Solar/Inverter Question

Thanks for the replies. My inverter remote has arrived and I'll be mounting that inside this week or next.
The battery monitor and another panel are on the short list.

flyfishing48 wrote:
Long time RVer, new solar user.

Just bought a new fifth wheel that came with solar. Equipment is:
One solar panel that I think is around 170 watts, a Zamp Solar Charge 30 amp Controller, a Xantrex X2000 Inverter. I should add we have a pair for 6 volt 235 AH Deep Cycle (Crown) Batteries.
Just did 3 nights dry camping, despite being in AZ, it was light overcast for the 3 days. System seems marginal under these conditions for using some lights, water pump for normal stuff, ran the furnace one morning for a few minutes and ran the coffee pot each morning. I did notice the solar panel is dirty from a desert shower on the previous trip. So that didn't help the cause I am sure.

I am not getting my mind around how to run the inverter. Mostly confused about what mode use, Auto On, standby, power save ?

Keystone mounted the inverter off the floor joist in the basement, so not to accessible for use. I will be getting the remote for it.

But I would love to hear from some experienced user about how to best use this system.

It is HIGHLY likely that if you just add one more 170w solar panel in parallel on your rooftop (which is fairly simple to add) you will not need to worry about power anymore. 340w on a sunny day should be able to add 90-100AH back into your batteries, and you likely aren't using more than 50-80AH of power daily.

Add a battery monitor is SOOOOO helpful as it pertains to all things batteries/charging. (And, if you are a nerd like me you'll find it interesting to see how much power each little thing in your RV uses). I installed a very good monitor for ~$45 (Aili...you can google it). A battery monitor really should come standard on an RV since they are so very helpful.

Happy Camping!
Chris

flyfishing48 wrote:
the furnace seems like the biggest user. When it turns on the battery voltage takes a pretty good dip, so I am thinking it’s pulling a lot from the batteries.

It's usually around 7 amps, and with fully charged batteries you shouldn't see that big of a dip. Maybe a tenth or two.

One approach is start smaller (like the OP) and then expand the system. As the saying goes you'll use all of the solar power and then want more.

My first purchase was a battery monitor. Several months later I knew 500W would be OK. So bought 3 panels in 2014 for 750W and have no reason to upgrade.

BFL13 wrote:
I don't understand how Wh work with inverters. I changed my Trimetric to read watts instead of amps and the initial draw with the small MW was 700 watts but that rose to 900 watts with the voltage getting lower. The Tri only does AH so I never found out what it all came to in Wh.

The inverter tries to maintain the 120v load, so it draws more DC amps or watts to try to keep up as battery voltage falls. So that skews whatever is going on. I don't think it makes it easier to use Wh instead of AH!

I still have not tried that with a DC load and no inverter in the mix, to see what it says in watts instead of amps as voltage falls. Someday maybe. :)

Don't worry about measuring too accurately for design purposes. It's best to add a fudge factor anyway as sometimes, you might warm up an extra cup of coffee in the microwave other times not. Plus there are inefficiencies when converting power. You lose some charging the batteries and then you lose some more pulling it out with the inverter.

For these calculations, W-Hr is simply voltage times amps. Then at the end add 15-20% for losses and you should be in pretty good shape. If your inverter is on all the time, you probably want to look up what it consumes in the resting state but good ones are in the milowatt range.

Lead Acid batteries do have issues when you get into large demands.
- Yes, as the battery voltage goes down, it will take more amps to generate the watts demanded but if you have a 20% fudge factor, it shouldn't be a big issue.
- Probably the bigger issue if you start pulling 1000w or more is the Puerket (spelling?) effect. Battery amp-hrs are rated based on how many amps are being drawn relative to size. The higher the amp draw, the lower the amp-hrs available. If you are pulling 1000amps to turn over a big diesel engine, the same battery will have a fraction of the available amp-hours. Not an issue if the diesel starts in 2-3 seconds. If you compare to a basic trailer just running some lights and maybe a furnace fan, it may be pulling under 10 amps. If you have a 200amp-hr battery, that's a 20hour rate (a common spec for batteries) or If you are trying to pull 100amps over a long period of time, that would be a 2 hour rate and the available amp-hr will be much lower. Of course, it would be unusual to pull 100amps for 2 hours straight but even 20-40amps would have an effect.

I don't understand how Wh work with inverters. I changed my Trimetric to read watts instead of amps and the initial draw with the small MW was 700 watts but that rose to 900 watts with the voltage getting lower. The Tri only does AH so I never found out what it all came to in Wh.

The inverter tries to maintain the 120v load, so it draws more DC amps or watts to try to keep up as battery voltage falls. So that skews whatever is going on. I don't think it makes it easier to use Wh instead of AH!

I still have not tried that with a DC load and no inverter in the mix, to see what it says in watts instead of amps as voltage falls. Someday maybe. :)

vahalla360, Agree but he also used DC power which could be converted to Wh but it's more common to convert to Ah and use the common battery Ah spec. Either way it's an estimate, but helpful.

flyfishing48 wrote:
Great discussions, this is very helpful.
For my none inverter usage, the furnace seems like the biggest user. When it turns on the battery voltage takes a pretty good dip, so I am thinking it’s pulling a lot from the batteries.

Furnaces do use more power for the motor. But you posted that you ran it for a few minutes one morning, which would be a limited power usage. 8A for 10 minutes is 8/6 = 1.3Ah for example.

Great discussions, this is very helpful.
For my none inverter usage, the furnace seems like the biggest user. When it turns on the battery voltage takes a pretty good dip, so I am thinking it’s pulling a lot from the batteries.

"Rules of thumb can often be way off the mark."

Yes but getting solar interested RVers to do a survey isn't easy. And you gotta start somewhere...so 1 to 1 is where I suggest they start.