DIY 280Amp LifePo4 With BMS voltage problem.

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
Well after making the changes I hooked up a 1500w heater to my 2000w inverter which works fine. Then I turned on the Voltstart, which starts the engine if the voltage of the house battery gets too low and the battery is charged from the High amp alternator. I just found out that it puts out 280Amps, the BMS is 150A, so after a minuet or so it shuts down. After another minute it restarts and so on. So what to do. What do you think? any solutions other than a 200A BMS?
 
Last edited:

hankcurt

Solar Addict
Joined
Feb 11, 2020
Messages
128
Location
Nebraska, US
There are some potential problems (such as frying your alternator) when charging LiFePo4 batteries from a vehicle charging system. I don't have any first hand knowledge of the best methods of dealing with this, so someone else would be a better source of information.

The basic problem seems to be that the charging systems were designed with lead acid in mind, and that chemistry has a relatively high internal resistance compared to lithium, so if the charging system relies on the battery internal resistance to limit current, stuff might burn out when charging lithium batteries. You may want to look at this thread - https://diysolarforum.com/threads/lifepo4-and-auto-alternator-concerns.9521/
 

shadowsteve

Solar Addict
Joined
Feb 11, 2021
Messages
245
How many charge amps does the BMS show when it shuts down? I charged my batteries this afternoon from the onboard Progressive Dynamics unit which is capable of 90A. The batteries were @ 80% and after a minute or two @ 60A they dropped to taking ~42A total (21A each).

You could use a DC to DC unit which is designed to isolate the alternator from the batteries and conform to the Li charge profile. Depending on the vehicle the onboard alternator can charge at >15v which isn't good for Li. Renogy and others make the units
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
Before I pulled the battery down with the 1500w heater It would charge the battery full without problems, but when the battery got low and the heater was running the current increased to about 180A, on my app, when the BMS shut down it dropped to 0A then back up to 180A, If I allowed it to cycle I'm sure it would eventually get lower than 180A but I don't think letting the BMS cycle is a good Idea, I don't know.
 

shadowsteve

Solar Addict
Joined
Feb 11, 2021
Messages
245
Before I pulled the battery down with the 1500w heater It would charge the battery full without problems, but when the battery got low and the heater was running the current increased to about 180A, on my app, when the BMS shut down it dropped to 0A then back up to 180A, If I allowed it to cycle I'm sure it would eventually get lower than 180A but I don't think letting the BMS cycle is a good Idea, I don't know.
No, not good to let the BMS act as the disconnect. You need to have equipment between the alternator and the BMS to control the charge current.

Like this: https://www.renogy.com/12v-60a-dc-to-dc-battery-charger/

BTW, I just disconnected the shore power from my trailer and the 12v draw dropped to 0.1-0.2A from almost 2A. I had the fridge running on AC power but it obviously draws some DC too for the controller.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
Ouch! The main interest in lithium was to be able to boondock and run the AC and let the engine Gen keep the batt charged. It worked with the 2 AGM batteries. If I have to limit the charge to 60 amps it would take 3 or 4 times longer to charge and wouldn't work because if the AC was running that draws 106 amps. so even with a 60 A dc to dc I would still be discharging until the AC shut off. I know of a couple guys with Battleborne batteries that say they have no problems with everything else stock. I need to rethink my setup.
 

shadowsteve

Solar Addict
Joined
Feb 11, 2021
Messages
245
There's a BMS parameter for max charging rate. You are likely exceeding that even with the 250A BMS. What voltage is the alternator putting out when it's running? You need to make sure you aren't too high for the Li batteries.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
150A BMS not 250A. 14.8v into the BMS 14.61 out of the BMS. At this point I have to come up with another solution.
 
Last edited:

S Davis

Solar Addict
Joined
Sep 25, 2021
Messages
178
You could parallel two or three dc/dc chargers, I am adding a second 50amp Redarc dc/dc charger. I have two 280ah batteries and will be able charge together or separately.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
I could do dc to dc chargers but high cost. I could also buy another BMS 150 amp $125 and run them in parallel, or how about replacing the 280 amp Alternator with a 150 amp one. About the same as another BMS. I think adding another BMS in parallel would be the cheapest and best solution as I can get the full 280 amps out of the alternator. What do you think?
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
7,688
Location
Somewhere South of Denver
Ouch! The main interest in lithium was to be able to boondock and run the AC and let the engine Gen keep the batt charged. It worked with the 2 AGM batteries. If I have to limit the charge to 60 amps it would take 3 or 4 times longer to charge and wouldn't work because if the AC was running that draws 106 amps. so even with a 60 A dc to dc I would still be discharging until the AC shut off. I know of a couple guys with Battleborne batteries that say they have no problems with everything else stock. I need to rethink my setup.

This may be a misnomer on your part. LiFePO4 batteries can charge much faster than lead acid. Some sites say four times faster.
 

S Davis

Solar Addict
Joined
Sep 25, 2021
Messages
178
So you have a dedicated alternator for charging and can use the full capacity? What size wire is the charge circuit?
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
This may be a misnomer on your part. LiFePO4 batteries can charge much faster than lead acid. Some sites say four times faster.
I don't follow your logic. What is wrong with my answer? Sdavis said to use dc to dc chargers but a 50A dc to dc charger is $239 on Amazon. 100A is double the cost. I realize that I can charge lithium with higher current but adding dc to dc to get to 150 amp cost way to much. There are much cheaper ways. I need a bigger BMS or 2 in parallel or smaller Alternator. However since the internal resistance goes higher as the Lipo4 charges it doesn't draw 280 amps for very long, it quickly drops to around 150a.
Sdavis Yes a dedicated alternator, and the wiring is what they originally installed, looks like 0 or 00 then splits to 2 runs of looks like 4 to various circuits with lots of inline fuses. The original batteries are AGM 100A, I had 2 of them.
 

S Davis

Solar Addict
Joined
Sep 25, 2021
Messages
178
So are you going to control charging manually to avoid over charging? With voltage at 14.6 to14.8 you will probably be at or over the max recommended charge voltage for LifeP04.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
At this point I don't know what I'm going to do, certainly NOT manually. I don't believe I eluded to that. The alternator is putting out 14.8 but the BMS is putting out 14.6 I believe. I think there is a Balmer on my alternator, right now its too cold to look, if its there I can adjust it for about 150A. If not Im thinking of adding a 2nd BMS. I can always drop the voltage by about 1/2 volt with a diode in series.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
7,688
Location
Somewhere South of Denver
I don't follow your logic. What is wrong with my answer? Sdavis said to use dc to dc chargers but a 50A dc to dc charger is $239 on Amazon. 100A is double the cost. I realize that I can charge lithium with higher current but adding dc to dc to get to 150 amp cost way to much. There are much cheaper ways. I need a bigger BMS or 2 in parallel or smaller Alternator. However since the internal resistance goes higher as the Lipo4 charges it doesn't draw 280 amps for very long, it quickly drops to around 150a.
Sdavis Yes a dedicated alternator, and the wiring is what they originally installed, looks like 0 or 00 then splits to 2 runs of looks like 4 to various circuits with lots of inline fuses. The original batteries are AGM 100A, I had 2 of them.

You were saying that a high amp charge worked for the AGM batteries but if you have to reduce the charge amps for the LiFePO4 then it will take longer. That may not be the case. Even with the lower charge amps, the LiFePO4 may reach a full state of charge faster than the AGM.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
Yes the 280 Alternator came with the MH and 1 100AH AGM battery. Im not so worried about the charge time with the Lithium due to the fact that most charging is done while charging. The only time fast charging would be nice is if I had to use the Air condition at night and pulled the battery down, then the engine starts and I wouldn't want to run the engine for 4 hours to get it back up. I could live with 150 Amps of charging current.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
75
I found this video by Will that talks about paralleling 2 BMS's but he doesn't talk about charging, only discharging, I am hoping that the charging would work the same.
 
Top