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Off grid inverter blending power sources


DeepBass9

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I have a JSM inverter charger, which is actually a very old school inverter given the way that technology is advancing, and there is one particular way in which it doesn't really work for me.

Being off grid, when it is cloudy or rainy I use a generator, and what the JSM does is put the entire house load on the generator, as well as the battery charging load. I can control the charging current, but that's about it.  What doesn't work so well is if a high load appliance is put on for a period (kettle for instance) then the battery charging, normal load and the kettle is too much for the generator and it slows under load and the inverter disconnects it eventually and switches to batteries. The inverter will try and reconnect, but if the big load is still there, then it overloads the generator and it loops through this situation a few times. 

This is a bit of a window shopping exercise, but which inverter would be able to blend the generator power with a bit of a boost from batteries if neccessary? 

Generators in general, and mine in particular work best at a constant load, so which inverter would be best to do that? Does that make sense?

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It really comes down to the type of inverter and how it uses the AC input to charge the batteries.

The JSM Inverter works the same way as the MLT Oasis, where the entire load is connected to the AC source and the Inverter stops inverting and becomes a charger.

I think the Axpert inverters are similar, but I'm somebody here who knows them better will correct me if I'm wrong.

Then you get another type of inverter, Like the Victron Quattro that @Kilowatt Power mentioned and the MLT Powerstar (and probably several others), where the Inverter continues to run

in parallel with the AC Source and can blend power like you have suggested, i.e. It could be charging the battery from the generator while the load is small, and if a large load is turned

on, it can use the battery to supplement the generator.

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There is also the opposite problem I experience where the generator is supplying a heavy load which then switches off. The genny throttle is now full open so when the load is removed it speeds up, then the inverter decides that is not good and removes the load entirely and switches back to batteries, and I have to then figure out what caused that, shut down the genny and start it up again to sync with the inverter. PITA. The main problem is the varying load confusing the generator and inverter.

Edited by DeepBass9
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12 minutes ago, DeepBass9 said:

There is also the opposite problem I experience where the generator is supplying a heavy load which then switches off. The genny throttle is now full open so when the load is removed it speeds up, then the inverter decides that is not good and removes the load entirely and switches back to batteries, and I have to then figure out what caused that, shut down the genny and start it up again to sync with the inverter. PITA.

Inverters that blend the power can have similar issues with big loads turning on and off. Whan a big load turns on, while the battery is being charged, the AC supply (Generator in your case) usually takes the knock until the Inverter decides to help by ramping it's power up. Then, when the big load turns off, the inverter is now supplying power, so it is possible that it then pushes power back into the generator for a short time until it can ramp the power back the other way. Depending on the inverter and how it controls this power while in parallel with the generator, the time it takes to ramp the power could be negligible, or it could be a few seconds.

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In my ideal world, if the generator is running it will be powering the load and then charging batteries with the excess. Say the generator is supplying 2kW,  the load is 1kW and 1kW is charging batteries. What I would like to happen if you put on a large load is that the genny still supplies 2kW and has no idea about any extra loads, the inverter then uses that 2kW and takes whatever extra is needed from the batteries. The generator keeps chugging away, blissfully unaware of multiple appliances being switched on and off. Is that possible? 

Edited by DeepBass9
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4 minutes ago, DeepBass9 said:

In my ideal world, if the generator is running it will be powering the load and then charging batteries with the excess. Say the generator is supplying 2kW,  the load is 1kW and 1kW is charging batteries. What I would like to happen if you put on a large load is that the genny still supplies 2kW and has no idea about any extra loads, the inverter then uses that 2kW and takes whatever extra is needed from the batteries. The generator keeps chugging away, blissfully unaware of multiple appliances being switched on and off. Is that possible? 

I suspect that the easiest way to guarantee that it does what you want would be to just get a separate battery charger that runs off your generator. That way you can keep your existing Inverter.

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3 hours ago, Stanley said:

Then you get another type of inverter, Like the Victron Quattro that @Kilowatt Power mentioned and the MLT Powerstar (and probably several others), where the Inverter continues to run

If you have a Quattro (two transfer switches, generator on the other one), and you configure it properly, then a Victron system configured with ESS (the grid parallel extension) will switch to battery charging if the active battery input is a generator. It still does PowerAssist and input current limiting, though, where you can configure the maximum input current and the Inverter/Charger will ensure that the combined battery charging power and loads remain under a certain limit. In other words, you can set the input current limit to 80% of the generator capacity and it will optimally load the generator by charging the batteries with the difference after powering the loads.

16 minutes ago, Stanley said:

Inverters that blend the power can have similar issues with big loads turning on and off. Whan a big load turns on, while the battery is being charged, the AC supply (Generator in your case) usually takes the knock until the Inverter decides to help by ramping it's power up.

Again, the blue inverters have something called Dynamic Current Limiting, which means that when a load starts it cushions the generator by supplying the load from the battery and then transferring it to the generator.

10 minutes ago, DeepBass9 said:

if the generator is running it will be powering the load and then charging batteries with the excess.

Then you need to look at something blue... 🙂

Edit: I also have to add, people with off-grid setups generally won't be running the ESS extension, and that turns the inverter into a normal "Axpert" style "charge the batteries as soon as you have AC on an input" setup, which is what you want when you're off-grid. Also, then you don't need a Quattro, a single input is enough. You don't even need the GX device. And you still get PowerAssist and Dynamic Current limiting.

 

Edited by plonkster
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Sure he could replace his Inverter with something Blue, and spend a lot of money, but if his existing inverter is sufficient for his needs and the only issue is when charging the battery from the generator then I think a 2kW battery charger would be a nice simple and relatively cheap solution that will decouple load fluctuations from the generator, so that the generator can run at a fairly constant load no-matter what the load does.

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Just now, Stanley said:

Sure he could replace his Inverter with something Blue, and spend a lot of money, but if his existing inverter is sufficient for his needs and the only issue is when charging the battery from the generator then I think a 2kW battery charger would be a nice simple and relatively cheap solution that will decouple load fluctuations from the generator, so that the generator can run at a fairly constant load no-matter what the load does.

Fair enough... I'm just getting excited since the product I support already ticks all the boxes. Almost like those crazy Dutch people had this problem already... just on boats 🙂

 

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39 minutes ago, Stanley said:

I suspect that the easiest way to guarantee that it does what you want would be to just get a separate battery charger that runs off your generator. That way you can keep your existing Inverter.

That may well be the simplest way as it is not dependent on any smarts inside the inverter. Thanks, I'll look into that.

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15 hours ago, DeepBass9 said:

when it is cloudy or rainy ... the entire house load on the generator, as well as the battery charging load.... if a high load appliance is put on for a period (kettle for instance) then the battery charging, normal load and the kettle is too much for the generator and it slows under load and the inverter disconnects it eventually and switches to batteries

 

57 minutes ago, Stanley said:

only issue is when charging the battery from the generator then I think a 2kW battery charger would be a nice simple and relatively cheap solution that will decouple load fluctuations from the generator, so that the generator can run at a fairly constant load no-matter what the load does.

learning opportunity for me - apologies...

Problem: If cloudy weather and the generator is supplying power to inverter for powering base (house) load and doing a bit of battery charging on the side. Now switch on kettle and the temporary overload causes the inverter to disconnect from the generator and switch full load to batteries (after a couple of unsuccesful attempts to re-connect to the generator).

Solution: Remove battery charge "decision making" and battery charging load from inverter and move to separate battery charger still connected to the generator.

Question: If all conditions remain similar (cloudy, house base load the same, batteries same level of discharge etc.) Unless the separate charger is way more efficient (or smaller?), why will the generator total load when switching on the kettle not still lead to a generator load to the point of slowing down and causing the inverter to disconnect?

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The generator is then only charging batteries. The inverter is only supplying the load. Changes in load don't affect the charging current. My problem is my inverter/charger does both at the same time, but the varying loads can confuse it.

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In the case of a separate battery charger, the inverter will not be connected to the generator at all anymore so it wouldn't disconnect if the generator slowed down. So even if the battery charger ramping the charging current up and down did affect the generator voltage and / or frequency, it wouldn't be noticeable on the load side of the Inverter and most battery chargers don't care as much about voltage and frequency as Inverters do, because Inverters need to make sure that the load sees an AC source that is in spec.

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That situation will actually be better for electronic equipment as I lost a satellite modem when I was running on generator, which may have been due a spike from switching from inverter to generator AC, its just a contactor that closes to switch between the sources. 

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3 hours ago, DeepBass9 said:

The generator is then only charging batteries. The inverter is only supplying the load. Changes in load don't affect the charging current. 

3 hours ago, Stanley said:

In the case of a separate battery charger, the inverter will not be connected to the generator at all anymore

Thank you, I missed that part and in my head still had the inverter running (directly) off the generator as opposed to the inverter running off the batteries, running off the charger, running off the generator (if that makes sense....)

3 hours ago, DeepBass9 said:

 I lost a satellite modem when I was running on generator, which may have been due a spike from switching from inverter to generator AC

Probably known to the people running generators and may not make a difference when switching source as opposed to load variation but I did come across this:

"Some generators will alter their voltage or frequency when loads change. This can be significant if the generator goes from no-load to full-load quickly. It can help to have a small 'stabilising' resistive load such as a 75W light globe smooth out this start up voltage/frequency variation."

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" It can help to have a small 'stabilising' resistive load such as a 75W light globe smooth out this start up voltage/frequency variation."" I was also thinking about that, to power something straight from the generator so the load doesn't drop to zero instantaneously if the inverter switches to batteries.

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