Genset To Battery Banks Charging Rate

MangasMangas Solar Expert Posts: 547 ✭✭✭✭
I have set my inverters to regulate charging my battery banks from the 15 Kw genset at 10 amps for two hours to bulk up the 64 x L16 batteries if they fall below 44 volts.

It is rare the genset energizes to do this, typically 3-5 times a year outside of self tests.

Everything has worked fine over 4 years. I was wondering if I could step up the charging rate to say 25 (more?) amps and reduce the genset run 2 hour run time?

I don't understand the optimal charging rate vs the genset run time relationship.
Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers

Comments

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Am I missing something, or am I just thick,, but 10 amps in to 64 L-16 sounds like a spit in the ocean. Also, 44 volts sounds kind of low if you have them wired for a 48vdc (nom) battery bank.

    What are L-16's about 300 ah+-? That would make ~2400 ah @ 48 vdc and you are only charging them from the genny at 10 amps? (5-15% would be 240-720 amps if my feeble math is right).

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Genset To Battery Banks Charging Rate

    Unless it is 10 amps at 240 VAC (some inverter/chargers allow you to program AC amp limits too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Genset To Battery Banks Charging Rate

    The source of the charge current is irrelevant; the charge rate has to be enough to negate the sulphation effects and long enough to "refill" (very inaccurate term) the batteries.

    Do you have L16-A, or L16-B?

    If you've got A's configured as 8 banks of 8 in series (48 V) then you've got 2600 Amp/hrs of battery and need to put at least 130 Amps DC to reduce sulphation. If they are B's, it's 3000 Amp/hrs and needs 150 Amps.

    Is your 10 Amp reading AC as Bill suggested? At 120 VAC, that would be equal to about 25 Amps DC on a 48 Volt system; way too little. The problem is that sulphation doesn't show up right away; it develops slowly. With it battery capacity is reduced; the battery may appear to charge to the proper Voltage, but that's only because it has lost a major amount of Amp/hr capacity.

    I'd advise getting a hydrometer and checking each cell's Specific Gravity. It sounds like you'd be chronically under-charging if you've relied on the generator too much. The gen's charging should be able to match the panels.
  • mike95490mike95490 Solar Expert Posts: 8,764 ✭✭✭✭✭
    Re: Genset To Battery Banks Charging Rate
    The gen's charging should be able to match the panels.

    Wow - I was going to go for about a c-30 rate, if my batteries get low, they NEED power, and if I'm burning fuel, may as well load the generator up.

    Actually, I have to load the gen to about 2/3 power, or the diesel carbons up, and slobbers oil.

    My case, about 2KW, which at 52V (battery charge voltage) which would be about 40A into the batteries. 400A, 6V batteries, so that's only about c-10 with a 3KW genset. I don't want to be running genset all that often.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Genset To Battery Banks Charging Rate

    I have two SW+5500's and two SW4048's.

    You listed four SW+5500's. There are a couple of things you should know about them when connected in common on the same battery.

    With eight strings of 325 A-H battery you can run up to 25% to 30% A-H rate when batteries are below bulk voltage. They will charge very efficiently in the less then 85% SOC range. This would be 8 x 325 x 0.3 = 780 amps, or about 48v x 780amps = 37 kW which is beyond your generator capability and the four SW+5548 capability.

    This is another issue with parallel SW+5500 charging. You will not get more then 50-65% their charge setting because they interact, faking each other out on the battery voltage. You still should be able to 'milk' the 15 kW gen to its limit. You didn't say what gen model but I would limit its max load to about 85% rated continuous power or about 12.5 to 13 kW. You will get the best kWH per gallon of fuel in this range. All four SW+5500 should be in charge mode at the same time otherwise the one's not charging will just suck from battery to take excess over float voltage and deliver it to A.C. load or any gen connected to AC2 port.

    The 44 vdc seems way too low but that will depend on what your discharge current is at that voltage reading. You listed a 2.5 ton central air conditioner that could draw 55-65 amps alone. You can raise the low battery voltage trip to gen activation and use the timer at low voltage trip to avoid triggering the gen on heavy load.

    I assume the four SW+5500's are two series stacked connected groups. The series stacking allows you to take the full 240 vac power from the generator.

    The generator is your limiting factor. Second thing to watch is balance across the eight battery strings to be sure you don't exceed 100 amps into any single string. You will find that typically the strings start out with one dominating then gradually the peak current moves to another string throughout the charging.

    The best way to figure D.C. charge current is by input power X 0.9 for inverter efficiency yielding output power divided by battery voltage. The A.C. charging current regulation will cause the output D.C. charging current to drop as the battery voltage rises during charge.

    Each SW+5500 will put out a maximum of 45A @120 v (5400watts) or about 4800 watts delivered to batteries. As I mentioned you won't get 4x this with four units running at same time. You will be able to fully load a 15 kW gen with a setting of A.C. charge current of about 26 amps on each of the four units. This should yield an overall D.C. charge current of 150 to 220 amps depending on battery voltage.

    Make sure you AC2 input current limit is set higher then A.C. charge current or the charger will limit to the max AC2 input current limit. Any A.C. output load will subtract from the AC2 input max current limit so the charger will back down if A.C. load demand takes up gen power.
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Thanks everyone. Better understanding now.

    The genny is an industrial grade 1800 rpm H Panel Generac propane 15 kw model rated at 62.5 amps and probably derated to about 13 kw at my altitude. So, at 85% I would be in the 11-12 kw range.

    Sorry, the current charging rate on the 5500 SW Plus inverters is 15 amps at 240 vac from the genny. I believe the voltage trip is 46 volts. They are Trojan L16Ps' 390A-H @ 20 Hrs. All the inverters are in charge mode.

    Year round the solar unit easily handles all our power needs including the high efficiency 2 x 2.5 ton A.C compressors/air handlers and the genny rarely is needed during the year. I've never seen the units draw more than say 16-18 amps when running at the higher speed and their low start up surge amps are amazingly low.

    "You can raise the low battery voltage trip to gen activation and use the timer at low voltage trip to avoid triggering the gen on heavy load". That's how we set ours up i.e. we programmed the timer to manage run time when tripped.

    I'll try raising the charging amps to 25 maybe 30 amps and leave run time at two hours. As Mike says might as well load it up anyway. I'll monitor the battery levels to see where I end up. Since the genny energizes so infrequently, I'll have to monitor an usually hot summer period where the generator is more likey to energize.

    "Make sure you AC2 input current limit is set higher then A.C. charge current or the charger will limit to the max AC2 input current limit". Don't know but will check where they're set at.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    I would consider raising the low voltage threshold some what. I think 44vdc is too low, assuming that is taken without some load.

    T
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Also keep in mind that, even with optimum charging, getting the bank from 20% SoC to 90% or so should take 4 to 8 hours. That is the bulk charge phase. The absorption phase can need another 8-12 hours or so.

    The chemistry can only run so fast and you don't want hot batteries, either.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Genset To Battery Banks Charging Rate

    My two cents--try to load the genset to 50% output, minimum, for bulk charging (and insure that genset+solar charging does not over current the battery bank if charging during full sun--and/or cycle the genset at dawn and let the panels take over mid-late morning)... That will put you in the most efficient kWhr/Gallon of Fuel range...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Ok thanks Bill.

    Your point was really the basis of my question i.e. can I save a little propane running everything at high charging rates with shorter run times. What I didn't consider was with my present timed run settings the batteries probably weren't being bulked up enough when the genny shut off. Batteries seem to be in good condition SG wise and plates look clean.

    I'll try your suggestion.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Genset To Battery Banks Charging Rate

    Mangas,

    I would also put a kWhr meter on your genset AC output and log fuel consumption (if you can) and see what your kWhrs/Gallons-lb-etc. ratio is...

    If you have one propane tank and multiple uses (gen, cooking, heating, hot water)--then you may have to do something like get a 100lb tank and plumb it to the generator directly and weigh the fuel usage after each run to get an accurate kWhr/lb reading. (note: I did not look up the size of tank needed to support running a 15kW genset and not have the tank freeze for your location).

    Otherwise a real propane meter of some sort would probably cost you somewhere in the $700-$800 range. Probably only worth it to somebody like us who spend why to much time and money monitoring energy use. ;)

    -Bill

    PS: There are lots of variables--gensets tend to reach minimum fuel flow at ~50% of rated power (if you are running at 25% of rated power, your fuel costs would be ~2x as much--so getting accurate kWhr/lb per unit of load can be a big cost savings).

    Also, lead acid batteries tend to be less efficient the higher the C/xx charge current is... Staying around C/10 maximum for a charging current is probably a good idea. Monitoring your bank temperatures to ensure they are not rising too quickly would tell you when you are charging them inefficiently (i.e., waste heat from battery bank).

    Obviouly, there are I^2 * R heating losses from wiring and electronic devices too... Graphing the efficiency curve of your system for AC power in vs the DC power out to battery at a few points (20%, 40%, 60%, 80%, 100%) may also reveal some interesting data.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Genset To Battery Banks Charging Rate

    Park your propane tank on a bathroom scale. Deduct the tare weight (should be stamped on the tank). It's not perfect, but it can give you a good idea of how much you're using over time ... and how much is left.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Only trouble with Marc's idea is that a 15 kw LP generator is probably running on liquid rather than vapour. My guess is that it might frost a 100# cyl enough to cause it to freeze, and then stop the liquid from flowing.

    Tony
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Genset To Battery Banks Charging Rate

    "Make sure your AC2 input current limit is set higher then A.C. charge current or the charger will limit to the max AC2 input current limit". Don't know but will check where they're set at. "

    See Basic Setup Menu 13B. 0 to 60 amp range. This is what is normally used to limit max draw on AC1 or AC2 inputs but since you have four inverters you would have to distribute the max currents across the four units to ensure you don't exceed the 62 amps from the generator. 62/4 = 15.2 amps for each. This is probably where the original 15 amp setting came from. If you are running central air from two of the inverters you can run these two inverters with a higher input limit and the other two with lower settings, sum of four units to equal 62 amps. You can set the two that don't get heavy load lower then expected maximum A.C. out load on them. When output load exceeds the input limit setting the inverter suppliments output to supply required load (up to max capability of inverter). This is also called load shaving (from grid or generator). It allows loads greater then could be supplied by either generator or inverter individually.

    I assume you have direct wiring from gen to get its full 62 amps as largest plug-in is 50 amps.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Genset To Battery Banks Charging Rate

    I don't have propane--so this is just my limited experience--Normally running a generator/etc. that runs from vapor is what frost/freezes a
    "too small" bottle.

    If this is the genset Mangas is using--then it appears to be a vapor fed Propane type.

    A liquid propane device would, if needed, have a vaporizer at the generator/flame.

    Here is one chart that list tank size vs btu/hr vs ambient temperature...

    I would guess, that this setup would want a 420 lb cylinder at 40F and 25% capacity... But, warm weather and a full 100lb tank--you should be able to do your measurements (kW vs fuel flow) to get a rough graph of efficiency.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    The industrial 15kw unit is fed by an underground 500 vapor fed propane gallon tank some distance from the genny and the ranch house. But, the main line is "teed" and stubbed off 5 feet from the genny i.e. main feed goes directly to the house and second feed to the genny with a thrid stub for future use. It would be easy to guage it at the genny. I may be able to borrow one.

    The two A/C compressors/air handlers run off different inverters for load/surge balancing. Generator is direct wired. So, do I understand each inverter input limit should be set evenly, 15.2 amps?

    Each of our two 100 amp AC breaker boxes at the house service one air compressor/handler for load balancing.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Genset To Battery Banks Charging Rate

    Bill,

    My point is, regardless of whether or not the genny is running on Vapor or liquid, the size of the BTU draw per hour regulates to a great extent how big a tank one would need to provide enough vapor. Your link that suggest a large tank confirms that one might run into trouble running it on a 100# bottle.

    Tony

    PS For those that are unfamiliar with LP gas, it is a liquid in the tank, with a head of vapor on top. The "boiling" of the liquid creates the pressure to force it out of the tank. As the liquid turns to gas, the phase change releases heat just as a fridge will. (In fact there have been fridges built with propane as a refridgerant). If you release gas too fast, the tank will ice up, causing the tank to reduce or even stop the flow of gas out of the tank. Systems that use huge amounts of BTU move the fuel as a liquid, (just like a gasoline or diesel engine) until it is to be burn, where it then is vaporized, much like a carburetor vaporizes liquid gasoline. Most homeowner and small commercial installations use vapor rather than liquid. The only use that I know of for liquid is large engines but I would guess that huge furnaces or boilers might also use liquid. Clear as mud?

    PPS At ~-40 the ability of L/P to boil is gone such that even a full tank of propane won't come out of the tank in any meaningful quantity. At -50 it won't come out at all!
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