Most cars take about 400 to 600amps on start up.
I am also curious about this. I think its worth thinking hard about the pros/cons before pursuing. Two other issues are low temperatures, and the consequences of a BMS disconnecting (will it harm the alternator?)
Yes some FET based BMS' advertise surge ratings (not sure how much I would trust them)
I have quite small car and checking alternator specs, it seems to be rated at 1200W/1400W.
Do you refer as what is labeled as 'sparkle current' on DALY BMS specs?
The reason is mainly curiosity and DIY...
The issue with temperature isn't the ability to start the vehicle, its that charging at low temperature (at or near freezing) will damage a LFP battery.
I guess this is bad chinese translation, probably refering to surge current instead.
Hmm didn't know that, will check if could be an issue in winter.
Some 'cold weather' lifepo4 batteries have builtin heating elements to keep the cells at a healthy temperature. This may be the case. If I were looking at replacing Lead Acid car battery with something else, I would look at LTO, it has a handful of properties that I would think make it better suited for that purpose than LFP
I was thinking about what you are commenting on and it has occurred to me to think, if so much power is needed, how is a small battery capable of starting a vehicle like the ones sold now? like this:
View attachment 665
Además, publiqué esto en otro lugar hace algún tiempo:
Actualización rápida para sistemas avanzados de células crudas LiFePO4 utilizando un Daly BMS:
En mi sitio web, recomendé usar un puerto BMS separado para protección contra sobretensión para la conexión mppt (si se usa el puerto común BMS, existe la posibilidad de destruir mppt durante la desconexión por bajo voltaje).
Bueno, ayer, un espectador y yo finalmente recibimos nuestro puerto BMS separado de Daly, y la clasificación del amplificador no era la que se anunciaba en la lista. ¡El puerto separado solo puede manejar 10 amperios!
Teniendo en cuenta la probabilidad de una situación de sobrevoltaje de la mayoría de los mppt de alta calidad, y la posibilidad de que las celdas LiFePO4 coincidentes se desequilibren es rara (y BMS corregirá la deriva de la celda con el tiempo), y que LiFePO4 puede sobrecargarse a 4.2v por celda antes de la degradación del electrolito ... Yo diría que es seguro conectar el mppt directamente al banco de baterías y evitar el BMS por completo. Lo hemos estado haciendo de esta manera durante años, pero la gente todavía quiere usar un BMS.
Yo diría que use BMS para cargas y no para cargadores. Si tiene celdas que no coinciden y algunas alcanzan un voltaje más alto con un SOC alto más rápido que otras, reduzca el voltaje límite superior de su controlador. 14.0-14.2v es un voltaje de carga seguro que puede proporcionar una capacidad total con LiFePO4 12v.
¡Espero que esto ayude! Apuesto a que la mayoría de las personas que construyen estos sistemas se darán cuenta de esto cuando vean este problema, pero si usted es un principiante que intenta construir un sistema de nivel avanzado, esta información será muy útil. Hazme saber si tienes al
I am somewhat confused with this information, is it possible that it is something old? and that the new separate port bms can handle 40/50 amps through the charging port?View attachment 665
Also, I posted this elsewhere sometime ago:
Quick update for advanced LiFePO4 raw cell systems using a Daly BMS:
On my website I recommended using a separate port BMS for over voltage protection for the mppt connection (if common port BMS is used, possibility of destroying mppt during low voltage disconnect).
Well yesterday, a viewer and I finally received our separate port BMS from Daly, and the amp rating was not as advertised on the listing. The separate port can only handle 10 amps!
Considering the likelihood of over voltage situation from most high quality mppt, and the chance of matched LiFePO4 cells going out of balance is rare (and BMS will correct for cell drift over time), and that LiFePO4 can be over charged to 4.2v per cell before electrolyte degradation... I would say its safe to connect mppt directly to the battery bank, and bypass the BMS entirely. We have been doing it this way for years, but people still want to use a BMS.
I would say use BMS for loads, and not for chargers. If you have mismatched cells, and some hit a higher voltage at high SOC quicker than others, drop the upper limit voltage of your controller. 14.0-14.2v is a safe charging voltage that can give full capacity with LiFePO4 12v.
I hope this helps! I bet most people building these systems will figure this out when they see this problem, but if you are a beginner trying to build an advanced level system, then this bit of information will be very useful. Let me know if you have any questions
I believe the answer to that is ‘capacitors’. There are people using LiFePo4 for vehicle starting, by adding capacitors. DCS is a brand of drop in replacement that is warranted for engine cranking and winching, which makes me think they are doing without capacitors. Most lithium drop in replacements aren’t warranted for use under the bonnet, the DCS does but at reduced life. Curious to know how the difference between theirs and others.
At the start of this thread, I thought I understood the difference between common and seperate port. The above post seemed to make it quite clear, the BMS would disconnect the battery from both load and charge for either an under or over voltage situation. Presumably this requires some form of intervention to reset the BMS, like applying a charge voltage to a depleted pack.
For example^
Without going back and reading the last couple pages (so I may miss some context) here are some generalized clarifications:
It certainly does or can, but what specifically are you saying this in reference to?
That’s a great document thanks Dzl.
Hi Will, I am designing and manufacturing BMS Systems for Winston LiFeYPO4 cells here in Germany. These cells can be charged to voltages up to 4.2 Volts. I was under the impression, that normal LiFePO4 cells like Calb Cannot be charged that high. Specs say that the charge cut off voltage is 3.6 Volts.
