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Noob question: 12V 100aH batts in series?

cyclingccrn

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May 21, 2022
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I am planning to wire 2 280W 12V panels in series to produce 24V into an MPP 2424 into my battery bank. I planned to do 2 renogy 12V 120aH batteries (just purchased on sale) wired in series. Ian @ Watts247 seemed to agree this is an ok plan. However, I am just reading Will's book and on page 36 he says he doesn't recommend wiring batteries in series.
Can someone please educate me on this or point me to a thread where it is answered? There is an incredible (and somewhat overwhelming) amount of information here.
Thanks in advance.
 
It's certainly easier if you use 24V batteries for a 24V system but putting two 12V batteries in series does work. I've been doing it since last summer and it is working just fine. The trick is to be sure you properly balance the two batteries together before putting them in series.

The most important first step is to ensure that the batteries you have can even be put in series. Many can't. I just looked at one of the Renogy 12V 100Ah LiFePO₄ batteries and it clearly states that they can NOT be put in series. If that applies to the ones you bought then you need to return them. Either find a 24V battery or find a 12V battery that can be put in series.
 
I mis-typed. They are 100aH. Thanks for the input. Noob mistake, I assumed that any battery could be wired in either series or parallel.
 
Bought 2 of these
 
Not all of them.
I hope you can return them.
Connection MethodParallel(Up to 8)
 
Way down on the page you linked you will find the following text:

Renogy said:
Please note that do not connect batteries in series, and the maximum number that can connect in parallel is 8.

If you end up shopping for other 12V LiFePO₄ batteries (instead of 24V), find an explicit statement that mentions being able to put them in series. If you find nothing either way then assume they can't be put in series.

You might want to start with Will's page:


There are some 24V batteries on that page (along with 12 and 48). Some of the 12V batteries on his page also come in 24V even if not shown on his page.

Noob mistake, I assumed that any battery could be wired in either series or parallel.
With LiFePO₄ batteries it is dependent on what the BMS supports.
 
Thanks so much. I did look at Will's page for options, appreciate the link. Renogy has a "no hassle" return policy. However, I am now reconsidering just going with 12V system (which would eliminate the necessity of conversion for all the 12V appliances, including fridge). Having looked more closely at the math, I think I can parallel the 240W panels that have max output 7.9A each using a 40A charge controller and still be able to use 10AWG wire from panels to controller. The all-in-one systems I was enamored with don't seem to have the output I want/need for the AC side in a 12V configuration. Does that seem right?
 
Having looked more closely at the math, I think I can parallel the 240W panels that have max output 7.9A each using a 40A charge controller and still be able to use 10AWG wire from panels to controller.
How many panels do you have? 40A on a 12V system means about 480W of solar. That's only 2 240W panels. With 24V you can double that.

With two panels you can put them in series which would be better than parallel unless you have lots of shading issues or if your SCC can't handle the voltage from two in series. Most likely it will be fine. Post the specs if you need help determining what will work.

The all-in-one systems I was enamored with don't seem to have the output I want/need for the AC side in a 12V configuration.
What output do you want/need?
 
I have 2 240W panels (you nailed it). I plan to have relatively low overall daily needs (<2kWh) but would like to be able to operate an 1100W 110 microwave for brief periods (most of these micros surge to ~2000W upon start but I'd like to have a cushion), as well as an electric tea kettle (again just a few minutes a couple times a day). Will's advice is to buy the biggest inverter you can afford but I don't want something huge. The 12V MPP has only 1000W of output. All that said, I have been looking at 2000-3000W inverters. The ability to increase solar array size was one of the reasons I was thinking of going to 24V. The other was controller size/price (60A gets spendy). The MPP 2024 seemed to check all the boxes. However, my space for batteries isn't very big and I haven't found a 24V battery narrow enough to fit.
I will be running 12V fridge, propane cooktop (only for incidental face lighting and electric start), water pump, usb outlets, heater fan, bathroom fan, maxxaire main fan, led light strip, 2 led ceiling lights, fan for battery box as needed. All these 12V loads make me not want to use a 24--12V converter. Seems like a lot of loads but they are all small and will only be in use intermittently. When we camp we are outside during 90% of daylight hours.
I appreciate the experience and willingness to help by those on this forum. Perhaps some day I will know enough to say something intelligent or helpful.
 
Welcome to the party cyclingccrn.

I miss things sometimes, the following may not make any sense.
I have yet to hear of anyone coming up with a 12, 24, 36 or 48 volt cell, so doesn't every battery have a series connection?
 
so doesn't every battery have a series connection?
Any battery made up of smaller voltage cells will have those cells in series. That's not related though. It's the BMS of some LiFePO₄ batteries that can't handle being hooked up in series (or in some cases, parallel) with another battery's BMS.

I plan to have relatively low overall daily needs (<2kWh)
That's actually not low. I average about 500Wh per day in my trailer. Maybe 700Wh on cold days when my propane heater fan has to run a lot. I have two Maxxair fans (12V), 54qt DC refrigerator (24V), lots of LED ceiling lights and strip lights (24V), composting toilet fan (12V), water pump (24V), mobile router (24V), Raspberry Pi (12V), and propane heater fan (12V) in the cold. I also have 12V plugs with various USB adapters for charging my phone and laptop. It's surprising how little all of that takes. Recharging my laptop is probably the biggest power hog. I do not have a microwave or other electric cooking-related items. Just a propane stove and oven. An 1100W microwave running for 5 minutes will be about 200-250Wh. A single 12V 100Ah battery only has 1280Wh of power so that 5 minute meal is 20% of the battery.

Probably wouldn't hurt to do a proper energy audit. See:


Then you can be sure about how much power you will really use.
 
Any battery made up of smaller voltage cells will have those cells in series. That's not related though. It's the BMS of some LiFePO₄ batteries that can't handle being hooked up in series (or in some cases, parallel) with another battery's BMS.
Good call, thanks.
I had not considered the BMS which is apparently what limits my battery's series and parallel connections.
My 12 volt, 200Ah batteries are limited to 4 in series to a total of 48 volts. They are also limited to 10 in parallel.

@cyclingccrn
I second the energy audit. Spending a little time now is better than crying for a long time in the future.
 
I'm still struggling to understand the reason that the renogy batteries can't work in series.
- I understand the need to properly match/balance the SOC and voltage of both batteries
- I understand that if (when) they do get out of sync, a manual balance would be necessary
- I understand that you may even need to put additional 'safeties' in place to prevent Over/Undervoltage on individual batteries
.... but I still don't understand why you can't put them in series.

Any additional thoughts?
 
I'm still struggling to understand the reason that the renogy batteries can't work in series.
Because Renogy specifically states that their LiFePO₄ batteries (at least the 12V 100Ah ones in question) can't be put in series.

It's the BMS that they use in their batteries that doesn't support being in series. The BMS probably can't handle the higher voltage.
 
Still doesn't make sense to me. The voltage potential across each BMS is the same (~12-14V). I get that you could run into a weird situation where the BMS on battery A turns off because the battery is full/empty, causing the entire pack to turn off.

Maybe I'll email Renogy and ask what the limitations are....
 
Still doesn't make sense to me. The voltage potential across each BMS is the same (~12-14V). I get that you could run into a weird situation where the BMS on battery A turns off because the battery is full/empty, causing the entire pack to turn off.

Maybe I'll email Renogy and ask what the limitations are....
If the batteries are in series though, the charge will be 24V+ not 12V+. Maybe that's why they cant be put in series, because the BMS cant handle a 24V charge. (I'm no expert, but that's my 2 pence worth ? )
 
Still doesn't make sense to me. The voltage potential across each BMS is the same (~12-14V). I get that you could run into a weird situation where the BMS on battery A turns off because the battery is full/empty, causing the entire pack to turn off.

Maybe I'll email Renogy and ask what the limitations are....
Like you were told, its the BMS (battery management system) that will not take the in series as higher voltage.
 
Generic response...
Unfortunately, our Lithium Batteries are only designed to connect in parallel as they may damage the unit if it is connected in series.
 
Interesting discussion. As a noob, I just accepted to info on the spec sheet that I hadn't seen when first ordering them. As a follower of Will's videos (although certainly haven't seen all of them) and a reader of his book, I had already done an energy audit, although I appreciate everyone's suggestion very much. The audit revealed a likely daily average usage of ~1600W (although it is likely I have forgotten some device or will add one at some point). That said, I added a margin of safety/error and decided on ~2000W.
The only 2 AC loads on the system will be the microwave and the tea kettle, both of which are used only intermittently for brief periods.
Because there are many 12V loads and because a 24V to 12V converter seems inefficient and would also likely be the weak link in the system, I am now deciding to go with a separate charge controller and inverter as show on Will's "blueprint". I plan to use his affiliate links to the Renogy controller and Giandel 2200W inverter.
Any further thoughts or suggestions are appreciated.
 
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