Dougiedanger

Done

Good afternoon Vaughan, Compliments of the season to you too. I have a similar setup to you in terms of size and age. My Must 3kva, 24v inverter is hooked up to 4 x 205ah SLA Trojan batteries. These were my second set of batteries, my first set (2 Chinese 280ah) although first use when installed had stood for a few years without any care so didn't last long coupled with my poor understanding at the time of how to use and care for LAs. I went the Trojan route as at the time I couldn't find a decent 24v lithium option and decided to get decent lead acids as a compromise. I installed them with an HA02 balancer and I also purchased a Victron BMV712 which I used as a warning a cut off to ensure the batteries don't discharge more than 40%. I have also taken to adjusting the bulk charge and float voltages twice a year to deal with the temperature fluctuations based on the data sheet for my particular batteries. It was interesting that when I installed the BMV I found a 0.7v difference between what the inverter was reading the battery voltage at and what the BMV saw, the BMV was accurate the inverter was not, so I used that info to adjust the charge parameters accordingly so I got voltages at the terminals in line with the battery data sheet. This set of batteries are coming up on 3 and a half years old now with no significant loss in performance, although they are Trojans and should mange that easily. The next 3 years will tell me if what I have been doing is of use or just a waste of time! Lastly it does take a long time for the batteries to get fully charged, from say 70% SOC it takes probably 5 hours to get to where they are not accepting any further charge.

Love my sonoffs!

I have a set of Trojan AGM batteries that are coming up on 2 years old, I have a HA02 balancer and a bmv on them and am pretty happy with them. Unfortunately I only came across this forum after I had already purchased a 24v inverter and when the first 2 batteries that I got failed(Due to my inexperience), I looked long and hard for an affordable 24v lithium battery before deciding to stick with AGMs and purchase decent ones. My theory was I should get 5 years from them to cover the extra cost, although Zims loadshedding is making them work quite hard these days.

Not sure who has come across this on Supersport? Second round on today and is a very interesting format with some big racing names involved. A electric racing SUV with a difference, amazing how they throw them around and how they perform. The have a 40kw usable battery developed by Williams Advanced Systems. Just thought this would be of interest for some forum members!

Hi @JpPaulKrugerI have a Must which is very similar to what you have and also experienced the same sort of issues. I have set mine up on either SBU or SOL they both seem the same and don't seem to do anything different. I choose to not charge from the Grid and have set my Go to Grid setting to swap to utility when my batteries are at about a 75% SOC. By setting the Go back to battery(Or something like that) setting to a higher voltage, say 28V(on my 24v inverter) this prevents the inverter cycling if the voltage raises slightly after the load is taken off. Not sure if this would work for you however if you can get ICC I think that would be a win, just wish they could get my inverter on their list!

Hi, what sort of load are you drawing on the inverter, ie how many Watts? Do you have panels attached to this setup? How old are the batteries? Unfortunately in my limited experience it is usually a sign of the batteries being on their way out.

If the inverter is set to use Solar when available, it will use solar supplemented by battery power when the solar yield does not meet the demand requirements. That means if it becomes fully overcast the battery will provide most of the demand until it reaches the preset low voltage back to grid value. Yes it should be on the data sheet

Think you would need to be cautious with this from solely a battery point of view. Assuming that is a Pylontech it is recommended to only discharge them at 0.5c, even at 1C you can only draw 2400w max, so if you are distracted when one of those bigger ones is on and it clouds over you would be pushing the battery close to its maximum rated discharge.

Sorry @nelian, I unfortunately learnt the expensive way that lead acids are not properly protected by the average inverter which uses battery voltage to guess at the SOC which is never accurate. Due to also purchasing a 24V inverter (killed my first set of lead acids inside a year, due to similar reasons) and finding that 24V lithium batteries were not readily available to replace them with, I had to stay on the lead acid path so opted for Trojans that have a good track record on handling some abuse and coupled that with a battery balancer and bmv to protect them. So far happy with my decision but had I been on this forum longer when I made the call, I may have thought more about dumping the 24V inverter and upgrading to a 48v one so I can could then explore getting a lithium battery instead of staying with the lead acids which need more attention.

True

@Achmatand myself commenting at the same time, basically your inverter size will tell us how your batteries are setup, either 24v or 48v. That will give you the size of the battery bank, which is basically the same in watts, either 24v x 400ah bank or 48V x 200ah, ie 9600w. As stated never take the batteries below 50% SOC so useable capacity is 4800w, or 10.5 hours at a 450w draw. However note that the lifespan of these batteries will be severely compromised by drawing to this level regularly. Also the inverter will not be able to determine SOC accurately and so it is highly recommended to have BMV to do this and to be honest a battery balancer. The inverter may well run these batteries to a lower SOC than 50% which will cause more or less permanent damage if done several times.

You won't have 800ah, in series add voltage ie 12v x 4 = 48v (if your inverter is a 48v model), then ah stays the same at 200ah.

Please confirm, you say a 5Kva system, is that a 24V system? That would be quite unusual... Just reading into saying you have 4 batteries in total and 2 were purchased bout 6 months ago. I have a similar system but on a 3kva, 24V inverter with 4 x 205ah batteries. That gives me a bank of 410ah. I also draw about the same watts as you at night and my setup will give me 12 hours at that sort of draw to a 50% SOC. I did this last night for the first time due to an unexpected fault. Normally I tend to draw about 30% out of my batteries on a daily basis just to get round poor incoming voltage from Zesa in the early evening. As you will see elsewhere in this forum, you can kill lead acids very quickly by drawing them down too deeply(like I did last night).

It can't hurt. I am in Zimbabwe and have learnt a great deal from this forum which has assisted me and where and when I can help others ask the right questions. It seems that this industry is a great opportunity for average electricians to make a quick buck by selling and installing a system that works ok initially and fails within a very short time but by then they are long gone or by then can hide behind a multitude of reasons that are blamed on the customer. I am not an installer but have enjoyed my solar journey as most have here and am always looking towards what I can do to improve my system, but it does irritate me to see people being advised and sold systems that are so clearly not sized or configured correctly for their requirements.