How to Charge Batteries in Parallel With Different Capacity

Рет қаралды 58,900

2 ай бұрын

Link to the diagrams: cleversolarpower.com/free-dia...
Link to my bestselling book on Amazon: cleversolarpower.com/off-grid...
MRBF terminal block: amzn.to/4bVvbpy
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In this video, I will show you the ins and outs of how to charge batteries in parallel, mainly focusing on charging lithium batteries and LiFePO4 batteries in parallel. I'll dive deep into what you need to consider if you're dealing with different capacity batteries in parallel, ensuring you understand the critical aspects of wiring batteries in parallel to maintain balance and extend their lifespan.
Wiring batteries in parallel is more than just connecting cables; it's about understanding the chemistry behind your batteries, whether lithium or lead-acid, and ensuring they're matched for optimal performance. I'll explain why it's crucial to use batteries of the same voltage and chemistry and what happens when you mix different types or capacities.
Charging lithium batteries in parallel comes with its considerations, especially when ensuring each battery shares the load equally to prevent premature aging called current sharing. I'll show you how connecting batteries in parallel differs from a series connection, including how batteries in parallel balance themselves automatically, a feature not shared when wiring in series.
The video also covers the importance of current sharing among batteries wired in parallel, demonstrating with practical examples how to achieve optimal wiring configurations for both small and larger battery setups. You'll learn why busbars may become your best friend for minimizing resistance and ensuring even current distribution across all batteries.
For those curious about wiring different capacity batteries in parallel, I'll address the common concerns and scenarios where it might be necessary, providing clear examples to help you understand the potential impacts on performance and lifespan.
Selecting the right fuse and wire sizes is critical when wiring batteries in parallel, and I'll guide you through the calculations to ensure safety and efficiency. Whether you're expanding an existing solar system or building a new one, understanding the role of fuses and the correct gauge of wiring is essential for protecting your investment.
Whether you're a seasoned solar power enthusiast or new to the concept of charging LiFePO4 batteries in parallel, this video is packed with valuable insights. I'll share tips on expanding your solar system by maximizing capacity without increasing voltage, ensuring your batteries deliver power more efficiently and last longer.

Пікірлер: 118

@cleversolarpower 11 күн бұрын

🎁 Free Diagrams: cleversolarpower.com/free-diagrams/ 📖 My Best-Selling book on Amazon: cleversolarpower.com/off-grid-solar-power-simplified 💵Use coupon code: clever6 to get 6% discount for Litime batteries: cleversolarpower.com/litime (cheaper than amazon)

@bradk8702 2 ай бұрын

Thank you so much for the generous candid info that is presented so CLEARLY. Received your book from Amazon three days ago 👍

@kenkrommenacker8649 2 ай бұрын

Thank You for all the info, and also just ordered your book.

@808pathfinder 23 күн бұрын

Just watching the video made me hit the like button and you showing all the wirering diagram made me hit the Sub, thanks for sharing

@cleversolarpower 23 күн бұрын

Thanks for the sub!

@philbrooke-little7082 2 ай бұрын

Lithium and lead acid work very well together so long as the lithium has a programable BMS. The advantage of doing this is that it saves the cost of having to get lithium profile chargers and it protects an alternator in the event of a BMS disconnect. It also gives redundancy. I’ve been running hybrid for several years and so have many other boaters.

@cleversolarpower 2 ай бұрын

What voltage are you setting your charge to?

@philbrooke-little7082 2 ай бұрын

@@cleversolarpower I set the BMS to disconnect charge at either 14 or 14.2v the chargers are set at standard lead acid so 14.4 and a float of 13.5 which suits both lead and lithium. Setting the BMS lower than the chargers ensures that you never get a ‘low voltage overcharge’ situation from the alternator or from solar controllers absorbing before going into float. The 14 / 14.2v is chosen as it allows the battery to enter the upper ‘knee’ portion of the charge curve and perform balancing if needed. I use 14v when solar is the main charge source and sometimes 14.2 if using the alternator as the current on mine can be fairly high (0.25+C) as that allows the battery to get a bit more full than it would at 14v. 14v works well with solar as, at the often lower charge rates, it gets the battery to around 99%+ full. My system is data logged at one minute intervals and I have used the data gathered to come up with those settings.

@cleversolarpower 2 ай бұрын

Thanks for your extensive answer. I might do a video about this when i run some tests.

@user-tn3sb2sv5m 2 ай бұрын

Very well explained

@MrDhandley 2 ай бұрын

What an excellent and very helpful channel. I have just installed 3 x 120a 12 volt batteries in parallel connected via two very thick solid copper busbars for a total of 360 amps. I took the negative off the first battery and the positive off the last and then ran them up to separate busbars for distribution to - 240vac/12dc charger, dc to dc converter and a 3000 watt inverter. I hope I did the right thing. I have now subbed to your fantastic channel. Thank you.

@cleversolarpower 2 ай бұрын

Thanks for the sub!

@russell7489 Ай бұрын

VERY clear You are brilliant

@aaronb483 2 ай бұрын

i never considered all those issues. Everything you said made complete since to me.

@cleversolarpower 2 ай бұрын

I'm glad it did!

@jhay_mstv6331 2 ай бұрын

Clear! Thank you sir , I'll subscribe

@earthenergyhex Ай бұрын

Great video, I learned alot

@cleversolarpower Ай бұрын

Thanks, make sure to subscribe so you don't miss out on future videos!

@donm1547 2 ай бұрын

Thank you for the PDF download, I just want to say that your disclaimer with conductor sizing based on the 90°C column really should be based on the 75°C column because most devices that will be terminated to that cabling will not be rated with a 90° C termination. Therefore the possibility of excessive heat being transferred through the terminations to the device could either destroy the equipment or cause a warranty issue.

@cleversolarpower 2 ай бұрын

I have never heard about lugs having a temperature rating. I researched it, and you are right; they do have a temperature rating. However, I do not think it plays a significant role as long as they are quality lugs and not cheap lugs. A welding wire rated at 105°C should then also be downgraded to a 75°C rating; that doesn't make sense to me. We did not take this into account when working for a major chemical company. I have a video about the quality of lugs coming out soon.

@darrylm3627 Ай бұрын

😄👍Good Stuff, Great Tips

@electroumit Ай бұрын

Thank you.

@jamesklingenberg9382 21 күн бұрын

Good to know. Thanks.

@majdgreen7983 2 ай бұрын

thank you for helpful explanation If I have 24v 200A lifepo4 battery used for about 1 year and I wanted to add another battery from same size and voltage and brand name could this be done ? what is the precautions ?

@cleversolarpower 2 ай бұрын

You can add the battery in parallel. Not a problem. The main positive from battery 1 and the main negative from battery 2.

@majdgreen7983 2 ай бұрын

@cleversolarpower thank you , but I was informed that the inner resistance of LiFePo cells becomes higher by time of using it .. and it is not recommended to connect new batteries with used one. Cuz there will be difference in cells resistance What do you think

@4115steve 7 күн бұрын

Do you need to worry about balancing when wiring batteries in series? Im on a facebook solar group there are mixed answers on this subject

@twiddler71 2 ай бұрын

Thank you for these great videos and I also have your book which has lots of great info. Is there a good way to test the capacity of AGM batteries? I have a bunch of used AGM batteries I'd like to use, but it's difficult to tell how much capacity each one has. I know some people say you have to run a load all the way down to 10.5v and measure the current draw, but I don't want to harm the battery.

@cleversolarpower 2 ай бұрын

Thank you for the kind words 🙏. If you have a shunt you can draw it down to 50% SOC and then double the capacity at the end. Then you know how much is left.

@twiddler71 2 ай бұрын

I was thinking about that, but then how can I know for sure when the battery is at 50%? AGM batteries will drop voltage under load. @solarpower

@cleversolarpower 2 ай бұрын

Good question, use a c-rate that is 0.05C for lead acid (20 hours). Then the voltage will not drop that much. Check by disconnecting the load and see if the voltage settles.

@twiddler71 2 ай бұрын

@@cleversolarpowerI tried using a DL24 load tester at 10amps load down to 12v, but my readings didn't seem consistent. I recharged all my batteries, then let them sit for 2 days and see which ones remained at the highest voltage. I had 3 out of 8 that were above 13v, so I'm guessing those are my best batteries.

@rb.tees2365 Ай бұрын

question?? i have 50ah lifeo4 24V series connection assembled and 75ah lifeo4 24V same series assembled..i am planning to parallel to parallel this so i can get 125ah...now the question... is it possible to use 1BMS 100A in this 50ah and 75ah if i combined it in parallel

@ivanwayne2507 Ай бұрын

Contemplating the following set up: adding 4 identical 100 amp Li batteries-3 will be in series for a 36 volt trolling motor. 1 will power an audio amp an isotherm 12 volt fridge. I will have a NOCO Marine 4 pole charger when plugged into shore power-thinking of charging when running motors with a DC-DC charger. Looking at the Vectran XS. Can I charge all 4 batteries with this DC-DC charger if I use a busbar? Thanks. Your videos are super helpful

@cleversolarpower Ай бұрын

Thanks for your sub! So your three batteries will run the trolling motor, and one battery will run a 12V fridge? Ideally, you need a 12V charger and a 36V charger. However, you can also charge the three 12V batteries if you manually switch them when one is full. However, this is not practical, so you need a separate 36V charger.

@ivanwayne2507 Ай бұрын

@@cleversolarpower Sort of: three of the batteries in series to run the trolling motor while the 4th one would be a house battery. Each battery will have a shore power charging from a 12 volt Noco Marine charger that will individually charge each battery as they are needed. When I am not on shore power I am wanting to charge the batteries with a DC-DC charger using a busbar. Not sure if the DC-DC charger will do that properly or do I need 4 DC-DC chargers

@neno2363 Ай бұрын

I have four GEL batteries. Two are 100 Ah each, and two are 120 Ah each. The inverter operates at 24V. I have three solar panels, each with 390W and 40V connected in series. The charge controller can operate at 12V, 24V, 36V, and 48V. What is the most optimal way to connect the batteries? Two batteries of 100 Ah in series, two of 120 Ah also in series, and then those two in parallel? Where should I place the fuses and of how many amperes?

@mortaneous 2 ай бұрын

Great video. Very informative. Question though: I built a 24v system using two 12v 200ah LiFePO4 batteries in series. Now I plan to increase the capacity to 300ah by adding a 24v100ah LiFePO4 battery in parallel. Assuming I have all the correct breakers/fuses and wire sizes in place, what (if any) should I be looking out for in this set up? Is this a safe configuration?

@cleversolarpower 2 ай бұрын

Run the third battery from the busbar like the diagram i showed near the end of the video. It will run perfectly.

@mortaneous 2 ай бұрын

I do have bus bars between the batteries and the inverter which I put there to facilitate addition of batteries in the bank. Thank you for confirming I'm on the right track!

@thetoolmat8632 26 күн бұрын

@cleversolarpower How many 100ah 12v batteries can i run on a 2000w Inverter? Is it up to 4 in parallel? Right now I have have 2 batteries and want to add a 3rd then a 4th when feasible.. thanks

@mirwanbaloch Ай бұрын

hi hello , i have two 12 volt 70 Ah battries and one big 12 volt battery of 120 ah , my solar inverter is of 24 volt and now how to connect these in series and parallel pls

@douggief1367 2 ай бұрын

Thanks for your great help. I have 3 LifePO4 12v batteries: 1 is 50 Ah, and 2 of them are 75 Ah. I also have a 1500w Pure Sine Wave Inverter. How many of these batteries should I run in parallel? I want to charge 48v EGO batteries as well as other low draw uses like 12v lighting. Many thanks. --Douglas.

@cleversolarpower Ай бұрын

You can run the 3 in parallel. other voltage systems should have different charge controllers and inverters.

@douggief1367 Ай бұрын

@@cleversolarpowerThankyou

@calumlovett7661 2 ай бұрын

Do you not need to worry about battery balancing as well? I would have though each pair of batteries in your diagram would need a balancer as they are in series? Can you confirm if batteries in series need fuses on each positive terminal or just the main out one?

@cleversolarpower 2 ай бұрын

Since the batteries are in parallel, they will balance themselves. The balancer inside each battery will take care of balancing the individual cells inside. Batteries in series don't need individual fuses. Just one at the positive lead.

@calumlovett7661 2 ай бұрын

@cleversolarpower I thought the diagram had 2 off 100ah batteries in series with 2 off 280ah batteries in series with both series "banks" then in parallel?

@cleversolarpower 2 ай бұрын

Ah, you are referring to the diagram. I don't think this will be a big problem. The BMS will regulate the individual cells of each battery. balancing happens when the battery is fully charged, so having the batteries fully charged from time to time will solve this problem of imbalance in a series connection. Every battery will balance to it's rated voltage independently. If the battery is cycled a lot at a high c-rate then this might become a problem.

@smartass5085 10 күн бұрын

Thanks for this. I have a technical issue with my setup. I have four 12v 200ah batteries from the same manufacturer. My inverter is a 24v system so I connected two batteries in series to give 24v and parallel with the other two series battery. Now I have the battery bank at 24v 400ah. After about 3 hours of use by the inverter, I noticed that the 2 batteries on the negative parallel line will drain to 10v while the 2 on the positive parallel line stays full at 13.3v. What could be the problem please? Could it be that the 2 batteries on the negative line draining to 10v are faulty? I have only used this setup for 2 days before noticing this as the inverter beeps low battery after 3 hours. Pls help.

@cleversolarpower 10 күн бұрын

What happens if you switch the leads over? Check your wiring again. Are there any imbalances in the batteries? If so, charge every battery individually with a 12v charger and connect again.

@dougiee6589 2 ай бұрын

This is good as for me

@chukwudinmaikechukwu Ай бұрын

Is it advisable to charger the battery with the ac output of the inverter charger, i.e the ac current the inverter charger produced?

@cleversolarpower Ай бұрын

You can charge the battery with the solar input or through the ac input. The output is used to power loads.

@parmeetsingh2381 Ай бұрын

i have two custom made 24v 100ah lifepo4 batteries made with 8 prismatic cells each. I used JK 100amp smart BMS. can these batteries be connected parallely? how BMS would handle the charging?

@cleversolarpower Ай бұрын

These can be connected in parallel. The BMS sees every battery individually. Because they are in parallel, they will be at the same voltage. One battery can charge with more current than the other, no problem.

@parmeetsingh2381 Ай бұрын

@@cleversolarpower thanks for explaining. Let me clear one more thing. i have two seperate custom made batteries EACH WITH A BMS. So there will be two batteries with two different BMSs. Still they can be connected?

@user-rp1vu1gk5u 15 күн бұрын

i have two power queen 12 volt100amp batteries. i am connecting in parallel with a renogy 700 watt inverter. can i use 6awg wires to connect both batteries?

@cleversolarpower 14 күн бұрын

Checkout my video about sizing wires. Then check my video about sizing fuses.

@sadohjoseph3888 Ай бұрын

Thanks for your tutorial. Please How can I get 48V and range of 3820Ah to 4000Ah when connected in series and parallel

@cleversolarpower Ай бұрын

Thanks! Why do you need that big of a battery? A 48V 5kW server rack is 100Ah. So you need 40 server rack batteries. That's $50,000.

@sadohjoseph3888 Ай бұрын

@@cleversolarpower please can I talk to you privately via email?

@LotsaThingsNstuff 28 күн бұрын

I have 8 batteries, should I do 2 sets of 4 to a bus bar?

@markpotter3057 2 ай бұрын

Hi there, mark here from Australia. I have two 135ah lithium batteries in parallel and two 300w panels in series . So I have 270ah and 600w of power going through the charge controller. Have I got that setup right or do you recommend another way if it’s an overkill. Kind regards, mark.

@markpotter3057 2 ай бұрын

Sorry I forgot to say I’m using a 2000w to 4000w pure sine wave inverter converter DC12v to AC240v unit

@markpotter3057 2 ай бұрын

Hi there I get the charge of the batteries thank you. When I send that charge to the inverter, how is that done please. 🤓🤓

@cleversolarpower 2 ай бұрын

600W/14.6=41A going to your batteries at max output. 2000W/12V=167A -> ok for lithium. Check my video on sizing wires and fuses.

@jamesalles139 2 ай бұрын

Personally, I would avoid mixing differing capacities with lead-acid chemistry. I believe that is following most manufacturers recommendations, also.

@simon359 2 ай бұрын

I have two battery banks. Eight 12 V Battle Born Batteries in series parallel at 48 V. The next battery bank is four SOK 12 V batteries wired in series parallel, for 48 V. The only difference is that the Battle Born Batteries are 1C and the SOK are .5 C. I have them on separate shunts, because the battery voltage charging is slightly different. Both battery banks are run to a positive and negative busbar. I put each battery bank at their proper amp hours. On the Battle Born Batteries shunt I have 200 amp hours and for the SOK I have 100 amp hours. This gives me a total of 300 amp hours. The only thing I’m unsure of is whether to have my Victron Quattro 5000/48V inverter set at 300 amp hours?

@cleversolarpower 2 ай бұрын

Yes, I dont see a reason why not. Since you said they have different voltage charging, why not set both to the lowest recommended voltage voor charging, for example 57.6V instead of 58.4V. then you can use one shunt for the whole battery bank, and every battery is in the recommended range.

@simon359 2 ай бұрын

@@cleversolarpower Using two different shunts, I can dial in the exact voltage recommended per manufacture, for each battery bank. There’s quite a bit of difference between each charge setting. 55.2 for SOK and 56.8 for BB. This gives me the ability to set the charge controllers for the best average. 🖖

@cleversolarpower 2 ай бұрын

Then i would set it at 55.2V, you are not going to 'waste' much capacity by lowering the voltage of your whole battery bank. And lithium likes not being charged all the way up to 100%.

@Entity005 Ай бұрын

Question. i got hold of 57 free batteries of 6volt 4,5Ah NiMH type of batterys .. Thats a lot of batteries.. i wish to make a giant powerbank in parallel connection .. Is there something i have to remeber? ... do i need thicker cables then the ones that already are on the batteries? how is it when i charge that many batteries in parallell ? do i need a super charger? or just use a normal charger that will just take much longer time? I also got a hold on 43 of 4 cells NiCd batteries with a voltage of 4,8 and they have 4,5Ah -- planned to make a 2nd powerpack with those. All batteries are only 3 years old and they are fully functional.. they had to be replaced because of strict rules on batteries that feed emergency light on ship .. they get replaced every 3 years even the law say 5 years.. guess shipping company just want to make sure their ok .. they have been maintain charged trough the years they been active.. and they only sometimes get used on test of the emergency light onboard.

@cleversolarpower Ай бұрын

The 57 batteries are not that big actually. Assuming they have 100% of their capacity left, it's only 1,500Wh. A little more than a 12V 100Ah battery which now cost $260. Your second battery is 928Wh, close to a 12V 100Ah battery. So would you rather spend a lot of time, money for a BMS and not knowing if it is safe than buying two 12V 100Ah batteries for $520? I think you know the answer.

@sinan1752 26 күн бұрын

I wonder if its possible to charge 4 serial connected batteries(48v) with a 12v charger with a ballance wirering

@cleversolarpower 19 күн бұрын

You can do that when there is no load attached. good for initially charging the batteries before commissioning them. But should not be done long term.

@user-lx9kj8qv3p 25 күн бұрын

So I have a question, I have a 24 volts inverter and from my calculations, 3 lead acid batteries of 200Ah will be enough for my daily usage. Now how do I go about this, can I connect two of the 200Ah batteries in parallel thereby giving me 400Ah at 12v then connect this to a single 200Ah battery in series to give me a 24v battery bank? If this can be done, what will the total battery bank capacity be.

@cleversolarpower 19 күн бұрын

You cannot connect different capacity batteries in series. You can only use 2 batteries.

@miroperinich2495 Ай бұрын

I am a qualified fitter for solar photovoltaic systems. I am interested in what would be the order of the budget for one system. What does it start from?

@cleversolarpower Ай бұрын

It depends on how much power you consume and how long you want the battery to last on cloudy days. off-grid is going to be more expensive than on-grid. But if the power company charges more than installing an off-grid system, then the choice is clear.

@RS474 2 ай бұрын

I must have missed the part where you explain what the Shunt is for?? Or is that in another video??

@rainerinedinburgh5807 2 ай бұрын

The shunt is for measuring the current going into and out of the battery bank. That way the charge controller (or perhaps a separate capacity meter) can keep track of, and show you, how full the batteries are.

@cleversolarpower 2 ай бұрын

Couldn't have said it better.

@taiwomathew8969 2 ай бұрын

How can I access your e-books

@cleversolarpower 2 ай бұрын

You get get it on amazon or on my website in the 'shop' section.

@rehoye 2 ай бұрын

What value is there in isolating the batteries with shotky diodes?

@cleversolarpower 2 ай бұрын

Never heard of it, so i assume nothing. Why do you think this is beneficial?

@sportsupdate1413 8 күн бұрын

Is this possible? = 2 batteries 12V 100AH each, connected in SERIES (Result: 24V 100AH). And after that this will be connected in PARALLEL with 1 battery 24V 100AH (Result: 24V 200AH). Thank you!

@cleversolarpower 8 күн бұрын

Yes

@christiangusy1246 Ай бұрын

Hello. Your books are no more available. What's the problem ? Thank You.

@cleversolarpower Ай бұрын

It has always been available on Amazon.com

@christiangusy1246 Ай бұрын

@@cleversolarpower thank You for your rapid answer. I wish You a good day. Chris

@ssekyanzirobert9401 Ай бұрын

What's the best way to wire 3 solar batteries in parallel ?

@cleversolarpower Ай бұрын

Check the diagrams in the video.

@josepeixoto3384 Ай бұрын

That's nic,but I do mix Li and Lead-acid, on separate parallel arrays; they work perfectly together with me,for 1.5 years now, and L-As need no BMS, they not have it in cars or trucks;

@Jon-fs2zj 2 ай бұрын

What if you wanted to charge 7 batteries go two groups 3 and 4?

@cleversolarpower 2 ай бұрын

Correct.

@mINGzTH Ай бұрын

I would like to be clear. Parallel different capacity batterries is ok to do or not?

@cleversolarpower Ай бұрын

It's ok.

@mINGzTH Ай бұрын

@@cleversolarpower thank you sir

@SamCarleton 2 ай бұрын

Last summer I bought a lithium battery and want to purchase another one and hook them in series, is that safe?

@cleversolarpower 2 ай бұрын

Yes, just be aware of balancing issues. Check my video about batteries in series.

@SamCarleton 2 ай бұрын

@@cleversolarpower thank you. I was going to use a battery balancer

@louf7178 2 ай бұрын

I trickle charged two batteries in parallel, but find this not good enough. The difference of conditions leads me to believe the weaker battery undercharges and therefore could sulfate. Therefore, I individually "top" them off.

@dnomyarnostaw Ай бұрын

I presume they are lead acid? You didn't say. He seems to think all examples have s battery management system.

@rainerinedinburgh5807 2 ай бұрын

I think you've made a mistake. You emphasize the importance of having the same series resistance in the charging wires. You correctly recommend a pair of bus bars from which the wires to all battery terminals are of equal length. But your alternative solution for 5 batteries does not achieve equal resistance. If you have five batteries with four red and four blue link wires as shown at 2:50, then for batteries 2, 3, and 4, the series resistance consists of two link wire resistances (counting from the points where the main red and blue cables first split). There are two blue links for battery 2, two red links for battery 4, and one red plus one blue for battery 3. So far, so good. But batteries 1 and 5 each have four link resistances (one red plus three blue, or three red plus one blue). Surely, for equality, the main red wire should go to battery 1 and the main blue wire to battery 5. That way each battery has four link resistances in series with it.

@cleversolarpower 2 ай бұрын

Indeed, it doesn't have equal resistance. This is how I would wire it if I don't want to use a busbar.

@diyEVguy 2 ай бұрын

@rainerinedinburgh5807: Agreed. See also Victron Wiring Unlimited.

@joemaxxcapri1799 Ай бұрын

I have only 3 Agm

@davemac521 18 күн бұрын

Know your battery chemistry.batteries should always be within a specific voltage when connectin in parallel or serial. Lithium batteries should always be fully charged and within .2 tenths of chage difference.

@cleversolarpower 18 күн бұрын

In series yes, not in parallel.

@davemac521 18 күн бұрын

Never install batteries of different ratings in any battery bank. The bank will not equalize and the lower capacity battery will reduce the capacity of the larger batterie. Reducing over all capacity of the entire battery bank over time.

@cleversolarpower 18 күн бұрын

Like I said in the video, you can parallel different capacity batteries.

@johnbrown6189 Ай бұрын

This expiation is not correct at all. If the voltage rating of the batteries is the same even though they are different capacity batteries they will supply the same current to the load.

@cleversolarpower Ай бұрын

No, try it yourself.

@rk_bhartiya Ай бұрын

Nooooo

@johnbrown6189 Ай бұрын

I don't need to. My statement is correct. Try looking at it like this. Using a 10L (10AH bat) tank, 5L(5AH bat) tank, 5mm tee hose where the tanks are connected and the third end goes to a valve then to atmosphere. The tanks are sitting in such a way that the water levels are at the same height. Now open the valve water will drain from both tanks equally same as in batteries. @@cleversolarpower