Go Back   iRV2 Forums > RV SYSTEMS AND TECHNOLOGIES FORUMS > Going Green
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-05-2016, 08:37 AM   #1
Member
 
Join Date: Nov 2013
Posts: 45
RV Solar and A/C when Solar exceed A/C draw

The Wynn's recent blog post got me thinking... See their post here.

Their 900+ watt solar system and LIPO battery was powering their 3000W inverter that was temporarily wired to their roof A/C. Because their solar system produced less power than the A/C drew, the batteries were discharging somewhere at around 35AH while the A/C was running.

Question to the IRv2 forum: What would happen long term to the battery bank if you could generate more power from a solar array than high draw device would consume, but not enough to consume all of the charge controllers output current? The Wynn's showed that they started their experiment with 100% SOC. I assume that meant that their charge controller was either in absorb or float and not pushing much current into their battery bank. As soon as the A/C kicked on, the inverter began drawing significant current from 12V battery and so the charge controller detected a drop in voltage and probably went into bulk charge mode. At that point the the Charge Controller is pushing as much current as possible at 13.4v (I think I saw in the video).

All of that current, plus more current being drawn from the battery was required by the Inverter to create the power needed to run the A/C in the Wynn's experiment.

So .. what would happen to the battery, if the solar system could generate more current in bulk mode than the inverter would consume? Since the voltage would continue to stay below the absorb set point, the charge controller would continue to push as much current as it could (the definition of bulk mode) at 13.4V. That excess current would have to go somewhere.. presumably into the battery...

My question is.. what is the long term impact to staying in bulk mode in a charge controller (because of a significant draw on the 12V system keeping the voltage below the absorb set point) but not enough of a draw to consume all the current that would be produced by the controller?

Could you damage a LIPO battery bank in this way? Would a LIPO battery resist the current enough to cause the system voltage to rise all the way to the absorb voltage? In that case the system would oscillate between bulk and absorb mode I would think.

From what I know about charge controllers they don't seem to have enough intelligence in them to detect this sort of condition and stay in bulk mode but limit the current output to the max required to effectively see 0A at the shunt to the battery bank... (in order to protect the battery from overcharging it).
__________________

__________________
SteveUpp is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 03-05-2016, 11:49 AM   #2
Senior Member
 
cruizerEd's Avatar
 
Winnebago Owners Club
Join Date: Apr 2014
Location: Florida Keys
Posts: 193
This is exactly what an MPP (maximum power point) solar charge controller is designed to do.
An MPP charger pulls current out of the solar cells at the rate that provides the optimum power production and rolls it back as the battery charges.

We have 2000 watts of solar power (12 panels) and only 600 AH of AGM batteries (haven't done the LIPO4Fe upgrade yet). Our panels top off our batteries in no time and the charge controller just rolls back the current going to the battery through the three stages of charging, bulk, absorb, float. We are using Blue Sky controllers and they are very programmable so you can set them up for a variety of battery technologies including LI, but the LI will still need to have a BMS (battery management system) to protect and manage them.

A big killer with running an AC is losses in the inverter. Inverters are seldom as efficient as 90% and under heavy load are probably under 75% efficient. To produce the approximate 2000 watts needed to run a single A/C I estimate you would need 2800 watts of generated solar power, and this would probably require considerable more than 2800 watts of installed solar since panels are rated under ideal conditions that practically never exist.

As for LI batteries. Properly engineered and sized an LI battery pack could safely and effectively run a heavy load such as an AC for hours. Such a pack would probably not be reasonable for an RV and would not be chargeable by a reasonable solar system. It would be reasonable however to setup a system that could for instance run an A/C for a few hours to knock the heat off a bedroom.

In a few years I expect graphene enhanced Lithium Ion (and other chemistries) with a 2 to 10 factor increase in storage and current capacities, making the battery operated A/C even more practical and possibly even providing the capacity for hybrid heavy chassis for RVs.
__________________

__________________
2013 Winnebago Journey 36M Diesel Pusher.
1987 FJ60 Land Cruiser Towed, Blue Ox Tow Bar (do not recommend), SMI Air Force One, 2000 Watts Solar.
cruizerEd is offline   Reply With Quote
Old 03-05-2016, 01:50 PM   #3
Senior Member
 
Join Date: Nov 2013
Posts: 741
Our system runs off the LFE battery suite. Believe the Wynn's system is also LFE and not LiPo.

CruizerEd is correct about inefficiencies of inverter at high load. It takes 2200 W from battery through inverter to A/C. Have noted earlier that we have run Air for 3.5 hours but usually just run at dusk to cool down the cabin. We have trailed battery suite at up to 3.5 kW.
__________________
Reed Cundiff is offline   Reply With Quote
Old 03-06-2016, 10:53 AM   #4
Senior Member
 
CountryFit's Avatar
 
Join Date: Sep 2011
Location: Between the Oceans
Posts: 3,508
Blog Entries: 1
Quote:
Originally Posted by SteveUpp View Post
Question to the IRv2 forum: What would happen long term to the battery bank if you could generate more power from a solar array than high draw device would consume, but not enough to consume all of the charge controllers output current?
in a short answer - no impact, or impact ignorable as only as you set the controller at a right voltage and it functions correctly.

let's think about a scenario - you have a large tote and a small pail standing side by side. the pail sits on a stool so that their rims are in the same level. there is a straight tube linking them at a position below the rims allowing the water to flow between them. a water pump with a level sensor to keep the water level in the tote at a fixed level above the tube but below the rim.

now the tote has the water to the fixed level and starts to flow to the empty pail. when the water in the pail gets to the same level in the tote, what will happen? the water stops flowing! when the level in the pail goes down a little, the flow resumes until it gets to the level again (this is how a float charger in battery system does). as only as the pail and the tote in the same level, there will be no flowing between them.

this is the same principle in my toad charge line i set up years ago. i connect my toad battery and the house battery with a pair of electric wire. there is a fuse on each end of it to protect the batteries in an unlikely event of shorting. when the toad is hooked up to the coach, no matter how many hours i don't need to worry about the batteries, as they will level. my coach battery is set at 13.4v floating, a perfect voltage for the toad battery. today my toad battery is 6 years old, no ill effect still going strong.

have fun with your solar system; cool with the a/c if you go with the wynns' .
__________________
2000 Country Coach Intrigue 40', ISC 350
2014 Ford C-Max Energi
CountryFit is online now   Reply With Quote
Old 03-23-2016, 01:09 AM   #5
Senior Member
 
Join Date: Feb 2016
Location: Jamestown ND
Posts: 102
Ok i have a question after reading this, I have a FlexMAx 60 solar controller ($500ish model), approximately 550Ah @20A between Lead acid and AGM batteries, I am pulling from 4 x 100W panels actually producing about 150W-200W per hour in most lighting up north here since we have shortish days right now. AND they were not tilted when I checked them.

My question on the inverter inefficiency since I have a Cotek ST1500-112 Pure sine wave inverter (also a $500ish model) its rated at full load of 88% efficiency, I was figuring the partial load efficiency would be in the 82-85% range.

i am not powering my roof unit as its extremely inefficient, I am testing 2 options
A. a Hi-efficiency portable 10,000 BTU unit that draws 630W-700W (depending on fan speed) AC when the compressor and fan are both running

B. Hi-Efficiency EnergyStar rated 8,000BTU unit that pulls 750W AC when on MAX

Both are rated for 350 sqft, the RV in use has had the insulation redone and will have all windows tinted out.

My question is, although my panels currently are surely undersized what should i expect to see for DC amp draws with either of those loads?

I do know that on an "average" day except on the hottest days of summer, the compressor usually runs for a total of 20 minutes for each hour, sometimes 30 minutes then cycles to fan. This applies to both units being used in a popup camper of similar size with canvas walls and windows with no insulation
__________________
MudiGGer25 is offline   Reply With Quote
Old 03-23-2016, 10:39 AM   #6
Senior Member
 
powercat_ras's Avatar
 
Winnebago Owners Club
Solo Rvers Club
Join Date: May 2015
Posts: 1,014
> DC amp draws with AC load?

Inverter draws aproximately 1 Amp DC per 10 Watts AC load over its base no output DC current draw, that is typically well under 1 Amp DC.

The latest split Air Conditioners use DC inverter technology to drive the compressor at variable power levels based on the cooling demand. Here is an example of a 20 SEER rated 12,000 BTU AC for under $ 400:

GREE 1 Ton 20 SEER NEO Ductless Mini-Split Indoor Unit 115 V
__________________
Randy - Manhattan, Kansas
2015 Vista 27N
2016 Honda HR-V
powercat_ras is offline   Reply With Quote
Old 03-24-2016, 07:08 PM   #7
Senior Member
 
Join Date: Feb 2016
Location: Jamestown ND
Posts: 102
Quote:
Originally Posted by powercat_ras View Post
> DC amp draws with AC load?

Inverter draws aproximately 1 Amp DC per 10 Watts AC load over its base no output DC current draw, that is typically well under 1 Amp DC.

The latest split Air Conditioners use DC inverter technology to drive the compressor at variable power levels based on the cooling demand. Here is an example of a 20 SEER rated 12,000 BTU AC for under $ 400:

GREE 1 Ton 20 SEER NEO Ductless Mini-Split Indoor Unit 115 V

That's not shabby at all and the price point isnt terrible either, only downside i really see is i think a hole would have to be cut in the side of the RV for the unit to expel the hot air, but i could not load the installation instructions to be sure.

I am just using what i have available before investing into something else lol
__________________
MudiGGer25 is offline   Reply With Quote
Old 03-24-2016, 09:41 PM   #8
Senior Member
 
Join Date: Mar 2014
Posts: 909
Take a look at the 4 part solar update over with Paul and Nina at Wheeling It – Living the Fulltime RV Dream with 12 Paws, 40 Feet and the Open Road. Lots of information from long time solar users. Great upgrade, got data points, lithium and running the AC from the solar/lithiums/Magnum Hybrid.
__________________
Gary 2017 Dutch Star 4369 Spartan
HWH Active Air Centramatic wheel balancers
Box Elder, SD and the road
ghaynes754 is offline   Reply With Quote
Old 03-25-2016, 10:14 AM   #9
Senior Member
 
BatteryPro's Avatar
 
Join Date: Jan 2015
Posts: 302
PV Charge Controllers Do Not Regulate Current

Quote:
Originally Posted by cruizerEd View Post
This is exactly what an MPP (maximum power point) solar charge controller is designed to do.
An MPP charger pulls current out of the solar cells at the rate that provides the optimum power production and rolls it back as the battery charges ...
Charge controllers do not pull current nor do they regulate current. The load, be it battery, DC loads or appliances, dictate how much current is flowing up to the maximum that can be produced by the PV solar modules.

In the scenario mentioned, if the PV controller is in bulk mode, that means it is allowing the full available current to flow without any regulation of voltage. If the battery voltage is lower than the voltage on the system, current will flow from the battery to power loads. If the system voltage moves higher than the battery voltage, current will flow into the battery.

With LFP batteries, once saturation is reached, the voltage will rise very quickly. Since the loads are holding the voltage down, this won’t happen until the loads are reduced. Once voltage does rise, the controller will eventually begin to regulate (CV) the voltage. It appears that the controller is regulating current but it is the load(s) that affect current flow. If you take away all loads, no current will flow.

So, there is no harm to anything in the system just because the controller is in the bulk mode.

Larry
__________________

__________________
I have a vast knowledge about PV solar, batteries and inverters. I'll try to provide the best answer if I know it and hopefully correct some "Campfire" talk. Full-time 1999-2004. Part time now. '92 Hawkins, 360AH Lithium Battery, 1480 Watts PV solar.
BatteryPro is offline   Reply With Quote
Reply

Tags
solar



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Headlights: strength and excessive draw Durabil Class A Motorhome Discussions 4 09-17-2014 02:23 PM
Inverter Power Draw and Battery Capacity Butte64 Palazzo Motorhomes 7 05-06-2014 08:19 PM
Advantages getting tires that exceed GAWR (rear)? Oregonbound Trailer Towing and Tow Vehicles Discussion 23 04-18-2013 04:39 PM
2a and 6a draw when on shore power - sound about right? vsheetz RV Systems & Appliances 2 01-23-2013 08:11 AM
RV converters and amperage draw Ray,IN RV Systems & Appliances 2 02-26-2011 10:53 PM

» Virginia Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 06:10 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.