Myth of alternator damage cause by BMS disconnect?

[goboatingnow]

Originally Posted by Dieseldude

Thanks for the schematics. The weak link in the system is its reliance on the ECU. If anything fails in this system, you loose use of the alternator. Centrally controlled systems have this inherent weakness. An alternator with an independent regulator avoids this. Alternators have existed for decades without need for ECU control. Of course if the ECU seriously fails, you have no propulsion. That's the strength of old basic diesels with mechanical injection. So modern alternators have the deficiency of no access to the exciter. This unfortunately prevents adding any external controls, unless the unit can be opened up and the exciter coil to regulator connection opened up and leads connected to run outside. Perhaps this would not be practical.

Nope you need to actually study the data sheets for the regulator. If the linbus fails the regulator will run like a conventional uncontrolled alternator , with a fixed set point voltage.

Anyone looking at this agrees the best method is field coil current control as opposed to any sort of output disconnect. The best way is via the existing regulator or modifying the alternator to make the field coil feed externally accessible.

[goboatingnow]

Originally Posted by PaulCrawhorn

EMP is another factor some want to plan for

If you are subject to serious EMP the last thing on your mind will be your alternator

[goboatingnow]

Originally Posted by PaulCrawhorn

Nothing about this topic is unique to boats, but even those there are now many thousands.


Then that system is not doing its job, the charge must be terminated long before the C-rate gets that low if you care about longevity.

No CV stage at all is best, charge to your voltage setpoint and stop, if that setpoint is properly low "avoiding the shoulder" the C-rate is still close to the max you allowed from the start

ideally 0.4C or below.

We have no idea of the exact configuration of lithium installations many are using complete manufacturer tech to control everything

The primary function of a BMS is to protect the lithium cells from either complete discharge or continuing charge past a safe point.

Anything else in a BMs is a secondary function

I fully agree HVC and LVC events should not occur in normal operation , all charge sources should automatically stop at the defined charge stop voltage

HOWEVER. HVC is a last gasp protective function where for whatever reason charging continues and the lithium terminal voltage rises beyond the charge cutoff point.

At that stage the BMS must protect the battery and hence open the HVC switch.

The issue is how do you protect the alternator and any connected electronics for the resulting load dump spike

You can

1. Ignore it and hope everything survives

2. Only assume best case disconnect with low alternator current and install minimal protection.

3. Assume worst case protection where load dumps occur at full alternator output and design in that level of protection. A small fully charged battery in parallel will not be typically sufficient to protect electronics from a voltage spike. It will dampen it somewhat.

[rgleason]

Here is another example "tytower" using FransVeldmann's unmonitered github Issues to create "Gossip Spreading" . Its probably not worth responding. https://github.com/FransVeldman/OpenHybridBMS/issues/2

[goboatingnow]

Originally Posted by rgleason

Here is another example "tytower" using FransVeldmann's unmonitered github Issues to create "Gossip Spreading" . Its probably not worth responding. https://github.com/FransVeldman/OpenHybridBMS/issues/2

It’s not because what he contends , ie you can just disconnect the alternator under load and nothing bad happens. This contention is nonsense at face value. L(di /dt) always happens , nor can the regulator control it. The alternator “ may” have avalanche diodes such that the output limited but often that clamp level is not consistent with ISO test 5b.

In a car in theory all connected devices including the alternator itself are “ supposed “ to survive load dumps that remain within test 5B or the harder one 5A.

On boats no such stipulation exists so cannot be sure what will survive and what will not. This then leads to the discussion about the extent and nature of any protection strategy.

There’s a good few threads on EEVBLOG forum where people designing automotive qualified equipment talk about the difficulties in designing electronics to repeatedly handle full current load dumps.

When you consider protection strategies you have to factor in worse case scenarios. You may decide to then ignore that case if it’s felt to be too difficult to manage ( ie you could simply decide to let the alternator feed for itself above a certain load dump threshold )

[Dieseldude]

Originally Posted by SOLAR SUPPORT

I experimented with the bridge ends that I soldered to the rotor warning brushes inside my Mitsubishi 115A alternator, which is in its own regulator, and took the outside of the alternator. While the engine is running and charging, the alternator charging stops when I disconnect the two contacting ends. I can track this on my battery monitor. When these ends are reconnected, the charge continues from where it left off. Meanwhile, many devices such as TV, inverter, lighting, refrigerator are on. I connected the ends of the cables to the 70 C° Thermostat that I had mounted on the alternator case and it was done. This protection circuit is sufficient for the alternator used for lead acid battery charging. For Lifepo4, it is sufficient to use a voltage sensitive relay in addition to this.

As a result of the measurement I made from the bridge connections while the alternator was running, I had the chance to measure the current transmitted by the regulator to the rotor warning brushes. The engine runs at idle and when the alternator is at ~50A load, this current is 8A. At this engine speed max. That's how much energy is produced. When the engine speed is increased to 1500 rpm, the current going to the rotor decreases to 3-4A, the alternator charge load becomes 90A. Since the simple thermostat used as a precaution against overheating has a capacity of 10A, I do not think that there will be a problem with the overheating protection circuit. The voltage sensitive relay to be used for the Lifepo4 HVCutoff protection is available up to 30A and is quite affordable.

Thanks for sharing your experiment. I'm not exactly clear on everything. What I understand that you did was to open up the exciter connection to the regulator, connected wires to each side and ran these outside the housing. The thermostat was connected across these wires. I'm not sure how the voltage sensitive relay is connected. Not sure what is meant by Lifepo4 HVCutoff. Is this an over voltage protection device that monitors the alternator output, and is connected in series with the exciter coil and thermostat? Does this device go open circuit if alternator output rises above a certain value?

[team karst]

It may be worthwhile to review the failure mode we are trying to make a solution for.

I thought that it was to accommodate an unexpected battery disconnect from an engine driven charge system. Further, accommodate, means protect the sensitive electronics powered by the alternator/battery.

BMS has been mentioned frequently. It is a protection system. Perhaps it activates when it shouldn't, or it is activating in the face of OV or UV. The suitable response is different in each case.

Some scenarios:

1- I have only one LFP battery in the charge circuit, and its BMS became defective; it called for a disconnect, during a strong charge with V bank within limits , and there is no other external defect. This seems like worst case load dump to me.
2- Same as #1, but I have multiple batteries, all with independent BMS in the system, and one battery/BMS opened. Not a load dump event.
3- My alternator regulator series pass semiconductor failed shorted. Now, i'm in uncontrolled full charge mode, and due to the Over Volt, all the BMS systems went open. No "non-BMS" battery in the system. This would be a good BMS action, but now the line is very high voltage, and current automation can't control it. Another bad load dump situation. Plus, the V bank is soaring out of control. Now its a severe non-transient high voltage killing loads.
4- BMS triggered due to a no, or not enough charge situation. Bank Voltage is very low. This might be a "mild to zero" load dump event.
5- The alternator B+ wire "came off" during charging; or its protection fuse blew. This would be a load dump, but only affecting the alternator itself. Bank V dropping slowly.


I'm sure there are others? But, most important, we make a risk assessment/list and make sure our fix, actually targets the likely events.

[SOLAR SUPPORT]

Originally Posted by Dieseldude

Thanks for sharing your experiment. I'm not exactly clear on everything. What I understand that you did was to open up the exciter connection to the regulator, connected wires to each side and ran these outside the housing. The thermostat was connected across these wires. I'm not sure how the voltage sensitive relay is connected. Not sure what is meant by Lifepo4 HVCutoff. Is this an over voltage protection device that monitors the alternator output, and is connected in series with the exciter coil and thermostat? Does this device go open circuit if alternator output rises above a certain value?

My experiments and the topics I have explained in the posts I have written before are the same as what you have envisioned. It is a logicaly based circuit order. They are connected next to each other between the rotor exciter leads. Thermal switch and voltage sensing relay which works as a switch. Both controls are normaly in closed state. Alternator's charge halted if any of these controls are reach their open action limit. In my setup thermal switch opens at 70C° and close again 60C°. Voltage sensing relay opens at 14.3V and close at 13.6V.

https://youtu.be/_IXdudVYtXk

[team karst]

Seems reasonable. The high set point would be too tight in some installs, perhaps.
Is the voltage sensitive relay electronic? Tested with radios keyed up?
Sorry, I’ve spent lots of fun times taming precision V ref IC’s and comparator chips from rfi.

[SOLAR SUPPORT]

Originally Posted by team karst

Seems reasonable. The high set point would be too tight in some installs, perhaps.
Is the voltage sensitive relay electronic? Tested with radios keyed up?
Sorry, I’ve spent lots of fun times taming precision V ref IC’s and comparator chips from rfi.

There is no radio stuff in this setup. Just check the product link I sent.

[SOLAR SUPPORT]

Originally Posted by Dieseldude

Thanks for sharing your experiment. I'm not exactly clear on everything. What I understand that you did was to open up the exciter connection to the regulator, connected wires to each side and ran these outside the housing. The thermostat was connected across these wires. I'm not sure how the voltage sensitive relay is connected. Not sure what is meant by Lifepo4 HVCutoff. Is this an over voltage protection device that monitors the alternator output, and is connected in series with the exciter coil and thermostat? Does this device go open circuit if alternator output rises above a certain value?

I need to correct one sentence in my previous post to make clear what I did in the alternator.

"bridge ends that I soldered to the rotor warning brushes"

Only one brush connection is cut and isolated and bridge ends soldered to each side of the cut.

[PaulCrawhorn]

An HVC can be the primary charge termination control, so long as it is robust and long-term reliable. IOW part of normal operations, CV stage being unnecessary even harmful.

My point was that the HVC included in a BMS is simply backup, redundant failsafe for when the primary fails. IOW not part of normal operations.

Same goes for LVC, the "normal ops user space controls" may have different setpoints so entertainment circuits get shut down before refrigeration, safety / nav / comms maybe allowed to go way low before that of the LVC in the BMS is reached.

Originally Posted by goboatingnow

A small fully charged battery in parallel will not be typically sufficient to protect electronics from a voltage spike. It will dampen it somewhat.

As stated I flat out disagree.

But of course if an owner believes your assertion, a larger unit can be bought for an extra $50 or so, dedicated to that purpose and kept at an SoC lower than Full.

[goboatingnow]

Originally Posted by PaulCrawhorn

An HVC can be the primary charge termination control, so long as it is robust and long-term reliable. IOW part of normal operations, CV stage being unnecessary even harmful.

My point was that the HVC included in a BMS is simply backup, redundant failsafe for when the primary fails. IOW not part of normal operations.

Same goes for LVC, the "normal ops user space controls" may have different setpoints so entertainment circuits get shut down before refrigeration, safety / nav / comms maybe allowed to go way low before that of the LVC in the BMS is reached.

As stated I flat out disagree.

But of course if an owner believes your assertion, a larger unit can be bought for an extra $50 or so, dedicated to that purpose and kept at an SoC lower than Full.

Test it and see , load the alternator , leave a typically LA fully charged starter style battery in the circuit. Kill the alternator output in 5uS or less

Watch with a scope.

I have ( not in a boat but that doesn’t matter ) this was a 100A alternator.

Everyone agrees LVC and HVC should not occur in normal use. Charge termination should occur below the HVC point.

[PaulCrawhorn]

Again, I am not in any way talking about killing any alternator output, the whole point is simply to remove the LFP bank from the charge buss circuit.

The alt continues servicing all the usual engine / nav / safety loads which remain connected, along with the lead / Starter batt acting as a buffer for the load dump.

I am using the terms LVC and HVC to refer to devices here, not their setpoints.

These are "normal ops userspace" devices, nothing to do with the BMS (if you have one), and they are all adjusted to different setpoints, as appropriate to their purpose.

If an HVC is used for charge termination - CC-only - yes it should be set to isolate House at a voltage point well below that of the BMS, whose "last ditch" setpoints are of course at the outer extremities.

[team karst]

Originally Posted by PaulCrawhorn

Again, I am not in any way talking about killing any alternator output, the whole point is simply to remove the LFP bank from the charge buss circuit.

....

Sorry; i'm trying to catch up with the rationale. Under what error/fault conditions do you want to remove the house bank? Seems like a drastic move to me. Invertor goes down; house loads go down... all you have are starter batts.