Generator / charger sizing

Re: Generator / charger sizing

Any glaring errors?
AC Input 120V, 60A passthrough, 30A charging
2,524w -- passthrough for other loads while charging

Yes. 2 inverters each accept 30A charging,
60A total for 2 chargers running full out.
21A for your pass thru loads

81A to be supplied by genset.

I'd guess a 100A @ 120V or 60A 240V genset would work. 15KW genset roughly.

I'd lean toward a 240V, and split the phases to feed each SW it's own phase.
I'd also have a spare, 60A 120V genset - just in case the big one is down for oil change or something, so you can limp along. Although having a clone to get spares from is a valid argument too.

This is some big power, so diesel is your only option, and look at 1800 RPM gensets. Consider an option for a propane/natural gas kit, so you can lean out the diesel to reduce carbon loading at lighter loads.

Re: Generator / charger sizing

To size a generator, you need to know what the load will be. I just took the portions of your data that spoke to load:

AC Input 120V, 60A passthrough, 30A charging
2,524w -- passthrough for other loads while charging

If you called the loads or pass thru something else, I can't help that.

Passthrough = Amount of load going thru the box. Like the gadgets that are turned on that drain your batteries, Fridge, radio TV, computer. Do you want those on while you are charging batteries - or will you charge in the dark with no lights?

30A charging if there is a way to regulate this, let me know, I can do it on my XW, but I don't know if the SW has it, so I'm assuming when you have low batteries, and you turn the charger on, you pull 30 A. from the AC source. 2 chargers= 60A

So when these condtions change, you can change the genset. I allowed a bit extra, and called 15KW, instead of 12.64KW. But you can't go too much over - diesels like to be loaded to about 50%. Altitude does have an effect too.

I think you just got too involved and thunk too much about it.

There is the end of charge taper, as the batteries come up, but the genset still has to support the beginning charge rate.

Re: Generator / charger sizing

CallMeChaz wrote: »

Hi lads,

Your calculations are very good.

The SW4048 will suck up 33 amps AC maximum for charging. (35 amp pushbutton breaker on top of unit)

The amperage the batteries will get depends on their voltage at a given point in recharge profile. The SW's regulate current based on AC input current and have no measurement capability for DC amperage.

Best way to figure battery current is power-in times efficiency loss of inverter, divided by battery voltage.

Inverter max capability is 33 amps x 120vac = 3960 watts (there is a 35 amp pushbutton breaker on top of unit)

For 240 vac input @ 33 amps for each leg (each SW4048 ) that is a 7900 watts from generator.

Charging DC for each unit will be 3960 watts x 0.87 = 3445 watts to battery. At 57.2 vdc battery that will be 60 amps per inverter or 120 amps total. 13.3% of battery AH rating current. At lower state of charge with lower battery voltage, the DC current will be higher. At 49.6 vdc battery, the charge DC current will be 3445 watts / 49.6 vdc = 69.5 amps, or 139 amps for two inverters. 15% of battery AH in DC current.

The SW's will automatically back off on charging current, as required, if there is ACout current needed to stay within the set AC2in AC amps max setting. The AC2in max amps must be equal or higher then the AC charge amps as the AC2in amps max sets the limit on generator feed current.

If you have a 10kW gen you can set the AC2in max amps to match the gen max of 41 amps and set the Chg AC amps to 30 amps. This will give you some margin for ACout loads.

10 kW will be fine, you are right on! A higher amperage generator will give you more margin for ACout loads. AC2in max can be up to 60 amps AC.

Sometimes when gen load goes from low load to surge load the gen will bog down and drop rpm's. This can cause the SW's to release from generator due to gen freq change. If this happens you have to lower the AC2in max to avoid the gen surge bog down. The inverter will suppliment ACout surge to supply the heavy output load. It will automatically revert from pushing current into battery to pulling current from battery to suppliment the ACout heavy load.


I have two SW5548plus series connected and two SW4048's in series connection. I have a 15kW Generac for generator.

If your generator is relatively new with electronic speed regulation you should be fine on 60 Hz accuracy.

Only problem I have sometimes with Generac 15kW is the throttle stepper motor increment resolution when generator has no load causes the speed to wobble a little bit. Sometimes the SW+'s have a little trouble locking on. The wobble is eliminated with just a small load on the generator.

The wobble is less then +/- 1 Hz but because it is changing at a couple seconds rate it causes a problem with the initial phase locking on the SW+'s. It only occurs once in a while and putting a 60 watt light bulb on generator 120v AC socket eliminates the wobble.

Re: Generator / charger sizing

PhilS wrote: »

BUT I've never seen a propane generator that runs at 1800rpm.

Phil

Onan green, baby! My 1800 rpm thumper will happily run for days and days on propane.

Re: Generator / charger sizing

I agree with diesel being the safest choice. A little fuel leak and you have a stinky oily puddle to clean up...a little leak of gasoline propane or natural gas and you might have to clean up the remains of a building.

Ralph

Re: Generator / charger sizing

My bad...Backroad from Bagdad had that misfortune. Diesel the cause or just lost with the rest?

Ralph

Re: Generator / charger sizing

Bottom line, S*%T can happen in any system, gas, diesel, L/P nat gas. Additionally electrical fires. Bottom line, design and build trying to anticipate the worst. The best solution is one that fits your needs the best. Full time, part time, standby, shops etc all might have potentially different answers. From a stability of fuel, Nat gas or L/P clearly wins, followed by fuel oil, lastly gasoline. From a leak equation, I would probably rate diesel as safest from a fire perspective, but worst from an potential environmental disaster in the event of a major leak. Gasoline in the middle on both counts, and L/P-Nat gas as the safest from an environmental leak stand point some what more dangerous than gasoline simple because it is pressurized.

Tony

Re: Generator / charger sizing

Phil,

I could tell some funny stories about sprinkler heads. Like the time I was working building out a store in a mall. The painters had stuffed all the can lights with masking paper. We came in the next morning, turned the lights on via the breakers, and started two work. In a few minutes, flaming balls of kraft paper were falling from the ceiling. The smoldering paper trigged a couple of heads. The system was designed such that if any one head triggered, you had about 5 minutes to get to the sprinkler control room, unlock it and shut down the system. The result of being to slow was the sprinkler surge pump firing up with enough pressure to blow ALL the heads in that sector, which was about 20 stores! So while someone went in search of a key, others were stomping out the balls of fire, and others were corraling the water from the tripped heads! (We got to the pump before it triggered,, I still don't know how!)

The other issue I encountered quite often were wet sprinkler heads in ceilings over covered walkways that would freeze, since there was no heat, causing lots of damage.

Tony