Generally speaking you don't want to parallel lithium with lead-acid. That doesn't mean that you can't, just that it isn't a good idea. I'll explain the reason in the second section below. Always size fuses to 125% of the amperage limit of the device or cabling (whichever is lower). So a 40A circuit should have a 50A fuse. The reason is that a 40A fuse that is constantly run at 40A might melt its casing or otherwise generate a lot of unnecessary heat without blowing. Its a bit of a safety issue. The fuses are there to protect against shorts, mainly, you don't want them running hot under "normal" operation. Of course if a particular circuit is sized for 40A but you never run more than, say, 30A through it, sizing the fuse to 40A is just fine. You generally don't want to directly charge lithium from an alternator, it can burn-out the alternator. The reason is that the lithium can suck up as much current as the alternator is able to put out, and the lithium can do that for hours on end with its voltage barely budging. While charging, LiFePO4's voltage doesn't really go up much past a certain point until it is nearly full. This can burn-out the alternator. Lead-acid behaves a bit differently with alternators because lead-acid voltages tend to rise up in response to the current sufficiently to regulate the current down a bit, even when the lead-acid battery is at a low SOC. So the alternator is not going full-out for hours on end with lead-acid. But with lithium, it will. This is why a DC-DC charger should be used between the alternator and the lithium. -- You generally don't want to parallel lithium and lead-acid. It isn't ideal for either chemistry. But it IS true that the voltages are mostly (but not entirely) compatible with each other. At least as long as you don't try to equalize the lead-acid (which would be bad for the lithium). There are several limitations: (1) Lithium can accept much more current than lead-acid. 1C is the typical limit (the BMS might have a lower limit so read the battery label), and it doesn't particularly stress the lithium to be charged that quickly. Lead-acid, on the other-hand, should generally not be charged faster than 0.1C. So you have to severely limit the charging rate if you parallel. This might not be a problem but remember that the lithium and lead-acid will accept current in different proportions and if the lithium disconnects for whatever reason, the lead-acid will take the full charging current. So you gotta be a bit careful. (2) The bigger problem is that lead-acid and lithium have vastly different resting voltages, and different characteristics at those voltages. 14.2V is an excellent bulk target for lithium iron phosphate, and works for lead-acid. But holding there for a long time isn't good for lead-acid. Similarly, the float voltage for LiFePO4 is roughly 13.4V - 13.6V, which tends to be more compatible. But the RESTING voltage for a fully charged LiFePO4 is basically its float, whereas for lead-acid it is far lower (like 12.8V). And 12.8V is significantly discharged for lithium. This means that the lead-acid is going to drain the lithium slowly, which is not ideal. This is the primary concern on the lithium side. (3) Because of the above, the lead-acid will be held at a higher than normal voltage more or less indefinitely. This can cause extra stress on the lead-acid and possibly more hydrogen outgassing, depending on the type. This is the primary concern on the lead-acid side when you fully charge a paralleled pack. (Some marine DIYers have gizmos to disconnect the lead-acid and lithium after charging is complete to allow the lead-acid to rest to try to get around this issue) (4) Obviously you can't equalize the lead-acid, the voltage would be too high for the lithium. This might or might not matter for the application. Often when people do this sort of paralleling they don't care if their lead-acid sees more stress. DISCHARGING: For discharging the compatibility is good. 12.0V is roughly 50% SOC for lead-acid (which is where you want to stop), and 5% SOC for LiFePO4 (also a good place to stop)... so 12.0V is a good lower cut-off. The lithium will take most of the load and if a big surge occurs the lead-acid will help. The lead-acid will take over as the lithium gets low. The problem is on the upper-end of the scale rather than the lower-end of the scale. (5) The cycle life of the lithium will be negatively effected due to the lead-acid yanking it around (current shuffling between the two types of batteries). Most people do not consider this to be a big issue though since LiFePO4 has a huge 3000+ cycle life. Calendar aging of the LiFePO4 might be accelerated though which is more of an issue. -- So can you do it? Yes, but it isn't ideal and care must be taken. I personally would not do it. And regardless of what you choose you do NOT want the alternator to directly charge lithium. Get a DC-DC charger designed for alternator-to-lithium. You don't want to smoke your alternator. -Matt
Ty. You saved me trying to explain similar things.....he's more at risk of diminishing the lifepo4 than anything......but why do that if you don't need to
I respect Andy’s extensive testing on DYI Off-Grid Garage his Bulk settings are 13.8vdc with 1 hour absorption, and Float 13.4vdc respectively. His Bulk settings allow the batteries BMS to level all the cells. To high of a bulk voltage will cause a cell to hit it’s voltage limit, and the whole BMS will quit charging, unit that cell goes down, then it restarts, and repeats. I believe the lead acid in parallel is fine, however if you have cloudy days and the lead acid’s fill in, then bulk charging them back up to avoid sulphation, is prudent. This is over the lithium’s 13.8vdc so if you have a lithium battery that’s connected via Bluetooth or R485/CAN then you can turn off the lithium’s charging, and top up the lead acid’s. Take care
@@murraysissons1809 A 13.8V target only works if you are able adjust the BMS's balance configuration to actually start balancing at that low a voltage. e.g. to program the BMS to start balancing at 3.40V/cell or 3.42V/cell or so. Most BMS's by default do not start balancing until 3.45V/cell (13.8V) or 3.50V/cell (14.0V), and you need to go 0.05V higher for your charge target to deal with sensor offset error. This means that for an unmodified battery, you should use 3.55V/cell (14.2V) for the target. 13.8V also only works well as a target at relatively warm temperatures. In cold temperatures, charging performance will be poor. Which Andy might not notice since he has three large 16s sets ganged together in parallel. Andy did some serious configuration adjustments and validated the voltage sensing error to use those numbers. I don't recall what his winter temperatures were inside his enclosed battery shelf, but given all the LEDs, the BMS, and the loads he puts on the system charging his Tesla, I wouldn't expect it to be cold. -Matt
Also the lead acid will stay at rest at a lower voltage slightly. They usually read about 12.8 v rested not charged recently. And your Lifepo4 battery will stay around 13.6v to 13.4v at rest not recently charged. So Lifepo4 battery will be taking up the slack slightly, it will work, but best to use in near future, only use all Lifepo4 batteries in your battery bank. All characteristics between batteries of same type work well together. You have to watch your voltages between different types of batteries in 12v range. Keep all batteries wired together at same voltage as best you can. I know batteries are not cheap. 😊
when you put two batteries in parallel, on a connection pole you put a shunt and digital ammeter that shows you the direction and the current which way they go. currents up to 3 A are not so problematic
Good morning friend, thank you for the comment and tip. If not done so please subscribe to my channel as I described to yours. Thank you for watching and may God bless you!
@@MegaCyrik Good morning new friend. Thank you for your comment. I believe they work well together as well! If not then so please subscribe to my channel as I have subscribed to yours. Thank you for watching the may God bless you!
URGENT: Have you strapped-down your lithium battery, did not notice it in the vid. 4:00 mixing batteries might be beneficial, or it might kill you. Sounds like a doctor's visit :):):)
Today I'm going to try to make a temporary battery box. My goal is to insulate it from cold weather which Off the Grid we're having. I should be able to strap it down somehow? If I were to visit a doctor I'm sure it'd be a psychiatrist! Thanks again and God bless you!
@@charlesvawter1527 You probably already figured out ways to strap it down! Regarding psychiatrists and their ilk: it is not a coincidence that "the rapist " and ""therapist" are spelled the same way. :):)
Actually your okay, the lead acid batteries are charging the Lifepo4 battery because they are at a slightly over voltage over Lifepo4. Lifepo4 battery can handle a 100 amp charge so the lead acid was maybe 1 amp of charge to the Lifepo4 battery. You can keep charging at 14.2v on lead acid, so lead acid charging is actually lower than Lifepo4 charging at 14.6v. You are not too far off your Lifepo4 battery charging volts at a slight lower 14.2v, but its okay to charge Lifepo4 at a lower charge voltage. Pretty close to the same run time charging Lifepo4 at 14.2v lead acid charging vs 14.6v Lifepo4 charging voltage. They say Lifepo4 will last longer at lower charge voltage but at the expense of a slightly less run time.
Good morning friend, thank you for your knowledge and wisdom. There's so much misinformation! Until you try it yourself you don't know what to believe? I'm not a tech guy, I'm the kind of guy just tries it and see what happens? It's not done so please subscribe my Channel that I have subscribed to yours. Again thank you for watching and may God bless you!
You can charge your setup, led and lithium in parallel from your alternator because your led will always be there. BMS in lithium might disconnect internally which causes trouble with the alternator and led does not. Otherwise, nice setup using led while still good and adding ample capacity with lithium.
Hello, thank you for watching the video. Thank you for reassuring me about charging the batteries with the alternator. So far I'm happy with the experiment it's keeping my lead acid batteries at a higher level throughout the night. It's not done so please subscribe to my channel as I have subscribed to yours God bless you thanks again!
I'm still watching the video but wait, no, that's not right. The problem with charging lithium directly from an alternator is that lithium can accept a massive amount of current for (literally) hours on end. This can burn-out the alternator. The reason this doesn't happen with lead-acid is that lead-acid naturally limits charging current... the voltage will get pushed up considerably by the charging current and naturally reduce the charging current. With lithium the voltage barely budges and the result is that the alternator doesn't get a break... it will max out and stay maxed out until the lithium reaches roughly 95% SOC. -Matt
@@charlesvawter1527 Mixing lead acid and LFP batteries can be dangerous because as you mentioned, leadacid batteries generate toxic and explosive gases when charged at high amperage(single spark goes boom), which LFP batteries can supply readily. The discharge rates also differ, causing the lead acid batteries to die prematurely due to the added stress of the LFP maintaining higher voltages. The LFP batteries won't reach their full capacity because the lead-acid batteries will drag them down when not charging. Charging your LFP batteries will also be slower because of the internal resistance of the lead acid batteries. LFP batteries charge quicker because they have a lower resistance which allows them to accept a higher amperage for longer durations, as the other person mentioned. A potential solution is to use a 500W switching power supply (less than $40) connected to an inverter(
@@dogdazetravellergarrett1367 Hello new friend, thank you for your comment and I believe you are correct. If not then so please subscribe to my channel as I have subscribed to yours Thank you for watching and may God bless you!
In my 2+ years doing it I have only extended the lifespan of my 28 GC2 batteries by years. The LiFePO4 are voltage support, the lead acid is the bulk. 70/30 split is optimum. Always set your chargers to GEL setting and nothing can go wrong. Holds float to 13.3 max and safe for them both. My system now uses 1/2 the water in the Lead Acid, and my LiFePO4 are still perfect.
Hello new friend, thank you for confirming what I thought. I'm going to have to try your suggestions. Thank you for them! It's not done so please subscribe to my channel as I have subscribed to yours. Thank you for watching the may God bless you!
I’ve had four GC2 210ah wired 12v with four 100ah lipho4 in a shed/cabin for years charging from 800w solar with no issues, run 10k window ac, small compressor, charge power tool batteries and ac/dc compressor fridge/freezer.
I’ve had four GC2 210ah wired 12v with four 100ah lipho4 in a shed/cabin for years charging from 800w solar with no issues, run 10k window ac, small compressor, charge power tool batteries and ac/dc compressor fridge/freezer.
Absolutely nothing wrong with connecting Lead Acid to LiFePO4. It's how you do it, not if. I have been running 1100 AH of LiFePO4 with 3300 AH of Lead Acid for 2 years. You use lighter gauge wire from the lithium so it's your voltage support, connect your big loads to your lead acid with heavy cables.
Hello new friend, thank you for your comment. I haven't seen the results of having a lithium batteries compared to the lead acid. It's not done so please subscribe to my channel as I have subscribed to yours Thank you and may God bless you!
![Adding LITHIUM to your LEAD battery bank [Capable Cruising Guides]](/img/n.gif)
Generally speaking you don't want to parallel lithium with lead-acid. That doesn't mean that you can't, just that it isn't a good idea. I'll explain the reason in the second section below.
Always size fuses to 125% of the amperage limit of the device or cabling (whichever is lower). So a 40A circuit should have a 50A fuse. The reason is that a 40A fuse that is constantly run at 40A might melt its casing or otherwise generate a lot of unnecessary heat without blowing. Its a bit of a safety issue. The fuses are there to protect against shorts, mainly, you don't want them running hot under "normal" operation.
Of course if a particular circuit is sized for 40A but you never run more than, say, 30A through it, sizing the fuse to 40A is just fine.
You generally don't want to directly charge lithium from an alternator, it can burn-out the alternator. The reason is that the lithium can suck up as much current as the alternator is able to put out, and the lithium can do that for hours on end with its voltage barely budging. While charging, LiFePO4's voltage doesn't really go up much past a certain point until it is nearly full.
This can burn-out the alternator. Lead-acid behaves a bit differently with alternators because lead-acid voltages tend to rise up in response to the current sufficiently to regulate the current down a bit, even when the lead-acid battery is at a low SOC. So the alternator is not going full-out for hours on end with lead-acid. But with lithium, it will.
This is why a DC-DC charger should be used between the alternator and the lithium.
--
You generally don't want to parallel lithium and lead-acid. It isn't ideal for either chemistry. But it IS true that the voltages are mostly (but not entirely) compatible with each other. At least as long as you don't try to equalize the lead-acid (which would be bad for the lithium). There are several limitations:
(1) Lithium can accept much more current than lead-acid. 1C is the typical limit (the BMS might have a lower limit so read the battery label), and it doesn't particularly stress the lithium to be charged that quickly. Lead-acid, on the other-hand, should generally not be charged faster than 0.1C.
So you have to severely limit the charging rate if you parallel. This might not be a problem but remember that the lithium and lead-acid will accept current in different proportions and if the lithium disconnects for whatever reason, the lead-acid will take the full charging current. So you gotta be a bit careful.
(2) The bigger problem is that lead-acid and lithium have vastly different resting voltages, and different characteristics at those voltages.
14.2V is an excellent bulk target for lithium iron phosphate, and works for lead-acid. But holding there for a long time isn't good for lead-acid. Similarly, the float voltage for LiFePO4 is roughly 13.4V - 13.6V, which tends to be more compatible. But the RESTING voltage for a fully charged LiFePO4 is basically its float, whereas for lead-acid it is far lower (like 12.8V). And 12.8V is significantly discharged for lithium.
This means that the lead-acid is going to drain the lithium slowly, which is not ideal. This is the primary concern on the lithium side.
(3) Because of the above, the lead-acid will be held at a higher than normal voltage more or less indefinitely. This can cause extra stress on the lead-acid and possibly more hydrogen outgassing, depending on the type. This is the primary concern on the lead-acid side when you fully charge a paralleled pack.
(Some marine DIYers have gizmos to disconnect the lead-acid and lithium after charging is complete to allow the lead-acid to rest to try to get around this issue)
(4) Obviously you can't equalize the lead-acid, the voltage would be too high for the lithium. This might or might not matter for the application. Often when people do this sort of paralleling they don't care if their lead-acid sees more stress.
DISCHARGING:
For discharging the compatibility is good. 12.0V is roughly 50% SOC for lead-acid (which is where you want to stop), and 5% SOC for LiFePO4 (also a good place to stop)... so 12.0V is a good lower cut-off. The lithium will take most of the load and if a big surge occurs the lead-acid will help. The lead-acid will take over as the lithium gets low.
The problem is on the upper-end of the scale rather than the lower-end of the scale.
(5) The cycle life of the lithium will be negatively effected due to the lead-acid yanking it around (current shuffling between the two types of batteries). Most people do not consider this to be a big issue though since LiFePO4 has a huge 3000+ cycle life. Calendar aging of the LiFePO4 might be accelerated though which is more of an issue.
--
So can you do it? Yes, but it isn't ideal and care must be taken. I personally would not do it. And regardless of what you choose you do NOT want the alternator to directly charge lithium. Get a DC-DC charger designed for alternator-to-lithium. You don't want to smoke your alternator.
-Matt
Ty. You saved me trying to explain similar things.....he's more at risk of diminishing the lifepo4 than anything......but why do that if you don't need to
Well written argumentation.
I respect Andy’s extensive testing on DYI Off-Grid Garage his Bulk settings are 13.8vdc with 1 hour absorption, and Float 13.4vdc respectively. His Bulk settings allow the batteries BMS to level all the cells. To high of a bulk voltage will cause a cell to hit it’s voltage limit, and the whole BMS will quit charging, unit that cell goes down, then it restarts, and repeats. I believe the lead acid in parallel is fine, however if you have cloudy days and the lead acid’s fill in, then bulk charging them back up to avoid sulphation, is prudent. This is over the lithium’s 13.8vdc so if you have a lithium battery that’s connected via Bluetooth or R485/CAN then you can turn off the lithium’s charging, and top up the lead acid’s. Take care
@@murraysissons1809 A 13.8V target only works if you are able adjust the BMS's balance configuration to actually start balancing at that low a voltage. e.g. to program the BMS to start balancing at 3.40V/cell or 3.42V/cell or so.
Most BMS's by default do not start balancing until 3.45V/cell (13.8V) or 3.50V/cell (14.0V), and you need to go 0.05V higher for your charge target to deal with sensor offset error. This means that for an unmodified battery, you should use 3.55V/cell (14.2V) for the target.
13.8V also only works well as a target at relatively warm temperatures. In cold temperatures, charging performance will be poor. Which Andy might not notice since he has three large 16s sets ganged together in parallel.
Andy did some serious configuration adjustments and validated the voltage sensing error to use those numbers. I don't recall what his winter temperatures were inside his enclosed battery shelf, but given all the LEDs, the BMS, and the loads he puts on the system charging his Tesla, I wouldn't expect it to be cold.
-Matt
Also the lead acid will stay at rest at a lower voltage slightly. They usually read about 12.8 v rested not charged recently. And your Lifepo4 battery will stay around 13.6v to 13.4v at rest not recently charged. So Lifepo4 battery will be taking up the slack slightly, it will work, but best to use in near future, only use all Lifepo4 batteries in your battery bank. All characteristics between batteries of same type work well together. You have to watch your voltages between different types of batteries in 12v range. Keep all batteries wired together at same voltage as best you can. I know batteries are not cheap. 😊
Hello again friend, thanks again for the additional information.
May God bless you!
when you put two batteries in parallel, on a connection pole you put a shunt and digital ammeter that shows you the direction and the current which way they go.
currents up to 3 A are not so problematic
Good morning friend, thank you for the comment and tip.
If not done so please subscribe to my channel as I described to yours.
Thank you for watching and may God bless you!
I use lead gels and lfp. Drain is like an amp a day. I charge that in an blink of an eye when the sun is up.
@@MegaCyrik Good morning new friend. Thank you for your comment. I believe they work well together as well!
If not then so please subscribe to my channel as I have subscribed to yours.
Thank you for watching the may God bless you!
URGENT: Have you strapped-down your lithium battery, did not notice it in the vid.
4:00 mixing batteries might be beneficial, or it might kill you. Sounds like a doctor's visit :):):)
Hey good morning again friend. Thank you for your comment/ concern.
Today I'm going to try to make a temporary battery box. My goal is to insulate it from cold weather which Off the Grid we're having. I should be able to strap it down somehow?
If I were to visit a doctor I'm sure it'd be a psychiatrist!
Thanks again and God bless you!
@@charlesvawter1527 You probably already figured out ways to strap it down! Regarding psychiatrists and their ilk: it is not a coincidence that "the rapist " and ""therapist" are spelled the same way. :):)
@@SunriseLAW Had to think about that a moment. Wow!😀
Actually your okay, the lead acid batteries are charging the Lifepo4 battery because they are at a slightly over voltage over Lifepo4. Lifepo4 battery can handle a 100 amp charge so the lead acid was maybe 1 amp of charge to the Lifepo4 battery.
You can keep charging at 14.2v on lead acid, so lead acid charging is actually lower than Lifepo4 charging at 14.6v. You are not too far off your Lifepo4 battery charging volts at a slight lower 14.2v, but its okay to charge Lifepo4 at a lower charge voltage. Pretty close to the same run time charging Lifepo4 at 14.2v lead acid charging vs 14.6v Lifepo4 charging voltage. They say Lifepo4 will last longer at lower charge voltage but at the expense of a slightly less run time.
Good morning friend, thank you for your knowledge and wisdom. There's so much misinformation! Until you try it yourself you don't know what to believe? I'm not a tech guy, I'm the kind of guy just tries it and see what happens?
It's not done so please subscribe my Channel that I have subscribed to yours.
Again thank you for watching and may God bless you!
You can charge your setup, led and lithium in parallel from your alternator because your led will always be there. BMS in lithium might disconnect internally which causes trouble with the alternator and led does not. Otherwise, nice setup using led while still good and adding ample capacity with lithium.
Hello, thank you for watching the video. Thank you for reassuring me about charging the batteries with the alternator. So far I'm happy with the experiment it's keeping my lead acid batteries at a higher level throughout the night. It's not done so please subscribe to my channel as I have subscribed to yours God bless you thanks again!
I'm still watching the video but wait, no, that's not right. The problem with charging lithium directly from an alternator is that lithium can accept a massive amount of current for (literally) hours on end. This can burn-out the alternator. The reason this doesn't happen with lead-acid is that lead-acid naturally limits charging current... the voltage will get pushed up considerably by the charging current and naturally reduce the charging current.
With lithium the voltage barely budges and the result is that the alternator doesn't get a break... it will max out and stay maxed out until the lithium reaches roughly 95% SOC.
-Matt
@@charlesvawter1527
Mixing lead acid and LFP batteries can be dangerous because as you mentioned, leadacid batteries generate toxic and explosive gases when charged at high amperage(single spark goes boom), which LFP batteries can supply readily. The discharge rates also differ, causing the lead acid batteries to die prematurely due to the added stress of the LFP maintaining higher voltages. The LFP batteries won't reach their full capacity because the lead-acid batteries will drag them down when not charging. Charging your LFP batteries will also be slower because of the internal resistance of the lead acid batteries. LFP batteries charge quicker because they have a lower resistance which allows them to accept a higher amperage for longer durations, as the other person mentioned.
A potential solution is to use a 500W switching power supply (less than $40) connected to an inverter(
It'll work fine....... They are wrong...... Huge myth spread by manufacturers. They will work great together.😎👍👍
@@dogdazetravellergarrett1367 Hello new friend, thank you for your comment and I believe you are correct.
If not then so please subscribe to my channel as I have subscribed to yours
Thank you for watching and may God bless you!
In my 2+ years doing it I have only extended the lifespan of my 28 GC2 batteries by years. The LiFePO4 are voltage support, the lead acid is the bulk. 70/30 split is optimum. Always set your chargers to GEL setting and nothing can go wrong. Holds float to 13.3 max and safe for them both. My system now uses 1/2 the water in the Lead Acid, and my LiFePO4 are still perfect.
Hello new friend, thank you for confirming what I thought. I'm going to have to try your suggestions. Thank you for them!
It's not done so please subscribe to my channel as I have subscribed to yours.
Thank you for watching the may God bless you!
I’ve had four GC2 210ah wired 12v with four 100ah lipho4 in a shed/cabin for years charging from 800w solar with no issues, run 10k window ac, small compressor, charge power tool batteries and ac/dc compressor fridge/freezer.
I’ve had four GC2 210ah wired 12v with four 100ah lipho4 in a shed/cabin for years charging from 800w solar with no issues, run 10k window ac, small compressor, charge power tool batteries and ac/dc compressor fridge/freezer.
Absolutely nothing wrong with connecting Lead Acid to LiFePO4. It's how you do it, not if. I have been running 1100 AH of LiFePO4 with 3300 AH of Lead Acid for 2 years. You use lighter gauge wire from the lithium so it's your voltage support, connect your big loads to your lead acid with heavy cables.
The lead batteries will drain the lithium and the charge profile wont fully charge the lithium.
Best bet would to be : run only lithium
Hello new friend, thank you for your comment. I haven't seen the results of having a lithium batteries compared to the lead acid.
It's not done so please subscribe to my channel as I have subscribed to yours
Thank you and may God bless you!