Can you put LiFePO4 batteries in parallel for RV electrical system?

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Rico.Chen

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Can you put LiFePO4 batteries in parallel for RV electrical system?

Now that we have talked about 12.8V, let’s deepen the understanding of lithium batteries. In fact, the nominal voltage of a single cell of lithium iron phosphate is 3.2V. When we use a 12V system, we connect four cells in series, so 12.8V is obtained. Many RV users are also very confused about the full voltage and the discharge voltage. This is actually very simple. The nominal value of a single battery cell is 3.2V. Generally, the maximum voltage of the built-in protection board is 3.65V, and the empty voltage can be up to 2.5V, but the basic setting is 2.8V. The conclusion is drawn: 4*3.65V = 14.6V when fully charged, and the voltage is 4*2.8V=11.2V when the battery is less than 10%.
Here a question that most concerned about is: If we feel that the battery in my RV is not enough, can I buy another set to increase the capacity? We see that many users are chaotic. For example, if they have a 400AH battery and a 600AH battery, the ideal state is to reach 1000AH, but this is not the case in actual use. When lithium batteries are connected in parallel, they will be based on the maximum capacity to calculate the cumulative value. Similar to the above parallel method, the number obtained should be 800AH, and this parallel method is not scientific and is prone to problems. So why is it so? Let’s explain. Assuming when you charge a 400AH battery, the single cell voltage is 3.2V/400AH (multiple blocks in parallel) and a 600AH battery, the single cell voltage is 3.2V/600AH (multiple blocks in parallel), you are charging two sets of batteries at the same time, and the capacity of the battery is related to the voltage. The built-in protection board also judges whether the battery is over voltage. Under the same conditions, when the 400AH battery is charged to 3.65V, it starts the protection, feedbacks the battery voltage to the charger, and let it stop charging. At this time, in fact, the 600AH battery is only charged to 400AH, it cannot reach 3.65V.

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Basic RV Electrical System Guide 2021- CNBOU

 

Gary RV_Wizard

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So are you saying that multipleLiFePO4 batteries should not be wired in parallel? Or maybe that the batteries should not have different AH capacities? I'm not seeing a solid technical reason for that in your explanation.
 

solarman

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Now that we have talked about 12.8V,
we haven't talked about anything yet, this is your first post.

let’s deepen the understanding of lithium batteries. In fact, the nominal voltage of a single cell of lithium iron phosphate is 3.2V. When we use a 12V system, we connect four cells in series, so 12.8V is obtained. Many RV users are also very confused about the full voltage and the discharge voltage. This is actually very simple. The nominal value of a single battery cell is 3.2V. Generally, the maximum voltage of the built-in protection board is 3.65V, and the empty voltage can be up to 2.5V, but the basic setting is 2.8V. The conclusion is drawn: 4*3.65V = 14.6V when fully charged, and the voltage is 4*2.8V=11.2V when the battery is less than 10%.
Here a question that most concerned about is: If we feel that the battery in my RV is not enough, can I buy another set to increase the capacity? We see that many users are chaotic. For example, if they have a 400AH battery and a 600AH battery, the ideal state is to reach 1000AH, but this is not the case in actual use. When lithium batteries are connected in parallel, they will be based on the maximum capacity to calculate the cumulative value. Similar to the above parallel method, the number obtained should be 800AH, and this parallel method is not scientific and is prone to problems. So why is it so? Let’s explain. Assuming when you charge a 400AH battery, the single cell voltage is 3.2V/400AH (multiple blocks in parallel) and a 600AH battery, the single cell voltage is 3.2V/600AH (multiple blocks in parallel), you are charging two sets of batteries at the same time, and the capacity of the battery is related to the voltage. The built-in protection board also judges whether the battery is over voltage. Under the same conditions, when the 400AH battery is charged to 3.65V, it starts the protection, feedbacks the battery voltage to the charger, and let it stop charging. At this time, in fact, the 600AH battery is only charged to 400AH, it cannot reach 3.65V.

See full

Basic RV Electrical System Guide 2021- CNBOU

basically Gary, he's talking about paralleling two batteries of dissimilar capacity and giving a rudimentary explanation of what would happen. something of course that should never be done,
if one were to add capacity then add a battery of equal capacity. I would wager this chap will soo try to advertise or sell something here. sadly I have seen this on other forums I frequent, some professional such as the Mike Holt code forum.. these posters usually end up attempting to sell something and I would certainly advise against buying china cells.
 

A Traveler

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That is one of the most confusing explanations of paralleling batteries I’ve ever seen. I don’t know what the OP was trying to accomplish here, but whatever it was, he missed the mark.

To reduce the OP’s post to the basic information, you can parallel Lithium batteries as long as they are all the same capacity…just like we’ve been doing for decades with lead-acid batteries.
 

Rico.Chen

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That is one of the most confusing explanations of paralleling batteries I’ve ever seen. I don’t know what the OP was trying to accomplish here, but whatever it was, he missed the mark.

To reduce the OP’s post to the basic information, you can parallel Lithium batteries as long as they are all the same capacity…just like we’ve been doing for decades with lead-acid batteries.
Hi, If you have the same brand of batteries, all new batteries with the same capacity and voltage, it can be connected in parallel, the market is now popular that 4 batteries can be connected in parallel. If different capacities, new and old together, then parallel connection is not recommended.
 

Rico.Chen

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we haven't talked about anything yet, this is your first post.


basically Gary, he's talking about paralleling two batteries of dissimilar capacity and giving a rudimentary explanation of what would happen. something of course that should never be done,
if one were to add capacity then add a battery of equal capacity. I would wager this chap will soo try to advertise or sell something here. sadly I have seen this on other forums I frequent, some professional such as the Mike Holt code forum.. these posters usually end up attempting to sell something and I would certainly advise against buying china cells.
We're a B2B company, we don't reference retail. So we don't sell products here. Most of the batteries' cells are Made in China.
 

Rico.Chen

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So are you saying that multipleLiFePO4 batteries should not be wired in parallel? Or maybe that the batteries should not have different AH capacities? I'm not seeing a solid technical reason for that in your explanation.
Yes sir, If you have the same brand of batteries, all new batteries with the same capacity and voltage, it can be connected in parallel, the market is now popular that 4 batteries can be connected in parallel. If different capacities, new and old together, then parallel connection is not recommended.
 

John From Detroit

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Can you put them in parallel for more Amp Hours
Battle Born does just that
Bioenno Power recommends against it.
Different battery managers I suspect
So if you want to parallel say 5 100 AH LiFePO4s Go with Battle Born.
 

Gary RV_Wizard

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These battery paralleling (or series wiring) discussions always end up debating optimal vs acceptable. There is a fairly broad gray area there where the losses from operating "less than optimal" are modest and often acceptable when cost and effort are factored in. Knowledgeable people can make that assessment, but those who are not wise in the way of batteries probably should not try it.
 

Rico.Chen

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Can you put them in parallel for more Amp Hours
Battle Born does just that
Bioenno Power recommends against it.
Different battery managers I suspect
So if you want to parallel say 5 100 AH LiFePO4s Go with Battle Born.
Yes, BMS is important, different brand, capacity, is not,
 

solarman

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Can you put them in parallel for more Amp Hours
Battle Born does just that
Bioenno Power recommends against it.
Different battery managers I suspect
So if you want to parallel say 5 100 AH LiFePO4s Go with Battle Born.

For drop ins, I would consult the manufacturer before doing so, some have BMS limitations and have a max of 4S4P configurations.

Normal practice for custom Li battery manufacture with large amperage is to parallel cells to meet capacity first, then series to meet voltage. For FLA we avoid parallel and go up in voltage to compensate hence most off grid is 48 V or higher.
 

Rico.Chen

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For drop ins, I would consult the manufacturer before doing so, some have BMS limitations and have a max of 4S4P configurations.

Normal practice for custom Li battery manufacture with large amperage is to parallel cells to meet capacity first, then series to meet voltage. For FLA we avoid parallel and go up in voltage to compensate hence most off grid is 48 V or higher.

Yes, but now have problem is RV battery system is 12VDC.
 

solarman

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Yes, but now have problem is RV battery system is 12VDC.
it's a simple matter to use a 48V to 12V buck converter of the type used on golf carts.
I have 2 in my system, not an issue.

48 V is used off grid mainly for telecom, for RV, very few people venture into 24 or 48 V.
only those with very high wattage demands would use higher voltage.
the main reason to use higher voltage is to reduce dangerous high currents.
 

Rico.Chen

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it's a simple matter to use a 48V to 12V buck converter of the type used on golf carts.
I have 2 in my system, not an issue.

48 V is used off grid mainly for telecom, for RV, very few people venture into 24 or 48 V.
only those with very high wattage demands would use higher voltage.
the main reason to use higher voltage is to reduce dangerous high currents.
But in the car, safety voltage is less than 36VDC, and One more device will have more failures. So 12VDC i think is good for RV.
 

DonTom

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higher voltage is to reduce dangerous high currents.
Dangerous to what? If you mean people, that is not correct.

12 volts from a billion amp supply cannot hurt anybody.

A person across a billion volts capable of 12 amps will be fried instantly.

Higher voltage is used so the current (amps) can be reduced in wires. So there is less heat loss at the same wattage. IOW, much better power transfer when stuff is designed for higher voltages. Such as EV motors. And that is very dangerous voltage for people to get across. That's why there is no frame ground used. It makes it more difficult to get across when there is no circuit possible to the frame. Such as if somebody needs to be pried out using metal tools after a serious accident.

However, there can be voltage so high with current so low that there is a big voltage drop when a person gets across it, but that is still then a low voltage when under the load of a person.

An example there will be an automotive ignition coil. Very high voltage with no load. The slightest load, because of the very low current capacity, will drop the voltage so much that it is unlikely to kill a person. But that is still LOW voltage under load. Perhaps that confuses some people.

Also what can be confusing is it is the current through the body that kills. Higher voltages will make a load draw more current until the load is high enough to make the voltage drop, then lowering the current draw.

Don't confuse current draw with current capacity from a supply. Higher voltages are more dangerous because a body will draw more current at a higher voltage.

-Don- Reno, NV
 

solarman

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Dangerous to what? If you mean people, that is not correct.
quite often with diy cables and lack of fusing with 6 batteries in parallel.... I've seen some real scary stuff with oversized inverters and under sized cables with hammer crimps, all just waiting for the right moment to meltdown. You may be technically competent, but there are many more who don't have a clue.


12 volts from a billion amp supply cannot hurt anybody.

A person across a billion volts capable of 12 amps will be fried instantly.

Higher voltage is used so the current (amps) can be reduced in wires. So there is less heat loss at the same wattage. IOW, much better power transfer when stuff is designed for higher voltages. Such as EV motors. And that is very dangerous voltage for people to get across. That's why there is no frame ground used. It makes it more difficult to get across when there is no circuit possible to the frame. Such as if somebody needs to be pried out using metal tools after a serious accident.

However, there can be voltage so high with current so low that there is a big voltage drop when a person gets across it, but that is still then a low voltage when under the load of a person.

An example there will be an automotive ignition coil. Very high voltage with no load. The slightest load, because of the very low current capacity, will drop the voltage so much that it is unlikely to kill a person. But that is still LOW voltage under load. Perhaps that confuses some people.

Also what can be confusing is it is the current through the body that kills. Higher voltages will make a load draw more current until the load is high enough to make the voltage drop, then lowering the current draw.

Don't confuse current draw with current capacity from a supply. Higher voltages are more dangerous because a body will draw more current at a higher voltage.

-Don- Reno, NV
not confused in the slightest
 
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