Safe to relly on LifePO4's BMS to protect the wire from battery to switch?

[donradcliffe]

If the drop BMS has overcurrent protection, it meets the basis of the ABYC standard and there is no reason for another fuse. The FET's should act as a fuse, even if their specs are exceeded. "the FET may explode" is exactly what a fuse does.

[mitiempo]

Originally Posted by Trimaran Ken

You are completely wrong! I have undersized LFP batteries in my golf cart and can easily get the BMS to shut down the battery by demanding more current than the BMS will allow on a continuous basis.


My BMS has has a maximum current which it will allow for 3 seconds and a continuous current maximum after that.

Depends on the BMS.

Top quality cells are able to have a very large continuous output. It is one of the advantages of Lithium. My 180 AH Calb cells are capable and rated for a continuous output of 360 amps. My external BMS has no restriction on amp output. That is not its job. It is there to protect the cells from voltage being too high on charging, too low on discharge. To do this it directly controls the AC charger, solar MPPT controller, and the Orion DC-DC charger.

Drop-in batteries are restricted on amp output to protect the BMS, many which only use 10 gauge wire - sometimes even smaller. Mainesail on his How To site has an example of a drop-in battery that is so restricted by its BMS that the battery will not match what a fla battery of the same size can efficiently achieve.

Drop-in batteries were never really designed for how they are being sold and used. Their main purpose was for lighting in third world countries without extensive power grids. The marketers have tried to change that but the fact remains that a 100 AH battery with a maximum draw of 50 amps is pretty lame compared to what lithium easily achieves if engineered properly.

There are good so called drop in battery systems available - Lithionics for
one. But the vast majority come nowhere close to what a proper system can do.

The Amperetime 300AH battery the op has looks better than many but leaves a lot to be desired in my opinion. Looks like Eve cells or similar with a JBD based BMS which is good quality. Curious why they warn against using it for electric trolling motors though. My 55lb thrust Minn Kota draws max 50 amps and I run it from a 100 AH portable lithium pack I made with a 120 amp Jbd BMS without any problem.

[mitiempo]

The other interesting fact is that the 300 AH Amperetime battery costs more (about 1425 Cdn after exchange) than the 400 AH grade A matched Calb cells I purchased. In Canada where I am I paid 1120 Cdn all in for my 8 cells (180 AH rated, over 200 AH tested) plus a good BMS for under 200 Cdn.

Everybody complains about the prices of Lithium batteries but if you buy properly they are not expensive. I purchased from a major distributor in China (LythBattery) that is near the manufacturer (Calb) without any issues. The price I paid per cell was a third of the price of the same cells from the US, Electric Car Parts for example. I have had 3 orders from China and have had no issues at all - actually their customer service is better that most companies I have dealt with in North America.

I am in the marine industry but the purchases I made can be made by anybody if they wish. The only small downside is that they don't arrive overnight, takes about 2 months.