charging back amps time
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buyselltrade9
Registered Users Posts: 9 ✭✭
i have a 48 volt lithium battery , at night i pull 300ah .i have a Victron 250/100. with 7400 watts of solar,, im confused about the charging time, its not in float after 6hrs something seems wrong but im not sure what , it seems to me it should be full by 2/3 hrs? thanks for all your help
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You need to look at the specifications for your Li Ion battery set/BMS (battery management system).
The rough charging instructions for LiFePO4 batteries is to charge to setpoint (bulk mode~80-90% state of charge), no temperature compensation, and either stop or possibly hold "absorb" for an hour or less.
The actual charging settings depend on the number of cells in series, your cells, and any BMS you may be using.
Hopefully somebody who knows more than i (@mcgivor, etc.) can help here...
Looking at charging:- 300 AH * 50 volts nominal bank voltage(?) = 15,000 WH overnight.
- 7,400 Watt array * 0.77 typical best harvest from array = 5,698 Watt average "best case" harvest
- 5,698 Watt actual array harvest / 58.8 Volts charging (estimated) = 97.7 Amps estimated "best case" charging (near noon/cool clear days/perhaps a few times a year)
- 15,000 WH per day / 5,698 Watt harvest = 2.63 hours of (noon time) Sun per day to fully recharge
http://www.solarelectricityhandbook.com/solar-irradiance.htmlMiami
Measured in kWh/m2/day onto a solar panel set at a 64° angle from vertical:
Average Solar Insolation figures
(For best year-round performance)
We are in August and the average hours of sun per day is 4.86 hours per day (from sunup to sundown)... Can go to a different website and get production/sun numbers by the hour--But just to make a quick and dirty estimate ('hours of sun per day" is assuming solar noon with panels pointing directly at sun and 1,000 Watts per square meter--In the mornings and evenings, you will have less than 1,000 W/m^2--So it takes something like 6-9 hours of "sun" per day to harvest 4.86 Hours of full noontime sun per day--If that makes sense):Jan Feb Mar Apr May Jun 4.61
5.25
5.54
5.88
5.58
4.90
Jul Aug Sep Oct Nov Dec 4.94
4.86
4.69
4.96
4.56
4.43
- 2.63 Hours of sun to charge / 4.86 hours of sun per August day = 0.54 or a little more than 1/2 a day of charging... Or by roughly by noon, the battery bank should be near charged--All things being equal.
Example of LiFePO4 charging profile from one vendor:
https://www.power-sonic.com/blog/how-to-charge-lithium-iron-phosphate-lifepo4-batteries/
Basically, if your controller holds "absorb" setpoint, it will drop from accepting full current to 1/5th or less after 1-2 hours... Absorb is holding set point voltage by the controller, and the battery bank "accepts" the amount of current it wants (plus whatever your DC loads are).
What are the details for your system?- Rough location (I guessed near Miami)?
- Battery Management System (BMS) you are using?
- What Watts/Voltage/Current are you seeing from your array (maximum you have seen)?
- What Voltage/Current are you seeing from the charge controller to the battery bank?
- What is the voltage on the charge controller output connections (under heavy charge)?
- What is the voltage at the Battery Bus (under heavy charge--looking for excessive voltage drop >~0.4 volts max suggested)?
- What is your float voltage set at (58.8 volts or 55.2 or what)?
- With any haze/high clouds/etc.-- it is easy to have 50% of harvest even though the day looks sunny (our eyes are not great at estimating solar energy).
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
dang bill you know a lot of stuff,,, (true) the system is in near Visalia, ca ,, i know bad, bad i have no bms/ 123 ish volts,@ 64amps from solar/ ive seen 50ish amps to the batts when the bats were like 50% or so/ the charge controller is a Victron 250/100 and can to 100amps to the battery max/ volt drop never even looked at it sooo ?/ my float volts is 48volts,there Nissan leaf battery packs in packs of 6 to make a 48volt battery pack then i made 13 of them, the volts i go with is max of 48.50volts,, and 42.0 max bottom with cut off battery disconnect/ thanks for your help,, i need all the help i can get on this,,lol
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- 64 amps * 123 Volts (solar array) * 0.95 mppt controller efficiency = 7,478 Watts to battery bank
- 7,478 Watts to battery bank / 48 volts = 156 Amps "available" (100 Amp max for controller)
- 50 amps to battery * 48 volts nominal bus voltage = 2,400 Watts to battery (measured?)
- 100 amps * 48 volts bus voltage = 4,800 Watts max possible with 100 amp controller
You have to measure/log everything at the same time (i.e., solar wattage on one day, and battery amperage/wattage on another day--Difficult to understand if problems or just day to day variations).
Do you have an DC Current Clamp Meter? Handy to figure out what is happening (measure current just clamping each wire, one at a time).
For example, check the parallel strings on the solar array to make sure each is providing its appropriate share of current... Measure the current in/out of each Li Ion pack to see that they are sharing correctly (bad back, bad/loose/dirty wiring connections, etc.).
https://www.amazon.com/gp/product/B019CY4FB4 (mid price AC+DC Current Clamp DMM)
Use a voltmeter to measure voltage drop from current source(s) to destination(s). For charging you want very little voltage drop (for accurate charging voltage)--Suggest 0.2 to 0.4 volt max drop. For loads (such as from battery bus to AC inverter DC input), you could allow as much as 2 volt drop without major issues (all things being equal).Fresno
Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
Average Solar Insolation figures
(For best year-round performance)
Lot more sun in southern central valley of California vs a semi-tropical climate of Florida.Jan Feb Mar Apr May Jun 3.77
4.85
6.13
6.74
7.02
7.21
Jul Aug Sep Oct Nov Dec 7.12
7.16
6.83
6.17
4.65
3.79
With highly variable solar power as the "source" and a charge controller potentially limiting current/voltage to bank--You have to be pretty sharp when you do your measurements. I.e., If you have 4 parallel strings of solar panels--String current should match pretty closely for each string--If yes, then most likely solar panels+strings are OK. If you find one string has low current relatively to the others, then you need to look for a bad connection/bad panel or similar... And you work your way through the rest of the system--Verify the upstream elements and work your way down.
If you see something "not right" such as 7,000 Watts into a charge controller and 2,400 Watts out (all measurements made within seconds/minutes of each other)--Then figure out what is happening (AC inverter on running loads you did not expect, etc.)....
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
thanks for the quick reply . i do have a clamp meter the way i do with the charging thing i turn off the inverter so there no drain in the batts, intill the batts are full, then let it set for a hr to just even out then i use them,, but lately ive been dipping in early, its not totally full close though, i have 7 parallel strings of solar panels, so if i get this right i need to look at the amps , because when i put it together, i checked each set they were 8.5amps per panel, bill the top comment you sad , that's why im like i should be better charging, now when i check the amps do i need to turn on a lot of stuff to get a big draw or just the normal recharging of batts be ok? not to get off topic but my charge controller has a monthly thing that keeps track of the watts i charge/use.. well sense the last update each day is cut in to 2 1 bar is up to like 4.30ish pm then it will start a new day in the middle on the day,, weird i don't know if its turning off for a sec or something alse?
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If your solar charge controller is acting "flaky"... The typical first steps are:
- Disconnect solar power
- Disconnect battery power
- Wait 5 minutes,
- Reconnect battery power FIRST
- Reconnect solar power SECOND
If that does not work, then the next step is to reset to factory defaults (aka clear configuration memory) and reprogram the controller--Then do steps 1-5 again.
I do not know about the Victron, but many higher end controllers have a "rebulk" voltage setting. The Battery Bus must fall below the rebulk setting first before the controller will go into Bulk (maximum current) charging mode. This is to prevent short charging cycles (i.e., 90% to 100% state of charge) from wearing out the battery bank (in theory, a short cycle like 90% to 100% SoC is a charging cycle and wears out the battery bank the same as charging from 20% to 100% SoC).
Using your Current Clamp Meter and a DMM to measure voltages--You need to carefully measure the current and voltage at major points in your system.
MPPT charge controllers are "constant power" devices... If you have 1,000 Watts of solar going it, you have 1,000 Watts of power going out to the battery bus (less maybe 3-5% for controller losses). Using made up numbers. And all current measurements assume that the sun is up and charging, and current is flowing (to battery bank, and/or AC inverter, etc.).- 1,000 Watts solar / 123 VDC solar = 8.1 Amps in
- 8.1 amps in / 7 parallel strings of panels = 1.16 Amps per string (if not relatively close, bad panel or string connection, or shading, etc.).
- 1,000 Watts solar * 0.95 controller losses = 950 Watts to battery bus
- 950 Watts to battery bus / 48 VDC battery bus voltage = 19.8 Amps to battery bus
If, for example, you see 48 volts at the Victron Battery output, and 46 volts at the battery bus terminals (while current is flowing)--That is too much voltage drop for the charging circuit/function.
MPPT chargers (and most any modern charger) has "memory" about what happened before and what is happening know... I.e., The charge controller will only go into bulk (maximum available charging current) if the Vbatt falls below "rebulk" voltage (if this controller has rebulk) and/or below "absorb voltage setting".
Say you program 48.5 volts absorb and 48.0 volts float and you measure 48 volts on your battery bus. That could because the charge controller is in "bulk" and supplying as much current as the solar array has possible... Or it could because earlier in the day the controller reached 48.5 volts "absorb" and held for 1 hour (if that is the absorb timer), and now has dropped back to float and is holding 48.0 volts.
Your 48 volt bus voltage could also be the AC loads are larger than the solar panel harvest (morning or evening) and the AC inverter is simply "dragging down" the battery bus voltage (some current supplied by charge controller, some current supplied by discharging battery bank).
There are "a lot of moving parts" here. Taking random voltage and current measurements without a plan, and then reviewing what you have measured--You get confused and confusing bits of data.
You need to figure out if:- Is solar array performing as expected (all parallel strings have very similar current). No shading from chminy, trees, leaves on panels (a little bit of shading can "kill" current output of string and/or array).
- Is your battery bus voltage what you expect. Lithium Batteries are near 100% efficient in power (charging energy in = discharging energy out). And from our point of view, 100% efficient regarding Amp*Hours (101 Amp*Hours to load, 101 Amp*Hours to recharge).
- Voltage drop... Voltage drop is only "meaningful/measurable" when you have a large amount of current flowing... 100 Amps of current and 0.40 volt drop is easy to measure. 1 Amp of charging current on the same wiring would give 0.004 volt drop--Real, but difficult to accurately measure with standard meters. Your DC wiring should have a small amount of voltage drop (heavy cables, relatively short wire runs) when you are moving 100 Amps for charging (0.40 max drop suggested) vs drawing 8 kWatts (8,000 Watts) from your AC inverter (8,000w/48v=) 167 Amps and an "suggested maximum" drop of 2 volts from battery bus to inverter)
Use your tools to help you understand what is happening in your system at that point in time. If it does not make sense, then you need to study the issue until it does. Electronics and wiring are pretty basic for solar--And you can usually figure out what and why something is happening... And if it still does not make sense, perhaps you have (for example) a bad charge controller (possibly) and you need to "prove that" to yourself.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
bill you were right the solar panels has a prob,, run with me on this,, lets say i have 4 panels in series so all together its a 120 volt .8.5 amp now you have 4 of those in parallel,, you should have 120volt at 34amps,,, right? if that's true, then mine has a prob i have the 120volts, but only15/17 amps all together, / on the controller stuff its set at absorb adaptive / max time 6hrs / tail current 2.0 / re-bulk volt offset 0.40v / , i did like you sad and disconnected the controller , i left it disconnected while i checked the panels, like (4hrs)
im confused about this?- 8.1 amps in / 7 parallel strings of panels = 1.16 Amps per string (if not relatively close, bad panel or string connection, or shading, etc.).
lol
all i do know is the panels wiring is wonkey i put 4 panels in series i get 120 volts,, each panel has 8.1 amps,, i connect them in
parallel,, the volts are just fine the amps are not,,,, i don't understand
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Nothing wrong with panels in parallel. In that case panel voltages should all be close to identical, amps don't matter. Heavier wire of course.Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
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BST9,
I am a bit confused (some typo's or are you trying different connection schemes)?bill you were right the solar panels has a prob,, run with me on this,,You have to understand how Solar Panels and MPPT controllers work... More or less, you should see somewhere between Vmp and 0.8*Vmp voltage. You have not told me the actual panel specifications (like Vmp, Imp, Voc, Isc, etc.).
lets say i have 4 panels in series so all together its a 120 volt .8.5 amp now you have 4 of those in parallel,, you should have 120volt at 34amps,,, right?
if that's true, then mine has a prob i have the 120 volts, but only15/17 amps all together,
More or less, the string voltage is an "agreement" between the solar panel and the MPPT controller... In theory, the Vmp-array should be somewhere between number of panels in series * Vmp (cold temperatures) and #series*0.8*Vmp (hot panels run lower Vmp and Voc voltages).
So--Guessing panels are Vmp-std = 37.5 volts (standard/marketing numbers). Imp~8.5 amps. P=V*I=37.5v*8.5a=319 Watt std panels (guess might be a little high for Vmp).
If you have 4x panels in series (+to-to+to-to+ etc.)...- 4 * 37.5 volts Vmp-std = 150 Volts Vmp-array-std
- 4 * 30.0 volts Vmp-hot = 120 Volts Vmp-array-hot
On wiring the array--If done "per code"--with 3 or more parallel strings, you should have a fuse or circuit breaker per string. If you use switched breakers, then you would have a 4 (7?) position Combiner Box:
https://www.solar-electric.com/misomnsoarco2.html (example of 12 position box)
If you had a breaker based combiner box... You could turn off all strings, then turn on one at a time (let the MPPT controller "settle") and you would have Vmp and Imp for each string--And quickly identify any per string issues (low voltage--perhaps a shorted panel. Low current perhaps bad wiring or failed panel).
If you do not have a combiner box... Use your DC Current Clamp meter and measure the current for each string... Ideally each string should be very close to the same current. And the sum of each string should add up to the current you see on the MPPT controller (or current clamp on main line to controller). Note--Current measurements within 5-10% are pretty much "close enough" to identical for our debugging purposes.
At this point--Looking for very close Amps per string... Without knowing/measuring amount of sunlight--If you think it is "very sunny"--I would accept 4.25 to 8.5 amps as "close enough" per string for Imp. (technically, solar panel short circuit current Isc is very proportional to Watts/sqmtr of solar energy... Isc=specification=Full noontime sun/spec.).
If your measurements are not around noon, you have hazy day, etc... At this point looking for near identical current from each string (all at 50% of Imp -- Probably all OK. If you have a couple panels below 4.25 amps and a couple more strings at 6-8 amps--I would suspect the low current string(s) as having issue.
You typed earlier about 7 parallel strings and here about 4 parallel strings (and you do have 4 series panels per string?)--Are your changing wiring/connections? If 4 strings "middle of relatively clear day", "good enough for now" I would accept anything equal to, or more than:- 4 * 8.5 Amps Imp * 0.50 decision breakpoint = 17 Amps or more--Array probably OK. Less than 17 amps on clear noontime day, does not sound right--But this is a fuzzy number without more knowledge.
on the controller stuff its set at absorb adaptive / max time 6hrs / tail current 2.0 / re-bulk volt offset 0.40v / , i did like you sad and disconnected the controller , i left it disconnected while i checked the panels, like (4hrs)Disconnected controller from both Array (disconnect first) and the battery bank (disconnect second) to reboot controller?
The rest of the numbers--set point voltages, actual li ion battery bank AH capacity, etc. to fine tune the controller settings--But seem to be working OK for the moment.
I hope you had the panels, MPPT controller, and battery bank connected and functioning so you could measure Vmp-array voltage and Imp-array and Imp-string currents.im confused about this?You are certainly keeping me on my toes here. What is the 8.1 amps? Is that Imp per panel? Or was that measured with one string connected to controller, or what (just me throwing numbers up in an example)?- 8.1 amps in / 7 parallel strings of panels = 1.16 Amps per string (if not relatively close, bad panel or string connection, or shading, etc.).
lol
all i do know is the panels wiring is wonky i put 4 panels in series i get 120 volts,, each panel has 8.1 amps,, i connect them in
parallel,, the volts are just fine the amps are not,,,, i don't understand
Remember, the charge controller will accept only as much current form the solar array as 1) there is sun and 2) as much as the battery will accept, and 3) as much as current as the controller "thinks" the batteries need.
The reason for measuring the current in each string under the same conditions (i.e., 10 seconds to measure the current per string)... We don't care (too much) about what the amount of sun, charge controller state, or battery bank state... Ideally, you want the batteries discharged and/or loads on the AC inverter (connect an electric space heater to the inverter, etc.).
We want current flowing (as much as we can get)--And look for "balanced" current flow for each string. Whatever the actual "total numbers" are--We are looking for "matched" results. None matching solar panel string currents generally means something is "not right" in the low current string(s).
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
what i have is 4 in series, and 7 in parallel that's it / the 8.1 is per panel / now so i get this right,
as long as the volts of each 7 strings are the same //
and the amps around 15ish would be good? -
8.1 is Imp (current maximum power) from panel label?
All 7 strings are connected in parallel--So by definition, all strings will have the same voltage (even if you have one or several "bad" strings/wiring).
However, each string will have its own current (zero to 8.1-8.5 amps).
You either measure each string's current with your DC Current Clamp Meter, or you can use your combiner box (if it is one circuit breaker per panel string--Switch all strings off, then turn on at a time and measure per string current and voltage--Since you are doing one string at a time). You could also (if combiner box) measure all 7 strings and see if the current drop is the same... For example, say you see 36 Amps from your array.- all on = 36 amps
- one off = 30 amps
- two off = 24 amps
- three off = 24 amps
- four off = 18 amps
- five off = 12 amps
- six off = 6 amps
- seven off = zero amps
Or simply use your DC Current Clamp meter (remember to zero the meter, with no wire in clamp, before making measurements--DC Current Clamp Meter tend to drift over short periods of time--Minutes or so?).
Obviously, you can only do this type of measure when the sun is up and battery is charging and/or AC inverter is loaded (battery full, no AC or other DC loads, no current drawn from solar array, no useful current draw).
If you have not used a DC clamp meter before--It is kind of fun to measure current in your car's electrical system and see how it works. Headlights on with motor stopped. Start motor and battery goes from 10 amps discharging to 30+ amps charging... Etc. Measure battery voltage resting, discharging, charging... See how much it changes (from perhaps 12.5 to 14.2 volts discharging to charging).
Li Ion batteries batteries typically have a much narrower "operating range" (less voltage drop when loads applied, less voltage rise when charging)... They are a "more perfect" battery type in many cases.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
In full noontime sun, guessing that you will see charging current of:
- 7 strings * 120 volts * 8.1 amps * 0.77 hot panel+controller derating = 5,239 Watts into battery bank
- 5,239 Watts into bank / 48 volts nominal bank voltage = 109 amps best case (cool/clear spring/fall day a few times a year around noon with discharged/loaded battery bank)
- 100 Amp charge controller = 100 Amp max controller output
- 109 amps * 0.5 good/bad break point at solar noon, discharge/loaded battery bank = ~54.5 amps or better is what I would expect from a well working system (no shade on solar panels) on a "reasonably" sunny day (note if controller thinks the battery needs to limit voltage/charging current--you will not see "max available" current).
Current = physical electrical flow (electrons moving from one end of wire to another)... Very much like water flowing in a pipe (gallons per minute flow).
Voltage = pressure... Just like water pipe with 40 PSI (pounds per square inch)... Water flowing or not--There is a pressure.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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