Hi all, new here and I will start by saying that batteries and associated calculations are not my forte, and so I’m here to seek advice from the much more knowledgable people here.
Essentially, we have a fridge that works with mains (UK) power via a generator during the day between 7am -7pm via a generator. When that generator powers down, the fridge is connected to a charger/inverter system with the following components to provide power whilst the generator is powered down:
1 x Victron MultiPlus Compact 24/1600/40-16 230V VE.Bus
2 x Rolls 12V S12-128AGM Deep Cycle Battery
The fridge the system powers states an Energy Consumption (kWh/24h) 1.04
We want to replace the AGM batteries for Lithium, and are looking at these:
Can we simply swap the current AGM batteries out for the new lithium ones? Will they work with the existing Victron MultiPlus Compact 24/1600/40-16 230V VE.Bus inverter/charger and/or does anything need to be done to it to make this work?
Would these be a suitable solution and how long would 2 of these batteries be able to power the fridge for?
Apologies for the long post but I wanted to provide as much information as possible.
Those 100Ah lithium batteries should be able to power the fridge for about 40 hours:
1.04kWh/day, 90% conversion efficiency = 1155 Wh/day, or 48W average power.
This is ~2A average draw from the battery, 80Ah @ 2A should give you 40 hours.
Settings: The voltage settings for the multiplus will need to be adjusted to suit the new batteries - this will require a Mk3/usb device, and Victron connect or configure software.
The fridge is actually a pharmacy fridge which holds a quantity of medication which must be held within a relatively small temperature range or it has to be destroyed which is very, very costly.
The existing AGM batteries are a few years old and are used every day. As far as I understand the degredation on these type of batteries means that their lifespan is much less than lithium ones. As such, I think that for the peace of mind and reliability of the system is worth the investment here.
If you still have the same voltage in the morning as you had a couple of years ago…they’re ok.
Record this voltage once per week, if you see its going down…replace the batteries.
Read this forum for a while, and you will find that in day to day use people have more problems with Lithium not charging or just shutting off because of “cell unbalance” etc. then AGM’s.
No lead-acid battery will shut off because the current is 100mA too high, or the cells have a difference of 0.1V…Lithium can and does.
Yes, they live longer, but they are not without problems. My opinion.
Your opinion and advice is appreciated, so thank you. Again, I am by no means very knowledgeable on this topic.
If the current system has been for around 4 years, do you know what the duration the batteries would/should be able to power this fridge for now? Just as an approximation of course.
So Mikes calculation for 1 Lithium is exactly what you should have now for the 2 AGM.
Something between 40 and 50 hours…
Main thing is too keep track of the performance, check voltage at end of discharge once a week, check charging time needed every week.
Also, just as a test, you can shut down the system before charging , disconnect the two batteries, note the voltages, let them stand for 10 hours and note the voltages again.
If they drift apart or lose more then 0.2V -->> replace them.
LiFePo4 can’t be charged or can only be charged very slowly below 0-5 degrees C. You can discharge below that temperature. Maybe something to consider for your setup. Heating the batteries keeping them above a certain temp will help of course.