Need some help with a genny instal question

Re: Need some help with a genny instal question

As always, confirm with the manual and the mfg (if still not clear). From the MS4448PAE manual (PDF):

Congratulations on your purchase of the MS-PAE Series inverter/charger from Magnum Energy.
The MS-PAE Series is a “pure” sine wave inverter designed to provide 120 and 240VAC in a single
unit to power loads when inverting and also while charging. It has two 120VAC lines (L1 and L2), a
neutral and a ground. The two 120VAC output lines are 180° out-of-phase with each other, so that
the combination of the L1 and L2 lines total 240VAC and the voltage between either L1 or L2 and
neutral is 120VAC. The MS-PAE Series charger can accept 120VAC input (to L1 or L2) or 120/240
VAC split-phase input power (to L1 and L2), the incoming AC power is shared with the charger and
the output continues to be 120/240VAC with either a 120VAC or a 120/240VAC input.

So, it looks OK to wire a 120 VAC genset and use it as a 120/240 VAC inverter.

You might need to read through the details, it is possible that with 120 VAC only input, that the battery charging circuit may have reduced 48 VDC battery charging output (i.e., 1/2 of 240 VAC rated charging current).

There is nothing dangerous wiring of L1/Neutral only in the 120/240 VAC split phase plug... However, on the down stream side, are there going to be unused breakers on the L2 phase?

-Bill

Re: Need some help with a genny instal question

Yes, you would have 1 unused breaker on the the L2 leg (I was not sure if this was a transfer switch with multiple taps or not).

Reduced charging output... Normally we start with ~5% to 13% of the battery bank's 20 Hour Amp*Hour rating as the "ideal" charging rate.

So, if the inverter has only 1/2 charging output on 120 VAC, then the size of battery bank you can charge at "desired" Amp rate would be cut by 1/2 (or whatever the inverter/charger's 120 VAC derating would be).

Second, I like to recommend that the genset and charger be "matched" as to optimum fuel efficiency (typically, running the genset at 50% of rated power (or more). The less power you draw from the genset, typically, the less fuel efficient the generator will be. So, how does the 120 VAC input affect the inverter/charger's charging output?

Looking at page 40 of the PDF manual in my previous post, it appears that ratings:

60 ADC (@56.4VDC) Charging
17.5 AAC (at 120VAC) per leg

Basically, the charger will only output a maximum of ~30 amps at 56.4 VDC if you use L1/Neutral only...

Plus there is an internal transfer relay--so you will only be able to run the L1 120 VAC circuits directly from your genset (need to run inverter to power L1 and L2 120/240 VAC loads).

But, that is the power limit of your genset anyway... It looks like you would need a 4kW+ or so 120/240 VAC genset to power the inverter's AC input to its full rating.

So, what is the "real ratings" that you need your inverter, battery bank, and genset to support.


Please note, I have only spent a few minutes reading the manual--You should look at see if you can program the AC input current Max. and/or the DC charger max output so you can keep the numbers within the range of your Yamaha 2000 genset. I have not read the manual front to back in detail--So these are my first guesses at the issues you will need to address/resolve.

But, assuming you can design the system to meet the needs of your AC loads (battery bank, genset, solar array, etc.)--I do not see any big stumbling blocks other than the usual (Bank AH capacity, surge/continuous watts from the inverter, and panels/genset recharge capabilities).

-Bill

Re: Need some help with a genny instal question

morpho wrote: »

Wow....you know this whole process has been amazing. Just when I think: "okay, now I can sit back and enjoy some of that electricity falling from the sky" I find out I can't. I still need to problem solve the next issue. Then I need to come onto a public forum and admit how ignorant I am still.

Try giving a couple wrong answers combined with bad spelling+grammar on a public forum... You want embarrassment? :roll:

So, I think you are saying that only one of the branches running to the service panel will be powered by the genny. The other will still be pulling off the Inverter?

I have not read the manual in detail--But, usually when you have AC power supplied to an inverter with a transfer switch, the inverter will simply just pass the AC from the genset directly to the loads this saves on losses (90% efficient charger * 85% efficient inverter = 77% overall efficiency). However, when you have a "missing" L2 leg, the inverter will need to supply the missing "phase"--And I would guess would run 100% of the time (i.e., the generator supplies charging current and energy for inverter; and the inverter supplies all 120/240 VAC power).

I have no 240 loads in the house, so if this is the case could I eliminate the second wire from AC-OUT and run a jumper in the service panel to make both sides of the panel hot and powered by the genset?
Or maybe I am confused on the whole thing.

Yes, but be careful... Many homes/branch circuits are wired with three conductor Romex or other cable... Basically Black/Red/White (plus safety ground).

On a 120/240 VAC split phase system--The power supply is a Center Tapped AC transformer. The center is your "neutral" and the outer two are your L1/L2 leads.

What happens is the the Center Tap will only carry the maximum current (say 15 amps for a typical branch circuit on 14 awg wire) when L1 is at 15 amps and L2 is at zero amps. Then Neutral carries the return current.

If L1 and L2 are both at 15 amps, they subtract from each other (they are 180 degrees out of phase--if that makes sense to you) and you will end up with zero amps on the Neutral.

If instead you use only L1 and Neutral in a 120/240 VAC breaker box, and jumper L1 to L2 so that both are really just L1, then you don't have the L1/L2 center tap configuration. Instead now, if you have a Black/Red/White setup, the L1+"L2" add up on the neutral. So if L1 and "L2" are 15 amps each, you will now have 30 amps on Neutral (white wire) which could overheat and start a fire.

So--if you do the L1 to L2 jumper with a >15 amp genset (or inverter), you need to make sure that none of your home/cabin wiring shares a common neutral with both L1 and "L2".

Sorry for the long, boring answer... This is a safety issue and I need to make sure you understands the issues before you "do it".

If you do not need 240 VAC, and you have no long runs of 120 VAC circuits (well pump, shed/barn/etc.), then the question is why a 120/240 VAC inverter? It sounds like you would be better off with a 120 VAC inverter instead (the Magnum 120/240 TSW inverter chargers are nice units, not taking away any thing from them).

Back to the battery charging:
So if there is reduced charging output, will this have an adverse affect on the batteries or will it simply be slower to charge?

For "optimum" charging (5-13% rate of charge), this means you will be able to support about 1/2 the size of battery bank by running a 1,600 watt genset on your 120/240 VAC inverter (in your case, it appears both the limiting factors are about the same--The limit of 120 VAC only on the inverter and the limit of a 1,600 watt genset result in the same ~30 amps at 56 volt maximum charge current instead of the 60 amps possible with a 4kW 120/240 PerVAC genset).

Perhaps you want to go back and evaluate your loads... A 4kW inverter would run my 3 bedroom/4 people suburban home very nicely, with lots of power left over (natural gas, reasonably efficient appliances/forced air heating system, etc.).

The inverters and generators are the "cheap parts" of the system... Battery banks (and their replacement every 5-10 years or so), a large solar array, and generator fuel costs can really drive up the total costs of your off grid/emergency power system.

If you are going to use a 2kW genset (again, a very nice Yamaha inverter/generator I believe), then a 4kW 120/240 vac inverter charger is probably overkill for your system and power needs.

Before you get to set on the equipment, instead look at your needs (watts, peak watts, Watt*hours, distances to send the power, etc.) and see if you can do something else.

Many times, people would do well with a 1,000 to 2,000 watt TSW inverter, and they get a less expensive 2+kW MSW inverter to run the occasional loads (shop tools, water pump). but, even then, a cheap 2.5-5kW Noise Maker/Fuel Swilling^TM generator to run the occasional heavy loads is a better use of your money (design the solar pv system to run 90% of your loads, and use the cheaper generator for the 10% that are too big for a small/efficient PV off grid system).

Sorry, it gets back to measuring your loads with a Kill-a-Watt type meter and/or a Battery Monitor. You could do some estimates with a DC Current Clamp Meter too.

-Bill

Re: Need some help with a genny instal question

I believe your genset should have a throttle control On/Off switch... Set the genset (inverter/generator) to full speed, at least until the battery charger is up to full power--and probably leave it there until the charger starts tapering the charging current down.

Next, have you had a chance to see if you can reprogram the inverter/charger to limit to 10-13 amps or so maximum AC input current (or dial back on the max charging current--which ever your unit has)?

And do you have any idea of the current state of charge of your battery bank? Specific Gravity, resting voltage, etc.?

Also, take a good volt meter/DVM/DMM and monitor the battery bank charging voltage... Presumably, when the battery reaches around 56-58 volts (whatever the maximum charging/bulk/absorb voltage you set it), then the battery bank is around 80-90% full, and you should begin to see the battery charging current start to reduce. Also, if there is temperature compensation, you will need to take that into account (cold batteries use higher charging voltages).

Ideally, start the genset up in the AM and get your battery bank to 80-90% state of charge, shut off the genset, and let the solar array finish the charging during the daylight hours.

If there are times you will need "high" charging current, it might be worthwhile to purchase a "cheap" 5kW genset. You can plug that in and quickly recharge the battery bank back to 80-90% and let the smaller genset/solar array finish off as needed. As long as you keep the 5kW genset loaded to ~40-50% rated power (minimum) it should be pretty fuel efficient (if the noise is acceptable for your area).

I may have missed it, but what are the basics of your system (solar array wattage, battery bank AH @ 48 volts, Yamaha 2000 inverter/generator, etc.).

-Bill