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wanderingaimlessly

Buggs Island lake

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Posted: 04/07/21 05:01pm Link  |  Quote  |  Print  |  Notify Moderator

So, the simple version of my question is,,,,,,,
does the higher voltage provide a gain?

If not,
should a single panel should suffice for 24 hrs on an 8 cuft absorbtion fridge and two cpap units drawing 70 watts max for 8 hrs per day? or should I add a second panel?

BFL13

Victoria, BC

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Posted: 04/07/21 05:13pm Link  |  Quote  |  Print  |  Notify Moderator

The fridge will pull about 17AH in 24 hrs on propane

70w will pull about 7 amps DC, so 8 x 7 =56AH

Total = 56 + 17 = 73AH from the full 240AH bank is down to 71% SOC. Second day with no sunshine is another 73AH down, so at 39% SOC. Oops got to get the gen out and recharge!


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CA Traveler

The Western States

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Posted: 04/07/21 05:28pm Link  |  Quote  |  Print  |  Notify Moderator

BFL He asked about 2 CPAP machines so 112Ah + refer + lights etc. Therefdore in one day he's at 50% SOC on his marine starting batteries.

OP I'll wager that you'll quickly want a second panel and 4xGCs won't wait for 2 years. But if you are frugal and camp for only 1-2 days then maybe or bring the gen.

Consider a nice 2 day plan, but the clouds didn't know your plan and you're out of power for the second night and no gen. Ruined trip?


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wanderingaimlessly

Buggs Island lake

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Posted: 04/07/21 05:41pm Link  |  Quote  |  Print  |  Notify Moderator

I'm not apparently making my question clear.
To take a different tack,
To charge a 300 Amp hr, 12 volt battery bank
Would 3, 100 watt ,solar panels such as
renogy 100 wired in parellel,
provide a substantial upgrade, or downgrade as compared to a single REC 325

The gain or loss due to voltage difference is my question.
Or is this a case of 300 watts is 300 watts,,voltage be damned?,,

BFL13

Victoria, BC

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Posted: 04/07/21 05:54pm Link  |  Quote  |  Print  |  Notify Moderator

Never mind the voltages. MPPT uses watts and PWM uses amps.

Three 100w at 6.3 each is 18.6 amps and your single 325 will do about 22 amps as seen above.

BTW is it two CPAPS at 70w total or is each one 70w? Wording not clear.

FWC

The Wilderness

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Posted: 04/07/21 05:56pm Link  |  Quote  |  Print  |  Notify Moderator

300W = 300W. Now we will argue all day about one way you could get 310W and the other way is 290W, but in the end it doesn't matter, the differences are small. The 325W panel will mate nicely with a Victron 100/30 or 100/50 MPPT charge controller. . Go with the 100/50 if you think there is any chance you may want to add another panel in the future.

wanderingaimlessly wrote:

I'm not apparently making my question clear.
To take a different tack,
To charge a 300 Amp hr, 12 volt battery bank
Would 3, 100 watt ,solar panels such as
renogy 100 wired in parellel,
provide a substantial upgrade, or downgrade as compared to a single REC 325

The gain or loss due to voltage difference is my question.
Or is this a case of 300 watts is 300 watts,,voltage be damned?,,


2oldman

NM

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Posted: 04/07/21 05:57pm Link  |  Quote  |  Print  |  Notify Moderator

wanderingaimlessly wrote:

Or is this a case of 300 watts is 300 watts,,voltage be damned?,,
Correct. Higher voltage will generally result in less line loss.

Lwiddis

Owens River area

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Posted: 04/07/21 06:13pm Link  |  Quote  |  Print  |  Notify Moderator

“BTW I generally use 66% output of a flat panel for 4+ hours.”

Agreed. Reasonable number.


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wanderingaimlessly

Buggs Island lake

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Posted: 04/07/21 06:15pm Link  |  Quote  |  Print  |  Notify Moderator

FWC wrote:

300W = 300W. Now we will argue all day about one way you could get 310W and the other way is 290W, but in the end it doesn't matter, the differences are small. The 325W panel will mate nicely with a Victron 100/30 or 100/50 MPPT charge controller. . Go with the 100/50 if you think there is any chance you may want to add another panel in the future.

wanderingaimlessly wrote:

I'm not apparently making my question clear.
To take a different tack,
To charge a 300 Amp hr, 12 volt battery bank
Would 3, 100 watt ,solar panels such as
renogy 100 wired in parellel,
provide a substantial upgrade, or downgrade as compared to a single REC 325

The gain or loss due to voltage difference is my question.
Or is this a case of 300 watts is 300 watts,,voltage be damned?,,

Thanks, that is the type of info I was looking for.
Effects of differing voltages was the other, The rest was already clear.

CA Traveler

The Western States

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Posted: 04/07/21 06:21pm Link  |  Quote  |  Print  |  Notify Moderator

wanderingaimlessly wrote:

The gain or loss due to voltage difference is my question.
Or is this a case of 300 watts is 300 watts,,voltage be damned?,,
Yes you got it!

A 300W panel delivers 300W of power regardless of battery voltage. A 48V battery would get 1/4 the amps of a 12V battery but both get 300W of power.

For a 12V battery bank or a 48V battery bank each RV would have the same about of usable power.

Try this: For the 48V battery a 48V 48W light bulb will draw 1A. For the same amount of light on a 12V battery a 12V bulb would draw 4A. ie 48V*1A = 48W = 12V*4A

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