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Axpert 3 kva vs 5 kva


PaulF007

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The question is does he really need power assist, if you look at the costs of running the gennie rather let it run the full load (also let the batts charge then because why not make most of the fuel burning) .
With the Axpert just put it on bypass mode and run the gennie through the inverter or put in a separate changeover switch for when the gennie is needed and bypass the inverter.

As TTT mentioned please do get the BMV and balancers as it will just make it possible to better manage the system and get more out of the bank

13 minutes ago, The Terrible Triplett said:

Can maybe a 225ah bank do the job, with careful adjustment of lifestyle, due to diesel generator to auto start and switch off, to stay within a good budget for system 1 to learn or at best, do it once and be happy? Far as I picked up, it is 5-10 minutes of microwave at night, lights, TV, all very small loads.

This should be enough but if budget allows go double that. He would be running basically the same load as mine and I go down to 80% SOC every day.
I'm just a bit scared of the microwave even if it is only rated 1500. From what I have seen on mine rated 900w it does however go over 1800w and if I turn on the grill at the same time 3300w (eina)

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Now we are talking Viper!!!

Paul, amen brother ... I did concede the Axpert is best value. :P

But still I "feel" the Multiplus with the generator in play is better, much more expensive yes(!) unless the Axpert can do it as smoothly. Last thing you want is wife and baby on your case if Microwave does not work at 3am after few days of no proper sun. 

But the Viper brings up a very good point, " ... if you look at the costs of running the gennie rather let it run the full load (also let the batts charge then because why not make most of the fuel burning).

The it hit me!!! Like my system, similar, the BMV's relay can start / stop the gennie based on SOC of batteries. If at 70% DOD, start gennie, at 90% or wot SOC switch off gennie. See where the bulk charge is and when it goes into float / absorb with no added load, switch off gennie or such a formula.

Jis, ek koop sommer 'n gennie vir net sommer to see this working automated!!!

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9 minutes ago, The Terrible Triplett said:

Jis, ek koop sommer 'n gennie vir net sommer to see this working automated!!!

Hierdie is my plan as Eskom wil begin met ek moet n connection fee betaal.

The Axpert 5kva (not sure of the smaller ones) does have this also

Capture.JPG

For off grid with a gennie, I would leave it on Utilty mode so that if it's available charge the batts and run the load from the gennie.
If the gennie switches off the system will transfer to  batt/solar mode and you won't even notice it except for the gennie noise that suddenly disappeared  ;)

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6 minutes ago, The Terrible Triplett said:

Lekker. 

But with volts jumping with say microwave coming on 2am, would it not be more "stable" on a BMV's relay working on SOC?

I'm sure if you give Edmund some time he can control this contact with software and use the BMV SOC. I need the BMV relay to start my geyser element on good sunny days ;)

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1 hour ago, viper_za said:

I'm sure if you give Edmund some time he can control this relay with software and use the BMV SOC.

I need the BMV relay to start my geyser element on good sunny days ;)

But Frans does not. So he can do it on SOC for I suspect by the time the smaller bank hits set SOC, the volts will fluctuate a bit. 

Frans does not need any software, use it as is with appropriate goed between relay and generator to start / stop it. Techie side escapes me ... just make it work - as I always say to the developers. 

Ps. Have asked Ed to look at altering BMV SOC settings, to trigger said relay, but for other nefarious reasons ... you just gave me another idea Viper. Thanks. 

 

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I got a price from a supplier being a importer, for a Victron part, who obviously makes a profit selling it on.

So I asked for a quote for exact same part from another reputable company, where one can also buy at "cost".

Ex VAT, a whopping 1/3 difference in prices quoted making the devices really expensive if I wanted to, not that would, but if I could want to sell it on.

I am beginning to get a itch to form a feeling that I want to get an idea that maybe a thought is going to form one of these days that Victron prices are maybe being inflated, that the middle men are pocketing a large portion, justified that the equipment lasts long and therefor no recurring sales from same customer. 

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You do need a gennie if you are matching your usage and system size closely. One day of clouds is ok if you want to punish your batteries, but 2 or more days will mean you are beyond off the grid and your lumens have reverted to candlepower....

Also, using a start relay to automatically start up you gennie is not necessarily a good idea, as you might find the gennie running at odd times, running out of diesel and needing to be bled etc. With experience you check how much solar you have generated, figure out how long the gennie needs to run, and run it for an hour or 3 to top up the batteries. I can set my inverter to charge at X amps, and Then the rest of the load runs directly from the generator. 

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4 hours ago, viper_za said:

costs of running the gennie rather let it run the full load

The point of the PowerAssist setup is to run a smaller generator at full load. One would have to carefully decide, for obviously this is not a one size fits all. THe PowerAssist option obviously works best where you have a very large generator and a variable load that is often less than half the generator capacity. The generator has to be sized for the maximum load, and you might literally only need maximum load for an hour or so in the day. In principle then, there is savings to be had in fuel if you use a different inverter with a smaller generator. Here is the question though: How long would it take to save 25k in fuel? That might well tip the scale in favour of the chinese contender.

I still think that people who buy the chinese inverter is going to end up buying two inverters over a 15 year period. The man who buys a big multiplus probably won't. But a 15 year old inverter might be rather hard to use by then, right? All considerations. I'm reminded of the old question of car batteries, do I buy the Sabat or the Bosch? I can buy two Sabats for the price of the Bosch, so simplistic math says get the Sabat. In reality, the Sabat is going to die around year 3 while the Bosch might see you to year 5, and when you buy the replacement Sabat in year 3 it is going to cost more than now, which messes up the two-for-one argument. Kinda have to decide how you're going to do it.

(On that note, I have Deltec battery in my Diesel sedan. It's in year 4, totally worth the extra couple hundred I spent on it).

But anyway, my head is sore from this flu thing. You guys must maar do your own arithmetic.

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Also something else I found out by experience, is than on a small battery bank you can't just put 5 kw from the generator and expect the batteries to soak up all that power, they won't. So I charge my 48v 300ah bank at about 1.5 to 2kw which gives some headroom to run the load of the house without overloading the generator.

Some sort of variable charge rate to allow for fluctuating loads would be noce, but my inverter doesn't do that.

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6 hours ago, viper_za said:

I'm just a bit scared of the microwave even if it is only rated 1500. From what I have seen on mine rated 900w it does however go over 1800w and if I turn on the grill at the same time 3300w (eina)

My Axpert 4kW handles my 1800W microwave without a hitch. In fact we have issues when running on gennie power. Before we had an inverter the voltage would dip a bit and lights dim and micro would work but not full power so the missus had to adapt her recipes. Now with the inverter in bypass mode the inverter does not allow the voltage to drop and so there is a clicking noise. So if we want to run the microwave it has to be not in bypass mode. She has also had to revert to her original cooking times as now the micro functions like it should.

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1 minute ago, Chris Hobson said:

My Axpert 4kW handles my 1800W microwave without a hitch. In fact we have issues when running on gennie power. Before we had an inverter the voltage would dip a bit and lights dim and micro would work but not full power so the missus had to adapt her recipes. Now with the inverter in bypass mode the inverter does not allow the voltage to drop and so there is a clicking noise. So if we want to run the microwave it has to be not in bypass mode. She has also had to revert to her original cooking times as now the micro functions like it should.

Chris I'm talking about the high load on the bank not a problem with the inverter running the microwave :)

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Morning gents. 

Had to spend some time with the family last night and I see I have missed a bunch of info , bogger I was almost sure I had it figured but luckily I stumbled on this site. I agree that if the gennie can link with the inverter for short periods it should not be a problem. I have been playing with a Arduino on the side with a relay board to get the Auto start going so I would just need a "Pulse form the monitor" to start and swich off -  Arduino will handle cool off periods and I could even add a schedule so that if you have a peak at night the gennie will only supply power when needed en the turn off but during day will stay on for 10 min or so for when you swich on a grinder that peaks above the supply, you get my drift .. Considering the gennie running out of fuel 

As I see it now - Clean the table with all the notes and start over decide what the bare minimum is what I need and build the system up from there. I suspect that I wont get away from the 5 kva size wise but lest see.

Thank you all for sharing your views it adds for some good reading!

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Just to labour my point above a bit. I have great angst before I went off grid about auto starting the gennie and so on, but as I said it is not the best solution, because what the auto start systems can't do, is anticipate what the load will be before it occurs. For example, I am going to be water pumping today, wife wanted to make pap in the microwave for breakfast and I fancy some toast. Fridges come on at 6.30. Solar power generation starts at about 8am. At 5.30 my battery state of charge was about 70%. So instead of waiting for the gennie to kick in at some preset state of charge, I start the sucker up at 6 and run it through to 8am meaning that my battery soc never drops below 70, all the peak loads are catered for, the batteries will be quite well charged by midday and the water pump, when I switch it on will run directly from solar.

You just need to know what your system can do and anticipate when there will be a problem. If you want to warm a bottle at 3am in the microwave, and the gennie starts up, wakes the baby up good and proper, you will find yourself disconnecting the damn thing in the middle of the night will a ringing in your ears administered by dearest. Anticipating that might occur will mean you run the gennie to top up your batteries at a convenient time, like early evening or whenever.

Just my 2c from experience.

Also running a microwave for 30 secs to warm a baby bottle is a minimal load in any case, but a microwave is 1500W + so it will cause a battery voltage dip, generator comes on, because it doesn't know you are only running the microwave for 30s.

Other scenarios : In the morning its cloudy so you start the generator as the batteries are pap (autostart may have done the same thing at 3am as well). 10 o'clock the sun comes out, you switch of the generator, because you know it is now unneccessary as the sun will do the work. Autostart generator continues running as the SOC is not correct. You are now wasting diesel as the autostart can't anticipate that the batteries will now charge by themselves.

You decide to weld, so start the generator, switch it off when you are done. With autostart you first start putting huge load on the batteries for a few seconds, generator kicks in, runs a bit, and then SOC charge recovers so generator switched off again. Next welding run, same story.

It *seems* a neccessary and desirable scenario to have autostart, but in retrospect If I had got that up and running (which I didn't), I would have disabled it by now.

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@PaulF007 when you made the new notes through them out here.

I agree with @DeepBass9 with the auto start. It has specific scenarios where you do want to auto start, running servers at work with UPS and gennie yes this is a definite must.
Only situation where you would want it at home is to auto start if you are away for holiday or so on but even then, I want an eye on that thing.running on it's own

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@PaulF007 I did a quick experiment for you yesterday when I got home.
Boiled my 1350w kettle with the base load running and still having about 200w of PV available while running the inverter on battery/solar mode.
It takes about 5min to boil 1.2liters of water.
Capture.JPG

Now the interesting part on the bank below.
Boiling the kettle took me from 100% SOC to 98.9% and consumed 1.99ah from the bank according to the bmv. This was a 1250w drain from the bank the rest was supplied by solar.
Capture.JPG

As a result of doing this, I went down on my SOC for the night to 78.8% where I normally go down to 81%

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1 hour ago, DeepBass9 said:

after you have fetched and chopped all that wood you are nice and warm!

You arrive back in the house with the wood 30 minutes later, explaining that you don't see a point making a fire as you're quite warm now... wife is usually not impressed by that :-)

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4 hours ago, DeepBass9 said:

Also running a microwave for 30 secs to warm a baby bottle is a minimal load in any case, but a microwave is 1500W + so it will cause a battery voltage dip, generator comes on, because it doesn't know you are only running the microwave for 30s.

Just want to make very sure we are on the same logic. BMV relay using battery SOC does not worry about voltage dips.

Take the 100% SOC down to 98.9% due to say a Microwave. If SOC is set at 70% to auto start gennie, you will net be bothered if you switch on the kettle and as with "... went down on my SOC for the night to 78.8% where I normally go down to 81%.", it is not 70% SOC, so gennie never starts.

I hate to use volts on solar system to do anything with, so therefor I have been using said SOC setting and relay now for 5 years to protect my batteries, where I swap back to Eskom on say 95% and back to solar at97% in winter. Summer it is more like 85% to Eskom and 97% back to solar. And I don't use software for that either. It is all hardware, for software can stop working. Only time my batts can go too low is if the BMV fails.

Now IF it was a good idea, which it may not be, to auto start the gennie, I wonder now like with cars temp gauge, you drive and next moment the engine car seizes, overheated. Why did the manufacturers not add a alarm buzzer on temp gauges? Older cars now, new ones with computers I suppose cuts out today.

And now I wonder on gennies, if temp goes above X, or fuel gauge drops below say Y, or current drawn drop below Z, why not auto stop it, using a Arduino to automate it all if you are brave, and if not, hardware? 

You guys have build some very clever things for yourself, why not go down this track too? Or am I missing something obvious?

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5 minutes ago, The Terrible Triplett said:

Why did the manufacturers not add a alarm buzzer on temp gauges? Older cars now, new ones with computers I suppose cuts out today.

It's interesting how people take different directions on this. If you have a sudden loss of all water in some engines, no system will warn you in time to avoid at least a top-end overhaul. Nevertheless, most engines can run for a minute or so without water. Some manufacturers do away with even the heat gauge and add just a warning light. Even for those who still have the gauge, I often question how useful it is: it normally sits there plastered to the middle of the range (in a Toyota at least) and when things go wrong it usually shoots right to the top, I actually cannot remember the last time I saw an engine running "slightly" hot, generally it's already quite binary, things are either fine or they are not. So maybe the warning-light people have a point.

Then you have this thing the modern VWs do. You just get this bright red warning triangle on the display and text that shouts at you "STOP IMMEDIATELY" with a warning buzzer going off. I kinda like that.

On a side note: Never remove a thermostat from a 2KD Hilux. The flow characteristics caused by the thermostat is actually designed into the system, if you remove it, you mess up the flow and it actually runs hotter in some engine areas.

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23 minutes ago, plonkster said:

Spoken like a man who has no idea how much software there is in that there BMV :-P

BWAHAHAHAHA ... you got me there! :D

But I did say ... if the BMV fails. I was more implying that SolWEB does not control my system, the BMV does, for BMV is 1000 times more reliable, as my "people" pointed out to me yesterday. 

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Just now, The Terrible Triplett said:

BMV is 1000 more reliable

Yup, which is why using Linux or Windows instead of a real RTOS for these things is positively looking for trouble. You need a backup strategy. I think using voltage or a hardware/firmware type SoC meter like the BMV is a good backup in such cases.

Take the Victron CCGX system of things: That is a linux machine. It is very useful for controlling power levels in your Hub-4 system, and it is certainly a heck of a lot faster to develop on, but what if it crashes? My Pi2 crashes randomly every few days because the 16ms transfer time back to grid in the evenings is sometimes enough to knock the wifi dongle offline, for example. When that happens, you need safe failure mode. Safe failure mode in a hub system means 1) no comms to the MPPT in 60 seconds, and we go back to default settings, and 2) no comms to inverter means we switch to bypass mode.

The idea is that you set the MPPT with safe default charge parameters no more than 13% of the Ah rating. This can be overridden by software (to accommodate oversized PV arrays and self-consumption scenarios) but if anything fails, the MPPT goes back to that safe default.

For such integration work, I would probably always back-up the BMV with battery voltage (10.5V per 12V cell? Better shut that down sir regardless of what the other guys think...).

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