charging battery bank with generator

raven8310 · March 2017

i am in the middle of installing my new solar system and i have a 48v 600 ah agm battery bank and a aims 12000 w inverter charger this is an off grid system i also have a 8750 w predator generator that i would like to hook to the inverter the manual for the inverter says i need a 150% higher capacity gen than my inverter that would be 18000 w gen so my question is i guess will my 8750 gen harm the inverter or just take longer to charge don't want to destroy my new inverter any input would be greatly appreciated thanks in advance

Estragon · March 2017

I'm not familiar with that inverter, but using a smaller generator shouldn't hurt it. You may want to limit charging amps on the inverter and/or avoid running large loads while running the generator so it doesn't overload.

You have pretty big inverter for the size of both generator and battery bank.

raven8310 · March 2017

It was sold as a kit it came with the 12000 w inverter 12 200 ah AGM batteries 12 250 w solar panels and a 60 A mppt charge controler all are aims brand you say my battery is undersized what would you recommend

Estragon · March 2017

Depends on your application. As a general rule, you wouldn't want a lot more battery for the panels you have unless you have really good sun.

The issue with the inverter is you can pull a lot of current. 12000w at 48v is 250a, potentially more in a surge like motor start. Deep cycle batteries are usually rated at a discharge rate of about C/20, or about 30a in your case. Pulling nearly 10x that, apparent capacity will be reduced considerably. Of course, just because you can pull that kind of current doesn't mean you will, but something to be aware of. I have a lot of inverter for my bank too, but that's mainly to support surges, and for redundancy in case an inverter fails. I keep a close eye on loads.

Off-grid, sometimes it's better to flip a breaker than having guests all running blow dryers and whatever all day, and then find you have to run the generator half the night.

Another thing to keep in mind is with 3 parallel strings of batteries it's important to keep strings balanced so they charge and discharge evenly. Heavy interconnect cable and proper wiring is important. AGMs have advantages, but can be tricky to manage because of the difficulty in measuring state of charge.

It sometimes takes some time to get things working properly in a new system. The key is to monitor closely and ask questions if something doesn't seem right.

oil pan 4 · March 2017

They say you need 150% more generator than what the charger is rated for because consumer and contractor generators are only designed to run at about half to 2/3 load continuously.
The wiring in them can't handle constant running at full power.
Battery chargers are a constant unforgiving loads to power.
You would need something like my 17.5kw generac, which is like a $3,600 machine, but it powers anything, air compressors, welders, plasma cutter, all the loads other generators fear are no problem for my generac.
Or get a smaller stand alone battery charger that doesn't use more than about 5 or 6kw.

raven8310 · March 2017

I apreciate all the info I am new to this and want to learn all I can I was just iffy about hooking that gen to the inverter mainly because it said it would void the warrent so I was afraid it would damage the inverter

mike95490 · March 2017

raven8310 said:

.... the manual for the inverter says i need a 150% higher capacity gen than my inverter that would be 18000 w gen so my question is i guess will my 8750 gen harm the inverter ....

Most inverter chargers have a way to control the charging amps from the generator,
So if you have a 8750 genset, it's what 7Kw cont ? I'd set the charger to only pull 5Kw from the genset, which at 58V charging, would be about 60A DC, when allowing for some reasonable losses and PF.

oil pan 4 · March 2017

If you are going to run an 8750w generator at 7kw continuous and it's above 40°F or 50°F be sure to have a spare.

raven8310 · March 2017

So the way it sounds I am more than likely going to destroy my generator not the inverter

mcgivor · March 2017

raven8310 said:

It was sold as a kit it came with the 12000 w inverter 12 200 ah AGM batteries 12 250 w solar panels and a 60 A mppt charge controler all are aims brand you say my battery is undersized what would you recommend

12 250W of solar panels, typo? 1250W would seem more realistic for a 60A CC, if so that would be undersized for the 12 000Ah battery, the array would barely cover the idle useage, at 200W, left on 24 hours.

raven8310 · March 2017

no typo they are 250 w panels it is suppose to be a 3kw array here are the specs 3000 Watt Off Grid Solar Kit with 12000 Watt Power Inverter Charger 120240 - 48 volt

3000 Watt Off Grid Solar Kit with 12000 Watt Power Inverter Charger 120240 - 48 volt

Maximum Power (Watts): 250 watts
Optimum Power Voltage (Vmp): 30.3 volts
Optimum Operating Current (Imp): 8.26 amps
Open Circuit Voltage (Voc): 38.0 volts
Short Circuit Current (Isc): 8.75 amps
Solar Cell: 156 * 156 Poly
Number of Cells (pcs): 6*10
Size of Module (inches): 64.56 x 38.97 x 1.57
Front Glass Thickness (mm): 3.2 mm
Temperature Coefficients of Isc (%) °C: +0.056
Temperature Coefficients of Voc (%) °C: -0.33
Temperature Coefficients of Pm (%) °C: -0.43
Temperature Coefficients of Im (%) °C: +0.04
Temperature Coefficients of Vm (%) °C: -0.35
Temperature Range: -40°C to +85°C
Tolerance Wattage (e.g. +/- 3%): +/- 3%
Surface Maximum Load Capacity: 5400Pa
Allowable Hail Load: 23m/s, 7.53g
Weight Per Panel (lbs): 41.00 lbs
Bypass Diode Rating (A): 12
Cell Efficiency (%): 16.77%
Module Efficiency (%): 15.37%
Backing (brand Type): TPT
Warranty: 91.2% of 12 years, 80.6% of 30 years
Standard Test Conditions: AM1.5 1000W/m 25 +/-2°C
FF (%): 70-76%

raven8310 · March 2017

and here is exactly what they sentPart # KITA-12K48240-C1
PERFECT FOR HOMES OVER 3500 SQ FT

This Kit Includes the Following Parts:

PICOGLF12KW48V240VS - 12000 watt pure sine inverter charger 120/240vac

PV240POLY - qty 12 - 250 watt solar panel

PV6X240RACK - qty 2 - 6 panel Ground Mount Solar Rack

PICGLFBATS - qty 1 - Battery Temp Sensor

SCC60MPPT - 60 amp MPPT solar charge controller

6FM200H - qty 12- 200 ah deep cycle battery

PVF100FT10AWG - 100 foot PV wire for solar panel (female)

PVM100FT10AWG - 100 foot PV wire for solar panel (male)

PVMC4.A-2F1M - qty 2 - MC4 Branch 2F to M

PVMC4.A-2M1F - qty 2 - MC4 Branch 2M to F

PVEXT15FT10AWG - qty 6 - 15ft PV extension wire

CBL08FT6AWGC- 8 ft 6WG cable to connect SCC to battery bank

CBL08FT1/0 - 8 ft 1/0 AWG cable set (inverter cable)

CBL02FT1/0 - qty 2 - 2 ft 1/0 cable (battery cables)

CBL01FT1/0RED - qty 11 - 1 ft jumper for fuse kit and battery jumpers

ANL300KIT - 300 amp inline fuse kit

mcgivor · March 2017

So it's 12×250 W panels, not 12 250W, that makes more sense for a 60A CC @ 48v. My estimation is that considering the demand the inverter is placing on the system, this is still undersized, if used 24 hours with an inverter rated at 200W idle.

raven8310 · March 2017

so i should proably get 6 more pannels and another charge controler?

mcgivor · March 2017

That all depends on your loads, reverse engineering is difficult, best to start with your loads, including the inverter demand, then size the battery according to the load, finally size the array to satisfy the charging requirements of the battery. It's all details and details are important, there is no point in building a system just to satisfy an inverter with no load, harsh realities, yes, we all started somewhere and all made mistakes along the way, myself included.
Just seems to me at least, that the system purchased couldn't power much other than the inverter. Was this intended as a standby system, rather than an off grid system? the reason asked is because it is in the off grid section.

mcgivor · March 2017

I'm sorry got lost along the way, started out with a question regarding generators, please forgive unless information is relevant .

raven8310 · March 2017

not a stand by it is compleatly off grid and not at all it is all very relevant i appreciate any info i can get this is all very new to me i was under the impression that this system would have no problem running my home coupled with a generator of course for days when there was no sun i guess ill just start with what i got and see what it does and add what i need you know learn from my mistakes and yours hopefully lol

Estragon · March 2017

@mcgivor makes a good point about the low-power efficiency of the inverter. If you are running small loads, the inverter won't go into search mode. With NO loads, specs for the inverter show tare losses at 40w. Although 40w*24hrs is about 1kw (not trivial off-grid), with small loads (eg. 100w lighting or wall warts overnight), the inverter will use 200w just to be on, plus the 100w load, or 300w, so now you could be looking at a 2500+wh draw overnight just for your light bulb.

You might want to consider a smaller inverter to handle small loads, and just use the big one for big loads. Knowing more about your loads would help..

raven8310 · March 2017

well i have 7.5 w led lighting *12 a pc 1 refridgeator 1 small chest freezer a washer and a 1/2 hp water pump 1 30 in flat screen tv and an x boxwill also run a vacume cleaner 1 time a day for like 10 min i need to get a killawatt so i know there exact wattage but this will kinda give you an idea of what i am using and i am currently using the 8750 w generator to power the whole house with no problem now that we got a gas dryer

Estragon · March 2017

Does the water pump fill a cistern, pressure tank(s), or ??.

raven8310 · March 2017

i have a spring feed systern that gravity feed to the house then the pump and pressure tank

SolarMusher · March 2017

raven8310 said:

and here is exactly what they sentPart # KITA-12K48240-C1
PERFECT FOR HOMES OVER 3500 SQ FT
This Kit Includes the Following Parts:
CBL08FT1/0 - 8 ft 1/0 AWG cable set (inverter cable)
CBL02FT1/0 - qty 2 - 2 ft 1/0 cable (battery cables)
CBL01FT1/0RED - qty 11 - 1 ft jumper for fuse kit and battery jumpers
ANL300KIT - 300 amp inline fuse kit

12kw inverter/300 amps inline fuse for 8 feet/1/0 wire...??? That will be perfect to start a fire for homes over 3500 SQ feet.
1/0 can take 150 amps max at 70°C. I hope that it's only a typo.
A+
Erik

raven8310 · March 2017

should i put a smaller fuse or change the cable size its no typo i just went and checked the wire size and it is 1/0 awg

raven8310 · March 2017

what is the best way to wire my batteries for the most even charge

mcgivor · March 2017

SolarMusher said:

raven8310 said:

and here is exactly what they sentPart # KITA-12K48240-C1
PERFECT FOR HOMES OVER 3500 SQ FT
This Kit Includes the Following Parts:
CBL08FT1/0 - 8 ft 1/0 AWG cable set (inverter cable)
CBL02FT1/0 - qty 2 - 2 ft 1/0 cable (battery cables)
CBL01FT1/0RED - qty 11 - 1 ft jumper for fuse kit and battery jumpers
ANL300KIT - 300 amp inline fuse kit

12kw inverter/300 amps inline fuse for 8 feet/1/0 wire...??? That will be perfect to start a fire for homes over 3500 SQ feet.
1/0 can take 150 amps max at 70°C. I hope that it's only a typo.
A+
Erik

Actually the rating for 1/O copper in free air is 245 A, 150 A is if it is in a raceway, and 125% of 245 A is 306 A, so it would appear the cable and fuse are sized correctly.

mcgivor · March 2017

raven8310 said:

what is the best way to wire my batteries for the most even charge

With the batteries you only have one option 3 parallel strings of 4. Connect the load and charge cables, load directly to the post charge on top, connect positive and negative diagonally opposite, for better ioad and charge ballance, refer to the link for more details.
http://www.smartgauge.co.uk/batt_con.html

raven8310 · March 2017

thanks mcgivor

mcgivor · March 2017

Took the time to look at the system you purchased, other than the inverter being so large, it looks ok. The reason for the statement, about the inverter being too large is that it may mislead an operator into thinking there is actually 12 Kw available indefinitely, when in fact using that amount of load would deplete the batteries in less than 2 hours and probably harm them. Having said that, it's a matter of understanding the limitations of both the battery and the ability to charge them and keeping within those limits. Knowing what the total consumption per day is, is key if the desire is to be predominantly solar. As there is generator backup to cover shortfalls in solar production or occasional over useage, is an additional safety. The suggested 150% generator requirement (18Kw) is to cover the maximum output of the inverter, however if your maximum load is for arguments sake 2Kw then a 4K generator would suffice, again it's knowing the limits.

Realistically, in my opinion, they should have promoted the kit as a 3Kw off grid system, but that doesn't sound quite as impressive, or at least a 12 Kw ( with 18Kw generator support ) Note how all of the kits they sell, from 2-12Kw, have the same array/ controller, just a larger inverter, a 3Kw 48v inverter from Cotek for example, I have the manual in front of me, uses 40w in no load and 9w in power save mode, as apposed to 200 & 40 for the Aims 12 000w.
The large inverter is a killer, it's self consumption is too high unless you use that much energy, and if you do, the ballance of system is too small to support it, without a generator. Truth in advertising comes to mind.

jonr · March 2017

> what is the best way to wire my batteries for the most even charge

However your clamp on ammeter (current in parallel batteries) and volt meter (series balance) shows is most balanced. Start with the recommended layouts and adjust as needed.

Estragon · March 2017

If you find the tare losses are eating up too much battery capacity, you could consider getting a second, smaller inverter and a lockout panel to run overnight.

To conserve pressure tank capacity, I supply toilets and other water uses not needing much pressure directly from gravity tank. The pressure tanks (2x30gal) easily supply overnight needs for me, so that pump stays off and I can use a really small inverter at night. You'd need a big enough inverter for reefers though, probably in the range of 1500w with decent surge capability.

raven8310 · March 2017

well i tried it out last night an it seemed to work just fine it lasted 12 hr to 40% dod and i put the gen to it and it seems to be charging just fine i shut the out put off so all power from gen goes directly to charging

charging battery bank with generator

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