Will a DC-to-DC charger protect the alternator from lithium BMS cutoff?

[goboatingnow]

Originally Posted by newhaul

Ok so tell us all that deal with this stuff every day .

What is HVC?



A BMS lists its disconnect on high voltage as a HVD situation .

Aka High voltage disconnect.

LVC HVC , C = Cutout ( or cutoff )

You are nitpicking and I don’t get your point if you know everything why post.

[goboatingnow]

Originally Posted by CatNewBee

No. It will not.

The question should be why would the battery disconnect in the first place if the alternator is working properly?

Because in a lithium system of a high voltage event occurs the charge sources must be disconnected , for solar or a battery charger this is no issue , it causes problems when the charge source is an alternator.

As I said , a dc dc converter drawing a reasonable load will prevent the alternator from load dumping

However the problem is you can’t predict that the dc dc convertor will be drawing current when a HVC occurs. Hence its not a reliable way to protect a alternator

You need a guaranteed load when the lithium battery is disconnected

[goboatingnow]

Originally Posted by newhaul

Ok so tell us all that deal with this stuff every day .

What is HVC?



A BMS lists its disconnect on high voltage as a HVD situation .

Aka High voltage disconnect.

I’ll humour your pedantry a little longer

HVC
https://taosailing.com/2017/12/batte...ipage/?lang=en

( read the “‘alArms section”)

HVC from Victron community forum

https://community.victronenergy.com/...-as-a-hvc.html

Ev bikes and HVC

https://sites.google.com/site/shelby...ery-management

Ocean planet BMS manual HVC

https://oceanplanetenergy.com/wp-con...dule-guide.pdf

Now enough is enough. I’ve been in automotive and heavy machinery dc design , embedded systems and lithium ( mostly 18650) for years. I don’t install it. I have designed it.

In fact HVD is not that common a TLA at all BTW primarily because it’s an incorrect term. A disconnect action may or may not occur. The best solution is not to disconnect the battery but stop the charge sources. Disconnect is a crude solution and renders the downstream Dc system dead. ( which is ridiculous given you just have a full battery ) hence HVC refers to the cutoff point where charging must STOP not where the battery is disconnected ( necessarily )

[CatNewBee]

Originally Posted by goboatingnow

Because in a lithium system of a high voltage event occurs the charge sources must be disconnected , for solar or a battery charger this is no issue , it causes problems when the charge source is an alternator.

As I said , a dc dc converter drawing a reasonable load will prevent the alternator from load dumping

However the problem is you can’t predict that the dc dc convertor will be drawing current when a HVC occurs. Hence its not a reliable way to protect a alternator

You need a guaranteed load when the lithium battery is disconnected

And from where would this high voltage event come from, if all charge sources behave to their settings?

Sure not from the alternator with 14.2V maximum output.

[goboatingnow]

Originally Posted by CatNewBee

And from where would this high voltage event come from, if all charge sources behave to their settings?

Sure not from the alternator with 14.2V maximum output.

Correct. In a sense.

Lithium tends to accept charge even when it shouldn’t , ( so to speak ) so even at 14.2 maintained for a significant time , there can be bad side effects including cell heating, micro shorts and internal plating effects. Continued application of a voltage is unwise in fully charged Lithum technology batteries and also has shown to have an adverse impact on cycle life. **

Hence as you say there is never any need to disconnect a lithium battery if the charge sources are stopped at the appropriate point. Disconnects are very much seen as an extreme “ last ditch “ approach , ABYC s forthcoming guidelines suggest an alarm should be issued etc before disconnect.

In a properly designed lithium system wide solution all charge sources should be controllable by the BMS. sadly marine dc electronics is a hodge lodge of incompatible , often user installed equipment of varying age, technology and often not interworked as a complete system. This is the opposite to modern car and truck systems.

Hence BMS introduced into this environment often have no means of controlling charge sources other then by a very crude battery disconnect

What’s a better idea of course is full control over each charging source. Failing that , the next best thing is charge source disconnects , rather then a battery disconnect , but this is often eschewed on cost grounds ( multiple disconnect devices ) . Of course charge source disconnects bring the issue of alternator control into play because it’s a load dump situation in many cases ( or can be)

In reality a good BMS has several escalating levels of alarm and subsequent response , with battery disconnect really being a last ditch “ I’ve lost control “ option. It’s rather like core dumping in Star Trek !!

————-
** a useful paper is the 2015 ieee conference paper “Research on overcharge and overdischarge effect on lithium-ion batteries” by Wu et al.

Also

Float Charging Performance of Lithium Ion Batteries with LiFePO4 Cathode
Masaya TAKAHASHI * and Takahisa SHODAI

[newhaul]

Originally Posted by goboatingnow

In fact HVD is not that common a TLA at all BTW primarily because it’s an incorrect term. A disconnect action may or may not occur. The best solution is not to disconnect the battery but stop the charge sources. Disconnect is a crude solution and renders the downstream Dc system dead. ( which is ridiculous given you just have a full battery ) hence HVC refers to the cutoff point where charging must STOP not where the battery is disconnected ( necessarily )

How does that high voltage disconnect situation affect the DC load system on my boat?
With a good well designed BMS my charging and discharging are split out from each other so that in the event of a high volt disconnect it would be the charging sources not the loads that are disconnected. That point on my unit is at 14.8vdc.

[goboatingnow]

Originally Posted by newhaul

How does that high voltage disconnect situation affect the DC load system on my boat?
With a good well designed BMS my charging and discharging are split out from each other so that in the event of a high volt disconnect it would be the charging sources not the loads that are disconnected. That point on my unit is at 14.8vdc.

I specifically mentioned that scenario as preferred , ie charge source disconnection , but many systems have one disconnect

As was mentioned there is no actual need for any disconnections at all , merely a system to stop charging sources, in that case they dont have to be disconnected . As I pointed out the industry uses HVC as a cutoff point not a disconnect point. If you have control over the charging sources there is never a need to have any disconnects at all.

[rgleason]

goboatnow wrote

Lithium tends to accept charge even when it shouldn’t , ( so to speak ) so even at 14.2 maintained for a significant time , there can be bad side effects including cell heating, micro shorts and internal plating effects. Continued application of a voltage is unwise in fully charged Lithium technology batteries and also has shown to have an adverse impact on cycle life. **

...and Battleborn likes charging to be between 14.4 and 14.6!!

I still don't get it.

[CatNewBee]

Originally Posted by rgleason

goboatnow wrote






...and Battleborn likes charging to be between 14.4 and 14.6!!

I still don't get it.

This is for the balancers to keep the cells happy.

[newhaul]

My primary solar is set to 13.8 and I only balance once a year if needed but so far havent lost an ah or needed balanced. Yes I liveaboard .

[SOLAR SUPPORT]

Hello Everyone, I am not a LFP user but I am planing to replace my four years old AGMs next year. I think LFP's self control by cuting off the circuit and alternator over heat problem is common both for RV and MV. Otomobiles do not have a house battery bank but have the same alternator to be protected against HVC. I started to think our genious inventors whom create a super battery made with Lithium Iron Phosphate are not enough genious to find a simple and cheap solution to common alternator HVC and over heat protection. I think those problems create a huge market for alternator producers to upgrade their existing Alternators working in those MVs an RVs. Replacing the Alternator's internal charge regulator with a LFP Friendly one for instance if possible technically. New regulator must have HVC & Over Heat Protection both.

[goboatingnow]

Originally Posted by newhaul

My primary solar is set to 13.8 and I only balance once a year if needed but so far havent lost an ah or needed balanced. Yes I liveaboard .

Yes this is my experience , and as a result I’m removing balancing from my own BMS design.

[goboatingnow]

Originally Posted by SOLAR SUPPORT

Hello Everyone, I am not a LFP user but I am planing to replace my four years old AGMs next year. I think LFP's self control by cuting off the circuit and alternator over heat problem is common both for RV and MV. Otomobiles do not have a house battery bank but have the same alternator to be protected against HVC. I started to think our genious inventors whom create a super battery made with Lithium Iron Phosphate are not enough genious to find a simple and cheap solution to common alternator HVC and over heat protection. I think those problems create a huge market for alternator producers to upgrade their existing Alternators working in those MVs an RVs. Replacing the Alternator's internal charge regulator with a LFP Friendly one for instance if possible technically. New regulator must have HVC & Over Heat Protection both.

I mentioned this upstream . In fact many new alternators conform to ISO 16750-2 test 2 which clamps load dumps to 35V and technically any electrical or electronic devices connected to a 12v car style system should also conform to ISO 16750-2, and hence be able to withstand the load dumping

Unfortunately ISO 16750-2 conformance is patchy at best.

Hence the need to prevent a load dump.

[barryglewis]

Given the OP's description of his alternator, sounds like it could be modified to take an external regulator. If he were to have that done, he could then use a programmable regulator fit for the lithium battery. The OP could then use all lithium. We have used a lithium system now for abt 50,000 nautical miles with the engine alternator rigged this way. No problems starting motor! We do have a small stand by LA battery kept charged with a tiny solar panel.
We have each charging device lithium compatible, a load controller to disconnect if voltage gets low, battery and cell monitoring and an automatic balancer.

[NPCampbell]

Originally Posted by newhaul

How does that high voltage disconnect situation affect the DC load system on my boat?
With a good well designed BMS my charging and discharging are split out from each other so that in the event of a high volt disconnect it would be the charging sources not the loads that are disconnected. That point on my unit is at 14.8vdc.

I'm curious as to your setup.

When an alternator is putting out high current, removing the load by the BMS disconnecting or the charge source disconnecting is still called a load dump.

The charging source will no longer see a load and the back EMF in the windings of the stator will generate a voltage spike. This spike can easily be 75-100v on a 12v system. If the charge source disconnects downstream of the regulator then the spike will burn the regulator out. If there are other electronics in the circuit outside of the disconnected load, they may be damaged as well.

If a load isn't presented to the alternator after a load dump, the time constant of the voltage spike will be incredibly long. A TVS diode like goboatingnow mentioned can clamp that spike at a preset voltage as long as the TVS diode is large enough to absorb the energy until the spike decays.

It sounds like you have a setup that clamps your output voltage at 14.8v?