We have been experiencing a lot of power outage ... over and above load shedding during the past few months ... this setup is only used as a backup power supply (old RCT 5 kva inverter)  

The pic attached is the  standard curve seen whenever we loose power ... as the batteries age and we add more load ... so the standby time shortens.

We could go 4 -5 months without loosing power ... for this reason I have set the charge current at only 10 amps ... and as you can see in the attached pic ... it only takes 3 hours to charge the batteries.

I cant add another set of 4 batteries because these batteries are already 3-4 years old. 

With my limited knowledge of inverters and batteries ...  The ideal setup would be a mecer king with a 5.5 kwh lithium pack - cost around R40 000.00 

Lets say I stick with the RCT inverter  ... which is not ideal for the application ...  because the unit is in bypass when the power is on and switches to inverter (pure sine wave) when the power switches off ... the mecer king can be stay "online" 

The batteries ... which will need to be replaced in the next couple months ... as noted by the reduced standby time in the past 2 months ... either we spend R16K ( a lot less than R40k) and just replace the 8 batteries which will give us 210 amp/hrs or add another 4 batteries (enetertec 105 amp/hr) = 315 amp/hr ... for the next 3 to 4 years again or maybe replace the batteries with a lithium battery now ... and at a later stage upgrade the inverter to a more suitable inverter.

 

battery curve.pdf

 

battery curve.pdf

Edited November 1, 20214 yr by isetech

One cannot see your attachment but you buy new lead acid batteries, you will be able to draw only 50% max of their capacity before recharging them. With lithium, you can draw 80% to 100% of the capacity. And on top of that, the lead acid will last much less. So, the upfront price might look cheaper but in a long term, that’s not the case. 
 

If you are planning to spend 40k, for a marginal more, you can get a SunSynk 5kW with a nice lithium battery to match it, instead of Mecer. 

From what I understand the newer mecer units can be set to stay "online" producing a pure sine wave all the time ... so for the "backup" application it would be best suited ... and we dont have any solar panels on the this site. 

However for a different application on a different site ... which has solar panels   ... the customer wants to "save" money by using a hybrid inverter ... so I have been doing some research into sunsynk inverters. 

I think I have fixed the attachment issue.

 

 

 

 

Can you please share the link for the Mecer.
If, you are not planning for solar, an online inverter would make more sense but the cost and need of pure sine wave should be justified first. A lithium battery would still be better in any case. 

Still trying to get the Pi and solar assistant to link to the mecer unit ... gonna try again tomorrow. 

The mecer has 240 amp/hr AGM batteries. 

I need to follow trends and graphs to tweek the settings on the mecer ... which will also allow me to make a better decision going forward.

Not having remote reviewing on an PV/inverter system. 

I need to figue out a way to start building smart electrical DB's. 

Looking at span .. .this is the way forward ... the controls and the app ... just what I have been looking for. 

https://support.span.io/hc/en-us

 

I pretty much only use my inverter as a UPS.

I initially ran an Axpert MKS 4kW/5000VA and then eventually switched over the Axpert King 5kW

Having run it a while now, I'll warn you that running from the Inverter all the time does have a draw-back.  Because my lights are connected permanently to the inverter, whenever a heavy load switches on, like the Fridge or home entertainment (TV + Amp + nVidia Shield Pro) the lights dim slightly.  That will happen with ANY inverter regardless of brand, they have impedance so any change in power will have some dimming.

That said, if your power quality is terrible, then you are much better off with a slight voltage drop now and then than running from a totally screwed up utility input.

Because I was using my inverter only as a UPS, I removed all the MPPT stuff (link above).  I also decided that Lead Acid is sufficient for my needs.

However even with only 2 hours at a time, the batteries I bought (100Ah) just don't last more than 3 years now.

I recently made my own Lithium battery pack for an eBike and using that experience decided to do the same now with my next battery replacement.

The total cost of switching to Lithium, for me is, once off:

• BMS: R2.5k
• Copper bus bar: ~R2k (let me know if anyone has cheaper price, haven't ordered this yet)
• I'm re-using my DC disconnector (probably not good enough, voltage is too high but I still have the fuse) and Class-T Fuse (don't be fooled the fuse is almost the size of your fist with 200kA breaking capacity @ 160v, so total overkill)

Recurring cost:

• Lithium Cells: 18x 100Ah LiFiPO₄ cells (I'm going for 18s which means a voltage range of 54v -> 63v) and 5900Wh: Cost R13k

Replacing just the Lead Acid 100Ah batteries at this point would cost me R2.6k per battery so ~R10.4k.  Thus my recurring cost is increasing by roughly R3k and would significantly increase the amount of usable power I can get from the batteries.  Definitely worth the extra R3k.

Of course if you are buying an off the shell Lithium pack your are automatically spending R20k

Edited November 2, 20214 yr by Gnome