3 KVA inverter

[Isetech]

Do you need all the "stuff" when installing a 3 kva inverter. I see on most small inverters, people just plug and play. I had a look at an installation in a commercial building 3 KVA axpert type. the batteries are just place directly on the floor, no combo breakers, isolators, changeover switch, no surge protection, nothing. The unit is mounted to the wall and a piece of trunking straight into the 3 phase DB. Fed from a single pole breaker and back onto a busbar at the top of the light circuit breakers.


I have never installed a 3 KVA unit, only 5 and up. We normally go the whole hog with components:

D/P combo breakers from the mains.
D/P combo breaker for the inverter output.
changeover switch.
Surge protection.
Fuses on the batteries (24 VDC - 2 X 100 amp/hr)
Maybe even earth leakage protection if it is not feeding dedicated blue socket outlets for essential items like, computers, alarms systems CCTV etc.

[Isetech]

Looking at the unit specs sheet, I certainly wouldnt trust it, but if the poo hit the fan blades, being the manufactures spec sheet, sold with the product at your local trusted wholesaler, I am sure it would hold some value in court.


Just something to be aware of the input\output boards sold by the supplier do "not" have any overload protection, so you would need to build another board to install overload protection. Or maybe just make up your own panel using combo breaker isolators, it would save have multiple boards to confuse people even more. Something to consider if you are concerned about warranty claims on an inverter.

I have experienced issues with a battery supplier, we tried to claim for 4 x 260 amp/hr batteries, the first question asked, do you have some form of thermal cutout in the battery compartment?


the If you have 2 x 100 amp/hr 12 VDC batteries in series to make up 24 VDC, what size fuse protection would you use and would you fuse positive and negative?

2 x 100 amp/hr batteries in series would make it a 100 amp/hr battery pack, taking into consideration the losses etc, I would think a 100 amp fuse would do the job.

[Dylboy]

With the fuses it can be said we protecting the cable and not the battery, also depends on the discharge and charge rate as well.

I normally take the wattage of inverter divide by battery voltage to get fuse rating. How ever on the bigger ones I see what the max discharge is in the peak discharge and then work of that I.e, Peak of 85Amps then I would have a 100A and make sure the DC cable can handle it.

Either way its quite a challenge to learn all that as not many people keen to share their knowledge hahaha.


Also the okes who just throw the inverter in got the job for being cheap as they don't have all that safety stuff. So many inverter installs won't even trip the ELU as the N E Bridge is gone.

Sent from my SM-N960F using Tapatalk

[Justloadit]

Phew, if the Boost Circuit in the Inverter fails as a short circuit, then effectively the battery input is a dead short.
There may be some fuses in the inverter which may blow, but if there is a fault on the battery cable, then there is no way to disconnect the battery, which may cause a battery melt down. I suppose it may not cause a fire, but there is sure going to be a lot of hydrogen, which with a spark will cause an explosion.

There should at least be a disconnect device close to the battery for safety sake, and not a No 13 spanner to attempt to dislodge the battery terminal.
Using an AC breaker is not recommended, as they will cause a fire when the breaker trips the DC current.

My take is that there should be a double circuit breaker to the input and output of the inverter. If not for anything else, there to safely isolate the inverter in the case of maintenance.

But I suppose you get what you pay for.

If it is a 3Kw inverter, it can draw up to 125A off the 24V DC supply.

[Isetech]

Phew, if the Boost Circuit in the Inverter fails as a short circuit, then effectively the battery input is a dead short.
There may be some fuses in the inverter which may blow, but if there is a fault on the battery cable, then there is no way to disconnect the battery, which may cause a battery melt down. I suppose it may not cause a fire, but there is sure going to be a lot of hydrogen, which with a spark will cause an explosion.

There should at least be a disconnect device close to the battery for safety sake, and not a No 13 spanner to attempt to dislodge the battery terminal.
Using an AC breaker is not recommended, as they will cause a fire when the breaker trips the DC current.

My take is that there should be a double circuit breaker to the input and output of the inverter. If not for anything else, there to safely isolate the inverter in the case of maintenance.

But I suppose you get what you pay for.

If it is a 3Kw inverter, it can draw up to 125A off the 24V DC supply.

From my limited experience with batteries, we have found that 3 and half years has become a rule of thumb for the lead acid batteries (100 amp/hr deep cycle) to start gassing. I can literally see it happen on the device we use to monitor the inverters. That rotten egg smell is a dead giveaway when they start gassing. Even positioning a fuse holder close to the batteries would not be recommended.

We have had some 260 amp/hr AGM batteries fail after just 14 months. I believe it could have been due to the installer setup. I have made a few minor adjustments and installed a device to monitor the system. The big thing seems to be the battery cutout voltage settings, in most cases the inverters are set to cutout at 10.5 VDC.

I am busy with this 3 KVA inverter install ( the smallest one so far), we will be installing 2x 100 amp/hr gel batteries. It is going to be interesting to see how they perform. I will install a fuse holder with a 125 amp fuse inside a small DB next to my input/output DB. My only concern is the gel batteries, do they release a gas while charging?

It makes you wonder about these plug and play systems, the battery is directly below the inverter, in some cases in the same compartment as the lead acids battery. It cant be such a big issue considering there are millions of them sitting in houses and office, etc. I have never seem one with a fuse.

[Isetech]

"A gel battery is a valve regulated, maintenance free, lead acid battery. Gel batteries are extremely robust and versatile. These type of batteries produce few fumes and can be used in places without much ventilation."

Interesting, so you can install a gel battery in a cupboard in the house. It wouldn't be a bad idea to fit an air vent low down on the side of the cupboard, for just in case.

"Finally, gel batteries are best suited for deep discharge as they are more acid starved, protecting plates better compared to AGM batteries. The AGMs are more compatible where high current is required."

I found the statement above rather interesting.

I am finding that most issues we encounter with "inverter installs", not enough information is collected prior to the installation.

The question is simple, do you want a "backup" system or a money saving system.

What is is the difference?

An example of a cheap backup system would be an expert type inverter with a lead acid of gel battery solutions.

A money saving system would be well designed solar system with a proper "hybrid" inverter and lithium batteries (still on the fence with the batteries due to the excessive cost)

[Alfred M]

From my limited experience with batteries, we have found that 3 and half years has become a rule of thumb for the lead acid batteries (100 amp/hr deep cycle) to start gassing. I can literally see it happen on the device we use to monitor the inverters. That rotten egg smell is a dead giveaway when they start gassing. Even positioning a fuse holder close to the batteries would not be recommended.

We have had some 260 amp/hr AGM batteries fail after just 14 months. I believe it could have been due to the installer setup. I have made a few minor adjustments and installed a device to monitor the system. The big thing seems to be the battery cutout voltage settings, in most cases the inverters are set to cutout at 10.5 VDC.

I am busy with this 3 KVA inverter install ( the smallest one so far), we will be installing 2x 100 amp/hr gel batteries. It is going to be interesting to see how they perform. I will install a fuse holder with a 125 amp fuse inside a small DB next to my input/output DB. My only concern is the gel batteries, do they release a gas while charging?

It makes you wonder about these plug and play systems, the battery is directly below the inverter, in some cases in the same compartment as the lead acids battery. It cant be such a big issue considering there are millions of them sitting in houses and office, etc. I have never seem one with a fuse.

Lead acid batteries wil go into gassing stage when they are over charged voltage exceeding 2.5 volts / cell. Lead acid batteries has a specific charging characteristics. Three stage charging c=capacity .First stage =c/5@2.3v/cell. Second stage =c/15@2.4v/cell.Third stage = c/30@2.5v/cell then shuts off or float charges @2.4v/cell @c/40. If lead acid batteries should have bulk charge then absorption charge the equilized until all cells reach 2.5 v. Lead acid batteries could last at least 4 years if charged correctly. Take for instance you car battery it will last for approx 4 years but all car alternators are designed for correct 2 stage charging. Lead acid are not ideal for solar due to its design it will handle high current drain but needs to be fully charged correctly and never left in a discharged state for long periods.So choose the correct charging method when using lead acid that rotten egg smell is lead acid being overcharged 2.5v/cell or > for long periods

[Isetech]

Lead acid batteries wil go into gassing stage when they are over charged voltage exceeding 2.5 volts / cell. Lead acid batteries has a specific charging characteristics. Three stage charging c=capacity .First stage =c/5@2.3v/cell. Second stage =c/15@2.4v/cell.Third stage = c/30@2.5v/cell then shuts off or float charges @2.4v/cell @c/40. If lead acid batteries should have bulk charge then absorption charge the equilized until all cells reach 2.5 v. Lead acid batteries could last at least 4 years if charged correctly. Take for instance you car battery it will last for approx 4 years but all car alternators are designed for correct 2 stage charging. Lead acid are not ideal for solar due to its design it will handle high current drain but needs to be fully charged correctly and never left in a discharged state for long periods.So choose the correct charging method when using lead acid that rotten egg smell is lead acid being overcharged 2.5v/cell or > for long periods

We generally set the batteries to float at around 54 VDC (2.25 VDC) This is why it is quite a challenge to setup an inverter. Typically the system would just sit in a floating stage, then load shedding will kick in and things change for a couple days or weeks. Ideally you need a smart system.

[Alfred M]

Correct you need a charging system that can sense the battery voltage and by using a shunt to calculate current draw from the battery

[Alfred M]

The PSS Soho series stand alone ups/ inverter are fuse protected and has a dc breaker i have used them and they are very good for stand alone supply cut off voltage set at 30% of dod. The bigger units Ap series used with solar arrays and uses mppt charging technology