An amp draw mystery

[Bill Hans]

Hello all.

I live very remotely with no access to grid power. I use a diesel generator without any real battery storage systems. I am in the process of adding a 48v battery system to power my house in the evenings so I can turn the generator off. Eventually, I will add solar to the system to charge the batteries, but I'm not there yet. I'm still new at this.

I recently purchased and hooked up a Sigineer M6048D 6KW inverter/charger. My generator puts out 240v through 3 conductors. 120v on each of two hot wires, plus a neutral (and a ground). That runs through a fuse box and then to a junction box that splits the power to run to a further three separate fuse boxes - one each for the barn, workshop, and house. All junctions are 240v so each fuse box receives the same power the generator puts out. Since I was only interested in running the house when the generator was off, I removed the house connection from the junction box. I then added a line from the junction box to the inverter input that requires the two hot wires and the ground (no neutral). Finally, the output of the inverter is wired back to the input of the house fuse box with both hots, a neutral, and a ground.

I have the inverter set up to only use battery power when it recognizes there is no power coming from the generator (or "utility" as the inverter calls it). If the generator is on, it presumably just passes the power straight from the generator to the house. It also charges the batteries when they need it through an Overkill Solar BMS.

In the old system, if I had a 120v heater pulling 10 amps in the house, I could measure the 10 amps with a clamp meter on the appropriate hot wire (leg 1) coming out of the generator. If I switched plugs so that the heater was drawing from the other hot wire (leg 2), I could see the 10 amps coming out of the other hot wire. After hooking up the inverter, no matter which plug I use, the generator puts out 5 amps on each hot wire. Well, obviously the inverter is doing some magic to spread the load evenly to each leg of the generator. Neat.

Here is the mystery: when I plug the same heater into an outlet in the workshop, the appropriate hot wire in the workshop fuse box shows a 10 amp draw, but THE GENERATOR STILL PUTS OUT 5 AMPS PER LEG. I have confirmed it multiple times with the clamp meter. I don't understand how the inverter even knows there is a draw coming from the workshop, or the barn. But all loads regardless if they are from the house, workshop, or barn all get equalized and pull the same amount from each leg of the generator. How does the fact that the inverter is drawing 240v from the junction box suddenly affect the whole system? I attached a little diagram to help visualize things. Am I ignorant, or is this magic?

 

[sunshine_eggo]

F'in magic. I have no explanation. Doesn't make any sense.

Wanted to make a comment on the Sigineer.

Friend has the same unit in 24V. It does not have a LFP battery option, but he has FLA, so no worries. It's a BEAST. Uses it exclusively for his deep well pump that pulls 4100W continuous with about 16000W surge. The thing doesn't seem to complain even with the surge.

Read the manual concerning absorption time, T0 and T1. The Sig has a crazy long absorption time 1-12 hours. LFP rarely needs more than bout 15 minutes. If you find it's in absorption for very long periods of time, you'll want to select one of the programs with a lower absorption so you're not hammering the cells at peak voltage for hours.

LFP is fully charged at 3.55-3.65V/cell and 0.05C (5A on a 100Ah battery). If it's forcing you into a long absorption time, best to do it at a lower voltage.

Lastly, it's HONGRY!!!! The idle burn is about 100W, i.e., it burns 100W even if you're not using loads. That's about 47Ah @ 48V or 2.4kWh. The low power consumption mode is only useful if you only have resistive loads (lights/heaters).

 

[Bud Martin]

So your generator is 240V split phase (L1, L2. N), correct?
The Sigineer M6048D 6KW is fed by L1 and L2 from generator, correct?
Your heater is drawing 10A at 120V = 1200W, so the current draw from generator at 240V will be 5A = 1200W.
So that is what you should see, it is still same amount of power.

6000W Solar Inverter 48V to 120/240V Split Phase Off Grid Hybrid 80A MPPT Charger ETL Listed

6000W Solar Inverter Converts 48V to 120V 240V ac split phase pure sine wave. With UPS transfer switch & 80A MPPT charger ETL Listed.

www.sigineer.com

Charger Specifications:
• Ac Input Voltage For Charger: Nominal 240Vac (154-260Vac)
• Output DC voltage: 48-58.4V
• AC Charger Rate: 0-60Amp
• MPPT Charger Rate: 0-80Amp
• Max Combined Charge Rate: 0-140Amp
• OverCharge Protection Shutdown: 62.8V
• Four Stage Smart Charger

FEATURES
• 6000 watt low frequency inverter
• 48Vdc input 120/240 Volt output
• 18000 watt surge for 5 seconds
• 4 Different Power Priority Modes
• Utility charger 60 Amp, MPPT Charger 80A
• 10msec typical transfer time
• Auto load sense with power saver
• Rich protective features
• Programmable low battery cut-off
• Extremely efficient stand by circuit with 15 watt idle
• No interference with equipments like TV, radio, etc.
• Capable of working with microwave ovens
• Exclusively designed AC- and DC – line filters for clean power output

 

[sunshine_eggo]

So your generator is 240V split phase (L1, L2. N), correct?
The Sigineer M6048D 6KW is fed by L1 and L2 from generator, correct?
Your heater is drawing 10A at 120V = 1200W, so the current draw from generator at 240V will be 5A = 1200W.
So that is what you should see, it is still same amount of power.

The generator is feeding the workshop directly with no inverter.

The power math works, but the current math doesn't.

It may be late, and my brain is foggy, but one can't have L1 and L2 coming out of the generator @ 5A and then somehow the hot the heater is using changes from 5A to 10A somewhere in the wiring.

Either there's a measurement error, or there's something amiss... or magic.

He should get 10A on 1 leg and 10A on the Neutral.

 

[Bud Martin]

The generator is feeding the workshop directly with no inverter.

The power math works, but the current math doesn't.

It may be late, and my brain is foggy, but one can't have L1 and L2 coming out of the generator @ 5A and then somehow the hot the heater is using changes from 5A to 10A somewhere in the wiring.

Either there's a measurement error, or there's something amiss... or magic.

I think I get it now!
Here is the mystery: when I plug the same heater into an outlet in the workshop, the appropriate hot wire in the workshop fuse box shows a 10 amp draw, but THE GENERATOR STILL PUTS OUT 5 AMPS PER LEG.
I think it must be measurement error because the L1 (or L2) line is connected directly the Hot terminal of the AC outlet via fuse, so he is measuring the current flowing in the same wire, at the outlet or at the generator.

Generator L1 ---AMP meter----> Fuse panel ------> AC outlet HOT --- AMP meter--->Heater
Generator N -------------------------------------------------> AC outlet N--------------------------->Heater

 

[sunshine_eggo]

So my understanding is, OP has no batteries yet, no solar yet, so right now he is feeding the Inverter with 240VAC from the generator, the spilt-phase output of the Inverter is fed the fuse box panel of the house.
May be English is confusing me again

He used present tense regarding the inverter and batteries. Future tense was for the addition of solar.

He included a sketch showing that the workshop, where the behavior is different, is only powered by the generator.

Even so, the inverter shouldn't behave any differently. With only one transformer, the inverter/charger can only do one thing at a time. It can invert from battery power, or it can pass through the incoming AC from the generator to the loads and use any surplus to charge the battery.

As such, a 1200W 120VAC load would pull 10A from one leg from the generator even if the inverter is in the middle.

Or it's late, and I have my head up my ass and can't see clearly.

 

[Bud Martin]

Sorry I update my reply in my post #5, I understand what the setup is now, OP is talking about the work shop which has nothing to do with inverter for supplying the power to the house, just plain heater and generator and he's seeing the current reading that does not make sense.

BTW: "I am in the process of adding a 48v battery system"
I think that is what thrown me off, I thought it means he does not have batteries yet but in the process of getting them but not having it yet in his hands. English is confusing.
And I failed to catch 'Work shop' where the current measurement is made.

 

[TacomaJoe]

Don't know inverters, but see that it is paralleled to the generator at the junction box. If the inverter input is a 240V transformer coil, it will provide an L2 path.

 

[RCinFLA]

That model inverter is apparently a low freq inverter/charger. The inverter's transformer is acting like an autotransformer with 240vac input and 120vac output.

240vac x 5 amps input transforms to 120vac x 10 amps output.

If you add in some battery charging, then the 5 amps input will go higher.

 

[sunshine_eggo]

That model inverter is apparently a low freq inverter/charger. The inverter's transformer is acting like an autotransformer with 240vac input and 120vac output.

240vac x 5 amps input transforms to 120vac x 10 amps output.

If you add in some battery charging, then the 5 amps input will go higher.

The inverter is not part of the circuit in question.

 

[Hedges]

The inverter is not part of the circuit in question.

The load isn't downstream of the inverter. But is inverter connected to junction box fed by generator, and load also connected to junction box with generator?
If inverter has closed relays to 120/240V transformer in inverter is connected to AC from "grid" (in this case generator), it sees voltage imbalance between L1 and L2, so tries to balance it.

That may even be a good thing in his case.
Would be a bad thing if connected to utility grid, and a couple neighbor were drawing 200 of imbalance.
As shown in Ian's video, with an added auto-transformer and grid connection (ignore the other issue of neutral/ground bond he discusses, which only relates to European 220V single phase inverter used in US 120/240V market.)

Safety hazard w/ Growatt 5000ES (European version) when connected to American grid

If you're using a growatt 5000es (European model that I don't use in my videos) with an auto transformer, you need to watch this video. The output of the inverter bonds the ground and neutral, which is designed for use with European grid. Conversely, American grid uses center tap transformer to...

diysolarforum.com

 

[RCinFLA]

On this type inverter with common output transformer, if AC input neutral is connected then transformer will try to correct any AC input L1-L2 voltage imbalance. This input does not need neutral connection but does require 240vac. Some units that allow 120vac only generators put a relay on input neutral to provide input neutral to allow 120vac only input. (like Conext SW series)

Bad part of this type configuration is 120vac output loads are supplied through output auto-transformer so pass-through 120vac power is limited by transformer size, not just relay contact current ratings. The better the L1 & L2 120vac load balance, the less power is supplied by transformer for 120vac loads, so this is usually not a major problem to inverter 120vac loads.

If you notice on terminal block (like AIMS inverter) 'neutral' is bracketed only for AC out and no neutral is shown under AC input bracket. Many folks tie the neutral in common with AC input and AC output, and their manual says nothing about the potential problems this may cause if input L1-L2 is voltage imbalanced.

 

[Bill Hans]

The load isn't downstream of the inverter. But is inverter connected to junction box fed by generator, and load also connected to junction box with generator?

Yes, the inverter is connected to the same junction box fed by the generator where the load from all other sources is also connected.

If inverter has closed relays to 120/240V transformer in inverter is connected to AC from "grid" (in this case generator), it sees voltage imbalance between L1 and L2, so tries to balance it.

This seems like it must be the case - but I didn't know it was possible for the inverter to "see" voltage draw from sources it is not connected to other than from voltage input.

That may even be a good thing in his case.

To be honest, I do like power being drawn equally from each leg of the generator. The inverter is rated for 6000 watts, because my house won't ever use that much. The generator is 20,000 watts because I sometimes need to power larger electric welders and heaters in the shop or barn. I thought the way I had it set up would isolate the inverter from the draw from the barn or shop, but it appears to not be the case. Does this mean I risk blowing the inverter should I draw 18,000 watts from the shop or barn even though they are not connected to the inverter output?

 

[Hedges]

If you draw 3000W or 6000W imbalance on one phase, inverter relay will pass current and transformer will try to balance.
A 240V load shouldn't be a problem. Isolation transformer (feeding shop 120V loads, or feeding inverter) would prevent inverter from seeing phase imbalance of generator.

Nasty inductive spikes or arc noise might be damaging.

 

[Bill Hans]

If you draw 3000W or 6000W imbalance on one phase, inverter relay will pass current and transformer will try to balance.

My generator can put out 20KW, and I sometimes will be create large 120V loads on only L1 or L2 . If I'm understanding you correctly, the inverter could see a 10KW imbalance from the shop and/or barn and try to rectify it. But I would assume the transformer in the 6KW inverter would be overtaxed.

 

[Hedges]

Yup.
I think it won't try to balance 100%, it only tries to balance voltage and transformer winding resistance limits that. Still too much current.
But you've got a split-phase source, single phase loads, and galvanic path to L1, L2, Neutral of inverter transformer.
A 240V to 120/240V isolation transformer feeding either shop single phase loads or inverter should solve that issue.

Feeding inverter only L1, L2 but no neutral of generator might look like it would work, but causes a problem of driving neutral current through the ground it is bonded to. (Or the earth if separate ground rods and no ground wire.)

So isolation transformer seems like the KISS solution. All ground can bond together, no current because galvanically isolated from loads on output of transformer. Neutral created by 120/240V split-phase secondary can either bond to ground, or not bond there instead carry back as neutral wire to a single bond elsewhere.

Inverter of course needs neutral to reach ground somewhere. Those meant for mobile use have a relay for neutral/ground bond only when shore power doesn't provide that. I don't think neutral gets isolated from input by most inverters, but we're seeing that for some European models.

 

[Bill Hans]

Yup.
I think it won't try to balance 100%, it only tries to balance voltage and transformer winding resistance limits that. Still too much current.
But you've got a split-phase source, single phase loads, and galvanic path to L1, L2, Neutral of inverter transformer.
A 240V to 120/240V isolation transformer feeding either shop single phase loads or inverter should solve that issue.

I guess I'd be interested in an isolation transformer (which is not something I knew about before this discussion) feeding the inverter. There is lots of info about sourcing inverters out there, but less it seems about isolation transformers. Where does one source a 6000W isolation transformer (if that's what I need)? I'm in Canada, if that matters.

I appreciate all the input on this.

 

[Hedges]

Here's one of many:

1-Phase 240x480 - 120/240

This transformer converts either 240V 1-Phase or 480V 1-Phase to 120/240V. This unit is great for lighting, CNC machines, and other business machines.

store.maddoxtransformer.com

Available used, cheap enough.
May have to shop on shipping. I think I saw prices from $300 to $8000 getting a 1500 lb. pallet from Canada to San Jose. In my case duty free because made in Canada, and I was able to complete forms as my own importer.

You should also have local vendors available, and eBay vendors.

Think also about surges and electrical hash from your shop equipment. Transformer may block some of that. Don't suppose you have any way (scope) to look at waveform of line voltage? Lightning arrestors (such as from Midnight Solar) might help. EMI filters might help.

It is usually said (by purveyors of protection devices) that transients from the grid cause most electronic failures.

 

[Bill Hans]

Thanks for that. When originally shopping for inverters, I also considered the MPP LV5048, which seems like it was two 2.5KW inverters mounted side by side in one case (no transformer?). Would something like that work in my setup, or would it have the same issue? Is the fact that the generator, load, and inverter input are all connected in the same junction box always cause issues?

I'm sorry for the very basic questions.

 

[sunshine_eggo]

How can the inverter change the generator's current on the inverter input in response to a separate load on the generator output/inverter input?