Making a cheap BMS ABYC compliant

[goboatingnow]

Originally Posted by RaymondR

Would putting one of these across the output of an alternator suppress the transient when the BMS disconnected?

It would help but you need to do the maths against the datasheet to ensure the power dissipated remains within limits of the package , this is the challenge with TVs design in particular alternator spikes are high energy and relatively long. Little fuse has a good application note on it. ( as does STM )

Secondly a 17v TVS is low as it would likely be triggered when you didn’t want it.

[RaymondR]

Originally Posted by goboatingnow

It would help but you need to do the maths against the datasheet to ensure the power dissipated remains within limits of the package , this is the challenge with TVs design in particular alternator spikes are high energy and relatively long. Little fuse has a good application note on it. ( as does STM )

Secondly a 17v TVS is low as it would likely be triggered when you didn’t want it.

The specs look pretty impressive and I suspect that with a couple of inductors and capacitors one could pretty well smother all the transients.

We need better information on the specification of alternator output transients and their causes. Unfortunately my oscilloscope didn't make it onto the boat and my wife would probably call the police if I went to get it and the software for my 10 channel 12 bit AD converter is on a 3 1/2" disc and I don't have any computers which run Win98.

[s/v Jedi]

Originally Posted by RaymondR

The specs look pretty impressive and I suspect that with a couple of inductors and capacitors one could pretty well smother all the transients.

We need better information on the specification of alternator output transients and their causes. Unfortunately my oscilloscope didn't make it onto the boat and my wife would probably call the police if I went to get it and the software for my 10 channel 12 bit AD converter is on a 3 1/2" disc and I don't have any computers which run Win98.

You are trying to make this: https://www.sterling-power-usa.com/S...iondevice.aspx

You must understand that it is impossible to calculate what will work and what not. Much is depending on the HVC event, how fast it switches, if it’s a contactor or a bank of MOSFET’s, how high the alternator output is at that moment etc. So all these devices do is provide a last resort attempt. You must have another, fail safe mechanism to prevent this from happening.

[RaymondR]

Originally Posted by s/v Jedi

You are trying to make this: https://www.sterling-power-usa.com/S...iondevice.aspx

You must understand that it is impossible to calculate what will work and what not. Much is depending on the HVC event, how fast it switches, if it’s a contactor or a bank of MOSFET’s, how high the alternator output is at that moment etc. So all these devices do is provide a last resort attempt. You must have another, fail safe mechanism to prevent this from happening.

Hi mate,

the manufacturer provides a fairly good set of specs, such as Reverse Stand Off Voltage, minimum Breakdown Voltage, maximum Breakdown Voltage, Peak Pulse Current, and Clamping Voltage and graphs for response times and other operating characteristics and claims up to 15,000 Watts TVS with a range of devices from 17-280 volts.

I'm just an amateur but the above suggests that if one could characterize the transient a solution could be engineered, being mindful that the transient only needs to be tamed back to being relatively benign. A solution would be nice to have even if one is not going to connect a BMS system. We tend to have a lot of expensive gear connected to our DC power systems these days.

My relationship with transients has pretty well been: "the backward connection" transient, often fatal where protection has not been designed into the device; the "excessive voltage transient" what bloody idiot put a 240 volt AC plug onto that 12V DC device; "the induced transient", damn that lightening strike was close and the TV and computer have quit working.

These are pretty well all acts of folly, God or nature and one can generally use the excuse "fate is the rationalization for doing (or not doing) something you knew you shouldn't have done (or should have) in the first place" to avoid subjecting yourself to accountable however knowing that most pribably inevitably going to create excursions with a BMS probably wont cut it.

[s/v Jedi]

Originally Posted by RaymondR

Hi mate,

the manufacturer provides a fairly good set of specs, such as Reverse Stand Off Voltage, minimum Breakdown Voltage, maximum Breakdown Voltage, Peak Pulse Current, and Clamping Voltage and graphs for response times and other operating characteristics and claims up to 15,000 Watts TVS with a range of devices from 17-280 volts.

I'm just an amateur but the above suggests that if one could characterize the transient a solution could be engineered, being mindful that the transient only needs to be tamed back to being relatively benign. A solution would be nice to have even if one is not going to connect a BMS system. We tend to have a lot of expensive gear connected to our DC power systems these days.

My relationship with transients has pretty well been: "the backward connection" transient, often fatal where protection has not been designed into the device; the "excessive voltage transient" what bloody idiot put a 240 volt AC plug onto that 12V DC device; "the induced transient", damn that lightening strike was close and the TV and computer have quit working.

These are pretty well all acts of folly, God or nature and one can generally use the excuse "fate is the rationalization for doing (or not doing) something you knew you shouldn't have done (or should have) in the first place" to avoid subjecting yourself to accountable however knowing that most pribably inevitably going to create excursions with a BMS probably wont cut it.

I have no idea what you are trying to tell me but it sounds like specs for the TVS diode. BTW, the part number is listed as obsolete and the part housing looks very different too so I’m not sure what you have.

Anyway, I wasn’t talking about the TVS but about the effects from a HVC, which can only be known by actual testing for every situation and every different system.

Also, ABYC and all who copy them, states it is mandatory to have a BMS and to have that warning level that stops the alternator so I don’t understand why you are so reluctant to just do it right.

[goboatingnow]

Originally Posted by s/v Jedi

You are trying to make this: https://www.sterling-power-usa.com/S...iondevice.aspx



You must understand that it is impossible to calculate what will work and what not. Much is depending on the HVC event, how fast it switches, if it’s a contactor or a bank of MOSFET’s, how high the alternator output is at that moment etc. So all these devices do is provide a last resort attempt. You must have another, fail safe mechanism to prevent this from happening.

The alternator load dump is well characterised so if you design to the SAE spec you can be as sure as practical you’ve covered your basis

I don’t Agree with your last paragraph. Tvs is much faster then any other mechanism and in the correct design capable of handling KW of spike power

There is no need for a other failsafe on top of tbd TVs.

I have TVs units all over the boat. Interestingly all the devices so protected survived the lightening strike. My next upgrade is to build a few specific can bus TVs protectors and dot them about.

[rgleason]

Originally Posted by RaymondR

Would putting one of these across the output of an alternator suppress the transient when the BMS disconnected?

Raymond you ask about use of these two semiconductors, give us a picture, but dont say what they are or provide a link to a description. Then everybody in the know proceeds to discuss them. Is this intentional or just an oversight?

[s/v Jedi]

Originally Posted by goboatingnow

I don’t Agree with your last paragraph. Tvs is much faster then any other mechanism and in the correct design capable of handling KW of spike power

There is no need for a other failsafe on top of tbd TVs.

Experts incl. ABYC do not agree with you and specify that the BMS must provide warning signals to be used as a means to prevent HVC.

To endorse the use of HVC as a normal means of charge termination is shocking.

[PaulCrawhorn]

I see what you did there...

Isolating the target bank from the charge buss via un-warned cutoff is perfectly fine, so long as the lead Starter batt remains hard-wired to continue buffering the charge source output.

In a small / simple design, all these electronic / mcu based "solutions" just make the system much more fragile overall.

If you need to comply with these guidelines to get insured, then all fine and good label the discussion as within that context.

[tanglewood]

Originally Posted by s/v Jedi

Also, ABYC and all who copy them, states it is mandatory to have a BMS and to have that warning level that stops the alternator so I don’t understand why you are so reluctant to just do it right.

Just to clarify, ABYC does not require or stipulate any advance warning prior to a BMS disconnect. The HVE event immediately begets the HVC action. It's an action of last resort. That's all the spec requires. Anything more is optional and at the discretion of the designer/builder.



Personally I think an advance warning signal should be required, and I wouldn't be surprised to see it show up in the next revision. It is currently suggested, but not required. The challenge is that drop in batteries are a reality and aren't going away, and none I know of offer any sort of external communications or warning. So requiring it will render all those batteries and boats non-compliant. But that my be the pill that needs to be swallowed.

[goboatingnow]

Originally Posted by s/v Jedi

Experts incl. ABYC do not agree with you and specify that the BMS must provide warning signals to be used as a means to prevent HVC.



To endorse the use of HVC as a normal means of charge termination is shocking.

Sorry I agree there should be advance warning of any disconnect. Other then that I usually ignore anything ABYC suggest.

[goboatingnow]

Originally Posted by tanglewood

Just to clarify, ABYC does not require or stipulate any advance warning prior to a BMS disconnect. The HVE event immediately begets the HVC action. It's an action of last resort. That's all the spec requires. Anything more is optional and at the discretion of the designer/builder.



Personally I think an advance warning signal should be required, and I wouldn't be surprised to see it show up in the next revision. It is currently suggested, but not required. The challenge is that drop in batteries are a reality and aren't going away, and none I know of offer any sort of external communications or warning. So requiring it will render all those batteries and boats non-compliant. But that my be the pill that needs to be swallowed.

Hmm E-13 is rather prescriptive

“13.5.6 If a shutdown condition is approaching, a BMS should notify the operator with a visual and/or audible alarm prior to disconnecting the battery from the DC system.”

[PaulCrawhorn]

"should" ≠ "must"

within the context that the whole document is just guidelines

[goboatingnow]

Originally Posted by PaulCrawhorn

I see what you did there...

Isolating the target bank from the charge buss via un-warned cutoff is perfectly fine, so long as the lead Starter batt remains hard-wired to continue buffering the charge source output.

In a small / simple design, all these electronic / mcu based "solutions" just make the system much more fragile overall.

If you need to comply with these guidelines to get insured, then all fine and good label the discussion as within that context.

Sorry this is technical nonsense

Damping a load dump event is required in cars under iso-16750-2- and iso-7637-2 and equivalent sae specs.

There is no issue protecting the alternator frin such events. It just requires the correct protection. Systems be installed.

As to how mcu solutions make systems fragile is also nonsense. It’s 2022 not 1822. Mcu running supervisor systems can enhance your security and safety.

There’s is absolutely no need to retain the hard wired starter in system. It just takes appropriate systems design to remove it. In fact with LFp it makes no sense to retain any lead on board.

Damping load dump merely requires appropriate technology. It’s easily done and no doubt we will see more such protectors fron the marine tech industry in the near future

There’s no need to retain lead in any form certainly not to protect your alternator.

This is the sae test model that the protection must dampen upper voltage is 140v time is 100 mS. 19
Such pulses must now be dampened. It’s a tall order for TVS solutions but it can be done ( and has been done )
Most new car alternators regulators can react so fast they can partially met the SAE specs. These days.

[goboatingnow]

Originally Posted by PaulCrawhorn

"should" ≠ "must"

within the context that the whole document is just guidelines

Yes but the same wording exists in the ISO specs and that will have legal standing in 2023
In ABYC should is must in the context that ABYC has no legal standing