Begginer working my way up - Am i beating around the bush?

[MrModules]

Heyo everyone, im new to solar setups although i have tried watching videos and tutorials. Ive been tinkering with a small battery bank with a friend for about a year and progress is kinda slow. Living in australia it can take a while for parts to come in. Skipping most of the background, Im using six of these 18650's to make a very tiny 24v battery bank. I have them place in one of these i find it a bit iffy to understand on where to charge/discarge from (ive been using the +/- Screw collum ports. Finally i have a small 500W 24v inverter 1x USB and 1x mains.

Ive seen some debates about begginers using 18650s, also probably impractical using only 6 of them. I work part time so investing straight into Deep cycles or more renowed 18650's + quantity would take me a fair time plus more parts. Wanting to start small and slowly build up as a hobby, our house has solar but a battery for 13kwh is $12-$14k and got me into making my own solar stuff. Straight up am i wasting my time being such a small battery bank (i have used the inverter to power 2 usb devices for a while before i guess the voltage dropped too low (currently waiting on a Battery Capcitor that i hope will read this right) multimeters read my batterys as max volts (as said im new and after using a battery i thought the volts were meant to drop i have a basic battery voltage reader i used too that stuck to 100% but the volts dropped until i disconnected the load then it began to rise again) But if its still worthwhile to tinker with this and slowly increase the Mah capacity, what kind of charge controller should i get, based on will's videos theres calculations but people also using 'C' like 0.2c or something as a charge rate (roughly 1amp i think) for 18650s. This is the part i get lost on. I have 6 bigger pannels i plan to use on the shed once i get a grasp and go bigger on a battery bank. Also what are the higher quality australian deep cycle batteries, prefferably Lifepo4.

Thank you for any future help/feedback, appologies about the read.

 

[Bud Martin]

Your battery is rated at 2200mAH = 2.2AH, I do not see max discharge C rating of that battery.
500W 24V inverter willl draw 500W24V = 20.83A! (actually to get 500W of AC power on the output of the inverter, the current will be about 20% higher due to conversion loss, and as the batteries Voltage goes down the current will go up) So you are trying to draw 20A from you batteries, it is not going to run very long with 500W load since 24V x 2.2A =52.8W.
1C of your battery = 2.2A
0.2C of 2.2A = 0.44A

BTW, are you using BMS with your battery pack?

 

[MrModules]

Yes, theres BMS attached to the battery pack holder. So i should increase my capacity by 10? being 10p6s (10 of the same stacked ontop of each other) unsure how popular these pack holders are but they are better than trying to make my own.

 

[Bud Martin]

How much power are you planing to use?
Do you know what the standby power the inverter use when it is on but no AC load connected?

 

[MrModules]

This is the inverter and as for its own draw 0.7A.
2200mAH is low, if i made it like 8800Mah, would that increase the charge controller and solar panels compared to the current 2200 setup? making a bigger battery bank my main focus prior to charging needs. I plan on using what ever the bottleneck is and just slowly adding to it as i get familliar and comfortable with whats going on unless that road the futile.

 

[Bud Martin]

This is the inverter and as for its own draw 0.7A.
2200mAH is low, if i made it like 8800Mah, would that increase the charge controller and solar panels compared to the current 2200 setup? making a bigger battery bank my main focus prior to charging needs. I plan on using what ever the bottleneck is and just slowly adding to it as i get familliar and comfortable with whats going on unless that road the futile.

For now without talking about the solar charger, so if you have inverter that use 500Wh of power, that means if you want to run it for 1 hour you will need 500Wh battery pack, but actually you will need about 600Wh battery, then in real world you should not be draining the battery down to 0, so if you factor in 10 ~ 15%, then you will need about 700Wh battery pack.
That is the simplest explanation I can give for you to get rough idea how to go about what size an how long the system will run, so you can just use the math to scale it up or down as needed.
When the time come to deal with the charging, you need to find out what the max charging rate your battery and the BMS can take so you can get the charger that has adjustable charging rate, I never do full charging rate per spec, I will do about 20% less if I can.
You also need to look at the BMS charge and discharge current spec since it will limit how much current you can draw from the battery or how much you can charge the battery with.

 

[MrModules]

the BMS ebay description says max 2A per layer, wouldnt 1A be more fitting for 18650s? putting it down to 0.8A per layer? i could buy better batteries with a actual brand behind it maybe these or other options. I dont know where to begin looking (australian based) so many types of chemical makes, protection, discharge rates etc. feels overwhelimg at times and i give up for the day, to stay up all night thinking of what i can do. Deep cycle lithium batteries are just as sketchy it feels, negetive reveiws outweigh the positive ones at times. theres this but i'd need two to make up the 24v. Thank you for teaching and sticking with me.

 

[Bud Martin]

the BMS ebay description says max 2A per layer, wouldnt 1A be more fitting for 18650s? putting it down to 0.8A per layer? i could buy better batteries with a actual brand behind it maybe these or other options. I dont know where to begin looking (australian based) so many types of chemical makes, protection, discharge rates etc. feels overwhelimg at times and i give up for the day, to stay up all night thinking of what i can do. Deep cycle lithium batteries are just as sketchy it feels, negetive reveiws outweigh the positive ones at times. theres this but i'd need two to make up the 24v. Thank you for teaching and sticking with me.

I never seen BMS current rating in 'Layer', I have no idea what that means.
1A rating current and the from factor of 18650 really has no direct relationship between each other, for example the battery pack with 18650 used in cordless drill has high C discharge rating made for power tools, they use BMS that can handle high in rush current.
You also dealing with Li-ion that you have to handle properly with proper safety since you do not want to have fire.
BTW, what exactly are you trying to accomplish? Learning by building small system to fully understand how all components works together first before going into bigger system later on?
May you should provide us what your need is so we can help design the system so you can get the correct components.
BTW, English is my second language so my writing is not very good and may not make sense to you, I am just trying my best to explain it.

 

[MrModules]

You're fine, easily understood. My plan is to power a shed. first using the 500W inverter then expanding. learning as i go and making bigger systems if i want. I dont have things like "i want to power X,Y,Z" getting a working 500W inverter in full use would be great. My grandfather has a bigger 2000W 12V interter that i might plan to use too once i can find specs on it (its in the shed i have to find) I can start from scratch, money spent so far is about $100 so thats all to current learning, some other things were gifts so im not out of pocket.

 

[Rednecktek]

You're fine, easily understood. My plan is to power a shed. first using the 500W inverter then expanding. learning as i go and making bigger systems if i want. I dont have things like "i want to power X,Y,Z" getting a working 500W inverter in full use would be great. My grandfather has a bigger 2000W 12V interter that i might plan to use too once i can find specs on it (its in the shed i have to find) I can start from scratch, money spent so far is about $100 so thats all to current learning, some other things were gifts so im not out of pocket.

Since you're just putting together a small learner system, have you considered grabbing a couple of cheap WallyWorld FLA batteries and get the rest of the system going? That ought to get you a functional system with enough capacity to really be able to test and calculate out actual draws and loads without nuking your tiny 18650 pack. Then once you have numbers you can plan out from there whether you want to stick with the 18650's or jump to the bigger EVE/Linshen/CATL type cells. You'd only be out about $200 for a 24v bank with 60Ah or 1440Wh of usable power.

Just a thought.

 

[MrModules]

Since you're just putting together a small learner system, have you considered grabbing a couple of cheap WallyWorld FLA batteries and get the rest of the system going? That ought to get you a functional system with enough capacity to really be able to test and calculate out actual draws and loads without nuking your tiny 18650 pack. Then once you have numbers you can plan out from there whether you want to stick with the 18650's or jump to the bigger EVE/Linshen/CATL type cells. You'd only be out about $200 for a 24v bank with 60Ah or 1440Wh of usable power.

Just a thought.

I'd need to find an australian counterpart. Using Deepcycles look like less hassle and work, need to research into reliable brands that we have here. Using non lifepo4 seems a bit of a drawback since i would have set ammount i can use of the batteries % but for a testing rig it shouldnt be that bad.

I could also try using these 12.8V 7Ah lithium deep cycles, $80AUD each so kinda the same price without conversion. still being ~$160 for a 24v 7Ah system

 

[Bud Martin]

But if are you not doing it for learning for now so you can figure how the system works before spending money on the big system with more money? It is like doing lab home work for now until you get more understanding.

 

[Rednecktek]

Something to keep in mind is that the acid based batteries (FLA, AGM) can only be discharged to 50% before you start damaging them. That and the voltage adds up but the Amp Hours stay the same. I think the term in your neck of the woods would be "Leisure Battery" and a 120Ah-ish battery should run you about the same price as those 7Ah batteries, give or take. and give you about 60Ah of usable power, or 1400Wh of run time.

So your 7Ah batteries are good for about 7h @ 24v or ~165Wh of usable power which doesn't last long, like 17 hours total run time for a LED bulb, 4 hours of 40w LED light strip, etc. Just to give you some perspective.

 

[MrModules]

AGM's interested me at first, but the thought of only being able to use a set % feels like a waste to me, I havent studied in any electrical classes or been in this hobby for too long to know pros/cons about most of the basics, appologies if it feels like im skipping what you are all saying. im trying to soak in the knowledge.

Havin a quick look around 6 of those 7Ah batteries work out cheaper than most AGM betteries, two 7Ah batteries are cheaper than a single 6/12V AGMs, this could be for numerous things (faults, not a good brand etc being cheap) it feels hard to source reliable brands in australia. 6x 7ah ($480 AUD) not including a bms, they have their own but a primary one would be nice, is within my budget if i save for a while and buy them in pairs and tinker with them powering the inverter. I also received this battery capacitity controller today. The wires are my own so yeah it looks a little dodgy.

 

[Bud Martin]

So where is the BMS? The green circuit board under the battery holders?
BTW, do not leave that monitor connected all the time, it will drain battery cell #1 and #2.
The capacity reading is also not very accurate since it is based on battery Voltage, it will not give accurate SOC (State of charge).
It is funny that meter is called "Capacity Controller".

About this item​

• Suitable - Use for LiPo / LiFe / Li-ion / NiMH / Nicd / battery, it can also display the voltage of each cell, so you know when they need to be balanced.
• Battery Capacity Checker - It can display the estimated capacity and voltage for battery. Use this function to quickly check if your battery requires charging before use.
• LCD - The screen displays highest and lowest voltage of cells and the difference between highest lowest cells.
• Display Mode - Battery cell voltages, total voltages, lowest cell voltage, highest cell voltage gap between highest cell voltage and lowest cell voltage, remaining battery capacity(%).
• Balance Function - Optimize your battery’s performance, and extend the overall lifespan, by ensuring the individual cells are balanced. Press TYPE and MODE button for 3 seconds, when you hear DIDI means Balance function opened.

 

[45North]

Sounds good!
I'm all for making a small inexpensive system to learn about solar. That's what I did (see my show-and-tell in my sig)
That way you can learn from your mistakes and it won't cost as much!
I'd suggest sticking with the lead-acid batteries for now 'till you know what you're doing and what you need. Li is still very expensive.

I started with Will's book to get a general idea of how solar worked first, and a step-by-step implementation.
But I know what you mean about the learning curve: there's a lot of info out there and it's overwhelming at first.

Try to get an idea of the forest before you get bogged down in the trees!

 

[MrModules]

So where is the BMS? The green circuit board under the battery holders?
BTW, do not leave that monitor connected all the time, it will drain battery cell #1 and #2.
The capacity reading is also not very accurate since it is based on battery Voltage, it will not give accurate SOC (State of charge).

the BMS is under the curcuit board, i had the capacitor only on while testing and seeing how it works. I generally disconnect everything after having a look.

Sounds good!
I'm all for making a small inexpensive system to learn about solar. That's what I did (see my show-and-tell in my sig)
That way you can learn from your mistakes and it won't cost as much!
I'd suggest sticking with the lead-acid batteries for now 'till you know what you're doing and what you need. Li is still very expensive.

I started with Will's book to get a general idea of how solar worked first, and a step-by-step implementation.
But I know what you mean about the learning curve: there's a lot of info out there and it's overwhelming at first.

Try to get an idea of the forest before you get bogged down in the trees!

cheers for the encouragement. at first when learning about it all and conversions, ohms, watts, volts, etc it was mind boggling, ill continue to gather info here and brainstorm with others before making my next move. yeah Lithium is very expensive, and australia isnt big on this yet despite there being many options.

 

[Bud Martin]

Here is an Aussie guy, he gets lots of stuff from China as well.

https://www.youtube.com/c/OffGridGarageAustralia

 

[MrModules]

Took a little refresher off thinking about the setup to come back using a few calculators. To run my 500 24v inverter (going at 450 Watts at 24V continuous) I'll be basing future 'needs' running my inverter at 450 watts or roughly 90% from full throttle, i dont like maxing machines.

Which equates to,


Meaning i should just save $12,000 AUD for one of these from my electrical company and have it all basically done neatly with warrenty (but basically saying bye to my hobby for a long time) Also, i wouldnt have to worry about solar pannels, it would be powered by my house. I feel like ive done something wrong, a 24v 500W inverter to run all day at near max needs one of these? Appologies if its something obvious or a miscalculation.

 

[Jordi]

Heyo everyone, im new to solar setups...

I have one test setup similar to what you are doing and that can help you understand the limits of what you are trying.

I have a 18650 8S2P battery made out of 2,5Ah LG cells. I am discharging it with a 590W MPPT grid-tied inverter. The MPPT function determines the best discharge point is at 170W when the batteries are full and that power goes down over time slowly. The current for that discharge is 6,5A, so 3,25 per group of cells. In terms of C-rating, this is 1,3; probably over the desired discharge rate. Your cells may do better but I would not expect miracles for such type of 18650 you have.

In my case, the cells get very hot and after 30 min I disconnect the battery based on how hot they feel to my hand. Perhaps that is no problem, but certainly a hot battery is undesired. Now back to your case; assuming a favorable 1 C-rating for 2,2Ah cells; you need 10P8S; If you go for 6S, the problem is that the voltage of the battery groups is lower and you need to draw more current per group to achieve same power; then with 6S you maybe should go 11P6S or 12P6S.

Another issue of the 18650 is that unless you have a programable inverter with fairly wide voltage ranges; protections might stop you from fully charging the 18650 cells or fully discharging which means you will have unused capacity.

Back to my case, my MPPT grid tied inverter cuts discharge at 22V. If I use a 8S group, that is 2,75V per cell; the battery is practically fully discharged when the inverter cuts the load. If the group is 6S, the inverter stops at 3,67V per cell; the 18650 still contain perhaps 50% charge but the inverter won't use it. Practically speaking the capacity of my battery became much lower.

I saw the holder has no BMS, with that big amount of cells I find the likelihood of one cell having a different voltage over time very high; when that happens the least worst that can happen is that you kill the cell. Without BMS do not operate continuously; without BMS experimenting with supervision should be ok.