Making a cheap BMS ABYC compliant

[goboatingnow]

Originally Posted by newhaul

Well I have confidence in one specificly my lightning arresting gear of my own design .
It involves a plate of copper on my keel and a heavy wire from my rigging

I have something similar and it physically saved the boat , but you still get ac coupling into network and power buses none of those protection devices will actually protect connected electronics from strikes. The strike is much too fast and powerful. It’s not even worth trying to and such protectors for strike protection.

[newhaul]

Originally Posted by goboatingnow

I have something similar and it physically saved the boat , but you still get ac coupling into network and power buses none of those protection devices will actually protect connected electronics from strikes. The strike is much too fast and powerful. It’s not even worth trying to and such protectors for strike protection.

For indirect strikes .. A friend was in San Andreas and a boat a couple hundred meters away got hit and the stray took out his newest charge controller which was on panels mounted on the rail but the ones on the arch had something like that in line it tripped saving the rest.

[Jammer]

Originally Posted by newhaul

Limited chance for a shorted cell in a good condition lead based battery

It's a common mode of failure that I personally have seen at least twice. The shorted cell then leads to overcharging and rapid loss of electrolyte in the remaining cells, and failure of the battery. Sources vary on the causes, age, vibration, manufacturing defects, etc etc.



And it's tricky to diagnose when you have parallel strings, even when separated with a contactor or MOSFET.


In the system proposed upthread, a shorted LA battery could end up seeing the full design charge current for the combined LA+LiFePO4 bank, with catastrophic results.

[s/v Jedi]

Originally Posted by Jammer

What happens when you get a shorted cell on your AGM start battery?

I guess it’ll explode and may even cause a fire. I never had that happen with an AGM battery, but did with a flooded lead acid battery and it was ugly.

[s/v Jedi]

Originally Posted by Jammer

It's a common mode of failure that I personally have seen at least twice. The shorted cell then leads to overcharging and rapid loss of electrolyte in the remaining cells, and failure of the battery. Sources vary on the causes, age, vibration, manufacturing defects, etc etc.



And it's tricky to diagnose when you have parallel strings, even when separated with a contactor or MOSFET.


In the system proposed upthread, a shorted LA battery could end up seeing the full design charge current for the combined LA+LiFePO4 bank, with catastrophic results.

Hold on, explain that. How is it different from every other boat ever built when you connect a dc-dc converter to your start battery? Or do you mean using an ACR, with the LFP dumping energy into the shorted LA cell? That will be bad.
It seems that the isolator is the best option for those who for some reason dislike dc-dc converters. It would prevent any of that happening.

[Jammer]

Originally Posted by s/v Jedi

Hold on, explain that. How is it different from every other boat ever built when you connect a dc-dc converter to your start battery? Or do you mean using an ACR, with the LFP dumping energy into the shorted LA cell? That will be bad.
It seems that the isolator is the best option for those who for some reason dislike dc-dc converters. It would prevent any of that happening.

3 cases


1) If you have a DC-DC sourcing from the LiFePO4 bank to the LA battery, the current into the LA is limited to the capacity of the DC-DC since they all (as far as I know) have current limiters. If the DC-DC is well chosen (there's no need to "supersize" these unless there are large 12v loads connected here due to the LiFePO4 bank being a higher voltage) then the ensuing drama will be limited.



2) If you have an ACR then, during charging, once the LiFePO4 bank reaches around 13 volts, then substantially all the charging current from all sources will go to the LA battery, because with a shorted cell, it is a 5-cell battery, and will sink current the way a healthy battery (one without a shorted cell) would at 15 volts. If the charging sources (engine, shore power, solar, combination; doesn't matter) are large and remain in their "bulk" stage, this could be hundreds of amps, since they would typically be sized to deliver C/4 or C/5 to the LiFePO4 bank.



3) The problem is the charging sources, not current from the LiFEPO4 bank, so the same problem exists with a diode or FET isolator.


The difference from "every other boat" is that the charge currents into large LiFePO4 banks are usually, well, larger. But, to your point, shorted cells are a serious problem any time there are parallel LA batteries or strings, not only because of overheating, but because they pull down the good battery/string(s) to a low SOC, lower than expected, lower than a coulomb-counting battery monitor says the SOC is. So some Friday night there's a funny smell you can't quite place and on Saturday morning you wake up and the beer is warm and the engine won't start from either bank, even though the battery monitor is fat, dumb, and happy.

[newhaul]

Originally Posted by Jammer

3 cases


1) If you have a DC-DC sourcing from the LiFePO4 bank to the LA battery, the current into the LA is limited to the capacity of the DC-DC since they all (as far as I know) have current limiters. If the DC-DC is well chosen (there's no need to "supersize" these unless there are large 12v loads connected here due to the LiFePO4 bank being a higher voltage) then the ensuing drama will be limited.



2) If you have an ACR then, during charging, once the LiFePO4 bank reaches around 13 volts, then substantially all the charging current from all sources will go to the LA battery, because with a shorted cell, it is a 5-cell battery, and will sink current the way a healthy battery (one without a shorted cell) would at 15 volts. If the charging sources (engine, shore power, solar, combination; doesn't matter) are large and remain in their "bulk" stage, this could be hundreds of amps, since they would typically be sized to deliver C/4 or C/5 to the LiFePO4 bank.



3) The problem is the charging sources, not current from the LiFEPO4 bank, so the same problem exists with a diode or FET isolator.


The difference from "every other boat" is that the charge currents into large LiFePO4 banks are usually, well, larger. But, to your point, shorted cells are a serious problem any time there are parallel LA batteries or strings, not only because of overheating, but because they pull down the good battery/string(s) to a low SOC, lower than expected, lower than a coulomb-counting battery monitor says the SOC is. So some Friday night there's a funny smell you can't quite place and on Saturday morning you wake up and the beer is warm and the engine won't start from either bank, even though the battery monitor is fat, dumb, and happy.

Now do it with the dc dc running the other way. Ie: from start bank to lifepo4 bank. No alternator running no charging.
Engines are not usually our primary hanging sources anymore so .

[s/v Jedi]

Originally Posted by Jammer

3 cases


1) If you have a DC-DC sourcing from the LiFePO4 bank to the LA battery, the current into the LA is limited to the capacity of the DC-DC since they all (as far as I know) have current limiters. If the DC-DC is well chosen (there's no need to "supersize" these unless there are large 12v loads connected here due to the LiFePO4 bank being a higher voltage) then the ensuing drama will be limited.



2) If you have an ACR then, during charging, once the LiFePO4 bank reaches around 13 volts, then substantially all the charging current from all sources will go to the LA battery, because with a shorted cell, it is a 5-cell battery, and will sink current the way a healthy battery (one without a shorted cell) would at 15 volts. If the charging sources (engine, shore power, solar, combination; doesn't matter) are large and remain in their "bulk" stage, this could be hundreds of amps, since they would typically be sized to deliver C/4 or C/5 to the LiFePO4 bank.



3) The problem is the charging sources, not current from the LiFEPO4 bank, so the same problem exists with a diode or FET isolator.


The difference from "every other boat" is that the charge currents into large LiFePO4 banks are usually, well, larger. But, to your point, shorted cells are a serious problem any time there are parallel LA batteries or strings, not only because of overheating, but because they pull down the good battery/string(s) to a low SOC, lower than expected, lower than a coulomb-counting battery monitor says the SOC is. So some Friday night there's a funny smell you can't quite place and on Saturday morning you wake up and the beer is warm and the engine won't start from either bank, even though the battery monitor is fat, dumb, and happy.

Yeah, I think you got things turned around. The alternator charges the start battery like for every oem boat. Solar, shore power etc. all charge the house LFP and the isolator keeps that all away from the start battery. Only the alternator is connected to the isolator input.

[britinusa]

Thanks for some very educating info.

On a more basic level:- If using the Externally regulated Alternator -> LiFePo4 House Battery -> DC-DC charger -> AGM Start Battery option then....

Would a shutdown of the LiFePo4 Battery with internal BMS during a high rate of charging from the Alternator lead to Alternator failure unless the DC - DC Charger was in float mode because the Start Battery was fully charged?

ie. Is the load dump mitigated due to the load of the DC-DC Charger?

[s/v Jedi]

Originally Posted by britinusa

Thanks for some very educating info.

On a more basic level:- If using the Externally regulated Alternator -> LiFePo4 House Battery -> DC-DC charger -> AGM Start Battery option then....

Would a shutdown of the LiFePo4 Battery with internal BMS during a high rate of charging from the Alternator lead to Alternator failure unless the DC - DC Charger was in float mode because the Start Battery was fully charged?

ie. Is the load dump mitigated due to the load of the DC-DC Charger?

No, you can’t count on the dc-dc charger to absorb the transient surge. Delaying the shutdown like I describe in this thread to provide enough time to shutdown the alternator is the only sure way besides the other way around with the alternator charging the start battery and one or more dc-dc chargers detecting the alternator and charge the LFP. The disadvantage of that solution is that you need more dc-dc charger capacity.

Edit: this is why ABYC introduced the requirement for this warning level to act upon.

[newhaul]

Originally Posted by britinusa

Thanks for some very educating info.

On a more basic level:- If using the Externally regulated Alternator -> LiFePo4 House Battery -> DC-DC charger -> AGM Start Battery option then....

Would a shutdown of the LiFePo4 Battery with internal BMS during a high rate of charging from the Alternator lead to Alternator failure unless the DC - DC Charger was in float mode because the Start Battery was fully charged?

ie. Is the load dump mitigated due to the load of the DC-DC Charger?

Which way is the dc dc running ? From lifepo4 to lead ? Or lead to lifepo4?

[britinusa]

When I upgrade my house battery from FLA to LiFePo4 the setup will be:-

Alternator -> LiFePo4 3x100Ah 12v Internal BMS House Bank -> Victron DC.DC 12|12 18Amp Isolated Charger -> Start Battery (Duracell 12v AGM).

[newhaul]

Originally Posted by britinusa

When I upgrade my house battery from FLA to LiFePo4 the setup will be:-

Alternator -> LiFePo4 3x100Ah 12v Internal BMS House Bank -> Victron DC.DC 12|12 18Amp Isolated Charger -> Start Battery (Duracell 12v AGM).

What size alternator and what external regulator?

Any solar?

[britinusa]

Here's the list of components of My System.

Victron Multiplus 12/3000/120/50
Victron Cerbo GX
Victron GX Touch 50
Victron Smart Shunt 500
Victron GX 4G LTE + T-Mobile Sim Card
Victron Mk3 - USB
Victron GPS Antenna
Victron Smart Battery Sense
Victron 100/20 Smart MPPT Solar Charger Controller with < 300w of solar panels.

Victron Orion DC/DC Charger 12|12-18

Starter Battery-12v Duracell AGM
House Battery 12V (2S2P Trojan T105 6V)
Balmar 100A ( Rod Collin's ) Alternator
Balmar MC 618 External Regulator with both Battery & Alternator Temperature Sensors


Plan is to change out the House Battery to LiFePo4 in the next few months. Hence why I'm asking about the protection of the Alternator

FYI, I'm also going to replace the solar panels and add a 2nd MPPT controller in the spring. That will probably be about 500w. 1 x 170w and 2 x 180w

Thanks.

Paul

[britinusa]

Originally Posted by s/v Jedi

No, you can’t count on the dc-dc charger to absorb the transient surge. Delaying the shutdown like I describe in this thread to provide enough time to shutdown the alternator is the only sure way besides the other way around with the alternator charging the start battery and one or more dc-dc chargers detecting the alternator and charge the LFP. The disadvantage of that solution is that you need more dc-dc charger capacity.

Edit: this is why ABYC introduced the requirement for this warning level to act upon.

Thanks.
I was wondering. If the B2B charger was at least in Float mode, then would there even be a transient surge? It didn't occur to me that it might ( or not ) absorb the surge. I'm not particularly educated about 'transient surges'