Myth of alternator damage cause by BMS disconnect?

[sailorboy1]

So based on the few yes or no answers given since I asked (all I looked for on the responses was Yes or No) it appears to not be determined yet. Please continue and I will try to remember to recheck next month.

But, just for a point of reference: I installed a fuse right on the output of my alternator and it broke (different unimportant story). So it had no output and since the sense wire is connected directly to my batteries it just kept on keeping on spinning around, making voltage and no current. I figure it went on for hours. When I fixed it the alternator works just fine.

[rgleason]

Sailorboy, just listen to goboatingnow. I have not done these tests, but I have seen enough sad stories about alternator failures and electronics to believe this statement, and there are many others who can confirm. Just one example

Originally Posted by sailorboy1

So based on the few yes or no answers given since I asked (all I looked for on the responses was Yes or No) it appears to not be determined yet. Please continue and I will try to remember to recheck next month.

But, just for a point of reference: I installed a fuse right on the output of my alternator and it broke (different unimportant story). So it had no output and since the sense wire is connected directly to my batteries it just kept on keeping on spinning around, making voltage and no current. I figure it went on for hours. When I fixed it the alternator works just fine.

[team karst]

Dumbing this down a bit, but still accurate: when a circuit opens an inductor, the current thru that inductor cannot drop to zero instantly. The associated voltages will insure that fact.
If the open is caused by a switch or fuse, an arc WILL develop. If its a semi, then some breakdown voltage rating is likely to be exceeded. Thus, the need for protection.

[sailorboy1]

Originally Posted by sailorboy1

But, just for a point of reference: I installed a fuse right on the output of my alternator and it broke (different unimportant story). So it had no output and since the sense wire is connected directly to my batteries it just kept on keeping on spinning around, making voltage and no current. I figure it went on for hours. When I fixed it the alternator works just fine.

that means that when I fixed the fuse issue by removing it, the alternator worked fine. I did nothing to the alternator.

[team karst]

Also important: semi voltage breakdown is not always fatal. It usually needs to be associated with a follow on large current.
Big exception tho with MOS devices and ESD.

[Wotname]

Originally Posted by sailorboy1

.....
But, just for a point of reference: I installed a fuse right on the output of my alternator and it broke (different unimportant story). So it had no output and since the sense wire is connected directly to my batteries it just kept on keeping on spinning around, making voltage and no current. I figure it went on for hours. When I fixed it the alternator works just fine.

Originally Posted by sailorboy1

that means that when I fixed the fuse issue by removing it, the alternator worked fine. I did nothing to the alternator.

The likelihood of alternator damage is directly proportional to the current flowing at the moment of disconnect.

You have no idea of the current flowing through the fuse when it failed, it may have been well under the rating of fuse as fuses will fail for a variety of reasons apart from over current (e.g. vibration, manufacturing defect etc). Unless the broken fuse was forensically examined, there is no certainly it was carrying a high current when it failed. However it may have and you might have dodged a bullet; even punks have the occasional lucky day.

Remember one swallow does not a summer make.

Rest assured alternators always follow all electrical laws all the time. It is only by knowing the values of all the variables, it is possible to determine the outcome of any disconnect. Like gravity, electrical components care not one wit about myths and beliefs.

Nevertheless feel free to follow the winds of the electrically illiterate if it floats your boat.

See ya in a months time!

[Dieseldude]

Originally Posted by Wotname

Why would the induced spike be negative?

The spike is generated in the stator coils and could be +ve or -ve depending on the direction of magnetic field of the rotor at the moment of disconnect.

The rectifier diode pack (being a full wave rectifier) will rectify the polarity of the spike to be +ve at the alternator output - assuming the spike hasn't already destroyed them.

Thanks for pointing out the problem. Yea, come to think of it positive spikes can be created and the despiking diode would be of no help. A clipping circuit consisting of a high current FET arrangement fed at the gate with a zener diode of about 14.6 volts should clip off any positive over voltage. Get a voltage of greater than 14.6 volts, the FET goes into conduction and shunts the high voltage to ground. May need to parallel several FETS to achieve enough current capacity. Clipping circuits were at one time, and perhaps still are, used in audio amplifiers to save the speakers from damage by over driving them. They worked for both the negative and the positive halves of the audio signal.

[NPCampbell]

Originally Posted by letsgetsailing3

C'mon.


Nobody wants to try it out on their own boat?

I tried it on my motorcycle with a drop-in 12V. It took about 5 minutes to cause problems.

The BMS cycled on and off about once per second making my dash flash like a yo-yo and triggering a CAN bus alarm. I hooked up a fishing light to the battery to discharge it half way and sure enough the problem went away ... until it reached full charge and then same problem. Others have had success with lithium drop-ins on that same bike so I guess it comes down to what the characteristics of your BMS are. I learned my lesson.

[Wotname]

Originally Posted by Dieseldude

Thanks for pointing out the problem. Yea, come to think of it positive spikes can be created and the despiking diode would be of no help. A clipping circuit consisting of a high current FET arrangement fed at the gate with a zener diode of about 14.6 volts should clip off any positive over voltage. Get a voltage of greater than 14.6 volts, the FET goes into conduction and shunts the high voltage to ground. May need to parallel several FETS to achieve enough current capacity. Clipping circuits were at one time, and perhaps still are, used in audio amplifiers to save the speakers from damage by over driving them. They worked for both the negative and the positive halves of the audio signal.

Haven't thought through your circuit description except to say the clipped voltage would have to be significantly higher than 14.6V.

The 14.6VDC is about the same as 14.6VAC (RMS). You will need to consider the AC peak voltage rather than the AC RMS volts.

[sailorboy1]

[QUOTE=Wotname;35543

Nevertheless feel free to follow the winds of the electrically illiterate if it floats your boat.

See ya in a months time![/QUOTE]

Well i dont know what “See ya in a month time” means. But if you plan to out of the wide blue throw “illiterate” at me don't seek me out as I am not interested.

[Wotname]

Originally Posted by sailorboy1

Well i dont know what “See ya in a month time” means. But if you plan to out of the wide blue throw “illiterate” at me don't seek me out as I am not interested.

Originally Posted by sailorboy1

So based on the few yes or no answers given since I asked (all I looked for on the responses was Yes or No) it appears to not be determined yet. Please continue and I will try to remember to recheck next month.

But, just for a point of reference: I installed a fuse right on the output of my alternator and it broke (different unimportant story). So it had no output and since the sense wire is connected directly to my batteries it just kept on keeping on spinning around, making voltage and no current. I figure it went on for hours. When I fixed it the alternator works just fine.

Not making a direct comment at you at all!!

It was your idea to come back in a months time.

However it was also your idea to determine the validity of the 'disconnect myth' by monitoring the 'yes' or 'no' responses rather than following the science so yeah it does sounds suspiciously science illiterate, especially given your personal example [perhaps] suggesting it was myth.

Happy to share beverage of choice

[s/v Jedi]

If you don’t want to prevent this by using a DC-DC converter then your only hope is to suppress it. This is done with a TVS (Transient Voltage Suppressor) which is a specialized diode.

https://m.littelfuse.com/~/media/ele...ation_note.pdf

[goboatingnow]

People need time understand there’s about 160 Joules of energy in the alternator spike. Mosfet crowbars typically have VDs of 40-60 V. Way too low , keeping the mosfet within its Safe Operating Area is a huge challenge and rapid Di/Dt changes cause unintentional mosfet operation

Secondly using TVS diode even big ones is a challenge to keep them within the absolute maximums. The problem being that each excursion beyond those limits weakens the TVS structure.

The other thing is TVS limits will be well above the operational voltage so electronics remaining in the circuit still needs to handle over voltage spikes.

It’s actually a very challenging design situation , I’ve a current auto qualified board on my pcb system and it’s a big challenge to make it repeatedly survive these incidents.

The best way is to avoid the

[team karst]

80 Watts for 2 seconds worth of energy. But much quicker. That takes a bit of mass to absorb.

[rgleason]

Frans Veldman replies to "tytower" who is spreading more misinformation here and he finally locks the thread after a rude response.


I had linked to littlefuse some time ago when I wanted to understand this better and because it looked like it could be an interesting backup. I don't recall who referenced it earlier, but one of the knowledgeable regulars here.

Do I understand correctly that littlefuse is a good solution for automobiles, but not our use case, in a marine environment, using larger alternators to charge large batteries?

Should we even bother to consider one as backup?

I wonder how the Balmar Alternator Protection Device works and what it's design approach is?

...protect the alternator’s diodes and internal voltage regulator against spikes (clamping up to 60V) and sustained over-voltage conditions (beginning around 20V for the 12V version). The APM can absorb multiple surges of such energy, and can absorb surges in excess of 200 amps without failure to continually protect your alternator. Visual and audible alarms indicate if the device has been compromised and needs replacement. Balmar APM devices provide intelligent, robust, solid state protection in a small easily mounted package at the rear of the alternator between the B+ and B- terminals. Balmar APM devices can be used to protect all alternator brands. Balmar APM devices meet ISO 16750-2 for Load Dump Protection and ISO 7637-2 for Surge Protection.

In this PDF

In certain cases it is possible
that the APM will provide protection, but in the process become damaged so
that it no longer provides protection. In this event, the APM LED will turn red,
and it will begin to give a chirping sound. In extreme cases such as lightning
strikes, the APM can be damaged to the point it no longer functions or provides
feedback.

I believe the APM is intended to be used as a backup only. But sailorboy perhaps could use this, and try a full dump to see how it works out.