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60 amp backup


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I have taken over a system which requires attention.

The system:

3 x meccer 5 kva inverters (linked to each to produce 60 amp backup)

3 sets of 4 x 100 amp/hr (48 volts) lead acid batteries (total 12 batteries)

A panel with a 60 amp manual changeover. 

A panel with the supply cable and 3 geyser circuits not connected to the inverter. A cable from this panel to a Sub DB's around the property.

The system ran for about 3 years. Then the backup time became shorter and shorter until one day there was a rotten egg smell. The system was installed in cupboard in the middle of the house ( by others). I bypassed the inverter and removed everything.


We selected the 4 best batteries and tried to connect them to 1 of the inverters, it worked for 1 night the next morning it went bang, we havent been able to find anyone who can repair it yet.

It is almost time to install the system in a new location and upgrade a few things, hence the thread.  I have installed a few inverters, mostly just small single units with 12 and 24 VDC batteries.

I need to make sure I get it right, from the location to the cabling layout, fuse and battery selecltion. I want to look into a better management/monitoring system to log events, battery SOC and DOD and system efficiency.

The first thing that requires attention is the supply cable, the utility supply is a 25 mm cable with an 80 amp MCB in the meter box. The previous system had a 16 mm supply cable from the meter box to the inverter DB. 

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  • 3 weeks later...
  • 2 weeks later...
On 2020/11/05 at 4:49 PM, Barryv said:

Did you come right @isetech?

No I havent had a chance to ge tback to site.

We still cant find anyone to fix the blown unit.

The customer is not prepared to spend that kind of money on lithium batteries ... in fact it is the thing that puts 90% of potential customers off the idea of installing solar ... when i mention the price of lithium batteries ... for people who understand the value in the lithium batteries it is worth the extra cost ... but most customers just want a cheap option.




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  • 2 months later...

It is time ... The builder is busy installing the beam and blocks ... then I will install the conduits from the house to the new location for the inverter and batteries (attached to the side of thehouse) the room will have a big jojo tank and a pump for the water reserve ... I have discussed solar and lithium batteries with the customer ... he is not interested at this point) 

I need to make sure I get this right ... so I will start by measuring the load at the meter box for a week or 2 to get an exact load profile and monitor the quality of the power on site.

The next step will be to get a plan for the site ... mark the DB and sub DB locations ... cable routes ... high load consumers ... like geysers ... stoves ... pool pump and any other power hungry devices which could create startup/inrush currents. (geysers will be replaced with gas in the near future ... stove is already gas) 

Create a list of the DB's with all the exisitng circuits connected to each DB ... make sure all the labeling is correct and add where required.

Climb in the roof spaces and check access and the route for the new cables ... while I am up there get an idea of the general state of the electrical installation ... cable joints ... junction boxes ... open wiring etc ... cheack that energy efficient lamps etc are being used to reduce the laod as much as possible.

Look into using VSD's for the pool pumps x2 and water booster pump to both reduce the inrush current and better control of the pressure etc. 

Work out what size conduits will be required for the cabling in the slab ... add a size bigger just in case.

Work out what size DB's to use for the inverter system and the new building and entertaiment area outside and make sure there will be enough space for what ever is going to be installed ... taking into consideration pool isolating transfomers ...smart technology for control of lighting ... pool pumps ... and the fountain and water feature ... alarm system and security lighting intergration etc. 






















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Some other things to take into considerations ... being able to determine if the grid power or inverter power is on ... using a wireless link to each building and solid state relays and energy control units to reduce the impact while running on the inverter power with visible indication.

The old system didnt have any type of battery monitoring or battery balancing ... the battery cost is going to determine the type of battery ... so once I know what typpe o battery ... I will then decide on the typew of monitoring. 

We will be using the 2 hybrid inverters and most likely going to purchase a new meccer inverter ... not sure if we can mix inverters ... still need to find out more information. 




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12 hours ago, isetech said:

not sure if we can mix inverters ... still need to find out more information. 

It's quite tricky, and not something the manufacturer or the resellers handle well. You don't have to match brands, but the models have to agree, and the firmware has to be compatible (not necessarily identical, but that guarantees compatibility, obviously). Getting new firmware for compatibility can be frustrating.

My firmware parallel compatibility guide: https://forums.aeva.asn.au/viewtopic.php?p=66644#p66644

Edited by Coulomb
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  • 2 weeks later...

The roof slab is complete and the room is ready (not plastered yet) to start planning the layout.

The old system will be relocated to the new outside room ... which will be fitted with adequate ventilation ( so we dont have a rotten egg smell again)

There will be a changeover/bypass switch fitted inverter/off/byass so that the system can be bypassed for maintenance or in case the system fails.

The supply cable will be a 25 mm square (eskom supply 80 amps) to the changeover switch 

The plan is to design the system in such a way that there are not numerous sub DB's scattered all over the walls ... rather 1 panel which will have internal pertitions seperating the DC and AC ... a built in changeover switch ... indicator lights to display the state of the system etc.

I still havent found someone to fix the blown 5 kva inverter (one of 3 in parallel) ... I have 1 of 2 options ... just keep looking for someone (or try import the damage components and do it myself) or find someone who is selling the same model unit with the same firmware second hand ... anyone selling ? 

Model name - RCT - Axpert -5K 

inverter mode:

Rated power 5000VA/4000W

DC input - 48 VDC , 93 Amps 

AC output - 230 VAC , 22 Amp 

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Just a note the 25 mm cable will feed the main DB ...then the changeover switch with a 16 mm tails.

I have a few questions - Batteries 

There will be 3 strings - 12VDC x 4 to make up 48 VDC (still deciding which batteries to purchase ... the battery cabinets are pre made for 4 x 105 amp/hr lead acid batteries) 

lets say the strings are made up of 4 x 105 amp/hr lead acid flooded batteries.

Fuse and busbar requirements -

If I have 3 strings (which might be upgraded over time to 9 strings) rated at 105 amp/hr each x 3 = 315 amp/hr ... and 3 inverters in parallel rated at 93 each.

I want to install a 35 mm cable from each string with a 120 amp fuse at the positive terminal on the battery ... up to a fused disconnect switch above the battery compartment ... from the disconnect to a busbar rated at 350 amp ...from the busbar to each inverter battery terminals using 35 mm flexible cables ( using the same cables removed from the old installation) ... does it sound right ? 

Fault level at the busbar to be calculated. 





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Recommended battery capacity as per installation guide - using 3 inverters in parallel = 600 AH ...  I only have 3 strings at 100 amp/hr each = 300 amp/h

As per the label on the side of the units - current 93 amps  (installation guide typical amperage 84 amps ... recommended cable size 14 mm square) I would say 35 mm square would be a wise choice. 

Bussbar size - 25mm x 5mm = 125 mm  or 40mm x 3mm =120mm (for around 360 amps .. more than I need at this point in time ) 




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If you have 100A/h by 48V per inverter in lead acid or derivative, these should only be used to 10% to 20% max of the current rating, thus MAX of 20A draw, which is about 1kW, so a total of 3kW to the house between the 3 inverters, that being the case, one inverter with a 3 battery strings would also do. If, of course, you want to replace the batteries again in under 3 years, then draw 100A out of the batteries, but don't expect any reasonable life out of them, I would think, also are these sealed type? (Bad idea, if you expect a long life), of course if they can be topped up with distilled water you should probably keep the batteries away in a seperate ventilated structure.

Had a mate charge his disabled daughters weelchair in his lounge every night and was wondering why every 13 months or so, his TV was stuffed and beyond reasonable repair. This was back in the late 80's/early 90's.

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Now the trick is to figue out how to fit all the electrical components into one DB within the SANS regulations ... I dont want a changeover/bypass panel ... a suppply DB ... an inverter DB scattered all ove rthe walls.

I want to install one DB with all the components required in one enclosure with indicator lights and partitions if required.

I have an 80 amp supply (25 mm supply cable) but only 3 inverters rated at 22 amps each ... total 66 amps ... there are no essential and non essential ... everything is connected to the inverter ... this system has been operational until the batteries packed up after around 4 years. 




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