24-2024, 10:40 AM   #16
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Just to close this thread…..I got a reply from the support center for Dometic Mobile Power/Zamp Solar.

On my model of controller (ZS-30AD) there is no ON/OFF switch. They suggest to either cover the solar panel completely, or unplug the panel.

I have not been able to locate the plug, so I’ll be covering the panel for my tests.

Thanks to all that responded.
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Old 05-24-2024, 10:53 AM   #17
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Amazing how people want to complicate the simplest things.

Yes your idea to toss a moving blanket or trap over the panels will work fine.

Rule number one ALWAYS is K.I.S.S. !!!
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Old 05-25-2024, 07:40 PM   #18
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Voltage test results

Today’s results….

830am…….30amp shore power…….13.3 volts

900am…….solar panel covered…….12.4 volts
1100am…..solar panel covered…….12.3 volts
300pm…….solar panel covered…….12.3 volts
500pm…….solar panel covered…….12.3 volts
700pm…….solar panel covered…….12.3 volts

800pm…….30amp shore power…….13.6 volts

Sunseeker manufacturer date 2/24/17
Group 27 AGM batteries could theoretically be from 2016, so 7-8 years old?

If we were to do dry camping, I’d be charging via the 100watt solar during the day. If the solar panel couldn’t match similar 13+ volts, I’d run the generator ahead of down time, to make sure batteries were fully charged.

My test proved my existing AGM batteries still performed for 10 hours as outlined in my original post, so I’m pretty satisfied.
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Old 05-26-2024, 07:01 AM   #19
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As long as this works for you great!

The shorepower voltage is the bulk charging voltage and expected but has nothing to do with the battery condition.

What's the load on the battery that's causing the instant drop from 12.6v to 12.4v -- roughly 75% charge? To test the battery: fully charge it for 24 hours, completely disconnect, and measure the voltage 24 hours later. Completely requires removing the cables -- no wires on the Negative pole.

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Old 05-26-2024, 07:13 AM   #20
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How long did you have the charger on before running the test?

The drop to 12.4 within 30 minutes is a bit of a worry, was the battery actually fully charged?

The initial 13.3v reading may have been the charger voltage,
you want to ... turn OFF all loads before starting test and measure voltage after the battery has rested an hour or so after charging you want to see about 12.8 resting voltage.

Then begin the load testing
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