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Dieseldude · 05-01-2022, 20:55

Quote:

Originally Posted by goboatingnow

The issue is not about protecting the alternator from temperature . The issue is what to do if a battery protection trips and the alternator is disconnected from its load

You cant fix that ( once the disconnect has occurred ) by controlling the field current.

we all agree the best way for a BMS to shut the alternator is either control the regulator, ie via a signal to the regulator , or directly via a field current control system that overrides the regulator.

by the way theres nothing particularly complex in a LinBus controlled regulator, its just a form of serial port . All alternators these days have microelectronics inside them anyway

Understood. But a battery management system could be wired to disconnect the exciter coil instead of disconnect the alternator output. This can be done with heat sensors at the batteries and a relay in the exciter circuit. No need for sophistication. Boats are getting this way, but modern cars have more computerization than did a Saturn 5 rocket. Do we really need rocket science just to run a boat? Simplicity generally means reliability.

goboatingnow · 05-01-2022, 21:04

Quote:

Originally Posted by Dieseldude

Understood. But a battery management system could be wired to disconnect the exciter coil instead of disconnect the alternator output. This can be done with heat sensors at the batteries and a relay in the exciter circuit. No need for sophistication. Boats are getting this way, but modern cars have more computerization than did a Saturn 5 rocket. Do we really need rocket science just to run a boat? Simplicity generally means reliability.

Fully agree, I have always advocated that the BMS should control the field coil current . The issue is that stock alternators do not make the field coil feed available externally. Hence the need to have the alternator modified

Note the "exciter " circuit is something different , an exciter current is an initial current supplied by the battery to initially allow the alternator to generate a magnetic field as it starts , once t he alternator was a magnetic field the field current is controlled by the regulator and derives its field current from the output of the alternator , this all occurs inside the alternator, turning of the exciter current does not disable a modern alternator

heres a modern LinBus alterantor regulator IC

Notice how the initial exciter current is actually supplied by the regulator and not via a separate excite feed

PaulCrawhorn · 05-01-2022, 21:09

Quote:

Originally Posted by goboatingnow

we all agree the best way for a BMS to shut the alternator is either control the regulator, ie via a signal to the regulator , or directly via a field current control system that overrides the regulator.

No we do NOT all agree, please speak for yourself. Please read my post(again) you are really overthinking, even misunderstanding the fundamental problem that needs solving here.

The controls I am talking about for isolating the LFP bank from its charge sources has nothing to do with any BMS.

If a system does include one, it should be used for redundant backup to protect the bank when the primary controls fail.

If everything is working properly, the protective functions of the BMS are never engaged.

**s/v Jedi** · 05-01-2022, 21:10

No the BMS will always switch the battery offline when needed. This is it’s primary function. Many can give a warning signal that can be used to stop charging, or maybe separate cell monitors can do that.

goboatingnow · 05-01-2022, 21:19

Quote:

Originally Posted by PaulCrawhorn

No we do NOT all agree, please speak for yourself. Please read my post(again) you are really overthinking, even misunderstanding the fundamental problem that needs solving here.

The controls I am talking about for isolating the LFP bank from its charge sources has nothing to do with any BMS.

If a system does include one, it should be used for redundant backup to protect the bank when the primary controls fail.

If everything is working properly, the protective functions of the BMS are never engaged.

The issue is how to protect the alternator and any electronics that remains connected to that alternator when you activate that battery protection , the best way and anyone that's understand this agrees is to control the alternator by removing the field current. ( or digitally signalling the regulator to do that ) The issue is not how to protect the Lithium battery , thats easy.

Typically a BMS controls the HVC and LVC protections ( High, Low voltage cutoff) in fact its a BMS's primary function. We all agree that HVC and LVC events should not normally occur, alternator and all other charging sources should taper off and stop without needing HVC in normal operations

with respect I have years in this arena, not on boats but in cars and industrial applications

PaulCrawhorn · 05-01-2022, 21:20

Quote:

Originally Posted by goboatingnow

Its really not quite as simple as that , a small ( say starter battery ) which is fully charged will not fully soak up the inductive spike due to the rapidly changing current . say where the alternator goes from fully loaded to virtually unloaded

Yes it will, good enough anyway, for normal loads like radios, radar, nav gear etc.

If you build a system with more sensitive components, then put them behind their own "UPS style" supply, or a DC-DC converter.

Don't extrapolate from your special case into generalised solutions that are crazy overkill for 99.99% of cruisers.

> a fully loaded alternator suddenly disconnected

My point is the standard solution is preventing that scenario, the alt is always connected to its Starter load buffer.

Works even with a 10+kW alt...

PaulCrawhorn · 05-01-2022, 21:24

Or of course just put an adjustable DC-DC charger jn front of your House bank

then no need to mod your alt/VR to get your requured current limiting, nor for your LCP's desired target voltage profjle

goboatingnow · 05-01-2022, 21:26

Quote:

Understood. But a battery management system could be wired to disconnect the exciter coil instead of disconnect the alternator output. This can be done with heat sensors at the batteries and a relay in the exciter circuit. No need for sophistication.

if you are asking me to read this again , Ive pointed out that in modern alternators you cannot control an alternator by its " excite " circuit , which is not the same as its field coil current . To control the field current you have to " break into " the field coil circuit inside the alternator unless you buy an alternator specially setup for external regulation

goboatingnow · 05-01-2022, 21:28

Quote:

Originally Posted by PaulCrawhorn

Yes it will, good enough anyway, for normal loads like radios, radar, nav gear etc.

If you build a system with more sensitive components, then put them behind their own "UPS style" supply, or a DC-DC converter.

Don't extrapolate from your special case into generalised solutions that are crazy overkill for 99.99% of cruisers.

> a fully loaded alternator suddenly disconnected

My point is the standard solution is preventing that scenario, the alt is always connected to its Starter load buffer.

Works even with a 10+kW alt...

Please take a big alt , and a small starter battery ( fully charged ) and try it , a scope on the 12V line is most useful , disconnect the alternator under full load, report back with the scope trace !!

most DC DC units for boats are not tested to IEC load dump specs certainly not to Test 5A

Again the point is that very few people have tested this under worst case conditions , under most cases the Lithium cells are only drawing a small amount of current when the HVC event occurs , that is not a proper test

PS lithiums on boats are very niche , there's no such thing as a " standard solution " sophisticated systems control the alternator not just arbitrarily disconnect its output

PaulCrawhorn · 05-01-2022, 22:06

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

Quote:

Originally Posted by goboatingnow

under most cases the Lithium cells are only drawing a small amount of current when the HVC event occurs

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.

Dieseldude · 05-01-2022, 22:09

Quote:

Originally Posted by goboatingnow

Fully agree, I have always advocated that the BMS should control the field coil current . The issue is that stock alternators do not make the field coil feed available externally. Hence the need to have the alternator modified

Note the "exciter " circuit is something different , an exciter current is an initial current supplied by the battery to initially allow the alternator to generate a magnetic field as it starts , once t he alternator was a magnetic field the field current is controlled by the regulator and derives its field current from the output of the alternator , this all occurs inside the alternator, turning of the exciter current does not disable a modern alternator

heres a modern LinBus alterantor regulator IC

Notice how the initial exciter current is actually supplied by the regulator and not via a separate excite feed

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.

PaulCrawhorn · 05-01-2022, 22:11

EMP is another factor some want to plan for

SOLAR SUPPORT · 06-01-2022, 01:11

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.