LiFePO4 reference diagram, Alternator version

[fxykty]

Originally Posted by svloki

Yes the reference diagram shows that connection scenario.

I take your point, very short duration pulse but still too much for the charger to handle. Also seems no way the fuses between the charger and the lead acid batteries would be fast enough to protect from such a short pulse. Good system.

I saw a schematic with BMS-controlled contactors to disconnect solar panels from the Victron MPPT controllers as well. Same logic here on load dump?

If your solar controllers have a remote on/off (all of the larger VE MPPT controllers do) then your BMS can use that. But if your solar controller doesn’t have a remote on/off you will need to use a contactor instead. Contactor should be placed between the solar panel and the controller.

[svloki]

Originally Posted by fxykty

If your solar controllers have a remote on/off (all of the larger VE MPPT controllers do) then your BMS can use that. But if your solar controller doesn’t have a remote on/off you will need to use a contactor instead. Contactor should be placed between the solar panel and the controller.

Thank you.

I am looking at Victron 100/50 MPPT controllers. It looks like that device has remote off through their RX port. Take RX pin to ground to disable. I think that would require a small relay connected to the BMS.

Is that solution preferred over a BMS-controlled contactor between solar panels and the MPPT? Is "remote off" is fast enough to prevent the damaging spike in current?

[CaptainRivet]

Originally Posted by svloki

I think Jedi has the BMS triggering alternator field disconnects. Good design for sure, save the bridge if BMS disconnects the lithium bank.



I'm just thinking the alternators may be able to stay online if enough output goes through the DC-DC charger to save them in a shutdown event.


Has anyone tested this scenario?

No need for that as the AGM starter are always there and floating so there is always a load on the alternator, doesn't matter if regulated or not.
Nothing happens to the DC2DC charger if the BMS disconnects.

[svloki]

Originally Posted by CaptainRivet

No need for that as the AGM starter are always there and floating so there is always a load on the alternator, doesn't matter if regulated or not.
Nothing happens to the DC2DC charger if the BMS disconnects.

How does that work please? In Jedi's reference diagram, the only path from the lithium bus to the LA bus is through the DC-DC charger if I see it correctly.

Starter motor connects to start bank, alternator connects to lithium bus.

[wholybee]

Originally Posted by svloki

Yes the reference diagram shows that connection scenario.

I take your point, very short duration pulse but still too much for the charger to handle. Also seems no way the fuses between the charger and the lead acid batteries would be fast enough to protect from such a short pulse. Good system.

I saw a schematic with BMS-controlled contactors to disconnect solar panels from the Victron MPPT controllers as well. Same logic here on load dump?

An MPPT cannot cause a load dump. That can only happen from an alternator.

[wholybee]

Originally Posted by CaptainRivet

No need for that as the AGM starter are always there and floating so there is always a load on the alternator, doesn't matter if regulated or not.
Nothing happens to the DC2DC charger if the BMS disconnects.

I am pretty sure that if there is a dcdc between the alternator and the AGM, there is no protection from a load dump. When the field collapses in the alternator, that energy needs to go somewhere. And the DCDC prevents it from going into the AGM. The resulting voltage spike will destroy the DCDC.

[svloki]

Originally Posted by wholybee

An MPPT cannot cause a load dump. That can only happen from an alternator.

Is there typically any need to turn off the MPPT controllers during a lithium shut-down then? Obviously a benefit to keep them on if possible.

[newhaul]

Originally Posted by svloki

I think Jedi has the BMS triggering alternator field disconnects. Good design for sure, save the bridge if BMS disconnects the lithium bank.



I'm just thinking the alternators may be able to stay online if enough output goes through the DC-DC charger to save them in a shutdown event.


Has anyone tested this scenario?

No my dc dc goes from lead to lifepo4. ( 70 amp alternator 40 amp dc2dc 250ah bank 12v nominal )

[CaptainRivet]

Originally Posted by wholybee

I am pretty sure that if there is a dcdc between the alternator and the AGM, there is no protection from a load dump. When the field collapses in the alternator, that energy needs to go somewhere. And the DCDC prevents it from going into the AGM. The resulting voltage spike will destroy the DCDC.

Wrong alternator ->AGM ->DC2DC -> lithium.
In Jedi's case, and I would do that everytime even if it's not an aluminium vessel, he uses the isolated version which galvanically isolates the alternator and AGM so all the spikes and distortions from the starter curcuit doesn't reach the Lithium and house curcuits under any condition.
If the lithium cut off the AGM is still connected and no spike occurs. If the field gets cut it delivers shortly what it has, because there is always a bit magnetization left, and then falls off to 0, called also soft cut off. No spike occurs as the AGM will always take that bit of charge even if at 100% SOC.
The 2nd DC2DC is there to charge, better float, the AGM starter from the Lithium.

[CaptainRivet]

Originally Posted by svloki

Is there typically any need to turn off the MPPT controllers during a lithium shut-down then? Obviously a benefit to keep them on if possible.

Why a benefit, the lithium shut down due to a reason that there is something wrong, so the 2nd best option is to cut the power coming from it, the best option shut it off with its remote because that's tested via the manufacturer that always works, with victron for 10 years. Your relay you put in nobody tested it...
For the 100/30 and 100/50 you need a adapter cable ve-direct remote cable. The big issue here is the MPPT is off when the circuit is closed, means if something disconnects the remote cable the MPPT is switched on. Really bad design from victron as this is a nogo. I switch all my 4 MPPTs off with a battery protect BP220 smart because of this and because I need the VE-DIRECT port to deliver data to the victron cerbo.

[s/v Jedi]

Originally Posted by svloki

Yes the reference diagram shows that connection scenario.

I take your point, very short duration pulse but still too much for the charger to handle. Also seems no way the fuses between the charger and the lead acid batteries would be fast enough to protect from such a short pulse. Good system.

I saw a schematic with BMS-controlled contactors to disconnect solar panels from the Victron MPPT controllers as well. Same logic here on load dump?

The input capacitance of chargers/converters can’t be relied upon to deal with a transient surge caused by the sudden drop in alternator output. In this diagram the BMS shuts down the alternator field at a warning level, before a HVC occurs which should also prevent the HVC from happening.

Some BMS’s support this, many don’t. I do not favor this setup but provide it for those who do. I don’t have enough confidence in BMS systems to run the whole boat, I think they have enough on their plate to deal with the battery. The setup of a whole system is complex and while a manufacturer like Victron has a system that does all, which could be bought and dropped in, it doesn’t allow the flexibility I demand. I must be able to pick up any brand battery and run it.

[wholybee]

Originally Posted by CaptainRivet

Wrong alternator ->AGM ->DC2DC -> lithium.
In Jedi's case, and I would do that everytime even if it's not an aluminium vessel, he uses the isolated version which galvanically isolates the alternator and AGM so all the spikes and distortions from the starter curcuit doesn't reach the Lithium and house curcuits under any condition.
If the lithium cut off the AGM is still connected and no spike occurs. If the field gets cut it delivers shortly what it has, because there is always a bit magnetization left, and then falls off to 0, called also soft cut off. No spike occurs as the AGM will always take that bit of charge even if at 100% SOC.
The 2nd DC2DC is there to charge, better float, the AGM starter from the Lithium.

Yes, that works fine. But the question was, if you reverse it Alternator->LFP-DCDC->AGM with the DCDC allow enough current through it to protect when the LFP disconnects. No, it will not. The DCDC will be blown up. You must do it as you say, with the Alternator directly connected to the AGM first.

[wholybee]

Originally Posted by svloki

Is there typically any need to turn off the MPPT controllers during a lithium shut-down then? Obviously a benefit to keep them on if possible.

There is no reason to turn off an MPPT before a BMS disconnect.

[svloki]

Originally Posted by s/v Jedi

In this diagram the BMS shuts down the alternator field at a warning level, before a HVC occurs which should also prevent the HVC from happening.

This sounds like a good strategy. Do you have any recommendations for a reliable BMS that can drive a relay from the warning signal output?

[s/v Jedi]

Originally Posted by svloki

This sounds like a good strategy. Do you have any recommendations for a reliable BMS that can drive a relay from the warning signal output?

I don’t because I don’t have the setup and zero experience with those BMS’s. Some have a warning level output like in my diagram, others use the Victron protocol over CAN-bus.