Hello

[Cathy smith]

Hello everyone
Currently fulling in my Travel trailer. Loving retirement on a budget! Built my own solar system and have modified it over the years from lead acid to lithium. Am still learning, still feel like a newbie.

Need help with my Xantex Prowatt Inverter 2000. The battery tests out at 13.6v at the battery terminals and the inverter terminals. The display reads 13.1. Tried different battery and same loss in readings. My inverter is little over 3.5 years old.
Called Xantex and they suggested unplugging it and letting it set for twenty minutes to reset it. Still have loss? I noticed my batteries seeming lower last few months or maybe that was cloudy weather. Lol
Am I loosing power or have a faulty display?
Thank you
Cathy

 

[snoobler]

Are you confident in the accuracy of the meter?

If you've confirmed the case on multiple meters sounds like a calibration error with the Inverter.

 

[Cathy smith]

I have only used this meter. Did tests on it when I first got it. Tested out spot on.
I think it is a calibrated issue too rather than a display issue but my question is will that effect a loss in power. The inverter is rated at 90 percent efficiency. 13.6 to 13.1 is 30 % loss using my lithium battery soc chart. I am still a newbie but that seems like a lot. And thank you for you help. I am learning.

 

[snoobler]

I have only used this meter. Did tests on it when I first got it. Tested out spot on.
I think it is a calibrated issue too rather than a display issue but my question is will that effect a loss in power. The inverter is rated at 90 percent efficiency. 13.6 to 13.1 is 30 % loss using my lithium battery soc chart. I am still a newbie but that seems like a lot. And thank you for you help. I am learning.

Too many variables to equate it to a 30% loss based on voltage. LFP has a VERY flat voltage curve during discharge, so it may not have a significant impact on the usable capacity of the cell.

Example: Let's say the inverter is going to cut off at 10.5V. It follows that the battery will be at 11V, which is a VERY low state of charge allowing you to capture almost all of the LFP capacity.

My only concern would be with over-charging if the Xantrax can charge from AC input. If the BMS is fully operational, then it should protect the battery.

Actually, if the Xantrax can charge via AC input, I would do that and see what the voltage deviation is during charge.

Always worth double checking that all your connections are secure and properly torqued.

 

[Cathy smith]

Thank you for the information. The inverter does not charge the battery. I only use solar/morning star controller.

I try not to use my batteries lower than 12.9. Except for voltage lag when using coffee pot. Can you go lower? Or should you?

 

[snoobler]

Under load, absolutely. No reason not to allow whatever sag is needed provided the current is within cell and BMS limits, AND you're above an acceptable SoC.

If you don't have a battery monitor, you should get one. Knowing the true SoC gives you a lot of flexibility.

These things are meant to deep cycle and shallow discharges don't necessarily extend life dramatically. What seems to extend cycle life is more gentle charges to a lower peak voltage with lower current and longer absorption time.

3.45V/cell seems to be the sweet spot allowing for a short enough absorption time to get fully charged and minimizing stress while still getting to 98%+ SoC. You can get to 95%+ SoC @ 3.4V/cell, but your absorption time will be very long. In either of those scenarios, your array will only output what the battery needs + your loads, so you may see your array power drop lower than you think is normal as the charge current is tapered.

 

[Cathy smith]

Thank you! for the information. I think I understand it but I need to chew on it.
Definitely need battery monitor!

 

[Hedges]

I noticed my batteries seeming lower last few months or maybe that was cloudy weather. Lol
Am I loosing power or have a faulty display?

PV panels have become the cheapest part of the system, so over-paneling can be a good way to deal with weather and extra loads.
Current will max out at what the charge controller can deliver. Extra panels all of same orientation will have it clip, producing max current longer, and achieving higher current under overcast conditions. Panels (or series strings of panels) with multiple orientations will produce max power for more hours - about 50% extra PV capacity can be added that way.

Lithium can take fairly high charge currents, like 0.5C, so if added panels let SCC deliver higher current they are still OK in mild weather. If your location gets cold, calculate what charge current extra panels would deliver and consider adjusting low temperature cutout. I think LiFePO4 needs to be < 0.1C charge rate down near freezing. If SCC can deliver 0.2C I would raise the temperature setting. Keeping the batteries at a comfortable temperature avoids having the protection kick in and stop charging.

Snoobler indicated lower charge rates extend life. I don't know the impact of 0.5C, and I think off-grid PV doesn't need higher than 0.15C to recharge during one day. It would be good to have enough PV to supply loads during the day and regulate charging to a flat 0.15C rate, but most SCC are unaware whether their current is flowing to the battery or to the inverter. Some systems can adjust current to regulate battery charge rate, but probably not something your charge controller can do.

 

[Cathy smith]

Good Morning
You raised a good point about adding solar panels that I have often considered. I have room for two more 100 watt panels on my roof. Have five up there now.
I am going to have to soak in the temperature information for charging. I live in az so out winters are warm like a few nights of barely below 32 degrees. The batteries are kept warm as they are inside. However I plan on traveling.
thank you
Cathy

 

[Hedges]

Some people have portable panels they can place in the sun with a tilt. Big ones are awkward, but 100W wouldn't be so bad.

What is the capacity of your battery?

If 100 Ah x 12V = 1200 Wh, then 7 x 100W = 700W PV is about 0.58C
(Of course, panels deliver a bit less than their rating most of the time, and flat on the roof produces less when sun is low in winter.)

If 320 Ah x 12V = 3360 Wh, then 700W PV is about 0.21C

The following link shows max charge rate vs. temperature for some brands. Near freezing, about 0.12C to 0.20C for some of them.
If your BMS has adjustable low-temperature cutout for charging, you could adjust it higher depending on the "C" rate your system can charge at.
Some BMS may not have a temperature cutout, in which case you might manually shut off charger if expecting a freezing night and bright morning. Some people insulate their battery pack.

Why you cannot charge LiFePO4 below 0 degrees Celsius

...I glazed over...Soooo far past me...... but, does this mean that the claims of the -20F chargeable LiFePO4 cells could be true? Based on what i’ve read in this forum, not for any practical use. I’m no expert on the matter, though.

diysolarforum.com

BigBattery 170Ah PowerBlock low temp cutoff does something for charging, but not sure at what temp or what happens with discharging

Test results video at end of post with description. Regarding Will Prowse's review of these nice batteries: Then Will commented on that video with this update: "Correction to this video: Unfortunately, I was correct about questioning the low temp charging protection on the powerblock...

diysolarforum.com

 

[Cathy smith]

I have two 200 ah lithium batteries with 400 watt solar. They are flat on roof so I get 288 to 318 watts when I checked. The batteries charge in a few hours in the sun. Adding two more 100 watt panels on roof for a total of 600.

I live in AZ so low temp cut off is not an issue. I do not have a low temp cut off. also my batteries are inside where it is heated.

I appreciate the video/links. Am a Will Prose fan!

 

[snoobler]

Some people have portable panels they can place in the sun with a tilt. Big ones are awkward, but 100W wouldn't be so bad.

Like this:

Cheap Dual Flex Panel Mobile/Tilting Stand

Here’s a super lightweight and cheap adjustable stand design that I use for 100w flex panel pairs. Each unit costs

diysolarforum.com

Also has the advantage of being able to take advantage of shade and still get some solar.

 

[snoobler]

I have two 200 ah lithium batteries with 400 watt solar. They are flat on roof so I get 288 to 318 watts when I checked. The batteries charge in a few hours in the sun. Adding two more 100 watt panels on roof for a total of 600.

I live in AZ so low temp cut off is not an issue. I do not have a low temp cut off. also my batteries are inside where it is heated.

Also living in AZ, trust me that there are areas that definitely see well under freezing. Our place is at 6700 elevation, so the occasional dip into the single digits is relatively common.

HOWEVER, if your batteries are inside a temperature controlled environment with no chances of dropping below freezing, then there is no concern.

Just know that charging LFP below freezing causes immediate and permanent capacity loss. Some batteries have their own low temp charge protection provided by the BMS. If yours do, then again, no concern.

 

[Cathy smith]

I am at 800 ft with Saguaros in winter and in the summer I venture towards your elevation to cool down. Used to live at 6200.
Batteries are inside my trailer in an heated environment.

Eventually I was planning on getting a Victron controller if my Morningstar can’t be programmed for low temp cutoff.

 

[snoobler]

What morningstar?

 

[Cathy smith]

Like this:

Cheap Dual Flex Panel Mobile/Tilting Stand

Here’s a super lightweight and cheap adjustable stand design that I use for 100w flex panel pairs. Each unit costs

diysolarforum.com

Also has the advantage of being able to take advantage of shade and still get some solar.

Thanks! This is a great idea.

 

[Cathy smith]

What morningstar?

Tristar 45 mppt

 

[Hedges]

I have two 200 ah lithium batteries with 400 watt solar. They are flat on roof so I get 288 to 318 watts when I checked. The batteries charge in a few hours in the sun. Adding two more 100 watt panels on roof for a total of 600.

With 4800 Wh, charge rate is just 0.066C today, grow to 0.10C
Some people have smaller battery, larger array, so for them I suggest higher temperature.
You should be safe down to zero degrees C.
Batteries have a lot of mass, so will remain warm for some time, also remain cold.
Just need a temperature sensor and 0C/32F cutout in the BMS if you'll be somewhere cold.

When I used an RV (on my land) or car camping (ski area parking lot), sleeping bag kept me warm but vehicle got cold. Things in it could freeze overnight.

 

[snoobler]

Tristar 45 mppt

I just checked the manual. This controller was designed completely around lead-acid batteries and has NO provisions for or direct support of Lithium batteries besides the ability to set custom charge values. Additionally, the addition of the temperature sensor automatically enables temperature compensation intended for lead-acid batteries and will damage your Lithium batteries.

https://www.morningstarcorp.com/wp-content/uploads/operation-manual-tristar-mppt-en.pdf

Table 4-2 indicates the temperature compensation is fixed for all battery types.

If you ever need low temp protection, you must protect against the Tristar with a secondary means.

 

[Cathy smith]

I just checked the manual. This controller was designed completely around lead-acid batteries and has NO provisions for or direct support of Lithium batteries besides the ability to set custom charge values. Additionally, the addition of the temperature sensor automatically enables temperature compensation intended for lead-acid batteries and will damage your Lithium batteries.

https://www.morningstarcorp.com/wp-content/uploads/operation-manual-tristar-mppt-en.pdf

Table 4-2 indicates the temperature compensation is fixed for all battery types.

If you ever need low temp protection, you must protect against the Tristar with a secondary means.

Thank you for checking. I am confused. I called both Morningstar and Renogy and manually set the controller to work with lithium according to what they sent me. I turned off equalization. My new batteries have similar settings.
this controller will damage my new batteries?