Active Current Limiting BMS - Alternator protection option?

[eXodus]

Hello,

I found this video from off-grid garage reviewing a SEPLOS BMS.

It seems like it has a configurable active current limiting feature. He describes it as PWM circuit.

A battery with something like this should solve most alternator related concerns correct? Two main things kill alternators:

1. Rapid disconnect (instead of limiting)
2. Prolonged running at max capacity and slowly overheating.

When the BMS controls the current into the cells is adjustable - could just put a clamp meter on the alternator - turn on everything in the vehicle - and then increase the charge rate to something below the rating of the Alternator.

 

[time2roll]

Yes this would appear to be a great feature to protect the alternator.
I would like to see similar protection for the discharge.

 

[eXodus]

Yes this would appear to be a great feature to protect the alternator.
I would like to see similar protection for the discharge.

I think it works in both ways. In the video he sets a current for discharge and charging. Both directions of the BMS have the same MOSFETS.

 

[time2roll]

I would be tempted to go without a main battery fuse. Crazy talk.

 

[eXodus]

a fuse is always advised, because a BMS is a computer, and people programming those make mistakes.
There might be and edge case where someone did not thinking about when building that thing.

But I would just size that fuse in a way that the BMS should catch it first. e.g. for 100A BMS - put the fuse at 125A or something like that. (wiring appropriate oversized as well)

 

[RCinFLA]

The alternate charging DC to DC converter in these type BMS's are limited to 10 or 20 amps of charging,

It opens charging high current MOSFET's in BMS just like an overvoltage/overcurrent charging shutdown then actives a buck-boost DC to DC converter as alternate charging path to supply the limited charging current. The current it actually allows for charging is modulated to keep a cell approaching overvoltage from tripping total charging shutdown by BMS. It allows BMS to have more balancing time.

It causes the DC input from inverter/charging to rise in voltage if inverter/charger is in bulk constant current mode jumping to inverter/charger's absorb voltage and reduces current loading on charger. This can make inverter/charger think battery is fully charged and drop to float voltage. If your inverter/charger has 'Lithium' battery type mode it may prevent any further charging current to flow into battery when it drops to float mode.

It can also screw up an external battery monitor's full charge Columb counter by resetting the 100% 'full' state prematurely.

 

[eXodus]

The alternate charging DC to DC converter in these type BMS's are limited to 10 or 20 amps of charging,

I am currently experimenting with a Elefast 100AH 12V battery. It seems like it has 50A charge limiter.

As soon as I start the engine - and the alternator comes up to speed - it looks like it starting to regulate after a while - I see 60-70A for a minute or so. Then something happens and the current drops to 49.xx Amp, and it stays there until the battery gets full.

This can make inverter/charger think battery is fully charged and drop to float voltage. If your inverter/charger has 'Lithium' battery type mode it may prevent any further charging current to flow into battery when it drops to float mode

When I am charging from my regular solar charge controller- 100W - everything is normal. The MOSFETS are connected 100% of the time.

Turn on the engine - the solar charger - thinks the battery is full (high voltage) and stops charging.

When you turn off the engine - it goes back and the solar controller works normal again.