Solar charge controller analysis paralysis

[shanna7]

I just purchased this 50Ah LiFePO4 battery and this 100W, 12V solar panel, and I estimate I'll use 300-400W/day, and max load of ~9A @ 12VDC. I camp mainly in the PNW, so I need to eek out as much juice as possible from a panel ideally even if skies are somewhat overcast.

Now I need a solar charge controller, but I keep stumbling. I'm not finding current info about choosing solar charge controllers for LFP batteries for small systems.

I know that MPPT is not necessarily worth it for the little systems (at least with with SLA batteries), but most companies seem to be recommending MPPT controllers with LiFePO4 batteries. I don't quite get if it has to do with the 14.6 charging voltage or if it's just the perception of MPPT being better than PWM in general.

Bioenno recommends this one, a cheapie "MPPT" from China you can get on E-bay for $10, and they are reselling it for $89. Of course and whether its actually MPPT is debatable. I'd buy it, but I want something with better indicators, such as this this "MPPT" one, which also may not actually be MPPT. I am a bit concerned that I'll be "getting what I paid for" though. I think the Morningstar Tristar PWM and the Genesun GV-10 MTTP are decent options, but I know there are more out there, I just don't know how to tell if they are LFP compatible.

So, if you were setting up a system with the above components, what solar controller would you buy for this setup and where would you get it from? Ideally I want to spend <$200, but if there's something for <$50 that is 95% as good as a a $200 controller, I'd also like to consider it.

THANKS IN ADVANCE!

[jss06]

You need to make sure that whatever charge controller you purchase can be programmed to match the requirements of the battery. That battery specifically states that it needs to be charged by a LFP charger. Using the lead acid battery settings can cause damage and possibly cause the battery to catch on fire.

You need to find out the charging specs of the battery and then find a charge controller that can be programmed to match those specifications. The blue sky controller I use can be programmed like that but it is specifically for high voltage panels.

[MtnDon]

I would be uber cautious about trusting the health of my $500 LFP battery to some cheap Chinese controller off ebay. A least if you buy the charger the seller recommends and something goes wrong you should have a reasonable chance of getting some warranty service. I would hope. Or just buy their PWM, 10 amp controller as long as they state full compatibility and warranty. I'm not convinced you will realize much gain with the MPPT and only a single PV panel.

I'm guessing that they have had those controllers tweaked to their specs as the instruction manual states they are for LFP only. The Chinese can be very accommodating when they are approached with a large enough order. Whether they actually do it right on merchandise being sold for low-ball prices is another thing though.

[Shadow Catcher]

All of the tests of Chinese suposed MPPT controllers seem to come up short.

My suggestion is a Morningstar Sun Saver MPPT It is programa
http://www.morningstarcorp.com/products/sunsaver-mppt/

" USB MeterBus Adapter for laptop compatibility. PC MeterBus Adapter for RS-232.
Fully adjustable user selection via on-board preset switches or customized with PC connection.

[shanna7]

I'm guessing that they have had those controllers tweaked to their specs as the instruction manual states they are for LFP only. The Chinese can be very accommodating when they are approached with a large enough order. Whether they actually do it right on merchandise being sold for low-ball prices is another thing though.

Good point. Leaning toward the Morning Star MPPT, but the Windy Nation PWM w/LCD is also a strong candidate. It's also user adjustable.

[Shadow Catcher]

The five year warranty from Morningstar is hard to argue with.

[ywhic]

Keep in mind not running the battery down to less than 50% to much or you will kill it. With that 100w panel and avg good day of 5-7 hours of good daylight your only putting in 400-600w into bank with nothing on. If your using 400.. Well you get the idea.

[shanna7]

Is that true for LiFePO4 batteries as well?

[MtnDon]

Is that true for LiFePO4 batteries as well?

Check with the manufacturer, but usually operating between 20% and 80 to 90% is fine for LFP, with no worry about being left in storage within that range.

[jss06]

Is that true for LiFePO4 batteries as well?

Check with the manufacturer, but usually operating between 20% and 80 to 90% is fine for LFP, with no worry about being left in storage within that range.

One of the pleasures of LFP, you can get the same storage capacity out of a battery half the size.

[OverTheTopCargoTrailer]

Shanna7

Never fear Dr Lithium is here, with 2,000 ah on my trailer overthetopcargotrailer.blogspot.com
Your in good hands.

1.) Be paranoid talking advice from folks who DON'T OWN ANY lithium batteries & don't charge if below 36F battery temp. Keep battery inside your trailer 40-80F is best.

2.) PMW controllers are garbage , but should not hurt your batteries. They will never deliver close to 14.5 v to hurt your battery.

MPPT is the very best, buy a larger unit and you can add more panels latter. If you can program set max absorb at 13.9 volts that gives you about 98% charge.

Never run your battery below 10 v or 2.5 v per cell. Usually cut out at 11 v is best. Almost always your battery will sit at 13.3 volts. I just use a $20 volt light and watch that. Don't worry about a bms in an RV application, watch the volt meter.

On a good day with a 100 watt panel you can pick up 500 watts, if you use daytime power under 80 watts 6-7 amps your battery will never go below 13.0v usually.

Congrats for joining the lithium club, as far as I know your member #2

What battery did you buy
GBS ? or CALB ? include a link if you can.

Cheers ottct

[shanna7]

We got this battery: http://www.bioennopower.com/products/12 ... w-pvc-pack

And this solar panel: http://m.ebay.com/itm/100-Watt-100W-12V ... nav=SEARCH

And I got this charge controller, thinking that since it was programmable and relatively inexpensive I can always upgrade later: http://www.windynation.com/Charge-Contr ... p=YzE9MTc=

I knew it wasn't widely adopted yet, but shocking to hear we're such early adopters! Might have to pick your brain more ...

[OverTheTopCargoTrailer]

Hi Shanna7

If you can send your battery back within the 30 days I would say get this one, their bms boards are $9 each ( one per cell ) you don't really need them.


http://elitepowersolutions.com/products/product_info.php?cPath=25&products_id=91


http://elitepowersolutions.com/products/product_info.php?cPath=42&products_id=152

Great price of $179 on 100 flex panels, you could almost run them straight to your battery as long as your watching voltage and disconect at 14 volts on your battery meter.

The lithium are really 5 times better, however we are really preaching the earth is round in 800 BC - the lithium lifep04 are really 30 years old , they are in every power tool, 300 million have been sold , but RV guys like lead invented in 1852 - as its proven technology.


[url]
http://overthetopcargotrailer.blogspot.com/[/url]
Cheers ottct

[OverTheTopCargoTrailer]

I have a set of 4 x 255 watt panels flat on my trailer roof. With flooded batteries best day ever was 2600 watts, with lithium batteries I can easily pull 5,000 watts.

It's the same example of pmw vs. mppt you can get 30-50% loss.

With flooded batteries if your volts are 12.6 you need 13.4 or better to charge. On lithium if your battery volts is 11.246 v and your source is 11.250 it will start charging ....if your source is 16 volts it will also charge , no problem at all .....BUT YOU OR A BMS MUST DISCONECT WHEN BATTERY VOLTS REACHES 14.5 VOLTS, I RECOMMEND 14.0 VOLTS IS SAFER to disconect.

If battery volts goes over 14.5 you can / will distroy your battery a 10 - 20 amp charger is max for your batteries, or 200 250 watts in panels is good also.

My advice is watch your battery while charging and get used to how / when it charges. You should get about 600 watts out of your batteries when new, overtime that will drop.

Cheers OTTCT

[Kaz]

I ave been using one of these for the last 4 years and couldn't be happier. I have had no issues and a lightning strike to the pole my 100 watt solar panel is mounted to. http://www.ebay.com/itm/30-Amp-Provista ... xy4~BSSb6-