Thrillhouse
1 mW
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- Dec 11, 2018
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Do you prefer to build 12v lithium batteries with 3 or 4 cell groups and why?
3s or 4s for 12v battery
- Thread starter Thrillhouse
- Start date
There are a number of discussions with relevant info for you, about the problems with each of these configurations, depending on your intended use; the links below are just a few. Hopefully they will help.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96710
https://endless-sphere.com/forums/viewtopic.php?f=41&t=92786
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92968
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96710
https://endless-sphere.com/forums/viewtopic.php?f=41&t=92786
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92968
spinningmagnets
100 TW
I've pondered this, and there are arguments for and against either configuration. In a power outage, I have a solar panel I can drag out into my back yard to charge a car battery, or perhaps a lithium pack. The solar panel has a charge controller that is adjusted for lead-acid voltage range, so it would overcharge a 3S lithium pack.
If a lithium pack had a reliable BMS, it might not be an issue, but I don't trust a BMS to be a vital link during a disaster. I would also want to have the option of using my car alternator to charge a lithium pack, which puts out roughly 14V.
Therefore, using 4S means that even though I would only be using half of the packs Amp-hours of "range" to charge my cell-phone, flashlights, or laptop...I can safely charge a 4S pack with my car or solar panel, and no BMS. I suppose the choice boils down to "what are you going to do with it?"
If a lithium pack had a reliable BMS, it might not be an issue, but I don't trust a BMS to be a vital link during a disaster. I would also want to have the option of using my car alternator to charge a lithium pack, which puts out roughly 14V.
Therefore, using 4S means that even though I would only be using half of the packs Amp-hours of "range" to charge my cell-phone, flashlights, or laptop...I can safely charge a 4S pack with my car or solar panel, and no BMS. I suppose the choice boils down to "what are you going to do with it?"
Lifepo4 is much better suited to 12v applications.
Having said that I prefer 4s for other li ion 12v packs as there is more at the top of the charge
If it's for an off grid application, I have an inverter which has the best range of any I have seen, around 10-17v
Having said that I prefer 4s for other li ion 12v packs as there is more at the top of the charge
If it's for an off grid application, I have an inverter which has the best range of any I have seen, around 10-17v
spinningmagnets
100 TW
I agree that 4S LiFePO4/LFP is pretty much ideal for replacing 12V lead-acids.
"...I have an inverter which has the best range of any I have seen, around 10-17V..."
What's the model number?
"...I have an inverter which has the best range of any I have seen, around 10-17V..."
What's the model number?
999zip999
100 TW
What's it purpose ?
Voltron
1 MW
Inverters turn DC into house voltage AC typically.
Thrillhouse
1 mW
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- Dec 11, 2018
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So if I'm understanding correctly the main drawback of 4s is that you won't be able to fully charge it and the main drawback of 3s is that if the bms fails you will overcharge it and damage the battery/burn your house down?
Thrillhouse
1 mW
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Are there any fancy balance chargers that could make 3s safe?
spinningmagnets
100 TW
You can occasionally charge a 4S pack from a home RC charger, in order to balance all the cells. I recommend 4.1V per cell, so 4S would be 16.4V.
12V lead-acid chargers sometimes stop at 13.0V, and even if I bypass the solar panel charge controller, the panels' max output is 14.0V, plus...my car alternator (in a disaster) also puts out 14.0V
12V lead-acid chargers sometimes stop at 13.0V, and even if I bypass the solar panel charge controller, the panels' max output is 14.0V, plus...my car alternator (in a disaster) also puts out 14.0V
Thrillhouse
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I think most of us are talking about 18650john61ct said:
999zip999
100 TW
Ttillhouse what are you trying to power.? At this point we can tell your amp and wattage needs. And that's a place to start what you need the battery for
spinningmagnets
100 TW
If you are buying new cells, then 4S of LiFePO4 is the best choice. However, many builders have access to near-free 18650 cells. Various builders have used 3S 18650 cells to replace a 12V battery for certain jobs, and others have occasionally used a 4S 18650 bank to replace a 12V lead-acid battery.
3S using 18650's is a little low in it's voltage range to be ideal for a 12V component, and 4S is a little high to be ideal. Either can be used, depending on the task that is needed.
An additional reason I hadn't mentioned before is...it is possible to use various voltage converter methods to raise the voltage or lower it, and lowering a packs voltage output after the converter is more efficient than raising it. .
Either conversion is a wasteful use of battery watts, but lowering a higher voltage is less wasteful. Plus I have components that are 12V, 9V, 6V, 4V, 3V etc, and by having a 16V 4S pack (instead of 12.3V 3S), a single adjustable DC/DC converter can supply all of the voltages I might need.
These adjustable converters need a volt or two of drop to work, meaning that a 16V pack can provide 14V or less on the output of the converter. A 12V 3S pack might provide 10V or less.
3S using 18650's is a little low in it's voltage range to be ideal for a 12V component, and 4S is a little high to be ideal. Either can be used, depending on the task that is needed.
An additional reason I hadn't mentioned before is...it is possible to use various voltage converter methods to raise the voltage or lower it, and lowering a packs voltage output after the converter is more efficient than raising it. .
Either conversion is a wasteful use of battery watts, but lowering a higher voltage is less wasteful. Plus I have components that are 12V, 9V, 6V, 4V, 3V etc, and by having a 16V 4S pack (instead of 12.3V 3S), a single adjustable DC/DC converter can supply all of the voltages I might need.
These adjustable converters need a volt or two of drop to work, meaning that a 16V pack can provide 14V or less on the output of the converter. A 12V 3S pack might provide 10V or less.
999zip999
100 TW
Why 18650 ?
spinningmagnets
100 TW
The best lithium battery replacement for a 12V car battery is a 4S pack of brand new LiFePO4 / LFP high-amp cells. They are expensive, and there is only a small selection to choose from.
18650 cells are usually the NCA or NCM Lithium chemistry, meaning a full charge is 4.2V per cell. Some builders have access to near-free cells. Not completely free, but VERY cheap.
18650 cells are usually the NCA or NCM Lithium chemistry, meaning a full charge is 4.2V per cell. Some builders have access to near-free cells. Not completely free, but VERY cheap.
999zip999
100 TW
I have seen piles of karma fisher battery modules lifepo4 A123 20ah cells . They are laser welded so No intress as would be hard to remake for ebike. But have 24s of A123 20ah 1,380 cycles over 5yrs 23,000 miles on them. So a high quality cell. Can be charged to 3.7v or 4s to 14.8v but is happy at 3.5v or 14v. Lot of junk lifepo4 cells out there. Yes lifepo4 is best for 12v as 4p. What the reason for 18650 ?
spinningmagnets
100 TW
Do you have a link for purchase?
Pouch cells are still pretty DIY.
Hard-case prismatics really the way to go.
Unfortunately USA has a very thin local distribution, importing directly saves a lot but roll of the dice, return shipping costs pretty much negate any possible warranty
Hard-case prismatics really the way to go.
Unfortunately USA has a very thin local distribution, importing directly saves a lot but roll of the dice, return shipping costs pretty much negate any possible warranty
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