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diy solar

Always on Bulk mode..

Treva31

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Joined
Jul 12, 2021
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Hi everyone!

I have a LiFePO4 100AH battery.
I am charging it with a Victron SmartSolar MPPT 75/10.

The battery says:
Operating voltage: 12.8
Charging voltage: 14.6
And it says for optimum performance you must charge at 14.6v.

My chargers battery settings are set to:
Absorbtion voltage: 14.2
Float voltage: 13.5

Should I change the settings?

The battery's LCD says it's on 100% and 13.4v but the charger always stays on Bulk mode.



Also, I have 300W of solar panels but they never seem to actually output more than 110W, is that normal?
It's a 200W and a 100W in paralell and outputs around 15-16v 7A.


Any upgrade suggestions?
I'm strongly considering adding another identical battery in paralell.

Thanks :)
 
300w should do OK into a 100ah battery. Need to figure out the solar. Any iota of shade on them? Have you tried one panel at a time?

If you disconnect a panel measure and post the Voc and the Isc. (opened circuit voltage and short circuit amps respectively)
Compare the results to the specs and post what you find.
 
14.6V / 4 cells = 3.65V/cell
People typically top-balance LiFePO4 to that voltage once, then set charge controller a bit lower.
But you do want it to charge high enough that BMS does balancing. Have more detailed documentation on the battery?

14.2V / 4 cells = 3.55V/cell sounds good as a charge voltage.
13.5V / 4 cells = 3.375V/cell. I'm less clear on optimum float voltage for these batteries.

What are the complete specs on the two PV panels? picture of label or link to data sheet?
Normal would be 70% to 85% of label wattage, sometimes higher in certain (cold) conditions.
They are probably different enough to drag down performance. But I would have expected them to at least behave like 200W, deliver 140W to 170W.
Measured Voc and Isc of each as Time2Rolls says would also be good.
 
I am charging it with a Victron SmartSolar MPPT 75/10.
This charger will limit your charging to 10A so its never going to be able to use more than your charge voltage at 10A (14.2V x 10A = 142W).
You maybe better off getting a second Victron, perhaps a 75/15 for your 200W panel and run 2 independent charging systems to your battery.
 
Thanks guys.

Here is the battery manual.

I will test the panels tomorrow.
 

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A 100W combined in parallel with a 200W panel will not typically give 300W, it's probably closer to 200-240W under ideal conditions. You can search "combining solar panels" for the reasons why.

The charger will stay in bulk mode until you hit absorption voltage - 14.2v per your numbers. The battery LCD % reading is not going to be very useful since it most likely uses voltage and not AH to show SOC.
 
Manual says if you do not charge to 14.6V you won't get full capacity. That's fine, OK to get 95% and have it last longer.
It say to charge to 100% before storage, and top off every 3 months. Other cells, we see a recommendation to store around 50% SoC.

It says charging on lead-acid setting could take 10 hours, otherwise less stored power. You can see how it performs for you. Possibly raising charge voltage will increase capacity and you decide it is worth possible shorter cycle life.

I don't see anything about accessible or adjustable BMS parameters.

It does say charging temperature range zero degrees C and above. I didn't see mention of BMS preventing charge below zero C. If it doesn't that will be up to you. Charging while battery is blow freezing would ruin it.
 
I don't see anything about accessible or adjustable BMS parameters.

My charger lets me select an Absorbtion and Float voltage value.
Should I change Absorbtion to 14.6?
Leave Float on 13.5?
 
Should I change Absorbtion to 14.6?
Leave Float on 13.5?
14.2 absorption, 15 min absorption time and 13.5 float are values I would use.

The battery has a power limited BMS with a suggested charge of 20 amps.

Are your pannels connected in series or parallel, with panels of different power should be in parallel. The controller is 10 amps max output.

Mike
 
Volta is minimally known but I have heard pretty good things, Will has not done a teardown that I am aware of.

When you push LFP to 3.650Vpc which is at Max Allowable Voltage (beyond full) the vast majority will never reach it because of at least one cell reaching 3.65 before the others and prompts a BMS HVD (Hi Volt Disconnect). Below 2.850 and above 3.500 Volts per cell only represents 5% total capacity at best. Nominal Voltage for LFP is 3.,200Vpc with the full working voltage range being 3.000-3.400 where the vast majority of the energy is stored, LFP has a very flat voltage curve.
Vpc = Volts per cell. Multiply by 4 for a 12V pack, as it takes 4x 100AH cells to make a 12V battery.

NOTE: You can charge LFP cells to 3.650 and fully saturate them to the point where they do not take any more amps. Within One Hour of stopping charge, those cells WILL settle to 3.550 +/- a bit, within TWO Hours they be settled at 3.500 +/- a bit. This is NORMAL !

I run 24V with multiple battery packs in the bank, here are my setting for my Midnite Classic 200 Solar Charge Controller, your Victron is similar. This never triggers an HVD and allows for the cells to nicely top off and balance up. The BMS per the specifications will allow for a max of 50A or 0.5 C-Rate (which is normal). A WORD, when pushed to max charge amperage, the battery cells will warm up, if there is one weaker cell it will be a Runner and reach "Full" well ahead of the others. This can be dealt with somewhat with the charge profile used. This is where being "conservative and not greedy" to squeeze Amp Hours works to your benefit.

Important Note: The BMS is the Guard dog / Watcher. It protects the cells within the battery pack. It does NOT control the voltage / amperage going to each cell, it just watches them so they do not go below 2.50 or above 3.65 which is the allowable functional voltage range. When a "fault" condition occurs it cuts off the battery. The Solar Controller & Inverter MUST manage the cutoff thresholds and act prior to the BMS being triggered to force a state.

All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

You should also follow the link in my signature to the LFP Voltage Chart and grab that too... The downloadable PDF is Hi Rez.

Good Luck, Have Fun
Steve
 
14.2 absorption, 15 min absorption time and 13.5 float are values I would use.

The battery has a power limited BMS with a suggested charge of 20 amps.

Are your pannels connected in series or parallel, with panels of different power should be in parallel. The controller is 10 amps max output.

Mike
Cool thanks.
Panels are in parallel.
 
Thank you so much guys, I will sleep a lot better knowing I have the right settings!

For completeness here are the other options I have available:
 

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Although the battery voltage is still never going above 13.4 and the charger is still always on Bulk mode, despite hours of over 100W available from the panels..
 

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300w should do OK into a 100ah battery. Need to figure out the solar. Any iota of shade on them? Have you tried one panel at a time?

If you disconnect a panel measure and post the Voc and the Isc. (opened circuit voltage and short circuit amps respectively)
Compare the results to the specs and post what you find.
This was measured in pretty good sun at midday in Brisbane Australia.

I'm actually not sure not what Wattage my old larger panel is, maybe 180 but the Voc is 20.2v.
I can't measure the Isc without a clamp meter right?
But when it is connected to the charger on its own the charger says:
88W , 14.7v , 5.8A

The smaller panel is 160W and shows a Voc of 21.7v.
When connected to the charger on its own the charger says:
55W , 18v , 3A

These were both off ebay so perhaps the specs were exagerated?
The large one is over 5 years old, new one is maybe 3 years old.

But as noted, my charger can only do 10A and in thier current state these are providing 8A+ so its not much of an issue unless I upgrade the charger.
 
Although the battery voltage is still never going above 13.4 and the charger is still always on Bulk mode, despite hours of over 100W available from the panels..
They will sit at that voltage for a long time before it comes up. How many hours has it been giving you 9 amps? You will need to consider giving it 100 amp-hours before full charge is achieved.
 
They will sit at that voltage for a long time before it comes up. How many hours has it been giving you 9 amps? You will need to consider giving it 100 amp-hours before full charge is achieved.
Oh ok, I will try to be more patient lol.
Thanks.
 
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