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16 cell 280ah 12v config, final answer?

Firstascent

Solar Enthusiast
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Mar 7, 2020
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So I've gone through many variations for my battery pack from 48v to 12v, what to parallel, what to series, what shape, using a bus bar to parallel each 4s pack, everything haha.

I think I've got my final answer. I now have the new MultiPlus II 12/120/3000 so I'm set to 12v now. I have a Victron Lynx Distributor I was going to use as the parallel connection for each 4S pack in my RV as an easy way to take a pack out of service. This would be nice, but I didn't want quite that many extra wires. So I'm doing a little of both.

As you can see in the photo, I'll be splitting it into two main batteries with the main leads still going to a Lynx Distributor as the final parallel connection. This will allow me to still take a pack out of service, just not quite as small as a single 4S pack. This also put the main leads exactly where I want them for a clean run to my Distributor.

Let me know what you guys think! I'm on about day 3 of top balancing these 16 cells and I'm only up to 3.35 volts haha, getting closer.

Still deciding on whether I want to run these through 1 battery ON/OFF switch with a dual circuit or have a separate switch for each battery.
 

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What you're building is 2p4s2p. Two distinct batteries that are 2p4s.

My preference would have been 4s4p, with a BMS on each 4s battery. I'm not a fan of paralleling cells, but it's not uncommon. I simply want more control/reporting over each cell.

I would have no problem with all the wires. I would bring all four batteries into a set of common battery bus bars, then run a big cable from that to the system common bus bars.

I have yet to have a situation in my system where I brought down one battery, to leave the other running the system. If you think that might happen, then a switch on each battery is appropriate. A fuse on each battery should also be considered.
 
What you're building is 2p4s2p. Two distinct batteries that are 2p4s.

My preference would have been 4s4p, with a BMS on each 4s battery. I'm not a fan of paralleling cells, but it's not uncommon. I simply want more control/reporting over each cell.

I would have no problem with all the wires. I would bring all four batteries into a set of common battery bus bars, then run a big cable from that to the system common bus bars.

I have yet to have a situation in my system where I brought down one battery, to leave the other running the system. If you think that might happen, then a switch on each battery is appropriate. A fuse on each battery should also be considered.
Yeah I'm definitely not saying it's the Best option, but I do like the layout.
I have a Batrium for partly this exact reason, I can do any config and monitor each and every cell, and can change config's at any time easily.

I do know some people's battery config is BMS dependent on its capabilities, I always wonder what everyone would do if their chosen BMS could do whatever they wanted it to do :)

Yes one of my first options was going to build a 4s4p with the paralleling done through a busbar. Really the only reason I went against this is because I didn't want the extra 4 wires :) so by just paralleling the two batteries it's kind of in the middle.

I do agree though and do not expect there to be a situation any time soon, or hopefully ever, where I need to take a battery out of service, but I'm still adding a switch for each battery. Still designing the system, adding/removing switches and fuses etc, choosing all my components, but it will be fused and switched. There will be a few more iterations of design before it's finalized for sure.

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High quality switches and fuses are expensive. I went with one switch and fuse combined for both batteries. Yeah, do as I say, not as I do. Space was at a premium. That's my excuse.
blush2.gif
 
High quality switches and fuses are expensive. I went with one switch and fuse combined for both batteries. Yeah, do as I say, not as I do. Space was at a premium. That's my excuse.
blush2.gif
I have a fifth wheel this is all going in so I definitely understand the space is a premium statement!
 
What you're building is 2p4s2p. Two distinct batteries that are 2p4s.

My preference would have been 4s4p, with a BMS on each 4s battery. I'm not a fan of paralleling cells, but it's not uncommon. I simply want more control/reporting over each cell.

I would have no problem with all the wires. I would bring all four batteries into a set of common battery bus bars, then run a big cable from that to the system common bus bars.

I have yet to have a situation in my system where I brought down one battery, to leave the other running the system. If you think that might happen, then a switch on each battery is appropriate. A fuse on each battery should also be considered.
How would a guy go about connecting a bms on this? ( very limited exp.) would i need a 16 line bms? 4. 4 line bms?
 
How would a guy go about connecting a bms on this? ( very limited exp.) would i need a 16 line bms? 4. 4 line bms?

No, it would be either two 4s BMS or one 8s BMS that can span batteries like a Batrium. The latter is going to be expensive and from what I hear is not designed for a newbie. I've had good luck running 4s BMS on each of my two batteries. After the first month or two, I didn't look at the BMS very often. Looking at two BMS isn't that tedious for me.
 
How would a guy go about connecting a bms on this? ( very limited exp.) would i need a 16 line bms? 4. 4 line bms?
Yeah the general options @HRTKD mentioned above would be your best bet. The Batrium is very flexible and can handle any config but yes it’s expensive and lead times from Australia are long, but that’s mostly due to supply chain issues I believe which is everything right now. My Batrium monitors each and every cell, I just tell it how many in series and how many total cells and it can take it. I would agree it’s not the most beginner friendly but also depends on how technologically savvy you are. It has a LOT of customizable settings, alarms, integration options to play with.
Here is a quick top view photo of my assembled pack. You can see the little circuit board on the negative terminal of each cell.
Just don’t judge the wiring and busbars as that is very temporary :) it’s what I had available with me in my RV until this Sunday.
 

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No, it would be either two 4s BMS or one 8s BMS that can span batteries like a Batrium. The latter is going to be expensive and from what I hear is not designed for a newbie. I've had good luck running 4s BMS on each of my two batteries. After the first month or two, I didn't look at the BMS very often. Looking at two BMS isn't that tedious for me.
does hooking two sperate batteries with two seperate bms cause any issues from the charge controller? this has been my hang up. tried searching maybe its just too obvious and im missing it lol
 
does hooking two sperate batteries with two seperate bms cause any issues from the charge controller? this has been my hang up. tried searching maybe its just too obvious and im missing it lol

The charge controller doesn't care or know what the configuration of the battery is other than the voltage. Are you going to parallel or series the batteries? Parallel is fine, wire each battery to the common bus bars, don't wire one battery to the other. Give each battery equal access to the load/charge. I'm not a fan of putting LiFePO4 batteries in series (two or more BMS). If you need a 24v or 48v battery, build that. Recently a forum member posted that a battery vendor no longer "allows" (recommends?) using their batteries in series.
 
The charge controller doesn't care or know what the configuration of the battery is other than the voltage. Are you going to parallel or series the batteries? Parallel is fine, wire each battery to the common bus bars, don't wire one battery to the other. Give each battery equal access to the load/charge. I'm not a fan of putting LiFePO4 batteries in series (two or more BMS). If you need a 24v or 48v battery, build that. Recently a forum member posted that a battery vendor no longer "allows" (recommends?) using their batteries in series.
Tbh. Im not sure what i need. 12v i think. Just running a 3 way fridge some 12v lights. A 12v hotwater heater( just the ignitor) a 2 or 3000w inverter for a tv computers and maybe a starlink set up.
But i want alot of reserve power so we can be off grid for a while. Ive ordered 16 304 ah cells. And was thinking two or three 320w solar panels on the roof. Combing through all these threads is exhausting
 
Tbh. Im not sure what i need. 12v i think. Just running a 3 way fridge some 12v lights. A 12v hotwater heater( just the ignitor) a 2 or 3000w inverter for a tv computers and maybe a starlink set up.
But i want alot of reserve power so we can be off grid for a while. Ive ordered 16 304 ah cells. And was thinking two or three 320w solar panels on the roof. Combing through all these threads is exhausting

LOL! Yeah, coming up with a design takes a lot of work.

A three way refrigerator is an energy (AC and DC) hog usually. Running it on propane is a very efficient way to go. It sips propane but gobbles electricity. It's just how they're built. If you have plenty of battery and solar, then replacing the three-way refrigerator with a DC-only compressor refrigerator (very efficient) is the way that many forum members are going. Even a dedicated 120v AC compressor refrigerator is often more energy efficient than a three-way refrigerator.

How you go about the design depends on how much you want to spend and how complicated you want to get.

Given my pocketbook and my level of experience this is how I would do it. This can be argued to death, of course. I'm just saying that given what I know and what I'm willing to spend this would be my plan.
1. Build four 4s batteries, each with it's own BMS. This is a 4s4p configuration.
2. Keep the entire system 12v if you're dealing with an existing 12v system
3. Run the refrigerator on propane as much as possible
4. Add a DC-DC charger to interface the charge from the tow vehicle to the LiFePO4. There's more to this, especially if you have a breakaway brake system!

If you're looking for adventure this is an alternate method.
1. Build one 16s battery, with a 16s BMS
2. 48v 3000 watt inverter
3. 48v->12v converter with sufficient amps to handle the largest load in the RV
4. 12v->48v DC-DC charger to interface the tow vehicle charge to the LiFePO4 battery bank.
5. Breakaway brake system would have to get power from the converter in #3.

A 4s4p battery bank could be converted to 16s or 8s2p later if you decide that a 12v system isn't going to cut it.
 
LOL! Yeah, coming up with a design takes a lot of work.

A three way refrigerator is an energy (AC and DC) hog usually. Running it on propane is a very efficient way to go. It sips propane but gobbles electricity. It's just how they're built. If you have plenty of battery and solar, then replacing the three-way refrigerator with a DC-only compressor refrigerator (very efficient) is the way that many forum members are going. Even a dedicated 120v AC compressor refrigerator is often more energy efficient than a three-way refrigerator.

How you go about the design depends on how much you want to spend and how complicated you want to get.

Given my pocketbook and my level of experience this is how I would do it. This can be argued to death, of course. I'm just saying that given what I know and what I'm willing to spend this would be my plan.
1. Build four 4s batteries, each with it's own BMS. This is a 4s4p configuration.
2. Keep the entire system 12v if you're dealing with an existing 12v system
3. Run the refrigerator on propane as much as possible
4. Add a DC-DC charger to interface the charge from the tow vehicle to the LiFePO4. There's more to this, especially if you have a breakaway brake system!

If you're looking for adventure this is an alternate method.
1. Build one 16s battery, with a 16s BMS
2. 48v 3000 watt inverter
3. 48v->12v converter with sufficient amps to handle the largest load in the RV
4. 12v->48v DC-DC charger to interface the tow vehicle charge to the LiFePO4 battery bank.
5. Breakaway brake system would have to get power from the converter in #3.

A 4s4p battery bank could be converted to 16s or 8s2p later if you decide that a 12v system isn't going to cut it.
what is the upside of a 48v system?
and also thanks for your reply!!
 
what is the upside of a 48v system?
and also thanks for your reply!!

You get to spend more money to get the voltage back down to 12v so your RV can use it.

The typical argument for the higher voltage is that you can use smaller wire. However, if you co-locate the batteries and the inverter in the same compartment, the wire distance is going to be very small. So the cost of big wire (like 2/0 or 4/0) isn't that much.

Check out this article that can be found in the Resources section of the forum:

 
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