BMS disconnect question?

[s/v Jedi]

There are a bunch of devices out there. I think the one from Sterling is better but we need someone to test these. Does Battleborn also have one?

[Statistical]

Originally Posted by SaylorMade

I just bought a 370 USD, 12V 100 AH pack as house battery, with BT and it let's me set all the different parameters, like cell voltage cut-off etc.
So I can just adjust the max to 3.4 if I so desire. I can see the voltage of each cell at any time as well as temperature etc.

I charge it with a cheap 12V charger, and I can see that it accepts the 10A (charger spec) until almost full, then slows down, and the BMS disconnects the charge-input when the first cell reaches the set max.

Balancing happens during AND after charge, so is typically within 1 mv an hour after full charge.

So I am reading this thread with interest, because I get the impression that I am doing something wrong now

You aren't doing anything wrong it just isn't the only option.

The most basic BMS (usually in cheaper drop in replacements) have no configuration or reporting of anything.

More advanced ones like yours allows some configuration and reported.

More advanced ones have some kind of relay output which would allow cutting an alternator regulator prior to the battery disconnect to avoid alternator voltage spike.

The most advanced BMS can communicate not just with the user but with compatible charge sources over canbus (and often have a relay pre-disconnect as a backup or for use with non-compatible sources).

There is more than one way to manage a battery. The problem is when people pretend there is only one right way. Obviously something like a rec bms on a tiny battery on a small boat with simple electrical system would just be overkill. Likewise trying to build a 48V or 72V electric propulsion bank using "dumb" drop in replacement batteries would likewise be a poor fit.

[witzgall]

This is NOT how the APM is designed, but there are other devices like this on the market. We chose not to take that particular path for a number of reasons, including that once the cap fills, protection stops.

The APM series uses the best whole vehicle surge/spike protection we could find, repurposed for this particular application.

Chris

Originally Posted by Jammer

I believe they are designed around a metal oxide varistor (MOV). As you may be aware, MOVs are devices that are high-impedance at low voltages but which begin to conduct when a certain threshold voltage is exceeded. There may be a capacitor in parallel with it. Typically they are used for shorter-duration surges than would occur from a BMS disconnect while the alternator is operating with full field, but if large enough the MOVs will clamp the surge and may even survive repeated hits.


https://www.mouser.com/pdfdocs/bourn...hite-paper.pdf

[Statistical]

MOV are relatively slow. While they don't state it outright pretty sure Balmar and others use TVS avalanche diodes. The big advantage is the are incredibly fast well under 1 nanosecond.

https://en.wikipedia.org/wiki/Transi...pression_diode

[SaylorMade]

Originally Posted by Statistical

You aren't doing anything wrong it just isn't the only option.

The most basic BMS (usually in cheaper drop in replacements) have no configuration or reporting of anything.

More advanced ones like yours allows some configuration and reported.

More advanced ones have some kind of relay output which would allow cutting an alternator regulator prior to the battery disconnect to avoid alternator voltage spike.

The most advanced BMS can communicate not just with the user but with charge sources (and often have a relay pre-disconnect as a backup).

There is more than one way to manage a battery. The problem is when people pretend there is only one right way. Obviously something like a rec bms on a tiny battery on a small boat with simple electrical system would just be overkill. Likewise trying to build a 48V or 72V electric propulsion bank using "dumb" drop in replacement batteries would likewise be a poor fit.

Good information - thank you.
And yes it is important to have the right context.
I have a fairly simple setup on a 27 foot boat, with no big loads on the battery (house).
Propulsion is from a larger 48V/12KWh bank, which can charge the 12V battery in an emergency (swith on the "engine" dashboard") with a Victron 48/12 DC DC Charger.

Just wanted to make sure that I am (probably) OK

[Statistical]

Originally Posted by SaylorMade

Good information - thank you.
And yes it is important to have the right context.
I have a fairly simple setup on a 27 foot boat, with no big loads on the battery (house).
Propulsion is from a larger 48V/12KWh bank, which can charge the 12V battery in an emergency (swith on the "engine" dashboard") with a Victron 48/12 DC DC Charger.

Just wanted to make sure that I am (probably) OK

I assume your alternator doesn't charge the 48V pack? (a joke). That is usually the most problematic charge source.

Having an emergency 48V to 12V option is smart.

[SaylorMade]

Originally Posted by Statistical

I assume your alternator doesn't charge the 48V pack? (a joke). That is usually the most problematic charge source.

Having an emergency 48V to 12V option is smart.

I hope it does not, since the alternator was seperated from the boat in May when the old Volvo har a new owner

Yes, well I don't know if we are ever going to need to tap into the propulsion bank, but the Victron unit was fairly cheap, and I needed something to put on the new panel, where the old engine panel was, so why not put a switch there for it

It is important to keep in mind though, that when doing that, the remaning distance shown in the engine display is no longer reliable.