Solar power

valhalla360 wrote:

swimmer_spe wrote:

pianotuna wrote:

swimmer_spe wrote:
OP here.

I plugged it back in. It rebounded to 11.9V

I now know.

Do you mean you were charging it? Or just measuring the voltage (at the battery posts would be preferred.

40% is a bit too low.

I was reading off my panel in the trailer. The rebound I am assuming was due to the solar panel. Not bad, but definitely not good.

I'm still not following.
- What did you plug in? If you mean shore power, that just means the charger (aka: converter) kicked on. In that case 11.9v is not indicative of the state of charge. In that case, the charger is likely trying to push somewhere north of 13v but the battery is sucking it up pulling the voltage down because the battery is dead. Using voltage to estimate state of charge only works if there is no charging or loads and the battery has been left to sit for a while.
- What were the sun conditions? Mid-day it might be the panel but same issue with it not being representative of the state of charge.

Shore power was disconnected for the test.
It dropped to 11.5v. I then checked it a few hours later and the panel read 11.9v. Then I plugged shore power back in.

It was actually cloudy.

valhalla360 wrote:

swimmer_spe wrote:

It was close to freezing.

I do not know how often it was on, but when on, it was only for a few minutes.

Fridge was off.
No other power draws. Lights were off.

My hope was that the existing solar panel could allow me to last 1 week in these weather conditions. Since i can't, I will be bringing a generator and running it for a few hours to recharge and have extra batteries to parallel or swap in/out.

How often/long it's on is what counts. Down into the 30's, ours doesn't run much.

Realistically boondocking, you will have the fridge, lights and other draws to add into the mix. Best to do an energy audit and estimate everything (what is the wattage and what percent of the time is it running to calculate total w-hr), then work from there.

For a day or two of boondocking, you can cheat and let the battery run down with the idea of plugging in at the next campground or when you get home to fully top it up.

For longer time periods, you basically, need to plan on replacing what you consume each day (or at least close to it). While you need at least 2 batteries (maybe more with a realistic energy audit), your big issue is sufficient charging. It's borderline running the fridge in cool conditions (when the compressor on-time is low) but once you add in the furnace, lights and other uses, not even close.

Best to parallel rather than swap batteries if at all possible due to the Peukert Effect. The basic idea is the larger the wattage draw relative to the total watt-hours of a batter bank that you draw, the fewer watt-hours you can pull from the battery bank without depleting it.

Example: Let's say you have 2 - 1200w-hr (rating) batteries (aka: 100amp-hr) and are drawing 240w
- If you parallel them, you have 240w out of 2400w-hr which is about 10%.
- If you swap them, you have 240w out of 1200w-hr which is around 20%, then you swap and are still at 22%.

Even though the ratings are the same, you might get 2600w-hr at 11% vs 2200w-hr at 22% once you are done (you would have to get the manufacturers specs for specific impacts but the principal holds)

Easy enough for me to do as I have a good second deep cell and was planning on getting a new one as I have another that is bad. If the good battery is the same, I'll use it, otherwise, I'll get a new one to match the one the trailer came with.

swimmer_spe wrote:

pianotuna wrote:

swimmer_spe wrote:
OP here.

I plugged it back in. It rebounded to 11.9V

I now know.

Do you mean you were charging it? Or just measuring the voltage (at the battery posts would be preferred.

40% is a bit too low.

I was reading off my panel in the trailer. The rebound I am assuming was due to the solar panel. Not bad, but definitely not good.

I'm still not following.
- What did you plug in? If you mean shore power, that just means the charger (aka: converter) kicked on. In that case 11.9v is not indicative of the state of charge. In that case, the charger is likely trying to push somewhere north of 13v but the battery is sucking it up pulling the voltage down because the battery is dead. Using voltage to estimate state of charge only works if there is no charging or loads and the battery has been left to sit for a while.
- What were the sun conditions? Mid-day it might be the panel but same issue with it not being representative of the state of charge.

swimmer_spe wrote:

It was close to freezing.

I do not know how often it was on, but when on, it was only for a few minutes.

Fridge was off.
No other power draws. Lights were off.

My hope was that the existing solar panel could allow me to last 1 week in these weather conditions. Since i can't, I will be bringing a generator and running it for a few hours to recharge and have extra batteries to parallel or swap in/out.

How often/long it's on is what counts. Down into the 30's, ours doesn't run much.

Realistically boondocking, you will have the fridge, lights and other draws to add into the mix. Best to do an energy audit and estimate everything (what is the wattage and what percent of the time is it running to calculate total w-hr), then work from there.

For a day or two of boondocking, you can cheat and let the battery run down with the idea of plugging in at the next campground or when you get home to fully top it up.

For longer time periods, you basically, need to plan on replacing what you consume each day (or at least close to it). While you need at least 2 batteries (maybe more with a realistic energy audit), your big issue is sufficient charging. It's borderline running the fridge in cool conditions (when the compressor on-time is low) but once you add in the furnace, lights and other uses, not even close.

Best to parallel rather than swap batteries if at all possible due to the Peukert Effect. The basic idea is the larger the wattage draw relative to the total watt-hours of a batter bank that you draw, the fewer watt-hours you can pull from the battery bank without depleting it.

Example: Let's say you have 2 - 1200w-hr (rating) batteries (aka: 100amp-hr) and are drawing 240w
- If you parallel them, you have 240w out of 2400w-hr which is about 10%.
- If you swap them, you have 240w out of 1200w-hr which is around 20%, then you swap and are still at 22%.

Even though the ratings are the same, you might get 2600w-hr at 11% vs 2200w-hr at 22% once you are done (you would have to get the manufacturers specs for specific impacts but the principal holds)

pianotuna wrote:

swimmer_spe wrote:
OP here.

I plugged it back in. It rebounded to 11.9V

I now know.

Do you mean you were charging it? Or just measuring the voltage (at the battery posts would be preferred.

40% is a bit too low.

I was reading off my panel in the trailer. The rebound I am assuming was due to the solar panel. Not bad, but definitely not good.

valhalla360 wrote:

swimmer_spe wrote:
Op here.

I am doing a test. Just the furnace on, started with 12.7V. 24 hours later and now it is 11.5V

What was the weather and what percentage of the time was the furnace actually operating? Running for 3-5min out of each hour in mildly cool weather is wildly different from running 30min out of each hour in colder weather.

Did you turn off the fridge?

Were any other 12v draws in operation?

Regardless, take the battery down to 11.5v (90% discharged) frequently and it will quickly lose capacity and need replacement. Generally, you don't want to go below 50% (around 12.1v after the load is removed).

A second battery would likely keep you up around 50% after 24hr but I'm not sure if it was a valid test (not knowing the full conditions).

The next question would be how are you replacing the energy consumed. We don't boondock a lot, so a bit of generator time in the morning & evening along with the 50w panel does fine. If we were boondocking a lot, we would want bigger panels.

It was close to freezing.

I do not know how often it was on, but when on, it was only for a few minutes.

Fridge was off.
No other power draws. Lights were off.

My hope was that the existing solar panel could allow me to last 1 week in these weather conditions. Since i can't, I will be bringing a generator and running it for a few hours to recharge and have extra batteries to parallel or swap in/out.

swimmer_spe wrote:
Op here.

I am doing a test. Just the furnace on, started with 12.7V. 24 hours later and now it is 11.5V

What was the weather and what percentage of the time was the furnace actually operating? Running for 3-5min out of each hour in mildly cool weather is wildly different from running 30min out of each hour in colder weather.

Did you turn off the fridge?

Were any other 12v draws in operation?

Regardless, take the battery down to 11.5v (90% discharged) frequently and it will quickly lose capacity and need replacement. Generally, you don't want to go below 50% (around 12.1v after the load is removed).

A second battery would likely keep you up around 50% after 24hr but I'm not sure if it was a valid test (not knowing the full conditions).

The next question would be how are you replacing the energy consumed. We don't boondock a lot, so a bit of generator time in the morning & evening along with the 50w panel does fine. If we were boondocking a lot, we would want bigger panels.

swimmer_spe wrote:
OP here.

I plugged it back in. It rebounded to 11.9V

I now know.

Do you mean you were charging it? Or just measuring the voltage (at the battery posts would be preferred.

40% is a bit too low.

OP here.

I plugged it back in. It rebounded to 11.9V

I now know.

If that 11.5v is with the furnace off the battery is at 10% SOC.
If furnace is on, turn it off and check the voltage an hour later. Let us know the result.